Why does my plane do this?
 

my plane used to be great. the only thing was when i gave it a knife edge, i had to give it just a litle down elevator, but other than that it was perfect.
Now, when i give it rudder when it is flying strait and level, the nose drops derastically, not to mention when i give it full rudder. either direction. also, when i bring it into a knife edge, it does the same thing. not tward the ground, but down as if it were flying level. Has my plane gone crazy? I need some ideas and fast.

Why does my plane do this?
 

You must have a Cap.

A great number of airplanes do a nose down tuck when the rudder is deflected. Some are moderate and others really gross. The pitch is caused by a pressure differential across the horizontal when the rudder/fuselage deflects.

The question needs some more information, what kind of airplane is it, what changed between the flights, CG or weight, incidence angles, etc.?

Aero work is somewhat repeatable and cause and effect is in place. There is always a reason why a change occurs. Just look for what is different including your preferences in airplane trim setup as experience levels increase.

Why does my plane do this?
 

yes, you are right i have a cap. However, the only thing i did was replace the spinner-nut with a spinner. also, it seems to be a bit tail-heavy because it takes some fancy maneuvering to get out of a knife edge spin. however, what is really interresting is that it never did that before, and i have not changed anything besides that spinner. also, it used to require a little down elevator to keep it strait in a knife edge, not it odes the nose tuck so harshly that it takes almost 1/3 of my elevator to compensate. that is a lot for a plane that is so responsive and has such big control surfaces. There see4ms to be no reason for the change

Why does my plane do this?
 

That it is interesting is no doubt, the why is beyond my experience level.

However the thing to do is replace the spinner with the prop nut and see if the characteristics you are seeing go back to the original ones. Then you know if something else changed.

Why does my plane do this?
 

Hi,
Firstly, your moto is really cool......nobody could have put it more simply than that, I think, deepdown, most of us are that anxious and it is most unfortunate that there are five days between sunday and saturday, and with weather considerations, we really need to work less and fly more.


As for your problem, If you have not crashed the plane and repaired it, Try the following,

1) control linkage binding, any push rod wraping around each other. This is easy to identify, deflect your rudder back and forward as you rotate the aeroplane around the prop, simulating a roll. Observe for uncommanded elevator movement


2) Is your new spinner one of those heavy chrome shining ones.
If so, I suspect that it is gyroscopic precession that is causing the pitching as you yaw. This is also quite easily simulated on grd. Just run your engine at 2/3rd, hold your ship at the c/g so that any resultant pitching will be apparent. deflect your rudder and almost always there will be a corresponding picthing. If so, repeat the process but using increasing or reducing throttle setting. Gyroscopic precession is dependent on RPM, Mass displacement from the prop axis and direction of turn. Solution, use a lighter spinner.

3)check you radio tx. But do it about 10 paces away with the antenna fully retracted. sometimes at weaker signal range, error signal emitted by a faulty tx is more apparent.

Good luck.

Why does my plane do this?
 

thanks. this is actually a very light spinner. it is made by tru-turn, and it is less than 1/16th. i will try, but as far as i know there is nothing going on. woth checking

Why does my plane do this?
 

As Ben notes in another, why bother with a CAP when there's much better airplanes available?
My CAP does the strangest things. When it crashes, I won't miss it.

Why does my plane do this?
 

well, becaue i have put over $1000 into it and it looks really nice. i am pretty edgy about gutting it and using it for something else. i mauy though. the covering is really cheap and is yellowing. it is so weak i managed to put by mig toe through it by bumping it. the foam of my flight box also went through it. the plane is fairly low quality. the surfaces aren't nearly as big as most caps out trhere, except for the legendary rudder. i just want to fix this one so that i can save up my money and get a .60 size 3d plane.

Why does my plane do this?
 

S-clam: What you are seeing now is what most people consider normal with the CAP. I had a CAP with massive rudder pitch coupling - and I understand that's normal. I put in a mix to negate the pitch coupling and then started fighting the adverse roll coupling with rudder. THat is, left rudder -> right roll. SO, the rudder causes changes in both pitch and roll. SO, if you like mixing stuff out, it's a cool plane.

Mine went in when the engine quit at a very bad time. I don't worry about what other folks fly, but I'm with Paul on this one. I sure won't be getting another one of those. I'd like one that you don't need a 'puter just to fly it straight, and you can move the CG around for 3D and still have it behave on landing. It did behave sweet in pitch for 3d with the CG set back though

Why does my plane do this?
 

So basically, caps aren't very good planes in that way. they have a lot of nasty habbits. my cap snap rolls really hard when i pull up. that's why i can't fly the normal landing pattern at my field (it is a really small one) because it snap rolls when i turn it. also, in order to "wall it" i have to do it when i am upside down. even then, it weighs so much it doesn't "wall" anyway. I am looking into a 3d plane, becaue this plane is not at all meating my expectations.

Why does my plane do this?
 

The last time at the flying field I played around with the Cap's elevator throw and making turns. The airplane is perfectly mannered with small elevator throws. Keeping the same throttle settings and just increasing the bank angle and elevator throw each time I found a elevator throw at which the airplane was departing and going the opposide direction in roll. The interesting thing is that there is no warning.

My other pattern airplanes that were set up for the older AMA pattern maneuvers (no snaps) don't do that but of course don't have the elevator power to get it into that flight regime either.

I don't have enough experience with airplanes in this flight regime to know how it compares with other airplane.

