160 FI Props
09-22-2004, 05:33 PM
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160 FI Props
I have an OS 160 FI running a Hatori header and pipe with an APC 17 x 12. Engine has about 5 flights on it so far.
Can you please advise what props you are running on this engine for pattern.
Thanks
Alan
Can you please advise what props you are running on this engine for pattern.
Thanks
Alan
09-22-2004, 07:11 PM
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RE: 160 FI Props
*Prop Load = DIA^4 x PITCH / 100
2B Prop ... Prop Load
17 x 13 = 10,900 @ 8450 rpm
17 x 12 = 10,000 @ 8600 rpm
18 x 13 = 13,700 @ 7800 rpm
18 x 12 = 12,600 @ 8050 rpm
19 x 12 = 23,500 @ 7500 rpm
3B Prop ... Prop Load
15.75 x 12 = 11,100 @ 8400 rpm
16 x 12 = 11,800 @ 8300 rpm
17 x 12 = 15,000 @ 7550 rpm
_________
Schpankme
* added "corrected" formula for finding prop load
2B Prop ... Prop Load
17 x 13 = 10,900 @ 8450 rpm
17 x 12 = 10,000 @ 8600 rpm
18 x 13 = 13,700 @ 7800 rpm
18 x 12 = 12,600 @ 8050 rpm
19 x 12 = 23,500 @ 7500 rpm
3B Prop ... Prop Load
15.75 x 12 = 11,100 @ 8400 rpm
16 x 12 = 11,800 @ 8300 rpm
17 x 12 = 15,000 @ 7550 rpm
_________
Schpankme
* added "corrected" formula for finding prop load
09-24-2004, 10:11 PM
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RE: 160 FI Props
Brain,
Your post recommends we use the formula by Dave Gierke (Model Airplane News - contributor), whos credited by many for creating the "Propeller Load Factor (PLF)". I'm not satisfied that this formula provides an acurate load factor.
PLF = diameter^2 x pitch
_________
Schpankme
"Incentives are good, I learned that in rehab."
Your post recommends we use the formula by Dave Gierke (Model Airplane News - contributor), whos credited by many for creating the "Propeller Load Factor (PLF)". I'm not satisfied that this formula provides an acurate load factor.
PLF = diameter^2 x pitch
_________
Schpankme
"Incentives are good, I learned that in rehab."
09-25-2004, 08:49 AM
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RE: 160 FI Props
The EFI 1.60 is the same powerhouse as the standard 1.60. I have run the following props with VERY good success; prop selection depends on your style, speed, and aircraft preferences.
Having said that, I'll list my preferred props, in order of preference....
15.75 x 12 three blade APC
15.75 x 13 three Blade APC
15.5 x 12 FOUR blade APC
17 x 12 Standard APC
17 x 13 Standard APC.
The top three provide EXCELLENT decelleration/braking, and have minimal "spool up" delay. The 13 pitch props tend to be a lot faster than I like to fly Masters, but that gets into the preference area. As you may note, "trying" all of these meant a LOT of extra spinner-buying, and prop buying. However - my 12 pitch three blade has probably 250 flights on it...hasn't been dinged and isn't worn out yet.
Having said that, I'll list my preferred props, in order of preference....
15.75 x 12 three blade APC
15.75 x 13 three Blade APC
15.5 x 12 FOUR blade APC
17 x 12 Standard APC
17 x 13 Standard APC.
The top three provide EXCELLENT decelleration/braking, and have minimal "spool up" delay. The 13 pitch props tend to be a lot faster than I like to fly Masters, but that gets into the preference area. As you may note, "trying" all of these meant a LOT of extra spinner-buying, and prop buying. However - my 12 pitch three blade has probably 250 flights on it...hasn't been dinged and isn't worn out yet.
09-25-2004, 02:30 PM
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RE: 160 FI Props
For me, the D^2 formula has worked very well in evaluating 12-16" and even 17-18" props. There does seem to be an issue with larger props, as niether PLF formula seems to hold up. the simple DxP models this even worse, as a 17x12 has the same loading factor as a 34x6, or a 51x4 
I think that the D^2 in the equation helps this, as more weight falls with the Diameter than the pitch. As I said, the D^2 workes very well for me in comparing props for .90-1.60 size engines, I think because the squared numbers are still close enough as compared to the squares of props 20"+. I think that we do need a better model for large props, esp. before you spend over $100 on a prop that realisticly will not work.
BTW, how do you get values in the 64000+ range? are you mult. by RPM or something?
