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Click to view full story of "Sling S-LSA vs. EAB vs. ???"

jake: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 11:44 am)

Ed,

You bring alot of experience to the forum and I appreciate your valid comments.

I also have to agree with Jim that its not always that black and white.

Most of the LSAs we are talking about here are flying at higher weights in other countries with no airframe changes. I dont believe that is true for many part 23 aircraft not held to an artificial weight limit. That puts LSAs in a unique position.

Ed,
How would you handle this situation? When I got my P2008 and were going back to Minnesota I did the preflight W/B before departing and determined with the instructor I had been given we could only put in 12 gallons to be legal. We were heading across the mountains and me having little experience with mountainous terrain I was uncomfortable. The instructor insisted he would not allow more fuel and we would be fine. Which is more dangerous?

How many accidents do we know that have been caused by running out of fuel?
How many accidents do we know have been caused by overloading?

I am not advocating flying overweight. I want to be clear about that.
I am just saying it is not as black and white as we would like.
I have suggested several times that the LSA weight limit is not practicle.
My suggestion would be to give weight exemptions for safety features such as the parachute.

And we havent even started the discussion on the pros/cons of building a stronger more substantial aircraft that is potentially safer VS a lighter built aircraft that is more prone to landing gear failures as we have regularly seen in LSAs.

Mark

cogito: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 12:03 pm)

The educated practitioner can assign risk and act accordingly.

As an educator, how could I possibly disagree? But, that education has to include the true risks. Those have little to do with structural failure, and everything to do with stall speed.

I read a lot of NTSB accident reports, and have noticed that a disproportionate number of stall/spin accidents mention aircraft over gross. So, consider this scenario: Pilot has a tailwind on base, overshoots the turn to final, steepens the bank in the turn, adds power (i.e., torque), and then gives rudder to further yaw the nose without having to bank still further. Let's say this is in an LSA with 45 knot stall speed. 20% overgross (not hard to do in an LSA) raises stall speed to 50 knots. A 60 degree bank, if you haul back on the stick and pull 2 Gs, can further increase stall speed to 70 knots. And, if you were approaching at normal speeds, you just entered the classic stall/spin domain.

Was the cause of the accident being overgross? I doubt that would be the NTSB's judgment. Proximate cause was that tight turn to final. But, had the plane not been overgross, might the accident have been prevented? That is at least arguable.

So, will the plane "handle it" at higher weights? Of course it will - unless the pilot screws up. Why paint yourself into that corner in the first place?
Question Paul: In your scenario, a 20% overload corresponds with a 5kt stall speed increase. An EAB Sling built to 700kg (rather than an LSA at 600kg) is 16% heavier but the factory specs page lists only a 1kt increase in stall speed either clean or full flaps. Do you believe the data sheet is incorrect or misleading? http://www.airplanefactory.co.za/sling2.asp

drseti: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 12:14 pm)

Do you believe the data sheet is incorrect or misleading?

Well, let's do the math. Stall speed varies with the square root of load factor. (700 kg / 600 kg) equals a load factor of 1.167. The square root of that is 1.080, or an 8% increase in stall speed. That means a 45 knot stall speed now increases 8%, to 48.6 knots ( a 3.8 knot increase).

To have an 8% increase in stall speed add only 1 knot, the original stall speed would have had to be 12.5 knots. I find that hard to believe. So, yes, I would question the published specs.

rsteele: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 1:00 pm)

Stupid idea I'm sure, but have any of you left your airplane unpainted? Might save 8 or 10 lbs and with all the polishing you'd make sure to never gain too much weight yourself.


Unpainted planes, like the one pictured are usually polished to get the shine and smooth the surface to reduce corrosion.

Polishing works, or not depending on the alloy used to build the plane. I'm building a Zenth which uses 6061-T6 aluminum. This aluminum is very corrosion resistant and there are quite a few polished Zeniths around. Polishing is said to save about 20lb on the Zenth 601, and I'll be polishing mine. On the other hand Vans are build of all-clad 2024 aluminum. I've never seen a polished Vans as the metal is prone to corrosion, or at least surface blemishes. You would have to put clear coat over polish. I was out at my hangar last weekend and cleaned off bird poop that had been there on the unpolished/unpainted surface for some time. It came right off with no indication it was ever there. Compare that to a friend's RV-7. Before it was painted, a drop of sweat would leave a mark.

