I have advanced to the point where I can build a model and fly a low wing sport plane. I generally don't like to build planes but, I do like to purchase an airframe and retrofit that plane with my own servos, engine, rx, etc. My problem is when I retrofit a plane, the last two maiden flights have gone badly. On take-off the plane will liftt off smoothly and then the wing will dip where it is perpetdicular to the runway. I adjust the throws according to manual. When I have my TX for 25% expo I am able to correct. When my settings were expo at 50% the plane was unable to recover and crashed. This has happened twice. What are some of the causes. Any help would be appreciated. Is this possibly due to lack of airspeed? Please help!!!

Either your ailerons aren't adjusted correctly and your plane isn't balanced latterly. Or most likely, both.

Of course you didn't mention what plane your talking about, but I have to ask. If your flying a low wing sport plane and have advanced that far, shouldn't you already know whats wrong?

Did some research and figured out the issue. The CG is correct and elevators and ailerons are trimed. I have been flying my trainer which has helped me develop some bad habits lately. Trainers are very forgiving. I have been using too much elevator on take-off the plane has stalled. The trainer has some slight down elevator because it will tend to just float on landing. On take-off you can give the trainer extra elevator to compensate. The plane I was referring to was a Goldberg Tiger 2. I also fly a World Model t-34. They are both low wing trainers. Just had to watch a clip on Youtube of someone doing the exact same thing with a scale sized Hurricane. It was rookie pilot error.

Balance is important but also being active on the controls. It does sound like a stall on takeoff. One wing side is more stalled than the other so it rolls. Another classic problem is not having the aileron servo going the right direction; when that happens your correction makes it worse and rolls the plane into the ground.

Just a note here. Upon take off, you should not pull in elevator until the plane is ready to lift off. A basic mistake is to pull the elevator at the same time as you push the throttle for take off.

BUT, prior to even going to the runway, I stand behind the plane and look at the wings. Right stick = right aileron moving up and left moving down. Right stick right aileron moves up. Simple. This way you know that the ailerons are connected correctly.

25% expo is more than enough.

CGr

On that type of airplane, expo is not really required. I usually don't bother with it unless the model has huge control surfaces.

It does sound like you are not gaining enough speed before lift off from the runway. If the wing drops like that, the only chance of recovery you have is releasing the elevator and picking up the wing with RUDDER, as attempting aileron correction will be of no value. I doubt that 5% of RC fliers would be able to respond quick enough to recover from it (or lucky enough), so avoiding is your best bet.

Like High Plains said, get your ground speed faster, the plane will almost lift off by itself, learn too use your rudder also for slow speed situations such as take offs and landings. When your ground speed is fast enough on take off feather in some up elevator, dont haul up on it like your fishing.

You've found out that you're pulling too much elevator. That's often the case.

What you might also discover is the elevator throw can be reduced a lot. I've had a couple of Tigers and a Calmato (tiger knockoff) and all of them flew much better (and safer) with dual rates set on the TX. Setting low rates and using them on the elevator is really worthwhile for most flyers. With my 3, around 50% for low rates made landing much smoother. That was after I'd adjusted the high rate by flight testing.

Flight testing showed that all 3 had more elevator throw than necessary when set as recommended in the assembly instructions. Throw affects how sensitive the plane is to land for one thing.

Hi!
Sounds like you not a club member?!
Could be many reasons to why your plane does not fly like it should.
First set up your radio correctly! That means using 100% trow or more on all channels but throttle.
Do not use any dual rates of differential or expo ...at least not the first flights.

The first thing to check on the plane if it doesn't fly straight is the wing! check for for warp. It's very vital that you have wash-out in the wing (wing tips) . If you have wash-in in the wing , your plane will behave like you tell us, drop a wing, and fly very badly!

Things I would check first:

1. Make sure your ailerons are aligned with the wing chord on each wing (Level to the wing) and your wing isn't warped.
2. Aileron servo isn't reversed
3. Make sure your elevator is level. This is especially important if you have a plane with two elevator halves with two elevator servos.
If they aren't aligned they can induce a roll especially if you are pulling back.
4. Air speed. You should only have to bump the stick back to get it to leave the ground. If it is a tail dragger, wait for the tail to come off the ground and gently pull back.

Think stick pressure movements on a maiden flights not full stick movements, never horse the airplane off the ground before it is ready to fly, just let the energy build and the airplane will fly itself off the ground. Here is a video of one of my maiden flights, watch the elevator, you will see that it stays neutral until it is airborn. you can double click for full screen viewing.

http://vimeo.com/22208107

Bob

You already have it sorted out..Tigers are fantastic planes..The Tiger 2 is a bit harder than the Tiger 60 because it seems to react faster..It almost is beyond a trainer in my opinion but if you can get past the first 10 or so flights you are going to love it...Set your throws up to low rate for take off...Let the plane build up speed. I hope you have about a 46 in it for power...It should fly itself off if everythig is set rite .. If it starts skipping easeback on the stick start climbing and be ready to slowly roll in whatever direction you do your circuits ..The trick is to be easy on the sticks...It would be a good idea to have a trusted friend take it up and trim it out for you prior to you flying it...That way it is so much easier to fly..You are not fighting the plane..

I had the Tiger 60 as a second plane. I was very reluctant to do anything more than fly orbits with it for the first 10 or so flights, then I began to get more bold with my flying technique. I did a lot of touch-and-go's, sometimes landing a bit further away from me than I realized I was, putting it in the tall grass a few times. It was a tough plane. I beat it up pretty much, but it took a beating and kept me in the air for several months until I upgraded.

That was back around 1999 or so. I since sold it to someone that just had to have it. As far as I know, he is still flying it.

My instructor, Ron, built a modified Tiger II kit that he heavily modified. He removed two wing bays and lengthened the fuselage, and lightened it considerably so that it would accomodate electric power. That plane is incredible. I've flown it and it flys like it's on rails.

I also have a Tiger 120, by the way, which flys great. The bigger they are the easier they are to fly, and the Tiger 120 is no exception. It is probably the most relaxing plane I've ever flown. I have an OS 1.20 AX on that plane and it pulls it along nicely.

CGr.

I sure learned a lot about taking off watching Bob's video, well, not really but I enjoyed the heck out of it though. My kingdom to ever locate a cameraman in our area that can even follow a plane with a camera even when you are telling him what your going to do. Great video. I wish I would have seen the video of the Cub on Floats too before I painted my float plane, I would have painted my floats the same way. Again, another outstanding video with a good cameraman.
I didn't learn anything about float flying watching that video either but I got a kick out of it.