I used to use the DxP about 9 years ago, after reading Dave Patrick's Proping for power artical in aerobatics made easy column in MAN. Boy, I wish he still wrote often. And Yes, I did adopt the D^2 from Dave Girke's MAN artical a couple years later.
I really would not use the DxP for props bigger than 12-13" and the D^2 after about 18-20". after that the formulas just dont hold up........
Thanks for reading, what do you think we should try- D^3 for big props? D^4???
Good Conversation
I think that the D^2 in the equation helps this, as more weight falls with the Diameter than the pitch. As I said, the D^2 workes very well for me in comparing props for .90-1.60 size engines, I think because the squared numbers are still close enough as compared to the squares of props 20"+. I think that we do need a better model for large props, esp. before you spend over $100 on a prop that realisticly will not work.BTW, how do you get values in the 64000+ range? are you mult. by RPM or something?
I used to use the DxP about 9 years ago, after reading Dave Patrick's Proping for power artical in aerobatics made easy column in MAN. Boy, I wish he still wrote often. And Yes, I did adopt the D^2 from Dave Girke's MAN artical a couple years later.
I really would not use the DxP for props bigger than 12-13" and the D^2 after about 18-20". after that the formulas just dont hold up........
Thanks for reading, what do you think we should try- D^3 for big props? D^4???
Good Conversation
09-25-2004, 02:44 PM
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RE: 160 FI Props
Also wanted to add....
When I have compared props in the past, I have neve really gone above 10" in pitch, and rarely above 8" pitch. I wonder if this has skewed my opinion of the model since I really havent seen 12-13" pitch props in action nor have a feel for how they turn the air. My largest pattern plane is a .90 size, using a 15x8, and most of my larger stuff is Scale Aerobatics, and even some straight scale stuff, where pitch simply is not as important. My point is, perhaps a 17x13 is the same load as a 25x6, but I doubt that it is from my experience. (Or any two props 8" differnt in dia for that matter) I wanted to clarify this to keep from falling into one of my own pet peevs- Those who know little quickly tell it!
When I have compared props in the past, I have neve really gone above 10" in pitch, and rarely above 8" pitch. I wonder if this has skewed my opinion of the model since I really havent seen 12-13" pitch props in action nor have a feel for how they turn the air. My largest pattern plane is a .90 size, using a 15x8, and most of my larger stuff is Scale Aerobatics, and even some straight scale stuff, where pitch simply is not as important. My point is, perhaps a 17x13 is the same load as a 25x6, but I doubt that it is from my experience. (Or any two props 8" differnt in dia for that matter) I wanted to clarify this to keep from falling into one of my own pet peevs- Those who know little quickly tell it!
09-25-2004, 02:58 PM
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RE: 160 FI Props
My experience has been that the various theoretical load calculations have little to no meaning in the dynamic, practical environment of Masters/FAI pattern. Of more value to me is finding the right combination of dynamic braking, ability to accelerate without overloading engine, and the ability to permit the motor to turn at or near it's peak bhp rating for full throttle.
We have to consider that todays Masters/FAI sequences hardly use full throttle settings, but moreso emphasize the ability of the power package to transition rapidly and smoothly from one power setting to another, and to behave somewhat "linearly", although this is a VERY subjective area.
We have to consider that todays Masters/FAI sequences hardly use full throttle settings, but moreso emphasize the ability of the power package to transition rapidly and smoothly from one power setting to another, and to behave somewhat "linearly", although this is a VERY subjective area.
09-25-2004, 07:13 PM
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RE: 160 FI Props
Hi Bob,
I think that we are just trying to compare props for pre-flight analysis, obviously our final opinion of a prop will lie within test flights. It is handy, however, to have a model that allows for guessing a good start point. case in point, say Schpankme wants to know if his 1.60 can swing a 25x6. IF our model works, than it says he can TRY it and EXPECT similar load and similar RPM as a 17x13. how the prop preforms in flight is a matter of opinion, as people themselves rank differnt preformance critieria in a differnt order, AND the feel of each prop is subjective. for ex., you said that you prefer good braking ability and fast transition, however someone else may prefer only max thrust, since they are doing 3-d or something else that requires a lot of "pull" (think 1/4 scale float plane?)
Schpankme (and others),
While trying to think of a better way to predict prop load, I was thinking. how about a measure of the Volume of air moved (moved through) in one revoulution of the prop?
the formula would be 3.14 x (D/2)^2 x P. for a 16x8, 3.14 x 8^2 x8 = 1608" cubed we can leave out Pi since it is a constant, or 8^2 x 8 = 512 loading factor???
