V-tail or Regular Tail

[nr5a]

If you were building a new plane and had a choice of V-tail or Regular tail which one would you use and why. I'm gettin the electric version of the Chrysalis.

CrashinJ

[DFW_HLG_TG]

If you were building a new plane and had a choice of V-tail or Regular tail which one would you use and why. I'm gettin the electric version of the Chrysalis.

CrashinJ


Regular tail. Though my best HLG is a V, the x tail seems to be more stable.

[Stan Myers]

Std rudder/elevator easier to trim. Most V's need differential.

Stan

[solo6796]

I asked the same question and ended up with a V Tail.

http://www.rcgroups.com/forums/showthread.php?t=334018

I'm really enjoying mine... Took Third place RES at the Mid South Soaring Championships. I've since bought a Super V 1000 that is a great flying model. I didn't find the V Tail to be any more "fiddly" than regular systems.

AJ

[Al M]

Put a v-tail on my GP Spirit and I like it. I never had one before and I decided to try one. I got a Chrysalis kit and plan to build the v-tail.

[DFW_HLG_TG]

I asked the same question and ended up with a V Tail.

http://www.rcgroups.com/forums/showthread.php?t=334018

I'm really enjoying mine... Took Third place RES at the Mid South Soaring Championships. I've since bought a Super V 1000 that is a great flying model. I didn't find the V Tail to be any more "fiddly" than regular systems.

AJ


I read the posts in your link. You had a V tail and nobody really answered the question.

[CHARLIE BRITT 7]

If you are big into competion go with the X-tail, otherwise whatever looks the best to you.
Charlie

[Sparky Paul]

In practical terms, the v-tail keeps the tips off the ground. Around here, the ground usually has rocks sticking up.
Or the flat tail scrapes on the runway.

[solo6796]

I read the posts in your link. You had a V tail and nobody really answered the question.


You're right... I got to read a bunch of stuff, and my take was that the performance is the same with the properly sized V-tail, possible weight savings, tail stays out of the grass, kind of a hassle for transport, looks cool.

My RES Yardbird does rudder rolls easily, and has great rudder authority. I did happen to luck out that the tail that was given to me by a friend was the right size for this particular ship.

Some people like them, some don't. Probably many who don't had a bad experience with one not properly sized and set up. Read all you can on those subjects and learn from other's experience... Then do what YOU think is best for you. That's what I did...

AJ

[Thermalin]

Though the area is basically the same.. would there be less drag since you only have two surfaces insteach of three and a more streamlined attachment? Or would drag be the same since leading / trailing edge lengths are basically the same on both x and v configuratoins.
Mike

[DFW_HLG_TG]

Though the area is basically the same.. would there be less drag since you only have two surfaces insteach of three and a more streamlined attachment? Or would drag be the same since leading / trailing edge lengths are basically the same on both x and v configuratoins.
Mike


Drag should be the same. The v tail combined area is eqaul to the same ship if it had a x tail. However, for structural support most v tails I have seen are a little thicker.

I have flown both in competition and I found the x tail more favorable in the landing circle. My partner, Gary Warner lost an Esprit on launch. It was a very windy day and he thinks the tail stalled. I really believe that the T tail is the most stable. The stab is up in nice clean air and is the least affected by the wing. The problem with the T tail is the weight in structural support to hold it.

[nr5a]

Ok, I think I'll go with what I've always used. Your everyday X-tail. I'm not into competion just want it for thermal duration. Besides nearest competions are probably around the Denver area a 8 hour drive. I'm just flying for the enjoyment. Thanks guys for your comments, the plane is ordered.

CrashinJ

[Don Stackhouse]

If you were building a new plane and had a choice of V-tail or Regular tail which one would you use and why. I'm gettin the electric version of the Chrysalis.


There's a lot of folklore out there about the different types of tails, most of it wrong. There's quite a bit on the subject int the "Ask Joe and Don" section of our website:
www.djaerotech.com

In a nutshell, if the three types of tail (conv., "T" or "V") are all equally well designed, then handling, stability and control authority should be essentially equal. There are minor differences, but they fall in the "splitting hairs" category. A V-tail has a little more drag than the others during a large rudder inputs, but a bit less during steady flight. Like I said, splitting hairs.

Most of the bad press V-tails have unfairly received over the years is due to bad design practices, in particular the infamous "projected area" design method. For all practical purposes, equivalent V, T and conventional tails for a given airplane should all have the same TOTAL area.

On models, the Reynolds number effects are more of an issue than on full-scale. The panels of a V-tail have either more span (less induced drag), or more chord (better Reynolds numbers) or both, than an equivalent T or conventional tail. The same total area divided into two pieces means the pieces are bigger than when the same total area is divided into three.

