spantax
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Why So Few V-tails?

Thu Apr 19, 2012 1:53 pm

After watching a video of the exciting Vision SF50 "personal jet" from Cirrus I was wondering why we don't have more V-tail planes in the skies. As far as I see the whole thing, with 2 instead of 3 surfaces you get lower weight, less drag and even more accesibility to hangars (less height). Perhaps in the old times the aerodinamic problems of the V-tail were a barrier but nowadays with fly-by-wire, auto-pilots and computing power, the handling of a V-tail ac should be equal (maybe even easier) than for a conventional tail. I look forward to fly on the A380 V-Tail. Regards.
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rwessel
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RE: Why So Few V-tails?

Thu Apr 19, 2012 5:35 pm

A significant practical issue with a Vee tail is that trimming, particularly in pitch, is not very efficient. Each surface produces force at an angle to the direction you want, but the unwanted side forces cancel out because the two surfaces produce them in opposite directions. Those unwanted side forces imply extra drag.

A conventional tail would also be inefficient for the same reason if asked to produce force at a 45 degree angle. But the problem is that it's not: Most of the time the tail produce a relative small amount of force in the yaw plane, and a relatively large amount of force in the pitch plane. This is particularly true of long "tube" designs with large CG ranges (like airliners). So a conventional horizontal stabilizer is well matched to the requirements.

Note that the common complaint about Vee tails having less directional stability is not really true - in most cases Vee tails are adopted to minimize drag, and tend to be sized as small as possible - the apparent lack of directional stability is the result of the undersized tail feathers.

While a Vee tail has advantages (less wetted surface, mass, etc), the disadvantages tend to outweigh the benefits in most applications. In the case of a couple of the VLJ designs, the Vee tail gives them space to mount the (single) engine.
 
srbmod
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RE: Why So Few V-tails?

Thu Apr 19, 2012 7:27 pm

The Eclipse 400 was also supposed to be a V-tail design. V-tails are not a very common design, as the most successful V-tail a/c is the Beechcraft Bonanza 35, which was in production for 35 years and they built 1500 of them. The a.c did have a bad reputation as the "V-tailed Doctor Killer" or "Forked Tail Doctor Killer", but it was not the design that resulted in a number of crashes, it was the inexperience of the pilot (It was a bit too much plane for less experienced pilots.).

The V-tail is a very common feature of UAVs though.
 
jetstar
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RE: Why So Few V-tails?

Thu Apr 19, 2012 9:15 pm

Quoting srbmod (Reply 2):
The Eclipse 400 was also supposed to be a V-tail design. V-tails are not a very common design, as the most successful V-tail a/c is the Beechcraft Bonanza 35, which was in production for 35 years and they built 1500 of them. The a.c did have a bad reputation as the "V-tailed Doctor Killer" or "Forked Tail Doctor Killer", but it was not the design that resulted in a number of crashes, it was the inexperience of the pilot (It was a bit too much plane for less experienced pilots.).

The V-tail is a very common feature of UAVs though.

Actually slightly over 10,000 V-tail Bonanzas were built starting from 1947 with the basic Model 35 and ending in 1982 with the last version, the V35B and yes they had the reputation for being doctor killers.

If I remember back to my days working as an A&P at an FBO, I worked on many Beech products including the Model 33 straight tails and the 35 V-Tails and if I remember correctly there were some structural issues with the mounting supports of the V-tail which was resulting in premature failure of the tail section in adverse conditions. I believe there was an AD note to reinforce the tail to fuselage supports.

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Goldenshield
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RE: Why So Few V-tails?

Thu Apr 19, 2012 9:57 pm

V-tails overall have less authorityat slower speeds than a standard 3-surface configuration, not that it's a problem for most aircraft.

Quoting JETSTAR (Reply 3):
I remember correctly there were some structural issues with the mounting supports of the V-tail which was resulting in premature failure of the tail section in adverse conditions. I believe there was an AD

That was for the lengthened version. The short model didn't have that issue IIRC, and yes, there was an AD to strengthen the support mounts and fuselage.

Also, V-tails are sexy.  

[Edited 2012-04-19 14:59:21]
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aklrno
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RE: Why So Few V-tails?

Thu Apr 19, 2012 10:43 pm

Quoting JETSTAR (Reply 3):
The V-tail is a very common feature of UAVs though.

Is that more an issue of radar cross section? I think all low radar observable aircraft have angled tail surfaces (if they have a tail). The radar cross section advantage outweighs any decrease in aerodynamic efficiency for military aircraft. Low radar cross section is probably a disadvantage for civil aircraft.
 
BMI727
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RE: Why So Few V-tails?

Fri Apr 20, 2012 4:39 am

Quoting spantax (Thread starter):
I was wondering why we don't have more V-tail planes in the skies.

They don't really help.

Quoting spantax (Thread starter):
As far as I see the whole thing, with 2 instead of 3 surfaces you get lower weight,

Not really. Often the necessary area is about the same. The best application of V tails is if there is a severe height restriction or low observables.
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sccutler
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RE: Why So Few V-tails?

Fri Apr 20, 2012 4:49 am

Nonetheless, the V-Tail Bonanza is a true work of aerial art. Just ask the man who owns one!  
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SAAFNAV
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RE: Why So Few V-tails?

Fri Apr 20, 2012 5:42 am

Quoting Goldenshield (Reply 4):

Also, V-tails are sexy.

Agreed, they look good!

What glider is that?
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rwessel
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RE: Why So Few V-tails?

Fri Apr 20, 2012 7:43 am

Quoting SAAFNAV (Reply 8):
What glider is that?

