Is lower wing loading safer?

Looking at the ultralight specs in Canada, they call for a max wing loading of 12psf. In fact, amateur built aircraft in Canada cannot have a wing loading over 20psf,I'm told.

While in the US, we see aircraft like Rutan's Boomerang at about 42psf.

Seems many GA aircraft seem to be stuck at 14-17psf range

With VG's or slats and flaperons (full length flaps) and then slatted (junkers flap(?)), Zenith is getting a nice cl of about 3.0, about double a typical ultralight

Why not higher wing loading? This would lead to smaller wings, better aspect ratios, less drag, which means smaller engines, which means more affordable GA aircraft.

In fact, Rutan's motorglider (solitaire(?)), had a top speed of about 200(?) mph, with just a 4 cycle 18hp industrial engine ( rated for continuous duty), the kind you can buy at a big box store for $500.

I understand M. Coulumban, the designer of the cri-cri, just switched to low cost industrial honda engines as well.

On a saturday morning 1,000 mile cross-country trip ( pretty routine for the long-eze crowd)and have engine problems? No problem. Just go to a big box store and buy a new one and install it in an hour. Might as well make it an inline twin for that low of an engine price. Rutan's twin Defiant could take off from either engine alone, or both. Seem's pretty foolproof to me.

Seems like pretty good economics for GA aircraft in my mind.

So..... why limit ultralights to 12psf. I assume lower wing loading means it's safer. Lot's of wing means it's harder to stall.

Is this correct?

  • $\begingroup$ Per Wikipedia, Solitair used Cuyuna 215 "The 2si 215 is a family of single-cylinder, fan-cooled, two-stroke, single ignition, aircraft engines that were designed for ultralight aircraft." I think you may be overstating the engine availability at Home Depot. All their engines are listed as "Ship to store for pickup", so you'll grounded for some number of days waiting on that. Removing gas tank and other configuration issues might add to the swap out time, and most seem to be 4 stroke engines also, and I suspect may need unleaded gas. Have to wonder if oil reservoir is large enough also. $\endgroup$ – CrossRoads Jul 15 '19 at 15:48
  • $\begingroup$ I understand the original Solitaire used a 18 hp Onan industrial engine designed for water pumps. In Canada we have a big box store called Princess Auto. They must have 20 gas engines just sitting on the shelf. I understand these engines are rated continuous duty at 75% rpm, so oil and heat shouldn't be a problem. Yes, they use unleaded gas but that's cheaper anyways. Rotax 912 engines are designed for unleaded gas, but you can use leaded gas in a pinch. Just reduces your TBO. $\endgroup$ – Fred Jul 15 '19 at 15:56
  • $\begingroup$ Wikipedia says "The initial engine was the 22 hp (16 kW) Zenoah G-25, but this was changed to a Robin engine and then later the 20 hp (15 kW) Cuyuna 215. The KFM 107e 22 hp (16 kW) engine has also been used." No mention of Onan. $\endgroup$ – CrossRoads Jul 15 '19 at 15:58
  • $\begingroup$ A book on Rutan's designs called Race to Space(?) mentions the Onan. It was a kit plane. I'm sure people used all sorts of engines. $\endgroup$ – Fred Jul 15 '19 at 16:03
  • $\begingroup$ @Fred You're thinking of the original tandem wing Quickie with the Onan. Solitaire was a motorglider using a folding engine. Solitaire was a flop because it was found that the canard config did not lend itself to flying close to stall with a decently low sink rate and it wasn't very good at thermalling. In a normal glider you thermal with the main wing on the edge of the stall (and often the lowest sink rate is with buffet onset) and canard by design doesn't allow for this. Anyway, the Onan was heavy for its power. In Europe the 2 cyl BMW with Rotax gearbox conversion is popular. $\endgroup$ – John K Jul 15 '19 at 16:39

Yes in general it's accurate to say that lower wing loading is safer, especially in the hands of a pilot with low experience flying in calm weather with an unreliable engine. Flying in gusty winds and strong turbulence, there would be safety advantages to a higher wing loading.

The basic idea of limiting the wing loading is to limit the stall speed and thus the destructive energy involved in a forced landing. As the question suggests, perhaps it would be wiser to limit the stall speed, or to allow deviations from the prescribed minimum wing loading in the case of a demonstrated low stall speed.

However the Canadian regs may also be written with the idea of limiting the top speed too. Exactly why that's a good thing is not completely clear, but in the US at least an ultralight must not be able to exceed 55 knots in sustained level flight.

  • $\begingroup$ Future edit- "perhaps it would be wiser to actually limit the stall speed" $\endgroup$ – quiet flyer Jul 16 '19 at 1:56

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