AvSport of Lock Haven -- 353 Proctor Street, Lock Haven PA 17745
Ask Dr. Wilbur
Ask Dr. Wilbur
Disclaimer: Dr. Wilbur is not a real doctor. For medical questions, consult a competent medical practitioner. His first name is not really Wilbur, and his last name isn't even Wright (although we hope his answers are).
- Determining approach speed
- Sport Pilot instrument training requirements
- No Pilot's Operating Handbook
- Renter's insurance coverage
- Nosewheel steering sensitivity
- Emergency equipment and survival gear
- What airports may a Sport Pilot use?
- Why is the SportStar maximum gross weight limit so low?
- Determining proper flap settings
- Flap setting for Short Field landings
- Single engine safety
- Acceptable altimeter error
- Why the sign-off for less than 87 knots?
- Selecting landmarks for navigation by pilotage
- Why did my plane stall?
- Lost communications procedures
- Estimating bank angles
- Required airspace endorsements
- Determining percentage of maximum power
- The Ercoupe as an LSA
- Taildragger training
- How do I get my Student Pilot Certificate?
- Flight Review without rudder pedals
- Veteran's benefits for flight training
- Constant airspeed in the pattern?
- Tandem seating vs. side-by-side
- Best Ercoupe ever made?
- Determining condition of an antique taildragger
- CG as a Percentage of Mean Aerodynamic Chord
- How can one avoid routings over water?
- Weigh before flying
What approach speed should I use in my Light Sport Aircraft? There is no POH (Pilot's Operating Handbook), and the AOI (Aircraft Operating Instructions) doesn't say.
Confused Student Pilot
The Doctor Responds:
The old rule of thumb has always been to approach at 1.3 times stall speed. Since all the modern LSAs stall at around 45 knots clean, add 30% to that, and approach at 58.5 knots if clean (OK, you can round that up to 60).
Stall speed with flaps extended will be lower, of course, so you'll have to experiment. Go up to a safe altitude, put the plane in the landing configuration (with whatever flap setting you would use for a normal landing; in my SportStar, that's 30 degrees), and stall the plane. Look at the airspeed indicator at the onset of the break. Let's say it reads 35 knots, as an example. Tack 30% on to that to come up with a speed of 45.5 knots going into the flare with 30 degrees of flaps.
This is how the recommended numbers in the POH or AOI (if your plane has one) were determined, by the way: somebody did a flight test, stalled the plane in various configurations, and then added that 30% safety margin.
I'm receiving conflicting information regarding instrument training requirements for the Sport Pilot license. Can you set me straight?
Minnesota Student
The Doctor Responds:
The confusion is understandable, Minnesota. FAR part 61.93(e)(12), which applies to all student pilots (whether pursuing a Private, Recreational, or Sport license), requires training (no duration specified) in "control and maneuvering solely by reference to flight instruments" prior to embarking on a solo cross-country flight. This seems to me perfectly reasonable. In my opinion, the student should be familiar with the operation of all equipment (including instruments) installed in the aircraft, prior to embarking on a cross-country flight.
In the original Sport Pilot rule, there was no specific requirement for any instrument training. When the FAA revisited the rules in 2009, they included a provision (proposal #5) that would require 1 hour of flight training on the control and maneuvering of an airplane solely by reference to instruments. This provision would have applied specifically to sport pilots operating airplanes with a VH greater than 87 knots CAS.
By the time the revised Sport Pilot rule became effective on 2 April 2010, this particular proposed change had been withdrawn. So, no, there is currently no instrument training requirement for Sport Pilots, other than those that apply to all student pilots prior to solo cross-country flight. However, many flight schools (including my own) had already implemented the change in their curricula, adding one hour of instrument training in anticipation that the provision would be adopted. Hence, your confusion.
That said, the FAA requirements are only a minimum; there is no reason why an individual flight instructor cannot impose higher standards. I still include that hour of instrument training in my Sport Pilot curriculum. The fact that this is a VFR-only rating will not prevent Sport Pilots from occasionally stumbling into clouds. I train for the 180 degree turn solely by reference to instruments. This additional training adds about $200 to the cost of obtaining a Sport Pilot license. If it keeps you out of trouble (or gets you safely out of the clouds right-side-up) only once, that's money well spent.
My flight instructor says I'm required to carry a Pilot's Operating Handbook aboard my aircraft. It doesn't have one. So, what should I do?
Try to Comply
The Doctor Responds:
Well, I'm certainly glad you're trying. FAR 91.9 says, in part: "No person may operate a U.S. registered civil aircraft ... for which a... flight manual is required ... unless there is available in the aircraft a current approved ... Flight Manual..." (emphasis added). All aircraft manufactured under FAR Part 23 are indeed required to have an "approved Flight Manual," commonly referred to as a Pilot's Operating Handbook (POH). So, your instructor is partly right. However, if you're flying a Special Light Sport Aircraft (S-LSA), the rule is a little different. There is no POH for S-LSA's, because they're not certified under Part 23.
Does that mean that 91.9 does not apply to S-LSAs? Hardly! It goes on to say that no person may operate a U.S. registered civil aircraft "for which a... Flight Manual is not required" (emphasis added), "unless there is available in the aircraft a current approved ... Flight Manual, approved manual material, markings, and placards, or any combination thereof." In other words, if a manual is not required, you still need to have onboard everything that would be in a manual, if it were required!
Even though there is no POH provided with your plane, if it's an S-LSA, it came with a book of Aircraft Operating Instructions (an AOI). As I interpret FAR 91.9, the AOI will serve as your approved Flight Manual, and you must carry that with you in the plane. Oh, and not just carry it; the FAR says "available in the aircraft." So, don't just throw it in the baggage compartment, make sure you can reach it in flight. (Yes, I know, in an emergency, the last thing you want to be doing is reading the manual. But if the FAA doesn't find it in the wreckage, you can expect to be cited.)
The aircraft renter insurance information I reviewed features 2 main categories of coverage: Bodily injury/Property Damage Liability and Aircraft Damage Liability. Do you have any advice regarding range of coverage I should be considering for the Aircraft Liability portion of the insurance coverage? Any suggestions would be appreciated.
Art
The Doctor Responds:
Art, you are wise to maintain renter's insurance. Even though most flight schools (including mine) have our own insurance, and even though that insurance offers you some degree of protection, you could still incur significant liability in the unlikely event of an accident or incident. My insurance, for example, caries with it a $1000 deductible. That means, should you bend my airplane, you will still be out of pocket for the first kilobuck. You may feel you're able to pay that sum out of pocket, in which case you may choose to forego hull coverage.
But, it gets worse than that. Even though my insurance company will instantly reimburse me for damage to my plane, there's no guarantee that they won't try to subrogate against the renter who was Pilot In Command (PIC) at the time damage occurred. That means they will fix my plane, and then try to get you to reimburse them for the whole amount. That's the main thing renter's insurance is designed to protect you against.
