LSA specs

"Kyle Boatright" wrote in message
. ..

"ET" wrote in message
...
wrote in
ups.com:

snip

Which part of my post that indicated the fuselage of the Sonex is a
lifting body confused you??? Steve Wittman is said to have won a bet or
two with the same issue on the Tailwind. I have not done it, but plug
the same numbers in for the Tailwind and see what pops out.

--
-- ET :-)

"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

Can you find a credible test of the Tailwind's stall speed on the web?
I've
looked for one, but without success. The CAFE report in the "members"
section of the EAA site doesn't show the stall speed, although the text
discusses stall speed testing. I seem to remember that Tailwinds with the
stock pitot/static system have an inaccurate ASI at low speeds, showing
much
lower airspeed than actual.

A buddy who owned a Tailwind described it as a fast airplane, but with
"mean" low speed characteristics.

I don't buy into the theory that Tailwinds or Soni (?) gain much lift from
the fuselage. The aspect ratio of a fuselage is too small to generate a
lot
of lift.

KB





It is also possible that your friend's plane was poorly rigged.

Some years ago, I saw a BD-4 that a guy had purchased and was trying to
repair sufficiently to complete. The biggest problem was that the fusalage
had a substantial twist. There can also be problems with a very heavy pilot
in a very small airplane--Steve Wittman was only a little bigger than Ken
Rand.

Peter

"ET" wrote in message
...
wrote in
ups.com:

Actually, the CAFE numbers come out a little better than what Van
states as the performance figures for the RV-6. And the stall speeds
that Van posts are pretty much what J. Roncz predicts in his
spreadsheets, even though Van's are a bit better. But then again
Van's planes may be operating at a slightly higher CL than what Roncz
uses. Which leads me to believe that the spreadsheets are quite
accurate.

This is why I'm having a hard time believing that the Sonex aircraft
meet the LSA rules as written. Even at the lightest version of their
aircraft ( Jabiru 2200 power and flown solo and no fuel ) the plane
would have a hard time meeting the stall requirements of LSA which
require max gross wt. figures with a 51 mph stall speed.

And my intention is to fully understand the LSA rules, not "down" the
Sonex aircraft or the people behind it. I believe the Sonex and its
people to be top notch, as do many others, evidenced by how many are
flying and continue to be built. They are reasonally priced,
economical to operate and good "all around" performers for their
power. And from what I have seen, several of the other "popular"
LSA's would have a hard time meeting the LSA specs. as I see them
written.

Neal



Which part of my post that indicated the fuselage of the Sonex is a
lifting body confused you??? Steve Wittman is said to have won a bet or
two with the same issue on the Tailwind. I have not done it, but plug
the same numbers in for the Tailwind and see what pops out.

--
-- ET :-)

"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

Quite true. Lifting bodies can generate a lot of lift, and airfoils vary
wildly in their maximum coeficient. Also, there is nothing in the LSA
rules, or any others that I can think of, to require that an aircraft be
able to maintain level flight at stall speed--so drag coefficient is not a
factor.

Peter

No part confused me. I just have a hard time believing that a fuselage
can accomplish 50 percent of the lifting force of the total body. Yes
I know that some lift comes off of the fuselage on planes, especially
the tailwind as you suggest and the hyperbipe type of designs, but I
didn't think the Sonex fuselage shape was that much different than most
other 2 seat SBS types, including the RV-6. I'll take this into
consideration, though I'm still not convinced that the fuselage lift is
what puts the Sonex into the LSA category.

Neal

ET wrote:
wrote in
ups.com:

Actually, the CAFE numbers come out a little better than what Van
states as the performance figures for the RV-6. And the stall speeds
that Van posts are pretty much what J. Roncz predicts in his
spreadsheets, even though Van's are a bit better. But then again
Van's planes may be operating at a slightly higher CL than what Roncz
uses. Which leads me to believe that the spreadsheets are quite
accurate.

This is why I'm having a hard time believing that the Sonex aircraft
meet the LSA rules as written. Even at the lightest version of their
aircraft ( Jabiru 2200 power and flown solo and no fuel ) the plane
would have a hard time meeting the stall requirements of LSA which
require max gross wt. figures with a 51 mph stall speed.

And my intention is to fully understand the LSA rules, not "down" the
Sonex aircraft or the people behind it. I believe the Sonex and its
people to be top notch, as do many others, evidenced by how many are
flying and continue to be built. They are reasonally priced,
economical to operate and good "all around" performers for their
power. And from what I have seen, several of the other "popular"
LSA's would have a hard time meeting the LSA specs. as I see them
written.

Neal



Which part of my post that indicated the fuselage of the Sonex is a
lifting body confused you??? Steve Wittman is said to have won a bet or
two with the same issue on the Tailwind. I have not done it, but plug
the same numbers in for the Tailwind and see what pops out.

--
-- ET :-)

"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

wrote in
oups.com:

No part confused me. I just have a hard time believing that a
fuselage can accomplish 50 percent of the lifting force of the total
body. Yes I know that some lift comes off of the fuselage on planes,
especially the tailwind as you suggest and the hyperbipe type of
designs, but I didn't think the Sonex fuselage shape was that much
different than most other 2 seat SBS types, including the RV-6. I'll
take this into consideration, though I'm still not convinced that the
fuselage lift is what puts the Sonex into the LSA category.

