Part103 in every way but does not meet stall speed? Thoughts?

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Hello All,

Since I currently have a Zigolo MG-12 and the owner now has the MG-21 in flight testing I have been working with the designer about the possibility of having it imported into the USA. He designed it for other specs that it meets in Europe but sadly is falling short on the Part 103 Stall Speed. It builds in at around 220lbs so meets weight easily. Its currently a bit too clean and fast but that can be addressed with a prop, but on stall speed he is in the 26 to 27kt range so missing it by a fair amount. Originally Francesco the designer planned to offer a larger wing version for the USA market to get the stall speed down, but now after setting up manufacturing, he has decided not to modify the design to make manufacturing easier having only one version. I also ran the numbers from the FAA circular released in 1984 that uses aircraft parameters to see if the design meets Part 103. Sadly it still comes up with a speed of 26kts. So my question is what viability is there in offering a kit that meets every aspect but speed. Suppose it can be offered as an experimental knowing that most builders will just build it and fly it as a UL but at least its not on Zigolo if they do that.

Second question, does the Hummel Ultracruiser actualy meet stall speed? Seems its too clean as well and not enough wing area when the numbers are run.

Thoughts?
 

Bigshu

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How hard would it be to add the tape/glue on vortex generators to the wings? You only need to lose a couple of knots to meet the reg. While the FAA might not expect you to demonstrate the stall speed, they can probably find a published spec showing the factory number if they really wanted to. Same with weight, if it looks light, ok, but if they weigh it, better be light.
 
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VG's might be worth a try. As for weight it comes in 30lbs less than Part103 weight. Its just the Stall speed spec he is not meeting since its so clean. The Ultracruiser must have the same issue being so clean and I hardly believe it hits the Stall speed spec either. But I could be wrong.
 

Vigilant1

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Is there a way to get there using "Step 3” of Appendix 2 of FAA AC-103-7? You don't need to reduce the actual stall speed, you just need to either hop onto a new Cl line on the graph or increase the wing area. Thoughts:

1) The plane has full span ailerons, no flaps, and a camber greater than 7%, right? So, you would use the 1.6 CL line on the nomogram. But, if it has a double surface wing with flaps more than 50% of the span, you can use the 2.0 CL line. So, if you can find any way to make those full span ailerons into flaperons (the FAA gives no spec on how much the flaps have to move, etc), then you'd probably be in good shape. Done.
2) Add panels between the V-struts on each wing? Even if they have symmetrical airfoils (zero camber), each square foot is credited with a CL of 1.4. You'd need to take care that they don't affect stability, but they'd be pretty close to the CG, so maybe not much of a factor.

Anyway, I suspect there's a way to achieve your goal by using the provided FAA method.

Also, it might be worth verifying the actual stall speed of a real Zigolo very accurately. Perhaps it already makes it.
 
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TFF

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Wing is too short. Pretty simple. Looks like it is 22-24 ft? Get them to build an option 5 ft longer wing. Airfoil looks “fast” too. It looks like the plane is designed for being sporty.

The guy flying the Ultracruiser at Oshkosh is always the fastest UL in the pattern. Does it stall slow, yes. Does it hit the numbers? Who knows but the owner. I bet it probably does close, but it has a thick airfoil close to a foot thick. Double just about everything else.
 

radfordc

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Very few "ultralights" are truly legal in every respect. Guess what....No one cares as long as it meets the "looks like an ultralight" test.
 
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Very few "ultralights" are truly legal in every respect. Guess what....No one cares as long as it meets the "looks like an ultralight" test.
More worried about a liability issue. Designer claims Part 103. Pilot kills himself. Family finds out it was part 103 in every way but stall speed. Says he should have known and legally he should not have been allowed to fly it with no license and im suing you.
 

GeeZee

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How about extended wing tips? Might require running the numbers as far as spar/wing strength but if that checks out you could make/ offer the kit with “USA tips”. I’ll bet extended tips and vg’s would get you there.
Also really interested in the “2minute wing fold without disconnecting the ailerons”. How is that managed? Teleflex cables?
 
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How about extended wing tips? Might require running the numbers as far as spar/wing strength but if that checks out you could make/ offer the kit with “USA tips”. I’ll bet extended tips and vg’s would get you there.
Also really interested in the “2minute wing fold without disconnecting the ailerons”. How is that managed? Teleflex cables?
Usure on the fold but it can be done with cables if they run through the rear tube and pivot on that tube. Maybe just loosen an idler pulley.
Marc
 

ragflyer

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Apart from VGs suggested above, you can add angles to the trailing edge of the wing to act as Gurney flaps. This would work even with full span ailerons. This will allow you to use higher cl curves in the FAA AC 103-7 which may then allow you to show compliance via the AC 103-7 route.

