| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 122.1 | | SPKALI::THOMAS | | Wed Apr 08 1987 11:22 | 7 |
| Marc,
I think it's great that you went thru that effort. Cold you
look at expanding your data to include pitches from 6-10 in diam.
sizes of 9-13? Also at RPM ranges of 1,800 to 13,000.
Thanks Tom
|
| 122.2 | A better equation | TONTO::SCHRADER | Share and Enjoy! | Wed Apr 08 1987 12:21 | 32 |
| RE: 0,1
I'm afraid that your equation isn't quite right.
The first thing to remember is that a propeller is an airfoil (i.e.
wing). From basic areodynamics...
Lift = Cooef_of_lift * Area * Air_density * Square_of(Velocity)
At a given radius from the hub, Velocity is proportional to Radius*RPM
So .... ( "=>" will be used to mean "is proportional to")
Lift => integral_of((Radius*RPM)^2)
with the integral taken from Radius=0 to Radius=Prop Diameter/2
Lift => Radius^3 * RPM^2
The Radius^3 looks a little strange at first. The reason for it
is that since the blade velocity increases as you go out from
the hub and lift => V^2 instead of just V^1, the lift distribution
is uneven with the blade area at the tips generating a lot more
lift that the blade area towards the hub.
This is pretty simplistic since it makes the assumption that the
propeller's cord and airfoil are constant along it's length.
A while back I wrote an IBM PC program which made graphic plots
of thrust/torque/power vs RPM/diameter/pitch. I'll try to find them
if anybody is interested.
GES
|
| 122.4 | so... | CLOSUS::TAVARES | John--Stay low, keep moving | Wed Apr 08 1987 17:21 | 14 |
| That integral just scared 10 years off my life! Which equation is
good? Is the first one a good simplification? Sure was fun; I
pushed some buttons to see if I could come up with the answers, and
by golly, it works. BTW -- my trusty HP says that the volume of air
moved by a 10/4 at 10K rpm is equal to pi X 10*6.
Doesnt this exercise prove what is intutively obvious, that a larger
pitch prop turning at higher RPM moves more air than a smaller pitch
turning at a lower RPM? I mean, what do we do with these wonderful
numbers?
Looking forward to the day when I get my 10/4 at 10K RPM and say to
the guys "this prop is moving pi x 10*6 volume of air"! Imagine
their amazement.
|
| 122.5 | REALITY LOOMS LARGE ON THE HORIZON | MJOVAX::BENSON | | Wed Apr 08 1987 18:13 | 6 |
| One must temper one's desire to move large volumes of air with the
reality of:
"Will a given engine be able to turn a prop that fast
to move that much air with an airplane hanging off of it???
|
| 122.6 | comments and another table | BZERKR::DUFRESNE | You make 'em - I break 'em | Thu Apr 09 1987 10:39 | 255 |
| re .1: Ok. I will generate a list for the range you mention.
Re .4: I am hoping that the equation is a good simplification
(aside: I do systems performance analysis for a living. One
of the tools of the trade is modeling. The equation I came up
with was a first rough cut. I will refine & change it as more info
come to the fore)
Re .4 and what to with it. well try this: Assume you know approximately
waht is the top end (in RPM) for you engine. Assume also you have
a tachometer so you can verify the actual value. The objective
is to have the engine turn a prop that will generate max thrust
(per definition in .0) at or very near to the top end. Now which
propeller to use ?? I resorted the list by ascending RPM, then
ascending thrust for a given RPM. (see attached.)
re .3 It is not clear to me how I relate lift to thrust.. can someone
expand on this for me. I'm a bit feeble minded in this area.
and lastly, does mr Chadd have anything to say on this subject ??
tx,
md
Page 1 of 5
PROP_DIAM PROP_PITCH RPM THRUST
7 1 10,000 384,844.77
8 1 10,000 502,654.40
9 1 10,000 636,171.98
7 2 10,000 769,689.55
10 1 10,000 785,397.50
11 1 10,000 950,330.98
8 2 10,000 1,005,308.80
12 1 10,000 1,130,972.40
7 3 10,000 1,154,534.33
9 2 10,000 1,272,343.95
13 1 10,000 1,327,321.78
8 3 10,000 1,507,963.20
7 4 10,000 1,539,379.10
14 1 10,000 1,539,379.10
10 2 10,000 1,570,795.00
11 2 10,000 1,900,661.95
9 3 10,000 1,908,515.93
7 5 10,000 1,924,223.87
8 4 10,000 2,010,617.60
12 2 10,000 2,261,944.80
7 6 10,000 2,309,068.65
10 3 10,000 2,356,192.50
8 5 10,000 2,513,272.00
9 4 10,000 2,544,687.90
13 2 10,000 2,654,643.55
11 3 10,000 2,850,992.93
8 6 10,000 3,015,926.40
14 2 10,000 3,078,758.20
10 4 10,000 3,141,590.00
9 5 10,000 3,180,859.88
12 3 10,000 3,392,917.20
11 4 10,000 3,801,323.90
9 6 10,000 3,817,031.85
10 5 10,000 3,926,987.50
13 3 10,000 3,981,965.33
12 4 10,000 4,523,889.60
14 3 10,000 4,618,137.30
10 6 10,000 4,712,385.00
11 5 10,000 4,751,654.88
13 4 10,000 5,309,287.10
12 5 10,000 5,654,862.00
11 6 10,000 5,701,985.85
14 4 10,000 6,157,516.40
13 5 10,000 6,636,608.88
12 6 10,000 6,785,834.40
14 5 10,000 7,696,895.50
13 6 10,000 7,963,930.65
Page 2 of 5
PROP_DIAM PROP_PITCH RPM THRUST
14 6 10,000 9,236,274.60
7 1 15,000 577,267.16
8 1 15,000 753,981.60
9 1 15,000 954,257.96
7 2 15,000 1,154,534.33
10 1 15,000 1,178,096.25
11 1 15,000 1,425,496.46
8 2 15,000 1,507,963.20
12 1 15,000 1,696,458.60
7 3 15,000 1,731,801.49
9 2 15,000 1,908,515.93
13 1 15,000 1,990,982.66
8 3 15,000 2,261,944.80
7 4 15,000 2,309,068.65
14 1 15,000 2,309,068.65
