Has it been measured?

[brs]

I am batting ideas around as to how to best pre-rotate my next gyro (tandem 2 place). A work in progress.

I will be using an IO-320 (actually IOX-340) but without mags (lightSpeed ignition). I was thinking of trying to use the accessory case mag pad(s) or other accessory spot (vac pump) to drive the pre-rotator. Either hydraulic or with a V-belt adaptor. But I don't know how much the accessory drives can be loaded.

Then I began to wonder "How much power/torque/whatever does it take to rotate a set of 28' blades to 250 rpm?". Has anyone measured this or have reasonable calculations?

Thanks in advance.
-brs

[Friendly]

I don't know the torque but this will get you in the air with plenty of RPM. I think Bill's normal spin up is 180 with 25 foot rotors, If you engage while taxie the torque requirment is less since the air is helping to drive the rotor.

[Dennis D]

Hi Brock.

Here are some torque specs for the accessory drives.

http://www.luscombeassoc.org/tc/Lycoming/1E12,%20IO320.pdf

Dennis

[brs]

I don't know the torque but this will get you in the air with plenty of RPM. I think Bill's normal spin up is 180 with 25 foot rotors, If you engage while taxie the torque requirment is less since the air is helping to drive the rotor.

Friendly - that is the kind of setup on my Vortex. I get 200 rpm out of it. Still my question is more of from an engineering standpoint as if I were to design it on paper first and want it to work with out guessing or figuring "Ah good'nuf".

BTW - I'd like to see more than 200 rpm and run it off the back of the engine if possible.

Here are some torque specs for the accessory drives.
http://www.luscombeassoc.org/tc/Lyco...2,%20IO320.pdf
Dennis

Thanks Dennis this is the kind of stuff I'm after. It's interesting to see that the prop governer can handle the most load. Do you understand what the Static (starting?) and "max overhang Moment" mean? 125 inch pounds does not sound like a lot compaired to moving a rotor.

[Mike G]

brs
From a mixture of measurementss and calculations I've made over the years, you need 7.5 kW (10 HP) to spin a 27 ' (8.2m) Magni rotor to 250 rpm.

Mike G

[Dennis D]

Brock.
I think what they mean by "Max Static Torque" is the max torque the drive can handle.
Say like when an accessory is first starting there will be an inertial load until the accessory comes up to its continuous operational RPM. Or maybe a maximum "intermittent" load torque. I'm not sure, both of those are assumptions.
My guess is they are referring to the mounting area regarding the "max overhang moment" but again that's just a guess.

[Dennis D]

Brock.
Make sure you consider drive rpm also. It looks like at 1500 prop RPM, the alternator drive will be at 1218 RPM while the prop governor only 335 RPM.

[Mike G]

Max static torque is exactly what it says, it is the max torque the material the parts are made out of can handle when nothing is moving. Once you start to rotate the parts you have to reduce the torque because as it goes faster you have to consider the power being transmitted and the fatigue loads that come from bits being slightly out of line and vibrating. Power is torque times speed and in transmitting power from one part to another there are always losses and those losses show up as heat. The more power you transmit the more heat you generate, when you're static no heat is generated.

Max overhung moment is the weight (lbs) of the part (say the starter) times the distance (in inches) from the mounting flange to the CofG of the part. It's not clear if this is refering to the moment that the flange can accept or the moment that the drive shaft can accept. Looking at the numbers I'd say it's what the drive can acce^pt but I don't know for sure.
Mike G

[brs]

brs
From a mixture of measurementss and calculations I've made over the years, you need 7.5 kW (10 HP) to spin a 27 ' (8.2m) Magni rotor to 250 rpm.

Mike G

Mike this is just what I needed - thnx!. I'm hoping someone can confirm this with similar information. But if not, this certainly gets me in the ball-park (information wise). Since the power required is sure to be logarithmic it would be nice to know what the curve looks like. Do you happen to have information to rotate to 200 rpm, 180 rpm, etc?

Make sure you consider drive rpm also. It looks like at 1500 prop RPM, the alternator drive will be at 1218 RPM while the prop governor only 335 RPM.

I realize this. Fortunately, as long as the power is available things can always be geared. Unfortunately, I don't think there is any safe way to extract 10 hp from the accessory case. I spoke to an engine builder guru at ECI this morning and he said they load the the prop governor to 1 hp for several hundred hours in testing (something like that). He promised to email me with more specific information on the various accessory pads.

[Mike G]

brs
Attached is the curve I plotted. You can see the test points up to 230 rpm and the curve fit equation that goes up to 450 rpm. I used a 3rd order equation because propeller power is a function of rpm cubed. I don't think this is correct because I'm sure the curve should rise faster after 250 rpm.
Mike G

[PW_Plack]

Mike, if the numbers assumed are winding up with a suspiciously low HP requirement at operating RPM, perhaps start with known horsepower required for flight RRPM, and work backward? We wouldn't need the whole curve to answer Brock's question about a specific RRPM, although it would be nice for calculating loads at other RRPM.

I used Chuck Beaty's rotor performance calculator, (found in this thread (http://www.rotaryforum.com/forum/showthread.php?t=14834),) and plugged in 1,000 pounds all-up weight, 28' rotor diameter, 8.5" chord, and it looks as though the total power consumed by the rotor at 30 MPH IAS is about 33 HP at 344 RRPM.

Working backwards, 250 RRPM is .727 of 344; the cube of .727 is .384; 33 HP x .384 would be 12.7 HP.

This is really rough, and I don't know how to adjust for zero airspeed, but it looks like it lands in the right neighborhood.

[Friendly]

Brock,
Bills set up is like your setup except the drum size is 12" He has the horsepower available but you must let the rotors build up to speed or you will wear out your drive wheel. Increase your drum size and you will get more out of your vortex.
It will be interesting to see how you decide to go and the results. I hope you will post something when you decide which path to take.

[Mike G]

Paul
I am quite confident that, within the limits of experimental accuracy, my results up to 230 rpm are pretty well in the ball park for my rotor on the day I did the measurements.
I assumed that the curve will rise more rapidly than it does because I suppose that as the rotor gets nearer to operating speed the induced drag and turbulance will play a greater part than it does at lower speeds. I'm a mechanical engineer so working out the torque/power is in my sphere of work, the impact of induced drag is not my department so it's just a hunch.
Out of curiosity I ran the curve from 230 rpm as a straight cubed curve and it looks a little better (to me).
Interestingly at 344 rpm it gives about 28 HP which isn't too far from CB's 33 HP.

[Mike G]

I've added CB's 33 HP and extended the simple cubed curve back to zero.
Mike G

[PW_Plack]

Brock, looks like you should plan on at least 10 HP, probably more like 13-15.

This might also vary with blade manufacturer. As an example, Sport Rotors are normally sized to run at lower RRPM than Dragon Wings, so 250 RRPM would vary as a percentage of nominal flight RRPM.

I also don't know if CB's spreadsheet was made to track properly with chords as wide as 8.5".

[brs]

I've added CB's 33 HP and extended the simple cubed curve back to zero.
Mike G

Ha, Mike I started reading at your first post and saved the xls file then I saved the second xls file when I came to it then I read your last post and saved again. I should have started looking from the bottom up.

Thanks both Mike and Paul. This should be enough information to get me going. Good stuff and once again the forum comes through where my experience falls short.

[Mike G]

brs
Don't forget that the power we're talking about is at the rotor hub. You will have power losses in your bendix set up, your flex drive (or right angle gear drive) and your clutch. Add another 10 or 15% to get the power you need at the engine and clutch.
Mike G