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av8rps(at)tznet.com
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 Posted: Tue Dec 26, 2006 11:01 am Post subject: Older Kitfox cruise speeds (and a new challenge for Michel's |
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Michel,
Well, I'm not sure about how two universes might stack up against eachother
in regards to Kitfox cruise speeds (??), but to answer the question with
accurate historical accuracy, it wouldn't matter. Thats's because Dean
Wilson had already designed the wing incidence into the Avid Flyer, which is
what was used on the first Fox. Not to rain on your parade, but that is
really the long story short.
Man, we really need to find a challenge for you with that flight
simulator/computer program you are playing with. I'll bet there's just
something out there that could help our group out with some question we've
been struggling with.
Here's a couple I have;
- How would cruise speed be affected by various landing gears (bungee or
spring) and tire sizes (and what the heck, see what it says about wheel
pants)?
- What impact would lengthening the wing another 2 feet have, as well as
shortening it to say 26-27 feet?
- What impact does moving the engine thrust line up 4-6 inches and/or left
or right a few degrees (along with the vertical fin) have on the flight
characteristics?
- Compare performance between the round cowl against the streamline cowl
- Compare a unfaired belly radiator against one with the speedster stlye
scoop cleaing it up
- Compare an 80 inch 2 blade prop vs a 3 blade 68 inch using an 80 hp engine
This should keep you off the eggnog for awhile..... 
Paul
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Michel
Joined: 10 Jan 2006
Posts: 966
Location: Norway
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| Posted: Tue Dec 26, 2006 1:11 pm Post subject: Older Kitfox cruise speeds (and a new challenge for Michel's |
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Hello Paul,
On Dec 26, 2006, at 8:00 PM, Paul Seehafer wrote:
| Quote: | Thats's because Dean Wilson had already designed the wing incidence
into the Avid Flyer, which is what was used on the first Fox.
|
It looks like once again, I am the victim of my own creative authoring.
Forget about the parallel universe and even forget about the Kitfox.
Rex wrote me privately the following: Usually our ultralight aircraft
have a wing AoA of 4 degrees, and a horizontal stabiliser AoA of 2
degrees. The difference of which is 4 - 2 = 2 degrees. My question then
is: Would a wing AoA of 5 and a stab AoA of 3 (5 - 3 = 2) make a
difference in the aircraft performance? My argument being: those angles
are relative to a reference line that is somewhat arbitrary, often
going from the prop axis to the aft end of the fuselage.
| Quote: | Man, we really need to find a challenge for you with that flight
simulator/computer program you are playing with.
|
There are many PC-based flight simulators on the market, Paul. I don't
know which one is the best but I know that X-Plane, the one that I use,
is based on the "blade theory." It brakes down any craft into a series
of airfoils each with its coefficient of lift, drag and moment. However
there are serious limitations. Here are a few:
1) While you can make your own airfoil, the simulator comes with a
library of common NACA airfoils. Unfortunately, those were tested in
wind tunnels only to -20 to +20 AoA because nearly all of them will
stall at a greater angle. But in e.g. a spin, the airflow comes a
angles much greater than that, and the value of those coefficients have
to be guestimated.
2) The drag of non-airfoils, such as wheels and fuselage, is
calculated from their frontal surface and therefore the drag of e.g. a
round cowl vs. streamline cowl cannot be evaluated. To do that, you
would need what is called Computational Fluid Dynamics (CFD) which
means, a modelling of air molecules as they pass by an object. And that
can't be done on a PC in real-time. Remember that a real-time simulator
needs more than ten cycles per second for the model to respond to
input. This is also the reason why no real-time simulators can simulate
spins because when it happens, angles of incidence are so great that
some surfaces as the tail, are in the "shadow" of other surface and
only CFD can show that.
3) Available data on airfoils, engines, etc. are optimal because
"clean." In real life, an airfoil is never perfect, an engine doesn't
deliver the optimal power and a propeller has some dead bugs on its
leading edge. While I did the best I could to model the Avid wing of my
model 3, I came up with unrealistic results. I had measured my wing
above and under, at each 10 cm, gave the data to a friend who has some
of the best virtual wind tunnel, and the result was a plane that flew
too fast and stall too slow. That is because reality is never as
perfect as a virtual model.