10 2 15,000 2,356,192.50
11 2 15,000 2,850,992.93
9 3 15,000 2,862,773.89
7 5 15,000 2,886,335.81
8 4 15,000 3,015,926.40
12 2 15,000 3,392,917.20
7 6 15,000 3,463,602.98
10 3 15,000 3,534,288.75
8 5 15,000 3,769,908.00
9 4 15,000 3,817,031.85
13 2 15,000 3,981,965.33
11 3 15,000 4,276,489.39
8 6 15,000 4,523,889.60
14 2 15,000 4,618,137.30
10 4 15,000 4,712,385.00
9 5 15,000 4,771,289.81
12 3 15,000 5,089,375.80
11 4 15,000 5,701,985.85
9 6 15,000 5,725,547.77
10 5 15,000 5,890,481.25
13 3 15,000 5,972,947.99
12 4 15,000 6,785,834.40
14 3 15,000 6,927,205.95
10 6 15,000 7,068,577.50
11 5 15,000 7,127,482.31
13 4 15,000 7,963,930.65
12 5 15,000 8,482,293.00
11 6 15,000 8,552,978.78
14 4 15,000 9,236,274.60
13 5 15,000 9,954,913.31
12 6 15,000 10,178,751.60
14 5 15,000 11,545,343.25
Page 3 of 5
PROP_DIAM PROP_PITCH RPM THRUST
13 6 15,000 11,945,895.98
14 6 15,000 13,854,411.90
7 1 20,000 769,689.55
8 1 20,000 1,005,308.80
9 1 20,000 1,272,343.95
7 2 20,000 1,539,379.10
10 1 20,000 1,570,795.00
11 1 20,000 1,900,661.95
8 2 20,000 2,010,617.60
12 1 20,000 2,261,944.80
7 3 20,000 2,309,068.65
9 2 20,000 2,544,687.90
13 1 20,000 2,654,643.55
8 3 20,000 3,015,926.40
7 4 20,000 3,078,758.20
14 1 20,000 3,078,758.20
10 2 20,000 3,141,590.00
11 2 20,000 3,801,323.90
9 3 20,000 3,817,031.85
7 5 20,000 3,848,447.75
8 4 20,000 4,021,235.20
12 2 20,000 4,523,889.60
7 6 20,000 4,618,137.30
10 3 20,000 4,712,385.00
8 5 20,000 5,026,544.00
9 4 20,000 5,089,375.80
13 2 20,000 5,309,287.10
11 3 20,000 5,701,985.85
8 6 20,000 6,031,852.80
14 2 20,000 6,157,516.40
10 4 20,000 6,283,180.00
9 5 20,000 6,361,719.75
12 3 20,000 6,785,834.40
11 4 20,000 7,602,647.80
9 6 20,000 7,634,063.70
10 5 20,000 7,853,975.00
13 3 20,000 7,963,930.65
12 4 20,000 9,047,779.20
14 3 20,000 9,236,274.60
10 6 20,000 9,424,770.00
11 5 20,000 9,503,309.75
13 4 20,000 10,618,574.20
12 5 20,000 11,309,724.00
11 6 20,000 11,403,971.70
14 4 20,000 12,315,032.80
13 5 20,000 13,273,217.75
12 6 20,000 13,571,668.80
Page 4 of 5
PROP_DIAM PROP_PITCH RPM THRUST
14 5 20,000 15,393,791.00
13 6 20,000 15,927,861.30
14 6 20,000 18,472,549.20
7 1 25,000 962,111.94
8 1 25,000 1,256,636.00
9 1 25,000 1,590,429.94
7 2 25,000 1,924,223.87
10 1 25,000 1,963,493.75
11 1 25,000 2,375,827.44
8 2 25,000 2,513,272.00
12 1 25,000 2,827,431.00
7 3 25,000 2,886,335.81
9 2 25,000 3,180,859.88
13 1 25,000 3,318,304.44
8 3 25,000 3,769,908.00
7 4 25,000 3,848,447.75
14 1 25,000 3,848,447.75
10 2 25,000 3,926,987.50
11 2 25,000 4,751,654.88
9 3 25,000 4,771,289.81
7 5 25,000 4,810,559.69
8 4 25,000 5,026,544.00
12 2 25,000 5,654,862.00
7 6 25,000 5,772,671.62
10 3 25,000 5,890,481.25
9 4 25,000 6,361,719.75
13 2 25,000 6,636,608.88
11 3 25,000 7,127,482.31
8 6 25,000 7,539,816.00
8 6 25,000 7,539,816.00
14 2 25,000 7,696,895.50
10 4 25,000 7,853,975.00
9 5 25,000 7,952,149.69
12 3 25,000 8,482,293.00
11 4 25,000 9,503,309.75
9 6 25,000 9,542,579.63
10 5 25,000 9,817,468.75
13 3 25,000 9,954,913.31
12 4 25,000 11,309,724.00
14 3 25,000 11,545,343.25
10 6 25,000 11,780,962.50
11 5 25,000 11,879,137.19
13 4 25,000 13,273,217.75
12 5 25,000 14,137,155.00
11 6 25,000 14,254,964.63
14 4 25,000 15,393,791.00
13 5 25,000 16,591,522.19
Page 5 of 5
PROP_DIAM PROP_PITCH RPM THRUST
12 6 25,000 16,964,586.00
14 5 25,000 19,242,238.75
13 6 25,000 19,909,826.63
14 6 25,000 23,090,686.50
|
| 122.7 | THRUST, LIFT, V^2, AND OTHER THINGS | TONTO::SCHRADER | Share and Enjoy! | Mon Apr 13 1987 13:54 | 24 |
|
re: -1
No, I do not beleive that your equation is a good approximation.
I think the basic misunderstanding is that thrust is proportional
to the amount of air being moved. It is not. It is proportional
to the amount of air being >>accelerated<< (Remember F=M*A,
or in our case, Thrust = Mass of air * Rate at which the prop
accelerates the air). These two things are ENTIRELY different.
If, say, you double the RPM. First you must accelerate twice
as much mass, and second you must double the acceleration to
twice as much mass through the prop in the same amount of time.
What you wind up with is four times the thrust since both the
mass being accelerated and the acceleration are being doubled.
This is precisely why the velocity squared term shows up in
the standard lift and drag equations. Any good aerodynamics
text will have a complete explanation of all of this stuff.
re: elsewhere
Thrust is related to lift because a propeller IS a wing. The
"lift" generated by this "wing" is called "thrust" by convention
since the force is in the forward direction rather than upwards.
|
| 122.8 | real stuff --- right from the textbook | TONTO::SCHRADER | Share and Enjoy! | Thu Apr 16 1987 13:55 | 39 |
|
I finally found my reference books.
From "AIRPLANE PERFORMANCE STABILITY and CONTROL" by Perkins & Hage
Thrust = Tc * Rho * (J)^2 * (RPM)^2 * (Diameter)^4
(Thrust generated by the prop)
YES! Those are the correct powers to raise the RPM and prop Diameter to.
A couple years ago I checked the derivations for these equations and
by golly, they turned out to be correct! (I didn't believe it at
first either) 100% of the wierdness is a side effect of the fact
that aerodynamic forces are non-linear functions of airflow
velocitys.
