Strega Questions: Can It Be True??

[Sparrow]

Re: Strega Questions: Can It Be True??

Just a few items to answer some of the comments here. Roush as far as I know at this point is not recasting cylinder heads or skirts, still a very costly proposition. Roller cams are a proven and working commodity. Roush and Co. are producing some consumable parts for Merlins. They operate a certified repair station for the Merlin engine and are beginning to take on some projects. Their main scope thus far has been sub-assembly build up and repairing components. Sparrow

[Peashooter]

Re: Strega Questions: Can It Be True??

Well, lessee. Tip speed for an 8' blade at 2000 rpm, when the plane is chocked on the test stand = (2*pi*r*2000*60)/5280 = 1142.4 mph. Supersonic!

At 1500 rpm it's still 856.8 mph.

What I don't know how to judge is the effect due to the fact that in flight, the prop blade's advancing through the air at 400+ mph at the same time the tip's going around in circles at mach 1-point-something. I suppose if the effective angle of attack of the blade at the tip is zero it's equivalent to the static case, but in that case the prop's not doing much useful work, so I dunno, really.

I'm just making it up as I go along...

KH: Did they teach you that in glider school? Peas

[Sparrow]

Re: Strega Questions: Can It Be True??

Prop speeds:

Merlin with .479-1 reduction gears can turn 3250 RPM with full length (11'2") prop and tips will be subsonic.

Merlin with .420-1 reduction gears can turn 3600 RPM with full length prop and tips will be subsonic.

Information from P&W pocket field book with engine speed/prop dia charts and graphs.

Sparrow

[Wilnit]

Re: Strega Questions: Can It Be True??

Hey Sparrow, you Tige and Curt ready to win Reno or what??? Glad you all are back!!!

[Air Race Addict]

Re: Strega Questions: Can It Be True??

Prop speeds:

Merlin with .479-1 reduction gears can turn 3250 RPM with full length (11'2") prop and tips will be subsonic.

Merlin with .420-1 reduction gears can turn 3600 RPM with full length prop and tips will be subsonic.

Information from P&W pocket field book with engine speed/prop dia charts and graphs.

Sparrow

So Sparrow,
Wouldn't that make the prop RPM in the neighborhood of 1400? 1500 or so, max? (quick math). I think Matt's thinking that prop and engine RPM are the same. I know I mentioned it in another post somewhere that the Prop RPM is arond 920 at cruise, 1020 at TO on the Q400 with P&W 150's. The actual turbine is turning somewhere in the vicinity of 13000 rpm, (don't quote me on that), and is actually measured in percent.(HP RPM). And this is pretty typical for most turbo-props. I would think that it would also apply to Merlins and Cyclones, just different gear ratios. Just to add a little clarity to the conversation in case anyone is confused.