But I solved the problem of accidental snaps on landing by setting the low rate at an elevator throw that will not cause the departure. It makes the landings a lot less interesting though.

I did see several big 35% or so Caps fly at the AMA Nats and was very impressed with how they flew when properly trimmed out. Not knowing anything different I wouldn't have hesitated in buying one. I guess it is more a tribute to the pilot than the airplane.

How does it compare to something like an Extra 300 or other designs?

Why does my plane do this?
 

what's interresting is that when i get slow over the runway, my right wing drops. that's the same direction it snaop rolls in when i give it elevator. so here's the big problem. our runway is short, and we are on top of a hill so there is always wind going from left-right. I can't do that sharp of a right-left lading approach because my plane snap rolls. you see, my splane stalls at a high speed. that means about 45 mph. then, i have to make that sharp turn into the wind. the plane snaps so badly i can't do that. so, i have to land at 45 mph and stop in 200 feet assuming i manage to touch down at the end of the runway. it is more like halfway down. so, it is very difficult to fly this plane in the wind, so i fly a lot at the basin. as soon as i come up with the money however, i am getting that 65 inch extra with the rediculously large control surfaces. this one is designed for 3d, but is a stunt plane similar in design to my own. so it will fly about the same with the only real differences being that i will have a lot more control authority especially at low speeds, as a wing loading that is about 10 oz sq/ft lighter than my own, is a mid-wing, and is a 3d plane. also, my plane is of niticably low quality and mega-cheap covering. it looks awsome, don't let me fool you, but that polycote ecs stuff is just cheap as can be. i managed to put my big-toe through it when i was replacing the ailerons. this stuff is crap.

Why does my plane do this?
 

My own CAP was bought to use the 3.2 engine that I'd had on my Stinger. The stinger was really well behaved but couldn't do 3-d. No coupling, no wierd snaps. Well, it would snap out if I got the controls way crossed up during a hover. I had it balanced for neutral elevator upright and inverted. If I could just have solved the wing rock it would have been a great 3d plane too.

I'd read about the ideosyncracies the CAP has and figured I'd just take on each of them and work it out. However, when I found that the landing approach and flare limits where you can put the CG, I wasn't happy. I tried various thrust angles, etc to get the plane to behave on approach as well as in the air with no luck. It's very frustratinig to have a plane that will perform well in the air at a rear CG location, then you need to hold forward stick on approach for some reason. That's uncomfortable as well.

The snapping on mine was strange, in that it was like a micro-snap - it would steepen in a left turn or drop the left wing on final without going hard over, and I could correct with opposite aileron. Still not sure what was going on there.

Anyway, I think both the Extra and the Edge are designed with the thrust line, wing and stab close to the same line (like a Stinger) and without the weird stuff that the CAP does.

Why does my plane do this?
 

How is it you work on your planes??? Sorry, just a little levity there.

/ visualizing someone holding a balsa stick with his toes, like a monkey :rainfro:

Why does my plane do this?
 

lol. i was barefooted, and the end of the wing was next to my foot. when i turned the wing, my big toe went through it. it is that brittle. as a matter of fact, it is so brittle that a weed managed to slice it open. it wasn't prop-kill i know because my engine had died before i rolled off the runway. sad, isn't it? so then, i get the recovering kit so i can patch it. the colors are off at least 15 shades. that's how low quality that recovering stuff is. don't by vmar products.

Why does my plane do this?
 

I noted on E-zone there's a small e-powered CAP kit available... $50.
Almost cheap enough to buy two, build one scale, the other with a positionable/low horizontal and fly both.
Being small, any twitchy stuff will be amplified (which is why 2 may not be enough! :) )
I do note that upright on my GP CAP, the horizontal is 5 inches above the wing chord line. Inverted, it's 5 inches below! This might have something to do with the excessive down-elevator needed inverted.

Why does my plane do this?
 

Hmm, if you are having a problem with snapping always in the same direction, or always dropping the same wing, try this as a test:

Go up high, roll right in to a 70-90degree bank and hold elevator to make a tight turn. Keep feeding elevator and hold the plane there in a tight turn until airspeed bleeds off and you snap out. Watch the direction of roll, do you roll "into" or up and out of the turn? Do it a few times, and see if it always goes the same way.

Then do it a few times by rolling left in to the turn. Again, which way do you roll?

If your plane snaps "into" the turn in one direciton and "out" of the turn in the other, ie, it always goes the same way, then you've got a problem that isn't fundimental to the planes design, it's something in setup. I usually add weight to the "up" wing, even if the plane appears laterally balanced on the ground.

Once the plane is set up so that it snaps out in both directions, and always one way in one turn and the other way in the other turn, your wings are now working at high alpha together, and you will discover that overall the onset of stall will be delayed.

(btw, you can also test by just pulling loops as much as you can, and seeing if you always snap out the same direction. But I find the loop is not as repeatable as a level highly banked turn unless you are able to always get your wings perfectly level and the nose perfectly in to the wing when starting your loops. The turns take the wind out of the equation)

I've found I can really improve my turning radius of my combat planes with this test. A little lead on the wingtip can make the difference between holding a constant high-G turn and snapping out of it. In fact, it's not uncommon for me to go from something like 75% rate on the elevator to 100% rate once things are balanced out in the air. (elevator rate is set to be as much as I can get while not snapping with in the first 2 loops or 720 degrees of turn at full throttle from level full speed flight, plus or minus a bit)

Why does my plane do this?
 

Cool! i will try it on sunday.