aircowboy

My Feedback: (10)

I have 2 trainers with flat bottom wings and every time I fly them, they go into a steep climb all of a sudden. They only do this for a breif moment and it scares the crap out of me! I dont know if its just air currents or balance of the plane. The radios seem to be working fine and the servos are in good shape. Has anyone else had this happen and know what causes it?

beavertail

Without touching the controls??

TRP

My Feedback: (1)

Do they recover by themselves?

Is it always in the same area of your flying field?

David Cutler

Do they always climb? If they are both doing that, and it's not all the time, it must be something to do with the transmitter, your use of it, or outside interference. It would be too much of a coincidence if both the planes radios were acting in the same way as each other. or it's being caused by balance or anything else in the planes themselves

Are you aware of anything that accompanies it like trains going past or what you ate for breakfast?

David C.

ho2zoo

My Feedback: (5)

I would say you are either getting a radio 'hit' or a sudden gust of wind. Are both planes on the same channel? Does this occur in the same part of the sky each time? Are your radios 1991 Narrow-Band? Does anyone else have a similar problem?

At our field we were getting so many radio hits on one particular channel that we had to 'close' it down for safety sake.

aircowboy

My Feedback: (10)

It is happening anywhere in my flying field. I am the only person flying there. The radios are brand new Futabas FM. They are both different frequencies.

I did switch the crystals in the transmitters because I wanted to use the 6 channel for a different plane. Is that OK? I guess I should have just swapped receivers, but it was easier to swap the tx crystals. The frequencies are 72.890 and 72.930.

aircowboy

My Feedback: (10)

would a gust of wind really cause the plane to go into a steep climb? By the way, the planes are an Aircore trainer 40 and 2 duraplanes. Also the planes seem to climb more abrutly than I can reproduce with the elevator. Pulling back hard on the stick and the planes just dont climb that fast. Its like someone is pushing down on the tail all of a sudden.

CafeenMan

Is it with application of power? It sounds to me like the wing or stabilizer incidence is wrong or the engine thrust line is wrong. I really doubt it's a radio hit if it's the same thing happening over and over.

Also, if it's not balanced properly then it will never be in trim for all speeds. Most planes are set up to be nose heavy because it's "safer." The fact is a nose heavy plane won't fly right, it's just not as sensitive as a tail heavy plane.

RCaeroguy

My Feedback: (4)

Is it when the power is reduced? A lot of the flat bottom trainers will "balloon" when power is reduced. More than likely, your engine has some down thrust. Maybe more than necessary. Try shimming the bottom of the motor mount with an 1/8" piece of ply.

mucksmear

Suggest you get an assistant to help you do a range check with the engine running:

Agree on a set of handsignals your assitant can use to communicate to you. Have him/her firmly hold the plane either in the air or on the ground.

Collapse the Tx antenna, and start walking away, working the controls and watching your assitant. Check the controls at different throttle settings.

regards,
-Elliot

aircowboy

My Feedback: (10)

My planes do have a tendacy to climb when power is applied and I am aware of the problem and in the process of fixing that. I will try a range test with a friend and see if the elevator moves, but like I said before, I can be flying nice and level with a steady throttle and the planes will turn and go straight up. And it happens FAST! Faster than I can reproduce with the elevator controls!

I appreciate everyone ideas! Keep them coming so I can figure this out. I have a feeling that it is wing gusts, as it doesnt seem to happen on very calm days. I have also checked all the linkages and the are in good condition, without any freeplay.

CafeenMan

Is the wing lifting by any chance? I've seen planes that didn't have enough rubber bands or loose dowels do strange things.

In fact, on one plane you could actually hear the wing slap down onto the saddle after a hard pull-up.

visioneer_one

My Feedback: (506)

This is the answer. Our club trainer does this if we don't use enough rubber bands (or if a couple snap off after the plane sits in the tropical sun for a bit)

Land, add a couple more bands and its fine.

jmulder

My Feedback: (6)

Its because of the dihedral. Thats why you need engine downthrust on trainers. When power is applied they climb. I would say to make sure you have enough downthrust on your engine. Make sure it is balanced properly as well. If you have to much engine on it and trying to go fast you are just spinning wheels so to speak..............................John

glowplug

My Feedback: (1)

I think CafeenMan and visioneer_one are right on....it's not enough rubber bands.....especially since you said it does it less in calm conditions (less force pushing on the wing)

Mike

Stick Jammer

aircowboy,

I am surprised that nobody mentioned the fact that you should not change the crystal in the transmitter. Here's some info right from Tower's website:

*Transmitter Crystals Can Not be changed to another channel except
by a licensed service center. It is against FCC regulations, and
illegal for the user to change a frequency determining component
of a transmitter. If the radio is not retuned, it can be a hazard
spectators, modelers or property, and void AMA insurance coverage.
*Check with the local R/C club for the frequencies used in your area

Ed_Moorman

My Feedback: (1)

Before you go trying any expensive stuff, check your rubber bands. If they are loose in front you can get a jump when the front of the wing picks up, then yanks the fuselage behind it. It'll scare the **** out of you.

Rubber bands should be installed from front to back. When you stretch them out and put the end on the dowel, that end has less stretch than the starting end. I'll bet you are installing yours from back to front, a common, but incorrect, way to do it.

For climbing under power, you need 2 popsicle sticks under the trailing edge of your wing. You'll know when you need them because on the ground, your elevator will be trimmed down. This is a sure fire indication of too much power for the incidence or too much incidence for the power. You may also notice you have to hold a lot of up elevator on final approach before landing.

Start with 2 popsicle sticks, and increase if you need them. You can glue them in after you find the correct amount.

By the way, I teach an aerobatic maneuver every month in my column. Some are advanced maneuvers, but many are able to be done by trainers. I have recently started over with the simple maneuvers like aileron roll, loop, etc.

aircowboy

My Feedback: (10)

Thanks for all the help! I think you guys solved the problem! I didnt realize that the rubber bands should be installed from front to back. I had some suspicions that it was something like that. I have been using only 4 rubber bands also. I am going to double that and see what happens. I also switched the crystals back where they belong(bad beginner idea). I will also try the popcicle stick thing and see if I can make the plane fly better under power. I dont want it to climb under power, just stay level. So where should I ad the popcicle sticks? leading or trailing edge of the wing?

CafeenMan

aircowboy - It's usually a bad idea to change more than one thing at once. I would change the crystal and use more rubber bands. Fly the plane and see if the problem is solved. If so then great. If not then try the popsicle stick. If you do everything at once you won't know what the actual problem was.

jmulder

My Feedback: (6)

If you werent using but 4 rubber bands that was probably the problem. I always use 10.

glowplug

My Feedback: (1)

Yes, as jmulder said, use at least 10.......12 in windy conditions.

Mike

MinnFlyer

My Feedback: (4)

12...

5 front to back

2 criss-cross

bear750

My Feedback: (30)

Mike, that's the new math... around here we'd say 10 front to back and 2 criss-crossed...

bentgear

Dang Bear, then you would be using 22 of them things............ed

Spaceclam

you arent EVER supposed to change crystals in a tx, you need to either change the module if it uses one, or send it back to futaba to have them change it. it is against the law to change it on you own