Ron

cogito: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 2:25 pm)

Stupid idea I'm sure, but have any of you left your airplane unpainted? Might save 8 or 10 lbs and with all the polishing you'd make sure to never gain too much weight yourself.


Unpainted planes, like the one pictured are usually polished to get the shine and smooth the surface to reduce corrosion.

Polishing works, or not depending on the alloy used to build the plane. I'm building a Zenth which uses 6061-T6 aluminum. This aluminum is very corrosion resistant and there are quite a few polished Zeniths around. Polishing is said to save about 20lb on the Zenth 601, and I'll be polishing mine. On the other hand Vans are build of all-clad 2024 aluminum. I've never seen a polished Vans as the metal is prone to corrosion, or at least surface blemishes. You would have to put clear coat over polish. I was out at my hangar last weekend and cleaned off bird poop that had been there on the unpolished/unpainted surface for some time. It came right off with no indication it was ever there. Compare that to a friend's RV-7. Before it was painted, a drop of sweat would leave a mark.

Ron

Ron,
20 lbs.? that could be very helpful, could make the difference between going LSA or EAB. Do you have any data on the 20 lbs? Anyone weigh an LSA-sized plane before and after paint? Online I've seen everything from 5-30 lbs. (and that a 747 carries 400-500 lbs. of paint.~) Sling uses 6061-T6, though I was planning on having it alodined to prevent corrosion. I wonder if they can do that on the interior parts only.

There are a number of polished RV's online. Not all look as good as this one:
http://www.pilotbill.com/Black-SilverRV.jpg

jake: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 2:26 pm)

As far as the stall speed formula it is a way to guestimate the effect. I would not count on it to be 100% accurate. I bet the it will be somewhere in the middle which is only a guess by me.

LSAs stall at such a slow speed already adding a few knots would seem to be insignificant. If the airframe is up to it wouldnt the extra wing loading allow the aircraft to actually handle better in crosswinds and landings? Just asking?

Mark

drseti: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 2:27 pm)

That RV looks beautiful. It also looks like one helluva lotta work!

jake: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 2:55 pm)

Another thing that has not been brought up is stall warning.

What does the sling use far stall warning?
What does the Evector uses for stall warning?
What does the CT use for stall warning?
What does the sky arrow use for stall warning?
What about the citabria?

Many of these aircraft have no stall warning or not a very good one.

I have debated the need with many who say it isnt needed in such a low stall speed aircraft and a pilot would be wise to get more training before spending $ on a stall warning.
This would seem to go against what Ed has said previously. Has anyone heard of Shawn Lunt?
He was a very experienced supercub pilot who stalled it in and lost his life.
I am only a 600hr PP but I believe if 10000hr pilot with most of his time in a cub can stall it in then maybe a good stall warning might be a good idea.

All of the Tecnams I have flown have an angle of attack with a LOUD audio into the headset that WILL get your attention before approaching full stall. The AOA gives stall awareness that you will never get with a horn. After using it I am amazed it has not been accepted as the standard for all aircraft.

Mark

drseti: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 3:00 pm)

LSAs stall at such a slow speed already adding a few knots would seem to be insignificant.

Mark, when everything's going well, a few knots isn't going to make any difference at all. It's when everything's going to hell that a few knots can be the difference between death and survival. Since every accident is a chain of events, why would anyone want to deliberately forge that first link before takeoff?

drseti: Re: Sling S-LSA vs. EAB vs. ??? (Tue Mar 05, 2013 3:04 pm)

Another thing that has not been brought up is stall warning.

What does the Evector uses for stall warning?

Mine uses the airframe buffet. Nothing else.

The AOA gives stall awareness that you will never get with a horn. After using it I am amazed it has not been accepted as the standard for all aircraft.

Very good point. An AOA indicator can certainly be a lifesaver.


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