Gerolf Heinrichs <<email>> writes:

The success of tails with rigid wing designs has apparently made some of us think tails are the solution to all pitch problems. Rigids certainly had no trouble with the rigidity of their wing trailing edges – their washout holds up fine. Their problem was that the pitch forces at work are just acting on a short arm only, due to the substantial nose angle of 140-148° of a modern rigid (as opposed to 128-133° for topless flex wings). New rigids have keels which are quite long and at the end of it they sport a more or less fix-mounted tail. The tail is of considerable size and, along with some undesirable side effects, does the job.

Flex wings have keel lengths that will not allow a mounted tail to reach further back than the wing tip area of the glider already does. For a very practical reason: if the keel was any longer you would either frequently break it on flaring while landing, or not be able to perform such flare. If it was any shorter the glider’s tips would be prone to damage upon setup and landing.

Tails on flex wings proved to be quite impractical, and the only reason you would want them on your glider is, that you had doubt the wing washout would be holding up sufficiently.

I acknowledge Aeros' attempt to give their gliders extra pitch stability which their sprog systems are not supplying to a desirable extent. However, the introduction of tails once again, raises a few questions instantly: How big does such tail have to be to be regarded a proper tail? At which distance from the glider nose and which angle to the keel does it have to be mounted? And how much are we willing to reduce the glider’s sprog setting requirements if said tail is used?

One would of course conclude that the tail in use has to be of exact size and shape and in the same position and angle as mounted as the one used while testing. This however should not be taken for granted right away.

When Aeros tested with the DHV, producing those so encouraging pitch figures which are now floating through the web, they showed up with a tail of substantial size (the word “enormous” was used from the German pilots who knew about it).

The tail Primoz recently flew and advertized in Bassano was on the other hand tiny. So small in fact, that Primoz claimed that despite it being fix-mounted to the keel one would not even feel it while thermaling.

Given the small size of the tail, this would not surprise me. However, it would surprise if this miniature tail would do much pitch work and thus improve the pitch figures substantially. It would also surprise me that it would it be this easy to cheat the pitch rule everyone of the CIVL sprogs workgroup is so eager to design.

So Primoz, is Aeros serious about their tail, is it just a nice PR gag or simply a “feel good fin” for those who have temporarily or permanently lost confidence in their topless wings?

As for the ruling now: If we go for simple and a tail will be a tail regardless of its size, we may see a lot of gliders equipped with credit card sized tails in Laragne.

I think we might even want to wait and see how the DHV rules on this matter in their upcoming event. I hope Primoz will compete with his Bassano version Combat and tail and not fly a Rigid like he did in the last German Open, as the DHV pitch police will be at work there.

Primoz Gricar <<email>> responds:

The question, which I get thankfully reading Gerolf's feedback, is what is actually science? At my (limited) knowledge science is to make an experiment and to observe the result. Thus we get information, which is authoritative and we can be sure of. The opposite of science is speculation. Speculation or assumption means personal opinion, which does only remotely refer to authorities, is subjected to mental modes and can be used to promote personal interests. It creates only disturbance. I am sorry for having to say this but there is quite a few nonscientific statements in Gerolf's statements below.

Gerolf wrote: "Flex wings have keel lengths that will not allow a mounted tail to reach further back then the wing tip area of the glider already does."

(speculation, not true for Combats, we can prove it)

Gerolf wrote: "Tails on flex wings proved to be quite impractical, and the only reason you would want them on your glider is that you had doubt the wing washout would not be holding up sufficiently well."

(speculation, not true for Combats, we can prove it)

Gerolf wrote: "I acknowledge Aeros' attempt to give their gliders extra pitch stability which their sprog systems are not supplying at the desirable extent."

(Speculation, not true, we can prove it)

Gerolf wrote: "How big does such tail have to be to be regarded a proper tail? At which distance from the glider nose and which angle to the keel does it have to be mounted? And how much are we willing to reduce the glider’s sprog setting requirements if said tail is used."

(For Combats this questions have been answered already to the satisfying extent. Development is of course going on.)

Gerolf wrote: "One would of course conclude that the tail in use has to be of exact size and shape and in the same position and angle as mounted as the one used while testing. This however should not be taken for granted right away."

(very true)

Gerolf wrote: "When Aeros tested with the DHV producing those so encouraging pitch figures which are now floating through the web, they showed up with a tail of substantial size (the word “enormous” was used from the German pilots who knew about it).

"The tail Primoz recently flew and advertized in Bassano was only tiny. So small in fact, that Primoz claimed that despite it being fix-mounted to the keel one would not even feel it while thermaling."

(speculation, hear/say, there is no substantial aerodynamic difference between proto and serial tail, we can prove it)

Gerolf wrote: "So Primoz, is Aeros serious about their tail, is it just a nice PR gag or simply a “feel good fin” for those who have temporarily or permanently lost confidence in their topless wings?"

(Aeros is serious about the tail)

Gerolf wrote: "I think we might even want to wait and see how the DHV rules on this matter in their upcoming event."

(That is the proper way of doing things.)

Gerolf wrote: "I hope Primoz will compete with his Bassano Combat and tail and not fly a Rigid like he did in the last German opens since DHV pitch police is at work."

(Gerolf, I will surely compete with my combat and tail at the German open. I hope you are also there to study it. I am speculating that the Aeros tail plane is something, which can also improve other gliders and fulfill desires of not only Aeros pilots.)