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Tail plane Configurations

T-tail, V-tail or conventional layouts

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chris basson07/05/2013 12:09:21
168 forum posts
7 photos
Had some feedback from my Wildthing thread about recommendations for my second Slope Soarer which pointed me in the direction of Stan Yeo's models on the Phoenix Model Productions site (Sorry can't insert link from my phone!).

Looking at these models it seems that the main difference between the different aerobatic models is the tail layouts.

My question is this...
What are the advantages/disadvantages to each configuration? T-tail, V-tail or 'conventional'...

Or is it purely down to aesthetics?

Looking forward to some debate on this one.

CB
GrumpyGnome07/05/2013 12:21:39
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567 forum posts
153 photos

T-tail - good for keeping out of the long grass; looks nice on gliders with long slender wings. Oh and on a Pucara....

Conventional tail (on fuselage) - simple, and works or else you wouldn't see on the majority of planes !

Cruciform (?) i.e. same shape as conventional but higher up the fin.... more complicated but I gues works as well.

V-tail - can't possibly give such good response as 'conventional', but looks nice on some planes. That French jet for example - but looks pants on a Bonanza . Maybe it's an effort to reduce drag ....

I have 20+ planes and only one has a T-tail - none have V-tails. Although some have none.

Easy to tell I'm no aerodynamicist ! Or aeroplane designer !

GG

chris basson09/05/2013 09:52:48
168 forum posts
7 photos
Thanks for that GG!

This hasn't produced the lively & informative debate I'd hoped for, even BEB with all his aerodynamic knowledge hasn't responded so at the moment I'm going to assume its mostly aesthetics & personal taste!...

Unless anyone can tell me otherwise.

CB
Olly P09/05/2013 10:09:11
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Well....

On some aircraft a conventional tail is less effective, or impossible, due to the engine location, and a T tail must be used.

On Full-Size Gliders T-Tail can often be used as this protects the elevator and tail during landing, especially rough field.

V-Tails tend to have less drag than conventional and T-tails, but have less control authority.

Edit - The other factor is the Disturbed flow from the wings and fuselage, and the tail plane needs to be reasonably clear of this most of the time - and this should be worked out in the 'dirtiest' configuration - including any flaps, airbrakes, etc.

I'm sure the prof will be along in good time to give a better answer than mine - afterall I failed my degree in what he teaches!

Edited By Olly P on 09/05/2013 10:11:41

chris basson09/05/2013 11:39:47
168 forum posts
7 photos
Thanks Olly!

That's Exactly the kind of info I was looking for!
Biggles' Elder Brother - Moderator09/05/2013 12:02:55
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Sorry chaps - been a bit tied up the last few days. Tail configurations eh? Well lets take the standard layout as a datum point and discuss the relative advantages and disadvantages of Vee and Tee relative to that.

The Vee Tail.

The main claimed advantages of the Vee tail are that it is lighter and has less drag. In practice in my view neither of these claims are actually realised. The tail itself may well be lighter, but any gain is usually off-set by the more complex control layout which adds weight.

The less drag argument is more complex. Basically the argument goes that the surface area of a Vee Tail is smaller so surface drag is decreased. But against that to be equally effective all the wind tunnel test tells us that a Vee-Tail's elements have to be bigger than just the projection of the vertical and horizontal surfaces on a convention layout. So in the end the surface area is about the same.

But Vee-Tails are subject to an additional drag force that conventional tails are not. Consider the case where we put in pure down elevator. The conventional tail just moves the elevatoir downwards relative to a purely horizontal plane. But in a Vee-Tail while both elevators do go down - because of their incline they have an outward component to their movement as well. So they create the down pitching moment we want but the right hand one makes a right yaw force as well - which is exactly balanced by left one making left yaw force. These unwanted yaw forces cancel out and we do get pure down in the end - but they still have to be produced, this means that some of the control surface effort is effectly wasted on yaw forces that cancel out. The consequence of this is that to create a given amount of down moment we actually need bigger control surfaces (because some of their effort is wasted)

The disadvantages of thr Vee Tail are mainly two: firstly they obviously require a more complex control system. Second they actually put more stress on the rear of the airframe. The second is not a big issue for most modellers as our airframes are usually well over engineered anyway. But the first is an issue.

So, to summarise on Vee-Tails - no real advantage, more stress and work. But they look nice.

 

Tee Tails.

The main advantages of the Tee tail (aerodynamically) is that it puts the elevator in clean air. In a conventional layout the elevator is working in the wash from the wings so is less effective than it might be. This advantage is definitely true.

Another advantage for modellers is that it puts the tail plane out of harms way in the case of a belly lander.

So, some advantages - but there are some pretty significant disadvantages. First Tee-tail aircraft can have problems with stall recovery. The elevator can end up in the "wind shadow" of the turbulent air coming off the stalled wing so you end up with not only a stalled aircraft but a stalled aircraft with a very ineffective elevator! This means you can't always simply push the nose down and re-establish clean flow over the wings.