So, how much hull insurance do you need? My insurance agent says a good rule of thumb is that renters should carry about half the value of the airplane. In the case of a used LSA that has a market value of, let us say, $80,000 to $100,000, that means you should typically carry hull coverage in the range of $40,000 to $50,000. With most companies offering aircraft renter's insurance, the premium for this added protection can run on the order of 1% of the insured value per year -- in this example, $400 to $500 a year. That's a relatively low cost to pay for peace of mind, don't you think?
Is there a trick to keeping the SportStar stable once on the ground or during the take off run? I have stable approaches and take-offs, but I am having some problems keeping the plane stable on the ground after touch-down. I understand there is a kit available to make the nosewheel steering less sensitive.
Guy
The Doctor Responds:
Yes, Guy, the nosewheel steering is quite sensitive. And, yes, there is a factory-authorized modification available to mitigate that. However, it is my opinion that if you reduce nosewheel steering sensitivity, you will significantly increase your turning radius on the ground, which may not be desirable when taxiing in close quarters.
There is an alternative, if your problem occurs primarily during takeoff and landing. That is to keep the nosewheel off the ground as much as possible. A modified soft-field takeoff and landing technique will let you do this.
On the takeoff run, hold back pressure on the stick to raise the nosewheel off the runway at the slowest possible speed (then relax it as your mains leave the ground, so you can accelerate in ground effect). That way, you'll be maintaining directional control through rudder deflection, which gives you more positive control than the nosewheel steering does.
Similarly, after landing on the mains, keep increasing back pressure gradually to keep the nosewheel off the runway, maintaining directional control with the rudders. When the stick is all the way back, your nosewheel is about to come down on its own, so neutralize your rudder pedals to make sure it doesn't come down sideways! But that way, when the nosweheel finally contacts the surface, you will already be slowed down enough that the sensitive steering will be much less of a problem.
Obviously, you should practice these techniques with a qualified instructor onboard. Good luck, and enjoy your SportStar.
Could you share what you carry in your airplane, in terms of emergency equipment and survival gear?
Clay
The Doctor Responds:
Gladly! I routinely carry ten pounds of survival gear in my plane (in addition to the installed GPS and ELT, both of which can be removed from the plane and thus constitute emergency equipment). This added baggage includes:
Note that survival experts recommend one gallon of water per day, per person. Since LSAs are two-place aircraft, and the average rescue can take three days, we should really be carrying six gallons. At eight pounds to the gallon, that's 48 pounds of water (and my SportStar's maximum baggage capacity is only 55 pounds!) Obviously, we're compromising here. If ever I have to do an emergency landing, I have to hope it's near a river or stream. (My Wilderness Survival Kit includes water purification tablets.)
I used to carry a whole lot more in the back of my old Beechcraft -- sleeping bag, tent, space blankets, camp stove, fuel, matches, kindling, fishing line, fish hooks, salmon eggs, tools... but that plane had a 270 pound baggage capacity!
What airports are available to me as a Sport Pilot?
Likes Busy Airports
The Doctor Responds:
A more relevant question would be: what airports are off limits to a Sport Pilot?
No Sport Pilot may operate in or through Class D, C, or B airspace (formerly called Airport Traffic Areas, Airport Radar Service Areas, and Terminal Control Areas, respectively) unless he or she has received specific instruction on required equipment and procedures, and a logbook endorsement from a flight instructor authorizing operation in such airspace. Once properly trained and endorsed, you have nearly the whole country (something like 15,000 airports) available to you.
There is a specific exception: the FARs list a dozen of the country's busiest airports, where Sport Pilot operations (takeoffs and landings) are explicitly prohibited. Pursuant to §91.131(b)(2), solo student, sport, and recreational pilot operations are not permitted at any of the following airports:
Other than the above, a Sport Pilot is authorized to operate into or out of any public use airport in the US, provided he or she has received the appropriate airspace training and logbook endorsement.
I notice the maximum gross weight of AvSport's SportStar trainer is only 1268 pounds. Why, when the LSA category allows 1320 pounds gross weight?
Heavy pilot
The Doctor Responds:
The Light Sport Airplane specifications in the USA do allow a maximum gross weight of 1320 pounds, as you have noted. Among other restrictions on an LSA is a maximum clean stall speed of 45 knots. Stall speed, you probably recall, increases with weight, and there is where the problem starts.
The SportStar was the first S-LSA approved in the US, when the Light Sport rule was released in 2004. Its airframe (derived from the popular EuroStar) is structurally sound up to about 1400 pounds, so the 1320 pound limit posed no problem. But since it was designed under European Microlight aircraft rules, the US stall speed limit did not apply at the time the plane was developed. During stall testing for ASTM certification, it was found that the plane's no-flaps stall speed hit 45 knots when the plane was loaded to 1268 pounds. Hence, that's where its max gross weight was set.
Of course, there are a number of ways to reduce a plane's stall speed, through slats, flaps, wing design, or the addition of vortex generators. Evektor came up with an optional Service Bulletin to raise the gross weight up to the LSA limit, by adding vortex generators in a line along the wing's upper surface, in order to lower stall speed. With these little airflow-modifying tabs added to the leading edge of the wing, stall speed drops enough not to reach 45 knots until the plane is loaded to an increased weight of 1320 pounds.
Ultimately, AvSport obtained the materials necessary to comply with the max gross weight increase Service Bulletin, and has installed them. Thus, our particular SportStar has now become a legal 1320 pound LSA.
I'm not exactly clear on what flap setting to use when. Last lesson, we had already done ten landings, mostly with one stage of flaps, but one or two with other configurations. I asked my flight instructor what he wanted in the next one, and he just said, "for the next few landings, do whatever you want." So, what do I want?
Guessing
The Doctor Responds:
Guessing is good, Guessing! Your instructor is helping you to develop the judgment to be Pilot In Command. Excellent.
Allow me to offer you a hint about flap management. I don't know what plane you're flying, so I'll use my SportStar as an example. (As always, advice you receive in this column is secondary to what your instructor recommends.)
Flaps modify two aerodynamic forces: lift, and drag. Obviously, increasing flaps increases both. The SportStar has three notches: 15, 30, and 50 degrees. The first notch increases primarily lift. The third notch gives predominantly drag. Halfway between, you get some of each.
So, when do you need primarily lift? If you said "on takeoff," you're on the right track. In my plane we use 15 degrees of flaps for all takeoffs. (Some argue that you should practice zero-flap takeoffs, so you know how to do them if the flaps ever fail. On the other hand, if the flaps fail before takeoff, why should you even be flying?)
