I've been flying my Avistar and it is now getting boring. Santa brought me a GP SuperSportster MKII 40. I got it together and put a OS .52 FS with a 12 X 6 prop on it. On take off (which was within 10 ft of roll out) it got about 15 ft high and then just decided to snap roll back down to mother earth. It is easily fixable and before I try it again, I would like some direction as to how to get it to behave. I'm thinking that the four stroke torque kicked in and snapped it. Maybe I shouldn't slam the throttle to full with a 4 stroke? Should I leave her on the ground longer before letting it lift? What is the proper way to run a 4 stroke?

Thanks!!

Re check your balance. A tail heavy condition would make a plane more apt to snap. Also recheck everything to make shure it is straight and true.

As mentioned by Goingstraightup your c/g may be off by being tail heavy, re-check the balance and set it slightly nose heavy with the the fuel tank empty.

By your discription it sounds like you pulled the plane off the ground too soon at a high angle of attack into a stall resulting in the snap roll/crash.

My advice is..

1- allow the model to build speed on the ground 50 to 100 feet take off run

2- apply elevator gently lifting off at a shallow angle of attack and climb out to a safe altitude before making the first turn.
you said that you have experience ,so I think that you should be able to handle it from there

3- also make sure that you don't have excessive elevator throw
I had a model that would snap on take-off 80% of the time due to ,too much elevator throw. I finally wised up and corrected that condition befor I destroyed the airplane!

I flew that model for many years

Good luck Roger

Ditto to what GIFLYRC said...

Check balance (and double check it acording to the plans), more ground speed before liftoff, shallow assent.

Might want to try another prop, OS recommends no bigger than 11x8 for the .52

Agree with GIFLYRC.

Good ideas, THANKS!!

I did double check the balance and it balanced according to the book. I have the great planes balance machine which is worth its weight in gold. So I can rule out the nose/tail heavy situation. I'll try moving down to a 11 X 6 prop. The only reason I used a 12 X 6 prop was that the book said that was what they tested with. But...since they have far more experience than I do, I'll try the less aggressive prop. What is the differences in numbers? Is the diameter smaller the less speed and the smaller the pitch the less torque?

prop you have is fine ,sounds as if the elevator is to much or you didn,t get enough speed before rotating,larger dia.less pitch will give more thrust less speed.

other way around... but only to a point, your engine has to be running at peak power rpms, so going down in size will possibly give you more power (torque and speed) than before, because the engine can actually run at full power now.

Don't wanna insult your intelligence, but I've made the same mistake.
Make sure you balance that low wing plane upside down.

GIFLYRC couldn't be more on the point. Remember, slow plane and lots of elevator = SNAP!

my extra 300 has massive amounts of elevator and it does not snap it just mushes out. A plane that is nose heavy will be prone to snap because of high wing loading. Don t be fooled by a SLIGHTLY tail heavy plane.

Agreed; all the other replies . .

A couple more points....

You say you are bored with your Avistar. Are you sure you have exploited all it's capable of? They are quite aerobatic, and great fun to spin, snap roll, fly inverted etc, and is still good for learning with.

As for your take off problems with the new model, all the suggested solutions are well worth looking into, but one thing is for sure, your wing, or, at least part of it, stalled when you took off, caused by one or all the suggested reasons.

Wings stall for many reasons, and it's worth learning what makes them stall, both to avoid it in the future, but also to actually exploit the phenomenon.

Hence me suggesting you learn to spin the Avistar. It's a fun way of experiencing a stall, as opposed to the uncomfortable stall you experienced on take off!

David C.

Dave is right on the mark about the wing being in a full stall. I'd say that about 75% of "radio failures" resulting in crashes are really just stalls which usually turn into a spin. One of the first things that lets you know you are stalling is your controls stop working (there's no air going over them). This lack of control is why most people blame radio failure. The very first thing to do when a stall is coming on is is to push the nose foreward. This is usually against our thinking because the ground is so close. Push the nose foreward anyway! This is the only way to get airspeed and to get air going over the control surfaces.

you have to check your balance and when you re try to take off you have to gain as much air speed as you can and when ready to be air born ease back on the elevator do not DO NOT put all the elevator up if you use to much elevator for take off you could loose air speed very fast and you wil stall and if you stall it will be hard to pull it back up because of the low altitude.




GOOD LUCK

I have the same plane with the same engine& prop ( I have 5 OS 52 and I run APC 12x6 on all of them) ( see my pic of Valley Forge Christmas) I am flying it on skis at this time. If you got that plane up as quickly as you say with that combination and it balances on the spar. It was forced into the air to quickly bottom line period. I have over 200 flights on mine I have never had a problem with it doing that. I always let the tail come up and run on the ground for a bit before I rotate. Is a wonderful plane. Can do almost anything with it.
The DiBo

I agree all the way with GI. Don't bother changing the prop, it's not the problem. 12/6 will give great climb, and slow you a little on the downward vertical lines, 11/8 will give more airspeed, something you don't really need.

Jetts