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Prop Effency

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NeilsenRM(at)comcast.net
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Posted: Mon Oct 16, 2006 8:01 am Post subject: Prop Effency

Richard



I changed the Subject



Prop efficiency is at least partly related to how fast the prop has to 

accelerate the air it is moving to get thrust. A small prop has to 

accelerate the air allot more to get its thrust and gets a smaller 

percentage of the input power changed into thrust. A large prop moves more 

air so it will need to accelerate the air less and gets more thrust for the 

same power. Now a prop with more blades is less efficient than one with less 

but is less pronounced than the, large verses small prop differences.



You are right that as you increase the volume of air that you move with a 

prop for the same power the speed range that the prop produces thrust gets 

smaller. At some point when increasing the prop area diameter, blade cord, 

and number of blades you have to pitch for climb or cruise. The advantage of 

a in flight adjustable prop is that doesn't have to stay at one setting it 

can get more thrust in both climb and cruise.



I don't think that the high fuel consumption is a result of the additional 

prop blade in this case unless he is cruising allot faster.



I base my claims on observations I have made on my airplane with two 

identical engines one turning a two bladed 60 inch prop at 3200 RPM and the 

other turning a three bladed 72 inch prop at 2000 RPM with a 1.61 to one 

reduction. The thrust is almost double for the larger prop. The trade off is 

that I have had to pitch for cruise. The up side is that I get more cruise 

speed 75MPH vs 65MPH and much better climb in spite of lower climb engine 

RPMs. My fuel consumption and the engine temps are a bit less with the 

larger slower turning prop flying faster.



Last night in the cool 45 degree air I was able to keep my big VW cool at 

higher power levels than I can normally sustain. I did some low level flying 

like we have to do going into Oshkosh (well maybe a bit lower) but last 

night the air was smooth and I was able to fly 85-90 MPH at 3600-3700RPM on 

the engine. Popping up over woods and tree lines at these power levels and 

speed is breathtaking. I suspect I was seeing power close to what you guys 

with the 100HP Rotes get wow what a kick. I'm tempted to do some better 

cooling work on the engine and maybe move the oil cooler to get more air 

flow. Well maybe not, It keeps me from over stressing my engine???



Rick Neilsen

Redrive VW powered MKIIIc



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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Mon Oct 16, 2006 10:16 am Post subject: Prop Effency

I mostly agree with you but I think there are a couple factors involved. 

Since you are using a VW and he & I a small displacement 2 stroke 582, you 

have a huge torque advantage when it comes to turning a larger prop. And 

from your post, it sounds like you have a great engine combination.



I was thinking about this whole deal a couple hours ago while out mowing the 

airstrip, (last time this year!) and back before my current 582, I had a 532 

on my MKIII. I had bought it from a guy in our EAA chapter who had it on a 

Zenair CH701. Zenair has persuaded him to put a 72" two blade Ivo on that 

poor 532, and while it certainly accelerated and took off quick, he was 

always flying it around at 6,200 rpm and only about 60 mph, because in order 

to get the engine to turn up, he had to take all the pitch out of it. And he 

burned over 5 gph. It was like the ultimate climb prop, but that was it's 

only useful function.



Now what if it had been an inflight adjustable prop? I think as soon as he 

would have cranked in more pitch, the engine would simply have slowed down, 

and the airplane would probably not have speeded up any, if at all, because 

there is no way the engine could have pulled that much prop with any sort of 

normal amount of pitch in it. Now obviously this is an extreme example, but 

I think that is what happens when you put a 3 blade 68" prop on a 582, and 

then attempt to compensate for too much prop by changing pitch, it is still 

too much prop. You can't get the speed, but you do increase prop load, and 

correspondingly high fuel burn.



When I owned that same 532, Ivo told me to use a 64" 3 blade prop, and it 

was too much prop. As John and I bantered about yesterday, a 532 is very 

pipey, and with the 3 blade 64" pitched to give any sort of decent cruise, 

the 532 given half a chance, would fall off the pipe. The only way it worked 

right was to have shallow pitch, and then I had to cruise at 5,800 rpm at 

about 60 mph.  I took away one blade and it worked great as a 2 blade 64" 

Went to a 2 blade 66", and it still worked great. Sold the 532 and got a 582 

and it works great with a 2 blade 68". Good acceleration & climb, good speed 

spread, and low rpm cruise.



I am not any great aerodynamicist, (probably didn't even spell it right) but 

between a lot of trial and error, and thinking about the results, this is 

how I think it works. Obviously subject to change, correction and 

instruction.



Richard Pike

MKIII N420P (420ldPoops)

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

NeilsenRM(at)comcast.net
Guest

Posted: Mon Oct 16, 2006 12:30 pm Post subject: Prop Effency

Richard



I only know what I have experienced and what I have been told by people that 

I think should know. I agree with you that a large prop depending on how 

large will get you into a situation where it is a good climb prop or a good 

cruise prop. I suppose you can get a prop the is just too large for 

everything. I have prop with a cruise pitch setting. The redrive guys tell 

me that I should see 3600-3800 in climb and 3200 in cruise I get a good 

cruise speed (74MPH) at 3200 but I only get 3400 in climb(50MPH).