When do you need primarily drag? Did you say "on landing"? Excellent - you get an A for the day. So, on normal landings, try to use full flaps. There are exceptions: gusts and crosswinds, for example, or if you find yourself low when you roll out on final. So, practice two-notch landings as well. (And yes, flaps can fail in flight, so you'll want to know how to get the plane down with zero flaps, probably using a slip.)
So, when do you use two notches of flaps? You want equal proportions of lift and drag for slow flight. In the pattern, turning downwind to base, with your airspeed stabilized for 1.3 times Vso, you can crank in that second notch of flaps (you probably put in the first notch already, when entering the pattern and slowing down inside the white arc.)
If it helps, you can mentally label those three flap settings "takeoff," "landing," and "slow flight" positions. Just be sure to check your POH or AIO, as well as with your instructor, since the specifics for your plane might vary.
Of course, as PIC, you will be making judgment calls in every phase of every flight. Enjoy, and remember that with great freedom comes great responsibility.
I have met all the prerequisites for the check ride, all required minimum hours and passed knowledge test. I'm pretty proficient in almost all maneuvers. There's only one thing where I'm kind of weak, landing with 30 degree flaps for a short field simulation. I can do the short field simulation well with 15 degrees flaps. But with 30 degrees, I get it right only half of the time; the other half I have to go around or end up with some bouncy landing. Mind you, I started practicing landings with 30 flaps on my last flying session last Saturday, so I have not practiced that much.
My question is, during the check ride, does the DPE ask for specific flap setting for short field landing or is that a decision for the student to make when requested to do the short field landing?
I'm confident that I can improve it with more practice, but I would prefer to concentrate on check ride practices if I don't have to use 30 degree flap landings during my check ride. My check ride is going to be in the Flight Design CTLS.
In the Home Stretch
The Doctor Responds:
Before we discuss specific flap settings, it is important to understand the purpose of the short field landing exercise. The idea is not only that the runway is short, but also that you have to clear obstacles at the runway threshold. (This is a realistic scenario for an off-airport emergency landing, where you have to clear trees to make an open field). Thus, your approach needs to be steeper than usual. Otherwise, after clearing obstacles at a normal 3 degree approach slope, you're going to land far beyond the obstacle, and touch down with as much runway behind as ahead of you.
And that's where flaps come in. They steepen your approach, while allowing you not to pick up excess airspeed. Without flaps, pointing the nose down will result in a steep approach. However, when you flare, you'll be going so fast that you will float just above the runway, for its entire length. And, you should remember, you never want to force a plane down onto the runway. If you don't let it land when it's ready, you'll end up breaking it.
So, how much flap to use in a short field, obstacle approach? All that you have available. (In your CT, that would be 35 degrees. In my SportStar, it's 50.)
Landing with that much flap just doesn't feel right, because the angle is much steeper than you're used to. That's the whole point - it's supposed to! The only way this is going to work is if you are very rigorous in airspeed control. And the airspeed to shoot for is generally about 10% slower than that you'd use for a normal landing.
I don't know the exact numbers for your Flight Design, so I'll just give you mine. A normal approach speed, in my case, is 60 knots indicated. So, with full flaps in an obstacle situation, I have my students approach at 55 KIAS. As long as they hold airspeed very exactly, the plane clears the obstacle at a steep angle, flares just past the runway threshold, settles nicely, and (with either aerodynamic braking or wheel brakes) gets stopped in minimum space.
Your goal should be to concentrate on airspeed control. Nail whatever the short-field approach airspeed is in your plane, with full flaps. Practice this at altitude, not on the landing approach. Memorize the pitch attitude that gives you the desired airspeed with full flaps and power at idle. Once you can nail that at altitude, you're ready to try it on approach to a runway. Keep the nose exactly where your practice sessions told you it should be, and you'll find the short field landing will take care of itself.
Remember that at full flaps you will not have as much float in the flare as you're used to. Thus, it will take more precise control in the flare to touch down smoothly. You may even want to carry just a touch of power into the flare, to make the touchdown lighter. This should be practiced with a qualified instructor onboard. Remember, if the approach isn't working out exactly right, or the flare just doesn't seem right to you, there's absolutely nothing wrong with executing a go-around and trying again.
The Practical Test Standards don't actually mention flap settings; for that, you should rely on your Aircraft Operating Instructions (AOI) or Pilot's Operating Handbook (POH). Your goal, in accordance with the PTS, is to maintain a stabilized approach, touching down smoothly, at the minimum controllable airspeed, within 200 feet of the designated landing point.
Best of luck on your checkride, and congratulations on coming this far along.
I am concerned about the safety of flying single-engine aircraft. If an engine fails, you have no redundancy, hence no margin for error. Isn't it much better to fly a twin?
Safety In Numbers
The Doctor Responds:
Actually, the "redundancy" of a second engine is of questionable safety benefit, if one is to believe the accident statistics. There are at least three reasons for this:
When you set your altimeter to Barometric pressure according to ATIS or other accurate info service, what is the general deviation you see on the altimeter vs. your known altitude? I'm curious because I noticed >100 ft variations while doing ground preps the other day on the aircraft I fly. The handbook of aeronautical knowledge says variations of >75 ft are not acceptable.
I also notice a considerable deviation from GPS altitude. So, I guess my question is: should a properly barometrically adjusted altimeter be showing relatively the same thing as the GPS? My thought would be yes (within 50 ft or so).
Target
The Doctor Responds:
First off, Target, you were right on target to go the Handbook to find the altimeter error spec. Well done!
GPS altitude accuracy can vary widely, due to a number of different factors (all beyond your control). The spec on a pressure altimeter is indeed +- 75 feet, when current barometric pressure is set in the Kolzman window. And the appropriate way to check it is against published field elevation. If you're outside that 75 foot limit, you can have an instrument shop recalibrate it for you. (This should be done anyway as part of the 2-year altimeter/transponder/encoder/static system check required by FAR 91.411 and performed in accordance with FAR part 43, Appendix E).
If this is a rental aircraft, ask the FBO for a look at the airframe logbook. The above check should be logged within the previous 24 calendar months. If it isn't, you might make a gentle suggestion that it be done, while mentioning that the altimeter seems to be out of spec. Although most renter pilots consider maintenance the owner/operator's responsibility, FAR 91.3(a) and FAR 91.7(b) can be interpreted as requiring the Pilot in Command to verify that all required maintenance and inspections have been performed.
The full-blown altimeter, transponder, encoder, and static system check costs around $200. It has been argued that, for a plane that flies only VFR, the full pitot-static system check is not really required. A simple functional check that verifies the transponder's power, frequency, and gray code output at local field elevation costs only about $75. However, I believe forgoing the thorough conformance test to save $125 is false economy.