Also you do not have to show compliance with AC 103-7 at full published gross weight. It is sufficient to show compliance assuming a 170lbs pilot and 30lbs of fuel.
 

Vigilant1

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Apart from VGs suggested above, you can add angles to the trailing edge of the wing to act as Gurney flaps. This would work even with full span ailerons. This will allow you to use higher cl curves in the FAA AC 103-7 which may then allow you to show compliance via the AC 103-7 route.
That would be nice and easy, if the FAA accepts it. Do we know if, for purposes of this requirement, the FAA considers these "Gurney flap" trailing edge devices to be "flaps"? FWIW, the glossary in the FAA Pilot's Handbook of Aeronautical Knowledge says that flaps are hinged. Flaps are most commonly understood to be movable surfaces, notwithstanding the "Gurney flap" label.
 
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ragflyer

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That would be nice and easy, if the FAA accepts it. Do we know if, for purposes of this requirement, the FAA considers these "Gurney flap" trailing edge devices to be "flaps"? FWIW, the glossary in the FAA Pilot's Handbook of Aeronautical Knowledge says that flaps are hinged. Flaps are most commonly understood to be movable surfaces, notwithstanding the "Gurney flap" label.

Why would they not? Flaps are movable (and are retracted) because they cause a lot of drag and are inefficient (and slow) during cruise. With ultralights the slowness at cruise is not an issue (in fact it would be an advantage). What AC103.7 is concerned is high cl max with flap. In that respect the Gurney flap is no different and just as effective with respect to cl max than a simple (or any other) flap for that matter.
 

Vigilant1

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Why would they not? Flaps are movable (and are retracted) because they cause a lot of drag and are inefficient (and slow) during cruise. With ultralights the slowness at cruise is not an issue (in fact it would be an advantage). What AC103.7 is concerned is high cl max with flap. In that respect the Gurney flap is no different and just as effective with respect to cl max than a simple (or any other) flap for that matter.
Because it isn't a flap?
I'd sure ask the question before assuming the FAA would accept it. The AC asks for flaps, and a strip of angle on the back of an aileron is not a flap no matter what somebody calls it.

Slats or slots would also improve the CL, or even a very thick wing with a lot of camber, but they aren't mentioned in the AC, so I wouldn't assume they'd be acceptable either.

I can definitely understand why someone would want to just give this a try with their own plane. But, if liability is the issue and wanting to assure the plane is a no-kidding legal Part 103 ultralight is key to that, then things need to be watertight.

It is possible, though, that a Gurney trailing edge device would be enough to let the plane meet the stall speed requirement by actual demonstration. That would be great.
 
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ragflyer

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On the contrary camber is explicitly mentioned and the way they measure it thickness comes into the picture.
Slats or slots would also improve the CL, or even a very thick wing with a lot of camber, but they aren't mentioned in the AC, so I wouldn't assume they'd be acceptable either.

On the contrary, camber is explicitly mentioned in AC 103.7 and the way it is to be measured per AC 103.7 means thickness comes into the picture as well.
 

Vigilant1

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On the contrary, camber is explicitly mentioned in AC 103.7 and the way it is to be measured per AC 103.7 means thickness comes into the picture as well.
Sure, but no matter what the wing's camber is, you don't get to use the CL 2.0 line in the nomogram if it has no flaps. To use the CL 2.0 line you must have flaps and they must cover more than 50% of the wingspan. It has nothing to do with aerodynamics, it has everything to do with semantics. Regardless of the camber, the wing must have flaps of more than 50% to claim CL of 2.0. And I strongly suspect the FAA knows what they mean by "flaps."
 
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ragflyer

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Look there are two ways to look at this- what the FAA intends and what the FAA literally say.

On the first account the intent is to lower the stall speed and Gurney flaps have been measured in the wind tunnel to give cl = 2.0. So no reason the Gurney flaps does not meet the intent.

Now as to what they literally say. They only say flap. They do not say split, plain, fowler etc. Open an airplane design text that covers various flaps and you will see Gurney flaps covered. As all trailing edge flaps, Gurney flaps work by changing camber. The only difference is a Gurney flap is fixed, though of course you could make it move if you like.

Finally, you might say this is all well and good but the FAA is a bureaucracy and may not accept it. Well then flight test it with Gurney flaps and show compliance with the stall speed that way. Gurney flaps are not some kind cheat, they work.

Honestly though a very high percentage of ULs are non compliant and the FAA turns a blind eye. I would be more than happy to show compliance this way ..... your milage may vary, in that case test with Gurney flaps.
 

ragflyer

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btw would a plain flap that is fixed be acceptable in your mind? What about a split flap that is fixed?
 

Mad MAC

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More the static port or the pitot head till the ASI gives the correct indication (&/or get an ASI with a courser scale on the ASI, works for Robinsons torque indicator).

ASI's are terribly inaccurate at that speed range, is the measured Stall speed correct?
 
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