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GSC Prop Blades Loose

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dpremgood(at)aim.com
Guest

Posted: Fri Apr 11, 2008 12:47 pm Post subject: GSC Prop Blades Loose

Hi Pete,



My understanding is that a larger diameter, slower turning prop is more 

efficient.



My concerns going with a larger diameter prop were:

1) The torque curve for the ROTAX 503 really drops off at lower RPMs

2) Tip speeds would increase

3) There would be at least 2-3 inches less ground clearance. 

(especially since I operate on skiis in the winter)



I was also limited to 60 inch 3 blade due to the prop inertia, since I 

have a 503 with a B reduction gearbox.



I also like the looks of a 3 blade 



Doug

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Fri Apr 11, 2008 1:09 pm Post subject: GSC Prop Blades Loose

I do too, Doug, and I can't imagine the P-40 with any other prop, but  

I was told in my model airplane days that a 2-blade was more  

efficient, and a single blade (club prop) even more so. I guess there  

are other factors to consider, however.



Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/487+ hrs/down for annual

do not archive

On Apr 11, 2008, at 4:42 PM, dpremgood(at)aim.com wrote:

 	  Quote: 	
		  

 I also like the looks of a 3 blade 



 Doug

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Apr 11, 2008 7:49 pm Post subject: GSC Prop Blades Loose

Lynn:



What we were told in school was that a single blade is always cutting into

clear undisturbed air.  As you add blades the air each blade cuts into

becomes more and more disturbed.  This is what caused the loss of

efficiency.



Multiple blades do however allow you to handle higher power loads at smaller

diameters.  The P51-D is one plane I can remember seeing with a four blade

prop that was able to soak up the full 1800 +- horsepower of the Rolls Royce

Merlin engine! Props on the PBY, also in the 1800 hp range were only three

blades but I assume are much larger.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

propellerdesign(at)tele2.
Guest

Posted: Sat Apr 12, 2008 3:40 am Post subject: GSC Prop Blades Loose

I have heard this before, and it would be true on ground, but it isn't 

really either.



In the air, say we have a kitfox or Cub or Aeronca, a relative slow plane, 

pitch is 40 inch or 1 meter.



we fly with 2500 rpm = 2500 meter/minute = 150 km/h = 93 MPH = 81 Knots



Every turn of propeller give us 1 meter in forward motion, so with 2 blade 

the next blade "follow" an half meter or 20 inch AHEAD of the "first" in 

undisturbed air

With 3 blade it will be 0,33 meter or 13,3 inch ahead of each other.



The propeller blade is 1 inch to a quarter of an inch thick and blade bottom 

is about flat with relative/incoming air.



Have you seen or performed a balloon chase? many times the balloon goes 

straight thru the prop disk unhurt, a balloon is maybe 6 by 10 inch so that 

isn't as strange as at first thought, we think the balloon must be sliced by 

the fast spinning propeller, but the distance between blades is greater then 

the size of the balloon.

A roll of toilet paper is fun too, but unroll a couple of meter before you 

throw it overboard, and don't dive into the balloon or paper, climb or level 

flight is safer.

if you dig your grave with your airplane and have toilet paper hanging on 

landing gear and antennas, NTSB will get the wrong conclusion.



There is NACA test showing that a 3 blade is more efficient then 2 and 4 

blade, with identical blades, others tests show different result, of course 

with 3 blades it takes 50% more power to turn the prop at the same rpm and 

forward speed, so we will never choose between 2 or 3 identical blades, with 

same pitch and diameter to compeer on our planes. a 3 blade will be smaller 

in diameter and/or have narrower blades. so it isn't really comparable. if 

the 3 blade is to large in diameter the pitch will be sat at a lower angle 

to get RPM up and top speed will suffer. climb will be good though.



An single blade prop is more efficient if the tip speed/rotation speed is 

slow enough to allow a bigger diameter, single blade have been used on 

Silent electric self launch glider, why? because when retracting the prop 

into the fuselage the heavy hole don't have to be that large.



