Global engine (Half VW)

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Propman

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Dana, no, the largest diameter that works well for the half is 56. And that's on the 45hp. Dia goes down from there as hp lowers. We've made larger dia , but with diminishing returns. Same with the full VW. 62 and under works best. Weasel has tested a 65" dia, If my memory serves me, and I had to trim it. He's running 85hp.

Now these are direct drive engines turning approx 3100 static an up to 3600 wot. If one wants to turn lower rpm the dia can go up.
 

Pops

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I used a 60" x 26" on my 1835 cc VW engine and it was perfect for the engine and airframe. If I was to enlarge it to a 2180 cc engine , I would go to the 62" dia.
 

N8053H

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Dana, no, the largest diameter that works well for the half is 56. And that's on the 45hp. Dia goes down from there as hp lowers. We've made larger dia , but with diminishing returns. Same with the full VW. 62 and under works best. Weasel has tested a 65" dia, If my memory serves me, and I had to trim it. He's running 85hp.

Now these are direct drive engines turning approx 3100 static an up to 3600 wot. If one wants to turn lower rpm the dia can go up.
At what pitch are you running a 56 inch prop on a 1/2 vw? It must be around 22 or less for this to work. If you do the calculation you will not be getting much in the way of cruise speed. But go down to a shorter prop with more bite or pitch and your speeds will increase accordingly. You need a MP gauge to set up your prop to match your airframe.

If I want lower RPM's I will increase pitch and decrease length. I will then increase speed and not decrease speed. Again use a prop calculator. A 28 Pitch prop will out perform the 22 pitched prop in speed, keeping mp and rpm the same..using a MP gauge.

If I want higher RPM's I will increase length and decrease pitch. This will bring my RPM's up throughout the RPM range but keeping WOT RPM the same.

Tony
 

Dana

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I'm currently running a 56" prop on my Mosler (supposedly 40HP though Scott Casler says it's more like 37). It's supposedly a 24" pitch but my measurement says it's more like 27.5" pitch. Turning 3200 rpm in a 45mph climb, cruise 55mph at 2900 rpm. This prop is a tiny bit better than the 56x26 (that I measured at 57x27.5) that was on the plane. I also have a 58x24 that I measured at 25.7 pitch that the original owner said wasn't as good, and a 55x24 (measured at 20.66 pitch), neither of which I've tried yet.

I'm much less concerned about cruise speed than I am with climb... right now I get around 300 fpm.

Once I get my operating limitations straightened out with a new test area I'm going to test all four props in a scientific manner.

Dana
 

fly2kads

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Remember that there are quite a few more variables than diameter and pitch. Some comments on other threads that mention "narrow" and "wide" blade variants of comparable props hint at this. Pitch is sort of an imperfect proxy for angle of attack, which can vary along the blade. Blade width, blade planform, and airfoil(s) all play a role as well. One can make some generalizations based on "typical" planforms, but without taking into account all of the design variables, it is easy to get "apples to oranges" comparisons.
 

Propman

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At what pitch are you running a 56 inch prop on a 1/2 vw? It must be around 22 or less for this to work. If you do the calculation you will not be getting much in the way of cruise speed. But go down to a shorter prop with more bite or pitch and your speeds will increase accordingly. You need a MP gauge to set up your prop to match your airframe.

If I want lower RPM's I will increase pitch and decrease length. I will then increase speed and not decrease speed. Again use a prop calculator. A 28 Pitch prop will out perform the 22 pitched prop in speed, keeping mp and rpm the same..using a MP gauge.

If I want higher RPM's I will increase length and decrease pitch. This will bring my RPM's up throughout the RPM range but keeping WOT RPM the same.

Tony
Tony,

On the Halfs the pitch is 18 to 28. Depends on what the person wants. There is a bit more to it than just diameter and pitch. Chord width and thickness will greatly effect the performance, then where surface area is distributed. I haven't found a prop calculator that gives good numbers yet.
 

N8053H

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I'm currently running a 56" prop on my Mosler (supposedly 40HP though Scott Casler says it's more like 37). It's supposedly a 24" pitch but my measurement says it's more like 27.5" pitch. Turning 3200 rpm in a 45mph climb, cruise 55mph at 2900 rpm. This prop is a tiny bit better than the 56x26 (that I measured at 57x27.5) that was on the plane. I also have a 58x24 that I measured at 25.7 pitch that the original owner said wasn't as good, and a 55x24 (measured at 20.66 pitch), neither of which I've tried yet.

I'm much less concerned about cruise speed than I am with climb... right now I get around 300 fpm.

Once I get my operating limitations straightened out with a new test area I'm going to test all four props in a scientific manner.

Dana
Please explain this scientific manner you plan on using to test these props?

Remember that there are quite a few more variables than diameter and pitch. Some comments on other threads that mention "narrow" and "wide" blade variants of comparable props hint at this. Pitch is sort of an imperfect proxy for angle of attack, which can vary along the blade. Blade width, blade planform, and airfoil(s) all play a role as well. One can make some generalizations based on "typical" planforms, but without taking into account all of the design variables, it is easy to get "apples to oranges" comparisons.
Tony,

On the Halfs the pitch is 18 to 28. Depends on what the person wants. There is a bit more to it than just diameter and pitch. Chord width and thickness will greatly effect the performance, then where surface area is distributed. I haven't found a prop calculator that gives good numbers yet.
I am the one who mentioned cord width and how this effects these props on the 1/2 vw. But for the 1/2 vw you want a narrow tipped blade. Go with a wide blade profile and everything changes respectively.
 
