Here is some follow up data to my Posts #1 and #37 for my 9A 0-320, 9:1 C/R, C/S prop. Gross weight approx.1420 lbs, C of G 15 % aft of the fwd. limit
Timed glides done between 9,000 and 8000 ft (altimeter set on 1026 mb), OAT 8 degrees C. Smooth air.
Engine “dead” – mixture full out and both ignitions OFF
Prop full back (coarse)
Throttle at idle (full back)
70 kts IAS 73 seconds (822 f/m)
75 kts IAS 70 seconds (857 f/m) (900 ft/min on the VSI)
80 kts IAS 70 seconds (857 f/m)
85 kts IAS 65 seconds (923 f/m)
90 kts IAS 61 seconds (984 f/m)
All these above glides were done with the throttle out. After one glide (I think it was at 75 kts) I left everything the same except I pushed the throttle full in. Even though the engine was “dead” it immediately felt to be working harder and the rate of descent increased by about 100 to 150 ft on the VSI (at the same 75 kts)
I later attempted to stop the prop. With the throttle in and the prop coarse it had not stopped by about 49 kts so I gave up. Tried again with the prop full fine and the throttle out (I think) and it stopped at about 51 kts. Contrary to what I expected, the sink rate at 75 kts was 1000ft/min on the VSI which is a greater sink rate than with the prop coarse and windmilling (900 ft/min on the VSI)
Based on these glides, my min sink rate is 822 ft/min at 70 kts ISA and my best glide speed is 80 kts IAS with a glide ratio of 1 : 9.5 (engine dead, prop coarse). (please feel free to check my maths!).
I realise these results are not 100 % accurate as they are based on IAS (no TAS correction) but they are relative to each other and to my way of thinking will give the appropriate min sink and best glide speeds. I presume with a TAS correction the glide ratio would be better?? Someone like to do the maths?? My next task will be to redo the engine “live” glides and see if I can find an IAS that gives about the same 1 : 9.5 glide and this will be the speed I will do my engine “live”, practice forced landings.
I was careful to try to minimize shock cooling on the engine and found that with the aircraft gliding and the engine dead, I would only briefly get the odd shock cooling warning on the engine monitor (set at 50 degrees F per minute). Naturally there were more warnings at the higher glide speeds. To do these tests as accurately as possible it helps if you regularly tap the ASI and the altimeter so the needles don’t stick.
In summary, for my aircraft with a dead engine, the best glide speed is 80 kts IAS with the prop coarse (rather than stopped) and the throttle out.
YMMV.
Comments welcome.
Fin
9A
Edit: If we assume IAS =CAS (big assumption) and the maths is correct then the glide ratio at 80 kts IAS or about 92 kts TAS would be about 1 : 10.9