Today's Message Index:
----------------------
1. 04:22 AM - Re: SV: "P" factor (Mark Schindler)
2. 05:11 AM - "P" factor (Michel Verheughe)
3. 05:58 PM - Re: "P" factor - tail wheel and "splitted" elevator. (Torgeir Mortensen)
4. 08:10 PM - Prop shortening (Clem Nichols)
5. 09:47 PM - Re: "P" factor - tail wheel and "splitted" elevator. (kurt schrader)
6. 10:28 PM - Re: Prop shortening (kurt schrader)
7. 10:39 PM - Re: SV: "P" factor (kurt schrader)
8. 10:46 PM - Re: Tailwheel Troubles (jimshumaker)
Message 1
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--> Kitfox-List message posted by: Mark Schindler <mtschindler@yahoo.com>
Kurt - that's a great explanation -
Mark
kurt schrader <smokey_bear_40220@yahoo.com> wrote:
--> Kitfox-List message posted by: kurt schrader
Michel,
I must respectfully and humbly disagree with what your
simulator friends taught you. Though helicopter
blades can do many things a propeller can't, I can see
no method of achieving significant P factor in a helo.
There are two very different causes of lift/thrust
loss between the two, though the results are somewhat
similar in one respect - thrust/lift moves off center
and that is what we have to control.
What your friends were talking about in helos has to
do with retreating blade loss of speed, and therefore
lift, that is corrected by increased blade pitch. The
more you move forward in a helo, the faster the air
moves over the advancing blade and the slower it moves
over the retreating blade. Very quickly, the
retreating blade root will have reverse airflow and
produce zero or even negative lift. The pitch has to
be increased on this blade to overcome the loss of
lift due to speed. This correction is designed into
the control system. As helo speed increases, more of
the root section goes to zero, then reverse flow. It
is not uncommon for 30% of the retreating blade to
produce zero or negative lift.
The average flow across the retreating blade decreases
with speed requiring more pitch to stay level.
Eventually you achieve retreating blade stall by going
too fast and needing too much pitch on the slow
reverse flying blade. But the advancing blade has
even more lift due to the speed, so the helo rolls
over uncontrolled. This is what usually determines
the top speed of helos.
P factor is very different. Speed is not the
controlling factor and doesn't change across the prop
significantly. Instead it is airplane's pitch or yaw
that causes the prop pitch to change relative to the
wind. No matter what speed you are going, if you take
the prop arc out of alignment with the air flow, you
change the angle of attack of the prop to the air from
one side to the other. This is because the prop's
pitch is fixed in relation to the crankshaft, but not
to the relative wind. So when the crankshaft is
angled by pitch or yaw away from the relative wind,
the blade pitch changes with it. It is not more or
less airflow or more or less speed, but more and less
pitch around the prop arc that causes the off center
thrust.
You can see the cause of P factor with the plane
parked. Just look at horizontal prop blade angles in
relation to horizontal wind with the plane leveled.
The angles are the same all around the arc. Then put
the plane's tail on the ground. Now the decending
prop blade will have a greater angle or bite to the
horizontal wind and the ascending blade will have a
smaller angle and less thrust. No speed required at
all. It is just a pitch change caused by angling the
plane. This pitch change is much larger than any
speed difference a prop sees since it is near 90
degrees to the wind.
A helo edge on to the wind sees speed changing around
the arc. The speed change is directly related to the
helo's speed.
A prop near 90 degrees to the wind sees pitch changes
around the arc. That pitch change is exactly related
to the planes pitch or yaw change.
Best I can explain it tonight.
Kurt S.
--- Michel Verheughe wrote:
>
> > From: kurt schrader [smokey_bear_40220@yahoo.com]
> > It isn't "less air passing it", but just more or
> less pitch to move more or less air.
