A Bush C150? With Leading Edge Slats?

Kevin,

There must be some typo in your formular. I looked up my book (Design
for Fly) and is something like:

V=16.2*sqrt(WL/Cl)

The book also states that the Cl for a Fowler flap could be 2.8
compared with 1.4 of no flap. So if I take your number of +1.0 for the
LES(leading edge slats), I think a Cl of 3.0 seems reasonable with
some flap.

Also remember my gross is reduced by almost 20% (not considering the
increase due to the additional slats because I don't how much more
weight) and the increase of the wing area by about 10%. For stock
C150, the wing loading is almost exactly 10 and V stall clean is
47kts. This will give a Cl of only about 1.2. Oh well. Anyway if we
use Cl=3 and wing loading of 7 let's see what we get:

V=16.2*sqrt(7/3)= 24.7 kts

Wow. Geez! I'm sure at 30mph the formula might break (or Cl will
change) but anyway, I still think 40mph is not that unreachable.

Jizhong

On Sun, 23 May 2004 16:58:25 GMT, Kevin Horton wrote:

On Sat, 22 May 2004 21:04:20 -0700, jizhonghe wrote:

Great. Thanks for the clarificaiton. I always thought they just give you a
low number. Now I know at least they are honest albeit misleading. So I
looked up the C152 POH and the CAS stall clean is actually 47kts (54mph).
I should re-adjust my goal. I think a CAS of 40mph should be quite
respectable for a little bush plane. And the square of (54/40)^2=1.83 with
the light weight should be able to reduce the T/O run by half.


The stall speed basically depends on the wing loading and the maximum
coefficient of lift that is achieved.

The stall speed in equivalent airspeed (which can be considered to be the
same as calibrated airspeed for low speed and low altitude) is:

VS = 0.8379 * sqrt(wing loading/CLmax)

VS is in knots,
Wing loading is in lb/sq. ft

I don't have data for the C150 at hand, but looking at the C182Q POH for
an example, I get wing loading of 2950/174 = 16.95 lb/sq ft. The forward
CG stall speed at 2950 lb is 54 kt CAS. This requires a CLmax of 1.72,
which is about what I would expect for a flapped wing with no leading edge
devices.

Several references indicate a well designed slat might give about an extra
1.0 CLmax, so you might be able to get the C182 CLmax to about 2.7. This
would give a stall speed of about 43 kt CAS, or about 80% of the original
value. You think you can get the C150 stall speed from 54 mph to 40 mph,
which would be a reduction to 74% of the original value. This seems
unlikely from just adding slats. You would need to also make a big
improvement to the flaps. These mods add weight, and they would require a
lot of knowledge of aerodynamics and structural engineering to actually
achieve the predicted performance, and to have a strong structure.

References:

Fluid Dynamic Lift, Hoerner
Theory of Wing Sections, Abbott and Doenhoff

Good luck.

I know I might get rediculous drag:

the induced drag C_Di = C_L^2/(Pi*AR)

On Sun, 23 May 2004 10:51:27 -0700, wrote:


Kevin,

There must be some typo in your formular. I looked up my book (Design
for Fly) and is something like:

V=16.2*sqrt(WL/Cl)

The book also states that the Cl for a Fowler flap could be 2.8
compared with 1.4 of no flap. So if I take your number of +1.0 for the
LES(leading edge slats), I think a Cl of 3.0 seems reasonable with
some flap.

Also remember my gross is reduced by almost 20% (not considering the
increase due to the additional slats because I don't how much more
weight) and the increase of the wing area by about 10%. For stock
C150, the wing loading is almost exactly 10 and V stall clean is
47kts. This will give a Cl of only about 1.2. Oh well. Anyway if we
use Cl=3 and wing loading of 7 let's see what we get:

V=16.2*sqrt(7/3)= 24.7 kts

Wow. Geez! I'm sure at 30mph the formula might break (or Cl will
change) but anyway, I still think 40mph is not that unreachable.

Jizhong

On Sun, 23 May 2004 16:58:25 GMT, Kevin Horton wrote:

On Sat, 22 May 2004 21:04:20 -0700, jizhonghe wrote:

Great. Thanks for the clarificaiton. I always thought they just give you a
low number. Now I know at least they are honest albeit misleading. So I
looked up the C152 POH and the CAS stall clean is actually 47kts (54mph).
I should re-adjust my goal. I think a CAS of 40mph should be quite
respectable for a little bush plane. And the square of (54/40)^2=1.83 with
the light weight should be able to reduce the T/O run by half.


The stall speed basically depends on the wing loading and the maximum
coefficient of lift that is achieved.

The stall speed in equivalent airspeed (which can be considered to be the
same as calibrated airspeed for low speed and low altitude) is:

VS = 0.8379 * sqrt(wing loading/CLmax)

VS is in knots,
Wing loading is in lb/sq. ft

I don't have data for the C150 at hand, but looking at the C182Q POH for
an example, I get wing loading of 2950/174 = 16.95 lb/sq ft. The forward
CG stall speed at 2950 lb is 54 kt CAS. This requires a CLmax of 1.72,
which is about what I would expect for a flapped wing with no leading edge
devices.

Several references indicate a well designed slat might give about an extra
1.0 CLmax, so you might be able to get the C182 CLmax to about 2.7. This
would give a stall speed of about 43 kt CAS, or about 80% of the original
value. You think you can get the C150 stall speed from 54 mph to 40 mph,
which would be a reduction to 74% of the original value. This seems
unlikely from just adding slats. You would need to also make a big
improvement to the flaps. These mods add weight, and they would require a
lot of knowledge of aerodynamics and structural engineering to actually
achieve the predicted performance, and to have a strong structure.

References:

Fluid Dynamic Lift, Hoerner
Theory of Wing Sections, Abbott and Doenhoff

Good luck.

