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peterz(at)zutrasoft.com
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 Posted: Wed Jan 27, 2010 3:14 pm Post subject: MG folding prop |
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The Carat has a neat idea for a prop for the MG wings - instead of a complex and heavy electrical prop (with all the failure modes that presents), it has a simple spring-loaded forward folding prop. The only downside is you can't wind-mill start, but that seems a small price to pay for the weight and simplicity. Short of throwing a blade, the only real failure mode would be prop open - the ideal default.
http://technoflug.de/referenzen.htm (the Carat with prop folded is pictured lower right)
I wonder if they are going to sell it outside the Carat product.
Cheers,
Pete
A239
[quote][b]
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Thu Jan 28, 2010 10:54 am Post subject: Re: MG folding prop |
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Hi Peter,
I am not sure what your criteria are for "heavy and complex".
To me, compared with certified hydraulic prop controllers are not on
both heavier and more complex but also more "stupid".
BTW: It is not possible to air-start a 912S in any case.
Cheers,
Ira
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terrys(at)cisco.com
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| Posted: Thu Jan 28, 2010 11:23 am Post subject: MG folding prop |
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Hi Ira,
I had also heard it was not possible to air-start a 912S, but it can be
done. We have done it with the Whirlwind prop and with the Airmaster,
both at about 110 knots. We were concerned about it in motor-glider
mode, both when it would stop windmilling after shut down (between 50-60
knots), and if we could do an air start if our battery went dead while
soaring with the engine off. The speeds worked out just right for our
needs.
Regards,
Terry
A135 / N135TD
XS with 912S, Airmaster prop, long and short wings.
--
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peterz(at)zutrasoft.com
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| Posted: Thu Jan 28, 2010 11:24 am Post subject: MG folding prop |
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Hi Ira,
Maybe not the 912S, but the 914 can air-start (as demonstrated to me by John in Lakeland a few years back).
I guess I should have said 'heavier' instead of heavy.
I consider any prop system which has multiple possible failure modes (other than the obvious throwing of a blade) which can result in loss of thrust (or reverse thrust) to be 'complex'. Personal opinion only, FWIW, YMMV, etc. etc.
If I could get beyond the lack of a streamlined spinner (prop folded out), the passive, forward folding prop seems to be an eloquent engineering solution for the long wings.... to me at least.
Cheers,
Pete
A239
On Thu, Jan 28, 2010 at 1:54 PM, rampil <ira.rampil(at)gmail.com (ira.rampil(at)gmail.com)> wrote:
[quote] --> Europa-List message posted by: "rampil" <ira.rampil(at)gmail.com (ira.rampil(at)gmail.com)>
Hi Peter,
I am not sure what your criteria are for "heavy and complex".
To me, compared with certified hydraulic prop controllers are not on
both heavier and more complex but also more "stupid".
BTW: It is not possible to air-start a 912S in any case.
Cheers,
Ira
--------
Ira N224XS
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[b]
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Thu Jan 28, 2010 5:21 pm Post subject: Re: MG folding prop |
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Hi Peter,
The 914 is a different kettle of fish when it comes to airstart because it
is a low compression engine (8.5:1 if I recall correctly) versus the 912S
which is 10.5:1. The required force to spin the prop to 600 rpm where
the ignition modules start to park is thus greater in the 912S
system. I was flying with John H the first time he shut-down the engine
in the 914 demonstrator and we battery restarted it. At the time, he
was the one who told me the 912S would not airstart because the
unaided airflow would not spin the prop fast enough. At the time he
had not ever shut down the 912S in the short wing demonstrator.
If a way to restart by air has been found as Terry says, that is a great
advance in my knowledge!
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rparigoris
Joined: 24 Nov 2009
Posts: 780
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| Posted: Thu Jan 28, 2010 10:35 pm Post subject: MG folding prop |
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Hi Ira"If a way to restart by air has been found as Terry says, that is a great advance in my knowledge!"I don't have any experiance with 912S, but with your ability to select course pitch on Airmaster, and ability to pitch nose at ground and quite easily select an airspeed in excess of 110knots, I have a hard time trying to figure that a combination of fine pitch (high gear)and fairly mild compression ratio (compared to a high performance motor) will not airstart a 4 cylinder motor with ~300CCs per cylinder. This takes into consideration gearbox, but also fairly large fan up front which is a pretty good force to be reckened with in hurricane speed wind. Course pitch of prop pseudo equates to a higher ground pounding transmission gear when bump starting. The hardest motor I ever encountered on a motorcycle trying to bump start was an all out road racing Cageva with a 2 cylinder Ducati engine with a compression ratio that was beyond high. Probably 500ccs per cylinder that absolute needed racing fuel octane. Several guys and top gear would in fact do the deed which is pretty amazing. This bike wouldn't think about idling below 3500RPM. The only thing I don't like about air starting a Rotax is once motor begins to spin up, it's going to go from stopped with no oil pressure to quite fast almost instantly. If you have cold thick oil on top of having a lot of oil drain away, that is not going to be a secret to long engine life. For a back up means of starting motor if starter will not do deed, this would be a good procedure to have figured out and information stored in your back pocket. Would you be interested in taking me for a ride over Brookhaven for a mission? We go up to 7500 or higher feet over airport, I will bring my variometer and we can shut off motor and test glide angle and sink rates with various configurations, windmilling prop course and fine, stopped prop course and fine and stopped prop feathered. By using GPS and variometer and altimeter readings we can fool with some different airspeeds into and with the wind. Once numbers are ground will have a better understanding of best thing to do. Of course with oil still warm we can practice air restarts. Ron Parigoris [quote][b]
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Fri Jan 29, 2010 2:00 pm Post subject: Re: MG folding prop |
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Hi Ron,
I have not tried powering down my engine as I don't see any point until
such time as I have my long wings. The data on inability to airstart
is direct from the factory. No real point in persevering over just how
much force at what prop pitch at what airspeed, etc. If Terry has done
it, that's great. I have tested my airframe at 110% Vne as per protocol during my Phase 1, 110kt is 15% below cruise.
I have compiled a great deal of test flight data as per the bootstrap method
outlined in John Lowry's great book. I have first cuts at my airframes
best Vspeeds etc and I believe I have posted those here in times past.
You and Wayne are of course always welcome for a ride! Just please
leave your memo pad at home.
Cheers,
Ira
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