Glide performance with dead engine improves with wide open throttle (also with propeller pitch)

Steve6443 wrote:

The info about the Dakota surprises me, especially because I was flying an old Arrow, pulling the prop lever to low had a marked effect on descent rate.

On any aircraft with fixed gear, the effect of different propeller pitch would be less noticeable.

Airborne_Again wrote:

On any aircraft with fixed gear, the effect of different propeller pitch would be less noticeable.

Gear retraction would not explain much of the difference. At a given airspeed, the change in drag (and so the change in vertical speed) would be independent of whether the gear is up, down or welded.

The immediately notable difference I have observed is that on e.g. the Cardinal, pulling the prop back reduces windmilling rpm dramatically, while pulling pack the same lever back at about the same airspeed in the Dakota hardly changes RPM at all. This would not be affected by undercarriage differences.

The difference is bound to be in the prop governor (2 hard stops and 2 RPM limits) and prop blade geometry. Pulling the prop back will only improve the glide if the minimum governed RPM is significally lower than the normal windmilling RPM. Minimum governed RPM is not (usually) in the POH but it is easily checked on the ground. With the engine idling, pull the prop lever all the way back. Slowly add power – and when the RPM stops increasing (and the prop noise changes due to the prop starting to twist) – then that is the minimum governable RPM. Somewhere between 1000 and 1400 RPM is my impression of usual values.
Another difference is the fine pitch stop. That blade angle is in the POH (typical 11 to 16 degrees as I recall, measured at approx 3/4 radius). There is a certification requirement that says something like if the engine goes to fully fine (unregulated) pitch during full power climb at Vx, the engine must not overspeed. That requirement means that for the Dakota with a max RPM of only 2400 RPM, a higher low pitch value is required to avoid overspeed, than if the max RPM were 2700 RPM, which it is for the Cardinal and the Arrow and a lot of other piston engine installations. I suspect that the higher low pitch limit on the Dakota (16,25°) means that during normal windmilling, the RPM is already fairly low, and therefore not much can be gained during slow glides by pulling the prop lever back to obtain minimum governable RPM.

huv wrote:

Gear retraction would not explain much of the difference. At a given airspeed, the change in drag (and so the change in vertical speed) would be independent of whether the gear is up, down or welded.

In absolute terms, yes, but not in relative terms. So the improvement in glide ratio would be less with gear extended (or welded).

Peter wrote:

Peter

14-Feb-18 21:48

#14

I assume I can instruct in N reg Bonanzas.

That is country dependent.
In the UK, I don’t think so without going through some hoops with the CAA, because paid work in foreign reg aircraft is generally not allowed. Permissions were available for instruction and tests for the aircraft owner, basically. Only recently they have removed the need to get the permission for these flights. So this kind of thing has tended to be done outside the UK, usually in France. If there is no payment made for the flying (e.g. only ground tuition is charged) there is no issue in the UK.

In principal you are correct, however, no non EU citizen is permitted to work without the correct visa.
I have organised X2 such events for the Comanche Society (one of them with the help of another pilot who was local to the meeting location). In both cases the instructors were approached and agreed to come over. In one case the instructor refused any pay and insisted to pay his own way (however we forced his hand and covered his hotel stay) and in the other we have covered all expenses.

US DPE was forced out from doing checkrides in the UK

Wasn’t this due to the local resident DPE complaining to NYC FAA? The monopoly fees charged by said DPE means it is just as easy to go to Florida and get a local DPE.

Airborne_Again wrote:

In absolute terms, yes, but not in relative terms. So the improvement in glide ratio would be less with gear extended (or welded).

Just as is the case with flaps extension.

Peter wrote:

read this in the US AOPA mag

Peter, which edition / date was this or what was the title of the article? Thx