On Sun, 23 May 2004 11:51:27 -0700, jizhonghe wrote:


Kevin,

There must be some typo in your formular. I looked up my book (Design for
Fly) and is something like:

V=16.2*sqrt(WL/Cl)

Whoops, I accidentally left the sea level density out of that conversion
factor. Once I move the sea level density inside the conversion factor, I
get:

VS = 17.18*sqrt(WL/CLmax)

Thanks for pointing that out.

Are you sure your book says 16.2 and not 17.2? Otherwise I'm not sure
where the difference is.


The book also states that the Cl for a Fowler flap could be 2.8 compared
with 1.4 of no flap. So if I take your number of +1.0 for the LES(leading
edge slats), I think a Cl of 3.0 seems reasonable with some flap.

A Clmax of 3 is achievable with complex, multi-sloted flaps and slats.
But you likely won't achieve such a CL unless you have the means to do
lots of wind tunnel and/or development flight te$ting.

See:

http://adg.stanford.edu/aa241/highli...liftintro.html


Also remember my gross is reduced by almost 20% (not considering the
increase due to the additional slats because I don't how much more
weight) and the increase of the wing area by about 10%.

A basic C150 doesn't have very much useful load at the stock gross weight.
What useful load do you require for your mission? Exactly how do you
plan to reduce the empty weight, while increasing wing area and adding
slats and complex multi-slotted flaps?

For stock C150,
the wing loading is almost exactly 10 and V stall clean is 47kts. This
will give a Cl of only about 1.2. Oh well. Anyway if we use Cl=3 and
wing loading of 7 let's see what we get:

V=16.2*sqrt(7/3)= 24.7 kts

Wow. Geez! I'm sure at 30mph the formula might break (or Cl will change)
but anyway, I still think 40mph is not that unreachable.

Let me know when you've got some credible flight test results, showing
calibrated airspeeds at the stall of 40 mph at a useful gross weight.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

A C150 isn't much of an airplane. We used to joke that we used ours
for taxi trainers. On hot days at our 3000' airport elevation there
were times that they wouldn't climb past 4000' when at gross. They're
a draggy design; the earlier straightbacked models were lighter,
faster and probably climbed better, too.
If you look at the 150's wing and then at a Super Cub's or some
other STOL airplane's you will see a big difference in camber and
leading edge treatment, both of which have a lot to do with low-speed
performance. I once flew a Super Cub that had vortex generators
installed on the wing, and it would approach at 30 knots. You'd never
get a 150 anywhere near numbers like that, even if you got slats to
work. The whole airplane needs to be purpose-designed, and the 150 was
designed to be a simple, strong, cheap airplane for training pilots,
not for flying into tiny unimproved strips.
I also have a few hours in a 90-hp Alon Aircoupe, the last
iteration of the venerable Ercoupe. It had factory rudder pedals in it
and a slide-back canopy, but the rest of the airplane was pretty much
the old design. It grossed 150 lbs less that the C150. Those 90 horses
outpulled the O-200's 100 hp by a wide margin; the airplane took off
shorter, climbed much better and cruised 20 mph faster than the 150.
It led me to believe that the O-200 is a bit over-rated, or that the
150 is a lousy design, or both. At any rate, we no longer run 150s in
our school.

Dan

We probably did the same thing by converting the air density etc. I
could be wrong because I used 5600 ft/mile, and I did not re-check
etc. So I'll say your number is correct.

I was hoping for a 450 useful. The stock empty is 950#. Someone
mentioned that tail wheel conv. will save some weight (but I doubt if
he really knows). And avionics and gyro will also go. So I said 900
empty as a ball park number. At 1350#, that's about 20% less.

Right now it's all hanger flying. No need for wind tunnel data.

Jizhong
On Sun, 23 May 2004 18:18:19 GMT, Kevin Horton wrote:

On Sun, 23 May 2004 11:51:27 -0700, jizhonghe wrote:


Kevin,

There must be some typo in your formular. I looked up my book (Design for
Fly) and is something like:

V=16.2*sqrt(WL/Cl)

Whoops, I accidentally left the sea level density out of that conversion
factor. Once I move the sea level density inside the conversion factor, I
get:

VS = 17.18*sqrt(WL/CLmax)

Thanks for pointing that out.

Are you sure your book says 16.2 and not 17.2? Otherwise I'm not sure
where the difference is.


The book also states that the Cl for a Fowler flap could be 2.8 compared
with 1.4 of no flap. So if I take your number of +1.0 for the LES(leading
edge slats), I think a Cl of 3.0 seems reasonable with some flap.

A Clmax of 3 is achievable with complex, multi-sloted flaps and slats.
But you likely won't achieve such a CL unless you have the means to do
lots of wind tunnel and/or development flight te$ting.

See:

http://adg.stanford.edu/aa241/highli...liftintro.html


Also remember my gross is reduced by almost 20% (not considering the
increase due to the additional slats because I don't how much more
weight) and the increase of the wing area by about 10%.

A basic C150 doesn't have very much useful load at the stock gross weight.
What useful load do you require for your mission? Exactly how do you
plan to reduce the empty weight, while increasing wing area and adding
slats and complex multi-slotted flaps?

For stock C150,
the wing loading is almost exactly 10 and V stall clean is 47kts. This
will give a Cl of only about 1.2. Oh well. Anyway if we use Cl=3 and
wing loading of 7 let's see what we get:

V=16.2*sqrt(7/3)= 24.7 kts

Wow. Geez! I'm sure at 30mph the formula might break (or Cl will change)
but anyway, I still think 40mph is not that unreachable.

Let me know when you've got some credible flight test results, showing
calibrated airspeeds at the stall of 40 mph at a useful gross weight.