My plane, for example, flies regularly in Class C and B airspace, underneath layers of C and B airspace, within 50 miles of the Washington DC SFRA, and sometimes on VFR flight plans within the SFRA. In such airspace, even if VFR, the clearances are very IFR-like. Assigned altitudes are binding, and Mode C accuracy becomes important. Let's say somebody busts restricted airspace because the pitot-static system hadn't been thoroughly checked. Or, maybe they didn't bust restricted airspace, but because the transponder codes were wrong, ATC says they did. How much lawyer time do you suppose that $125 will buy them?
But even outside a radar environment, remember that TCAS interrogates transponders, and determines separation from Mode C returns. It isn't hard to imagine an accident caused by an inaccurate encoder (if someone wants to make this a research project, there's probably a doctoral dissertation in it somewhere, and plenty of NTSB and ASRS data to be mined). An erroneous Mode C code could trigger a resolution advisory in a nearby TCAS-equipped aircraft, resulting in improper avoidance maneuvers, possibly climbing or descending an aircraft into a target that was not previously a conflict. How would the FBO then feel about the $5.21 a month saved by not doing the full check?
I see that the FAA is requiring Sport Pilots like me to get instruction and a logbook endorsement to fly aircraft with a Vh less than 87 knots. What is so different about a Vh < 87 Kt plane that it needs a special sign-off?
Sport Pilot Jon
The Doctor Responds:
You should know, Jon, that the number 87 is not at all arbitrary. That equates to exactly 100 mph (rounded off, of course). Specifically, a nautical mile is 15% longer than a statute mile. (There are 5,280 feet in a statute mile, but 6,079 feet in a nautical mile. The ratio [6079 / 5280] equals 1.15.) So, multiply 87 knots by 1.15 and you get: 100.05 MPH. (They had to draw the line somewhere...)
The Light Sport Aircraft movement is an outgrowth of the FAR Part 103 ultralights that became popular in the 1970s and '80s. Ultralights (and those ultralights converted to LSAs over the past few years) have very little kinetic energy in flight. Kinetic energy varies directly with mass, and with the square of speed. So, make an airplane slow and light enough, and KE approaches zero.
These types of aircraft are considered low-speed, high-drag machines. Because of their low KE, they have very little inertial stability, so they have to be flown somewhat differently from the more conventional LSAs. Originally, Sport Pilots were thought to be transitioning from ultralights, which are Vh < 87 knot machines. So, instruction and a logbook endorsement were required to transition to the faster machines.
When the LSA rules were rewritten in 2010, the FAA realized that now, most Sport Pilots train in faster (and somewhat heavier) aircraft than the traditional ultralight. So, for those who want to transition in the opposite direction, an equivalent endorsement was added. It's not a bad idea, since the training emphasizes how to manage an aircraft with considerably lower kinetic energy than the one in which you may have trained.
One exception to the Vh < 87 knot endorsement requirement is that anyone who had acted as Pilot In Command of such an aircraft before the new rule went into effect is grandfathered. If you are too young to be a grandfather, Jon, I suggest you take the training!
As I prepare for my cross-country flights, I'm a little challenged to find appropriate landmarks for navigating by pilotage. I have no problem with the math or concepts, but I don't have enough experience correlating symbols on sectionals to views from the plane to feel confident in my choices of checkpoints. I've been wishing for something that would show a sectional chart and aerial photos from various points on that sectional, to help connect chart to view.
Sport Pilot Jon (again)
The Doctor Responds:
Nice hearing from you again, Jon. As usual, you raise a good question. In fact, you already have a resource available to concoct just such a comparison. It's called Google Earth. You can tell it the altitude from which you wish to view any part of the world, and then compare that view to your sectional aeronautical chart. My students practice flying every XC on Google Earth before they head out to the airport. (Some even print out those altitude views in color, and carry them in the plane -- though I think that's probably overkill).
One thing to remember is that everything on the chart exists somewhere on the ground. The converse is not always true. So work from chart to ground, not vice versa.
I was flying dual practice in a Cessna Skycatcher, when it stalled in the traffic pattern. I'm not exactly sure why. I was too low on base and tried to pull up to a high pitch then it stalled. I think from then on, the CFI helped me by immediately pushing the throttle back up and lowering the pitch. I think what happened was that I was busy looking when to turn to final when I should have been looking what the plane is doing. A lot of things go on my mind when I fly the plane that it overwhelms me trying to focus and trying to listen to my CFI.
Student pilot Kevin
The Doctor Responds:
Kevin, I'm sure your CFI has already told you this, in which case, permit me to reiterate: it's a common misconception that elevator controls altitude, and power controls speed. In slow flight, exactly the opposite is true. If you want to go faster, push the nose down. If you want to be higher, add power. So, pulling up when low on base is exactly the wrong thing to do. Instead of getting higher, you got slower, and stalled. This is actually a very good experience to have (with a CFI on board, of course!) because you will now begin to think "pitch controls speed, power controls altitude", and will not make that mistake again.
There's an old adage: "to go up, pull stick back. To go down, pull stick way back."
Congratulations -- you're now on your way to becoming an airplane driver. Next step is to become a pilot.
One of my study test questions reads: "If the aircraft's radio fails, what is the recommended procedure when landing at a controlled airport?"
My question: Even though B would be correct procedure... Would you or would you not want to Squawk 7600 in addition to "B"? My line of thinking is that this would be an additional layer to assure the controller that your not just being rude/knuckehead, jumping into the pattern. Or am I wrong in what the correct scenario would be for using 7600?
Drew
The Doctor Responds:
Drew, not all Class D (towered vs. non-towered -- I don't like the terms "controlled" and "uncontrolled"; that implies chaos at the latter) airports have radar or the ability to monitor transponder signals. In fact, the majority of towered fields do not. So, while a transponder-equipped aircraft can (and should) certainly squawk 7600 in the event of a communications failure, there is no assurance whatever that the controllers have any way of seeing that squawk.
Remember that there are at least three kinds of radio failure: transmitter works and receiver doesn't, receiver works but you can't transmit, or both receiver and transmitter have failed. In the first case, there are two possibilities: you can transmit a carrier but no audio (as in, a failed microphone) or no transmit function at all. In the second case, there are two possibilities: no audio (as in, a broken headset cord) or no receiver function at all. And in the third case, it's possible that whatever killed both the rx and tx (for example, an electrical failure) may also have killed the transponder. So, there are several permutations, involving totally lost comm, halfway comm, and 1 1/2 comm. Thus, several scenarios suggest themselves.
Let's say you are in a radar environment when comm is lost. The controller may transmit to you and get no response. Sensing that you may still have receive capabilities, the controller may say "N12345, if you read me, squawk ident." If the same scenario but no radar, it may be "N12345, if you read me, click your mike" (if the tower is receiving carrier but no audio) or "rock your wings" (if no carrier is being received). Once one-way communications has been established, it then becomes two-way, the pilot responding through mike clicks, ident button pushes, or wing rocking. It's an old joke that if you are receiving nothing from ATC, and suspect their transmitter is out, you might transmit "ATC, if you read me, rock the tower."
