Jocelyn

Hi Mark,

I sent you a PM instead of a message here - got all the words in one post!

Hi Mark,

Start reading from the bottom post!

Are you following the French P/V Yahoo group? Unfortunately the one person who was building one gave up because it was too heavy. He didn't fully explain so I don't know if it was too heavy for the engine/power or too heavy for European regs. Shame, I was looking forward to his progress reports. If my test flight isn't a disaster I'll update the old P/V thread. Let me know what you're up to if you decide to build.

Cheers,
Leland

So, I did a bit of a redesign using the Fraser F5 13% airfoil and the stability and trim characteristics are just perfect for an ultralight with a 60 mph max speed. The airfoil Cm is almost zero so it's easy to balance out the moments over the speed range - max elevator deflection is less than 10%. I've just completed a 1/5 scale model and am waiting for a calm day to test fly it. One thing that does concern me for the full size model is the really narrow CG range - half an inch makes a huge difference on trim and control. But I guess if the Pelican flew nicely it should be possible to get it close to optimum.

Hi Mark,

I gave up trying to analyze the Vampyr given what I saw in the plans. One thing that really puzzled me was when I put the airfoil coordinates into several different programs the results always showed a negative pitching moment - surprising because of the reflex TE. But then looking on airfoiltools it shows a positive Cm which makes more sense. Then there's the slanted thrust line which appears to create a positive moment - nice to offset a negative airfoil Cm but not for a positive Cm. The lack of angle of the wing confused me as well (the Pelican has a positive AOI which I get). I think the Pelican was balanced and stable at its slow flight speed but any faster (ie: Vampyr with a larger engine) and the trim calculations don't work out. (I'm out of characters so another message coming).