Glide performance for SEP(L) Pipers
I wonder about the book glide performance figures for different PA-28 models.
From instructing on Piper Warriors (PA-28-151) I know the book glide performance of 2,1 statute miles per 1000 feet, corresponding to a best glide ratio of 11,0. I always considered this a little optimistic (glide performance figures usually are) but I have never done a flight test.
For myself I often fly a Piper Dakota (PA-28-236), which has the same wing, a slightly longer fuselage and a somewhat larger engine with a c/s prop. Until today I never checket its book glide performance although I often consider gliding distances when crossing domestic waters here in Denmark. But according to the book the Dakota glides only 1,30 NM per 1000 feet, or a best glide ratio of only 7,9.
This is a very large difference - 40% - between two very similar airplanes.
If the difference is real, I cannot think any other significant reason than the greater drag of windmilling the larger-displacement engine in the Dakota (O-540 vs. O-320).
But could it also be different ways of compiling glide data for presentation in the handbook? The Pilot's manual for the Warrior seems older than that for the Dakota; maybe the FAR 23 was changed in-between? There is no clue in the CS-23, but I do not not have the older standards. (The Archer II, PA-28-181, with an O-360 engine, is the ~same vintage as the Dakota and its glide ratio is 9,9 according the AFM. This seems to support that the difference is due to the engine.)
Yes, I do intend to test it, but not until summer with more pleasant air temperatures for the engine.