In terms of parasite drag, the V-tail also comes out the best. The T-tail and conventional tails both contain two 90 degree intersections causing interference drag. A V-tail only has one, and it's usually wider than 90 degrees, a factor that also reduces interference drag. The cruciform tail (i.e.: where the stab is mounted part way up the fin, so the fin extends both above and below the stab) is the worst in this regard, with four 90 degree intersections.

There's a lot of talk about a T-tail supposedly being able to get away with less stab area than the others because the stab is supposedly up out of the wing wake. In actual practice I haven't found this to be true to any significant extent.

The twisting moments applied to the tail boom by a V-tail during a rudder input are typically greater than for the other two, which can be important on full-scale tails.

However, on models, the typical stress that defines the required tailboom strength and stiffness is the twisting and bending effects due to bad landings. In this case, the V-tail comes out on top by a significant margin.

The T-tail puts the mass of the stab way up on the fin, which also requires more structure in the fin. All of that mass up high causes all sorts of nasty bending and twisting stresses in the tail boom in a dork landing or a ground loop.

Meanwhile, and as mentioned by others on this thread, the conventional tail tends to drag the stab through every rock, weed and grass clump in the landing area, resulting in the tips of the stab getting yanked on very hard on a regular basis. This also creates massive bending loads on the tail boom. We do mitigate this somewhat on the Chrysalis by the shape of the tail surfaces. That graceful curve in the leading edges is not there just to look pretty, it also helps obstructions to slide off easily instead of breaking the tail boom.

The V-tail keeps the mass of the tail panels low (i.e.: close to the tail boom) and to a minimum, both of which eliminate the disadvantages that plague the T-tail. At the same time, the V-tail keeps most of the tail surfaces (especially the tips) up high, clear of obstructions. In addition, on lighter weight airplanes, the sideways airflow past the tail during a ground loop tends to lift the tail up, clear of obstructions. The same is not true of the T or conventional tails.

Then there is basic structural weight. A V-tail has two joints that have to be reinforced enough to carry the loads, while the other options all have at least three.

So, overall, the net advantages tend to favor V-tails for many applications in the model world. One area where it can be a problem is on beginners' airplanes, and another is on planes owned by people who for one reason or another have a phobia about V-tails. Also, some folks still have very simple radios that don't have the "elevon" mixing needed for a V-tail (non aileron) model, or their owners don't feel comfortable figuring out the programming needed to activate the mixing. Those are the main reasons why the Chrysalis HLG and 2-meter kits include parts and instructions for both conventional and V-tails.

I've built and flown both versions, and my personal favorite is the V-tail, for the reasons listed above. However, the control and stability of the two versions are esentially equal, and you should get excellent results with either one.

Don

[nr5a]

Thanks alot Don, now you go and complicate matters again for me. Might as well try a V-tail I guess, since I've never had one before, and I seem to be following your instruction/advice per the book. ha ha Have you shipped the plane yet? hahahahaha

CrashinJ

[Don Stackhouse]

Thanks alot Don, now you go and complicate matters again for me. Might as well try a V-tail I guess, since I've never had one before, and I seem to be following your instruction/advice per the book. ha ha Have you shipped the plane yet? hahahahaha

CrashinJ

The bottom line in all of this is that regardless of which way you build the model, it should fly very well. And of course all the parts and instructions for both types are in the kit, so you don't have to decide till it's time to start gluing things on.

As far as your second question, I'd have to check with Joe Hahn, he handles all the orders and shipping (I'm just the engineer).

[Hoot]

V tails look great but are much more dificult to haul around if the stab isn't detachable. Even in the shop and car I am constantly banging the V tail. I've learned that by carrying the V tail by the tail, you don't bang it up as much. Conventional plug in stabs are easy to adjust and easy to haul.

[Don Stackhouse]

V tails look great but are much more dificult to haul around if the stab isn't detachable. Even in the shop and car I am constantly banging the V tail. I've learned that by carrying the V tail by the tail, you don't bang it up as much. Conventional plug in stabs are easy to adjust and easy to haul.

My experience has been the opposite.

Conventional tails and T-tails do not lay neatly in a corner, or nest with each other. You can lay a V-tail fuselage along the back edge of a car seat, with one tail panel extending horizontally along the seat bottom and the other panel extending vertically along the seat back. The same holds true of the floor+wall of the back of an SUV or pickup truck, or the inside of a shipping box. You can also nest several V-tailed fuselages together this way, and still have plenty of room left alongside them for wings. Note, all of this is possible without the extra weight, complexity and expense of making a removable tail.