Whatever the level of comm you may or may not have, in the event of losing clear, two-way communications, your best course of action is to get the plane back on the ground, and troubleshoot there. In some cases, this might involve leaving the pattern, flying to a non-towered field, landing there, and figuring things out. at your leisure (without burning avgas or running up the Hobbs meter).
Speaking of old jokes, you already know the transponder codes for VFR, emergency, radio failure, and hijacking. So, what's the transponder squawk for a failed transponder?
Last Sunday I was doing Turns around a Point, S-Turns across a road, etc. with my flight instructor. Luckily I had a 10-12kt wind to use while learning them. My CFI is fantastic, and I'm comfortable with him, but when it comes to this specific area he's too vague. Whenever I enter a turn, I am having a hard time judging my bank angles. The plane I train in does not have an Artificial Horizon, so I don't have anything on the panel to really follow. My CFI responds with "Yeah, that's about 30 degrees... looks fine." I see your plane has glass panel, so I am assuming your students have something to refer to. Do you have any advice regarding me possibly putting some tape or something on the canopy out in front of me? Would a DPE bounce me for that?
Luke
The Doctor Responds:
I can assure you that your Designated Pilot Examiner will not be carrying a protractor on your checkride, so neither should you. What's critical here is not the precise measure of the bank angle, but its appropriateness to the maneuver being attempted. Remember that turns around a point, S-turns across roads, and rectangular tracks are all ground reference maneuvers. That means they are to be performed by visual reference to the ground, rather than by using an attitude gyro, artificial horizon, EFIS, or any other instrument. If, during ground reference maneuvers, I find my students staring at the screen instead of looking at the sky and the horizon, I turn the EFIS off!
Consider, for example, turns around a point. The objective is to compensate for winds so as to describe a true circular flight path, always equidistant from your reference point. To maintain that constant distance, you will of course have to vary your bank. But don't get hung up on what the actual bank angle is. If you're drifting too far from your point, steepen your bank to bring yourself closer. If you're crowding the point, shallow your bank and you'll end up further from it. With practice, you will find the bank that works, without even thinking about banking the plane.
You can, of course, put tape on your canopy, to help you learn what different banks look like. After a while, you can remove the tape, and you'll find that you have memorized the required sight picture. If you still need that tape, you're not yet ready for your checkride.
In short, trust your feelings, young Skywalker. Turn off your R2 droid, focus your senses on the surface of the Death Star, and use the Force to fly your X-wing fighter.
I've got some plans coming up (assuming I pass my checkride) to be flying into some class D/C airports, but I've got a question that has come up with my instructor (as well as how to handle it)...
First off, as to the letter, what type of instruction do I need -- do I need a sign off for 1 of each? One class B to cover all? Or a sign off for each airport I intend to visit?
I fly near KRDU -- so obviously I'll get a ride there with an instruction, same for a couple other local-ish ones -- but what if I want to fly down to Florida? Will I have to get an individual sign off? Also, what happens if I'm en-route and 'plans change' -- how in the world do I get a sign off in the middle of flight? Am I just SOL?
My CFI seems to feel that I'll need an endorsement for each specific Class D, C, or B area that I plan to visit. I don't think he assumes he'll need to ride along to each first, but... Any advice here would be great.
Carolina Skunk
The Doctor Responds:
Skunk, the good news is that, according to the FARs, a single, one-time sign-off will suffice for all three types of airspace (D, C, and B), if you're a licensed Sport Pilot. Now, from a practical standpoint...
As the owner of the aircraft, I am free to set standards more rigorous than the FAA's in deciding who I'll rent the plane to, and what they are allowed to do with it. I like to give my Sport Pilot graduates three post-license lessons, one each in class D, C, and B airspace, with a separate flight into each, if they want the blanket sign-off. If they choose not to go the whole way, I will give individual endorsements for the particular airspace in which I have given them training and they have demonstrated competence. Nobody has yet complained, since their goal is to be safe in the particular airspace in which they intend to operate.
The idea that an individual checkout and sign-off is necessary for each individual Class D, C, or B area in which you are going to fly only applies only to student pilots. Once a Sport Pilot, you are PIC, and (if you've received the blanket endorsement) are free to use any similar airspace. Sport Pilot altitude, daylight, and weather restrictions still apply, of course, as well as the restriction against flying into the 12 airports from which Sport Pilots are always excluded (see this column for the list).
What exactly does it mean when the aircraft manufacturer gives speed/performance figures at 75% power? It seems to me, with fixed pitch propeller, percentage of maximum power is just a direct function of engine rpm. E.g., with a Rotax 912ULS, 100% power = 5800 RPM, so 75% power should be (5800)x(0.75)= 4350 RPM.
Howard, California
The Doctor Responds:
I wish it were that simple! In fact, for either carbureted or fuel injected engines, % power is a function of air passing through the carb or injection airbox. You can see that RPM doesn't tell the whole story, if you consider that a given RPM at one altitude will produce a very different power level from the same RPM at a different altitude (considering that air density varies with altitude). Plus, you can point the plane downhill and throttle back, producing a very high RPM at almost no power. Thus, rather than RPM, the best direct indicator of power is intake manifold vacuum (usually, erroneously called manifold pressure). But even that is not a simple linear relationship.
Aircraft power is actually a function of three factors: engine power (a function of airflow for a proper fuel/air mixture), engine torque (a function of engine RPM), and thrust (a function of propeller RPM). The engine RPM that produces optimum torque is generally quite high. The propellr RPM that optimizes thrust is significantly lower, because of drag effects. This is why Rotax, for example, uses a prop gearbox - so both torque and thrust can be optimized simultaneously. As for engine power, since it's related to air flow (and the corresponding fuel flow to achieve efficient mixture), turbocharged engines obviously produce more constant power (at a given RPM) than the normally aspirated ones most of us fly.
Bottom line: "75% power" is actually a meaningless designation. But, to see a sample breakdown of performance at various power levels for a typical LSA, see the table at http://avsport.org/acft/performance.pdf.
I noticed you are a CFI in Ercoupes. I have been fascinated with that unique little aircraft ever since I first read about it. I am curious about your experience and impressions. I understand that they are LSAs. How do you feel it compares with other LSAs you fly? Easier to fly and land? I understand the Ercoupe has some dangerous issues with sink rate if you get low and slow. Due to the lack of flaps maybe?
James, Florida
The Doctor Responds:
The Ercoupe is a delight to fly, James, and fairly easy to learn in. There are some quirks, of which you need to be aware when you train in one. One of those is its high sink rate at slow speeds. This is actually a useful feature for a plane without flaps or the ability to do slips, if you have an instructor who understands it. The idea is that, if you're high on final, you can bring the power back and the nose up, and lose altitude under positive control. The wing washout makes the wing root stall, but the tips (where the ailerons are) continue to fly, so you have roll control all the way down. When you get on the glidepath, you simply release back pressure on the yoke, and increase airspeed going into the flare. Somewhat counterintuitive, but it works.
