View Full Version : For people besides Oleg who want to know about props.

10-07-2004, 08:12 PM

Lots of general info in detail, surprises about efficiencies.


10-07-2004, 11:14 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WWMaxGunz:

Lots of general info in detail, surprises about efficiencies.



"As mentioned, a propeller's performance suffers as the blade speed exceeds the speed of sound. As the relative air speed at the blade is rotation speed plus axial speed, a propeller blade will reach sonic speed sometime before the rest of the aircraft (with a theoretical blade the maximum aircraft speed is about 845 km/h (Mach 0.7) at sea-level, in reality it is rather lower). When a blade tip becomes supersonic, drag and torque resistance increase suddenly and shock waves form creating a sharp increase in noise. "

Plus the overrevving and there might be quite a bit of differences in diving performances http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

10-08-2004, 12:17 AM
Thanks for posting Neal. Props have to be one big factor that has not been discussed much here. I sure know how important small prop differences can be on my bass boat. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

10-08-2004, 05:43 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Ugly_Kid:
Plus the overrevving and there might be quite a bit of differences in diving performances http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif <HR></BLOCKQUOTE>

The one thing I've seen mentioned that FB supposedly gets dead wrong is the whole 'dive 90 degrees vertical with 110% power and boost'. Seems like a good way to make an engine unhappy but we seem to be able to do it without issue until the airframe breaks.

Still - do you remember how pissed off people were at the 'exploding diving P-40' back in the release version? :>

10-08-2004, 05:45 AM
S! Faustnik you lucky dog, to be able to afford running such a boat! http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Ugly, I think that prop tip speed is why not to run 100% pitch at high speed,
when the prop is already travelling so fast in the forward direction a finer
pitch helix will have to travel further than a coarser one in the same amount
of time. It's also not just tip mach but efficiency over how much of the
prop twist and effective AOA where the prop is biting not dragging, that more
than anything. I see it in different planes running 90% power and 400+ kph
in the sim -- the nose lifts a bit when I drop 5% from the pitch then I trim
it out and gain some speed.

But mostly I posted that because one question of dives we didn't have any real
info on (okay, now just a little to confirm some ideas) where prop efficiency
and drag might come in. Oleg has responded in a thread recently about the props
and efficiency making differences which I think were taken into what the prop
parameters or power to thrust parameters of the FM, it would maybe say something
of the La-7 shake speed in highspeed dive maybe and some others. A great prop
for the highest speeds is not as good down slower and look at the La-7 best
performance band of speeds being so good. From there is also the question of
which prop and control is modelled on which planes in the sim if more than one
was used as to why some player tests don't agree with tables they find.

IOW, we find the sim maybe gets deeper instead of more wrong. At least there
are issues to suspect that. I think 'Oleg the Fox' may surprise us yet again.


10-08-2004, 05:57 AM
"As mentioned, a propeller's performance suffers as the blade speed exceeds the speed of sound. As the relative air speed at the blade is rotation speed plus axial speed, "

I hope they don't mean you just add the two speeds up. Thats not how you do it, you add the squares and take the sq root. Pythagoras.

10-08-2004, 09:47 AM

Here's me and my bass rig at a tournament a few years ago. Here's what I know about boat props, I would think something similar would apply to aircraft propellers.

The finer the pitch the more weight you can push. The more coarse the pitch the faster you can go. Most WW2 aircraft props have adjustable pitch so they get the best of both worlds here.

Number of blades has an effect too. More blades are generally better for heavy loads. Fewer blades are more efficient and run higher speeds. I have a heavy boat so I generally use a 4 blade prop. The 4 blade tends to run smoother compared to the 3 blade. With a 25 pitch 4-blade my boat runs 68 mph loaded. With a light load and a 3 blade 27 pitch my boat runs 73 mph.

I would suspect that aircarft are similar. For best climbing power and heavy loads a 4 (or even 5 blade) prop might be better. For top speed a 3 blade might be best.

10-08-2004, 10:05 AM
Boats operate in the same density of water all the time. While your observations about boat props are right, the aircraft prop has to operate in air varying in density by a factor of three or more.