Tc is a proportionality constant (i.e. fudge factor).
To find actual value Tc would need to be measured but it can be
ignored if you are just comparing relative magnitudes. Rho is the air
density, ignore it for the same reason.
J is the "advance ratio". This is the prop diameter divided by the
distance the prop will move forward with each revolution. The best thing
that I have found to use for a W.A.G. is the Diameter divided by the Pitch.
In real life this will be too small since the actual pitch will be
a little less than the physical pitch of the blades due to slippage,
but since we're only after an approximation it should be good enough.
If we substitute Diameter/Pitch for J in the thrust equation we get...
Thrust = Tc * Rho * (Dia)^2/(Pitch)^2 * (Rpm)^2 * (Dia)^4
or
Thrust = Tc * Rho * (RPM)^2 * (Dia)^6 / (Pitch)^2 !!!
Enough beating my head against the wall for now...
GES
|
| 122.9 | let through some computes at this | BZERKR::DUFRESNE | You make 'em - I break 'em | Thu Apr 16 1987 16:12 | 4 |
| Neat !!! Let put this equation through my data and see the differences.
md
|
| 122.10 | | BZERKR::DUFRESNE | You make 'em - I break 'em | Thu Apr 16 1987 16:15 | 4 |
| ...and thank for the reference.. I think I will go out & buy the
book..
md7
|
| 122.11 | Doest moving the plane faster reduce thrust?! | ANKER::ANKER | Anker Berg-Sonne | Thu Apr 16 1987 16:30 | 18 |
| Re:< Note 122.10 by BZERKR::DUFRESNE "You make 'em - I break 'em" >
The entire discussion seems to assume that the prop is
attached to a plane that isn't moving. In reality, as the plane
moves faster and faster the prop generates less and less thrust
(assuming constant RPM). A really useful tabs would be one that
gave thrust as a function of velocity. If you know what the drag
of your plane is and you plot that and the drag. Where the lines
cross tells you how fast your plane will move.
Another approach is to take the horsepower of your
engine, calculate how fast that should be able to move your plane
(which is calculated from drag and velocity) and then find a prop
that will generate the same thrust as your drag at the max HP RPM
of your engine at the velocity that the plane is moving at. See
that I would find useful.
Anker
|
| 122.12 | OH NO! airFOILED AGAIN! | TONTO::SCHRADER | Share and Enjoy! | Fri Apr 17 1987 09:37 | 29 |
| re: .11
The previous equation actually assumes that the forward velocity
is proportional to RPM. The advance ratio ("J" in the equation)
is actually the Prop diameter / Forward movement per prop rev.
By plugging in Dia/Pitch we are assumeing that forward velocity
(in/min) = RPM(Revs/min) * Pitch(in/rev). Another way of looking
at it is that we are assumeing a constant angle of attack for the
blade airfoil section. Of course, this is not really true, but to
get closer to real life you need to start looking at blade
airfoil shape VS airfoil lift VS angle of attack VS angle of
attack differences along the blades VS blade shape (most have
some sort of taper) VS all of the other stuff that each prop.
mfg. does to make his prop. different from the rest of the crowd.
In short, rough comparisons between props, operating RPM, etc.
can be done with some reasonably (?) simple equations. Actual
performance predictions, (i.e. what prop should I use for my
xx plane/yy engine) would at a very minimum require a wind tunnel
(& associated equipment) in order to characterize prop performance
over a reasonable range of operating conditions.
One last point. Even when running the engine on the ground,
there is still forward airflow through the prop (the prop
is blowing air). As far as the prop is concerned this is just as
good as forward motion, so there is never a case where the prop is
running at zero airspeed (relative to the prop blades, anyway).
GES
|
| 122.13 | To Much Detail | SPKALI::THOMAS | | Fri Apr 17 1987 10:08 | 20 |
|
BOY !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Are we trying to power the space shuttle with a piston engine
or trying to fly our RC aircraft?? I'M confused?? You guy's
can stay here and debate this issue till your blue in the face.
I'm going flying................................
What ever happened to KISS??????
Bye
Tom
P.S. I thought this was going to be a meaningful subject that the
average flyer could utilize. Not a debate on the theory of aerodynamics.
|
| 122.14 | I plan to KISS it. | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 11:59 | 17 |
| I am trying to get an reasonable approximation of prop thrust.
I have no intention in getting in gorry details.
let me see what the equation in .11 gives and let work from there.
If we can get a measure of relative power (on paper) then one can
verify/sanity check the results (hopefully) by picking a few props
and trying them out and see what happens (like you go fly. If the
results are as expected then the equation is reasonable. If not,
then we try to understand why. Eventually we may get a coobook
list. As long as it work, who cares ...
(Hey Thomas, I just can see you showing up at a race with a plane swinging
an oddball prop and wiping the competion into the ground.)
|
| 122.15 | gentleman, pls sit down!! | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 13:03 | 229 |
| Ok... Here are the number... I'm completely flabbergasted
The factor with the most effect on performance is J : (dia)^2/(pitch^2)
From these numbers, the prop with the lowest pitch & largest diameter
does best.
either the prop makers are taking us for a ride or the is something else that
as to be accounted for !!! (or maybe helicopter makers have the secret: low
angle of attack & long blade) ... Hummmm!