Neal

ET wrote:
wrote in
ups.com:

Actually, the CAFE numbers come out a little better than what Van
states as the performance figures for the RV-6. And the stall
speeds that Van posts are pretty much what J. Roncz predicts in his
spreadsheets, even though Van's are a bit better. But then again
Van's planes may be operating at a slightly higher CL than what
Roncz uses. Which leads me to believe that the spreadsheets are
quite accurate.

This is why I'm having a hard time believing that the Sonex
aircraft meet the LSA rules as written. Even at the lightest
version of their aircraft ( Jabiru 2200 power and flown solo and no
fuel ) the plane would have a hard time meeting the stall
requirements of LSA which require max gross wt. figures with a 51
mph stall speed.

And my intention is to fully understand the LSA rules, not "down"
the Sonex aircraft or the people behind it. I believe the Sonex
and its people to be top notch, as do many others, evidenced by how
many are flying and continue to be built. They are reasonally
priced, economical to operate and good "all around" performers for
their power. And from what I have seen, several of the other
"popular" LSA's would have a hard time meeting the LSA specs. as I
see them written.

Neal



Which part of my post that indicated the fuselage of the Sonex is a
lifting body confused you??? Steve Wittman is said to have won a bet
or two with the same issue on the Tailwind. I have not done it, but
plug the same numbers in for the Tailwind and see what pops out.

--
-- ET :-)

"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

Hrm,

Well, where can I get a copy of this spreadsheet?... either you've got
the wrong dimensions, or the spreadsheet is flawed.

The Sonex stalls clean at 46mph, and those are real verified numbers (no
I cant point you to a cafe study or anything but all builders on the
list who have actually flown one have verified their numbers..)

Is the airfoil type taken into account??


--
-- ET :-)

"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

wrote:
Could someone clarify something for me concerning LSA's. The websites
that have the detailed LSA aircraft limitations listed say that the
plane must have a maximum stalling speed of 51 mph at the maximum gross
takeoff weight WITHOUT the use of high lift devices.

I plugged the numbers for a Sonex into the John Roncz spreadsheets. (
Max Gross TOW of 1150 lbs, stall of 46 mph ) and it reports that I need
a wing area of 180 sq. feet. The Sonex only has 98 square feet of
wing. What am I missing?

Thanks
Neal


You are not missing anything Neal. The Sonex stall numbers are plainly
bogus. I will venture that Monnet is using indicated stall speed, not
true. That way he can say anything he wants because who knows what the
installation errors are. The calculated stall for the Sonex is 51-52
mph clean at 1100lbs, using the formula that is the basis for
certificated aircraft and assuming a Cl max of 1.6-1.7 for the NACA
64-415 airfoil.

The proof of the pudding? Monnet has contradictory information right on
his site. Go to the Xenos part of the site and look at the claimed
stall, which in this case DOES agree with the standard calculation.
With 158 sqf of wing area it is 44mph, which is right on the money.
Whereas the Sonex stalls clean ONLY 2 MPH FASTER with 60 sqf LESS wing
area! How can this be??? It's magic! Nah, he just fudged the numbers.
Airfoil differences do not account for this as the variation in Clmax
values of a point up or down have surprisingly small effects, maybe 1
mph for each point above or below 1.6.

For when you don't have software available, just a calculator, memorize
the simple formula in your head and apply it to any aircraft's specs you
come across to assess their accuracy:

Sea Level Stall in Kts = Sq root of: [(295 x Gr Wt) Divided by (Clmax x
Wing Area)]

Multiply by 1.15 for mph.

Assume 1.6 for the Clmax. Almost all airfoils are between 1.5 and 1.7,
which gives a 1 mph or so variation up or down relative to 1.6.

That is not to say that the Sonex is not a very clever design.

John

wrote:
Could someone clarify something for me concerning LSA's. The websites
that have the detailed LSA aircraft limitations listed say that the
plane must have a maximum stalling speed of 51 mph at the maximum gross
takeoff weight WITHOUT the use of high lift devices.

I plugged the numbers for a Sonex into the John Roncz spreadsheets. (
Max Gross TOW of 1150 lbs, stall of 46 mph ) and it reports that I need
a wing area of 180 sq. feet. The Sonex only has 98 square feet of
wing. What am I missing?

Thanks
Neal

There's something very wrong with your spreadsheet. A quick sanity
check shows that a Cessna 172 doesn't have 180 sq feet of wing (it is
174 sq ft) and it carries four people, baggage, 320 pounds of fuel and
still manages a stall speed of 51 knots (no flaps, "R" model), only a
little higher than LSA requirements.

I have flown most all of the S-LSA aircraft and a lot of experimetals
that are LSA compliant. I am fairly confident that their figures are
not exaggerated.

