Rag and tube construction and computer models?

Stealth Pilot wrote:

On Sat, 10 Apr 2004 16:06:27 GMT, Richard Lamb
wrote:

hedge trimming

From the plans, the CG Range is 15% to 28% of the chord.
Figuring the chord as 48 inches, that means 7.2 inches forward limit,
(aft of leading edge) to 13.44 for the aft limit (also aft of LE).

(That 15% forward limit seems awful far forward to me - but it woiks)

the actual flight tested values for my aircraft are 10.4" forward
limit and 16.5" aft limit.


That sounds like a lot more reasonable range to me.
20.8 to 34.3 percent chord.


1300lb auw (well actually 590kg with an empty weight of 362kg.
empty cg moment arm is 214mm.

See, THAT's the problem with the metric system...

Is that supposed to be mm, or cm ???

Also, where is your datum for this measurement?

Knowing where the datum is located, we could "load 'er up"
and really see whazzappening.


hedge trimming

But different assumptions will give different results.
All depends on how valid our assumptions are at the beginning...

I'm real skeptical that the tail on the Tailwind is producing an
upload at high speed. The airplane handles too well for that to
be the case.

Remember that the leading edge of the stab is probably a little nose
down. Full forward trim _should_ still result in a net down load on
the tail.

I tend to agree although I'm sometimes not sure. I'd love to see a
windtunnel test on the "new" aerofoil to see just what the pitching
moment was.

Man, me too. If we had solid numbers on the airfoil it would be then
be possible to do a little comparative shopping.

This one has the thickest part of the airfoil WAY forward.
Contemporary theory moves the thickest part of the airfoil aft
to increase the laminar area on the front of the wing.
THIS one can't possibly have that much laminar wing flow.

Steve's airfoil is supposed to be a TLAR modification.
Something like a 2309 top curve and M6 (or?) bottom?

Like someone else pointed out in another thread,
TLAR is definitely in the eye of the beer holder...

On the other hand, we _are_ talking about the Wittman Tailwind.
The little airplane that somehow flies better than it should.
I'll bet a steak dinner it's not just the airfoil.

Richard

On Sat, 10 Apr 2004 21:08:10 GMT, Richard Lamb
wrote:

Stealth Pilot wrote:

On Sat, 10 Apr 2004 16:06:27 GMT, Richard Lamb
wrote:

hedge trimming

From the plans, the CG Range is 15% to 28% of the chord.
Figuring the chord as 48 inches, that means 7.2 inches forward limit,
(aft of leading edge) to 13.44 for the aft limit (also aft of LE).

(That 15% forward limit seems awful far forward to me - but it woiks)

the actual flight tested values for my aircraft are 10.4" forward
limit and 16.5" aft limit.


That sounds like a lot more reasonable range to me.
20.8 to 34.3 percent chord.


1300lb auw (well actually 590kg with an empty weight of 362kg.
empty cg moment arm is 214mm.

See, THAT's the problem with the metric system...

Is that supposed to be mm, or cm ???

millimeters.

Also, where is your datum for this measurement?


214mm is a tad over 8 3/8" back from the only datum used on the
tailwind :-)
recall that it will always have a pilot added to the empty weight and
you dont actually fly with empty fuel :-)

crumber nunch away. I'll bet you get close to 65lbs as the maximum
download.

(just remembered where my number comes from. future son in law is
doing his commercial studies, worked the numbers with a few
guestimates where there are no aerofoil data. aerofoil data is what's
needed.)
Stealth Pilot

Stealth Pilot wrote:


1300lb auw (well actually 590kg with an empty weight of 362kg.
empty cg moment arm is 214mm.

See, THAT's the problem with the metric system...

Is that supposed to be mm, or cm ???

millimeters.

Also, where is your datum for this measurement?


214mm is a tad over 8 3/8" back from the only datum used on the
tailwind :-)
recall that it will always have a pilot added to the empty weight and
you dont actually fly with empty fuel :-)


Actually, 1425 is the GROSS. If yours is that heavy without pilot
and fuel, then yes, maybe you'll have a 600 pound load on the tail.

Please recall that I was talking about straight and level flight.
Pull G's and the load goes up.

But 75 pounds S&L load still shouldn't make 650 pounds at 4 Gs.

Look. how about a reality check?

Have your bright boy check to see how much the stab spar will bend
at 650 pounds load.

crumber nunch away. I'll bet you get close to 65lbs as the maximum
download.

(just remembered where my number comes from. future son in law is
doing his commercial studies, worked the numbers with a few
guestimates where there are no aerofoil data. aerofoil data is what's
needed.)
Stealth Pilot

"Veeduber" wrote

PS -- I don't mean to say NACA figured out the cottage cheese. I figured
that
one out myself when I was designing my All-Dairy composite... the one with
the
bricks of butter for the landing gear.

It does make it easy to "grease" a landing, doesn't it? groan
--
Jim in NC


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On Sun, 11 Apr 2004 14:16:32 GMT, Richard Lamb
wrote:

Stealth Pilot wrote:


1300lb auw (well actually 590kg with an empty weight of 362kg.
empty cg moment arm is 214mm.

snip

Actually, 1425 is the GROSS. If yours is that heavy without pilot
and fuel, then yes, maybe you'll have a 600 pound load on the tail.


you've lost me totally there.

590kg and 362kg are the measured weights of the aircraft, full to the
gunnls and empty. they are not the downloads.
65kg download was the worst case calc at cruise and max auw as I
recall.
at 4g we could say that it is the equivalent of 4 people, 2 a side,
standing on the elevator spar. it might deflect a little but I think
it is feasible.
the tube concerned is 1 1/8" dia by 65 thou wall thickness.

Stealth pilot