Hi everybody,

Out of sheer boredom, and the want to glue a few sticks together, I picked up an old Ace Alpha 15 kit. Built it, covered it, and took it out for a maiden flight.

I came home confused.

Let me start by saying this in not my first plane. More like my 40th. I have been flying for 20+ years. Mostly .15 sized combat and small electrics for the last 5 years. So while I am no means an expert, I would not consider myself a novice either.

So here are my issues.

The plane is set up rudder/elevator only, powered by a LA15, and is a high wing with a semi-symmetrical airfoil.

I took the plane out to my normal field on a flat calm day. Range check, etc, lined up for a takeoff. Pretty smooth takeoff, with a steep climb out. FULL down trim was added to achieve level flight, but I have flown plenty of trainers that want to climb under power. A couple of clicks left trim were added and we were straight. I took a few passes around the field at ½ throttle with no problems. Gave it a little gas and pulled into a loop. It nosed up and snapped HARD left. Ok I though maybe a little too much elevator throw. I circled around, lined up for a loop again, eased up on the elevator and it nosed up and snapped HARD right.

I decided that was enough and brought it in for a nice floating landing to check things out.

I double checked the balance point, all linkages, reduced the elevator throw, and decide to take another crack at it.

Lined up for takeoff, the plane scooted down the field and just leaped (vertical stall) off of the ground. Luckily I recovered and got some altitude. I assumed bad bounce on the field cause the abrupt takeoff.

Flew around a little more. Same problems with loops, hard snaps, one way or the other. Plane was quite stable on the flat and level at high and low throttle.

Landed, refueled, and lined up to take off. Same as last time, the plan just jumped off the field into a vertical stall. No way I had the same bad bounce as last time.

Circled, landed, and took it back to the shop.

These are the things I then double, double checked.

Wing: No twists, no washout (maybe I should add some?)

Elevator: Strait in relation to wing.

Rudder: Perpendicular to the elevator, and in line with the fuselage.

Down thrust: According to planes

Right thrust: According to planes

Wing Incidence: According to planes

Center of gravity: Under main spar, according to planes (4oz fuel tank so I am pretty sure I was not nose light)

Landing gear angle: Neutral to slightly nose high.

So now I am confused, as I cannot find anything obviously wrong. I can take it out for a few more flights, but I don’t just randomly want to start changing things. I just have a feeling that I am missing something.

And I don’t really want to take it out until I can figure out the leap off the ground takeoffs. The only thing I can think of is the full down trim is causing the plane to stick to the ground and when I give it a little up elevator, it is causing the wing to quickly change angle and leap into a stall.

So that’s my long list of confusion. Does anyone have any words of wisdom?

Thanks

Sounds like excessive wing incedence or way too little downthrust.  If it loops with added throttle there is little else it could be.

Currently it has 5° downthrust and a wing incedence of +3°. Does this seem about right? Both numbers match the planes.

And just to clairify it will not loop with just additional throttle, if anything I would call it extreamly pitch sensitive.

I have experienced this with not enough rubber bands on the wing on a couple of planes. The lift of the wing lifts the front of the wing high, causing a temporary incidence issue, followed by the fuselage snapping back UP to the wing, changing angle of attack and the whole thing just snowballs. It sounds crazy and took me a while to figure out what was going on, but check that first.

Thanks, that was not one I had thought of. I was using 10 #64s, but I will recheck to see if that is enough. I was taught to hold the wing dowels with your index fingers and press the wing up with your thumbs, and if you can move the wing, it was not enough rubber bands.

Sounds like the angle of attack on the wing is simply too high or the wing is loose, but 10 rubber bands ought to be enough...

How did you measure the angle of incidence, it can be tricky to get the correct angle measure on a flat bottom wing as it is highly dependent on the profile of the leading edge. I would just shim the trailing edge until it flies well.

I used a Robart incidence meter. And since it is a semi-symmetrical wing I measured it at several points along the wing to compensate for any leading edge irregularities.

I think I will shim it closer to +1° for the next flight.