Although all the early Ercoupes were built without rudder pedals, there is a Supplemental Type Certificate out there to add them. That mod gives you the ability to do slips, so the above problem goes away. However, adding rudder control also negates the greatest advantage of the Ercoupe, in that it will then no longer be the spin-proof airplane it was designed to be.
Now, at the risk of sounding pedantic, let me point out that no antique aircraft (Ercoupe included) can ever be a Light Sport Aircraft. Only those planes built under the ASTM guidelines (which didn't even exist "way back then") are LSAs. Those certified 'Coupes, Cubs, Champs, T-Craft, Luscombes, etc. that meet the LSA performance restrictions can be what's called "Sport Pilot Eligible aircraft," but are never actually LSAs. This is important because a true LSA has a Special (pink) Airworthiness Certificate, while the Sport Pilot Eligible certified aircraft has a Standard (white) one. And, it is the color of the Airworthiness Certificate that dictates the maintenance rules.
For example, the owner/operator of an LSA can take a repairman's course, get a certificate, and do his or her own annual inspections. Not so for the Ercoupe, or any certified aircraft with a Standard Airworthiness Certificate -- that inspection needs to be done by an A&P mechanic with an IA rating. Even if the plane is Sport Pilot eligible.
That said, very few 'Coupes are Sport Pilot eligible anymore, since over the years most model 415Cs were modified for higher gross weight, and can never go back. Those that do qualify have doubled in price over the past few years. So be very cautious in shopping. Take someone along who really knows these planes. Join the Ercoupe Owner's Club for all the help you could possibly need.
Remember that a 65 year old aircraft is an antique, and antiques are constantly undergoing restoration. Be prepared to put about as much additional money into the plane as you spent purchasing it, even if it seems airworthy when you buy it. It's not at all uncommon to double your investment in the first year or two.
You should also be aware that if you train in an unmodified 'Coupe and then transition to something more conventional, you will need to get training on the proper use of rudders. And, if you get your license in a rudderless Ercoupe, that license will carry a restriction. To remove the restriction, you'll have to take another checkride, in something with rudder pedals. For that reason, many Sport Pilots opt to get their license first in something else (with rudders), and then fly the 'Coupe.
I want to get back to my Sport Pilot training after several months' hiatus. I am considering switching to a 7BCM Aeronca Champ (old school, high-wing taildragger); all my prior training was in a Sport Cruiser (modern, low-wing tricycle).
I will interview the new CFI later this week and will get an intro flight in the Champ. What surprises should I look for? I have read about flying a taildragger and have seen references to common errors made by transitioning students but I don't know what those are.
Any advice or suggestions? Thanks!
Dave in Texas
The Doctor Responds:
Dave, the Champ is a delight to fly, and an excellent, honest trainer that will make you a competent pilot. I started in one (50 years ago), and have always had a soft spot for them. You need to check the list of Sport Pilot Eligible certified aircraft on the EAA website -- not all Champs qualify. I know the classic 7AC (circa 1946) does; not sure about the 7BCM.
I prefer the Champ over the Cub because the wing fuel tank moves the CG back, so you solo it from the front seat (with the Cub, fuel tank is on the firewall, so you have to solo from the back to keep the CG in the envelope -- which leaves you with no forward visibility whatever).
The trickiest part of flying Champs and Cubs is the heel brakes -- much harder to operate than the toe brakes on other planes. With any conventional landing gear, you have to be serious about footwork, and remember that the landing is not complete until the plane is in its chocks and tied down.
Biggest mistake one can make in a taildragger is to heave a sigh of relief as soon as the plane touches down, and relax your grip on the stick. Touchdown is when the real work begins, and you have to keep full back stick to keep the tailwheel firmly planted (all the while maintaining precise directional control with the rudders, until you're stopped). Aelirons into the wind while taxiing will help counter the weathervaning tendency.
These birds are very economical to operate, and relatively easy to maintain. Unfortunately, since they're a certified airplane, a Sport Pilot owner/operator cannot perform preventive maintenance (you need to be a Private pilot or above to do that). And, if you plan to own one, be prepared for a shock when you see the insurance bill -- for low-time pilots, it costs twice as much to insure a conventional landing gear as it does for a tricycle gear aircraft.
Make sure your flight instructor is really dedicated to taildraggers -- many will avoid them. There are some fine flight schools out there that specialize in these machines -- see if you can find one. I know it's a long way from Texas, but if you ever happen to be in the San Francisco Bay Area, one of the best places in the world for taildragger training is at Reid Hillview Airport in San Jose -- AeroDynamic Aviation (formerly Amelia Reid Aviation) even has a fine old 7AC Champ on the flight line.
Taildragger flying is basic flying at its best. Go for it, if you possibly can!
I am working to become a Sport Pilot, and have yet to figure out how and where to get a Student Pilot certificate. Is this something I can do via mail, or does it have to be issued in person? Also, am I required to have this prior to solo, or just sometime before I do my check ride?
Skunk
The Doctor Responds:
Skunk, this is something your flight instructor should be working with you to obtain. You have to apply in person, to any Designated Pilot Examiner (DPE) or at any FAA Flight Standards District Office (FSDO). You will need an appointment, and you need to bring along photo ID.
Many DPEs and FSDOs are requiring that applications for student pilot licenses be done only through the FAA IACRA website (that's an acronym for Integrated Airman Certificate and Rating Application). You can visit iacra.faa.gov by yourself, and create an account (you'll make up your own username and password; the system will then assign you a Federal Tracking Number. You will need to give this FTN to your instructor, DPE, FSDO, etc, so they can access your records).
Once your account is created and you have an FTN, you can then begin to fill out the FAA Form 8710 on the iacra website. This is your application for a Student Pilot certificate. When you go to get your certificate issued, the FSDO or DPE will be able to access the form on their computer, by using your FTN. (Of course, you should always carry a printout of the application with you, in case the system decides not to cooperate!)
You can also get a Student Pilot Certificate issued by an Aviation Medical Examiner (AME) -- but only if you are taking a physical exam and applying for a medical certificate. Since Sport Pilots don't need an FAA medical, this is probably not what you want to do.
You will also be using IACRA (with that same FTN) to create your application for your Sport Pilot license, when you're ready for your checkride. Most DPEs won't give you a practical exam until you've filled out the 8710-11 on IACRA, had your flight instructor endorse (digitally sign) it online, and then provided them with your FTN. Again, you'll want to have a printout with you when you report for your checkride, just in case.
I'm surprised your flight instructor hasn't discussed all this with you. It's normally the CFI's responsibility to walk his or her students through these procedures. (In your instructor's defense, it's possible that he or she hasn't yet figured out IACRA. The FAA doesn't make it easy!)