The second big disadvantage of the Tee tail is that, for a prop driven model, the elevator is now largely out of the prop wash. This impairs slow speed control. This is the reason why while you may see many jets with Tee-Tails you don't see many prop driven aircraft with them.

Hope this helps

BEB

Edited By Biggles' Elder Brother - Moderator on 09/05/2013 13:03:21

chris basson09/05/2013 12:19:28
168 forum posts
7 photos
Wonderful! Thanks BEB!

The only thing is I have to disagree with your opinion on V-tails!

I'm not keen on how they look!(running for cover RIGHT now ) so I guess I'll be going for a standard layout!

CB
Biggles' Elder Brother - Moderator09/05/2013 13:04:58
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Beauty is in the eye of the beholder Chris! smile

BEB

Tom Satinet09/05/2013 21:25:28
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519 forum posts
Posted by Biggles' Elder Brother - Moderator on 09/05/2013 12:02:55:

Sorry chaps - been a bit tied up the last few days. Tail configurations eh? Well lets take the standard layout as a datum point and discuss the relative advantages and disadvantages of Vee and Tee relative to that.

The Vee Tail.

The main claimed advantages of the Vee tail are that it is lighter and has less drag. In practice in my view neither of these claims are actually realised. The tail itself may well be lighter, but any gain is usually off-set by the more complex control layout which adds weight.

The less drag argument is more complex. Basically the argument goes that the surface area of a Vee Tail is smaller so surface drag is decreased. But against that to be equally effective all the wind tunnel test tells us that a Vee-Tail's elements have to be bigger than just the projection of the vertical and horizontal surfaces on a convention layout. So in the end the surface area is about the same.

But Vee-Tails are subject to an additional drag force that conventional tails are not. Consider the case where we put in pure down elevator. The conventional tail just moves the elevatoir downwards relative to a purely horizontal plane. But in a Vee-Tail while both elevators do go down - because of their incline they have an outward component to their movement as well. So they create the down pitching moment we want but the right hand one makes a right yaw force as well - which is exactly balanced by left one making left yaw force. These unwanted yaw forces cancel out and we do get pure down in the end - but they still have to be produced, this means that some of the control surface effort is effectly wasted on yaw forces that cancel out. The consequence of this is that to create a given amount of down moment we actually need bigger control surfaces (because some of their effort is wasted)

The disadvantages of thr Vee Tail are mainly two: firstly they obviously require a more complex control system. Second they actually put more stress on the rear of the airframe. The second is not a big issue for most modellers as our airframes are usually well over engineered anyway. But the first is an issue.

So, to summarise on Vee-Tails - no real advantage, more stress and work. But they look nice.

 

Tee Tails.

The main advantages of the Tee tail (aerodynamically) is that it puts the elevator in clean air. In a conventional layout the elevator is working in the wash from the wings so is less effective than it might be. This advantage is definitely true.

Another advantage for modellers is that it puts the tail plane out of harms way in the case of a belly lander.

So, some advantages - but there are some pretty significant disadvantages. First Tee-tail aircraft can have problems with stall recovery. The elevator can end up in the "wind shadow" of the turbulent air coming off the stalled wing so you end up with not only a stalled aircraft but a stalled aircraft with a very ineffective elevator! This means you can't always simply push the nose down and re-establish clean flow over the wings.

The second big disadvantage of the Tee tail is that, for a prop driven model, the elevator is now largely out of the prop wash. This impairs slow speed control. This is the reason why while you may see many jets with Tee-Tails you don't see many prop driven aircraft with them.

Hope this helps

BEB

Edited By Biggles' Elder Brother - Moderator on 09/05/2013 13:03:21

What this complex control system vtails have? You only need two pushrods connected to a horn on each tail surface like you would with a rudder and elevator. in fact I would say vtails are the simplest because you don't run in to problems with the rudder pushrod interfering with the horizontal tail.

They are certainly simpler than all moving tails (and obviously T tails with the servo in the front of the fuse) and the pushrods are kept internal, which doesn't hurt drag.

You will notice virtually competition gliders for f3f and f3b are vtail - i.e where speed counts.

The last f3j world championship (and 3rd place) was a vtail model.

 

To the op - just go for whatever model you take a fancy too. There are good models of all tail types.

The theoretical aerodymanic pros and cons of each tail type are going to make no difference to you if you are looking to progress from a foamy. And if you are good enough you an go and win the thermal soaring (f3j) world championship with a vee tail or a xtail.

That being said the big advantage of "normal" tails (plus T, and X) over vtails is that the rudder is a separate function which is much better for aerobatics - e.g spins and flicks.  If you are talking about a wooden kit such as one of stans designs for general flying I would go for a normal tail as they are usually a bit easier to setup and have a better rudder.

 

Edited By Tom Satinet on 09/05/2013 21:33:58

Edited By Biggles' Elder Brother - Moderator on 09/05/2013 21:35:35

Biggles' Elder Brother - Moderator09/05/2013 21:38:44
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Posted by Tom Satinet on 09/05/2013 21:25:28:

You will notice virtually competition gliders for f3f and f3b are vtail - i.e where speed counts.

