V-tail, pitch down on left rudder  
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All Forums >> RC Airplanes >> Pylon Universe - RC Pylon Racing >> Q-500 Racing >> V-tail, pitch down on left rudder
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V-tail, pitch down on left rudder - 4/18/2007 11:00:34 PM   
wkevinm


 

Posts: 139
Joined: 9/17/2004
From: Sherwood Park, AB, CANADA
Status: offline

I recently flew a new Q500 airplane with the following flight characteristics;

The plane is a Seeker with a vacuum bagged wing. The wing is straight, the airfoil is NACA 66-012, the ailerons are skin hinged with .010 FG sheet. The fuselage again is from the Seeker kit, has been fiber-glassed. The V tail is 110 degrees and was also glassed with skinned hinge (.010 FG sheet). The balance is at 2 7/8” from the LE.

On the maiden flight
The plane flies straight out with only 2 clicks of down elevator trim, there was no roll or yaw trimming required.

The ailerons were set up with low rates and differential rate.
The elevator and rudders were set up with no differential.

When all seemed good I tested out the yaw response….. wow….left rudder and the plane dives like it was a Stuka , on right rudder the plane yaws to the right as would be expected.

I then made the following changes:

Put differential in the elevator / rudder servos (by placing the servo arms at about 30 degrees from the centre) thereby reducing down travel on the V-tail elevators. I then reduced end point on the radio to further reduce the down travel of the rudders. The result is that I have very little elevator movement in the down position for both pitch and yaw.

Next Test flight
Again all flies well straight and level. I applied left rudder… all is good…. Yaws to the left without pitching up or down. I yaw right and the plane pitched way up. Now… I can live with this a lot better than down but would prefer it did not pitch at all with rudder input.

My next thought is to bring back a little more down rudder on the end point adjust to reduce the pitch up if possible without introducing any down pitching.

I have no idea what would cause this affect, any experience or ideas?

Kevin M
       Post #: 1

RE: V-tail, pitch down on left rudder - 4/19/2007 12:59:24 AM   
Druce



Posts: 79
Joined: 1/6/2002
From: Edmonton, AB, CANADA
Status: offline 		Kevin.. is both rudders moving moving the same or is one moving up and down more than the other? maybe one is higher than the other in the nuteral position, sometimes its kind of hard to tell. Are the wings balanced (one side isn't heavier than the other??) Maybe the plane just doesn't like you..

(in reply to wkevinm)
       Post #: 2

RE: V-tail, pitch down on left rudder - 4/19/2007 2:22:09 AM   
wkevinm


 

Posts: 139
Joined: 9/17/2004
From: Sherwood Park, AB, CANADA
Status: offline 		John,
As best I can tell there is no measurable difference with the rudder / elevator throws. As far as wing balance I have not checked.
Would that cause this?

What does happen though is there is some warping / stressing of the tail planes due to stresses from the skinned hinge (using .01" FG sheet) but again minor. (next time I am using FG 1.4 oz S cloth).

Kevin M.

(in reply to Druce)
       Post #: 3

RE: V-tail, pitch down on left rudder - 4/20/2007 1:30:01 AM   
AllanU



Posts: 27
Joined: 7/19/2002
From: St.Albert, AB, CANADA
Status: offline 		Hi Kevin

Is 110 degrees for the vtail too flat? I have mine at 115 degrees and there is no issue.

Al

(in reply to wkevinm)
       Post #: 4

RE: V-tail, pitch down on left rudder - 4/20/2007 2:02:51 AM   
wkevinm


 

Posts: 139
Joined: 9/17/2004
From: Sherwood Park, AB, CANADA
Status: offline 		Al,
It is set at 110 degres, since this is the same as other planes have been, no problem. In fact 115degrees is flatter than 110.