HP-18, maybe?
 
Goldenshield
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RE: Why So Few V-tails?

Fri Apr 20, 2012 2:14 pm

Quoting rwessel (Reply 9):
Quoting SAAFNAV (Reply 8):
What glider is that?

HP-18, maybe?

Correct!
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rcair1
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RE: Why So Few V-tails?

Sat Apr 21, 2012 1:40 pm

Quoting JETSTAR (Reply 3):
Actually slightly over 10,000 V-tail Bonanzas were built starting from 1947 with the basic Model 35 and ending in 1982 with the last version, the V35B and yes they had the reputation for being doctor killers.

There was quite an active debate when the V-tail was being built. Proponents pointed at the pilots - the famed 'doctor killer' syndrome where they claimed that rich doctors bought them but did not spend enough time flying. Opponents would point out that the crash rate was much higher in the V-tail than the straight tail and point at the aircraft and that there was no data that said doctors only bought the V-tail.

The most common crash was overspeed followed by in-flight breakup. I remember an interesting simulation/study done by one of the aviation safety magazines I used to get that showed how a structural breakup occurred in the V-tail and it was quite impressive. It started with a flutter and my recollection was that once it hit critical flutter (which took well less than a second), the plane broke up in under 2 seconds. The progression was quite interesting and non-intuitive. This was in the '80's so I'm not sure how valid the simulation was - pretty complex mathematics.

My own experience with the 2 aircraft (have flown both - but only a few hours in each and far fewer in the V-tail) was that the V-tail was very slippery and gained speed much more rapidly than the straight tail. I'm not sure why - but it was a definitive impression - it was very easy to drop the nose in a turn and man - it picked up speed very quickly. I learned to watch the V-tail very carefully - never had the issue in the straight tail. I'm not sure the V was any slipperier, but it was easier to gather speed and get behind the aircraft. The first time we flew it my IP was flying and I remember him going 'whoa' as we suddenly picked up speed in a turn.
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longhauler
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RE: Why So Few V-tails?

Sun Apr 22, 2012 3:01 pm

Quoting sccutler (Reply 7):
Nonetheless, the V-Tail Bonanza is a true work of aerial art. Just ask the man who owns one!

I envy you, and certainly agree. A timeless design that is as beautiful as the day the first came off the line.

Quoting rcair1 (Reply 11):
I'm not sure the V was any slipperier, but it was easier to gather speed and get behind the aircraft.

Only think I can imagine, is that it is less pitch stable than the conventional tail. When the nose is allowed to drop, either aircraft will pick up speed, as it is a very slippery aircraft ... however, the nose dropping is probably more likely with the V-Tail.
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Goldenshield
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RE: Why So Few V-tails?

Sun Apr 22, 2012 3:24 pm

Quoting longhauler (Reply 12):
Only think I can imagine, is that it is less pitch stable than the conventional tail. When the nose is allowed to drop, either aircraft will pick up speed, as it is a very slippery aircraft ... however, the nose dropping is probably more likely with the V-Tail.

This isn't as big a problem with the Bonanza, perse, but with the above HP-18, there are issues with the low-speed regimen---particularly with stalls/spin entries; one tends to run out of rudder/elevator authority fairly quickly. That particular model actually has extended tail feathers to help mitigate it compared to others in the family, and it helps a lot. The issue is still there, but not near as bad as its sister models, from what I hear.
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spantax
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RE: Why So Few V-tails?

Mon Apr 23, 2012 1:09 pm

Thank you to all for your comments. It is always a pleasure to learn interesting things from you.

But let me come back to the reasoning. If with V-tail trimming is not efficient because of the extra drag created by the 45 degree configuration, why not to eliminate this 45 degree limitation by passing to a 90 degree configuration, i.e. that of a bird?. And in this case the directional stability should be no problem with fly-by-wire and a powerful computer.

And another point: as somebody said, UAVs are often V-tail. If (the reasoning goes) UAVs are a kind of vanguard of things to come, does this means that V-tail could be a common feature at some point in the future?
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tdscanuck
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RE: Why So Few V-tails?

Mon Apr 23, 2012 1:55 pm

Quoting spantax (Reply 14):
If with V-tail trimming is not efficient because of the extra drag created by the 45 degree configuration, why not to eliminate this 45 degree limitation by passing to a 90 degree configuration, i.e. that of a bird?. And in this case the directional stability should be no problem with fly-by-wire and a powerful computer.

No matter how powerful your computer, you need some kind of directional control surfaces. Birds do it with wing warping, which we don't yet have on airliners. Things like the B-2 do it with split ailerons, which work but are draggy.

In order to withstand an engine out with the other at takeoff thrust on a twin and meet certification requirements, I don't think we can get away from a vertical surface for a long time.

Tom.
 
FlyHossD
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RE: Why So Few V-tails?

Tue Apr 24, 2012 6:19 pm

Quoting tdscanuck (Reply 15):
n order to withstand an engine out with the other at takeoff thrust on a twin and meet certification requirements, I don't think we can get away from a vertical surface for a long time.

Here's a link to the twin engine conversion of the V-tailed Bonanza, known as the Super V - so it can be done:

http://www.airbum.com/articles/ArticleSuperVTwinBonanza.html

Great looking airplane, me thinks.
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Starlionblue
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RE: Why So Few V-tails?

Wed Apr 25, 2012 8:48 am

Quoting tdscanuck (Reply 15):
In order to withstand an engine out with the other at takeoff thrust on a twin and meet certification requirements, I don't think we can get away from a vertical surface for a long time.

Vectored thrust. 
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