md
Page 1 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
7 6 10,000 1.36 326,536.00
7 5 10,000 1.96 470,596.00
8 6 10,000 1.78 729,088.00
7 4 10,000 3.06 734,706.00
7 6 15,000 1.36 734,706.00
8 5 10,000 2.56 1,048,576.00
7 5 15,000 1.96 1,058,841.00
7 3 10,000 5.44 1,306,144.00
7 6 20,000 1.36 1,306,144.00
9 6 10,000 2.25 1,476,225.00
8 4 10,000 4.00 1,638,400.00
8 6 15,000 1.78 1,640,448.00
7 4 15,000 3.06 1,653,088.50
7 5 20,000 1.96 1,882,384.00
7 6 25,000 1.36 2,040,850.00
9 5 10,000 3.24 2,125,764.00
8 5 15,000 2.56 2,359,296.00
10 6 10,000 2.78 2,780,000.00
8 3 10,000 7.11 2,912,256.00
8 6 20,000 1.78 2,916,352.00
7 4 20,000 3.06 2,938,824.00
7 3 15,000 5.44 2,938,824.00
7 2 10,000 12.25 2,941,225.00
7 5 25,000 1.96 2,941,225.00
9 4 10,000 5.06 3,319,866.00
9 6 15,000 2.25 3,321,506.25
8 4 15,000 4.00 3,686,400.00
10 5 10,000 4.00 4,000,000.00
8 5 20,000 2.56 4,194,304.00
8 6 25,000 1.78 4,556,800.00
8 6 25,000 1.78 4,556,800.00
7 4 25,000 3.06 4,591,912.50
9 5 15,000 3.24 4,782,969.00
11 6 10,000 3.36 4,919,376.00
7 3 20,000 5.44 5,224,576.00
9 3 10,000 9.00 5,904,900.00
9 6 20,000 2.25 5,904,900.00
10 4 10,000 6.25 6,250,000.00
10 6 15,000 2.78 6,255,000.00
8 3 15,000 7.11 6,552,576.00
8 2 10,000 16.00 6,553,600.00
8 4 20,000 4.00 6,553,600.00
7 2 15,000 12.25 6,617,756.25
11 5 10,000 4.84 7,086,244.00
9 4 15,000 5.06 7,469,698.50
7 3 25,000 5.44 8,163,400.00
12 6 10,000 4.00 8,294,400.00
Page 2 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
9 5 20,000 3.24 8,503,056.00
10 5 15,000 4.00 9,000,000.00
9 6 25,000 2.25 9,226,406.25
8 4 25,000 4.00 10,240,000.00
11 4 10,000 7.56 11,068,596.00
11 6 15,000 3.36 11,068,596.00
10 3 10,000 11.11 11,110,000.00
10 6 20,000 2.78 11,120,000.00
8 3 20,000 7.11 11,649,024.00
7 1 10,000 49.00 11,764,900.00
7 2 20,000 12.25 11,764,900.00
12 5 10,000 5.76 11,943,936.00
9 4 20,000 5.06 13,279,464.00
9 2 10,000 20.25 13,286,025.00
9 3 15,000 9.00 13,286,025.00
9 5 25,000 3.24 13,286,025.00
13 6 10,000 4.69 13,395,109.00
10 4 15,000 6.25 14,062,500.00
8 2 15,000 16.00 14,745,600.00
11 5 15,000 4.84 15,944,049.00
10 5 20,000 4.00 16,000,000.00
10 6 25,000 2.78 17,375,000.00
8 3 25,000 7.11 18,201,600.00
7 2 25,000 12.25 18,382,656.25
12 4 10,000 9.00 18,662,400.00
12 6 15,000 4.00 18,662,400.00
13 5 10,000 6.76 19,307,236.00
11 3 10,000 13.44 19,677,504.00
11 6 20,000 3.36 19,677,504.00
9 4 25,000 5.06 20,749,162.50
14 6 10,000 5.44 20,898,304.00
9 3 20,000 9.00 23,619,600.00
11 4 15,000 7.56 24,904,341.00
10 3 15,000 11.11 24,997,500.00
10 2 10,000 25.00 25,000,000.00
10 4 20,000 6.25 25,000,000.00
10 5 25,000 4.00 25,000,000.00
8 1 10,000 64.00 26,214,400.00
8 2 20,000 16.00 26,214,400.00
7 1 15,000 49.00 26,471,025.00
12 5 15,000 5.76 26,873,856.00
11 5 20,000 4.84 28,344,976.00
9 2 15,000 20.25 29,893,556.25
14 5 10,000 7.84 30,118,144.00
13 6 15,000 4.69 30,138,995.25
13 4 10,000 10.56 30,160,416.00
11 6 25,000 3.36 30,746,100.00
Page 3 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
12 3 10,000 16.00 33,177,600.00
12 6 20,000 4.00 33,177,600.00
9 3 25,000 9.00 36,905,625.00
10 4 25,000 6.25 39,062,500.00
8 2 25,000 16.00 40,960,000.00
12 4 15,000 9.00 41,990,400.00
13 5 15,000 6.76 43,441,281.00
11 3 15,000 13.44 44,274,384.00
11 4 20,000 7.56 44,274,384.00
11 2 10,000 30.25 44,289,025.00
11 5 25,000 4.84 44,289,025.00
10 3 20,000 11.11 44,440,000.00
14 6 15,000 5.44 47,021,184.00
7 1 20,000 49.00 47,059,600.00
14 4 10,000 12.25 47,059,600.00
12 5 20,000 5.76 47,775,744.00
12 6 25,000 4.00 51,840,000.00
9 1 10,000 81.00 53,144,100.00
9 2 20,000 20.25 53,144,100.00
13 6 20,000 4.69 53,580,436.00
13 3 10,000 18.78 53,637,558.00
10 2 15,000 25.00 56,250,000.00
8 1 15,000 64.00 58,982,400.00
14 5 15,000 7.84 67,765,824.00
13 4 15,000 10.56 67,860,936.00
11 4 25,000 7.56 69,178,725.00
10 3 25,000 11.11 69,437,500.00
7 1 25,000 49.00 73,530,625.00
12 2 10,000 36.00 74,649,600.00
12 3 15,000 16.00 74,649,600.00
12 4 20,000 9.00 74,649,600.00
12 5 25,000 5.76 74,649,600.00
13 5 20,000 6.76 77,228,944.00
11 3 20,000 13.44 78,710,016.00
9 2 25,000 20.25 83,037,656.25
14 6 20,000 5.44 83,593,216.00
14 3 10,000 21.78 83,670,048.00
13 6 25,000 4.69 83,719,431.25
11 2 15,000 30.25 99,650,306.25
10 1 10,000 100.00 100,000,000.00
10 2 20,000 25.00 100,000,000.00
8 1 20,000 64.00 104,857,600.00
14 4 15,000 12.25 105,884,100.00
12 4 25,000 9.00 116,640,000.00
9 1 15,000 81.00 119,574,225.00
14 5 20,000 7.84 120,472,576.00
13 4 20,000 10.56 120,641,664.00
Page 4 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
13 2 10,000 42.25 120,670,225.00
13 5 25,000 6.76 120,670,225.00
13 3 15,000 18.78 120,684,505.50
11 3 25,000 13.44 122,984,400.00
14 6 25,000 5.44 130,614,400.00
12 3 20,000 16.00 132,710,400.00
10 2 25,000 25.00 156,250,000.00
8 1 25,000 64.00 163,840,000.00
12 2 15,000 36.00 167,961,600.00
11 1 10,000 121.00 177,156,100.00
11 2 20,000 30.25 177,156,100.00
14 2 10,000 49.00 188,238,400.00
14 4 20,000 12.25 188,238,400.00
14 5 25,000 7.84 188,238,400.00
14 3 15,000 21.78 188,257,608.00
13 4 25,000 10.56 188,502,600.00
12 3 25,000 16.00 207,360,000.00
