LSA specs

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

"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

"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

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

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

snip

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 :-)


The Sonex numbers are believable, but absolutely DO NOT trust performance
figures provided by builders. Pitot/Static systems are notoriously
inaccurate at low airspeeds and owner/builders are notoriously optimistic in
their performance reports. In addition, without very expensive and
sensitive test equipment, you're not going to get accurate figures. There
isn't a CAFE report on the Sonex, so unless Sonex Ltd. has invested the time
and money to conduct private tests, my guess is that accurate testing simply
hasn't been done.

KB

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

The Roncz spreadsheets were published in Sport Aviation from February
1990 thru January 1991 ( I believe ). The one I am referring to ran in
the March 1990 issue. I'm not at the house at the moment but I'll
check when I get home and verify.

Neal

ET wrote:
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

Is it possible that maybe it all could be just an interpretation of the
LSA rule? I mean does the "aircraft" have to be LSA legal or does the
"flight" have to be LSA legal? Say the Sonex could indeed stall at 51
mph ( flown solo in a lightweight condition ). Technically the
"flight" would have a max gross takeoff wt.and stall conditions that
would satisfy the LSA rule. But then if you loaded the aircraft to
it's max. designed takeoff weight and then it couldn't meet the 51 mph
stall speed, then it couldn't be flown under LSA rules. In other
words, flown solo, yes you're LSA legal, but flown at max design, no,
you're not legal. Could this be what the Sonex guys are doing? You
know.......I could just call Jeremy and ask him.

Neal


Richard Riley wrote:
On Sat, 23 Sep 2006 19:50:36 -0400, "J.Kahn"
wrote:

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.

Yeah, I ran it the other way and got a CLmax of 1.623 at 1100 gross
and 52 mph.

That's ambitious for the 64-415 clean. Not flatly false, just at the
top end of achievable in the real world. And it's got a flat bottomed
fuselage, so that will fudge stall speed down a little. (Not like the
DreamWings, a few years back, that was claiming speeds that meant a
CLmax of 4). I wouldn't bet it's that good, but it's plausible.

The key is that it's still just legal for LASt - the min stall speed
is 45 knots, or 51.8 mph.

It's entirely possible that the builders are reporting accurate
speeds, but aren't getting those speeds at full gross weight. They
claim an empty weight of 620 lbs, useful load 480, 16 gallons of fuel.
So, 96 lbs of fuel and two 192 lb occupants. Let's assume our
reporting pilot is flying alone and he has 3/4 full tanks. That puts
him at a gross of 884. If the 1.6 (and change) CLmax is true, he'll
stall at 46 (and change) mph. Throw in a little pitot error and it's
very believable.

wrote:
Is it possible that maybe it all could be just an interpretation of the
LSA rule? I mean does the "aircraft" have to be LSA legal or does the
"flight" have to be LSA legal? Say the Sonex could indeed stall at 51
mph ( flown solo in a lightweight condition ). Technically the
"flight" would have a max gross takeoff wt.and stall conditions that
would satisfy the LSA rule. But then if you loaded the aircraft to
it's max. designed takeoff weight and then it couldn't meet the 51 mph
stall speed, then it couldn't be flown under LSA rules. In other
words, flown solo, yes you're LSA legal, but flown at max design, no,
you're not legal. Could this be what the Sonex guys are doing? You
know.......I could just call Jeremy and ask him.

Neal


Richard Riley wrote:
On Sat, 23 Sep 2006 19:50:36 -0400, "J.Kahn"
wrote:

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.
Yeah, I ran it the other way and got a CLmax of 1.623 at 1100 gross
and 52 mph.

That's ambitious for the 64-415 clean. Not flatly false, just at the
top end of achievable in the real world. And it's got a flat bottomed
fuselage, so that will fudge stall speed down a little. (Not like the
DreamWings, a few years back, that was claiming speeds that meant a
CLmax of 4). I wouldn't bet it's that good, but it's plausible.

The key is that it's still just legal for LASt - the min stall speed
is 45 knots, or 51.8 mph.

It's entirely possible that the builders are reporting accurate
speeds, but aren't getting those speeds at full gross weight. They
claim an empty weight of 620 lbs, useful load 480, 16 gallons of fuel.
So, 96 lbs of fuel and two 192 lb occupants. Let's assume our
reporting pilot is flying alone and he has 3/4 full tanks. That puts
him at a gross of 884. If the 1.6 (and change) CLmax is true, he'll
stall at 46 (and change) mph. Throw in a little pitot error and it's
very believable.


