Ep pitts 42" - hobby king model

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Ep pitts 42" - hobby king model

Postby spitfire2010 » Mon Oct 11, 2010 11:12 am

I've recently built and maidened the pitts and it's flys well. I've noticed that at high throttle it baloons up. What causes this issue and what things should I look for to resolve the issue
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Re: Ep pitts 42" - hobby king model

Postby pushinoldrc » Mon Oct 11, 2010 1:23 pm

Since biplanes have different types of wing mounts, it is important that the incidence on each wing, and the stabilizer is checked every so often. I usually check the wing incidences every month, or every 4 to 5 flights. If the incidence of either wing is more than +2 degrees,the airplane will balloon under power. If the tail (horizontal stabilizer) is more than -2 degrees, then the same thing will happen.
I usually set my incidence at 0 for the bottom wing, and +1 to +2 degrees on the top wing with the tail at 0 to -1 degrees on biplanes with ailerons only on the bottom wing.
This allows for a bit of washout for landing. The top wing will stall slightly before the bottom wing, allowing the airplane to settle on landing.
If I am setting up for a biplane with ailerons on both wings, I try to mix slightly less throw on the top wing with the same incidence settings so that I still have some control when it begins to stall.
Usually smaller bipes have greater incidence settings than I prefer, I guess to make them self correcting. I generally try for 0,0,0 if I am trying out a new design to see how it should handle at stall speed.
A few fellows at the field I fly at have gotten bipes, and not been able to fly them because they are used to flying at full throttle for the duration. Most bipes do much better at slow speeds, and perform ALL aerobatic maneuvers quite well.
Besides, a 15 MPH knife edge looks really good.
Bryan
Landing is one aerobatic maneuver that MUST be perfected!
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Re: Ep pitts 42" - hobby king model

Postby RCModelReviews » Mon Oct 11, 2010 10:37 pm

Welcome to the wonderful world of decalage and pitch-stability.

The reason the bipe pitches nose-up when you apply power is because the thrust of the engine causes it to fly more quickly and the faster it flies, the more lift the wing(s) create. With the wings creating more lift -- they cause the nose of the plane to pitch up.

You can reduce this effect by adding downthrust to the motor so that the extra lift is canceled out by the way the motor is angled down.

Why are planes like this designed to pitch up when they fly faster?

Simple - it makes them more stable.

The idea is that if the plane is flying at a regular speed -- it will fly straight and level -- the lift of the wing (trying to pitch the plane up) balancing the weight of the nose (trying to pull the nose down).

Assuming a constant power...

If the model's airspeed slows then there will be less lift so the weight of the nose will cause the model to pitch slightly down -- which will in turn cause it to dive slightly and pick up speed -- until the lift of the wings again balances the weight of the nose.

If the model's airspeed increases, there will be more lift and this will be greater than the weight of the nose so the model will pitch up and climb. In climbing, it will also slow down -- so the lift from the wing will be reduced until it again balances the weight of the nose.

In effect, this automatic correction means that once trimmed, the plane will fly "straight and level" without input from the pilot. In fact, when properly set up, you can fly a model like this without even using the elevators. I demonstrate this to student pilots and they're amazed (some seasoned pilots are also amazed).

What model-fliers sometimes forget is that: throttle controls your altitude, elevators control your speed.

When you fly a model like this -- adding power will make it climb, removing power will make it descend -- without even touching the elevator stick.

Of course many RC fliers prefer a "neutrally stable" model that doesn't pitch up or down in response to throttle input but it's almost impossible to achieve this with a lifting wing-section because the amount of lift such a wing creates is always proportional to its speed through the air.
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Re: Ep pitts 42" - hobby king model

Postby spitfire2010 » Mon Oct 18, 2010 5:38 am

Ok, I've just finished rebuilding parts of this model and I was checking out the angles of the wings.

Bottom wing is about + 2/3 deg and the top wing is 0 deg.

Now I'm scratching my balding head????
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Re: Ep pitts 42" - hobby king model

Postby RCModelReviews » Mon Oct 18, 2010 6:09 am

Sounds about right for a bipe
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Re: Ep pitts 42" - hobby king model

Postby JBC » Thu Dec 09, 2010 7:12 am

Interesting reading, I must be lucky as my Hobbyking/Art-tech Pitts handles really well, no hint of ballooning. Must be something to do with the all epoxy in it :oops: :D
Helping the glue industry, one crash at a time.....
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Re: Ep pitts 42" - hobby king model

Postby Buzzkill » Sun Jan 30, 2011 4:36 am

I have an E-Flite Model 12 15e and a ZeroGravity Pitts Python and neither balloons with increased speed. Thrust angles I suppose or luck? Both seem to fly "goes where you point it".
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