>
> I think we all agree, Jim and Kurt. The reason I
> wrote "less air passing it" is that, in a previous
> discussion with my simulator friends, we were
> explained the P-factor as a comparison to an
> helicopter's rotor where one blade is going in the
> direction of the flight (thus increasing the air
> speed passing it) while the other is going the other
> way. Of course, the helo is an exaggerated (nearly
> 90 degrees) example of the P-factor but something
> that worked for my comprehension of it. Also, the
> difference of air speed passing the blade is the
> difference of pitch above-mentionned. Just a way of
> saying the same thing in a different manner, I
> think.
>
> Cheers,
> Michel
>
> do not archive
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--> Kitfox-List message posted by: Michel Verheughe <michel@online.no>
I hate computers! I am sure I already answered this one but ... I find no trace
of it. If I really did, please excuse the double posting.
> From: kurt schrader [smokey_bear_40220@yahoo.com]
> I must respectfully and humbly disagree with what your
> simulator friends taught you.
I agree with everything you say, Kurt. I would like, however, to quote what Austin
Meyer, the American creator of the flight simulator X-Plane, says about it.
What do you think of it?
Cheers,
Michel
A climbing airplane is the same [as a helicopter]: The DESCENDING blade is actually
ADVANCING INTO THE AIR A LITTLE BIT (THUS MOVING FASTER) SINCE THE PLANE
IS TILTED UP! The CLIMBING blade is retreating away from the onrushing air a bit
for the same reason! Thus, the DESCENDING blade puts out more lift from it's
HIGHER SPEED when the airplane is at high angle of attack.
Message 3
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| Subject: | Re: "P" factor - tail wheel and "splitted" elevator. |
--> Kitfox-List message posted by: Torgeir Mortensen <torgemor@online.no>
Hi Michel,
Long time.. long seen..
You are not that far out...
How about this:
Pasted from this site:
http://www.drag-on-fly.com/B263.html
.......................
P-factor:
[rotor] The term P-factor is defined to mean ``asymmetric disk loading''.
It is an extremely significant effect for helicopters. When the helicopter
is in forward flight, the blade on one side has a much higher airspeed
than the other. If you tried to fly the blades at constant angle of
attack, the advancing blade would produce quite a bit more lift than the
retreating blade.
[propeller] Asymmetric loading is caused by the resultant velocity of the
propeller in its plane of rotation and the velocity of the air through the
propeller disc. With the airplane at positive angles of attack the right,
or down swinging blade has a higher velocity than the left, or up swinging
blade. Since the propeller blades are in themselves airfoils increased
velocity results in increased lift, and the increased lift on the right
blade tends to yaw the airplane to the left.
.........................
And some more (practical) from this site:
http://www.helicopterpage.com/html/dol.html
..........................
As for your "soft" tail wheel: YES it's better, in two ways! But it can't
prevent ground loops..
There is a physical explanation on this, and you should be able to figure
out...
..........................
The splitted elevator is made to improve the sensitivity of the elevator
around the neutral position.
I.E. A flat foil stab. with no split, will have a dead spot around neutral
position (boundary layer), besides, this "instability" also tend to create
oscillation / flutter.
There is a "small" roll component- and a "micro" yaw component... :)
...........................
I'm on my way.. this weekend
Cheers
Torgeir.
On Thu, 29 Jul 2004 14:11:27 +0200 (CEST), Michel Verheughe
<michel@online.no> wrote:
> --> Kitfox-List message posted by: Michel Verheughe <michel@online.no>
>
> I hate computers! I am sure I already answered this one but ... I find
> no trace of it. If I really did, please excuse the double posting.
>
>> From: kurt schrader [smokey_bear_40220@yahoo.com]
>> I must respectfully and humbly disagree with what your
>> simulator friends taught you.
>
> I agree with everything you say, Kurt. I would like, however, to quote
> what Austin Meyer, the American creator of the flight simulator X-Plane,
> says about it. What do you think of it?
>
> Cheers,
> Michel
>
> A climbing airplane is the same [as a helicopter]: The DESCENDING blade
> is actually ADVANCING INTO THE AIR A LITTLE BIT (THUS MOVING FASTER)
> SINCE THE PLANE IS TILTED UP! The CLIMBING blade is retreating away from
> the onrushing air a bit for the same reason! Thus, the DESCENDING blade
> puts out more lift from it's HIGHER SPEED when the airplane is at high
> angle of attack.
