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Why So Few V-tails?  
User currently offlinespantax From Belgium, joined Nov 2004, 323 posts, RR: 1
Posted (2 years 4 months 1 week 4 days 15 hours ago) and read 4466 times:

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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17 replies: All unread, jump to last
 
User currently offlinerwessel From United States of America, joined Jan 2007, 2346 posts, RR: 2
Reply 1, posted (2 years 4 months 1 week 4 days 11 hours ago) and read 4350 times:
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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.


User currently offlinesrbmod From , joined Dec 1969, posts, RR:
Reply 2, posted (2 years 4 months 1 week 4 days 9 hours ago) and read 4282 times:

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.


User currently offlineJETSTAR From United States of America, joined May 2003, 1645 posts, RR: 10
Reply 3, posted (2 years 4 months 1 week 4 days 8 hours ago) and read 4227 times:
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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.

JetStar


User currently offlineGoldenshield From United States of America, joined Jan 2001, 6014 posts, RR: 14
Reply 4, posted (2 years 4 months 1 week 4 days 7 hours ago) and read 4204 times:

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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User currently offlineaklrno From United States of America, joined Dec 2010, 934 posts, RR: 0
Reply 5, posted (2 years 4 months 1 week 4 days 6 hours ago) and read 4176 times:

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.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15735 posts, RR: 26
Reply 6, posted (2 years 4 months 1 week 4 days ago) and read 4068 times:

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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User currently offlinesccutler From United States of America, joined Jan 2000, 5508 posts, RR: 28
Reply 7, posted (2 years 4 months 1 week 4 days ago) and read 4060 times:

Nonetheless, the V-Tail Bonanza is a true work of aerial art. Just ask the man who owns one!  


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User currently offlineSAAFNAV From South Africa, joined Mar 2010, 271 posts, RR: 1
Reply 8, posted (2 years 4 months 1 week 3 days 23 hours ago) and read 4036 times:

Quoting Goldenshield (Reply 4):

Also, V-tails are sexy.

Agreed, they look good!

What glider is that?



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User currently offlinerwessel From United States of America, joined Jan 2007, 2346 posts, RR: 2
Reply 9, posted (2 years 4 months 1 week 3 days 21 hours ago) and read 4000 times:
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Quoting SAAFNAV (Reply 8):
What glider is that?

HP-18, maybe?


User currently offlineGoldenshield From United States of America, joined Jan 2001, 6014 posts, RR: 14
Reply 10, posted (2 years 4 months 1 week 3 days 15 hours ago) and read 3898 times:

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

HP-18, maybe?

Correct!



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User currently offlinercair1 From United States of America, joined Oct 2009, 1317 posts, RR: 52
Reply 11, posted (2 years 4 months 1 week 2 days 15 hours ago) and read 3678 times:
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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.



rcair1
User currently onlinelonghauler From Canada, joined Mar 2004, 4929 posts, RR: 43
Reply 12, posted (2 years 4 months 1 week 1 day 14 hours ago) and read 3484 times:

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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User currently offlineGoldenshield From United States of America, joined Jan 2001, 6014 posts, RR: 14
Reply 13, posted (2 years 4 months 1 week 1 day 13 hours ago) and read 3473 times:

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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User currently offlinespantax From Belgium, joined Nov 2004, 323 posts, RR: 1
Reply 14, posted (2 years 4 months 1 week 16 hours ago) and read 3314 times:

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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User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 15, posted (2 years 4 months 1 week 15 hours ago) and read 3294 times:

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.


User currently offlineflyhossd From United States of America, joined Nov 2009, 872 posts, RR: 2
Reply 16, posted (2 years 4 months 6 days 11 hours ago) and read 3097 times:

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.



My statements do not represent my former employer or my current employer and are my opinions only.
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17026 posts, RR: 67
Reply 17, posted (2 years 4 months 5 days 20 hours ago) and read 2993 times:

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. 



"There are no stupid questions, but there are a lot of inquisitive idiots."
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