Nope. It is the other Tom (me) who races sailboats, both full size and RC.
I'm sure I can make heads and tails of this if I try. My dad was an
Aeronautical Engineer, and we used to discuss these things a lot. I also did a
lot of work for Boeing simulating aircraft. But I just didn't want to wrap my
head around the aerodynamics at this time.
Tom (the other)
On Apr 7, 2020, at 4:36 PM, ORCA <ORCA@xxxxxxxxxxxxx> wrote:
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 ;
<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