LeSving wrote:
That I have never tried with a Rotax. Will a Rotax windmill, or will it stop?
It will windmill as long as the airspeed is above 60 kts. According to the POH a still standing propeller will start to turn at 120 kts (for “manual” restarting of the engine).
With all respect, @MedEwok, I don’t think such a blanket statement can be made. Too many variables. What you state may well apply for one particular type of plane, or rather for a given type of 912 and a given propeller with a given blade angle (if ground adjustable, as most are). Just for one illustration: 120 kts is well above Vne for my 912-powered ultralight, so your statement could never apply.
Jan_Olieslagers wrote:
With all respect, @MedEwok, I don’t think such a blanket statement can be made. Too many variables. What you state may well apply for one particular type of plane, or rather for a given type of 912 and a given propeller with a given blade angle (if ground adjustable, as most are). Just for one illustration: 120 kts is well above Vne for my 912-powered ultralight, so your statement could never apply.
Of course you’re right. What I wrote is applicable for the Aquila A211 only. It does show however that a Rotax 912 can windmill
Yes, of course it can. But the question was will it 
If the POH says it will start rotating at 120kt then that “should” have been tested. On an ICAO certified aircraft one can be damn sure that number would have come from a flight test. The Aquila A211 is a VLA, and I don’t know the protocol for those.
The problem is that if a prop actually stopped (and you didn’t do some stunt to achieve that deliberately, like described higher up above) then it is pretty unlikely it is going to restart at any airspeed. If it windmills above 60kt (again, has this been flight tested?) then it isn’t going to just stop randomly. If it stops then maybe all the oil has gone.
Peter wrote:
The Aquila A211 is a VLA, and I don’t know the protocol for those.
Many years ago I was at a flying instructor seminar where the test pilot of the Aquila gave a talk. AFAIK, the test program was almost identical to that of a “regular” part 23 aircraft. Anyway, if there are numbers or procedures in the POH which were not obtained by flight testing but by theoretical considerations instead this must be clearly stated.
Peter wrote:
The problem is that if a prop actually stopped…
You are certainly right. If it stops by itself above typical windmilling speeds then it is better left alone with all efforts dedicated to a decent forced landing… Also what people often forget is that there usually is a choice of propellers which can be fitted to any particular aircraft and which behave differently in that respect.
there usually is a choice of propellers which can be fitted to any particular aircraft and which behave differently in that respect.
as was already pointed out in #22 above. In fact even “the same propeller” may well be set to a different blade angle, making it NOT “the same propeller”. Though I do not know how that works with certified planes, which indeed includes VLA’s. Is re-approval/certicifation required after adjusting the prop?
Generally speaking, it was always my impression that the difference in legal terms between a VLA and a “real” aeroplane such as a C152 or PA28 is very very limited.
Jan_Olieslagers wrote:
Generally speaking, it was always my impression that the difference in legal terms between a VLA and a “real” aeroplane such as a C152 or PA28 is very very limited.
I don’t know what paperwork is involved, but at our flying school we have – otherwise identical – Cessna 152s one of which has a “climb prop” and the other one has a “cruise prop”. The first one is better for pattern work but lacks some knots in cruise speed and the other one is better for cross-country flying. I am not aware that the manuals (both of which are the very worn and stained originals from the 1970ies) are any different.
The limits for a fixed pitch propeller on a certified aircraft are given in the TCDS. Usually there is manufacturer and model data (often more than one), diameter limit and minimum static rpm. Anything that fits within the spec is legal and the AFM doesn’t address every possibility. In relation to windmilling, there is a lot of variation other than pitch, for example wood props have a lot less inertia to carry them through engine compression and therefore stop at a higher airspeed than metal props.
Peter wrote:
If the POH says it will start rotating at 120kt then that “should” have been tested. On an ICAO certified aircraft one can be damn sure that number would have come from a flight test. The Aquila A211 is a VLA, and I don’t know the protocol for those.The problem is that if a prop actually stopped (and you didn’t do some stunt to achieve that deliberately, like described higher up above) then it is pretty unlikely it is going to restart at any airspeed. If it windmills above 60kt (again, has this been flight tested?) then it isn’t going to just stop randomly. If it stops then maybe all the oil has gone.
Durch Andrücken des Flugzeuges auf ca. 120 kts kann der Propeller zum Drehen gebracht und der Motor daraufhin angelassen werden. Es entsteht dabei ein Höhenverlust von ca. 1000 ft / 300 m.
The procedure for restarting the engine with the propeller still windmilling says right at the beginning:
Bei abgestelltem Motor dreht sich der Propeller bei Fluggeschwindigkeiten > 60 kts.
When the engine is turned of, the propeller will windmill at airspeeds > 60 kts (my translation)
As for turning shutting the fuel off, as suggested by what_next in an earlier post, that is of course also possible. The fuel switch on the A211 has a “right”, “left” and “off” position.
Of course as Peter says wheter the prop will start turning at all depends on the reason why it stopped in the first place. Much like with cardiac arrest actually, something I’m much more knowledgeable about
