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Old Jul 29, 2004, 11:12 PM
BOP spotter
Omaha, NE
Joined Jun 2003
144 Posts
V-tail differential

I just finished a v-tailed Sovereign, my first v-tail sailplane. In the build thread we started talking about optimizing v-tail design, and especially surface movement setup.

I don't have a computer radio, just an on-board electronic mixer, so I think I'm stuck with a 50-50 mix, but for those of you with more sophisticated gear, how do you set up your ruddervators? Do you use more servo travel for the rudder function and less for elevator? Do you use differential? Seems to me the combinations could get rather complicated!

Bill
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Old Jul 29, 2004, 11:45 PM
Registered User
Rancho Santa Margarita
Joined Jan 2004
101 Posts
I have found that I use more rudder throw than elevator. Especially for slope when sometimes i need to crab it in sideways to get a landing.

I am using a Futaba 9C so I get to use the computer.
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Old Jul 30, 2004, 12:25 AM
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Wisconsin
Joined Apr 2002
281 Posts
I think most sailplanes will use a lot less elev. than rudder no matter what tail design is used.

I read an article, a couple of years ago, about adjusting v-tail models. Can't remember by who or where I found it but I will try to explain the details. When, as an example the ruddervators are moved for a left turn the left half in a sense moves left or down and the right half moves left or up. The instruction said to fly level and smooth and quickly apply full left rudder. Watch for any up or down movement of the tail along with the right movement. If the tail moved up the instruction was to increase the throw on the right side and or decrease the throw on the left. Opposite adjustments would be made if the tail dropped. Of course the same test was done for a right turn.

Sounds simple enough.

Boy, I hope I got that right!
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Old Jul 30, 2004, 01:37 AM
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I use full rudder and less elevator. Becuase sometimes you really need rudder while flying. Other times I just use ailerons.

-Tomi
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Old Jul 30, 2004, 05:52 PM
BOP spotter
Omaha, NE
Joined Jun 2003
144 Posts
I found a lot of information on v-tail design at DJ Aerotech's web site. Go to http://www.djaerotech.com/dj_askjd/, enter "v-tail" into the search field, and get a bunch of articles on v-tail design, adjustment, etc.

Bill
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Old Jul 30, 2004, 06:21 PM
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Torrance, CA, USA
Joined Jan 2001
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Bill,

You don't need a computer radio to optimize your v-tail mixing. You can do it mechanically.

With your servos in neutral, move the servo arm one or two splines forward or backward (depending on your v-tail horns being on top or bottom). This is the way it was done before "computers made or life so much easier".

Regards,

Steve
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Old Jul 30, 2004, 06:57 PM
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Miami Lakes, Florida, USA
Joined Mar 2003
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I think Kestrel's post is the most interesting one in this thread so far. I'd sure like to read that article.
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Old Jul 31, 2004, 11:04 AM
BOP spotter
Omaha, NE
Joined Jun 2003
144 Posts
Thanks for everyone's input so far.

The servo arm or control horn angle will help optimize the response of the tail so that when you give a pure rudder input, the plane just yaws, without any pitch-up or down. I think that's all the differential adjustments can do.

What I'm more interested in is changing the total throws for rudder and elevator individually. It seems that can only be done with a mechanical mixer or a computer radio.

Without changing the surface throws, the other way to balance the control response is to change the v-tail angle, and then perhaps the surface area as well. So for example on the Sovereign, if I have the chance to rebuild the tail, I think I would decrease the tail angle quite a bit, maybe to as little as 90 degrees (it's 106 as built), and increase the surface area a little more. This should add to the effectiveness of rudder inputs, and decrease the elevator effect. It would be interesting to try, at any rate.
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Last edited by bfretless; Jul 31, 2004 at 11:47 AM. Reason: typed too fast!
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Old Jul 31, 2004, 12:04 PM
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Athens, LA, United States
Joined Apr 2002
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If you do that experiment, please let us know how it worked out.

EJ
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Old Jul 31, 2004, 11:19 PM
Registered User
Wisconsin
Joined Apr 2002
281 Posts
Quote:
Originally Posted by bfretless
Thanks for everyone's input so far.

The servo arm or control horn angle will help optimize the response of the tail so that when you give a pure rudder input, the plane just yaws, without any pitch-up or down. I think that's all the differential adjustments can do.

What I'm more interested in is changing the total throws for rudder and elevator individually. It seems that can only be done with a mechanical mixer or a computer radio.

Without changing the surface throws, the other way to balance the control response is to change the v-tail angle, and then perhaps the surface area as well. So for example on the Sovereign, if I have the chance to rebuild the tail, I think I would decrease the tail angle quite a bit, maybe to as little as 90 degrees (it's 106 as built), and increase the surface area a little more. This should add to the effectiveness of rudder inputs, and decrease the elevator effect. It would be interesting to try, at any rate.
I think that once you make the differential adjustments you will find that you still have enough up and down elv. throw to easily fly the model. You may not have to make a lot of adjustment to get the job done.

The changes that you are talking about in your last paragraph are essentially what Dr. Drela has prescribed for the Majestic.
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Old Jul 31, 2004, 11:30 PM
Registered User
Wisconsin
Joined Apr 2002
281 Posts
Miami Mike,

I have looked in my mess of sailplane papers and cannot find the info that I reffered to . However, if you do a search on the Net for "v-tail differential" you will get a few hits that may be of interest. Also, Sherman Knight has some info posted on the programing of some Jr radios. There is some info in them about setting up v-tail models. If you don't have a JR radio, the specific programming may not be of use but I think you will get the general idea. He explains some of the basic ideas. Interesting reading none the less. From what I have looked at, my basic description is accurate. At least with some radios, the differential adjustments are done using the End Point Adjustment feature.
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