Rick Pellicciotti
LightSportFlying.com

Rick,
I really wish I could claim it is my spreadsheet. I've been
referring to the spreadsheets written for Sport Aviation by Jonh Roncz.
Upon looking at his spreadsheets closer, I remembered that he had TWO
of them that calculated stall speeds and they had different results for
stall speeds. He gave an explanation of why there are 2 different stall
speeds but I'll have to go back to the magazines and look it up to find
out exactly why. I think this may be the answer I've been searching
for. I'll try to do this tonite and reply. Thanks

Neal

rpellicciotti wrote:
wrote:
Could someone clarify something for me concerning LSA's. The websites
that have the detailed LSA aircraft limitations listed say that the
plane must have a maximum stalling speed of 51 mph at the maximum gross
takeoff weight WITHOUT the use of high lift devices.

I plugged the numbers for a Sonex into the John Roncz spreadsheets. (
Max Gross TOW of 1150 lbs, stall of 46 mph ) and it reports that I need
a wing area of 180 sq. feet. The Sonex only has 98 square feet of
wing. What am I missing?

Thanks
Neal

There's something very wrong with your spreadsheet. A quick sanity
check shows that a Cessna 172 doesn't have 180 sq feet of wing (it is
174 sq ft) and it carries four people, baggage, 320 pounds of fuel and
still manages a stall speed of 51 knots (no flaps, "R" model), only a
little higher than LSA requirements.

I have flown most all of the S-LSA aircraft and a lot of experimetals
that are LSA compliant. I am fairly confident that their figures are
not exaggerated.

Rick Pellicciotti
LightSportFlying.com

I think I may have found my answer. It is located on page 42 of the
June 1990 edition of Sport Aviation. But first, I have found another
source of information. Currently on the EAA website are articles and
spreadsheets written by Mr. Neal Willford, a frequent contributor to
Sport Aviation. His formulas reach the same conclusions of the
formulas suggested by John Kahn. And John Roncz has TWO formulas. The
first one ( spreadsheet) reaches the same conclusions as do those of
John Kahn and Neal Willford. But his SECOND spreadsheet reaches a
conclusion that requires the plane to have more wing area. Here is his
explanation. I'll quote him here....I'm sure EAA won't mind.

" A couple of EAA'ers have noticed that if you plug the same
parameters into the first and second spreadsheets, you get different
answers for wing area required. This is true. The first spreadsheet
calculates wing area based on the AVERAGE lift coefficient of the wing.
The second is more sophisticated, and takes into account the fact that
the wing is not evenly loaded, and will begin to stall when any one
portion of the wing reaches its maximum lift capability. Ideally, you
want the root part of the wing to stall while the aileron part of the
wing still has not begun to stall, so that you can still operate the
ailerons. Thus, you end up adding a bit more wing area so that you can
protect part of your wing while the rest is stalled. You want to use
the AVERAGE lift coefficient of the wing to set your incidence angle,
while you want to use the second spreadsheet to set your wing area."

For this reason, I have always used Mr. Roncz's second spreadsheet to
calculate wing area and I was supposing everyone else was using this
theory also. I'm assuming that if you show the FAA a formula that is
widely used to calculate stall speed, as Mr Kahn and Willford are
using, that's good enough for them. Heck, I'd use the smaller wing too
if I were marketing a plane. As long as the ROC is sufficient, the
plane would be faster, lighter, easier and cheaper to build .

Thank goodness for guys like Neal Willford, John Roncz and Barnaby
Wainfain. What these guys know.......and more importantly, what they
are willing to divulge.

And Mr Wanttaja.....I think I may have found my missing wing area.

Neal


wrote:
Rick,
I really wish I could claim it is my spreadsheet. I've been
referring to the spreadsheets written for Sport Aviation by Jonh Roncz.
Upon looking at his spreadsheets closer, I remembered that he had TWO
of them that calculated stall speeds and they had different results for
stall speeds. He gave an explanation of why there are 2 different stall
speeds but I'll have to go back to the magazines and look it up to find
out exactly why. I think this may be the answer I've been searching
for. I'll try to do this tonite and reply. Thanks

Neal

rpellicciotti wrote:
wrote:
Could someone clarify something for me concerning LSA's. The websites
that have the detailed LSA aircraft limitations listed say that the
plane must have a maximum stalling speed of 51 mph at the maximum gross
takeoff weight WITHOUT the use of high lift devices.

I plugged the numbers for a Sonex into the John Roncz spreadsheets. (
Max Gross TOW of 1150 lbs, stall of 46 mph ) and it reports that I need
a wing area of 180 sq. feet. The Sonex only has 98 square feet of
wing. What am I missing?

Thanks
Neal

There's something very wrong with your spreadsheet. A quick sanity
check shows that a Cessna 172 doesn't have 180 sq feet of wing (it is
174 sq ft) and it carries four people, baggage, 320 pounds of fuel and
still manages a stall speed of 51 knots (no flaps, "R" model), only a
little higher than LSA requirements.

I have flown most all of the S-LSA aircraft and a lot of experimetals
that are LSA compliant. I am fairly confident that their figures are
not exaggerated.

Rick Pellicciotti
LightSportFlying.com