As a final note: In 1979, I bought my first computer to help me to
design yachts. Then I attended a conference in Brighton, UK, where I
was shown how model tank testing data could be used in computers to
design full scale yachts. Testing showed that full scale vessels were
within 20% of the computed data. ... 20%? Was it worth it? While
computers have increased many tenfolds in speed and capacity, I still
wouldn't trust them too much for real-life modelling. I think few
people have worked, as I have done, to test a real plane and model it
in a simulator. Usually, real-life pilots can't be bothered to play
with those "video games." But I do, by curiosity. And if moving weight
or AoA in a simulator like X-Plane doesn't really correspond 100% to
reality, it sure gives a feeling of how the forces involved in aviation
work. For example, my X-Plane Kitfox mushes down pretty much like the
real one. I don't know any other X-Plane aircraft doing that. Probably
because designers are often more interested to show a nice livery than
a close-to-reality aerodynamic model. Eye candy is important, you know.
Just look at how much women spend on cosmetics!
Cheers,
Michel
do not archive
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_________________
Kitfox 3 - Jabiru 2200 |
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Tue Dec 26, 2006 1:44 pm Post subject: Older Kitfox cruise speeds (and a new challenge for Michel's |
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And to think, folks, he does it all on a Mac! : ) go Michel!....
Lynn
do not archive
On Dec 26, 2006, at 4:10 PM, Michel Verheughe wrote:
| Quote: |
Hello Paul,
On Dec 26, 2006, at 8:00 PM, Paul Seehafer wrote:
> Thats's because Dean Wilson had already designed the wing
> incidence into the Avid Flyer, which is what was used on the first
> Fox.
It looks like once again, I am the victim of my own creative
authoring. Forget about the parallel universe and even forget about
the Kitfox. Rex wrote me privately the following: Usually our
ultralight aircraft have a wing AoA of 4 degrees, and a horizontal
stabiliser AoA of 2 degrees. The difference of which is 4 - 2 = 2
degrees. My question then is: Would a wing AoA of 5 and a stab AoA
of 3 (5 - 3 = 2) make a difference in the aircraft performance? My
argument being: those angles are relative to a reference line that
is somewhat arbitrary, often going from the prop axis to the aft
end of the fuselage.
> Man, we really need to find a challenge for you with that flight
> simulator/computer program you are playing with.
There are many PC-based flight simulators on the market, Paul. I
don't know which one is the best but I know that X-Plane, the one
that I use, is based on the "blade theory." It brakes down any
craft into a series of airfoils each with its coefficient of lift,
drag and moment. However there are serious limitations. Here are a
few:
1) While you can make your own airfoil, the simulator comes with a
library of common NACA airfoils. Unfortunately, those were tested
in wind tunnels only to -20 to +20 AoA because nearly all of them
will stall at a greater angle. But in e.g. a spin, the airflow
comes a angles much greater than that, and the value of those
coefficients have to be guestimated.
2) The drag of non-airfoils, such as wheels and fuselage, is
calculated from their frontal surface and therefore the drag of
e.g. a round cowl vs. streamline cowl cannot be evaluated. To do
that, you would need what is called Computational Fluid Dynamics
(CFD) which means, a modelling of air molecules as they pass by an
object. And that can't be done on a PC in real-time. Remember that
a real-time simulator needs more than ten cycles per second for the
model to respond to input. This is also the reason why no real-time
simulators can simulate spins because when it happens, angles of
incidence are so great that some surfaces as the tail, are in the
"shadow" of other surface and only CFD can show that.
3) Available data on airfoils, engines, etc. are optimal because
"clean." In real life, an airfoil is never perfect, an engine
doesn't deliver the optimal power and a propeller has some dead
bugs on its leading edge. While I did the best I could to model the
Avid wing of my model 3, I came up with unrealistic results. I had
measured my wing above and under, at each 10 cm, gave the data to a
friend who has some of the best virtual wind tunnel, and the result
was a plane that flew too fast and stall too slow. That is because
reality is never as perfect as a virtual model.
As a final note: In 1979, I bought my first computer to help me to
design yachts. Then I attended a conference in Brighton, UK, where
I was shown how model tank testing data could be used in computers
to design full scale yachts. Testing showed that full scale vessels
were within 20% of the computed data. ... 20%? Was it worth it?
While computers have increased many tenfolds in speed and capacity,
I still wouldn't trust them too much for real-life modelling. I
think few people have worked, as I have done, to test a real plane
and model it in a simulator. Usually, real-life pilots can't be
bothered to play with those "video games." But I do, by curiosity.
And if moving weight or AoA in a simulator like X-Plane doesn't
really correspond 100% to reality, it sure gives a feeling of how
the forces involved in aviation work. For example, my X-Plane
Kitfox mushes down pretty much like the real one. I don't know any
other X-Plane aircraft doing that. Probably because designers are
often more interested to show a nice livery than a close-to-reality
aerodynamic model. Eye candy is important, you know. Just look at
how much women spend on cosmetics!
Cheers,
Michel
do not archive
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http://www.matronics.com/Navigator?Kitfox-List |
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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smokey_bear_40220(at)yaho
Guest
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| Posted: Tue Dec 26, 2006 3:53 pm Post subject: Older Kitfox cruise speeds (and a new challenge for Michel's |
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Michel,
Since we are off dreaming....