Prop-driven WW2-derived planes, racers, lap Reno at 490mph average. The level speed record is 519mph IIRC. This must involve considerable blade length in the supersonic zone, but obviously efficiency is holding up. Anyone know the figures for Rare Bear or Dago Red? RPM, HP, gear ratio etc.

I always thought the late LW fighters, 109K and 190D, were a little under-propped compared to the Allied planes. Looks like you need a blade per 500hp, or a massive diameter, on the Allied side. Could merely increasing blade chord work as well? The germans only had four-bladers on He177, Do217M/N and BV138's middle engine.

10-08-2004, 11:48 AM
That site covers the multi-blade effects and the whys to some depth. I liked the
business of ducted fans and how even the duct intake shape affects efficiency at
speed. Didn't read the boat prop part though.

They also cover the blade twist which there is some even in CSP blades if I read
that right. Less than fixed pitch and less in high performance props which then
end up with better speeds of efficiency/acceleration/power which agrees with what
Oleg posted on props.

Years ago I had read that paddle-blade props are less efficient than thinner ones,
in my own poor words. The site says;
"Increasing the aspect ratio of the blades reduces drag but the amount of thrust
produced depends on blade area, so using high aspect blades can lead to the need
for a propeller diameter which is unusable."
That's where they are into number and shape of blades, plusses and minusses of both.
Reducing diameter cuts tip speed. Widening the prop increases drag but when you
can generate more power by far than a thinner prop can use, the wider blades let
you get more thrust, in general. For sure there's conditions where that ain't true,
no blanket there.
Of course the higher drag prop and engine to match are gonna use more fuel per
and what Rall said about having range and time being great assets is another
balance so I think that's why there were not all planes using "the best way" as
it's only best at some things.

And then there's the monster prop on the Corsairs. It must have been able to
pitch really coarse to get the top end that plane had. Was that a 13 foot prop?

Probably every kind of design that made sense for one job or another was tried
except maybe the fans/ducted fans which perhaps they didn't know enough about
shockwaves then to see through the designs.


Faustnik... 68mph - 73mph! I've seen racing hydroplanes up home when I was a kid,
can't remember the speeds and anyway they had to turn in the races. Did you know
that A.G.Bell made a hydrofoil in the 20's that made IIRC 70-some knots on the
Charles River (think that's Boston). I'm waiting to see what happens when the
Trifoiler system hits motorboats -- it's wicked just on sailboats -- consider your
boat doing 90+! Oh yeah, are there variable-pitch motorboat props for boats
smaller than, well ships? I understand that on really big ones that cavitation
tearing up the prop itself over time is a big problem.


10-08-2004, 01:58 PM
Yes neal they make a nice automatic variable pitch prop for small boats. It's expensive, but, definately provides the best of both worlds, low end hole shot and high end speed.

In a tournament a few years ago I was humming down the lake at 65mph and was passed by another bass boat that had to be doing high 70's! http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif Of course how fast you go has very little to do with how many bass you catch and more to do with the fisherman's ego.

10-08-2004, 02:36 PM
one of my buddies in college did his senior project on cavitation in boat props. You wouldn't believe how fast cavitation can rip a prop apart, and to think its only little air bubbles!

10-08-2004, 03:24 PM

You sig courtesy of Copperhead just cracks me up every time. I need to add the "190ubern00b club" under my sig too. Maybe Copperhead will make us logo too. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

10-08-2004, 04:05 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by faustnik:
I sure know how important small prop differences can be on my bass boat. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif <HR></BLOCKQUOTE>

Redneck! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

10-08-2004, 04:06 PM
It's even parked in my front yard. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

10-08-2004, 05:21 PM
Big redneck question... is the boat worth more than the house?

Did you hear about the fire at the <insert redneck state> capital?
Terrible tragedy. By the time the firetrucks got there it was burned clear down to the axles.