>
>
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--> Kitfox-List message posted by: "Clem Nichols" <cnichols@scrtc.com>
On a more practical note, any advice about shortening a Warp Drive prop? My last
wheel landing was not my best, and I sustained damage to about 3/4 of an inch
of the tip of one blade, and a tiny amount to another blade. I spoke with
one of the people at Warp Drive about purchasing replacement blades. He thought
that shortening the blades by no more than 3/4" would not have any significant
effect on performance, and suggested going that route instead. He said the
critical part was in cutting the metal leading edge so as to not separate it
from the blade. He suggested cutting it (the metal leading edge) half way through
from one side and the rest of the way from the other side. I was considering
cutting the leading edge with a Dremel rotary tool and using a hack saw
to cut the blade proper. Of course I can always send the blades to Warp Drive
and have them shortened and balanced for about $100 plus shipping charges. New
blades with the metal leading edge would run about $250 each. Original diameter
70" on an NSI Subaru EA 81 engine. Obviously I don't wish to spend money
unnecessarily, but by the same token don't want to risk my life to save a few
dollars. Advice appreciated.
Clem Nichols
Message 5
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| Subject: | Re: "P" factor - tail wheel and "splitted" elevator. |
--> Kitfox-List message posted by: kurt schrader <smokey_bear_40220@yahoo.com>
Well guys,
This may not be a subject that everyone wants to get
so deeply immersed into. It is one of the "whys" of
why the plane likes to yaw during maneuvers. The
first importance is controlling it, not defining it,
so I don't blame anyone for not wanting to read all
this detail. But for you who do want to go there,
here goes. :-)
I am going to stick to my guns on this subject. I
went to the home page of the drag-on-fly site to see
who was giving the p factor definition and it said
this in bright red:
"This material is being constantly expanded and
revised. ~ It contains many errors"
I agree. :-) This is a salesman's site for very
lite/ultra lite helos. They are making it up as they
go. The other site is a good site, but does not
define P factor in any way that I saw. Just helo
aerodynamics.
I'll comment in each e-mail section for clarity (with
deletions for brevity) separated by "KFKFKF"
KFKFKFKFKF
--- Torgeir Mortensen <torgemor@online.no> wrote:
>
> Hi Michel,
>
> How about this:
>
> http://www.drag-on-fly.com/B263.html
>
> .......................
>
> P-factor:
>
> [rotor] The term P-factor is defined to mean
> ``asymmetric disk loading''.
> It is an extremely significant effect for
> helicopters. When the helicopter is in forward
> flight, the blade on one side has a much higher
> airspeed than the other. If you tried to fly the
> blades at constant angle of attack, the advancing
> blade would produce quite a bit more lift than the
> retreating blade.
KFKFKFKFKFKF
Analogy: We can turn on the ground with rudder and we
can turn with brakes. Both cause yawing, but we don't
call both "braking".
Helos and planes both achieve "asymmetric disk
loading" as I explained previously as the one
similarity between them. But both are not "P factor".
He should have said "RE defined" instead of "defined"
as "P factor" because he is borrowing the term to
apply it to helos. Better, he should have just called
both "asymmetric disk loading". That would be
correct. "P factor" is not really correct for helos.
After all, it is "prop factor" shortened to "P
factor".
But his reason for helo asymmetric disk loading is at
least correct.
KFKFKFKFKFKF
>
> [propeller] Asymmetric loading is caused by the
> resultant velocity of the propeller in its plane of
> rotation and the velocity of the air through the
> propeller disc. With the airplane at positive angles
> of attack the right, or down swinging blade has a
> higher velocity than the left, or up swinging
> blade. Since the propeller blades are in themselves
> airfoils increased velocity results in increased
> lift, and the increased lift on the right
> blade tends to yaw the airplane to the left.
KFKFKFKFKF
Who started THIS definition of P factor? I need trig
tables or a trig calculator to give a more exact
answer and I don't have either. Maybe someone would
like to do the math.
