Extreme stall & snap with very little elevator input

[hyper7]

Hi Guys,

I have recently completed a CA Models Extra 330L 26%. It is built from a kit (not ARF).

The plane is exhibiting a weird behavior, I hope somebody can give me an idea where to look. It stalls and snaps violently with very little (less than half of the recommended elevator throw, about 2mm on the stick). This happens even with the throttle at 50% open, so it is not just a slow speed stall. What can cause this? I am thinking incidence (wing or stab?) or wingloading?

Thanks!

[Blip]

Well first of all you need to exclude the obvious. Right now there could be any number of things. Start with what checks you have done such as, is the CG in the right place according to the manual/plan? If you suspect the CG isnt correct try the online CG calibrator to verify the results.

Is there a wing incidence problem? what brings you to that conclusion? Have you checked it during the build?
Wing loading problem! what engine are you using? what engine is the model designed for? Have you added weight with some fancy mods of your own during the build. Was the wood all used from the kit or did it get swapped for your own version?

You need to do some research and deductions before more help can be offered right now its a very gray area with the info youve provided.

[hyper7]

Hmm, let's see what I can answer so far:

The cg is rearward of where it is "supposed" to be, but I have tried both adding and removing quite a bit of nose weight with no significant change.

Incidence seems ok, all surfaces is zero degrees, except the right wing is +1deg (trailing edge lower) Could that be the problem?

I am using a DL-50, seems to have more than enough power. The powersystem is all Lipos, so no unnecesary weight there.

Where is the online CG calibrator? Could CG cause a problem like this? In my inverted flying test, the CG seems perfect, just a touch of up elevator to keep her level. It is just as soon as I give a little bit more elevator she tipstalls.

[bodywerks]

a DL-50 on a 26% plane? I'm guessing 15 pounds, and with only 1150 squares that's heavy. also if you require up elevator when inverted then you are WAY tailheavy or have serious incidence issues.
We need to know how much the plane weighs to have a better idea of what's going on. Also, have you made sure you are getting the exact same travel between both elevators throughout their entire range of travel?

[FENWAYFLYER]

What about servos.

[3D-Seth]

Have you checked your elevator throws to make sure they are traveling up and down equally?

Yes, if you use up elevator when inverted, your tail heavy (for IMAC at least, maybe a little for 3D).

Seth

[3ddd]

roll inverted on a 45 degree upline.if you need lots of down to hold it then you are nose heavy,if you need up you are way too tail heavy.. measure the root of the wing,find 27% of that and set the cg there.this will fly right.but most columbos are balanced on the wing tube

[Blip]

	Quote:
	Incidence seems ok, all surfaces is zero degrees, except the right wing is +1deg (trailing edge lower) Could that be the problem?

Ok well that wont have such a dramatic effect on your flying as to snap it so violently. At worst you will probably have to add a few clicks of opposite trim to level the model out.

Servos where mentioned and so were elevator surface movement. Are the servos the same speed, power, movement and direction? Are they set up correctly if using a transmitter mix? Do they function as they should? by this i mean check them for a full movement under some load (use your hands) in both directions. Its possible for a servo to jump from A - Z if its had a crash and broken some teeth even a dirty pot can make the servo jump. From what you describe sounds like a simple oversight during setup or build. It takes something serious but relatively simple to induce a snap in a model after moving the stick only a few millimeters!
Your using a gas engine. Are you shielding the cables? range checking? using 2.4GHz or PCM receivers? Are the cables running close to the receiver, loose metal to metal contact etc. Get a major glitch from a gas engine in the right place and watch that baby dance.

Suggest you start over from scratch. Look over the model piece by piece/ if your certain the CG is right check wires for damage, loose plugs, engine interference and re check the manual and the moving surfaces.
Whilst your at it, check your Tx for good working condition through the stick range.

online CG calc link here if needed
http://www.nasascale.org/howtos/cg-calculator.htm

[FENWAYFLYER]

	Quote: Originally Posted by Blip
	Ok well that wont have such a dramatic effect on your flying as to snap it so violently. At worst you will probably have to add a few clicks of opposite trim to level the model out. Servos where mentioned and so were elevator surface movement. Are the servos the same speed, power, movement and direction? Are they set up correctly if using a transmitter mix? Do they function as they should? by this i mean check them for a full movement under some load (use your hands) in both directions. Its possible for a servo to jump from A - Z if its had a crash and broken some teeth even a dirty pot can make the servo jump. From what you describe sounds like a simple oversight during setup or build. It takes something serious but relatively simple to induce a snap in a model after moving the stick only a few millimeters! Your using a gas engine. Are you shielding the cables? range checking? using 2.4GHz or PCM receivers? Are the cables running close to the receiver, loose metal to metal contact etc. Get a major glitch from a gas engine in the right place and watch that baby dance. Suggest you start over from scratch. Look over the model piece by piece/ if your certain the CG is right check wires for damage, loose plugs, engine interference and re check the manual and the moving surfaces. Whilst your at it, check your Tx for good working condition through the stick range. online CG calc link here if needed http://www.nasascale.org/howtos/cg-calculator.htm

Hey Blip-
Where in Lowell do you live. I lived in the area for 15 years. I miss it as crazy as that sounds.

[Blip]

Hey Fen
Hillsborough county is my home near Manchester and I work abroad for several months at a time so I miss it more than you.

[ericb]

Like blip mentioned, apply some force on the elevators while you are moving them. One might be going bad.