For a range of props that work on my O.S. .91 FX's here are some numbers, I currently have a .91 in my WB 60:
14x8 = 392
14x10= 490
15x6= 337.5
15x7= 394
15x8= 450
16x6=384
Just a way to play with the numbers, but comparing these with RPM figures, the 14x8 and the 15x7 turn very close tach readings.
I think that we are just trying to compare props for pre-flight analysis, obviously our final opinion of a prop will lie within test flights. It is handy, however, to have a model that allows for guessing a good start point. case in point, say Schpankme wants to know if his 1.60 can swing a 25x6. IF our model works, than it says he can TRY it and EXPECT similar load and similar RPM as a 17x13. how the prop preforms in flight is a matter of opinion, as people themselves rank differnt preformance critieria in a differnt order, AND the feel of each prop is subjective. for ex., you said that you prefer good braking ability and fast transition, however someone else may prefer only max thrust, since they are doing 3-d or something else that requires a lot of "pull" (think 1/4 scale float plane?)
Schpankme (and others),
While trying to think of a better way to predict prop load, I was thinking. how about a measure of the Volume of air moved (moved through) in one revoulution of the prop?
the formula would be 3.14 x (D/2)^2 x P. for a 16x8, 3.14 x 8^2 x8 = 1608" cubed we can leave out Pi since it is a constant, or 8^2 x 8 = 512 loading factor???
For a range of props that work on my O.S. .91 FX's here are some numbers, I currently have a .91 in my WB 60:
14x8 = 392
14x10= 490
15x6= 337.5
15x7= 394
15x8= 450
16x6=384
Just a way to play with the numbers, but comparing these with RPM figures, the 14x8 and the 15x7 turn very close tach readings.
09-25-2004, 09:46 PM
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RE: 160 FI Props
O.K., nevermind. The (D/2)^2 formula simply yields a value 1/4 of the D^2 one. I just realized that rethinking the Math.
How about D^3 x P 15x15x15x7=23625
14x14x14x8=21952
and for the 17x13: 17x17x17x13=63869
22x22x22x6 = 63888 <- real close!!!!
or D^4 (17^4) x 13 = 1085773
20^4 x 6 = 960000 <- also close!
So try a 25x6, 22x6, and a 20.5x6, and the one that turns closest to the 17x13 rpm value shows the correct equation!?!?
How about D^3 x P 15x15x15x7=23625
14x14x14x8=21952
and for the 17x13: 17x17x17x13=63869
22x22x22x6 = 63888 <- real close!!!!
or D^4 (17^4) x 13 = 1085773
20^4 x 6 = 960000 <- also close!
So try a 25x6, 22x6, and a 20.5x6, and the one that turns closest to the 17x13 rpm value shows the correct equation!?!?
09-25-2004, 09:53 PM
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RE: 160 FI Props
Good info, Brian and Schpankme....however....the gentleman from NZ probably needs prop sizes that he can BUY. The current Pattern world - whether we like it or want it - RUNS on APC props as "the Standard".
So...
17 x 12
17 x 13
and all of the 16 x whatevers...
Goin' out on a limb, here, but I'll bet a barrel of Nitro they don't have 22.5 x 6 two blade prop ANYWHERE. And =- if they DID -= what kind of landing gear would a guy have to run to make it work?
I think off the shelf advice would help this particular gent.
So...
17 x 12
17 x 13
and all of the 16 x whatevers...
Goin' out on a limb, here, but I'll bet a barrel of Nitro they don't have 22.5 x 6 two blade prop ANYWHERE. And =- if they DID -= what kind of landing gear would a guy have to run to make it work?
I think off the shelf advice would help this particular gent.
09-25-2004, 11:01 PM
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RE: 160 FI Props
I agree, but Schpankme said he could have props custom made. Of course to run them.... Think of a Corsair/Focus hybrid...
