Sonerai II Stretch LSA Legal?

[jondorb1]

Happy New Year everyone! Looking at the January 2012 Kitplanes Plansbuilt Buyer's Guide, I noticed the Sonerai II Stretch is not annotated as LSA legal while the Sonerai II is. I've read the rules; is it the maximum speed?
Jon

[dlynd]

Jon,

The LSA question comes up quite a bit. I'm guessing they probably didn't include it because the stall speed is so close. I'm currently building a 2LS and from my conversations with the FAA as long as your finished airplane meets the LSA requirements it may be flown by a light-sport licensed pilot. Because the stretch is so close on stall speed a heavy airplane might not meet the requirements where a light one may. At least that is the way I understand it.

Any stretch pilots want to comment on their stall speed? If you know your flying weight that would be a bonus.

Derrick

P.S. I should clarify that I believe that stall speed for LSA is at gross weight, so with the light airplane you would need to limit your gross to whatever gets the stall speed under the LSA limit. Again, just my understanding. May not be the FAA's understanding. ;-)

[peterzabriskie]

Just my 2cts but I agree. From my inquiries about LSA for my SIIL I have been told more than once that my biggest hurdle will be to get my stall speed to the LSA standard. The plans John Monnett made quote a passable stall speed, but most if not all SII builders have said their stall speed was higher.
-Pete

[jondorb1]

Derrick, Pete, thank you. I'm a long way off knowing empty weight or stall speed. Jon

[maddog]

Jon,
I am looking to build a SII LTS and license it as a EAB. Then fly it under Light Sport Rules. I am planning to use it off a grass strip, therefore I am not looking for a racer but I want to bump the top end of light sport categories. I am planning on using a climb prop, and no wheel pants. This will help with the maximum Continuous power setting.

As far as my understanding goes, it is where one placards, and marks their rpm's and IAS's during the test Phase1. But be honest, you will not always be the one flying this aircraft.

One thing that I have read about building the wing is not to over bend the leading edge, only bend the sheet to ~90 degrees so that the leading edge is sort of under negative tension during construction.
This is supposed to help lower the stall speed and its trueness.

Note, that I have not built anything yet, and/or am still looking at using a Riblett airfoil, I just don't if I want to deviate from the plans yet.

Mike

[schrome]

When I checked over a year ago my stall speed was 58 mph at about 740 lb flying weight but I've made some changes since then and ought to check it again. The sharpness of the leading edge has an influence, as Mike said, and so does the amount of droop in the ailerons.

Ed
2LS

[dlynd]

I think we can calculate the stall speed at gross with this formula from those numbers:
Vs new = Vs old weight x √(new weight / old weight)

That would put the stall speed at gross (1150) around 72mph. If I'm doing this right. To be LSA legal the stall speed at 740 would need to be about 40-41 mph.

Even if I've got the formula right, this is just a vague estimate. Still, I don't see how you could slow it down enough.

Anyone else with stall and weight numbers? How low can we go?

Derrick

[4trade]

With that airfoil and wing area it is impossible to achieve LSA stall speed. That airfoil Cl is approx 1.5 and when multiply 0.85 it will be close to real number what you get in a real life.

Here is calculator for you, so forget it, it is just daydream: www.ajdesigner.com/phpwinglift/wing_lift_equation_force.php

Edit: Too sharp leading edge will drop your AoA where airfoil stall and therefore it will stall even higher speed, because it cant reach those Cl numbers that airfoil is design. If LE is rounded with bigger radius than design, it will add small amount of drag, but give more AoA usually.

[4trade]

If your plane gross weight is 720 lbs or less, it will achieve LSA stall speed (52 mph) at original wing and original 64A212 airfoil.

Like i say before, mission impossible.....

[raceair]

Unfortunately, A 720 pound gross weight is even hard to do today with a Sonerai 1....let alone a Sonerai 2....
When I first built Sonerai 1 'Blueberry', It weighed 520 pounds empty, add a 200 pound pilot, fuel for one hour, and oil, and you are already up over 750 pounds, and the Sonerai 1 has less wing area than a 2.......My stall speed was over 58 mph indicated....
Regardless of what you read, My personal experience with several Sonerais tells me that 'I' would never call it an LSA compliant aircraft....Just my opinion......Ed Fisher

[dlynd]

I'd have to agree 4trade and Ed. You'd have to modify the wing considerably to do it. I think that airplane is called a Sonex ;-) To Jon's original point, curious that kitplanes would think a 2 is and a 2LS is not. The wing is the same on both correct?

[4trade]

There is false stall speed information, and that is main reason for "LSA legal" fast planes in a market. Nobody really check that stall numbers are true and most of stall numbers are indicated, not true airspeed.

Stall speed numbers can also measured wrong way, like slamming stick in your guts with some speed, so it will be slower than stall speed with right way...that is with glide mode and very slowly add back pressure for stick until it stall.

So, most designer or manufacturer just lie for stall speed to get better advertise numbers. Like some Super Cub type planes....those stall numbers and weight will actually beat the law´s of physics....really! So be careful there with ad´s!

[wafer]

"Maddog" Mike-

Something to consider....as I understand, the tri-gear version is really not designed for sod usage.

Mike

[4trade]

I put here two example....Sonerai 2 and advertised stall speed 45 mph...makes coefficient of lift 2.25 at that wing area.

Sonerai 2 stretch....50 mph advertised stall makes Cl 2.18.....

Every Sonerai use NACA 64A212 airfoil, and this airfoil Cl is 1.5 at theory, but designer´s multiply that theoretical numbers 0.85, and got close to the real numbers at real wing. So we have 1.275 Cl max....if we build perfect wing without any rivets to bother airstream and so on..

Even with good flaps that Cl 2.2 numbers are really hard to get, and with good flaps that 2.2 is good only that area flaps cover...so 50% plain wing + 50 % flaps makes whole wing average Cl less than 1.8 WITH FLAPS that cover half of span...and they advertise 2.2 Cl plain wing numbers.....

Now if you put these numbers at calculator, you get some clue what is true stall speed numbers...>Try here: www.ajdesigner.com/phpwinglift/wing_lift_equation_coefficient.php

[racegunz]

No one is going to have a radar gun on your airplane when testing, the airplane "Police" only show up when you have smashed your plane into something other than the hangar door, then they check your paper work. The manufacturer's specs imply it can be flown under light sport so no one is going to come and test your Sonerai to see if it complies, there are many Sonerai being flown under the new Sport Pilot rules, there really is no drama here......really.
Now as far as I know only one Sonerai has ever been registered as a ELSA and no one seems to be coming off the method used to do so, yours will be EAB and the speeds noted during testing will be the final say so if it's legally eligible for Sport Pilot usage.