Today's Message Index:
----------------------
1. 09:54 AM - Re: loose parts and drag (Bob Hodo)
2. 10:24 AM - Re: loose parts and drag (Gary Vogt)
3. 10:52 AM - Tiger Elevator (923te)
Message 1
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| Subject: | Re: loose parts and drag |
Ned asks:
The
real question is if the elevator halves are mechanically forced to be
symmetric will that alignment cause more drag thus loss in speed?
The
question has had me thinking, and this is gonna be a long response that
even Ned and Gary may not wish to endure, but here goes.
These
are some of my assumptions: We have three horizontal surfaces on our
empenage, 1) Horizontal stabilizer (HS) which is fixed, 2) elevator (EL)
which moves up and down, and 3)trim tab (TT)which moves in the same
direction but further than the EL.
The cleanest configuration of
those three surfaces is when they are all aligned in the same plane. As
soon as the EL moves all three surfaces are in their own plane and
being this close together, drag
is induced. We also know that there is only one airspeed that will
nail that perfect alignment for any given aircraft and its own weight
and bal configuration at that moment.
Now, if our aircraft were
being towed by a long string in clear air, yes, having both elevator
tips aligned with the leading edge of the HS would be the cleanest
configuration. We also know that since we are being dragged along in
clean air in a typical nose heavy W&B situation that the slower we
are moving the more the tail has to push down to compensate, and the
faster we are moving the less it has to, but we want each side to push
down the with same amount of force as the other.
But Ned has
observed that we know the prop wash corkscrews around the fuselage,
striking the pilot side HS from the bottom and the other side from the
top.
This fact means that if we are mechanically symmetrical, the
pilot side of the HS has to push down more than its share
since it is being lifted by the prop wash, while the co-pilot's side
has to do less of the pushing, and therein we have induced drag, because
we have ignored the fact that the apparent wind on one side is arriving
at a slightly different angle of attack than what the other side is
seeing.
..................
Now I do not know what the
difference is back there at any high speed strait and level
configuration. But it would be my opinion that to simply provide a
different angle of attack for the elevator on one side would find us
sacrificing the loss of that drag, for the increase from having those
three surfaces out of plane with each other. I guess what I am
suggesting is that to truly mitigate this prop-wash effect, one would
need to adjust the angle of attack of the HS on the pilots side to be
lower than the angle of attack on the co-pilot's side HS.
...............
Final
thoughts: I've never met anyone who can picture air
molecules in his mind moving about an airframe the way Gary can. And I
am confident that if the picture my mind's eye is seeing is out of
whack, he will grin really big and very patiently explain to me where I
got off the bus.
Bob Hodo
one pretty quick cheetah
Message 2
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| Subject: | Re: loose parts and drag |
What Bob says has merit. -How much? -I don't know. -A short while bac
k I found computer simulations on the internet that showed areas of high an
d low pressure in flight, with a propeller. -As I recall, most of the pre
ssures were uniform by the time it got to the tail. -=0A=0AOne way to tes
t it would be to tape tufts of yarn onto the elevator tips and watch. -If
they aren't straight back, I'd be surprised.=0A=0A=0A_____________________
___________=0A From: Bob Hodo <bob.hodo@yahoo.com>=0ATo: teamgrumman-list@m
atronics.com =0ASent: Friday, November 18, 2011 9:52 AM=0ASubject: Re: Team
Grumman-List: loose parts and drag=0A =0A=0ANed asks:=0AThe real question i
s if the elevator halves are mechanically forced to be =0Asymmetric will t
hat alignment cause more drag thus loss in speed?=0A=0AThe=0A question has
had me thinking, and this is gonna be a long response that=0A even Ned and
Gary may not wish to endure, but here goes.=0A=0AThese =0Aare some of my as
sumptions: We have three horizontal surfaces on our =0Aempenage, 1) Horizo
ntal stabilizer (HS) which is fixed, 2) elevator (EL)=0A which moves up and
down, and 3)trim tab (TT)which moves in the same =0Adirection but further
than the EL.=0A=0AThe cleanest configuration of =0Athose three surfaces is
when they are all aligned in the same plane. As=0A soon as the EL moves al