I myself use apc. The Std pattern would be the 17" variety. With the 1.60FX making so much power, and the 1.60 DZ due soon, are there any 18"+ diameter props being used for pattern? Or does ground clearance become the issue? will we ever need more power for 5 kg planes? oh well, I guess these questions will be obsolete ikn about 3-5 years, when our planes will all run on electrons
I myself use apc. The Std pattern would be the 17" variety. With the 1.60FX making so much power, and the 1.60 DZ due soon, are there any 18"+ diameter props being used for pattern? Or does ground clearance become the issue? will we ever need more power for 5 kg planes? oh well, I guess these questions will be obsolete ikn about 3-5 years, when our planes will all run on electrons
09-25-2004, 11:08 PM
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RE: 160 FI Props
Volume of Air Per Minute = DIA^2 x 0.7854 x PITCH x RPM
Lets compare props and calculate the volume of air per minute (million cubic inches per minute):
two blade props
17x12 @ 8000 rpm = 22,000,000 - Eric's "Evil" setup
19 x 10 @ 8000 rpm = 22,700,000
three blade props
15.75x12 @ 8350 rpm = 29,300,000 - aerobob's setup
17x12 @ 7800 rpm = 31,900,000
18x10 @ 7800 rpm = 29,800,000 - [>:]
_________
Schpankme
Lets compare props and calculate the volume of air per minute (million cubic inches per minute):
two blade props
17x12 @ 8000 rpm = 22,000,000 - Eric's "Evil" setup
19 x 10 @ 8000 rpm = 22,700,000
three blade props
15.75x12 @ 8350 rpm = 29,300,000 - aerobob's setup
17x12 @ 7800 rpm = 31,900,000
18x10 @ 7800 rpm = 29,800,000 - [>:]
_________
Schpankme
09-26-2004, 12:14 AM
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RE: 160 FI Props
How are you calculating?
For a two blade I get your answer,
pi x radius^2 x pitch x rpm = cubic inches of air per minute
but I dont know how you are figuring a three blade.
Also if you know how much air is displaced, and if you know how much the air weighs, if you multiply them don't you get thrust?
But to know how much the air weighs you need the pressure of the air, and since the air is moving fast (is it?) the pressure is less than the atmosphere. (talk to Mr. Bernoulli, I dont have anything to do with it)
For a two blade I get your answer,
pi x radius^2 x pitch x rpm = cubic inches of air per minute
but I dont know how you are figuring a three blade.
Also if you know how much air is displaced, and if you know how much the air weighs, if you multiply them don't you get thrust?
But to know how much the air weighs you need the pressure of the air, and since the air is moving fast (is it?) the pressure is less than the atmosphere. (talk to Mr. Bernoulli, I dont have anything to do with it)
09-26-2004, 12:29 AM
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RE: 160 FI Props
I see, you took your two blade equation and multiplied it by 1.5, But I don't think it is right, because you left out the equation if you had a 1 blade prop......
also, although Aerobob loves the slow flight preformance that he gets from his 3 bladers, he is NOT moving (29.3-22) / 22 = 33% more air than a 17x12. unless, of course three bladers really ARE that much less efficiant.
Perhaps your equation is for a single blade, and it doubles for a two blade, then mult. by 3/2 to go to a two, then 1/2 to go 4 blade, etc.......
Using your equation, does Bobs' 4 blade 15.5x12 = 15.5^3 x 12 x 2 = 89373? that would be sweet........
Your mileage may vary....
also, although Aerobob loves the slow flight preformance that he gets from his 3 bladers, he is NOT moving (29.3-22) / 22 = 33% more air than a 17x12. unless, of course three bladers really ARE that much less efficiant.
Perhaps your equation is for a single blade, and it doubles for a two blade, then mult. by 3/2 to go to a two, then 1/2 to go 4 blade, etc.......
Using your equation, does Bobs' 4 blade 15.5x12 = 15.5^3 x 12 x 2 = 89373? that would be sweet........
Your mileage may vary....
09-26-2004, 08:38 AM
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RE: 160 FI Props
Bob,
I've been using the 17x13 on my 160. It works well, but I would like to limit the top speed of the plane more. It gives almost unlimited verticals, the 17x12 does give unlimited verticals, but at the expense of more noise and RPM. Does the 3 blade work better in that respect? Is the 4 blade just as good? I REALLY don't wnat to buy two more spinners; one is enough, and the 4 blade is readily available.
Jon Lowe
I've been using the 17x13 on my 160. It works well, but I would like to limit the top speed of the plane more. It gives almost unlimited verticals, the 17x12 does give unlimited verticals, but at the expense of more noise and RPM. Does the 3 blade work better in that respect? Is the 4 blade just as good? I REALLY don't wnat to buy two more spinners; one is enough, and the 4 blade is readily available.
Jon Lowe
ORIGINAL: aerobob
My experience has been that the various theoretical load calculations have little to no meaning in the dynamic, practical environment of Masters/FAI pattern. Of more value to me is finding the right combination of dynamic braking, ability to accelerate without overloading engine, and the ability to permit the motor to turn at or near it's peak bhp rating for full throttle.
We have to consider that todays Masters/FAI sequences hardly use full throttle settings, but moreso emphasize the ability of the power package to transition rapidly and smoothly from one power setting to another, and to behave somewhat "linearly", although this is a VERY subjective area.