If you're really dead-set on a removable tail, it's no more difficult (and often easier) to make a bolt-on V-tail than a removable conventional or T-tail.

It's also not that difficult to make a plug-in V-tail, or even an all-flying V-tail. However, I am not a big fan of all-flying tails, V-tail or otherwise. The supposed aerodynamic benefits of eliminating the hinge line are not that significant at our Reynolds numbers if the hinge is done right.

OTOH, the all-flying tail needs more total area to develop the same control force as a two-part fixed surface + control surface.

When you make a control input to a stabilator, all you do is change its angle of attack.

Conversely, when you move the elevator of a two-element tail surface, you change its angle of attack AND its camber. Thus, the two-part tail, besides being structurally more efficient, can also develop a greater lift coefficient and therefore more control force from the same number of square inches.

[skybenchone]

Hi Don,

From one kit mfg to another, can you help me with this question ? I have an old v-tail Nostalgia design coming with a 144" span that was designed with somewhat oversize stabulators ( I haven't measured them yet to get a fix on what percent they are to the wing area), but was wondering if you had a rule of thumb percentage to use as a starting point for oversizing v-tails. I'm considering offering the builder option of stab/elev or stabulator. TIA.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters.

[mmartin55]

Excellent Don. Useful and unbiased. Build or fly what you like and look carefully at durablility issues most of all, the rest is noise. But you definately don't want to have to be doing repairs after every third landing or constantly tinkering with trim due to bad design, so continue to observe, ask questions, and listen to what other have to say.

[Don Stackhouse]

Hi Don,

From one kit mfg to another, can you help me with this question ? I have an old v-tail Nostalgia design coming with a 144" span that was designed with somewhat oversize stabulators ( I haven't measured them yet to get a fix on what percent they are to the wing area), but was wondering if you had a rule of thumb percentage to use as a starting point for oversizing v-tails. I'm considering offering the builder option of stab/elev or stabulator. TIA.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters.

The "rules of thumb" you're looking for are called "tail volume coefficients". They're discussed in a number of articles in the "Ask Joe and Don" section of our website. Go to AJ&D on our website, type "tail volume coefficients" into the search engine, and it will give you a list of links to the articles on that subject.

One article in particular you should start with is:
http://www.djaerotech.com/dj_askjd/dj_questions/tail_coef.html

It goes through the use of tail volume coefficients, as well as something I call "dynamic tail volume coefficients", that put a number on the tail's effect on dynamic stability (i.e.: the ability ot damp out oscillations). For static stability and control authority, tail effects are linear for both tail area and tail moment arm. However, for dynamic stability, the tail effects are linear with tail area but proportional to the square of the tail moment arm. My "dynamic tail volume coefficient" puts a number on this effect. This parameter, in combination with the static tail volume coefficients, will help settle the question of how much tail area vs tail moment arm you need.

Once you have the static and dynamic tail volume coefficients for a similar airplane whose stability and handling you want to emulate with your new design, figure the tail moments and areas for your new design that will give it those same static and dynamic tail volume coefficients. A small spreadsheet in a program like Excel can be very helpful with this.

There are other factors including some structural ones, but this should put your design "in the ballpark". You can usually refine it from there with flight tests.

Don

[Salto]

Don,
Thanks for that excellent summary of the differences between tail configurations that you posted earlier in this thread. Your conclusions seem logical to me, and are certainly backed up by my own building and flying experiences.

But I have some questions. I've been thinking about the almost universal adoption of the X-tail configuration for discus launch models. Is this simply for structural reasons? Or is there some aerodynamic advantage of the configuration related to the high yawing forces encountered during the launch? Could a correctly sized V-tail provide the same yaw control forces and damping?

An in-line X-tail has four 90 Deg. intersections, so there would be some disadvantage in terms of interference drag. How much is this reduced with an offset design like that used on the Supergee where the stab is in front of the fin? Does this design effectively have zero surface intersections?

Graham.

[jrerickson]

Salto,

You don't see many v-tail DLG's. There are two reasons why.

1) Not good at dampening yaw during the release.
2) High torsional loads applied to the boom.

My buddy Arthur flies one with a sub fin ( a "tri" fin design) and does fine, but the plane still has quite a bit of yaw on the launch. The clean intersection is sort of lost with the sub fin...

JE

[Salto]

jrerickson,

So how does your first point sit with Don's statement "In a nutshell, if the three types of tail (conv., "T" or "V") are all equally well designed, then handling, stability and control authority should be essentially equal."

I understand the torsional load issue, but I'm wondering if there's some aerodynamic advantage of the X-tail.

Graham.

