Thanks for such a lucid and instructive post. When discussing cruciform, T, and Conventional tails, does the interference drag disappear when the control surfaces are separated; that is, the elevator ends before the horizontal stabilizer begins?
There's one element you didn't discuss (and I don't remember if you brought it up in an earlier thread): the inverse V-Tail. If built with a skid at the bottom (or a twin boom, made magically as light as a single boom), would the increase in proverse (?) roll mean a need for less dihedral, meaning less interference drag on the wings? Is this splitting a split hair? Are there other advantages? - On Sun, 30 Dec 2001, Don Stackhouse @ DJ Aerotech wrote: > Zbigniew Michalczyk writes: > > >Canard concept is like a V-tail concept... > >Once only build the V-tail > > > >for museum statistics ,of course > > I'm afraid I have to disagree with you on that comment. V-tails work fine > on most models as long as they are designed properly. They do have an > advantage on interference drag in most cases, but otherwise they are > essentially equivalent to T-tails and conventional tails in actual > practice, IF THEY ARE DESIGNED PROPERLY. Unfortunately there are too many > folks out there who don't know how to do that, and they have given the > concept a bad name. > > We have kitted a number of models that come with an option for both > conventional tail and V-tail. Handling and stability are essentially equal > on each of these. The Chrysalis series even come with all parts included in > the kit for BOTH tail types. > > The aerodynamic differences among the different tail types are extremely > small, to the point that it's splitting hairs to find the differences in > most cases. The main difference is the interference drag, as I mentioned > above. A V-tail has one inside corner, a T-tail and a conventional tail > each have two, and the worst in this regard is the cruciform tail, which > has four inside corners. > > An upright V-tail does have more adverse rolling effect than an equivalent > T-tail or conventional tail although this is only a factor during strong > rudder inputs, and even then is normally not a significant factor, because > of the much larger span of the wing in comparison to the tail. There is > theoretically some "destructive interference" between the two panels of a > V-tail during a rudder input, although in actual practice we have found > this to be usually insignificant' perhaps in part to the fact that the > V-tail's wider chord and/or longer span panels tend to have better Reynolds > numbers and/or span loadings than the smaller panels of the equivalent > other tails. > > The primary advantages of the V-tail are structural, and these can be very > significant. First of all, the V-tail can in many cases be structurally > simpler than the other types, and therefore lighter. This weight in the > tail has a significant effect on pitch inertia, which can significant;y > influence the tail size needed for adequate dynamic stability. The biggest > factor is that it keeps the mass of the tail structure low, unlike a > T-tail, so it doesn't tend to twist off the tail boom in a ground loop. > OTOH, most of the tail especially the tips, is up in the air, out of the > grass and rocks, so it does not tend to snag tips and break off the tail > boom like a conventional tail. The cruciform tail has some of this same > property, although its more complex structure and its still marginal stab > tip clearance (only a little better than a conventional tail's) tends to > negate this. On full-scale sailplanes the dynamics of tail loads in > off-field landings and their effects on the tail are a bit different, and > in those cases the T-tail generally comes out ahead. This is one reason why > so many full scale sailplanes have T-tails. > > Construction wise, the V-tail has only two things to build. OTOH, they > don't do as well with all-flying surfaces, a stabilizer-ruddervator > two-piece panel design needs less area to achieve the same control force. > The differences among the different tail types are minor enough that it > usually comes down to the details of the individual aircraft design in > question. > > In our experience, the best combination has often been the V-tail, which is > why we've used it so often on our sailplane kits. I have no particular > allegiance to V-tails, in each case we used them simply because the were > the best at getting the job done in each of those designs. > > On the Chrysalis series we include the parts for a conventional tail > because some beginners are afraid of V-tails. However, when I build a > Chrysalis for myself I use the V-tail because it handles the same, but > weighs less and does not drag the tail through the grass on landing. > > > > Don Stackhouse @ DJ Aerotech > [EMAIL PROTECTED] > http://www.djaerotech.com > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and >"unsubscribe" requests to [EMAIL PROTECTED] > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
