SonexBuilders.net

When people are discussing fitting geared engines such as Rotax to the Sonex a topic that is often raised is how big a prop you can fit. A recent completion by Carl Bejvel in Sweden is fitted with a Rotax 912 turning a Woodcomp SR3000 two-bladed CS propeller, 1700mm, that's 67 inches. Gear appears to be standard with larger tires.

I have run a 60" prop with standard gear, small tires and no problems, but 67" is getting pretty big. See his first flight https://www.youtube.com/channel/UCtjBcD6BDuKPinH1ngUnJRw

Peter

That certainly is a long prop, I am presently using a Sensenich 64" ground adjustable prop on my Bristell NG5 aircraft which is powered by a Jabiru 3300. At 2000" and WOT I can achieve 155mph, the engine rpm at this speed is 3250, the prop is adjusted to give 2780 static rpm. I always thought the Sonex was limited on prop length due to ground clearance, so my question is, are there any Jabiru 3300 aircraft out there operating with longer props as the SPA offers a 62" prop for the Corvair powered Panther but only 54" for the Corvair powered Sonex.

The issue of propellor selection may come up for discussion more often as Sonex has "approved" more engine options for the Sonex "B" model, including the geared Rotax engine. I haven't seen where Sonex has recommended specific props for these engines, but I could be wrong.

Just my opinion, but I think a three blade prop could be the way to go. My Viking powered Waiex (geared engine) spins a 62" ground adjustable three blade Warp Drve propellor. Nice prop! Many Rotax powered light sport type aircraft are using three bladed props. I have seen photos of Rotax powered Sonex aircraft with three blade props.

That 67" prop looks pretty long, I hope he can keep it out of the turf.

Fly safe, whatever engine/prop combination you choose.

Don Bowen
Viking Waiex N49YX
Rebuild finished - getting ready for Phase 1 flight tests

Part 23 is a ood starting place...


Unless smaller clearances are substantiated, propeller clearances, with the airplane at the most adverse combination of weight and center of gravity, and with the propeller in the most adverse pitch position, may not be less than the following:

(a) Ground clearance. There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level, normal takeoff, or taxing attitude, whichever is most critical. In addition, for each airplane with conventional landing gear struts using fluid or mechanical means for absorbing landing shocks, there must be positive clearance between the propeller and the ground in the level takeoff attitude with the critical tire completely deflated and the corresponding landing gear strut bottomed. Positive clearance for airplanes using leaf spring struts is shown with a deflection corresponding to 1.5g.

Gordon