A Bush C150? With Leading Edge Slats?

Hello, I have a long term goal of making a small bush plane: 450lbs
useful load, 35mph clean stall, 600 ft clear 50ft. I know there are
quite a few designs out there, PA-11 Cub, Bushcaddy, Zenith CH701 to
name a few that I'm kind of familiar. But here, I'm looking into the
possiblity of working it out on a c150.

First of all, I want to say that this C150 will have a much lower
gross when used for bush flying, I know it'll be 1400# with no mods
but I like to see if I could push it down to 1300#. And now I want to
tackle on one aspect this time, how to improve the wings to
significantly reduce the stall speed.

First a question, anyone knows how far away the C150 wings is from an
ideal high lift design, i.e., if you would design it again (keep the
area and weigh the same and also conventional shape etc) how much can
you lower the stall speed?

I'm guessing for a certain design the stall speed is proportional to
the square root of the wingloading. The stock C150 is 10lb/ft^2 and
stalls at 48mph, while, for example, it is 8.9 and 30mph for the
Bushcaddy R120. So if I trust the number, the wings for the Bushcaddy
must be way more more efficient than that of the C150. What's the deal
here?

Now the CH701 is interesting that it has a leading edge slats. I'm
wondering how much improvement you can make if you put one set on the
C150 wings? As far as I know, there is noboby working on that. (I'm
aware of the Dakota slotted wing for the Cubs.) But it does not look
like too difficult. Any slats expert here?

Oh, let's not worry about the FAA part for now.

Thanks,

Jizhong

On Sat, 22 May 2004 19:38:56 -0700, jizhonghe wrote:

I'm guessing for a certain design the stall speed is proportional to the
square root of the wingloading. The stock C150 is 10lb/ft^2 and stalls at
48mph, while, for example, it is 8.9 and 30mph for the Bushcaddy R120. So
if I trust the number, the wings for the Bushcaddy must be way more more
efficient than that of the C150. What's the deal here?

The airspeed of interest for this calculation is equivalent airspeed,
although that is almost exactly the same as calibrated airspeed at low
speeds and altitudes. But the BushCaddy stall speeds are almost certainly
indicated airspeeds, as kit aircraft companies rarely have the resources
to determine the airspeed position error. Indicated stall speeds are
almost always lower than calibrated stall speeds, so they like to quote
the lower number.

Bottomline - the BushCaddy might very well have an indicated stall speed
near 30 mph (there web site claims 32 mph, but it isn't clear whether this
is power off or power on), but the calibrated stall speed would almost
certainly be higher than that.

For example, the C182Q POH that I am looking at shows a full flap, power
off stall speeds of 38 kt IAS which equals 50 kt CAS. With flaps up, the
error is even larger - 41 kt IAS = 56 kt CAS.

Don't pay too much attention to quoted stall speeds unless you have
proof that they are calibrated airspeeds.

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

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.

Anyone know what's the calibrated clean stall for a PA-11 Cub?

Jizhong
On Sun, 23 May 2004 02:01:56 GMT, Kevin Horton wrote:

On Sat, 22 May 2004 19:38:56 -0700, jizhonghe wrote:

I'm guessing for a certain design the stall speed is proportional to the
square root of the wingloading. The stock C150 is 10lb/ft^2 and stalls at
48mph, while, for example, it is 8.9 and 30mph for the Bushcaddy R120. So
if I trust the number, the wings for the Bushcaddy must be way more more
efficient than that of the C150. What's the deal here?

The airspeed of interest for this calculation is equivalent airspeed,
although that is almost exactly the same as calibrated airspeed at low
speeds and altitudes. But the BushCaddy stall speeds are almost certainly
indicated airspeeds, as kit aircraft companies rarely have the resources
to determine the airspeed position error. Indicated stall speeds are
almost always lower than calibrated stall speeds, so they like to quote
the lower number.

Bottomline - the BushCaddy might very well have an indicated stall speed
near 30 mph (there web site claims 32 mph, but it isn't clear whether this
is power off or power on), but the calibrated stall speed would almost
certainly be higher than that.

For example, the C182Q POH that I am looking at shows a full flap, power
off stall speeds of 38 kt IAS which equals 50 kt CAS. With flaps up, the
error is even larger - 41 kt IAS = 56 kt CAS.

Don't pay too much attention to quoted stall speeds unless you have
proof that they are calibrated airspeeds.

Go and get a "Texas Taildragger" C 150 conversion. Maybe even an aerobatic
one.....

You don't really want a C150 nosewheel to hit a rabbit hole.....

Hope this helps,
Peter

Oh yes that's for sure (and big fat tires). Like I said, for now, I
just want to focus on the wing. Do you know if I'm going to save some
weight with the conversion?

Jizhong
On Sun, 23 May 2004 13:45:19 +1000, "Bushy"
wrote:

Go and get a "Texas Taildragger" C 150 conversion. Maybe even an aerobatic
one.....

You don't really want a C150 nosewheel to hit a rabbit hole.....

Hope this helps,
Peter

wrote:

Oh yes that's for sure (and big fat tires). Like I said, for now, I
just want to focus on the wing. Do you know if I'm going to save some
weight with the conversion?

Jizhong

A better starting question might be "do you know what you are doing"?

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.

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