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

I read it somewhere a while ago but have yet to test it.

As an engine out & emergency landing procedure it is questionable because with fully open throttle, depending of the nature of the engine problem, there is a risk that the engine will roar to life just as you line up for that perfect low final to the short but adequate landing site with tall trees at the end. I know you are supposed to close the mixture and cut the ignition but in the heat of the moment, in an actual emergency, that could be forgotten.

Still interesting, and makes for a better understanding of the engine as an air pump, which also explains the mystery of why the manifold pressure moves when changing RPM without touching the throttle…

I have not played with throttle position in the glide, but the Prop control on My Bonanza has an enormous effect. With the prop set to anywhere near a normal setting for powered flight (above 1800 RPM), the prop is driven by the air stream and is up at the mechanical hi speed, low pitch stop. Until I lower the Prop control to a point where it comes off of the low pitch stop, the RPM remains around 1600 to 1800 RPM and the descent is roughly 1400 FPM at best glide. Pulling the prop control to the rear stop lowers the RPM to 1100 to 1200 RPM, and the best glide descent rate reduces to 800 FPM. One has to pitch up to a near level attitude to maintain the more efficient glide and the acceleration is very noticeable as a function of the Prop control position.

NCYankee that’s very very helpful, thank you ! Did you make pulling the prop lever part of your emergency procedure and if yes, at what point ?

NCYankee, that is indeed interesting! As someone who has barley experimented with prop settings, it is very interesting to know it could be a game-changer in a glide…

Isn’t all this very dependent on engine architecture? Can this apply to any gear-reduction equipped engine?

There has been a very nice little series of such experiments made by Barry Schiff, which appeared in one of his videos. Don’t know if this episode is now on youtube or similar.

EuroFlyer wrote:

NCYankee that’s very very helpful, thank you ! Did you make pulling the prop lever part of your emergency procedure and if yes, at what point ?

I am an ABS BPPP (Beechcraft Pilot Proficiency Program) instructor and it is part of the glide demonstration. It is also listed in the POH as part of the Emergency Procedure, Maximum Glide Configuration:

1. Landing gear – up
2. Flaps – Up
3. Cowl Flaps – Closed
4. Propeller – Pull for LOW RPM
5. Airspeed – 105 Kts

If the engine failure is not catastrophic, such that you have oil pressure, then the prop governor should work and failure to pull the prop control to the full aft position only reduces the glide. In BPPP training, it is such a dramatic effect, you won’t forget it, so it is standard to demonstrate it. I would recommend pulling it as soon as you can while you troubleshoot. If you notice an un-commanded increase in the prop RPM and the oil pressure is zero, the engine is likely to seize within a minute when a rod punctures the case. The POH says the following:

Propeller Overspeed

1. Throttle – retard to red line
2. Airspeed – reduce
3. Oil Pressure – Check Warning if loss of oil pressure was the cause of over-speed, the engine will seize after a short period of operation
4. Land – Select nearest suitable sited and follow emergency landing procedure

I have added an additional step, after retarding the throttle and confirming the oil pressure, I recommend immediately pulling the fire wall shut off. Every case I am aware of where this happened, the cockpit was immediately filled up with white smoke from hot oil smoke entering the cabin to the point that the pilots reported they could not see the instruments. The only good news when a catastrophic engine failure occurs is that the prop often stops or the rotation is greatly reduced, this enhances the glide as well.

Jan_Olieslagers wrote:

Isn’t all this very dependent on engine architecture? Can this apply to any gear-reduction equipped engine?

Yes, the bigger engines create more drag as does a three blade prop over a two blade prop. Of course with a fixed pitch prop, one would need to get the prop to stop to improve the glide. If altitude is abundant, it might sometimes be worth slowing the aircraft to the point the prop stopped and then resume the glide.

Good to know that. I’ve done most of the BPPP online seminars but must have missed that point somehow ! Would like to attend one of the real course but afaik they’re not offered in Europe….