SonexBuilders.net

SonexFlight Episode 69 "AllenFlight Extended Wingtips" is available for download!

Tim Allen and Jerry Friedman of AllenFlight speaks with us about his wingtip extension modification, and hear about the installation process and results he's achieved.

http://sonexflight.com/69

Jeff

I enjoyed this episode. The question about flutter and spin recovery was asked. It would be nice to hear a follow-up to the question of spin recovery.

I have to say though, as someone that is somewhat disappointed with the Sonex useful load capability, it's not because of it's flying characteristics, or climb rate (I have a Jabiru 3300) at gross weight. It's simply due to the stated design limitation. I also admittedly fell for the advertised 620lb empty weight specification, but later learned that 660lb is more typical. Mine was 663 lbs before I added upholstery and wing tanks.

It's been asked, "why would anyone ever fly a plane beyond the gross weight design limitation?" Well, I think it's a combination of the above paragraph, and statements that have been make from various sources over the years. I've hear statements such as "the wings are built that same as race planes that typically pull 10 g's all day long", "it's built like a tank", "the wing didn't fail until 11 g's gross", and "it has a very generous load safety factor".

On the other hand I've also seen analysis that indicated the relatively weaker center portion of the spars will be in the "plastic" stress region of the material at as little as 2 g's. Not that it would break, but it would fatigue much faster in that area.

Having said all that, I think my main concern with this upgrade would be it's potential effect on maneuvering speed. In other words, will the wings still stall before they break? If so, what is the safety factor. I think the industry standard is 1.5. Would using these wing tips still provide the 1.5 safety factor. Only the Sonex factory could tell us, and they haven't been willing to say in the past.

I have the Jabiru 3300, so this modification doesn't really appeal to me as it would someone with an 80 hp engine. To be honest, I'd be interested in a reduced wing area modification for smoother ride, and maybe a little more speed. With the Sonex having a wing loading of 11 to 12 lbs/sqft, it can be a bumpy ride with it's fast cruise speed at times. For comparison, a plane such as the RV-7 has a wing loading closer to 15 lbs/sqft, where some Lancair have over 20.

With the reduced wing loading, I would expect a bumpier ride, and possibly more spar fatigue.

I do, however, hope this project is successful. It would be nice if the factory would adopt, and approve it, even if other structural changes are required.

End of Monday morning rant.