KR> Useful Load

[Tony King]

Another thing to keep in mind in relation to meeting the LSA performance
criteria is who, besides you, is going to know for sure what the stall
speed (or any other parameter) really is.  If you say the stall speed is 51
mph, as long as that's plausible who's going to even give it a second
thought?  The regulator's certainly not going to get in the plane and
verify it.

I'm not suggesting you falsify your test data or anythig like that, but
aviation is full of optimistic numbers, and the difference between 51 mph
and 55 mph could well be within the margin of error of your instruments in
any case.  ASIs tend to get inaccurate at low speed and high AoA.

Cheers,

Tony

On 30 November 2016 at 00:31, Kayak Chris via KRnet 
wrote:

> thanks, I agree with mark not to misuse our precious time!
>
> my question is related to that I simply may want my bird (KR1) to be
> light sport compliant. 51mph does it, 55 doesnt. but I plan mine to be
> simple and light, so I guess it should be fine.
>
>
>

KR> Useful Load

[Kayak Chris]

thanks, I agree with mark not to misuse our precious time!

my question is related to that I simply may want my bird (KR1) to be
light sport compliant. 51mph does it, 55 doesnt. but I plan mine to be
simple and light, so I guess it should be fine.


>
> There are plenty of KRs flying. The stall speeds are pretty close to the
> published data. Keep it light and it will stall at 50-55 mph.
>

KR> Useful Load

[Rob Schmitt]

Chris,

Concur with Mark.

I don't think there is going to be any value in doing the calculation. As I
recall from my engineering courses on aerodynamics, the equations are just
predictors - you must test the airfoil to get the results. It is a circular
loop; calc - test - revise your original data to conform to results, do all
over again. That is why wing tunnel testing is still required. 

There are plenty of KRs flying. The stall speeds are pretty close to the
published data. Keep it light and it will stall at 50-55 mph. 

Thanks,

Rob Schmitt
N1852Z
Kansas City, MO

-Original Message-
From: KRnet [mailto:krnet-bounces at list.krnet.org] On Behalf Of Mark Langford
via KRnet
Sent: Tuesday, November 29, 2016 6:51 AM
To: KRnet 
Cc: ml at n56ml.com
Subject: Re: KR> Useful Load

Kayak Chris wrote:

> Can i assume that no one has used the formula to determine stall 
> speed? Not sure how to with the RAF48, no idea what the Coefficiant of 
> Lift is, although the "new" airfoil probably has it someplace, or what 
> to input with the density of air number. Anyone care to take a stab at 
> it with the KR1 or 2?

See the diagram next to the bottom of http://www.n56ml.com/kraf48.html for
the max lift coefficient, which is the Eppler code diagram, and was done
fairly recently, calculated from the coordinates of the RAF48.  I don't
claim to be an aerodynamicist,  but I would choose use the solid Re
(Reynolds number) line (1x106) curve to be conservative (based on 50 mph
stall at 15 degrees AOA, standard air density, and 42" average wing chord
(anal extraction).  This gives a ~Re of 1.7M or so (and the solid plotted
line represents 1.0M).  

I'd work the details and give all my assumptions, but as soon as I do, some
real aero engineer will pick it apart to make me look stupid, so I'll let
him make the assumptions and provide results, and take the glory.  I did
this calc 20 years ago, and the units were the PITA, but using an online
converter, it makes it easy.  If nobody's done it by this weekend, I'll do
it again.  I haven't volunteered because I've
(almost) learned to quit volunteering to do stuff that other people can
do...I couldn't get everything done that I plan to do before I die, even if
I lived another 50 years!  [I'm getting selfish with my time].

The table at the very bottom of the page is for the RAF40, which is
something like 1.33 at 16 degree AOA "un-flapped", which is what almost all
of the KRs are.  And the KRs that have flaps are not full span, for sure.
It's provided as it probably came from real wind tunnel data, but was likely
generated in the 1930's or 40's, although the thinner chord would likely
have a little less lift anyway.

Density of air is "standard air density", which you are probably familiar
with, standard pressure and temperature.  Either find a density that's in
the proper units, or put conversion factors in the equation.

I'm supposed to be working right now...

Mark Langford, Harvest, AL
ML "at" N56ML.com
www.N56ML.com



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KR> Useful Load

[Kayak Chris]

Hi I posted this a while back,

Can i assume that no one has used the formula to determine stall
speed? Not sure how to with the RAF48, no idea what the Coefficiant of
Lift is, although the "new" airfoil probably has it someplace, or what
to input with the density of air number. Anyone care to take a stab at
it with the KR1 or 2?