10-08-2004, 05:38 PM
Found some info on variable pitch prop development:
Variable Pitch Props (http://www.centennialofflight.gov/essay/Evolution_of_Technology/props/Tech14.htm)

and here:



We live in an upscale Bay Area neigborhood, which makes having the bass boat out front all the more fun. http://forums.ubi.com/images/smilies/icon_twisted.gif

10-08-2004, 07:00 PM
There's also good info at the Hamilton site in the history section and the
Curtiss-Wright site in their history section.

While trying to find details on the VDM props, I came across this site:


EDIT: Holy crow, the main page is packed! Just clip the fw190-dot-html off the end!
Sources listed are Joe Baugher (main source), Emmanuel Gustin, Ruud Deurenberg,
Steven Jacobs, Jason Hodgkiss and Maury markowitz.
Listing shows 6 Brit, 1 Canadian, 1 Egyptian (Helwan HA-300), 1 French, 15 German,
1 Israeli, 13 Japanese, 1 Polish (PZL P-7/11/24 series), 1 Romanian (IAR 80) and 10 US.
All either plane models including development and variants or just articles -- one of
the US titles is "The Atomic Powered Aircraft Program).
The site lists the last update as 9 March, 2001. Title is Aircraft of the World.
Then I go up another level and hoooweeee, enough to keep any grog busy!
[End Edit]

which it would be nice if Butch took a look -- it gets into details but not performance
numbers. LOTS of detail on variants including how many made, field mods and kits, and
some on relative performance as words only. A very interesting read but I can't begin
to say if it's all correct.


p.s. All the boat in the front yard needs is some dummies wearing 'neck fishing gear
with poles and line like they're trying to fish in the front yard. Scarecrow dummies
would do, even just one or two and you can explain it off as for Halloween after
waiting for the "bad" neighbors to throw a particular fit! It'd be a bit like the
Jeff Foxworthy tale where his Dads' friends stayed fishing in the boat while it was
being towed up the road and stopped by the cop. "tell your friends to get out of
the boat" -- a running line in thatun.

10-08-2004, 10:18 PM
Hey faustnik, would the picture of your boat have been taken in Martinez? The wife and I were riding our motorcycles up to Oregon a couple of months back and stopped in there for a short stay. While we were down at the marina for a look, they were loading several off shore racing boats into the water(if it has an engine in it, then I am attracted to it) for some racing on the river. I believe that k5054s' comment about water having a constant density is wrong; as after a few minutes practice all the boats were back in doing prop changes. Considering that the American River changes clear vs salt levels when ever the tide changes one can only relate this as simular to the air changing density as one climbs in elevation.

No one political, religious, ethnic, or sexual group has a monopoly on saints or sinners

10-09-2004, 01:05 AM
This was taken in Stockton on the California Delta. You are correct that salinity is not constant and can vary with tides throughout the Delta. I've never gone far as to change props due to salinity factors though.

10-09-2004, 10:17 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by HerrGraf:
I believe that k5054s' comment about water having a constant density is wrong; as after a few minutes practice all the boats were back in doing prop changes. <HR></BLOCKQUOTE>

While it's true that the density of water is not constant, what he meant is that it changes very little over short periods of time and even the difference between freshwater and seawater is fairly small. In contrast, the density of the standard atmosphere at 30,000 feet is 1.5% that of sea level (2 orders of magnitued).


10-09-2004, 12:58 PM
And where are you guys going with this... if you don`t mind me asking? Eh?

10-09-2004, 06:00 PM
Not really sure Ivan, I just found a chance to talk about fishing. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

But seriously, prop performance is a major factor that has not been discussed much. I'm glad Neal brought it up here.

10-09-2004, 10:30 PM
H'lo Ivan!

Prop types, controls and efficiencies are things that rarely come up in discussions
on speed, acceleration, climb and dives. Yet to understand what we have and how it
works is very important. It may also answer why som game models match performance
on data in one place but not another.

Note that Oleg has recently brought up props in discussion as something that the
plane in the game differs from what the plane in a test had. And that was only
one thing of what he wrote.

