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Old 05-06-2012, 09:27 PM   #1
npowell28
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Default Setting up a PUSHER prop

Hi,

Just taken my home made UAV out for it's first fly. Flew really nice apart from when i put the power on it climbed really fast. It has a pusher prop. I was wondering do i put a bit of down angle on it as you would with a normal tractor prop to solve the climbing under power issue?

Cheers Guys
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Old 05-08-2012, 12:53 AM   #2
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sure, we do the same to edfs on the back of the falcon 25s

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Old 05-12-2012, 08:21 AM   #3
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Originally Posted by npowell28 View Post
Hi,

Just taken my home made UAV out for it's first fly. Flew really nice apart from when i put the power on it climbed really fast. It has a pusher prop. I was wondering do i put a bit of down angle on it as you would with a normal tractor prop to solve the climbing under power issue?

Cheers Guys
Yes you can ... by adding a washer or two to the motor mount bolts so that REAR of motor is lower than the front ... but you should set the motor thrust line so that at cruising power you are level flight ... that will mean that full throttle will still induce a climb.

Many use a mix to get around it ... set up thrust line to be level at cruise throttle, then as throttle is opened up to full, the Tx mixing adds a touch of down elevator to compensate for the climb tendency.

What you should not do though is consider the opposite and add up elevator mixing as you close throttle !! That is a recipe for a stall and crash.

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Old 05-12-2012, 09:16 AM   #4
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What's the configuration of the plane?.. Planes with props mounted behind the wing and with the tail directly in the prop wash (a common layout on a UAV) can be counter intuitive when it comes to adjusting thrust angles. You need to consider the effect of the angle of the prop wash over the tail.

The other thing that can make a plane climb strongly under power is if the CG is too car forward. A dive test should indicate if you need to adjust the CG.

Dive test: Trim the plane to cruise straight and level 'hands off'. Push into a steep dive (at least 45 deg). Allow the plane to continue it's dive 'hands off'. Does it rapidly pull up all on it's own?.. If so it's nose heavy. For most planes you should aim for the plane to very gently recover from the dive. Carrying on straight with no recovery is a neutral stability trim and may be ok for aerobatic models. If the dive gets steeper or maybe goes vertical and recovers inverted than the CG is too far back.

A photo of the plane might help.
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