davis da-5

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Vigilant1

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Who doesn't LOVE a flying V-tail?
Sorry--I'm the wet blanket here. Compared to "conventional" tail: No drag advantages (equivalent wetted area, virtually equivalent intersection drag), less effectiveness in crosswind takeoffs and landings, increased control linkage complexity. So, it's just for show, and that
makes it less attractive, to me.

But that's just a minor quibble. I'll agree wholeheartedly that Leeon's designs are wonderfully efficient, original, and good looking.
 

Victor Bravo

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Hey Bert ! Welcome to HBA ! Glad to have someone of your caliber here. The place just got classier and smarter :)

Bill B. / EZ Flap


Less interference drag with V-tails, lower parts-count, etc.
With all respects for Leeon Davis, there are some aspects of his designs that are brilliantly simple, such as making a cheap wood tool to bend the dihedral angle into spar caps. Saves a bunch of fittings, stress engineering on fasteners, doubler and tripler plates, shear pins, etc. Really interesting.

But some aspects of the DA-5 are more complex than they need to be. The V-tail is one of the negatives in my personal opinion. Take a look at that steel tube weldment where the V-tails mount, and tell me that it's simple or un-complicated.

Now take a look at Michel Colomban's Luciole tail. Because the stabilator and vertical/rudder are offset, there is essentially no stabilizer-fin intersection to make any drag. The H-stab is hinged to the longerons, and the rudder is hinged to the fuselage sides. The Luciole tail has fewer intersections than a conventional or V-tail, it has the same number of intersections as a T-tail (two), with NONE of the structural or weight penalty of a T-tail. It has the same parts count as the V-tail... except there is no complex weldment to cut the tubes, file the "cope" notches, mount the tubes onto the jig (which took time to build), tack weld, measure the angles, tap everything straight and probably re-tack weld, then finally finish weld, and then align it onto the bulkhead, and then drop plumb bobs and inclinometers to make sure the angles are correct, and then carefully drill the holes, and then rivet and bolt everything into place, and then finally mount the ruddervators on the weldment.

Sorry to rain on anyone's DA-5 parade, it's a really interesting airplane. I laid hands on the prototype and record breaker airplane. Would have bought it in a heartbeat.

But in my humble, uneducated, slack-jawed hillbilly opinion it fails to meet one of the primary objectives of being extremely simple and easy to build.
 

billyvray

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To me the only thing the Vtail brings is looks- they look cool and make the aircraft stand out.

I agree the steel weldment that supports the Vtail is complex. I think it could possibly be redesigned with plate and be just as stiff and light and reduce the complicated tube fitting that would be needed.
An example: I've attached a standard DA5 pic, and one that was built with a straight tail. To me it ruins the uniqueness of the aircraft and make it somewhat forgettable. If I hadn't been told it was a DA5 I would never have known it was.
DavisDA-2AandDA-5.jpg DavisDA5(2).jpg

Bill
 

ironnerd

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Yup. Just like a T-tail, H-tail, or Y-tail. They all have pros and cons. The nice aspect of Leeon's tails is that they are stabilators, not rubbervators (except for the DA-11).

I looked the weldment over in the DA-2 plans. It's not really that bad. Ol' Leeon managed to do it.

I've read as many flight reports as I can get my hands on for the Davis Series. I've never read anything bad about the tail. I have read that the DA-2's fly and land just fine in a crosswind. I think it was Budd Davisson who said it was a "Shrunk Bonanza that flies like a Cherokee".
 
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TFF

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Budd Davisson is biased; I think the DA2 was the first homebuilt he ever flew. Cant hate the memory of your first date.
 

Victor Bravo

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Ol' Leeon managed to do it.
Eeehhhh.... "Ol' Leeon" was an experimental prototype shop sheet metal and fabrication expert at Aero Commander. He was not a highly educated or scientific man by any means, but I am informed he was a gifted fabricator and a genius at bending tin. This was explained to me by someone who knew him. I never had the pleasure of meeting him.

(From Wikipedia: "Davis specialized as an aircraft mechanic while in the Air Force.[1] Davis worked as a sheet-metal worker at Aero Commander before undertaking his own designs.)

Like a LOT of homeuilt airplanes, the DA-5 was designed to be do-able on a budget for the type of home craftsman airplane builder (with the expectations and attention span) that existed in 1975. Just like the 40 year period before 1975, there have been plenty of new ideas, changes, advances, and different expectations in the 40 years since 1975.

Fast forward to today, where the average guy has less shop skills, less attention span, less time, less perseverance, and (unfortunately) less interest in the art and science of homebuilt airplanes. Today's builder may not give a crap about anything like craftsmanship or an historically significant aircarft, he may well only be interested because it allows him to have lower fuel costs and sidestep most of the FAA burden.

To avoid the risk of crashing this DA-5 thread into the VP-21 discussion, IMHO what is relevant on this thread is that there would have to be a completed tail weldment assembly available or supplied with a kit, in order to interest any significant number of people in building a DA-5. Like the "Phlogiston spars" that were almost a must-have on the RV kits. A completed tail weldment, and pilot-hole-punched skins, and perhaps the engine mount, would go a LONG way toward getting people to buy a DA-5 kit. Hell I'd likely buy one of those kits if it came with those parts.

The DA-5 is a really neat little airplane I'd be proud to fly. Pete's O-100 engine would be a huge winner on this airplane. I would bet that someone selling engine mounts and tail weldments might do reasonably well as a small side business for a welder, because it would probably get a lot of people interested in the design again. Little Scrapper.... :)
 

ironnerd

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A biased pilot? The deuce you say!

