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  #16  
Old 06-17-2004, 04:14 PM
John Slade's Avatar
John Slade John Slade is offline
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Quote:
if I could save a chunk of $ on the used tranny...
I was just mentioning it as interesting. Not recommending it. George is only using about 140 HP or so. I doubt that the stock transmission can handle 200+ HP continuous. I sure wouldnt want to be the one to try it.

Spend the money. Get some piece of mind
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  #17  
Old 07-03-2004, 01:05 PM
Dale_R Dale_R is offline
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Quote:
Yes, jacking up the Cozy (making it a misquito-zy) makes for some interesting boarding problems. I wonder if you can put internal fuel cells on a gimball?

At least bring a milk crate....no sense in diving into the cockpit, unless you're Indiana Jones

hmmmmm. could Dust be right again? naw!
Actually, I could see an application for a variant of
the idea. Think: a two-position gear down. Position 1:
normal attitude. Going down, gear hits first limit switch,
and stops - gear down light goes green. For soft field
take-offs, gear could be extended a few inches by overriding
the limit switch - when gear hits next limit switch, another
light (blue) goes on. No changes in strut lengths, wheel
well, or gear up procedure.

Just a thought,
Dale R.
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  #18  
Old 11-19-2006, 04:42 AM
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tnt tnt is offline
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Default Performing props for rotarys

Quote:
Originally Posted by John Slade View Post
Not me. I was out flying among puffy blue clouds with 100 miles visibility and 47F OAT. Wow!

Compared to 97F the take-off run is kinda short. I'm at pattern height half way down the runway. Yah hooo!

Nothing else to report on the flight. Everything worked.
Hey John, hows that adjustable pitch Ivo performing for you? You still have it? I get the feeling that you're not getting the cruise performance you'de like with it. You're probably not getting the rpm's you're capable of or cruise speeds. I think I have the answer. Really.

It's late and I want to go to bed but I'll give it a shot. You can get beyond peak-torque rpm to where greater horspower is found. Of course greater horsepower should result in greater speeds. Bottom line, use a shorter propeller. This is contrary to what I've been thinking all along.

I've always assumed that smaller diameter propellers mean less power, and less efficiency. My assumption was you always wanted as long a prop as you could and that to get a prop to spin faster you would flatten the pitch but you never wanted to go shorter. Flatter pitches to me mean better climbs but not faster speeds and shorter props meant spinning wheels to me. And I thought that with a constant or adjustable propeller it was just a matter of finding the best balance between pitch (for that length), rpm, and airspeed.

But still, in the case of the rotary's with their peaky torque curve, a larger propeller would tend to limit rpm's at the peak-torque rpm. And this limits the horsepower.

So how does a shorter propeller help here? A propeller blade isn't only a wing, it's a lever. And the longer the lever arm the more force it applies on the prop hub working against the motor. bing! It makes sense to me that the outermost section of a prop blade contributes significantly to the force that the blade applies on the prop hub. Shorten that lever-arm and the motor can go faster and horsepower output goes up! Increased horsepower should mean faster speeds and better climbs too.

What about propeller efficiency? I can't say myself but earlier this evening I looked at Phillip Johnson's page on propellers. http://www.canardzone.com/members/Ph.../propeller.htm
Read what he claims for Myth #2. I'd bet prop money on that myself.

A few months ago I watched a guy fly an electric airplane with a tiny propeller. The wingspan was about 36inches and the prop diameter was about 2inches. I thought "man that thing is ridiculous!". But I was amazed when he launched it how it went vertical until it was only a spec. It ran against my understand of small props.

Anyway...........

I still intend on dyno-ing my motor before mounting on the airframe so I'll know what it's putting out and help a prop guy, help me, pick an appropriate prop.

Thoughts?
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Last edited by tnt : 11-19-2006 at 04:52 AM.
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  #19  
Old 11-19-2006, 07:26 PM
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John Slade John Slade is offline
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Interesting. Phil Johnson usually knows what he's talking about. I wonder where his data comes from. Those graphs LOOK convincing, but they represent an enourmous range of prop sizes, and I'd expect much larger variances in the results. Presumably the pitch is much higher on the smaller props. You can't just vary pitch indefinately. There has to be a point where the blade stalls - no?

