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dashvii(at)hotmail.com
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 Posted: Thu Jan 25, 2007 3:43 pm Post subject: prelim drag reduction |
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I've ran some preliminary numbers, which are mainly just theoretical
guestimates of a sort. The only thing that I didn't know was what the exact
amount of surface area for the lightning was. I used a Lancair 320's
surface area in it's place as I figure they're about the same size. That
gave me a reduction of about 11% frontal area by using the gap seals alone!
Now independent of those numbers I have a similar experiment that I know
that was done using a Piper Arrow II. Following the same format there I
find that the gap seals alone are on the order of 3 times the amount of drag
reduction than on the Arrow. I still have to add in the flap hinge fairings
too! Now the Arrow included fuel tank screw fairings, wheel well fairings,
flap gap seals, aileron gap seals, and flap hinge fairings! I figure our
flap hinge fairings will add slightly more to the above number. Now this is
all assuming that I ran the numbers right. Even then it's still just a
theoretical value and until tested we can't be sure that we'll get this much
even. Although the actual results could be way more as well.
Just for reference the Arrow experiment gained 2.5% speed at 75% cruise at
6,500 feet and about 5.5% range. If we apply that to the Lightning we'd get
about a 5mph increase in cruise at 75% throttle. I still believe that the
actual results will be 8mph or more though. Even though these are just
estimates the numbers seem promising. More to come. Brian W.
_________________________________________________________________
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pequeajim
Joined: 03 Sep 2006
Posts: 708
Location: New Holland, PA
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| Posted: Thu Jan 25, 2007 6:33 pm Post subject: prelim drag reduction |
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Cool information Brian. What kind of affect does drag reduction have on the
stall speed?
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dashvii(at)hotmail.com
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| Posted: Thu Jan 25, 2007 6:44 pm Post subject: prelim drag reduction |
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Jim,
Well, we won't be sure until we actually do the flight testing, but I can
tell you what I think will or could happen and why. In some applications
the flap and aileron gap seals increase speed, range, endurance, rate of
climb, rate of roll. Those are all good things in my book. It also can
increase stall speed and landing roll, those would be undesirable things.
Now the reason that it would increase stall speed is because in some
aircraft there is a slot which allows air to pass through the wing and
reenergizes the boundary layer on the top side. It particularly does this
at higher angles of attack. Now on the Lightning the top of the flap is
tightly sealed inside the wing and so it is my belief that in a clean or
flaps up configuration that we'll see no increase in stall speed. So that
leaves the question of a stall in the dirty configuration. I believe that
we will see an increase in stall speed here. I think that most of the time
it is about 1-2mph. So it's not like you'd have to come over the fence
10mph faster. The landing roll is increased because the lift is increased
and the drag is decreased, so it takes a little more to get it slowed and
stopped. Again it's usally like 3% or something. 3% of what is it 500 feet
is, well, it's not very much. I'll have to of course verify this
experimentally to see what the real numbers are. Sometimes in these kinds
of things you think one thing and something totally different is what you
see, then you have to figure out why. We'll see. Brian W.
From: "Jim Langley" <pequeajim(at)gmail.com>
Reply-To: lightning-list(at)matronics.com
To: <lightning-list(at)matronics.com>
Subject: RE: prelim drag reduction
Date: Thu, 25 Jan 2007 21:32:55 -0500
Cool information Brian. What kind of affect does drag reduction have on the
stall speed?
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