[Ib Jensen]

The X tail should actually be the least efficient form because you have more tip vortecies and disturbed airflow at the corners. I have tried to do a DLS using a V tail and all I got was broken booms. The X configuration realy removed the torque and allows for a lighter structure and harder launches.

A number of fancy tow line gliders are coming out which look like scaled up DLG gliders with X tails. I believe (no confirmation on this) that this is being done to allow the horizontal stabilizer to be placed high above the grass and rocks that could damage them. A lot of molded gliders do this buy placing the horizontal stabilizer high on the fin to form the X tail. This also helps place the horizontal stabilizer above the turbulence of the fuselage and the wing. If it was not for the structural problems and weight penalty associated with placing the horizontal stabilizer on top of the fin that would be the best location from an aerodynamic standpoint.

My 2 cents and may be wrong, but seems reasonable.

Ib

[jrerickson]

Graham,

I think Don's statement of "well designed" pertained to a normal gliding state. All three forms of tails, even the fourth type that I mentioned (which had anhedral and an upside down V) are used successfully in gliders.

The design problem is the launch. If you comb through the archives you can find lots of pictures and information about the initial and secondary yaw "excursion" when the glider is leaving your hand at 80 mph.

I'd say if you are curious just build a couple of different tail groups and give them a try! You might come across something that works for you.

Don and Joe's beautiful Monarch ruled the hand launch scene when we threw overhand; the v-tail is absolutely fine for this application. Too bad Joe got his allergic reaction to epoxy (and the soft hand launch market) because we may have seen what they would have come up with for a discus launch glider.

JE

[mdennis]

How do you measure the incidence angle with a V tail?

It seems to me that the construction, mounting and setup would be harder to determine and measure with a V tail. You would have to make sure that there is no twist in either side of the V and any adjustment made to one side will effect both vertical, (elevator), as well as yaw, (rudder), trim. This would make for a lot of tinkering with the trim until you get it right.

[Don Stackhouse]

Graham,

I think Don's statement of "well designed" pertained to a normal gliding state. All three forms of tails, even the fourth type that I mentioned (which had anhedral and an upside down V) are used successfully in gliders.

The design problem is the launch. If you comb through the archives you can find lots of pictures and information about the initial and secondary yaw "excursion" when the glider is leaving your hand at 80 mph....

Don and Joe's beautiful Monarch ruled the hand launch scene when we threw overhand; the v-tail is absolutely fine for this application. Too bad Joe got his allergic reaction to epoxy (and the soft hand launch market) because we may have seen what they would have come up with for a discus launch glider.

JE

As I mentioned previously in this thread, a V-tail does (generally speaking) put higher torsional loads on the tail boom during a rudder input. The same is true when it is naturally producing a yaw correction force in response to large amounts of yaw, which is exactly the situation faced by the tail of a DLG during launch.

However, there are other parameters that come into play, and it is indeed very possible to make a V-tailed DLG (particularly if you can keep the required span of the tail panels to a minimum) that retains most of the advantages of that tail type, including lower weight, while still withstanding the rigors of a discus launch. I know this for certain because just prior to our decision to abandon the competition sailplane market, we had successful prototype DLGs (based on the design concepts in our Spectre series, which by their nature just happened to need very small tails) in development with V-tails.

As far as the decision to leave the composite competition sailplane market, Joe's epoxy allergy was only a contributing factor, and in fact we had produced epoxy composite aircraft for a number of years after Joe had first developed his allergy.

However, to produce the parts on a production basis we had to use full-time employees, not just family labor, and that drives up overhead. In addition, there are fixed costs associated with full time employees, so if you hit a slow period in terms of sales volume, you have to either absorb potentially huge losses, or else lay off employees that you had to invest quite a bit in to train, and might not be able to get back if/when business improves. Neither is an attractive proposition.

However, the biggest problem is that while competition sailplanes are a great way to build a reputation, they are a TERRIBLE way to make a living. Unless you completely redesign your entire product line every 3-6 months or so, the buying public assumes they aren't the "latest and greatest" any more, and stops buying them. That completely saps the engineering resources of a small company, and can potentially stunt its growth, perhaps fatally.

If you come out with something really revolutionary (with notable exceptions, like our original Monarch HLG, or the first DLG's), it looks too different, and folks won't buy it either.

Add to that the fact that the technology evolved much faster than the contest tasks, so that the tasks became more gimmicks like precision times and landing tasks, rather than the test of pure soaring ability that HLG's were back in the early to mid 90's, and we ended up with a case where the tasks were no longer particularly challenging to the airplanes. Any decent airplane flown by any decent pilot could get maxes most of the time, which is why we had to have things like those aforementioned precision time and landing tasks to keep from getting too many ties for first place. The net result was that producing a model with particularly outstanding flying qualities did not necessarily translate into equally outstanding sales statistics.