9 1 20,000 81.00 212,576,400.00
13 3 20,000 18.78 214,550,232.00
10 1 15,000 100.00 225,000,000.00
13 2 15,000 42.25 271,508,006.25
11 2 25,000 30.25 276,806,406.25
14 4 25,000 12.25 294,122,500.00
12 1 10,000 144.00 298,598,400.00
12 2 20,000 36.00 298,598,400.00
9 1 25,000 81.00 332,150,625.00
14 3 20,000 21.78 334,680,192.00
13 3 25,000 18.78 335,234,737.50
11 1 15,000 121.00 398,601,225.00
10 1 20,000 100.00 400,000,000.00
14 2 15,000 49.00 423,536,400.00
12 2 25,000 36.00 466,560,000.00
13 1 10,000 169.00 482,680,900.00
13 2 20,000 42.25 482,680,900.00
14 3 25,000 21.78 522,937,800.00
10 1 25,000 100.00 625,000,000.00
12 1 15,000 144.00 671,846,400.00
11 1 20,000 121.00 708,624,400.00
14 1 10,000 196.00 752,953,600.00
14 2 20,000 49.00 752,953,600.00
13 2 25,000 42.25 754,188,906.25
13 1 15,000 169.00 1,086,032,025.0
11 1 25,000 121.00 1,107,225,625.0
14 2 25,000 49.00 1,176,490,000.0
12 1 20,000 144.00 1,194,393,600.0
14 1 15,000 196.00 1,694,145,600.0
12 1 25,000 144.00 1,866,240,000.0
Page 5 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
13 1 20,000 169.00 1,930,723,600.0
14 1 20,000 196.00 3,011,814,400.0
13 1 25,000 169.00 3,016,755,625.0
14 1 25,000 196.00 4,705,960,000.0
|
| 122.16 | What does thrust mean to you? | HPSCAD::WFIELD | | Fri Apr 17 1987 15:25 | 5 |
| I have a question. Why do you want to maximize thrust? When
I think of thrust I think of power as opposed to speed. As you
have noticed from the equation, thrust is inversely proportional
to pitch. Do you want to go fast, or fly a large heavy plane at
a lower speed?
|
| 122.17 | move lots of air & go fast | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 16:03 | 11 |
| At the risk of sounding dumb and stupid: I want to move lots of
air in given a unit of time. My intuition (and I may be wrong) would
lead to believe that the more air you can move, the faster you will
go.
The numbers I got tell me that for a given rpm (say 10000),
14-1 prop beats everything else by a substantial margin. Generally
speaking, again from the numbers a long prop with low pitch does
better than a short prop with high pitch. This is very perplexing...
what did I miss ??
|
| 122.18 | advance ratio is killer | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 16:27 | 5 |
| My basic problem is with the advance ratio. The proposed equation
(prop diam div by distance prop moves per rev.) confuses me.
The higher the pitch, the more the prop should advance. The equation yields
opposite results. why ??
|
| 122.19 | Thrust = force, not speed | HPSCAD::WFIELD | | Fri Apr 17 1987 17:06 | 6 |
| I think the whole problem is with the definition of thrust.
From looking at the equation it seems that thrust is how much pressure
or force the prop can generate, not how fast it can do it.
Aircraft speed would be pitch (in inches/revolution) * rpm * prop
efficiency. The whole problem is to determine prop efficiency. It
is going to be different on every plane.
|
| 122.20 | ERROR! ERROR! | TONTO::SCHRADER | Share and Enjoy! | Fri Apr 17 1987 17:24 | 20 |
|
My error on this one...
The advance ratio should have been pitch/diameter (blush).
This will no doubt change things quite a bit.
The combined equation changes to ...
Thrust => Fudge Factor * RPM^2 * Diameter^2 * Pitch^2
re: -??
There is a VERY good reason for this discussion. Propellers are widely
misunderstood. The more that you know about the basic principles
behind how things work, the easier it is to make intelligent decisions.
The other alternative is to consult with the local witchdoctor and/or
make a wild guesses.
GES
|
| 122.21 | looks like I was close | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 17:32 | 7 |
| ok.. i redo my number... BTW, check the equation in .1 - It's the
same except for the ^2..
stand by for yet a new set of numbers
md
|
| 122.22 | the last word ? | BZERKR::DUFRESNE | You make 'em - I break 'em | Fri Apr 17 1987 18:16 | 257 |
| Ok, here are the lastest numbers.
Prop_thrust was computed as J_factor * (rpm_sq / 100000) * diam_exp_4
where:
J_factor = (prop_pitch / prop_diam) * (prop_pitch * prop_diam)
rpm_sq= rpm * rpm
diam_exp_4 = (((prop_diam *prop_diam)*prop_diam)*prop_diam)
(I did computed it this way in order to see intermediate value & because
TEAMDATA is a bit dumb with formulas)
rpm_sq was divided by 100000 because I can only print 15 digits and the last
6 digits where always 0
Bottom line so far: we have come a full circle. This order of this list
matches my first one (see .0). The orginal rough model is good one
to use to measure relative performance of a propeller, ALL OTHER THINGS
BEING EQUAL, ie:
don't didle the engine
don't didle the plane
"identical props" (dain-pitch) from different manufactures
may perform differently. I would think the disfference should
be marginal
etc..
Now, unless someone comes up with an other oversight, I can satisfy thomas's
request & gen a table over the range of diam & pitch he had in mind.
I can also get back to FOX & tell them that their original suggestion of a
14-1 prop was not quite right.
This was fun.