It also needs to be considered when looking at different data tables that they may
not be from planes with the same props, etc, even if they are the same airframe/same
name. If one source gives climbs and another speeds, they may be with planes of
different props/controls, they may have better efficiencies over different speed
ranges, the person presenting the data may have just picked the best and matched
those even though the same plane that did well at one part like climb may not have
done as well at speed as the plane (airframe, engine, prop, etc, combined) that the
speed data came from. So then you have people saying the data was the plane and
it may or may not have been.

As the 1st post here mentions, one thing in the dive acceleration discussions that
was a much unknown factor was prop efficiency and drag at high speed. That site has
a little info on mach value and a lot of general background of what, why and how so
I thought it's a good thing to know about and keep in consideration.

I could say 'I trust Oleg'. You can. Clint can. Others can but it don't stop the
b!tching the way that information and understanding can. Not that anything can ever
completely stop the b!tching because ... well I leave it at that. There is also that
no sim can be perfect -- if it matches table data it won't handle natural and if it
handles natural it won't match all the data so there is always a crack to wedge in
and pick at which for some people that is what life is all about.


10-10-2004, 05:27 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
The propeller efficiency, η, at full throttle and 2700 rpm at sea level is adequately represented by

η = 0.268587 + 1.233106J - 0.6111475 J^2

where J = V/nd is the advance ratio with the velocity V in mph, n in revolutions per second, and the diameter, d, in feet.

Neal, though you'd like this formula. It's for a modern Hartzell three-blader on a Bonanza, so the constant values are probably not applicable to a WW2 prop. The shape of the equation probably is, and this gives what I think is a parabola, belly up, but with a fairly flat curve. Anybody got this for a VDM, Rotol, Hamilton or Curtiss? Anyone know how the formula changes when we add blades, chord, length, whatever?
I substituted the diameter and rpm for a Spit 9 prop, and got 80% eff from 150mph to 375mph, peaking at 89% around 250mph. By 400mph it's down to 70%, which I'd think is too low for a WW2 prop, so the substitution obviously doesn't work well enough.

For a Spit with a 10.75ft prop at 3000rpm engine speed a speed range from 50mph to 450mph takes 35degrees of pitch change, which is about what the Rotol had. That means that a WW2 prop had adequate pitch range to cope with any reasonable speed. (It would be rigged to bottom out at more than 50mph, I guess). Tip speed at 450mph is around 1040 ft/sec, about M 0.93 at S/l and M 1.08 at 36,000ft

10-10-2004, 08:57 AM
Good math with the resulting efficiency curve but I think it only applies
to a resonable speed range, the shape at the far end should drop rapidly
once the prop tips hit mach which as alt increases you show is gonna
happen. If the tips are at 1.08 at 36000 ft then, well I expect the
pilot of even the control system won't let that happen? WWII fighters
in dives may not have the luxury and certainly simmers pushing for most
speed to compare planes in dives do not bother with such details, we know
that it's been discussed to a near death OBE state. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif
That's for the dives issues which IMO are still not closed. But as for
accel and speeds, that kind of curve you show is sweet. Only things left
to get are what props the models are modelled as using and at least some
close parameters to plug in...... and that's all just to satisfy ourselves!

You definitely have better info and practice than I do though, but we both
have known that for a year or more haven't we?


10-10-2004, 12:16 PM
Well it is not that simple...

Here are couple of diagrams for Hamilton etc. different activity factors and number of blades etc.


10-10-2004, 01:14 PM
I wouldn't mind a bit more of that, might help me to understand. I can see from the three and four-blade curves that the four blader has lower peak efficiency but can maintain it better at higher powers, but not quite as well at high speeds. That lets us into the decision making process for the designer, who also has to worry about keeping the blades from digging a hole and whether the prop he wants is in the prop company's catalogue.

10-10-2004, 11:31 PM
I'm no longer able to see the whole picture here. Woods for trees, I can see parts and
that the site I first pointed to does have the general case but I'm not relating the
terms well enough to get what I want in one mental view.

It should be possible from that data to come up with a curve of efficiency versus speed
at some altitude and engine power for those props, given either most efficient pitch or
what the CSP system should do? Any other givens? Somehow, I wouldn't bet against that.

