ASH25M -> Technoflug prop vs AS prop?

[Nik]

Hi all,

I recently bought an ASH25M, which still got the Technoflug prop. Now many PPL advice to go for the AS prop. I asked Schleicher and Rolf went like: "At least we can repair it, if it has a crack or so." - But I could not manage to get information about performance.

Anyone switched to the AS prop? Is there some worth mentioning difference in performance? Like aceelartion or climb rate? What about weight difference?

Thanks in advance for any hint, Nik

p.s.: If anyone is looking for an ASW27, I just got one too much ;)

[jfitch]

I do not have numbers for you. The reason for the change to the AS prop was supposed to be for acceleration, particularly operating off grass runways, not climb rate performance. Comparing climb rates on the ASH26 between Technoflug and AS there does not seem to be a lot of difference. I changed the engine (to injected) and prop together in a 26, and got a substantial improvement in climb performance (about 25%). I cannot say how much is due to the engine and how much the prop. The AS prop is heavier (it says this in the TN) and when you change it you must also change the lower drive cog and guide (27T replacing 26T) as the ratio is different. This makes the belt tighter so you hope there is enough adjustment left in the screws, otherwise the arms must be changed as well. It is not a simple bolt on.

[JS]

The engine bay doors may need adjustment over the root of the blades for the AS prop to fit.
My only experience is flying the same ASH25, as an M then an Mi. The better climb is probably more from the horsepower improvement, but if I remember correctly that happens at a slightly higher RPM than the non-injected engine, and the AS prop will turn faster.
It's been years since comparing the two.
Jim

[waremark]

I seem to remember from the ASH 26E documentation that the ground roll reduced approximately from 300m to 200m. Engine RPM at wide open throttle is signicantly higher with the AS prop, to the extent that you have to throttle back very early after coming off the ground (RPM over 7,500 was allowed IIRC for only 20 secs, though I used to leave the throttle wide open for a bit longer). Quoted climb rates and cruise speeds did not change.

[jfitch]

The max on the original 26 (carbureted) is 6900 continuous, 7500 for 3 minutes, 7800 for 20 seconds. Mine (Technoflug) would not achieve more than 6900 at full throttle and 51 knots anyway. The specs are the same for the AS prop, except the ratio has been changed from 3:1 to 2.78:1 so the prop itself is turning faster at the same engine RPM. Reports are that the flatter pitch of the AS prop allows the engine to run faster. The Mi engine specs are 7100 continuous, 7750 for 3 minutes, 8000 for 20 seconds. Also in some models, the ratio was changed again, this time to 2.68:1 so the prop runs faster still (presumably to absorb the additional horsepower without having to throttle as much). My ASH26 Mi (with 2:68 gearing) will run about 7550 rpm at full throttle and 51 knots. No need to pull the throttle until the 3 minute mark has been hit (the small Illec will beep) or temp has been exceeded (I've not seen this). There is at least one 25 Mi owner who has also changed the ratio to 2:68 and reports noticeably improved climb over the original 2.78. The 2:68 gearing was delivered in (at least) the 30, 32, and later 31. The change to 2.68 is not without complications, you may want to email me or Rex at Williams if you are contemplating this change.