Thus, even though we had some truly amazing DLG's and open class models in the works, we had no viable reason to believe that they could be counted on to result in even a modest amount of financial success for our company, and the investment in time and money required to finish developing them and get them into production would require literally "betting the farm". It was a risk we simply could not afford to take.

The one potential saving grace was the UAV market. We had an interesting little UAV in development for the US military (and were expecting to get a big order very soon for a batch of them for field tests, with the expectation that more orders would probably follow after that), and the possibility of supplying wings for another UAV to an overseas customer. Those projects would have provided the steady volume we needed in our composites manufacturing operation to keep it commercially viable, and we could continue dabbling in competition composite sailplanes on the side.

Then came 9-11-01.

As of 9-12-01, suddenly all that UAV work evaporated. The Pentagon was busy trying to figure out who was still alive under the rubble and how to mobilize for Afganistan, and all the long-term development projects went on indefinite hold. Similar things apparently happened to our overseas customers. We'd been keeping our production employees in anticipation of that military order, long past when we should have laid them off. We kept them on long enough after that to give them time to try to find other jobs, but then it was either let them go or else go bankrupt. We had no choice.

Years ago, Bob Dodgson wrote an article "Don't Become an R/C Sailplane Manufacturer". I'd have to say he was pretty much right on all counts. We've been in this business since the early 90's, over a decade, and we've seen a lot of folks come and go.

We're still trying to recover from the damage we did to ourselves during that whole sorry state of affairs. However, in the meantime we've found that laser-cut wooden models can be produced economically with family labor and a minimum of overhead, sport sailplanes and electrics can benefit significantly from the same quality of engineering work and innovative thinking that goes into a competition sailplane, and that a good sport model this year will still be a good sport model next year, and the year after that.

So, thanks to the Chrysalis family, and a group of little profile electrics that just happen to be named after some other creatures who suffered a calamity on the highway of life, we're still here. Not out of the woods by any means, but still here. There are a lot of folks in this business, including some good personal friends of mine, who I'm afraid cannot make the same claim.

[Don Stackhouse]

How do you measure the incidence angle with a V tail?

It seems to me that the construction, mounting and setup would be harder to determine and measure with a V tail. You would have to make sure that there is no twist in either side of the V and any adjustment made to one side will effect both vertical, (elevator), as well as yaw, (rudder), trim. This would make for a lot of tinkering with the trim until you get it right.

It is different, and trying to measure it "after the fact" can be a problem, although in all fairness to V-tails, much of that difficulty is because we're all using measuring tools and methods that were developed for conventional tails. If V-tails were the norm and "conventional" tails were unusual, we would all be discussing how hard it is to measure incidence of a conventional tail, all their supposedly inherent handling problems, and the way they get snagged on everything in sight on landing (oops, they ARE the norm, and we STILL talk about at least some of those things!).

The key on V-tails is to plan ahead in the design so that the correct incidence naturally results from the building process.

For example, on the Chrysalis series, the fuselage structure formed by the tail bulkheads and the upper longerons creates a saddle that the V-tail naturally nestles into with the correct alignment and incidence.

On the Spectre series models we had flat surfaces designed into the tail surfaces where they contacted the tail boom that accomplished the same thing. In some cases, such as the 2-meter and open class Spectres, we had to mold those flat reference surfaces into the bagged tail surfaces using some rather interesting production tooling. However, once we had that tooling sorted out, the system worked very well with a minimum of trouble. In my experience it was no more difficult to get the tail aligned properly on one of these than it would be to build a properly aligned conventional or T-tail.

For a tail that had none of these "self-jigging" features designed into it, probably the best option is to build a small jig to hold the tail in reference to the fuselage and building surface. I did this on the old HLG and 2-meter Monarchs when I formed the tail saddle portion of the plug we used to make the fuselage molds. Once that saddle was properly aligned and the molds made from it, alignment of the tails during final assembly was nearly guaranteed.

The other method is to simply pick a point on the nose as a measuring reference, then measure back to corresponding points at the roots and tips of the tail surfaces for setting the pitch and yaw alignments. That may take a little math in some cases to figure out what the numbers should be, but it's not too difficult.

A similar method in concept was used on Brian Agnew's old "Vertigo" HLG. The hinge line of the tail panels was perpendicular to the underside of the fuselage, so you just put the fuselage flat on the floor, with the tail back against a wall. Of course this assumed that the floor was flat and level, and the wall was flat and plumb. I've lived a few places where that could not be taken for granted!