My experience has been that the various theoretical load calculations have little to no meaning in the dynamic, practical environment of Masters/FAI pattern. Of more value to me is finding the right combination of dynamic braking, ability to accelerate without overloading engine, and the ability to permit the motor to turn at or near it's peak bhp rating for full throttle.
We have to consider that todays Masters/FAI sequences hardly use full throttle settings, but moreso emphasize the ability of the power package to transition rapidly and smoothly from one power setting to another, and to behave somewhat "linearly", although this is a VERY subjective area.
09-26-2004, 09:10 AM
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RE: 160 FI Props
Thank you for your feedback.
Currently running on 10% nitro with 20% Klotz Benol castor for running in. Will switch to 10% nitro with 18% Klotz SuperTechniplate after 2 gallons.
Model is a Matrix Euro designed by Frazer Briggs, Ewan and Hamish Galloway (Team Bogworm). Frazer carried out the test flights and initial trim flights. The Euro version has the wing span reduced by 4" to assist in the snap.
At the moment the 17x12 is performing well but at the top of the RPM range. After the engine is run in, I am looking at trying an APC 17x12.5N, 17x13 and an APC 18x12 to load the engine a bit more and to reduce noise.
Thank you for your replies
Alan
Currently running on 10% nitro with 20% Klotz Benol castor for running in. Will switch to 10% nitro with 18% Klotz SuperTechniplate after 2 gallons.
Model is a Matrix Euro designed by Frazer Briggs, Ewan and Hamish Galloway (Team Bogworm). Frazer carried out the test flights and initial trim flights. The Euro version has the wing span reduced by 4" to assist in the snap.
At the moment the 17x12 is performing well but at the top of the RPM range. After the engine is run in, I am looking at trying an APC 17x12.5N, 17x13 and an APC 18x12 to load the engine a bit more and to reduce noise.
Thank you for your replies
Alan
10-20-2004, 01:32 AM
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RE: 160 FI Props
ORIGINAL: Schpankme
*Prop Load = DIA^3 x PITCH
*Prop Load = DIA^3 x PITCH
Obviously electric motors are different from engines, but I don't have a pile of money laying around to buy a pile of 16x15, 16x14, 3 blade 15.75x11, 15.5x12, etc, but I can afford to cut up a bunch of 9x6, 10x4.75, etc, for experiments.
On my motors, if you replace one prop with another having this same "load" figure, it will turn the same RPMs and draw the same amps at full throttle static. I was just curious if there is a textbook or something your formula came from that I might benefit from reading, instead of fiddling around with more cut-down, epoxied together frankenstein 6-blade 7x4.75 slow-flight props. (They never do balance right anyway.)
FWIW, a 17x13 two blade, by my formula is equal to a 15.67x12 three blade, or a 14.58x12 four blade. That's not so far off from what people are actually using on the OS 160.
10-20-2004, 07:50 PM
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160 FI Props
As in post #7, you arrive at the same conclusion.
Note: I'm rounding down, not being to concerned with the decimal point
Here's the corrected Formula used in my spreadsheets and charts:
Two Blade = D^4*P/100
Three Blade = D^4*P*3/200
_________
Schpankme
Note: I'm rounding down, not being to concerned with the decimal point
Here's the corrected Formula used in my spreadsheets and charts:
Two Blade = D^4*P/100
Three Blade = D^4*P*3/200
_________
Schpankme
10-21-2004, 10:25 AM
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RE: 160 FI Props
Hi Guys,
very interesting discussion. You are, of course, making one critical assumption: %100 prop efficiency. Unfortunately, we don't get %100. Aerodynamically, a 1 bladed prop would be ideal and as you increase the number of blades the propeller efficiency declines as a result of interference/turbulence caused by the 'leading' prop blade. Empirical experience is still the best from a practical perspective, especially considering the aerodynamic variables involved such as air density, airframe aerodynamics, etc.
I don't have enough ground clearence to run a 25" diameter prop!!
Happy flying,
Will B.
very interesting discussion. You are, of course, making one critical assumption: %100 prop efficiency. Unfortunately, we don't get %100. Aerodynamically, a 1 bladed prop would be ideal and as you increase the number of blades the propeller efficiency declines as a result of interference/turbulence caused by the 'leading' prop blade. Empirical experience is still the best from a practical perspective, especially considering the aerodynamic variables involved such as air density, airframe aerodynamics, etc.
I don't have enough ground clearence to run a 25" diameter prop!!
Happy flying,
Will B.
