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5 Answers

Glide Configuration

Asked by: 5412 views Aerodynamics, General Aviation

If performing a glide with a constant speed prop. (assume piston single engine, not piston multi-engine), The FAA Airplane Flying Handbook says on pg. 3-17 to place the prop. in the low pitch (high RPM) position.

Why is it stated this way?

My reason for this question is that placing the constant speed prop. in the low pitch position creates more drag and degrades the glide or reduces the glide range. If placed in the high pitch (low RPM) position, the prop is more streamlined to the relative wind and reduces drag. And of course with full feather props., placing the prop. in the feathered position is essentially putting the prop. beyond the high pitch limit to aid in an even better streamlined position of which reduces drag.

Any feedback appreciated.

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5 Answers



  1. John D Collins on Jun 19, 2014

    Good catch Dan. It is a clear error, report it to the FAA. FYI following their incorrect recommendation, my Bonanza descends at 1400 FPM, but as you suggest, with the prop control pulled to the rear stop, it descends at 800 RPM.

    This handbook is published by the U.S. Department of Transportation, Federal Aviation Administration, Airman Testing Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125. Comments regarding this handbook should be sent in e-mail form to AFS630comments@faa.gov.

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  2. Dan Chitty on Jun 19, 2014

    Thank you for the feedback John.

    I will submit the error to the department you mention and I will share their feedback to this post once received.

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  3. Dan Chitty on Jun 19, 2014

    Here are some additonal thoughts I found in the Airplane Flying Handbook:

    1.Power off stall diagram (figure 4.5) page 4-8 illustrates to retract /raise flaps after lowering the airplane nose as the diagram illustrates the airplane nose pointing downward at mentions “raise flaps as recommended”. Page 4-9 top left paragraph states to retract/raise flaps after positive rate of climb is established. Is the diagram 4.5 correct or is the language in the paragraph on page 4-9 correct?

    2. NOTE: This question regarding go-around procedures is based upon the following: Assume the POH/flight manual does not have published go-around procedures as some older POHs/flight manuals are absent of go around procedures. In this case, my understanding is to follow the guidance in the FAA Airplane Flying Handbook.

    Go-around procedure diagram (figure 8-14) illustrates the aircraft in a climb attitude and to retract flaps to an intermediate setting. The first paragraph under the configuration section page 8-12 says flaps may be partially retracted after descent has been stopped and does mention to assume a climb attitude and flaps adjusted to an intermediate setting.

    Which is correct—8-14 diagram or language in the paragraph for this particular phase of the go-around? In other words, should one partially retract flaps after descent has stopped and then adjust to climb attitude? Or…. Adjust to climb attitude and after the attitude is established then partially retract flaps?

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  4. Brian on Jun 26, 2014

    “my Bonanza descends at 1400 FPM, but as you suggest, with the prop control pulled to the rear stop, it descends at 800 RPM.”

    If you’re ever in the NJ area I’d like to take you to lunch and in the meantime you can demo this for me. Since reading this I’ve done my own tests in two different Bonanza’s. While I found a notable difference, roughly 100-150 FPM, I’ve been unable to replicate your near 200 percent increase in glide efficiency. Am I doing something wrong.

    PS, Flying best glide adjusted for weight.

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  5. John D Collins on Jun 30, 2014

    Brian,

    I have an IO520BA with a three blade C406 prop. I reduce power to idle, which is about 600 RPM static. In the air, my RPM drops from the vicinity of 1800 RPM to 1200 RPM depending on where the prop control is set. Different aircraft will give different results because of Prop differences (2 blade seems to have less of a penalty): engine idle differences (I see some which have idle set as high as 1000 RPM static and thus deliver more power at idle than mine is set up for; and finally, the prop governor and the the mechanical prop stops can be different between aircraft and thus limit drag on both the high end and on the low end.

    On the lower powered Bonanzas IO470 with a two blade prop I see less of an affect. Also at lower weights the glide speed if adjusted will be slower and thus generate less drag at the high RPM setting. I use a glide speed between 100 and 105 Kts in my V35A, 3400 Max GW. When I glide in the high drag landing configuration, gear and flaps down, speed is lower near 80 to 85 Kts and at the lower speed the difference although very noticeable is much less.

    As a BPPP instructor, I demo this to all pilots on insurance checkouts and during BPPP program training. I suggest you note the RPM differences as well as the static RPM at idle.

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