I currently have a Sport Pilot Certificate for 3 control aircraft, and have logged over 110 hours within a 2 year period. I plan to purchase and fly a 2 control Ercoupe (no rudder pedals). I intend to fly more than 50 hours with it over the next 14 months, whereupon my Flight Review will be coming due. Would it affect my BFR and ratings when I show up with a 2 -control Ercoupe? Would it cancel my 3-control ratings?
California Sport Pilot
The Doctor Responds:
Absolutely not, Sport. Once you've earned a rating in a given category and class of aircraft, it's yours forever (unless you do something to tick off the FAA, and they revoke it!) You can take your flight review in any aircraft for which you are rated. Since there is no restriction on your license, you can take a flight review with or without rudder pedals -- your choice -- as long as the aircraft is either an LSA or a Sport Pilot eligible certified aircraft. (Of course, unless you have a tailwheel endorsement, you'd need to take your flight review in a plane with a tricycle landing gear. Don't worry, the Ercoupe is such a plane.)
That said, it would be to your advantage to find a flight instructor who is familiar with the Ercoupe, both for some transition training (they have a few quirks that you will want to learn) and for your flight reviews. I'd recommend that you join the Ercoupe Owner's Club. They list qualified 'Coupe CFIs on their website.
Can I use my VA/GI Bill benefits to pay for my flight traning at your school? I am planning to complete my private pilot's license and move on to commerical. I have already done my first Solo at University of Oklahoma (Norman, Oklahoma), but I haven't done much since then.
Oklahoma Veteran
The Doctor Responds:
Welcome home, Veteran, and thanks for serving. It is my understanding that the GI Bill currently covers only vocational or occupational training. Therefore, it will cover advanced flight training (for the Commercial pilot license and beyond) only after you have earned your Private rating. I can certainly work with you toward your Private Pilot license (either directly, or via the Sport Pilot stepping-stone first), but it would be at your expense. After that, you may be eligible for VA assistance if you decide to go on.
I've seen in your forum posts that you advocate glider landings, maintaining constant airspeed in the traffic pattern. Are you saying fly the entire pattern at one speed? I've never heard that recommended.
Iowa CFI
The Doctor Responds:
I know it's unconventional, Iowa (like much of my curriculum). But there are some definite advantages to reducing the number of variables. Here's the routine I teach:
I have my students complete a pre-landing checklist and establish slow flight on downwind, 1000 AGL, 1/2 mile or so from the runway. (In the SportStar, that's left tank, fuel pump on, monitor ATIS, set 4000 RPM. Slow down inside the white arc, set flaps 15, trim for level flight, and you'll find yourself stabilized at 60 kts). You can fine-tune airspeed with elevator, altitude with power.
Abeam the numbers, my students close the throttle and glide, still at 60 kts. (Carb heat on if relative humidity is high and temp/dewpoint spread is narrow). The plane will try to nose down and accelerate a bit, so they may need some back pressure on the stick to hold 60 kts -- but, they're maintaining that speed primarily by monitoring pitch angle, cross-checking the airspeed indicator only occasionally.
While rolling onto base, I have the students set flaps 30. In this plane, the extra drag just about compensates for the effects of the back-pressure being held following the power reduction. In other words, by adding flap, relaxing stick pressure, and doing nothing else, the plane will continue to glide at 60 kts, pretty much hands-off. No re-trimming required.
If all this is done correctly, and absent any adverse winds, you end up turning final about 500 AGL and 1/2 mile from the threshold. Once lined up, assess the glidepath. If on target, just keep gliding at 60 kts, flare over the threshold, and land. If high or landing long, you still have another notch of flaps available. If low or landing short, one can always bring some power back in.
If really low, or not lined up properly, or airspeed not stabilized, or anything else not perfect, just go around and try again. Since you've been gliding at (and are already trimmed for) 60 knots, which is normal climbout speed, the go-around requires merely easing in full power, compensating for torque with right rudder as required, and holding the speed at 60 on the climbout, with elevator pressures as necessary. Once established in the climb, one can bleed off the flaps gradually, a notch at a time.
The nice thing about doing constant-airspeed glider landings is that, if the student ever has an engine failure requiring a for-real emergency landing, it becomes a non-event (you've already done this a hundred times).
I've been teaching pattern work this way for a couple of years now. It doesn't work for everyone, and isn't always the right technique (short field, soft field, obstructed, cross-wind, or gusty wind landings require tricks of their own), but it's a good place to start.
Students, try this sometime (only, discuss it with your instructor first).
Can you comment on the relative advantages of tandem vs. side-by-side seating? I'm really interested in feedback on training in a tandem aircraft.
Designer
The Doctor Responds:
When many of us old farts started out (in Champs, Cubs, and T-Craft), tandem was the standard seating arrangement for trainers. I didn't particularly like the limitations that imposed on communications (both verbal and non-verbal) between instructor and student. I believe side-by-side seating promotes better interaction. Plus, the instructor can see exactly what the student is seeing (and vice-versa).
Which is not to say that tandem can't work. In the Champ, where the student sat in front, the instructor trying to get the student's attention could always hit him or her over the head with a rolled up sectional chart! This didn't work as well in a Cub, where the student sits in back...
The real advantage of tandem seating becomes apparent in underpowered aircraft. They allow a considerably narrower fuselage, which significantly reduces drag, permitting greater speed. Just compare an Aeronca Champ to an Aeronca Chief -- the latter is somewhat slower with the same engine/prop combination, because of its wider fuselage, necessitated by its side-by-side seating.
In your opinion (which I respect very much), what is the best Ercoupe that was made? Putting LSA aside, from the perspective of a private pilot license holder, which one would be the best one to have?
John J. in PA
The Doctor Responds:
John, if the medical certificate were not an issue, I think I'd go with the 1950 ERCO 415-G. They use the 85 HP Continental engine, have 1400 lb gross weight, and with the fabric wing, have plenty of useful load. I'd want one with the rudder pedal mod, as well as the dual fork nosewheel. There were only 40 built, so they're hard to find.
This aircraft is similar to the model 415-E except for installation of a "Kiddy Seat", increased baggage capacity, double curvature windshield, revised nose cowling support, revised engine baffles, revised seat back structure, and other minor changes.
I don't think I'd want one of the Forneys or Alons. They do have 5 HP more, but with the metal wings, they need that just to drag around the extra weight. And I'd never consider one of the Mooney models. With the single tail, it's just not an Ercoupe!
Of course, the risk of owning the 415-G, or any other aircraft that's not Sport Pilot eligible, is that one needs a medical certificate to fly it. I had to give up a wonderful aircraft, at a huge financial loss, three years ago, after my open heart surgery. So it's a little hard for me to put LSA aside... But you did ask my opinion (yours may differ).
