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Old Mar 18, 2011, 01:16 PM
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Clarkston, MI
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V tail vs. X tail

I'm considering buying a full house TD molded sailplane and I see both tail configurations...my question is:does one tail configuration have advantages over the other. Thank you in advance for responding.
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Old Mar 18, 2011, 01:23 PM
Detail Freak
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Harbor City, CA
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V-tails are lighter.
Cross tails usually have more tail volume and so are more stable.
Cross tails usually have a joiner and full flying horizontal stab, and so very easy to break down and travel and store.
V-tails are a pain to remove and store normally.
For a cross tail, you might want a bigger servo for the stab.
V-tails can get by with fairly small servos for the fuse usually...

Hope that Helps you.

R,
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Old Mar 18, 2011, 01:37 PM
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My experience is that V-tails are better suited for slope flying and the X-tails are better for thermal flying.

The reason is that the V-tails do not stabilize the plane in its yaw axis as well at slower speeds typical of thermal flying. They tend to let the plane dutch roll more when rolling in and out of bank changes. Dutch rolling causes loss of energy and can hurt thermal performance in light conditions.

On the slope, speeds being flown are typically faster and v-tails do very well at stabilizing the yaw excursions.

Personally I like v-tails for the slope and X-tails for thermal flying.
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Old Mar 18, 2011, 02:02 PM
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Target's comment on the removal of the V-tail should not be under valued. Unless it is a two piece V-tail, traveling with a one piece V-tail model is a pain. For TD planes in the US , cross tails are dominant in competitions due to a percieved advantage in the landing zone. V-tails dominate in F3B and slope racing. If you want the lightest version of the plane you're considering, go with the V-tail. If you aren't flying competitions that require precision landing, then buy the one that looks the best to you!

Clay
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Old Mar 18, 2011, 03:46 PM
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Quote:
Originally Posted by V1VrV2 View Post
My experience is that V-tails are better suited for slope flying and the X-tails are better for thermal flying.



Personally I like v-tails for the slope and X-tails for thermal flying.
I agree 100% with this summary. It is a good simple statement.

I went into a little more details of day in and day out use, but it's true that most V-tail designs have less tail volume than their cross tailed sisters, so, they work better going fast than slow.

There are a few exceptions, though, and TD planes are coming out now with more appropriate sized v-tail panels....
Therefore, you might post which plane you are thinking of getting, and look for direct experience from someone that has flown both tail styles of that plane.
Again, as both guys above indicate, it really depends on what you intend to do with the plane. Both have advantages/disadvantages.

Oh, and V-tails sometimes fair better in rough landing zones, since they are up and away from ground issues. That is more of a slope flying thing, though.

R,
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Old Mar 18, 2011, 04:23 PM
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Again, thank you all for your insight. My interest in in thermal duration flying.
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Old Mar 18, 2011, 05:33 PM
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When mixing elevator compensation in landing configurations, a V tail will receive unwanted pitch inputs when yaw inputs are given and vice versa ... a cross tail has no such interractions.

tk
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Old Mar 18, 2011, 08:44 PM
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Its not that noticeable if the the V-tail differential is set properly to exclude pitch input with yaw application....

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Old Mar 18, 2011, 09:05 PM
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You pays yer money, and you takes yer choice.

I've flown both, and like them both. My current most active non-DLG glider has a conventional tail, but once that one goes into the shop, my alternate for thermal duration will be a V-tail. I like them both.

My conventional tail glider is fairly short-coupled, and needs a lot of rudder which I do with my thumb. For no real reason, I keep it coordinated manually, not with rudder-aileron (or aileron-rudder) mix. My v-tail glider used to use a mix, but the last time I flew it, I removed all mixing and didn't see any large need for it. Rolling with some differential aileron seemed very axial. These aren't the usual reportings, but what worked for me.

As long as you are having fun, it shouldn't matter too much.

Yours, Greg
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Old Mar 18, 2011, 10:18 PM
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If the v-tail is properly sized, it seems to behave just the same. Or at least that's how it's seemed flying my Mantis. However, the v-tail puts more of a torsional load on the tailboom, which is something you can really notice with the old Mantis. I think there is no inherent disadvantage in flying performance with v-tails except that people tend not to design them properly.

I've found v-tails annoying to handle and more prone to hangar rash.
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Old Mar 18, 2011, 11:25 PM
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TK is referring to just when getting close to the landing bullseye while flaps are
deployed during "crow". I understand why he says it will cause trouble, but I can't
say I have used a V tail for TD contest work.
Its true that lots of folks prefer cross tails, but someone must have figured out
how to either mix out, or avoid that problem in the LZ; there have been V tails in
the winners spot before. They made it work somehow with consistancy.

R,
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Old Mar 18, 2011, 11:39 PM
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Depends on the model.

IF they have the same volume, there's not much difference in performance. Full treatment on the subject (actually, several treatments) here: http://www.djaerotech.com/dj_askjd/d...ilsurarea.html

However, many models that come with both tail types have undersized V surfaces.
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Old Mar 19, 2011, 11:13 AM
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I've flown a couple of different Manti (plural of Mantis?) quite a bit, including in some thermal contests. Never really noticed a problem landing them. I'd say I landed them about as well as any glider I've ever owned. Very similar to Aegea Mantis with conventional tail.
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Old Mar 19, 2011, 04:39 PM
Marc PUJOL
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I flew the same plane with V tail or X tail. Both with the same projected surface. The difference is quiet obvious. V tail is "b... sh...". Sorry to be so clear, but it is the reality.

It is always heavy in yawing. And those who says the contrary should change the configuration and try with the same model.
For the same efficiency, it is not lighter. It is strictly equivalent. And the issue of a tail is efficiency. Not surface, or projected surfaces.
If normaly V tail has less drag, it is only when it doesn't produce any lift. As soon it does produce one (means >80% flight time), then it does produce more drag.

On the top, if tends to stall earlier than X tail when you are acting on both ruder and stabiliser commands.

For me it is then realy clear that V tail is a matter of fashion, not a matter of efficiency.
I love the design of V tail but I dislike piloting them.

If it does product any advantages, be sure that all commercial plane should have addopted it.

If you are not in agreement, please make few trial with XFLR5 and test the dynamic aspects. Then make comparison experiences. You will change your mind. Every ones that does it went to my mind.

I have writen a comparison between V and X tail that try to be objective (sorry in French only for the moment). You can download it on www.xerivision.com.

Marc
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Old Mar 19, 2011, 07:58 PM
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Just watchin'...


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