We do lose 3-15% of power to tipspeed effect!



Many test have been made with different result, why? sometimes they have 

admit that the tested blades wasn't really identical, in thickness, pitch 

distribution and so on.



What propeller is best then? As asking what car is best, or whose wife is 

best, it all depends on what we use them to do.



If we want good take off a slower! turning prop with large diameter is best, 

if it isn't become to slow with to coarse pitch that will stall on take off. 

So some trade off here.



If we want high speed we need to squeeze the air through a smaller disk area 

to get it up to higher speed. (Mustang v. PBY) also at higher speed the 

thrust is less with constant power.



We chose if we want, a climb, a standard or cruise propeller, difference 

will be an inch or two between each in diameter and pitch.



Ok now we have the diameter, now we need blade area to "brake" the power, if 

the blades is becoming to wide, we can chose more blades instead. a slender 

blade will have better L/D then a wide one, you don't see a Cherokee wing on 

a sailplane!

if the blade become to narrow we get structural problem.



We can chose 2 wide blade or 3 narrow blade, total area should be the same 

with same diameter, if pitch and pitch distribution is the same I think the 

3 blade will become the most efficient.

If we chose blades with same Aspect ratio, the 3 blade will have less 

diameter. note that the 3 blade with same aspect ratio will be narrower and 

thinner if diameter is smaller.

With 2 narrow blade the diameter will be larger, fine if no problem with 

ground clearance or high tip speed or noise. will give good take off and 

climb and speed.



A single blade prop is most efficient? Yes if design and need is right

a 3, 4 or 5 blade is best? Yes if needed.

2 wife's? downside is 2 mother in laws.



Jan

JC Propeller Design



attached a reason for wood prop.





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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Sat Apr 12, 2008 4:42 am Post subject: GSC Prop Blades Loose

That's what I learned from my reading too...that singles were the  

most efficient. I suppose at a certain point efficiency must give way  

to the horsepower to be handled. I'm thinking of the Merlin of  

course, and what engine does the Sea Fury have in it? That's a 5- 

blade as I recall.



Another factor to consider is the engines' needs. Early on, I was  

told that my Jabiru needed the 2-bladed wooden prop to absorb the  

torsional vibration of the engine, and that ground adjustables of the  

time had too large a hub, and that the hub interfered with air going  

into the cooling ports of the cowl. Later this info changed, and some  

ground adjustables were now OK'd to use....different info as the  

times change and equipment becomes available.



Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/487+ hrs/down for annual

do not archive

On Apr 11, 2008, at 11:47 PM, Noel Loveys wrote:



 	  Quote: 	
		   



 Lynn:



 What we were told in school was that a single blade is always  

 cutting into

 clear undisturbed air.  As you add blades the air each blade cuts into

 becomes more and more disturbed.  This is what caused the loss of

 efficiency.



 Multiple blades do however allow you to handle higher power loads  

 at smaller

 diameters.  The P51-D is one plane I can remember seeing with a  

 four blade

 prop that was able to soak up the full 1800 +- horsepower of the  

 Rolls Royce

 Merlin engine! Props on the PBY, also in the 1800 hp range were  

 only three

 blades but I assume are much larger.



 Noel

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Apr 12, 2008 6:15 am Post subject: GSC Prop Blades Loose

Thanks Jan... Very in depth, however, your idea that each blade at 40 inches

of pitch advances 40 inches with each revolution  assumes no drag on the

plane...  If that were true we wouldn't need props or engines at all.... I

made the same argument in school.



I was wondering if with each additional blade there is also an additional

root area which gives no appreciable thrust to the plane?  And in fact can

increase load by pushing air at a flat cowl.



I agree with your reason for a wood prop.  

Beautiful craftsmanship!