And, yes, Leeon was pretty gifted, but he also created a plane that was (other than the wings and the tail weldment) all flat sides.

Yeah, the flying V-tail was his "thing", and to him it was no problem. I would send the tail mount out to be welded - I can technically weld, but it's uglier than Nixon's @$$.
 

lr27

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Sorry--I'm the wet blanket here. Compared to "conventional" tail: No drag advantages (equivalent wetted area, virtually equivalent intersection drag), less effectiveness in crosswind takeoffs and landings, increased control linkage complexity. So, it's just for show, and that
makes it less attractive, to me.

But that's just a minor quibble. I'll agree wholeheartedly that Leeon's designs are wonderfully efficient, original, and good looking.
Can you explain about the less effectiveness in crosswinds? In the RC glider world, I've heard all sorts of bad things about v-tails, but many of the v-tails I've seen are undersized. I currently have a glider with an undersized v-tail, and it's really annoying. However, I've also had a glider with a properly sized v-tail that flew almost exactly the same as another one from the same family of designs, but with more conventional tail surfaces. Of course in the RC world, we don't have more complex linkage as the transmitter takes care of it.

The wetted area may be the same, but on the v-tail the Reynolds number will be a bit higher.
 

Vigilant1

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Can you explain about the less effectiveness in crosswinds?
Not with any real expertise. Several people have told me that crosswind control in a taildragger is easier in a plane with a conventional tail, and I did not press them for an aerodynamic explanation. But here's how I think it probably works:
Say we are taking off with a heavy direct crosswind from the left, and we are in a tailwheel plane with a conventional tail. I've got full use of the rudder to put in as much yaw as I need to keep the nose pointed down the runway. I also have full elevator authority to keep the tail heavily down and the tailwheel on the runway, also providing yaw to counter the weathercocking. Every control surface is contributing positively to my goal--tail left and down.
If I'm in a V-tail, wind still coming directly from the left, I can't use all my available control surfaces at full scale deflection to achieve what I want, because to get my right ruddervator to give me full "tail left" control, it will also be "tail up", which is the opposite of what I need. Also, with the breeze from the left, the right V-tail/ruddervator will be at least partially masked by the left tail surface (in its "shaddow,") as the takeoff roll starts. This effect will diminish in relative strength as I gain speed, but some portion of the downwind tail surface will remain masked. With a conventional tail, the right side of the elevator will be masked a bit by Vertical stab/rudder, but that is less important to me in this scenario than the fact that all my yaw control (the rudder) is unmasked and available.
And, another factor: In a V-tail the wind from the left will strike my left tail surface laterally and tend to move the tail up (exactly what I don't want in the scenario, I want more downforce), Yes, the right surface is tilted the other way and would be expected to provide a downward force, but it is at least partially on the lee side of the left tail surface and occluded by it, so this force will be less.

On landing rollout the situation would be much the same, but even more pronounced due to the lack of propwash to help increase the effectiveness of the control surfaces. The breeze from the left will tend to lift the tail, and the right tail surface will be masked partially by the left tail surface.

That was my rationale, and it might be incorrect. I have not put pen to paper or done any calculations. I'm sure it is possible to make V-tail surfaces that are large enough to make the plane fly similarly to a conventional tail, but this low-speed taildragger/crosswind scenario is about most challenging situation for the V-tail, and a V-tail big enough to work as well here as a conventional tail will be bigger/draggier than a conventional tail. I suspect the "Y-tail" on the Waiex is designed to overcome some of this--to use that small vertical tail/rudder to get some "pure yaw" for use in situations such as these. If I'm all wet, I'd welcome a smarter answer to your good question.
 
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lr27

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My take is that the Y-tail on the Waiex may be to help with spin recovery. Maybe, in a spin, the v-tails get in each other's way a little bit. I know this is a problem with some conventional tails. The wake from a stalled horizontal stab blanks out the rudder. Perhaps this is something similar.

As far as control authority, if you are using a lot of elevator and rudder at the same time, one of the two v-tail surfaces may be exactly aligned to produce the force you want, while the other doesn't do much. OTOH, if you do the same with conventional rudder and elevator, both are at angles to the force you want to produce. Hard to do the math, though, without specific examples, and the math, at least if I did it, would be oversimplification.

On landing, I expect the airplane to be going fairly slowly before there's a problem. If you're landing at 50 knots and the wind is 15, and I've got my mind on straight, that's "only" something like 17 degrees away from straight ahead, so I don't see the "downwind" v-tail getting blanked. I don't know what happens when taxiing, though.
 

bmcj

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Off the top of my head, I'm not sure why a V-tail would be less effective in a crosswind. One possible reason I can think of is that a crosswind from the side will blow against the bottom of the tail and try to lift it requiring a little bit of down elevator to counteract it, which would actually feed rudder into the wrong direction for the crosswind (since the leeward panel with the upward deflected surface might be slightly blanked out and less effective). Of course, this is just amateurish guesswork and the effect is probably minimal at best.
 

Vigilant1

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V-tail with the same size will fly the same as a conventional tail. The prop wash will dwarf a crosswind once start rolling.
I'd agree that, if there is any difference, it would be most pronounced at lower speed and on landing (i.e. power at idle).
 
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Victor Bravo

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Propwash??? Wait, aren't you a glider guy? :gig:
I think he's referring to the bucket of prop wash that the old feller at the airport said he'd throw at the tail. BMCJ I'm sure that as an old-time ramp rat at Fla-Bob you are personally familiar with this type of prop wash, however some of our younger aviators on this site have not been exposed to it yet :)
 
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