Any numbers quoted for speeds are always based on the published max
gross weight (maximum certified wing loading in other words) unless
otherwise stated. That fact that the Sonex may stall at 46 mph solo is
not relevant for the purposes of whether it meets LSA requirements.
And the speeds that builders see are generally meaningless since ASIs
are very inaccurate at these speeds and usually read 5-10 mph low.

I find it puzzling that Monnet uses a viable stall speed claim for the
Xenos but not for the Sonex. While the Sonex does meet LSA requirements
(just), the claimed stall speed of 46, which is normally assumed to be
for max gross, is simply mathematically impossible. I think you may be
on to something though. If someone was to question his claimed stall of
46 he will probably state that it's for solo weight but that's not
stated on his site and is misleading.

Does the LSA rule have anything to say about advertised stall speeds?
Can they be indicated or at less than gross without notation in ads?

John

John,
I hear what you're saying, but with all that's been said here, and
investigated via spreadsheets, etc., I still don't think the Sonex can
stall near the LSA requirement at max gross wt. and no flaps which
means it is not LSA qualified. And just for grins, I looked up the
figures for the CT Flight Design ( which is a popular seller ) and
guess what. IT doesn't meet the LSA criteria. And I also looked up
the new Vans RV-12 "LSA" and you guessed it....IT doesn't meet the
stall speed criteria ( at least not on paper...I don't think it has
flown yet.) So I'm convinced that something is amiss. I'll keep
researching.

Neal

J.Kahn wrote:
wrote:
Is it possible that maybe it all could be just an interpretation of the
LSA rule? I mean does the "aircraft" have to be LSA legal or does the
"flight" have to be LSA legal? Say the Sonex could indeed stall at 51
mph ( flown solo in a lightweight condition ). Technically the
"flight" would have a max gross takeoff wt.and stall conditions that
would satisfy the LSA rule. But then if you loaded the aircraft to
it's max. designed takeoff weight and then it couldn't meet the 51 mph
stall speed, then it couldn't be flown under LSA rules. In other
words, flown solo, yes you're LSA legal, but flown at max design, no,
you're not legal. Could this be what the Sonex guys are doing? You
know.......I could just call Jeremy and ask him.

Neal


Richard Riley wrote:
On Sat, 23 Sep 2006 19:50:36 -0400, "J.Kahn"
wrote:

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.
Yeah, I ran it the other way and got a CLmax of 1.623 at 1100 gross
and 52 mph.

That's ambitious for the 64-415 clean. Not flatly false, just at the
top end of achievable in the real world. And it's got a flat bottomed
fuselage, so that will fudge stall speed down a little. (Not like the
DreamWings, a few years back, that was claiming speeds that meant a
CLmax of 4). I wouldn't bet it's that good, but it's plausible.

The key is that it's still just legal for LASt - the min stall speed
is 45 knots, or 51.8 mph.

It's entirely possible that the builders are reporting accurate
speeds, but aren't getting those speeds at full gross weight. They
claim an empty weight of 620 lbs, useful load 480, 16 gallons of fuel.
So, 96 lbs of fuel and two 192 lb occupants. Let's assume our
reporting pilot is flying alone and he has 3/4 full tanks. That puts
him at a gross of 884. If the 1.6 (and change) CLmax is true, he'll
stall at 46 (and change) mph. Throw in a little pitot error and it's
very believable.


Any numbers quoted for speeds are always based on the published max
gross weight (maximum certified wing loading in other words) unless
otherwise stated. That fact that the Sonex may stall at 46 mph solo is
not relevant for the purposes of whether it meets LSA requirements.
And the speeds that builders see are generally meaningless since ASIs
are very inaccurate at these speeds and usually read 5-10 mph low.

I find it puzzling that Monnet uses a viable stall speed claim for the
Xenos but not for the Sonex. While the Sonex does meet LSA requirements
(just), the claimed stall speed of 46, which is normally assumed to be
for max gross, is simply mathematically impossible. I think you may be
on to something though. If someone was to question his claimed stall of
46 he will probably state that it's for solo weight but that's not
stated on his site and is misleading.

Does the LSA rule have anything to say about advertised stall speeds?
Can they be indicated or at less than gross without notation in ads?

John