At 11:11 AM 7/08/05 +0930, you wrote:
>There are no tail-lets yet because the amount of induced drag from the
>tailplane is relatively small compared to the rest of your drag. I am not
>sure that the reduction in induced drag will compensate for the increased
>profile drag of having the tail-let.
>
Also the tail load may be up or down. The tailets will only work for one
case and you want to minimise tail loads in any case. This is one advantage
of flapped airfoils.
>However, I am sure that something similar will come along. As sailplane
>designs strive to get ever closer to the theoretical maximums I am sure we
>will see people playing with that style of idea. Some things we have
>already seen:
>
>- Ballast in the fin will reduce your required tailplane down load and hence
>reduce the induced drag from the tailplane,
I think this is to compensate for the forward CG of water ballast.
Sailplanes with excessive pitch stability are a bad idea as they try to
line up with the vertical gusts and become unpleasant to fly. Moving the CG
aft decreases the pitch stability.
>- More complex tailplane planform. A straight taper planform isn't that
>efficient in induced drag, a double taper like on the tailplane of the
>DG-1000 is more efficient (a triple or quadruple taper like a Discus wing
>planform gets you ever closer to perfect efficiency). The trade off is the
>additional cost of manufacture for that fraction of a percent improvement in
>performance.
If the tail loads are done right this is a styling department thing. I did
hear a talk by a Dr Ilan Kroo (aero engineeering department at Stanford
Uni)once where he said a slightly higher aspect ratio for the tailplane
than was commonly used would be a good idea but again if tail loads are
minimised this won't have any effect except making the tailplane easier to
stall.(low aspect ratio wings stall at higher AOA).
In some powered aircraft(Piper Malibu) an older airfoil with lower pitching
moment is used on the wing to minimise trim drag vs using a modern laminar
flow airfoil with higher pitching moment.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
phone Int'l + 61 746 355784
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Int'l + 61 429 355784
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