Maybe Tom is thinking of racing sailboats instead of airplanes . . .
Rick
From: LEE LANNOYE
Sent: Tuesday, April 7, 2020 4:13 PM
To: orcachat@xxxxxxxxxxxxx ; Tom Speer
Subject: [orcachat] Re: SHOW AND TELL..
Tom, if you thought the rest of us would understand your analysis, I think you
are going to be disappointed, lee
On April 7, 2020 at 4:01 PM Tom Speer <me@xxxxxxxxxx> wrote:
So far, I haven't tried to analyze how the wake will roll up. I've only used
a vortex lattice method that has the wake trailing straight back. I've
attached a plot of the spanwise load distribution (green line) and the
corresponding lift coefficients (orange).
There are two principal sources of drag for a glider - profile drag and
lift-induced drag. The induced drag dominates at low speed, while in a
thermal, and the profile drag (plus other parasite drags) dominates at high
speed when penetrating the wind. Compared to Mark Drela's Allegro-Lite, this
design has 20% less induced drag.
I've also been toying around ideas for a flexible trailing edge. This would
act like a flap, increasing the camber at low speed and flattening out at high
speed. It would be totally passive, though, and not require a servo. So it
meets the rules for RES gliders. The flexible upper skin has to have a precise
stiffness in order to get the desired effect, and I haven't yet experimented
with what material to use. I'm thinking molded paper might do the trick. The
paper would be molded to the low-speed shape and then put into a jig where I'd
load the trailing edge with a whiffle tree. The paper would be sanded until I
got the desired deflection for the design load.
I'm also concerned about flutter, so I want to mass balance the trailing
edge. I'm thinking of using something like 1/32" balsa sheet for the lower
surface and putting a piece of music wire on the forward edge of the balsa.
There should be enough room inside the wing for this to move up and down as the
trailing edge flexes. A thin flexible piece of plastic (Mylar?) would seal the
gap on the underside.
The attached plot shows the profile drag for the section with flexible
trailing edge compared to several sections by Prof. Mark Drela of MIT. It is
competitive at high speed and has significantly less drag, and higher maximum
lift, at low speed. When you combine it with the savings in induced drag, it
may be feasible to get a 20% reduction in total drag at low speed while still
being competitive at high speed. I've corresponded with Drela about it, and
he's intrigued by the concept.
One big problem may be wing flutter, due to the mass of the fins and
horizontal stabilizers behind the elastic axis of the wing. The wing will need
to be stiff in torsion, so composite wing skins with the fibers oriented at +45
deg would be in order. I've not done an vacuum bagging, so I've that whole
adventure ahead of me as well.
Cheers,
Tom
On 4/7/20 11:09 AM, Jake Boyd wrote:
Hi Tom S
Your 2m wing design is interesting. It would be interesting to see see what
effect the inboard wing tip vortices will produce.
Jake
Sent from EKAJDYOB
On Apr 6, 2020, at 21:53, Tom Speer mailto:me@xxxxxxxxxx wrote: ;
Not my design. It's by 3DAeroventures
(https://www.3daeroventures.com/shop/infinitywing). My only contribution is to
print it in LW-PLA instead of PLA.
However, I do have a 2m glider on the drawing board that is a bit
unusual. The configuration only makes sense because of the 2m span limit.
Cheers,
Tom