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Apr 12, 2008 6:46 am Post subject: GSC Prop Blades Loose

Lynn:



I'm sure a three blade could absorb even more TV (Torsional Vibration).  I

just Googled (is that a real word???) up the Sea Fury.  One version had a

2550 hp Centaurus XV air cooled engine with a five bladed Rotol prop.

Being a naval plane it had to take off in surprisingly short distances even

with catapult assist this would require a lot of power to be sunk into the

prop.  The idea of the bent wing one the F4-U Corsair was to allow a bigger

prop on a smaller plane.



Back to our props..



I don't think composite props handle the vibration as well as wood.  



In the early days of the Corvette, with our notoriously bad roads, the

bodies of the cars cracked profusely and were always undergoing repair.

Since then there have been many advancements in composite construction but I

think it just doesn't stand up to vibration as well as natural wood.  Wood

on the other hand won't age nearly as well as  composite.  



Neither prop should be flown through rain. 



The prop that came with my 912 is a two blade GA Warp.  I'm hoping it will

work well for me.  Time will tell.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Rex Hefferan

Joined: 10 Jan 2006
Posts: 147
Location: Olney Springs, Colorado USA "NOT a Kitpig"

Posted: Sat Apr 12, 2008 7:21 am Post subject: GSC Prop Blades Loose

Noel Loveys wrote:



 	  Quote: 	
		    The idea of the bent wing one the F4-U Corsair was to allow a bigger

prop on a smaller plane.



True, but to complete the reason as I recall reading about it, at the 
	


time they couldn't design landing gear long enough and strong enough for 

carrier landings with the required prop diameter.



-- 

Rex Hefferan

SE Colorado / K-II / 582-C / still waiting repairs

_________________
Rex
N740GP - M2/582
Colorado

propellerdesign(at)tele2.
Guest

Posted: Sat Apr 12, 2008 8:19 am Post subject: GSC Prop Blades Loose

Yes I mean that with 40 inch we will go 40 inch, or 38 or 42 inch forward.



I have the short coming that I don't understand when other people don't 

understand what I am thinking, or forget to say. 



pitch on propellers is mostly referring to the flat bottom, not the cord or 

aerodynamically correct the zero lift line.



at cruise, if diameter is correct the flat bottom is about flat with 

incoming air, with a longer prop this angle will be negative!, and a shorter 

prop will have a positive angle.

this vary also with thickness of blade, thinner blade need more angle, and 

opposite.



the lift or thrust is generated from the angle between zero lift angle and 

the angle of relative wind! 6 or so degree higher at 75% radii of the blade, 

going from 40 inch to 58.5 inch at the Zero lift line.



The number I closed to use was just even nr's close to the real kitfox 

world, I didn't bother to check it up with my propeller program, but just 

did.



if we say by some reason we have 65 hp and is going 92 mph, propeller 

thickness at 75% = 12% and turning the prop at 2500 rpm we (I) get 40.02 

inch or 14.02 degree at 75%, diameter 68" and aspect ratio 6,12 = 5,55 inch 

wide blade at 45% radii 2 blade.



other way of see it! is to just look out to your left when flying, specially 

you with flat bottom wings, it is almost flat with the horizon, at higher 

speed it is a negative angle, ( leading edge down a bit) it still fly and 

lift is most of the times, or at least sometimes equal to the weight, (if we 

don't go into the negative pitch moment of wing and down or sometimes up 

lift of the tail, because it will be a very long story then I don't have 

time to type much more because my wife want me to go out with 6 month son to 

by groceries)



the area near hub is also interesting, I go there when back from walk.



Jan



---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Apr 12, 2008 8:33 am Post subject: GSC Prop Blades Loose

The funny thing about it is I think is saw very little, if any, carrier

service.



Noel



Do not archive



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Apr 12, 2008 8:50 am Post subject: GSC Prop Blades Loose

Thanks Jan... I, for one will be waiting.



Noel

Do not archive this one.