I am considering starting flight training in an antique taildragger. Do you think it's safe to fly in a 1947 Aeronca Champ that is well maintained? How can you judge whether a plane is being maintained well? Do you look at things like cosmetics? This plane looks pretty tired.
Steven in San Diego
The Doctor Responds:
Steven, my first lesson was in a 1946 Champ, but that was in 1961, so the plane was almost new! These antiques are now as old as I am, so one does indeed need to consider safety.
Cosmetic appearance tells you very little, beyond the age of the plane (which is a given in this case). You should ask to see the engine and airframe logbooks. Is every annual inspection logged? Are the Airworthiness Directives documented? Has the engine been receiving regular oil and filter changes? Regular compression checks? If the compression numbers are not logged with every annual, or if AD compliance is not documented, these would be red flags. If repairs are mentioned, are they detailed, in a manner that makes it clear what exactly was done? How often are tires replaced? Brakes? Other common wear items? For major repairs (which are bound to have happened over the past 65 years), are there copies of the FAA Form 337 present with the logbooks? How many hours is the plane flying every year? (More is actually better than too few.) How many hours since the last engine overhaul? Have there been prop replacements (possibly indicating a prop strike?) Has the plane been ground-looped? (Not at all unusual for taildraggers, and not a problem as long as properly logged and repaired).
Next, can you talk to some others who have flown this particular plane? They may be able to tell you about things that don't appear in the logbooks.
These old planes don't have to be pretty to be safe, but they do require a lot of attention and TLC.
My plane's manual shows all Weight & Balance calculations done in Percentage of Mean Aerodynamic Chord (% MAC), instead of determining Center of Gravity in inches aft of datum. What's that all about?
Pete
The Doctor Responds:
Actually, MAC (as a percentage) makes quite a lot of sense, when you understand where it comes from. Switching on pedantic mode for a moment:
First, we define aerodynamic chord as the straight line distance from the leading edge to the trailing edge of the wing. "Mean" means average. So, if the wing is a flat slab, with constant chord (a Hershey-Bar wing), then MAC is just the chord, measured anywhere along the wing. If the wing is some other shape, you have to use calculus to figure out the average chord dimension along the entire span of the wing. But that's just math.
Consider that all arms and moments are normally calculated with respect to some arbitrary (but defined) point of reference -- the datum. That can be the firewall, the instrument panel, the leading edge of the wing, the prop spinner, the prop backing plate, or anywhere else the manufacturer decides it is. So, CG is also calculated relative to that arbitrary datum, which makes it hard to compare the CG of one plane to that of another (unless both use the same datum).
Now, using Mean Aerodynamic Chord, you get a CG measurement that is always related to the same reference point (the leading edge of the wing), regardless of what datum the manufacturer picks. Not only that, but if you express it as a percentage, you always know where it falls on the wing, again regardless of the width of the wing or the location of the chosen datum. 25% MAC always means that the CG is falling a quarter of the way back on the wing, regardless of anything else.
Why is this useful? Because we know that the center of lift is always pretty close to the middle of the wing's chord (that is, about halfway back on a straight line drawn between the leading and the trailing edges of the wing). It is desirable for the loaded CG to always fall forward of the center of lift -- that makes the plane slightly nose-heavy, which is a good thing in a stall (the nose will just naturally drop, the plane will accelerate, airflow across the wing will increase, lift will go up, and the plane will tend to recover all by itself). So, it would be good for the CG to fall at about 20% or so of MAC.
The exact figure involves a whole bunch of other engineering considerations, and the range of acceptable values defines the loading envelope of the plane. But you can guess that a plane with its CG at only 5% of MAC will be really nose-heavy, so you might not have enough elevator authority to raise the nose and flare for landing. Similarly, a CG at 95% of MAC will make the plane really tail-heavy, so the plane's angle of attack will be too high, and it will stall before it even gets airborne.
The thing to remember is that "mean" means average, so if you have a fancy wing shape, some math will be required. All this is of course easiest to visualize (and to apply) if you have a Hershey-bar wing. That would make the chord length constant, all the way from the wing root to the wing tip. The leading and trailing edges of the wing would be parallel, and both would be perpendicular to the plane's longitudinal axis. My SportStar happens to be built that way, as is the Ercoupe wing, as well as the original Piper Cherokee wing (which was designed by the same guy who designed the Ercoupe), and a whole bunch of LSAs.
OK, so if you have a tapered wing, or an elliptical wing, or any other non-symmetrical wing, it gets quite a bit more complicated. But the same principle still applies: you want the CG to be back on the wing a little bit, but ahead of the center of lift. MAC tells you how far back it is, and allows you to compare apples and kumquats.
Pedantic mode off.
My college roommate is flying from Jefferson City MO to Chicago to pick up a mutual friend, and then they're flying to KBED (Hanscom Field outside Boston). He will be departing from KPWK (Chicago Executive, just north of O'Hare), and he'd like NOT to be given a climb over Lake Michigan if possible. How might he be able to get a routing that does not go over the lake?
Geoff
The Doctor Responds:
I understand your roommate's concern about flying over water. Departing from KIPT for KOSH about 22 years ago, IFR, I was given a heading that took me right out over Lake Michigan. I was at 10,000 ft, measured the over-water leg length, quickly calculated my gliding distance, and decided I was safe.
Midway across the lake, the ARTCC controller said: "66 Tango Xray, descend and maintain 4,000."
My reply was, "Unable." He left me up at ten, but vectored me all over the place!
Since then, I've learned to put in the remarks block of my flight plan, "negative flotation equipment -- no over-water routings, please!" So far, that's worked.
I understand that you have to keep the gross weight of an LSA below 1320 pounds. Just how do you weigh an airplane? Is there someone at the airport every time you are going to fly so that they can weigh it?
John G. in PA
The Doctor Responds:
Not exactly, John. The plane gets weighed by a mechanic, at least once in its lifetime (I have three digital scales in my hangar; one goes under each wheel for this purpose). You first offload all fuel, baggage, and anything not permanently installed in the plane. The total Empty Weight is just the sum of the three individual measured weights. Based upon the location of the wheels relative to specified reference (called the Datum), the empty weight center of gravity (EWCG) of the plane can then be calculated. The documents showing these figures must be carried in the plane at all times.
Berore you fly, you are supposed to add to the empty weight the weight of the pilot, passengers, fuel, and baggage, and ensure it is within the plane's maximum gross weight limits. Then, using the measured locations of the seats, fuel tanks, and baggage compartments, there is a procedure for computing the loaded center of gravity. The pilot must ensure this is within the manufacturer's specified limits. You'll learn the procedures as part of your flight training.
Email your questions to Dr. Wilbur via fly_at_AvSport_dot_org.
If you can drive, you can fly!
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Dear Dr. Wilbur,