When aircraft are designed, they are usually initially
layed out to be most efficient at a given cruise speed
and weight. That means all parts are meant to be at
their best when at that speed. The fuselage is
aligned to the wind for least drag. The wing is then
either given a zero incidence with an airfoil that
will give 1 G lift at that speed, or placed at an
incidence that gives 1 G lift, if the wing is designed
to other special needs, like STOL flight.
The tail is then set to give stability and counter the
pitching moment of the wing. It must then be modified
to account for landing and takeoff requirements.
| Quote: | From this point, the design is modified to achieve the
other goals of the design. Say a wider cruise range,
|
slower takeoff and landing speeds, more useful loads,
etc. Flaps are added to help with the bottom end
speeds. Incidence or wing span may be changed to help
too, compromising top speeds. Everything is adjusted
away from perfect at one speed, to acceptable for all
design goals. And the tail must be modified to deal
with it.
Sounds like prop design problems too....
When we start with a KF I and then grow it to much
greater weights and faster cruise speeds, the
origional design no longer fits so well. The faster
speed will necesitate the fuselage and wing being
pitched nose down below the best drag profile. The
greater weights mean higher stall speeds and longer
T/O and landing distances. Simply changing the
airfoil can give a new compromise in performance, but
eventually nothing fits efficiently.
Making major changes means new tooling and new parts
that don't fit the earlier series. Bigger inventory.
My guess is that the I-III Fox's were similar, but had
to be modified to the IV's weight and speeds. Then
the -5 and on needed major changes to deal with a
larger aircraft, more weight and even higher speeds.
But we builders don't leave it alone as designed.
Different engines, the quest for more speed, etc make
us fly outside of the angles that the planes parts
were origionally set for. (Not to mention a little
over weight?)
So there we are with the nose tucked down because the
high lift wing is flying faster than its origional AOA
and incidence were designed for. The fuselage is more
draggy to lower the wing's AOA at the designed
incidence. The wing uses the wrong airfoil for that
speed, so it is more draggy too. The tail has to trim
to a draggier profile to accomidate the fuselage
angle, weight changes, higher speeds, etc.
Or we could reflex the flapperons up and take some
lift off the wing.... That changes the pitching
moment though (tail), but may align the fuselage and
wing to a less draggy profile. Quick fix?
Or change the wing and tail incidence? Now that needs
complete testing for stall and spin characteristics
too. And what did we do to the CG envelope?
I think we are beyond X-Plane for giving the answers
to these questions as you said Michel. And changing
wing incidence on our own means some good testing
needs to be done.
What we can do is move the battery to give a little
better CG taking the load off or adding it on to the
tail to avoid trim drag there, or reflex the
flapperons to increase the cruise without modifying
parts.
Since the lower flapperon deflections can lead to
trouble anyway, maybe setting full up handle
deflection to the most allowable flapperon down angle,
then testing the plane for best reflex angle, handle
down, might be a useful way to find some more speed
for the I-III series?
Just some thoughts...
Kurt S. S-5
--- Michel Verheughe <michel(at)online.no> wrote:
| Quote: | Hello Paul,
On Dec 26, 2006, at 8:00 PM, Paul Seehafer wrote:
> Thats's because Dean Wilson had already designed
the wing incidence
> into the Avid Flyer, which is what was used on the
first Fox.
It looks like once again, I am the victim of my own
creative authoring.
Forget about the parallel universe and even forget
about the Kitfox.
Rex wrote me privately the following: Usually our
ultralight aircraft
have a wing AoA of 4 degrees, and a horizontal
stabiliser AoA of 2
degrees. The difference of which is 4 - 2 = 2
degrees. My question then
is: Would a wing AoA of 5 and a stab AoA of 3 (5 - 3
= 2) make a
difference in the aircraft performance?
|
__________________________________________________
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Dec 26, 2006 4:56 pm Post subject: Older Kitfox cruise speeds (and a new challenge for Michel's |
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When I was training I used the MS Flight Sim to practice procedures and to
navigate within a hundred miles of the flight school. Practice a procedure
( forced approach or diversion ) on the Flight Sim in the night and it made
doing it in the real world a lot easier. The only thing I found harder in
the real world was the smooth landing. I had to train myself not to fixate
on the ASI after turning on final.
Mind you the virtual world is only similar in geography to the real world
but that just adds interest.
I also have a couple of kitfoxes which I adjusted to fly more like the real
thing. I don't know if they will fly on your X-Plane. Do you have a 'Fox
on floats that may work on the MSFS??
Noel
[quote] --
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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