Clean I get a definite break at 45mph. Full flaps it just sinks at 45mph. Didn’t really try any slower. I’m spinning an 80 in prop at 680 rpm at idle. At that time I had about 20 deg pitch in the prop. This prop throws a LOT of air, even at idle!
Clean I get a definite break at 45mph. Full flaps it just sinks at 45mph. Didn’t really try any slower. I’m spinning an 80 in prop at 680 rpm at idle. At that time I had about 20 deg pitch in the prop. This prop throws a LOT of air, even at idle!
Jeff
KF 5
340KF
I think I have an idea why this happens, similar on mine where I saw a large decrease in stall speed clean and one notch but very little with full flaps. My thinking is that if the VGs aren't far enough forward, the airflow separates before reaching them at the highest angle of attack (full flaps), but they are very effective at the lower angles where they are in front of the separation point. On the standard wing, as I said above you can only put them so far forward.
I'm guessing you have a very forward CG. Are you running out of elevator? Adding flaps definitely gives a down pitching moment and makes it harder to hold your nose up.
Do you have the elevator trim assist spring? If so it might be good to take it out temporarily so you can feel the actual pitch forces.
FYI I have a forward CG too, but my plane is not as heavy. I am typically at 1200 to 1250 lbs flying weight. Each notch of flaps on mine decreases my stall speed by 3mph. At GW mine stalls at 49/46/43 mph. No VGs.
Phil Nelson
A&P-IA, Maintenance Instructor
KF 5 Outback, Cont. IO-240
Flying since 2016
the effect of the Laker leading edge should be showing up in how one measures the chordline for VG's, that doesn't seem to be taken into account in these random performance numbers so how can we compare? does the factory spec sheet help out there with some kind of baseline? (pardon me but I'm back with model IV wings)
and I would like to bring emphasis back to what was said earlier in this thread, VG's bring an extra factor of safety in the flight speed envelope ... to take that one step further, other pilots have shown that turning base to final while dropping airspeed has been shown to produce stall spin situations ...
and my take-away from this thread? nice to hear VG's on the horizontal being praised, a timely reminder for where I am in the rebuild ... this winter will be ideal for installing those ... and that would be going with the idea that it would provide the best effort / benefit ratio for flight control feedback / improvement ...