Q-talk 92 - Proper Flying Airplane
- Category: Q-Talk Articles
- Published: Thursday, 21 February 2013 10:57
- Written by Larry Koutz
- Hits: 4257
by Larry Koutz (via Q-Llst)
I have been reading about all the agonizing about CG, tail lifting, wing incidence, etc. I have been there, done that, and I have got to say--- it is all relative. What is YOUR airplane telling you?
You can have the CG perfect and have a plane that doesn't fly "right". You can have the CG out of the Quickie envelope and the plane can still fly OK.
How is that possible? There are TWO factors going on with the Q plane. #1 ---- Distribution of the weight. I.E. the CG and #2 ---- Distribution of lift. Center of lift at different airspeeds!
Everyone is agonizing over the CG because wheel weight is easy to get then it is relatively easy to figure the CG, and it IS important to get the CG in the ball park, but it is NOT, I REPEAT, NOT the only factor going on with this tandem wing plane to make it fly OK. The shape of your flying surfaces and the angle of incidence to the fuselage and to each other is also tremendously important!
Since we build the flying surfaces, they are all different in shape, surface finish, twist, lift and incidence angles. This is critical to understanding why some planes fly OK right out of the box and some planes are hanger queens because they scare the heck out of you if they do fly.
I have to say I have flown Q-2's, Q-200's, TQ-200, D-fly MKII, Tri gear D-fly, tail draggers, jets and X-wing fighters. Only kidding on the last plane! Some of the tandem wing planes were KILLERS, if not flown properly and my own Q- 200 had bad lift distribution problems. I have changed the canard angle of incidence--twice, main wheel axle location, canard fore/ aft location, weight distribution, tail wheel height, and tail cone angle. I have seen a bunch of changes!!! Now you know my experience with this type of aircraft.
What do YOU do if the plane doesn't handle "right"? One, you could sell it, or two, you could fix it! This plane HAS to handle OK on the ground or you WILL be fixing it when it gets away from you. Been there, done that! My plane would ground loop at 10 MPH! So fix the ground handling first.
I installed a rear gas tank and moved the axles forward to add more weight on the tail wheel. I fmally did the "Gall" alignment and that made a WORLD of difference in how scared I was to land this beast. I had been flying this Q-200 for 8 years! Now the handling has gone from very twitchy to fairly stable and I don't worry about landing anymore. Again, if you can't control your plane on the ground, fix that FIRST!
Next, get the CG in the ballpark. You can use the "official" Q weight and balance figures, but remember, it is for someone else's plane, not yours! If your plane is sufficiently similar to the original plane, then that weight and balance diagram is probably OK. You can shift things like live ballast, battery, etc. to get the CG in the ballpark. Moving the axle location doesn't change the CG location significantly, but it does change the weight on the tail wheel, which is usually important (some Q's have light tail wheel weight and are still good ground handlers). Also a lighter total plane weight is better for first flights (don't fill up the fuel tanks. You shouldn't be up more than an hour).
Now, how do you know if the plane is ready for flight? In addition to all the things above, make sure the plane is physically ready to fly, because it just might while testing. In-flight is not the time to worry about a cowl held on by 3 screws, loose items in the cockpit, etc. When you get out on the runway for high speed taxi tests, a pilot can find out a lot of things about this plane at speeds below flying speeds. Longer, wider runways are better and safer! 5000' XIOO' for first flights gives a pretty good margin for full throttle accelerations to below flying speeds, then pull power back, check out control responses, pull off power and slow down. Its your plane and shorter narrower runways just increase your risk of damage. Sometimes it is safer to trailer to another larger airport than fixing the damage when you run off the runway, or brake too hard and put it on its nose!
What should the plane do as you accelerate down the runway? Track straight for one thing! You can try aileron steering. It is very effective on my plane. If you don't feel comfortable with the ground handling on slow down and braking, it won't get any better for your first landing! I was still able to land my bad handling plane hundreds of times but it was never what I would call fun. Your choice, fix the handling or fix the damage, I did both! Guess which one came first.
Next, what will the tail wheel do on these tandem wing planes? Some lift, some don't, during the takeoff roll! The reflexor is very effective in modifying this effect in my plane (the T -tail may do the same thing, I have never flown one). One thing I know NOT to do is use full aft stick to takeoff. I nearly "bought the farm" trying that trick once. Several Q-2's have crashed with the full aft stick at take off.
When the plane is below flying speeds, aileron effectiveness and rolling tendencies can be checked. Runway flights or just go for flight? Your choice. With a long runway, flying speed, power pulled back and a little aft stick, my plane just sort of levitates at the ground angle of attack. Then the additional drag of the aft stick causes the plane to settle back into the runway. This feels safe to me and I will probably do this on my next test flight, as I can get a feel for how the plane will fly without ever getting more than 2-3 feet off the ground. With a shorter runway, the dangeris braking too hard and nosing over. Oops, there goes the prop! It has been done before. If the tail comes off the ground (a lot) as the plane accelerates and a little aft stick doesn't cause the plane to fly, you probably have a lift distribution problem (for your CG). I have twice taken off for first flights and had to use FULL aft stick to stay airborne. Not a fun feeling! I hear a lot of comments about the rear wing (tail wheel) lifting early. My reflexor fixed the first lift distribution problem and I landed with the ailerons reflexed up 45 degrees! No kidding!
I flew around with the ailerons reflexed up 30 degrees for several years. My other experience with an aft distribution problem was in a D-fly that supposedly had flown over 100 hours. I took off and flew around with full aft stick the whole time (no reflexor) and only 3-5 MPH between pitch buck and the max speed I could get at full power. Just what is this lift distribution problem? Mostly I have heard of stories (and mine) that involves the rear wing having more lift than is necessary for the weight it is catTY,- ing. To fly requires aft stick and elevator to be down (to generate the additional lift at the front) and generating a lot of drag. So the plane is flying but the drag limits speed. My solution in my Q-200--- More aft weight (5 Ibs oflead on tail stinger, 60 Ibs of gas in aft baggage gas tank) and up ailerons (remember the 30 degrees up reflex for less lift). I flew around like this for years. Guess where my aft CG was at max weight. The plane was real twitchy. How much aft CG I could handle, was part of the test program. Just shows it can be done, but the ultimate solution was to fix the lift imbalance.
I increased the angle of incidence of the canard by cutting it off. How much? Just a wild guess, and using other's experience, I added another degree to the one-degree incidence put in originally. Remember, this is my lifting airfoil and your lift WILL be different. It is the principal that I want you to understand. Everyone is asking, "What is the "right" angle of incidence?" There is no "right" angle of incidence for YOUR airfoils until your plane flies and then the plane will "tell" you if you got it right. So build per plans FIRST! Then test! If your plane doesn't fly "right", you can change the weight distribution for smaller problems or modify incidences for larger lift distributions problems. Did I get it "right" with my one-degree increase in angle of incidence to the canard? Yes---and NO. I had to get rid of the 5 Ibs of lead on the tail stinger and decreased my up reflex to about 5 degrees.
That is my reality and my experience. I did run off the runway due to fmgers slipping off a brake handle and lack of attention. I broke the canard, fixed it and put it back on with another 112 degree incidence increase and now I fly around with the ailerons a couple degrees down. That is about as close as I can get!