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Sat Apr 12, 2008 9:28 am Post subject: GSC Prop Blades Loose

Not to pick nits or anything, but wasn't the reason for the bent wing  

to be able to use a shorter landing gear BECAUSE of the larger prop?  

The way I heard it was the engine needed a larger prop to absorb  

horsepower, then that dictated the longer landing gear, and that was  

out of the question (less the plane take on the Storch look), so they  

bent the wing to get the gear shorter...or so I'm told. Maybe that's  

what you said.



Lynn Matteson

Grass Lake, Michigan

Kitfox IV Speedster  w/Jabiru 2200

flying w/487+ hrs/down for annual

do not archive

On Apr 12, 2008, at 10:43 AM, Noel Loveys wrote:



[quote] 



 Lynn:



 I'm sure a three blade could absorb even more TV (Torsional  

 Vibration).  I

 just Googled (is that a real word???) up the Sea Fury.  One version  

 had a

 2550 hp Centaurus XV air cooled engine with a five bladed Rotol prop.

 Being a naval plane it had to take off in surprisingly short  

 distances even

 with catapult assist this would require a lot of power to be sunk  

 into the

 prop.  The idea of the bent wing one the F4-U Corsair was to allow  

 a bigger

 prop on a smaller plane.



 Back to our props..



 I don't think composite props handle the vibration as well as wood.



 In the early days of the Corvette, with our notoriously bad roads, the

 bodies of the cars cracked profusely and were always undergoing  

 repair.

 Since then there have been many advancements in composite  

 construction but I

 think it just doesn't stand up to vibration as well as natural  

 wood.  Wood

 on the other hand won't age nearly as well as  composite.



 Neither prop should be flown through rain.



 The prop that came with my 912 is a two blade GA Warp.  I'm hoping  

 it will

 work well for me.  Time will tell.



 Noel



 --

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

propellerdesign(at)tele2.
Guest

Posted: Sat Apr 12, 2008 12:09 pm Post subject: GSC Prop Blades Loose

Back to real life of airplanes and propellers.



the inner parts of propellers is something that haven't been investigated 

that much, some just use the true helical prop. = constant pitch along the 

blade. ( not const. angle)



naca and others have made some tests, but test prop's with different twist 

is more expensive then test propellers with different P/D (pitch/Diam.) 

because they use ground adjustable blades.



it is shown that with a radial engine and big prop, the inner part of prop 

was seeing about 60% of the forward speed, so the pitch have to be 

compensated for this and often is.



if true helix the high angle of the inner blade will stall, specially during 

take off.



a propeller with round shanks will not produce any thrust at the inner part, 

just drag ( to plane and engine)

if it is a radial engine that is slowing down airspeed, that will reduce the 

drag from the round shanks. and a spinner will not increase speed.



a slender fuselage (water cooled engine) a spinner that cover the hub and 

inner blade root is very help full, the mustangs even had a sleeve covering 

the round shanks



a test I read about had a very low drag fuselage just little bigger then the 

spinner in diameter, it showed a reduced air speed near the spinner of 90% 

of forward speed, reduction in speed was seen out to about 60 % of the 

radii.



if we want a good take off and climb it is better with reduced pitch near 

hub, but even if we want good speed, the inner parts is seeing 60-90% of 

forward speed, depending of what the airplane looks like.



Jan



---

Fox5flyer
Guest

Posted: Mon Apr 14, 2008 3:32 am Post subject: GSC Prop Blades Loose

Great essay Jan.  Very informative and enlightening.

Keep 'em coming.

Deke Morisse

Mikado Michigan

S5/Subaru/CAP 355+ TT

"The aim of an argument or discussion should not be victory, but progress."

- Joseph Joubert



[quote]I have heard this before, and it would be true on ground, but it isn't

 really either.