Assume a 10 degree aircraft pitch change as an
example. How much faster will the prop blade travel
on the down side than on the up side? The difference
would be the increase of the hypotenuse length over
the base length. Now squared this because the lift
increases with the square of the speed. That should
give the difference in thrust due to speed when
tilting the disk from 90 to 80 degrees.
Compare this to the thrust difference from prop pitch
change. The math is more difficult for this part, so
we need to imagine the difference in thrust on one
side of the propeller compared to the thrust
difference on the other side when you add 10 degrees
prop pitch to one side and subtract 10 degrees of
pitch on the other.
I think you will find that the lift increase due to
the speed chnage is much smaller than that due to the
pitch change. That is because there is so little
speed change from 90 degrees to the wind vs 80 degrees
to the wind. But a difference in prop pitch of 20
degrees total will cause a great asymmetry difference
in thrust.
This difference in pitch will cause a big difference
in prop blast from side to side, which is a much
bigger airspeed difference than changing the disc arc
10 degrees. The key word is "cause". The pitch
difference causes the prop blast speed difference from
side to side. The prop arc speed difference is far
smaller.
My conclusion is that asymmetric loading is due to
pitch not speed differences for planes, and speed not
pitch differences for helos, due to their very
different angles to the wind.
And only planes have "P factor". (Aren't we splitting
hairs on that?)
KFKFKFKF
Next subject...
> ..........................
>
> The splitted elevator is made to improve the
> sensitivity of the elevator around the neutral
> position.
>
> I.E. A flat foil stab. with no split, will have a
> dead spot around neutral
> position (boundary layer), besides, this
> "instability" also tend to create oscillation
> / flutter.
>
> There is a "small" roll component- and a "micro" yaw
> component... :)
>
> Torgeir.
KFKFKFKF
Exactly right. The key is the boundry layer being
thicker on flat airfoils and the need to be up against
it for flutter and flight control purposes.
KFKFKFKF
>
> On Thu, 29 Jul 2004 14:11:27 +0200 (CEST), Michel
> wrote:
> > I agree with everything you say, Kurt. I would
> like, however, to quote what Austin Meyer,
> the American creator of the flight simulator
> X-Plane, says about it. What do you think of it?
> >
> > Cheers,
> > Michel
> >
> > A climbing airplane is the same [as a helicopter]:
> > The DESCENDING blade is actually ADVANCING
> > INTO THE AIR A LITTLE BIT (THUS MOVING FASTER)
> > SINCE THE PLANE IS TILTED UP! The CLIMBING blade
> > is retreating away from the onrushing air a bit
> > for the same reason! Thus, the DESCENDING blade
> > puts out more lift from it's HIGHER SPEED when the
> airplane is at high angle of attack.
KFKFKFKF
The Key phrase Michel is, "a little bit" as 10 degrees
is a little bit of 90 degrees. A helo has a huge
difference in speed edge on. The plane has so little
speed difference nearly 90 degrees off the relative
wind. But the prop pitch difference CAUSES the prop
to create a much bigger wind speed or prop blast
difference. IMHO
Pant pant. Think I am out of breath on that one. :-)
Kurt S. S-5/NSI turbo
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| Subject: | Re: Prop shortening |
--> Kitfox-List message posted by: kurt schrader <smokey_bear_40220@yahoo.com>
Clem,
Oops? Guess that is just a ding?
I was thinking along the same lines as you when I read
this. Maybe jury-rig a ficture so that you can cut
the exact same amount off each blade like a miterbox.
Then use a dremel to cut the metal from each side,
followed by cutting the blade in your ficture for
exact length. Finally weigh each blade and see if you
got it accurate.
Does your post office have a package scale in the
lobby? Just an idea. I think some will compare
accurately to the gram for something that light. If
you walk in with 3 blades and a file, tell them it is
a ceiling fan or something. :-)
If there is even a little seperation of the metal, you
need to send it in. They will work lose and fly off
making for way too much vibration.
Next point: Sawing carbon fiber. Will a new fine
blade hacksaw do it without seperating the end fibers?
