Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Differential

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Old 11-01-2008, 02:35 AM
  #1  
Vendata
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Default Differential

Can anybody tell me why is it important to use Differential in 424 & 428 class of racing, & what is the benefit of using it.
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Old 11-01-2008, 09:21 AM
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Default RE: Differential

I considered differential when building my last 424 Q-500.

I ended up not installing differential on my high wing model.

For everyday racing there is no issue in turns or general flying.

When not racing the rolls are barrel shaped instead of axial. That is what you will see on a high wing racer without differential.


Installing differential to the ailerons is relatively easy:

1) Use a round control horn on top of your aileron servo.

2) Drill a hole for the aileron push rod approximately 20 degrees in front (toward the engine) of the normal aileron holes.

3) Use Z-bends to connect the aileron push rods to the servo.

4) Connect to the aileron normally.

When testing the differential there should be more up aileron than down.
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Old 11-01-2008, 11:41 AM
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PylonDave
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Default RE: Differential

Without differential, when you rollup to turn at #1 the right airloin (which is deflected down) has more drag than the left airloin (which is deflected up) and causes the plan to yaw toward the right wing, which pitches the plane up when you are rolled at 90* getting ready to pull around #1. Then you are out of wack when heading back to @2. The difference is subtle, but i could see the difference when i put the differential in.
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Old 11-01-2008, 11:45 AM
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djlyon
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Default RE: Differential

Nobody has ever suggested to me that differential was desirable on a 424 or 428 and I have asked a couple of top racers. In theory differential would result in less induced drag as a result of roll input. The drag coming from the increased left from the upward moving wing (down aileron) and adverse yaw from the increased drag from that same wing. Kind of a clumsy explanation sorry but just trying to keep it short.

Denis
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Old 11-02-2008, 02:33 AM
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Default RE: Differential

unless your flying F3D , you only need normal R/C controls to fly / race 424 - 428 class. keep all control surfaces down to minimum throws and just hit the ailerons and elevators when you want to turn . really its all to do with flying skills.
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Old 11-02-2008, 06:01 AM
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daven
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Default RE: Differential

I normally add mechanical differential to my racers, but don't really notice any difference. In theory it should be less drag, but I'm not sure I've actually seen it. I suppose you could measure it with data collection if you were really curious. Eagle Tree has a nice system, and their new e-loggers are relatively inexpensive.
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Old 11-03-2008, 12:58 AM
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garys
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Default RE: Differential

I'm one of the few that uses differential on almost everything. I can fly without it, but where I really notice it is if I have to make a correction that requires using more aileron. If there is adverse roll because the airplane needs some differential, it will throw the heading off while your making a correction, compounding the error you already made. A big key to going fast and winning is minimizing mistakes, and when you do make them, keeping the time to correct them to a minimum.
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Old 11-03-2008, 09:56 AM
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Default RE: Differential

I started using it a couple years ago and while it wasn't a huge change but it was noticeable when making corrections between poles (which I have to do more than I would like ) I also noticed a difference when entering the turn, it seemed a little more true if that makes any sense..
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Old 11-03-2008, 12:59 PM
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Default RE: Differential

EXACTLY! Also, if the differential isn't correct and the airplane loses its heading from adverse yaw, you're more likely to need more corrections, in addition to the additional drag caused by the adverse yaw itself.
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