 In the air, say we have a kitfox or Cub or Aeronca, a relative slow plane,

 pitch is 40 inch or 1 meter.



 we fly with 2500 rpm = 2500 meter/minute = 150 km/h = 93 MPH = 81 Knots



 Every turn of propeller give us 1 meter in forward motion, so with 2 blade

 the next blade "follow" an half meter or 20 inch AHEAD of the "first" in

 undisturbed air

 With 3 blade it will be 0,33 meter or 13,3 inch ahead of each other.



 The propeller blade is 1 inch to a quarter of an inch thick and blade 

 bottom

 is about flat with relative/incoming air.



 Have you seen or performed a balloon chase? many times the balloon goes

 straight thru the prop disk unhurt, a balloon is maybe 6 by 10 inch so 

 that

 isn't as strange as at first thought, we think the balloon must be sliced 

 by

 the fast spinning propeller, but the distance between blades is greater 

 then

 the size of the balloon.

 A roll of toilet paper is fun too, but unroll a couple of meter before you

 throw it overboard, and don't dive into the balloon or paper, climb or 

 level

 flight is safer.

 if you dig your grave with your airplane and have toilet paper hanging on

 landing gear and antennas, NTSB will get the wrong conclusion.



 There is NACA test showing that a 3 blade is more efficient then 2 and 4

 blade, with identical blades, others tests show different result, of 

 course

 with 3 blades it takes 50% more power to turn the prop at the same rpm and

 forward speed, so we will never choose between 2 or 3 identical blades, 

 with

 same pitch and diameter to compeer on our planes. a 3 blade will be 

 smaller

 in diameter and/or have narrower blades. so it isn't really comparable. if

 the 3 blade is to large in diameter the pitch will be sat at a lower angle

 to get RPM up and top speed will suffer. climb will be good though.



 An single blade prop is more efficient if the tip speed/rotation speed is

 slow enough to allow a bigger diameter, single blade have been used on

 Silent electric self launch glider, why? because when retracting the prop

 into the fuselage the heavy hole don't have to be that large.



 We do lose 3-15% of power to tipspeed effect!



 Many test have been made with different result, why? sometimes they have

 admit that the tested blades wasn't really identical, in thickness, pitch

 distribution and so on.



 What propeller is best then? As asking what car is best, or whose wife is

 best, it all depends on what we use them to do.



 If we want good take off a slower! turning prop with large diameter is 

 best,

 if it isn't become to slow with to coarse pitch that will stall on take 

 off.

 So some trade off here.



 If we want high speed we need to squeeze the air through a smaller disk 

 area

 to get it up to higher speed. (Mustang v. PBY) also at higher speed the

 thrust is less with constant power.



 We chose if we want, a climb, a standard or cruise propeller, difference

 will be an inch or two between each in diameter and pitch.



 Ok now we have the diameter, now we need blade area to "brake" the power, 

 if

 the blades is becoming to wide, we can chose more blades instead. a 

 slender

 blade will have better L/D then a wide one, you don't see a Cherokee wing 

 on

 a sailplane!

 if the blade become to narrow we get structural problem.



 We can chose 2 wide blade or 3 narrow blade, total area should be the same

 with same diameter, if pitch and pitch distribution is the same I think 

 the

 3 blade will become the most efficient.

 If we chose blades with same Aspect ratio, the 3 blade will have less

 diameter. note that the 3 blade with same aspect ratio will be narrower 

 and

 thinner if diameter is smaller.

 With 2 narrow blade the diameter will be larger, fine if no problem with

 ground clearance or high tip speed or noise. will give good take off and

 climb and speed.



 A single blade prop is most efficient? Yes if design and need is right

 a 3, 4 or 5 blade is best? Yes if needed.

 2 wife's? downside is 2 mother in laws.



 Jan

 JC Propeller Design



 attached a reason for wood prop.





 ---

propellerdesign(at)tele2.
Guest

Posted: Mon Apr 14, 2008 4:01 am Post subject: GSC Prop Blades Loose

thank you guys.



Jan



do not archive



---

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