I think it will be OK, but don't know for sure. A
big rotory cutoff disk on a table saw might cut carbon
too and you can set it accurately for length. I'd ask
Warp what's best. Phone calls are cheaper than
experience.
I'd also like to know how well it works for you - for
when I do it... Bound to happen to me too.
Kurt S. S-5 /NSI turbo
--- Clem Nichols <cnichols@scrtc.com> wrote:
> --> Kitfox-List message posted by: "Clem Nichols"
> <cnichols@scrtc.com>
>
> On a more practical note, any advice about
> shortening a Warp Drive prop? My last wheel landing
> was not my best, and I sustained damage to about 3/4
> of an inch of the tip of one blade, and a tiny
> amount to another blade. I spoke with one of the
> people at Warp Drive about purchasing replacement
> blades. He thought that shortening the blades by no
> more than 3/4" would not have any significant effect
> on performance, and suggested going that route
> instead. He said the critical part was in cutting
> the metal leading edge so as to not separate it from
> the blade. He suggested cutting it (the metal
> leading edge) half way through from one side and the
> rest of the way from the other side. I was
> considering cutting the leading edge with a Dremel
> rotary tool and using a hack saw to cut the blade
> proper. Of course I can always send the blades to
> Warp Drive and have them shortened and balanced for
> about $100 plus shipping charges. New blades with
> the metal leading edge would run abou!
> t $250 each. Original diameter 70" on an NSI Subaru
> EA 81 engine. Obviously I don't wish to spend money
> unnecessarily, but by the same token don't want to
> risk my life to save a few dollars. Advice
> appreciated.
>
> Clem Nichols
Message 7
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--> Kitfox-List message posted by: kurt schrader <smokey_bear_40220@yahoo.com>
Thanks Mark,
Maybe I should have just called it aerodynamic
dyslexia? No, even I don't understand that.... :-)
--- Mark Schindler <mtschindler@yahoo.com> wrote:
> Kurt - that's a great explanation -
>
> Mark
Do not archive
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http://mobile.yahoo.com/maildemo
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| Subject: | Re: Tailwheel Troubles |
--> Kitfox-List message posted by: "jimshumaker" <jimshumaker@sbcglobal.net>
Yes Scott,
locking out the freewheel release may prevent some inadvertant ground turns.
I once had an excursion into the grass when landing is a slight (8 to 10
mph) crosswind. I landed a little too relaxed and veered a little. then
corrected with a quick stab of the rudder to catch the veer. That released
the tailwheel and I then slowly turned into the crosswind, even with full
opposite rudder. I was only about 50' short of the taxi way so I just kept
going right back onto the pavement. Maybe my plane just likes grass ;
)
Jim Shumaker
----- Original Message -----
From: "Michel Verheughe" <michel@online.no>
Subject: Re: Kitfox-List: Tailwheel Troubles
> --> Kitfox-List message posted by: Michel Verheughe <michel@online.no>
>
> Scott McClintock wrote:
> > Want to share your opinion on this, Michel?
>
> Well, I never had a ground loop so it is not easy for me to talk against
the
> free-castoring, Scott.
>
> Yesterday evening, I flew to a nearby airfield where a friend is
re-building a
> Kitfox from scratch (used as a seaplane, the frame is rusted and needs
> sandblasting, etc.) Beautiful flight just before the legal VFR night (six
> degrees under the horizon) in silk smooth air.
> That airfield is grass, a smooth landing compared with my asphalt home
field. I
> taxied out of the landing stripe then pressed the right pedal and brake,
and
> did an elegant 180 turn on one wheel, pointing the nose toward the stripe,
> ready to leave. Wow! I love that free-castoring wheel! It's also very
handy
> when I have to do a complex manoeuvre to get my plane in the hangar that
is
> barely as wide as half my wing span.
> ... but, as I said, I still have to experience the bad side of it. Maybe
the
> best would be to have the locking device controlled from the cockpit, like
on
> the DC-3.
>
> Cheers,
> Michel
>
> do not archive and do not misquote! :-)
>
>
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