Kevin M

< Message edited by wkevinm -- 4/20/2007 2:03:42 AM >

(in reply to AllanU)
       Post #: 5

RE: V-tail, pitch down on left rudder - 4/20/2007 4:14:53 AM   
Clark L



Posts: 145
Joined: 1/22/2003
From: So-Cal, USA
Status: offline 		Kevin,

Check that not only the throws are equal but that the surfaces move at the same speed. Depending on the servo, I've seen even new ones move at significantly different speeds. Maybe one elevator is binding a bit or you just have a slow (or fast) servo.

Also, It doesn't take much rudder to do the job on a V-tail and any amount of input more than "a little" will probably cause some adverse effects. I set my rudder throw so that I've got enough for a takeoff in a left crosswind, which isn't very much. I'm pretty much done with rudder once I get to the first pylon anyway.

Clark

(in reply to wkevinm)
       Post #: 6

RE: V-tail, pitch down on left rudder - 4/20/2007 4:04:54 PM   
diggs_74



Posts: 1268
Joined: 1/20/2004
From: Emerald, WI, USA
Status: offline 		Ok Kevin, I'll give you my .02 worth...

I believe the difference in left yaw that you are seeing has to do with the torque of the engine.. Once you dialed out most of the down on the left side it started to act normally. However, since you've also dialed all of the down out of the right side, when you key right rudder the right ruddevator (sp?) is moving down very little and the left one is going up much more causing the plane to pitch up becuase the torque from the engine is acting against the right yaw.

As far as the laterial balance is concerned, this will mostly show up when doing a full pull (up elevator) from knife edge. If the plane pitches up during the turn, a couple quarters may be required on the left wing tip.. Believe it or not, this is all it takes to see a noticable difference in how the plane turns.

I hope this wasn't too vauge..


_____________________________

Lee LaValley
NMPRA# 33w

(in reply to Clark L)
       Post #: 7

RE: V-tail, pitch down on left rudder - 4/21/2007 8:12:19 AM   
wkevinm


 

Posts: 139
Joined: 9/17/2004
From: Sherwood Park, AB, CANADA
Status: offline 		Thanks for the suggestions, I will check out those items.
Kevin M

(in reply to diggs_74)
       Post #: 8

RE: V-tail, pitch down on left rudder - 4/22/2007 3:11:56 PM   
StanDouglas


 

Posts: 112
Joined: 8/28/2003
From: Austin, TX, USA
Status: offline 		110 deg. is pretty much the standard and appears to be the optimum angle, not 115. But I'm wondering if you don't have something else going on. How does it behave at different throttle settings? Does it appear to be pitch sensitve and hunt a little? I had a Q500 that was exactly the same as others I built and was pitch sensitive It turned out that I had to raise the leading edge some to cure it. Easy to do, just shim under the bolts; once you get the right angle of attack repot the wing saddle.

I wouldn't be afraid to check things outside the box, thrust line, sloppy control linkages etc. You can check thrust by pulling verticle at about 3/4 throttle and observing if it pulls to the left or right, if it consistently goes left you need right thrust etc.

You also didn't mention if you were running a Nelson or Jett with those engines a whole set of speed and vibration come into play that don't with a TT Pro 40.

SD

(in reply to wkevinm)
       Post #: 9

RE: V-tail, pitch down on left rudder - 4/22/2007 4:58:38 PM   
wkevinm


 

Posts: 139
Joined: 9/17/2004
From: Sherwood Park, AB, CANADA
Status: offline 		Stan

I was running with a TT40 pro for test flights. This week I put a nelson on the airplane now that I am comfortable with the feel, and will be testing again when the weather coorperates. In Canada we run the Nelson with a detuned pipe and the engine is not as strong as a result. The is TT40 Pro for club racing, detuned Nelson for Canadian Prairie Circuit and then those so inclined could put the Nelson pipe on for 428 racing.

Once I can get out to fly it I will test out a few more things.

Kevin M

(in reply to StanDouglas)
       Post #: 10

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All Forums >> RC Airplanes >> Pylon Universe - RC Pylon Racing >> Q-500 Racing >> V-tail, pitch down on left rudder
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