>
> https://www.quora.com/How-do-you-calculate-the-stall-speed-of-an-aircraft
>
>
> Now from an engineering Point of View
> The stall speed of an aircraft is dependent on four parameters,
>
> Air Density
> Wing Area
> Coefficient of Lift
> Weight of the Aircraft
>
>
> The exact formula is
> V = ?( 2 W g / ? S Clmax )
>
> Where,
> V = Stall Speed
> W = Weight of the aircraft
> g = 9.81 (Acc. Due to Gravity)
> ? = Density of Air
> S = Wing Area
> Clmax = Coefficient of Lift at Stall

KR> Useful Load

[ml at n56ml.com]

Kayak Chris wrote:

> Can i assume that no one has used the formula to determine stall
> speed? Not sure how to with the RAF48, no idea what the Coefficiant of
> Lift is, although the "new" airfoil probably has it someplace, or what
> to input with the density of air number. Anyone care to take a stab at
> it with the KR1 or 2?

See the diagram next to the bottom of http://www.n56ml.com/kraf48.html
for the max lift coefficient, which is the Eppler code diagram, and was
done fairly recently, calculated from the coordinates of the RAF48.  I
don't claim to be an aerodynamicist,  but I would choose use the solid
Re (Reynolds number) line (1x106) curve to be conservative (based on 50
mph stall at 15 degrees AOA, standard air density, and 42" average wing
chord (anal extraction).  This gives a ~Re of 1.7M or so (and the solid
plotted line represents 1.0M).  

I'd work the details and give all my assumptions, but as soon as I do,
some real aero engineer will pick it apart to make me look stupid, so
I'll let him make the assumptions and provide results, and take the
glory.  I did this calc 20 years ago, and the units were the PITA, but
using an online converter, it makes it easy.  If nobody's done it by
this weekend, I'll do it again.  I haven't volunteered because I've
(almost) learned to quit volunteering to do stuff that other people can
do...I couldn't get everything done that I plan to do before I die, even
if I lived another 50 years!  [I'm getting selfish with my time].

The table at the very bottom of the page is for the RAF40, which is
something like 1.33 at 16 degree AOA "un-flapped", which is what almost
all of the KRs are.  And the KRs that have flaps are not full span, for
sure.  It's provided as it probably came from real wind tunnel data, but
was likely generated in the 1930's or 40's, although the thinner chord
would likely have a little less lift anyway.

Density of air is "standard air density", which you are probably
familiar with, standard pressure and temperature.  Either find a density
that's in the proper units, or put conversion factors in the equation.

I'm supposed to be working right now...

Mark Langford, Harvest, AL
ML "at" N56ML.com
www.N56ML.com

KR> Useful Load

[Kayak Chris]

I went you these links and understand a bit better but I dont have the
Clmax curve for the RAF48 or the "new" wing (at least the latter must
be around someplace). BTW I have never heard of this being discussed
to consider an aircraft for LSA compliant, has anyone else? Anyway not
sure what to use for air density. But its four numbers into the
formula and two are easy (aircraft weight and wing area). I would like
to practice this with a KR1 or KR2 built to plans then I can adjust
things like gross weight and wing area to bring it within the envelope
if necessary.

What is Clmax and how to put a number to air density at sea level
standard day? (I am NOT that good at math)




https://www.quora.com/How-do-you-calculate-the-stall-speed-of-an-aircraft


Now from an engineering Point of View
The stall speed of an aircraft is dependent on four parameters,

Air Density
Wing Area
Coefficient of Lift
Weight of the Aircraft


The exact formula is
V = ?( 2 W g / ? S Clmax )

Where,
V = Stall Speed
W = Weight of the aircraft
g = 9.81 (Acc. Due to Gravity)
? = Density of Air
S = Wing Area
Clmax = Coefficient of Lift at Stall

KR> Useful Load

[Larry Flesner]

At 08:38 AM 11/20/2016, you wrote:
>  "Kayak Chris" wrote:
>
> > What does "utility category" mean?
>
>Google for "utility category aircraft", and
>https://en.wikipedia.org/wiki/Load_factor_(aeronautics) is at the 
>top. Utility means 4G load factor, and Normal means 6G.