md
Page 1 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
7 1 10,000 1.00 240,100.00
8 1 10,000 1.00 409,600.00
7 1 15,000 1.00 540,225.00
9 1 10,000 1.00 656,100.00
8 1 15,000 1.00 921,600.00
7 2 10,000 4.00 960,400.00
7 1 20,000 1.00 960,400.00
10 1 10,000 1.00 1,000,000.00
11 1 10,000 1.00 1,464,100.00
9 1 15,000 1.00 1,476,225.00
7 1 25,000 1.00 1,500,625.00
8 2 10,000 4.00 1,638,400.00
8 1 20,000 1.00 1,638,400.00
12 1 10,000 1.00 2,073,600.00
7 3 10,000 9.00 2,160,900.00
7 2 15,000 4.00 2,160,900.00
10 1 15,000 1.00 2,250,000.00
8 1 25,000 1.00 2,560,000.00
9 2 10,000 4.00 2,624,400.00
9 1 20,000 1.00 2,624,400.00
13 1 10,000 1.00 2,856,100.00
11 1 15,000 1.00 3,294,225.00
8 3 10,000 9.00 3,686,400.00
8 2 15,000 4.00 3,686,400.00
7 4 10,000 16.00 3,841,600.00
7 2 20,000 4.00 3,841,600.00
14 1 10,000 1.00 3,841,600.00
10 2 10,000 4.00 4,000,000.00
10 1 20,000 1.00 4,000,000.00
9 1 25,000 1.00 4,100,625.00
12 1 15,000 1.00 4,665,600.00
7 3 15,000 9.00 4,862,025.00
11 2 10,000 4.00 5,856,400.00
11 1 20,000 1.00 5,856,400.00
9 3 10,000 9.00 5,904,900.00
9 2 15,000 4.00 5,904,900.00
7 5 10,000 25.00 6,002,500.00
7 2 25,000 4.00 6,002,500.00
10 1 25,000 1.00 6,250,000.00
13 1 15,000 1.00 6,426,225.00
8 4 10,000 16.00 6,553,600.00
8 2 20,000 4.00 6,553,600.00
8 3 15,000 9.00 8,294,400.00
12 2 10,000 4.00 8,294,400.00
12 1 20,000 1.00 8,294,400.00
7 6 10,000 36.00 8,643,600.00
7 3 20,000 9.00 8,643,600.00
Page 2 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
7 4 15,000 16.00 8,643,600.00
14 1 15,000 1.00 8,643,600.00
10 3 10,000 9.00 9,000,000.00
10 2 15,000 4.00 9,000,000.00
11 1 25,000 1.00 9,150,625.00
8 5 10,000 25.00 10,240,000.00
8 2 25,000 4.00 10,240,000.00
9 4 10,000 16.00 10,497,600.00
9 2 20,000 4.00 10,497,600.00
13 2 10,000 4.00 11,424,400.00
13 1 20,000 1.00 11,424,400.00
12 1 25,000 1.00 12,960,000.00
11 3 10,000 9.00 13,176,900.00
11 2 15,000 4.00 13,176,900.00
9 3 15,000 9.00 13,286,025.00
7 5 15,000 25.00 13,505,625.00
7 3 25,000 9.00 13,505,625.00
8 6 10,000 36.00 14,745,600.00
8 4 15,000 16.00 14,745,600.00
8 3 20,000 9.00 14,745,600.00
7 4 20,000 16.00 15,366,400.00
14 2 10,000 4.00 15,366,400.00
14 1 20,000 1.00 15,366,400.00
10 4 10,000 16.00 16,000,000.00
10 2 20,000 4.00 16,000,000.00
9 5 10,000 25.00 16,402,500.00
9 2 25,000 4.00 16,402,500.00
13 1 25,000 1.00 17,850,625.00
12 3 10,000 9.00 18,662,400.00
12 2 15,000 4.00 18,662,400.00
7 6 15,000 36.00 19,448,100.00
10 3 15,000 9.00 20,250,000.00
8 5 15,000 25.00 23,040,000.00
8 3 25,000 9.00 23,040,000.00
11 4 10,000 16.00 23,425,600.00
11 2 20,000 4.00 23,425,600.00
9 6 10,000 36.00 23,619,600.00
9 4 15,000 16.00 23,619,600.00
9 3 20,000 9.00 23,619,600.00
7 5 20,000 25.00 24,010,000.00
7 4 25,000 16.00 24,010,000.00
14 1 25,000 1.00 24,010,000.00
10 5 10,000 25.00 25,000,000.00
10 2 25,000 4.00 25,000,000.00
13 3 10,000 9.00 25,704,900.00
13 2 15,000 4.00 25,704,900.00
8 4 20,000 16.00 26,214,400.00
Page 3 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
11 3 15,000 9.00 29,648,025.00
8 6 15,000 36.00 33,177,600.00
12 4 10,000 16.00 33,177,600.00
12 2 20,000 4.00 33,177,600.00
7 6 20,000 36.00 34,574,400.00
14 3 10,000 9.00 34,574,400.00
14 2 15,000 4.00 34,574,400.00
10 6 10,000 36.00 36,000,000.00
10 4 15,000 16.00 36,000,000.00
10 3 20,000 9.00 36,000,000.00
11 5 10,000 25.00 36,602,500.00
11 2 25,000 4.00 36,602,500.00
9 5 15,000 25.00 36,905,625.00
9 3 25,000 9.00 36,905,625.00
7 5 25,000 25.00 37,515,625.00
8 5 20,000 25.00 40,960,000.00
8 4 25,000 16.00 40,960,000.00
9 4 20,000 16.00 41,990,400.00
12 3 15,000 9.00 41,990,400.00
13 4 10,000 16.00 45,697,600.00
13 2 20,000 4.00 45,697,600.00
12 5 10,000 25.00 51,840,000.00
12 2 25,000 4.00 51,840,000.00
11 6 10,000 36.00 52,707,600.00
11 4 15,000 16.00 52,707,600.00
11 3 20,000 9.00 52,707,600.00
9 6 15,000 36.00 53,144,100.00
7 6 25,000 36.00 54,022,500.00
10 5 15,000 25.00 56,250,000.00
10 3 25,000 9.00 56,250,000.00
13 3 15,000 9.00 57,836,025.00
8 6 20,000 36.00 58,982,400.00
14 4 10,000 16.00 61,465,600.00
14 2 20,000 4.00 61,465,600.00
10 4 20,000 16.00 64,000,000.00
9 5 20,000 25.00 65,610,000.00
9 4 25,000 16.00 65,610,000.00
13 5 10,000 25.00 71,402,500.00
13 2 25,000 4.00 71,402,500.00
12 6 10,000 36.00 74,649,600.00
12 4 15,000 16.00 74,649,600.00
12 3 20,000 9.00 74,649,600.00
14 3 15,000 9.00 77,792,400.00
10 6 15,000 36.00 81,000,000.00
11 5 15,000 25.00 82,355,625.00
11 3 25,000 9.00 82,355,625.00
8 6 25,000 36.00 92,160,000.00
Page 4 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
8 6 25,000 36.00 92,160,000.00
11 4 20,000 16.00 93,702,400.00
9 6 20,000 36.00 94,478,400.00
14 5 10,000 25.00 96,040,000.00
14 2 25,000 4.00 96,040,000.00
10 5 20,000 25.00 100,000,000.00
10 4 25,000 16.00 100,000,000.00
9 5 25,000 25.00 102,515,625.00
13 6 10,000 36.00 102,819,600.00
13 4 15,000 16.00 102,819,600.00
13 3 20,000 9.00 102,819,600.00
12 5 15,000 25.00 116,640,000.00
12 3 25,000 9.00 116,640,000.00
11 6 15,000 36.00 118,592,100.00
12 4 20,000 16.00 132,710,400.00
14 6 10,000 36.00 138,297,600.00
14 4 15,000 16.00 138,297,600.00
14 3 20,000 9.00 138,297,600.00
10 6 20,000 36.00 144,000,000.00
11 5 20,000 25.00 146,410,000.00
11 4 25,000 16.00 146,410,000.00
9 6 25,000 36.00 147,622,500.00
10 5 25,000 25.00 156,250,000.00
13 5 15,000 25.00 160,655,625.00
13 3 25,000 9.00 160,655,625.00
12 6 15,000 36.00 167,961,600.00
13 4 20,000 16.00 182,790,400.00
12 5 20,000 25.00 207,360,000.00
12 4 25,000 16.00 207,360,000.00
11 6 20,000 36.00 210,830,400.00
14 5 15,000 25.00 216,090,000.00
14 3 25,000 9.00 216,090,000.00
10 6 25,000 36.00 225,000,000.00
11 5 25,000 25.00 228,765,625.00
13 6 15,000 36.00 231,344,100.00
14 4 20,000 16.00 245,862,400.00
13 5 20,000 25.00 285,610,000.00
