A Bush C150? With Leading Edge Slats?

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"?

"Richard Lamb" wrote in message
...
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"?

I didn't want to ask that first, but now that you did....

Conventional wisdom says that adding any extra systems, such as slats, will
not save any weight, but rather, add weight. You were talking about taking
away some substantial weight, right? Where is that coming from?

Doubtful that the airfoil would be the right one to take full advantage of
slats, either. It is also likely even more weight would have to be added to
the wing structure to handle the extra lift, if you got the slats to work.

You dismissed the getting around the FAA, like it was of little consequence.
It is not, and might be the greatest hurdle to jump.

Things that make you go "hummm."
--
Jim in NC


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On Sun, 23 May 2004 11:21:43 -0400, "Morgans"
wrote:

:
:"Richard Lamb" wrote in message
...
: 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"?
:
:I didn't want to ask that first, but now that you did....
:
:Conventional wisdom says that adding any extra systems, such as slats, will
:not save any weight, but rather, add weight. You were talking about taking
:away some substantial weight, right? Where is that coming from?

Yep.
:
oubtful that the airfoil would be the right one to take full advantage of
:slats, either. It is also likely even more weight would have to be added to
:the wing structure to handle the extra lift, if you got the slats to work.
:
:You dismissed the getting around the FAA, like it was of little consequence.
:It is not, and might be the greatest hurdle to jump.

If he's not doing it in the US, FAA would be of no consequence.
Though in most areas, the local authority makes dealing with FAA look
like a walk in the park.

I'd think it'd be better to look at STOL wing tips and vortex
generators. Or look at one of these http://tinyurl.com/37tws

On Sun, 23 May 2004 08:42:50 -0700, Richard Riley
wrote:

On Sun, 23 May 2004 11:21:43 -0400, "Morgans"
wrote:

:
:"Richard Lamb" wrote in message
...
: 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"?
:
:I didn't want to ask that first, but now that you did....
:
:Conventional wisdom says that adding any extra systems, such as slats, will
:not save any weight, but rather, add weight. You were talking about taking
:away some substantial weight, right? Where is that coming from?

Yep.
:
oubtful that the airfoil would be the right one to take full advantage of
:slats, either. It is also likely even more weight would have to be added to
:the wing structure to handle the extra lift, if you got the slats to work.
:
:You dismissed the getting around the FAA, like it was of little consequence.
:It is not, and might be the greatest hurdle to jump.

If he's not doing it in the US, FAA would be of no consequence.
Though in most areas, the local authority makes dealing with FAA look
like a walk in the park.


Yes, the "doing" will definitely not be in the US. By the way, I
thought I'm in the R.A.H. Where is the "spirit"?

I'd think it'd be better to look at STOL wing tips and vortex
generators. Or look at one of these http://tinyurl.com/37tws

I'm really asking about the possibility of a slats'd wing. I guess
nobody is working on that. But really nobody else interested in a bush
150?

On Sun, 23 May 2004 11:21:43 -0400, "Morgans"
wrote:


"Richard Lamb" wrote in message
...
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"?

I didn't want to ask that first, but now that you did....

Conventional wisdom says that adding any extra systems, such as slats, will
not save any weight, but rather, add weight. You were talking about taking
away some substantial weight, right? Where is that coming from?


I was asking what the tailwheel conversion would do to the weight.
This has been done a lot and I think someone here might know.

Doubtful that the airfoil would be the right one to take full advantage of
slats, either. It is also likely even more weight would have to be added to
the wing structure to handle the extra lift, if you got the slats to work.

You dismissed the getting around the FAA, like it was of little consequence.
It is not, and might be the greatest hurdle to jump.

Things that make you go "hummm."

On Sun, 23 May 2004 15:07:11 GMT, Richard Lamb
wrote:

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"?

I know what I'm asking. It's a difference between starting doing
something and discussing something.

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.