For example, the US 
Federal 
Aviation Regulations prescribe the following limits (for the most 
restrictive case):
* For transport 
category airplanes, from -1 to +2.5 (or up to +3.8 depending on 
design takeoff 
weight)[9]
 

* For normal category and commuter category airplanes, from -1.52 
to 
+3.8[10]
 

* For utility category airplanes, from -1.76 to 
+4.4[10]
 

* For acrobatic category airplanes, from -3.0 to 
+6.0[10]
 


The KR plans state that the design load factor is +or- 7G's at 800 
pounds.  7x800=5600 pounds.  If you fly the KR at 1200 pound gross 
you have a "design" structure of +or-4.6 G's.  I say "designed" as in 
assuming it is built properly. I licensed mine at 1350 pounds 
gross.  While the structure is quite strong remember that even slight 
increases in weight have a substantial effect on performance.  More 
weight necessitates more horsepower which comes with more weight 
which necessitates more horsepower which comes with more weight, and 
on and on and on.

Larry Flesner  

KR> Useful Load

[Mark Langford]

I should have included this one too:

http://www.experimentalaircraft.info/flight-planning/aircraft-stall-speed-1.php

Mark Langford
ML at N56ML.com
http://www.n56ml.com

KR> Useful Load

[Mark Langford]

  "Kayak Chris" wrote:

 > What does "utility category" mean?

Google for "utility category aircraft", and
https://en.wikipedia.org/wiki/Load_factor_(aeronautics) is at the top. 
Utility means 4G load factor, and Normal means 6G.

 > Where is this formula, not sure what to look for (I tried)

I googled "aircraft stall speed equation example", and the one at the top is
https://www.quora.com/How-do-you-calculate-the-stall-speed-of-an-aircraft
and the third one on the list is
https://www.rcgroups.com/forums/showthread.php?t=789635

For the lift coefficient of the "new" airfoil (Cl), see the wing lift 
polar diagram at http://www.krnet.org/as504x/design.html , which shows 
it to be about 1.55 at stall angle of attack.

Mark Langford
ML at N56ML.com
http://www.n56ml.com

KR> Useful Load

[Kayak Chris]

"You could also build it by the plans and consider it "utility category"."

What does that mean?



> If you wanted to make it "Light Sport" compatible, you could add several
> inches to the wing length to get the gross weight to wing area ratio to fit
> that category.

I did not know there was such a formula, I thought since every plane
comes out different, if tested to stall at LSA speed, you're good.
Where is this formula, not sure what to look for (I tried)

KR> Useful Load

[John Lange]

Sorry, we are looking at a KR2 that is partially built.  Has fuselage, tail
and stabilizer built, no start on the wings yet.

On Sat, Nov 19, 2016 at 11:06 AM, Mark Langford via KRnet <
krnet at list.krnet.org> wrote:

> John Lange wrote:
>
> > Is there a way to increase the useful load by 50 pounds?
>
> Is this question about an airplane being built, or already finished and
> registered?  KR2 or KR2S?
>
> Mark Langford
> ML at N56ML.com
> http://www.n56ml.com
>
>
>
> ___
> Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search.
> Please see LIST RULES and KRnet info at http://www.krnet.org/info.html.
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> options
> To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org
>

KR> Useful Load

[Mark Langford]

John Lange wrote:

>>> Is there a way to increase the useful load by 50 pounds?
> Sorry, we are looking at a KR2 that is partially built.  Has
> fuselage, tail and stabilizer built, no start on the wings yet.

Lots of folks have built KRs and simply placarded them at 1100 pounds or 
more.  There's evidence that the spars and the rest of the plane can 
handle that easily.  It's up to you, as the builder, to declare the 
gross weight when you get it inspected and fill out the airworthiness 
paperwork. You could also build it by the plans and consider it "utility 
category".

If you wanted to make it "Light Sport" compatible, you could add several 
inches to the wing length to get the gross weight to wing area ratio to 
fit that category.  We only miss the stall speed by one or two knots. 
If you add 50 pounds to the gross weight, it might be a foot added to 
each wing.  Check the web for the equation, which involves lift 
coefficient of the wing, air density, gross weight, and wing area.

Plenty of ways around this problem, but don't fall into the trap of 
"beefing" anything up.  This plane doesn't need it, unless you hang a 
very heavy engine off the firewall, and even then, the reinforcements 
required are minimal.

Mark Langford
ML at N56ML.com
http://www.n56ml.com

KR> Useful Load

[John Lange]

Is there a way to increase the useful load by 50 pounds?  My wife and I
would fit, but we could not carry any fuel or baggage. lol

JOhn ><>

KR> Useful Load

[Mark Langford]

John Lange wrote:

 > Is there a way to increase the useful load by 50 pounds?

Is this question about an airplane being built, or already finished and 
registered?  KR2 or KR2S?

Mark Langford
ML at N56ML.com
http://www.n56ml.com