l three surfaces are in their own plane and =0Abeing this close together, d
rag=0A is induced. We also know that there is only one airspeed that will
=0Anail that perfect alignment for any given aircraft and its own weight
=0Aand bal configuration at that moment.=0A=0ANow, if our aircraft were =0A
being towed by a long string in clear air, yes, having both elevator =0Atip
s aligned with the leading edge of the HS would be the cleanest =0Aconfigur
ation. We also know that since we are being dragged along in =0Aclean air i
n a typical nose heavy W&B situation that the slower we =0Aare moving the m
ore the tail has to push down to compensate, and the =0Afaster we are movin
g the less it has to, but we want each side to push =0Adown the with same a
mount of force as the other.=0A=0ABut Ned has =0Aobserved that we know the
prop wash corkscrews around the fuselage, =0Astriking the pilot side HS fro
m the bottom and the other side from the =0Atop.=0A=0AThis fact means that
if we are mechanically symmetrical, the=0A pilot side of the HS has to push
down more than its share=0A since it is being lifted by the prop wash, whi
le the co-pilot's side =0Ahas to do less of the pushing, and therein we hav
e induced drag, because=0A we have ignored the fact that the apparent wind
on one side is arriving=0A at a slightly different angle of attack than wha
t the other side is =0Aseeing.=0A=0A..................=0A=0ANow I do not kn
ow what the =0Adifference is back there at any high speed strait and level
=0Aconfiguration. But it would be my opinion that to simply provide a =0Ad
ifferent angle of attack for the elevator on one side would find us =0Asacr
ificing the loss of that drag, for the increase from having those =0Athree
surfaces out of plane with each other. I guess what I am =0Asuggesting is
that to truly mitigate this prop-wash effect, one would =0Aneed to adjust t
he angle of attack of the HS on the pilots side to be =0Alower than the ang
le of attack on the co-pilot's side HS.=0A=0A...............=0A=0AFinal=0A
thoughts: I've never met anyone who can picture air=0A molecules in his mi
nd moving about an airframe the way Gary can. And I=0A am confident that i
f the picture my mind's eye is seeing is out of =0Awhack, he will grin real
ly big and very patiently explain to me where I =0Agot off the bus.=0A=0ABo
========
Message 3
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Bob,
That was a good explanation and helps me to visualize.
Below I copied an email from someone who became a grumman guru long ago.
I think Maynard adds an important concept to include in this discussion.
The dorsal fin affects the local flow around the tail.
Bob is getting real close to giving one of the best speed mod secrets
away. That is:
I find that if I adjust weight so that the elevator is neutral AND the
elevator trim is neutral I achieve the highest speed. We're talking up
to 10kts speed "mod" here.
If I add in flap reflex and try and get the canopy rails at 0 with a
level then it is even faster. That's right, I sometimes fly with a level
on the canopy rails;)
Now if Gary would participate in telling secrets maybe we could
collectively break his 165 ktas goal
Ned
From: Gary L Vogt
Sent: Saturday, October 08, 2011 12:52 AM
Subject: TeamGrumman-List: Engine thrust angle.
<teamgrumman@yahoo.com>
I found something regarding the effect of engine thrust angle and best
trim at high speed. Let's just say its my secret.
Gary
Sent from my iPad
----- Original Message -----
From: maynardccrosby@earthlink.net
Sent: Thursday, November 17, 2011 4:08 PM
Subject: Re: Tiger Elevator
Ned,
This is new information, The elevator should have the same shape on
both sides. The factory incidence is 0 degrees. If this is increased to
a + insidence then it i'll take attitional trim - to fly level.
The 0 position is the factories best engineering and FAA certfication to
Part23.
Now as to corkscrew from the P factor, it is broken up by the dorsal
fin.
I found this out may years ago.
I was flying with the Last yankee and two others, one was a AA-1
Blackman's
and a AA-1A in formation. The other two tails were continually in motion
But they cound't see it or feel it. They responded that my tail was
still.
It had the first mod with the AA-5A/B's dorsel fin. That was good enough
for
me to add the dorsel to these air planes. Here the results. as Blackman
did
the finization on the LastYankee's STC. He wrote a seperate STC
application
that gave him my dorsel fin Mod in His Name. Therefore he stole it.From
me.
I didn't fine it out for several years.
Maynard
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