You indicated I have allot of torque in my engine and I do but it is the 

reduction ratio that can make a low torque high RPM engine into a high 

torque low RPM prop drive.



When I bought my prop Stuart at PowerFin said that the prop I have is the 

perfect prop for a 582 on a Kolb. My prop is a F model three bladed 72 inch 

PowerFin. This model prop has a wide cord so this is a big prop.  I don't 

remember what reduction ratio this would be the best prop for but Rotax does 

sell some optional ratios for their engines that are in the 3-4 to one area 

and this must be what he was talking about. There are just too many 

variables in this area for most of us and to get the best of everything with 

out allot of experimentation. The guys that make my redrive sell engine 

packages for those Newport replicas and they swing a 8 foot prop so that 

they look right. What they didn't expect was the large performance gains 

they got. Again the Newport engines are using  better than 3 to one 

reduction ratio.



I still think the air adjustable prop would work just about perfect in 

situations were you have a good climb prop but need more pitch for cruise. 

They biggest problem I could see would be cranking in too much pitch. The 

difference between climb and cruise pitch on Kolbs isn't much. From my 

experimentation with my ground adjustable a small change can have a big 

effect.



But what do I know?????



Rick Neilsen

Redrive VW powered MKIIIc



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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Oct 16, 2006 12:39 pm Post subject: Prop Effency

| Last night in the cool 45 degree air I was able to keep my big VW 

cool at

| higher power levels than I can normally sustain. I did some low 

level flying

| like we have to do going into Oshkosh (well maybe a bit lower) but 

last

| night the air was smooth and I was able to fly 85-90 MPH at 

3600-3700RPM on

| the engine. Popping up over woods and tree lines at these power 

levels and

| speed is breathtaking. I suspect I was seeing power close to what 

you guys

| with the 100HP Rotes get wow what a kick. I'm tempted to do some 

better

| cooling work on the engine and maybe move the oil cooler to get more 

air

| flow. Well maybe not, It keeps me from over stressing my engine???

|

| Rick Neilsen



Rick:



Shoot!  Do some better cooling work and have fun with your VW powered 

mkIII.



Welcome to what it is all about..........



Can you imagine flying coast to coast like that?  Sometimes, it is the 

only way to stay awake and enjoy the ride.



john h

mkIII

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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Oct 16, 2006 1:14 pm Post subject: Prop Effency

Richard:



Never had a problem with two blade wood, three blade wood, or three 

blade Warp Drive props.



Prop them all the same way, WOT straight and level, bump the red line 

for max continuous duty, which is 6,500 rpm for Rotax two strokes and 

5,500 rpm for Rotax four strokes.



Still get the best combination of cruise and climb.  Of course, my 

cruise and climb ain't the same as your cruise and climb.  Anything 

over 80 is gravey.  Anything less than 80 mph ground speed is 

depressing.



The mkIII is an 85 mph cruise airplane.  Anything over that and you 

are wasting horses.  90 mph and you hit that invisible wall.



I sure have a lot of fun between take off roll and 90 mph though.  



BTW  Fuel burn for my 582 at 5,800 rpm and 80 mph was 5 to 5,5 gph.



Fuel burn on my 912UL at 5,000 rpm and 85 mph was 4 gph.



Fuel burn on my 912ULS at 5,000 rpm and 88 mph was 5 gph.  Noticed I 

said "was" because that engine is gone and I have not flown the new 

912ULS.  Maybe it will get better fuel burn.



As another added note, Jim Ballenger flew my old 912ULS on his MKIIIx. 

He is one happy camper after pulling off the 582 which mysteriously 

seized on takeoff on his last flight with that engine.



Take care,



john h

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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

pj.ladd(at)btinternet.com
Guest

Posted: Tue Oct 17, 2006 10:23 am Post subject: Prop Effency

<<



Hi Richard,

<< where it is a good climb prop or a good cruise prop. >>



I guess if that were not so there would be no market for variable pitch 

props??



By the way `Nieuport` not Newport please.



Incidentally, while speaking French, I found out on holiday that `denim` 

which America has made more or less its own through jeans and other working 

and fashion clothes etc was in fact invented in France.  Theres a bummer. 

It is actually `de Nimes` after the town of Nimes.

Can`t actually tell you anything about Nimes, even if you wanted to know as 

the nearest I got was the `Pont du Gard` just outside the town. This is a 

tremendous Roman Aquaduct across a valley. It is awe inspiring. Three rows 

of arches on top of each other engineered to be just enough  out of level 

for the water to flow. Built 2000 years ago and looks good for another 2000. 

If you haven`t come across it before look it up on google. Amazing. I have 

been trying to visit it for 20 years. The wait was well worthwhile.

Incidentally in a town just beyond Nimes I found an advert in my hotel for a 

`bapteme de l`air` in an ultralight on floats.Phone call to try and organise 

this only to find that the guy had finished his season the day before. Great 

shame as it was a super evening, no wind and a calm  sea flat as a table 

top. I couldn`t talk him into it though. French!!!!



Cheers



Pat



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