13 4 25,000 16.00 285,610,000.00
12 6 20,000 36.00 298,598,400.00
14 6 15,000 36.00 311,169,600.00
12 5 25,000 25.00 324,000,000.00
11 6 25,000 36.00 329,422,500.00
14 5 20,000 25.00 384,160,000.00
14 4 25,000 16.00 384,160,000.00
13 6 20,000 36.00 411,278,400.00
13 5 25,000 25.00 446,265,625.00
12 6 25,000 36.00 466,560,000.00
Page 5 of 5
PROP_DIAM PROP_PITCH RPM J_FACTOR PROP_THRUST
14 6 20,000 36.00 553,190,400.00
14 5 25,000 25.00 600,250,000.00
13 6 25,000 36.00 642,622,500.00
14 6 25,000 36.00 864,360,000.00
|
| 122.23 | The witch doctor is fired !! | BZERKR::DUFRESNE | You make 'em - I break 'em | Sat Apr 18 1987 00:18 | 56 |
| {From RCm, May issue, p 14
report from Tangerine International RC championships (reported by Don Lowe)
"...Notice that some fliers are now using 11" pitch props ! This is because
static rpm is not what counts -- its how it performs in the air. Static rpm
is good only for comparing different set-ups on the ground. Typically most
modelers under-pitch on their prop choi. As you may recall, what we are af
seeking is an optimum airspeed and vertical performance IN the AIR. A fixed
pitc propeller thst might give exciting rpm and thrust on the ground is often
useles in the air. The reasoning is simply thu: airspeed is responsive to{
engine rpm and ptch or prop blade angle of attack. As the ship moves f
forward,the angle of attack of the blade is decreased due to the vector
addition of forward velocity (don't sweat it - just accept it. Unless the
engine increases in rpm significantly in the air, the rpm times the blade
angle of attack will not drive the aircraft at airspeed desire. Its the
old story: max thrust statically is not max thrust at speed. A constant speed
prop (variable itch) is an ideal solution since the blade angle adjusts to
meet the forward speed requirements. If we use a fixed pitch prop, as lmost
all of us, then is a trial and error proces. "
(Editor note: Not if one uses ones head and does what a little of research, viz
the model in previous notes)
"It would be neat is could have an adjustable pitch prop that we could set on
the ground to seek the best ccombination. Lacking that we need a good supply
of diameter/pitch combinationsto try."
(Editor Note: Ugh.. tinkerer.. use your head)
"Many modelers follow the route of pitch reduction to gai rpm on the g
ground. That is usually the WRONG action. Quite often trimming diameter
while retaining pitch is a better approach. For a typical FAI set-upNEVER
go below 9" pitch -- note that some fliers are using 11" pitch -- for a
2-stroke engin. NEVER use less than a 10" on a 1.2 cu in 4-stroke; some are
using a 12"pitch.
Th old AMA prop/engine set-up for pattern ships was 11" by 7-8" pitch. This
provide{ adequate airspeed ONLY is the engine turns MUCH higher rpm -- and
that's nois. Remember, airspeed is basically rpm times pitch with suitable
conversion & efficiency factors thrown in. Don't get caught with your pitch
down & your rpm up. For example, 11000 rpm with a 10" pitch prop will give
the same airspeed as 7" pitch turning around 16000 rpm"
(Editor note: Pick say a 12" diam prop. Apply model:
12 * 10 * 11000 = 1320000
12 * 7 * 16000= 1344000
Margin of error : 2% -- close enough fo mee !!
With this kind of evidence, who want the witch doctor ?
md
|
| 122.24 | | CLOSUS::TAVARES | John--Stay low, keep moving | Mon Apr 20 1987 11:48 | 18 |
| Do we have a contradiction here? Don says that you want a large
diameter prop with high pitch...if I read him right. The
conclusion stated in .15 and discussed in the next few notes says
that a large diameter and low pitch is what you want. I know
that Don, being the president of AMA, has a sound (they call it
sound, not noise) axe to grind, but his point about the
difference between static and in-flight test seems well put. The
equation that our data comes from does only model the static
case; doesn't it? For myself, because I like quiet engines, any
argument that tells me to slow engine speed by swinging a large
high pitch prop sounds good.
Maybe its because the original idea was for flat-out speed (low
drag) type models, and Don is talking pattern, where the draggy
models are becoming vogue. What with turnarond, and all.
I'm at the edge of my understanding, someone else has to
straighten out this apparent contradiction.
|
| 122.25 | frly em | DPDMAI::GREER | | Mon Apr 20 1987 13:07 | 13 |
| " ALL PROPS ARE NOT CREATED EQUAL " WOODEN ONES AT LEAST. Buy a
bag of 12 props. Use your PRATHER prop guage and check the pitch.
You will find that bag of 7" pitch props will vary from 6.5 to 7.5.
Then bend the prop in your hands to check how stiff they are. It
will vary widely. The more flexable ones will straighten out to
some unknown pitch at rpm. One way to find out what they are pulling
is to put them on a two horse eletric motor in series with an ampmeter.
See which ones pull the most amps vrs rpm. The net net is you will
get maybe two good props out of that bag of twelve. I have no
experience other than wood.
bob
|
| 122.26 | it's all in the thread | BZERKR::DUFRESNE | You make 'em - I break 'em | Tue Apr 21 1987 10:37 | 23 |
| re .-1: The way I read the article is the one should use tradeoff
rpm for higher pitch. A side effect may be that you will use smaller
diameter prop. I will have more example latter (when I get home
tonite, I plan to redo the tables.
Also re large prop & low pitch: The J-factor first given was **WRONG**,
I repeat: **wrong**. The correct value was pitch / diameter. I
used the opposite (diam / pitch) the first time around, yielding
these strange results. To use an anlogy: a fine thread screw (that
kind use to hold things) take many more turns to get where is going.