Yes, I still have the IVO, or should I say I still have AN IVO. Actually I have two. The one on the plane is 68 inch, 3 blade. It provides LOTS of thrust on take off, but I havent done much "cruising" with it yet. The other one (which suffered a little FOD) will be a 64" 3 blade when I get it back from IVO, so eventually I should be able to supply practical experience data on the difference. I know Buly's operating his 68"? IVO as a 2 blade which gets him a much higher static rpm now that he's removed the turbo. This works well for take-off and climb, but may not get him enough thrust to achieve the higher speeds. Time (and hopefully Buly) will tell. I will also be able to experiment with 2 and 3 blade configurations, but changing the blades around is a pain because you have to retorque it every flight for the first few hours which means I can't use the spinner.

When it comes to high speed cruise obviously the efficiency of the prop is very important, but it also has to be able to absorb the power and turn it into thrust. I suspect a two blade IVO at max pitch will let the rpm get too high without producing the thrust. I dont have any evidence for this - just gut feel. Personally I'd rather keep the engine around 5000 - 6000 with 6300 - 6500 as a red-line. If I remember the numbers correctly, I was able to turn my high pitch Performance wood prop at the 6100 rpm sweet spot (engine - 2.17 ratio) for a straight & level speed of 190 kts IAS at 11,000' ft. Clark Lydick designed that prop for 6300 (engine) max rpm and I expect that it's VERY efficient at that speed. I doubt that the IVO will be as efficient at these speeds, but the additional pitch availability might make up for this.

As I say, I haven't had a lot of chance to experiment with high speed cruise since the initial flight testing with the Performance Prop. The wheel pants have only recently gone back on, and I'm waiting for a few more hours and torquing sessions before fitting the spinner. When I get a chance I'll see how the 3 blade 68 IVO handles high power cruise and will report the results (including altitude and OAT). At some later date (no promises when) I'll try the same tests with the 64 inch blades.

If someone had to make a prop decision for a rotary today I'd recommend the IVO from what information and experience I have so far. It certainly costs MUCH less to make a mistake - a full set of replacement blades is only around $750. If you get a severe ding in a wood prop you're out $2000+ and have to wait a while to get a replacement. With the IVO you can run on two blades, or get them to ship one replacement blade for about $300, usually in less than a week. The variable pitch means that you'll have no trouble on take-off and climb during flight testing (when this capability is very nice to have). Maybe later, once you've perfected you're landing techniques and can handle the longer take-off roll, it might be interesting to try a cruise pitch Catto optimized for 200+ mph and 200+ HP at your choosen max rpm. I suspect this might provide better "pedal to the metal" speed but I wouldnt start off with it.

What we're after in the long run is good take-off capability and maximum cruise efficiency (not max speed) in the same prop. I think the IVO is more likely to satisfy these criteria than any fixed pitch prop. Pity the LCY guys (and the CONT guy) can't use it.
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  #20  
Old 11-19-2006, 11:17 PM
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I'd agree on not being able to increase pitch indefinitely to make-up for shorter lengths. Last night I did make a minor effort to try to see what size your Performance Prop was. I thought it was something like 72-74 inches, after the asphalt trim. With Nat's 70" max recommended length I thought you might have some length to trade for rpms. But now with your 64 and 68 inch Ivo's, I wouldn't think you have excessive length. I can understand wanting to keep your rpm's at 5000-6000 which is where your peak-torque should be. Above that you may not be getting a fair trade of extra heat, fuel-flow, and spewed lubricants for increased speeds.
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  #21  
Old 11-20-2006, 06:13 AM
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Kumaros Kumaros is offline
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[QUOTE
if I could save a chunk of $ on the used tranny...[/quote]
To quote Eddie Murphy: who's spent all night at the chicks with dicks pages?
Seriously now, please keep the information on the IVO coming. I'm sure it's the optimal choice for would be canardians strapped for cash.
Kumaros
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