The last f3j world championship (and 3rd place) was a vtail model.

If so then its purely fashion - there is no independent objective experimental evidence that the Vee-Tail offers any speed advantage.

BEB

Concorde Speedbird09/05/2013 22:17:55
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2735 forum posts
650 photos

Interesting BEB, if I achieve my dreams of becoming an Aviation engineer then much of my knowledge of aerodynamics will be thanks to you, thanks!

Now then, ogival delta wings...

CS

John Olsen 109/05/2013 23:48:23
446 forum posts
23 photos

The more complex control system with V tails would apply more with full size, where you have to combine the fore and aft movement of the stick with the movement from the rudder pedals to create the correct movement for each surface. While this still has to be done for a model, it is most likely to be done with mixing in the TX these days.

John

Tom Satinet10/05/2013 07:56:47
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519 forum posts
Posted by John Olsen 1 on 09/05/2013 23:48:23:

The more complex control system with V tails would apply more with full size, where you have to combine the fore and aft movement of the stick with the movement from the rudder pedals to create the correct movement for each surface. While this still has to be done for a model, it is most likely to be done with mixing in the TX these days.

John

Interesting, but not really relevant to model flying. I thnk if you say that to the OP you could be misleading him. Vtails have a dead simple control arrangement on models (2 pushrods). There aren't many non computer TXs about.  The OP is already flying an elevon models so we can assume that he either has a computer radio or the knowledge to use a vtail mixer.

 

 

Edited By Tom Satinet on 10/05/2013 08:04:42

Tom Satinet10/05/2013 08:03:19
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519 forum posts
Posted by Biggles' Elder Brother - Moderator on 09/05/2013 21:38:44:
Posted by Tom Satinet on 09/05/2013 21:25:28:

You will notice virtually competition gliders for f3f and f3b are vtail - i.e where speed counts.

The last f3j world championship (and 3rd place) was a vtail model.

If so then its purely fashion - there is no independent objective experimental evidence that the Vee-Tail offers any speed advantage.

BEB

I don't think the top f3b/f3f guys go on fashion, they look for the best performance.

If you are going to start talking about vtails you should talk about the real world things that would matter to an rc modeller - e.g having the rudder and elevator function tied together is worse for aerobatics. Vtails sometimes require "differential" on the rudder to avoid pitch changes, which is harder to setup, especially for the beginner.

The other obvious point about building a vtail from a woody kit is that it requiures more precison to get the correct angle (typically around 100 degrees) than a normal tail (90 degree angle). And sometimes the joiner/reinforcement situaton is more complex. I recommend a normal tail from one of stans kits as I don't think the vtail offers any advantage to what the OP wants the model for.

chris basson10/05/2013 08:16:24
168 forum posts
7 photos
Hmm.. now at the moment my entry level (futaba 6ex) Tx had got V-tail mixing but I've already realized that it won't control a 4 servo wing so will need upgrading eventually (Taranis, taranis, salivate, salivate), but as I'm more interested (at the moment) in aerobatics than racing I think a "normal" or possibly cruciform tail (i think they look coolest) would be the way forward?

CB
Biggles' Elder Brother - Moderator10/05/2013 11:39:22
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Posted by Tom Satinet on 10/05/2013 08:03:19:

I don't think the top f3b/f3f guys go on fashion, they look for the best performance.

If you are going to start talking about vtails you should talk about

Then they are "looking" based on no hard quantifiable evidence! And frankly I beg to differ - the racing world (in all its manifestations) has a long an honourable record of things coming in and going out based on "follow my leader" type fashion whims that have little or no scientific foundation. In my view its highly probable the same pilots would have finished in the same positions with conventional tail arrangement.

On the second point I'll do a deal with you Tom,...I wont tell you what you "should" talk about and you afford me and others the same courtesy.

BEB

BEB

Olly P10/05/2013 11:44:56
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3215 forum posts
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Posted by Biggles' Elder Brother - Moderator on 10/05/2013 11:39:22:

On the second point I'll do a deal with you Tom,...I wont tell you what you "should" talk about and you afford me and others the same courtesy.

BEB

BEB

Except on CoC related issues of course! As we would hope, expect and need to keep the forum the friendly and helpful place it is!

Edited By Olly P on 10/05/2013 12:05:28

Bob Cotsford10/05/2013 11:53:56
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I thought one of the claimed advantages for V tails was that there is only one included angle join between surfaces so it should cause less interference drag - V one included angle, T two included angle, + four angles? I'm probably talking out of my orifice as to me drag just means the need for a bigger enginedisgust

Biggles' Elder Brother - Moderator10/05/2013 11:54:59
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No Olly - there I only tell you what you shouldn't say! wink 2

BEB

Steve Hargreaves - Moderator10/05/2013 12:06:41
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I thought one of the main advantages of a Vee tail (certainly on a slope soarer) was that it kept the tail out of the long grass on landing & reduced the possibility of damage.....wink 2

steve hargreaves....no aerodynamicist but practical thinking dept....teeth 2

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