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Dana

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Please explain this scientific manner you plan on using to test these props?
On as close to a "standard" day (59°F and 29.92) as possible, I'll test each prop in a series of climbs at several speeds above, at, and below Vy as well as cruise and WOT, noting airspeed and rpm. Record everything with my GPS that includes a pressure altimeter for accurate ROC information, and graph the results with GPLIGC. Send that data, along with measurements of each prop, to Frank at Performance Propeller and ask if he can do better.

Remember a draggy biplane like mine will need a different prop than a cleaner design like your Avenger.

Frank, I know chord is a major factor, but I had always thought blade section thickness didn't make that much difference (within reason)?

Dana
 

weasel

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That's a nice, clean exhaust setup you've got there!
If you want to build one get the flange and tube kit from great planes and weld it up then go the the Airplane section in the local lows store and get the longest sink drain tubes you can find. I could only find 14" or 16" runs IIRC. the joints slip together and have 1 stainless steal 1/8" pop rivet under the hose clamp to keep them from slipping apart. The entire Exhaust system ended up something like 5.5 or 6 lb. I would have used the sink drain to start earlier on the rear cyl's but I could not find the correct mandrel bends so I wasted about a lb or so extra running the steel to the strait section.

Dana, no, the largest diameter that works well for the half is 56. And that's on the 45hp. Dia goes down from there as hp lowers. We've made larger dia , but with diminishing returns. Same with the full VW. 62 and under works best. Weasel has tested a 65" dia, If my memory serves me, and I had to trim it. He's running 85hp.

Now these are direct drive engines turning approx 3100 static an up to 3600 wot. If one wants to turn lower rpm the dia can go up.
We started with a 64 inch with a very thin cord to keep the parasitic drag low at the tips. Later we thought maybe the tips were fluttering so I sent it back and the last 4 inches or so were reinforced with fiberglass then re-finished. This made no change at all in the performance. The new prop which is 60 inch with a slightly bigger tip cord out performed the 64 inch prop on take-off and climb.

At somewhere around 5:43 you can hear the 64" stick talking.

[video=youtube_share;kqtZ0Q8QQG8]https://youtu.be/kqtZ0Q8QQG8[/video]
 

N8053H

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On as close to a "standard" day (59°F and 29.92) as possible, I'll test each prop in a series of climbs at several speeds above, at, and below Vy as well as cruise and WOT, noting airspeed and rpm. Record everything with my GPS that includes a pressure altimeter for accurate ROC information, and graph the results with GPLIGC. Send that data, along with measurements of each prop, to Frank at Performance Propeller and ask if he can do better.

Remember a draggy biplane like mine will need a different prop than a cleaner design like your Avenger.

Frank, I know chord is a major factor, but I had always thought blade section thickness didn't make that much difference (within reason)?

Dana
If your not using a MP gauge you are missing part of the equation. Cessna and any other manufacturer that did the R&D for their engines to find the prop that worked used this gauge. How else can you compare what is happening at the same throttle setting. RPM tells you nothing but what the engine is turning. It does not tell you how far open the carb butterfly is in the carb. The rpm's can be different at the same butterfly opening. Only the MP gauge will tell you this. If you want to get numbers you can compare side-by-side you will need this MP gauge. Without this gauge you are pis#ing into the wind.

Tony
 

N8053H

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Blade thickness will have the same effect on a propeller as it does on a wing. The thicker the wing the slower the plane will move through the air using the same HP. Same goes for a prop blade. A thicker blade will require more power to spin it the same speed as a thinner blade will. Because of this the rpm's will be the same but at different MP readings or the MP will be the same with different RPM reading. Why a MP gauge is needed to do these test and do them with any usable data. Any other data gathered not using a MP gauge is useless data.

Tony
 

Dana

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RPM tells you nothing but what the engine is turning. It does not tell you how far open the carb butterfly is in the carb. The rpm's can be different at the same butterfly opening. Only the MP gauge will tell you this.
Since I'm focusing on climb performance at WOT, the butterfly will be fully open. Percent power at lower throttle settings is the cube of the percent rpm compared to WOT at the same airspeed.

Dana
 

N8053H

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Since I'm focusing on climb performance at WOT, the butterfly will be fully open. Percent power at lower throttle settings is the cube of the percent rpm compared to WOT at the same airspeed.

Dana
And what I thought. But what I found in the real world testing, different prop blade profiles will yield different results throughout the RPM band or range at the same MP. I have the proof to prove what I say. I saw this when I did my testing. But the only way I knew this..I used a MP gauge, along with a tach. You are not getting enough info from just a tach. Again I found this when I did my testing. Been there done that type of thing. For those who say they have, been there and done that, if you did not use a MP gauge you have half the info needed to make an educated assumption.
 

N8053H

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Since I'm focusing on climb performance at WOT, the butterfly will be fully open. Percent power at lower throttle settings is the cube of the percent rpm compared to WOT at the same airspeed.

Dana
Dana I tested two props both being 54x24. One was a narrow tipped prop and one was a wide tipped prop. Both gave me around the same RPM at WOT 3500 -3600 respectively. But all other numbers throughout the RPM range was different. At the same MP settings the two props had different numbers. I found the wide blade prop worked best testing these two props against each other on a 40 something HP engine. On a 38 HP engine the narrow tipped prop worked best.
 
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Dana

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But rpm at WOT at what airspeed? The same? Or different?

Dana
 

TFF

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For an engine of marginal strength it would be smart to know the load you are putting on it. Remember in the 70's when GM and others put "economy" gauges in cars? Piston helicopters use MP gauges as kind of a "torque" meter; turbines have direct torque meters which is how turbines are measured. Turboprop and helicopter rotors are run at a narrow band of rpm. Idle power still has to have same RPM as full power. MP is a good reference of work being done by the engine vs what you are getting out of the prop. It would be a good test gauge. But I still would prefer an engine that will not grenade at full power for longer than a minute or two.
 
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