That is similar to a low pitch prop. A coarse thread screw goes
in a lot faster. That is similar to a high pitch prop.
Now You are going to need more force to drive the coarse thread
screw. (ie: you are going to get a lower rpm) but you may finish
the job faster (or get more thrust).
I have a another little bit of data to give about props and engines
latter. (from Clarence Lee's engine clinic in the May RCM).
md
|
| 122.27 | | SPKALI::THOMAS | | Tue Apr 21 1987 11:50 | 16 |
|
One factor you haven't brought into the picture about choosing
the correct prop is engine desidn related to torque/stroke length.
I think you will fine that in practical use your engine will rev
up only to a certain RPM and no more. One easy way to increase
engine revs is to file the exhaust port top from the inside.Angle
the top of the port down. This will allow the exhaust port to open
sooner and increase engine rpms. A second alternative is to angle
the boost port from the outside edge of the liner upwards. Take
material off of the bottom of the port. Don't make the port any
larger just create an angle across the thickness of the liner.
This will improve fuel intake. If I were you I wouldn't expect this
engine to last to long. Your efforts to increase rpm's will be adding
a strain to the engine parts.
Tom
|
| 122.28 | big prop kills engine | BZERKR::DUFRESNE | You make 'em - I break 'em | Wed Apr 22 1987 14:04 | 32 |
| CLarence Lee (in the May issue of RCM) ran a test on the new OS 40 SURPASS.
As part of the evaluation, he ran some tests with different propellers.
He also compared the results with the OS 40. The SURPASS is rated to have its
max HP at around 12000.
Just for kicks, I decided to apply the pitch * diam * rpm equation to his
readings and see what came out of it.
The table below summarizes the readings.
PROP_DIAM PROP_PITCH RPM RPM THRUST THRUST RATIO
SURPASS OS 40 SURPASS OS 40
10 6 12,200 10,450 732,000 627,000 0.86
10 7 10,800 0 756,000 0 0.00
11 6 10,000 8,750 660,000 577,500 0.88
11 7 9,600 0 739,200 0 0.00
12 6 8,600 7,900 619,200 568,800 0.92
12 7 7,600 0 638,400 0 0.00
13 5 8,200 0 533,000 0 0.00
13 6 7,200 0 561,600 0 0.00
Compare the thrust number with the prop & rpm colum. I found it to very
interesting. For my money, a go choice of props would be either a 10-7 or 11-7.
The 12 & 13 props appear to overwhelm the engine.
Also, the SURPASS appears to be definetly more powerful, especialy at high RPM.
(an indirect measurement of more torque).
md
|
| 122.29 | | GIDDAY::CHADD | Go Fast; Turn Left | Sat Jul 09 1988 21:21 | 18 |
| This subject has been quiet for a time so I thought I might kick it back into
life with something I saw last week.
I saw a program that produced a graph of propeller performance plotting thrust,
required input power and therefore efficiency. a propeller designed by
this program is being used by Chris White who is flying F3A at your Nats. It
looks very strange however it is efficient and quiet, Chris is now under 90db at
1 meter.
If you get a chance have a look at the prop.
Incidentally the program runs on a HP computer and requires input of RPM and
available BHP and produces the design as pitch/cord and profile at various
stations on the props diameter.
Any body seen this program, it was supposedly used for the design of full size
props.
John
|
| 122.30 | MA had some stuff | BZERKR::DUFRESNE | VAXKLR - You make'em, I break'em | Mon Jul 11 1988 10:13 | 17 |
| well, now that you mention it, there was a small blurb on the current
issue of Model Aviation about the their researcheffort into props.
There was a equation given that apparently measure the BHP _absorbed_
by the prop as a function of pitch, diam & RPM. The equation is
similar to the one presented in earlier responses of this notes
This I found to be useful 'cause one usually does not get a BHP
curve for an engine and measuring one is a pain. (I haven't come
up with a simple test stand set-up to do so..).
Alose mentioned in the article is a reference to the october 1986
issue of Model Aviation where there was a detailed article on props.
COuld anyone look up their archives and possibly send me a copy??
tx,
md
|
| 122.32 | I don't understand the code | CHGV04::KAPLOW | sixteen bit paleontologist | Wed Jul 13 1988 18:49 | 7 |
| I've got a prop design program used by both MIT and MacCready for
their human powered aircraft. I just don't understand it enough to
make it do anything useful. Copies available upon request via
VAXmail.
I'm in the process of tracking down another famous program, Dr.
Eppler's airfoil code. If I get it, I'll let folks know.
|
| 122.37 | it's with everything else | CHGV04::KAPLOW | Set the WAYBACK machine for 1982 | Thu Jul 14 1988 19:35 | 27 |
| Alright, already. I don't have time to read this conference every
day. The program isn't that big, but I'd rather continue with the
pointer so that we don't fill up this file with dozens of versions
of the same code. I've announced the location of all my model
realted programs before, but PROP.FOR and others can be found in:
CHGV04::DISK$RGK:[ROCKETS.PROGRAMS]
Also there is a PROP.DAT file which will at least run and cause
the code to print something out without aborting. I have NO IDEA
WHATSOEVER what this thing is doing. Anyone who can explain it to
me has my thanks.
^
/ \
/ \
| |
| |
| ! |
| b |
/| o |\
/ | B | \
/__|___|__\
.
o
oOo
oO!Oo
|
| 122.38 | More prop formulas | K::FISHER | Kick the tires, light the fires, and GO! | Wed Dec 28 1988 13:17 | 29 |
| >< Note 122.22 by BZERKR::DUFRESNE "You make 'em - I break 'em" >
> -< the last word ? >-
>
>Ok, here are the lastest numbers.
>
>Prop_thrust was computed as J_factor * (rpm_sq / 100000) * diam_exp_4
>
>where:
>
>J_factor = (prop_pitch / prop_diam) * (prop_pitch * prop_diam)
>rpm_sq= rpm * rpm
>diam_exp_4 = (((prop_diam *prop_diam)*prop_diam)*prop_diam)
>
>(I did computed it this way in order to see intermediate value & because
>TEAMDATA is a bit dumb with formulas)
>
>rpm_sq was divided by 100000 because I can only print 15 digits and the last
>6 digits where always 0
>
In the Dec-1988 issue of Model Builder in the Electric Power column by
Mitch Poling he published a formula:
Horsepower = P x D^4 x rpm^3/1.4 x 10^17
Bye --+--
Kay R. Fisher |
---------------O---------------
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|
| 122.39 | Pounds ? | BLARRY::Bonnette | | Thu Mar 17 1994 09:26 | 4 |
| Does anyone know of a formula that produces thrust in pounds instead of
cu inches of air moved ?
Larry
|