We still don't have data for the props used or even what props are modelled in the sim
on a plane by plane basis.... (well, just more data we don't have)

Other than that, it is interesting that deep down data of such accuracy if not perfect
is available and that generalizations of one site can be backed even better by that data
or have I got that wrong?


10-11-2004, 02:52 AM
While we're at it (the prop issues) seems like adjusting prop pitch in game manualy has a noticable effect only on aircrafts that had auto prop pitch (especially FW-190). All other planes are at 100% pitch default and do their best climb, dive full speed, climb, high alt flying, acceleration etc. at 100% pitch. Who ever flew a real prop aircraft knows that this is very wrong. I think a good analogy with prop pitch would be manual gears in an automobile (I know this might be a hard concept to grasp for US drivers http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif, no insult intended). You cant drive a car in the first gear all the time.

I was under the impression that auto prop pitch management (together with auto mixture management) was an advantage that german planes had over the allied planes.
In game german planes need more manual work then the rest, I mean if let's say P-47 dive with full power at 100% pitch 750km/h ...wouldn't that damage the engine?

10-11-2004, 09:19 AM
With CSP planes the word says pitch but really it is engine speed.
Watch the tachometer. Only thing not correct is the label it seems.

At higher speeds I get better thrust at less than 100% rpm depending
on engine power. The less power and more speed, the less rpm I want.
At very high speed, full rpm may push the prop tips into compression
and maybe more than just the tips, I don't know the details of the

Ugly Kid, tell me if I'm right about this. It looks as if those props
in the charts have a very wide range of pitch, far more than 15 degrees
or so.


10-12-2004, 03:15 AM
I€d take that article with more than a grain of salt. It bears all the trademarks of a highschool cut-and-paste job, adding information from a lot of sources without quite understanding them.

The level of technical detail is varying, and it combines very advanced concepts with very basic errors and at times interesting language. E g €œHowever with a propeller at a pitch angle of 45? at low flight speeds the angle of attack will be high, possibly high enough to stall the aircraft.€ Uh-huh...

There is better information out there in just as easily digested formats. Googling on the terms used on that site should find them.


Edit: Lenguiche

10-14-2004, 10:23 AM
It should probably say stall the prop depending on rpm, but if you stall the
prop for long, you will probably also stall the plane.

Maybe look over the site itself, I don't know where a highschool student would
get the time to assemble that much material not to mention their own dot com just
for something like what it is. I've seen far worse published in printed volumes
before, like the Funk and Wagnalls Encyclopedia in general, by professionals.
Just because it's not as tech heavy as it gets is no reason to go as far as say
thrown together by a highschool student with no understanding. It looks more
like an adult effort with little deep understanding but more than average with
average being in general -- well it took me decades to understand that and I was
an Army enlisted so not exactly sheltered.

How about laying out all the errors instead of just writing it all off, huh?


10-15-2004, 08:15 AM
it was only a friendly warning not to take what is on the site as gospel. Sure, I could nitpick over it endlessly but what would be the point? Much better if those interested to that degree google about a bit or get a book or two on the subject!

The site isn€t dedicated to propellers, nor is it run by one person alone. It would appear to be one of those online dictionaries, where everyone is free to submit entries.


10-15-2004, 02:12 PM
Very true.
It's a launching point and more than we've previously seen and only supposed about.
And it has brought out K5054 and Ugly Kid with deeper information which I can hope
might get to some more general or usable by non-experts forms or at least find
ways to let the experts better evaluate the roles of props in dive speed limits.
Of course then comes the gearboxes and engines.... all because we don't have much
real dive speed data. I'm hoping for some kind of closure on the issues or even
to know more of why not. And then, there's acceleration which there is data on.

Remember that one part is about people comparing performance figures where the
prop and/or controls used doesn't match what is modelled in the sim, as Oleg
noted, and may not match from one data set to another which may be a source of
why we've seen so much arguement back when the Chimp, Milo, Isegrim and Huck
used to have at it so much.