Author Topic: Which Is The Slower Prop? (Read 4834 times)

Dick Pacini · « **on:** June 05, 2013, 10:50:30 PM »

Which prop would give a slower lap, a Cyclone 11X4.5 or an APC 10.5X4.5? Application is a Brodak 40 on a P40 ARF on 60' lines.

Mark Scarborough · « **Reply #1 on:** June 05, 2013, 11:32:26 PM »

Dick, respectfully, is there any reason not to just bolt each up and see what they do?

I find that depending on all the parameters,, airframe weight, drag, balance, lines, things like that,,it may vary,, I never liked the 10.5 x 4.5 on my stuff,, others swear by it,,
I really cant speak to the Cyclone,,
guess that really doesnt help ,,

Dick Pacini · « **Reply #2 on:** June 06, 2013, 12:02:16 AM »

Mark, I am going to try flying again probably tomorrow. After a 38 some odd year hiatus, I have tried a couple of times and really have an issue with dizziness. I had difficulty running a 10-5 prop on the B40 which was faster than I can handle so far. Just trying to sneak on board a little at a time.

Rick_Huff · « **Reply #3 on:** June 06, 2013, 03:48:50 AM »

Dick,
I started flying again last year after a 40yr hiatus and also had a dizziness issue. It got better after about the 10th flight, but I understand the desire for a slower lap time. I'm flying a B40 on a Vector 40 with an APC 10.5 x 4.5 and am getting 5.4 sec lap times. A small fuel tank will help you get through the flights until you get over the dizziness.
Good Luck,
Rick

55chevr · « **Reply #4 on:** June 06, 2013, 05:31:48 AM »

Since I am coming back to control line after a 25 year layoff, I guess I should forget about the Veco Renegade with the Fox Combat Special for awhile. I could fly a Shoestring with a Fox .29 Stunt engine ... Good thought about a less aggressive pitch prop.

Joe

C.T. Schaefer · « **Reply #5 on:** June 06, 2013, 06:45:26 AM »

Joe, Are you the the same Joe from ECTA etc. If so, you will know me from there. (PRT BSA's). We are still going in circles out here in NJ! Instead of trying to get the planes faster, we are slowing them down some so we can keep at it.

john e. holliday · « **Reply #6 on:** June 06, 2013, 08:00:41 AM »

If you are trying to get over the dizzies and not do maneuvers, just open the needle a bit. Put in enough fuel so the pick up will get you airborne. Then as you get over the dizzies lean it out. Otherwise when I have a little trouble with dizziness I start doing 8's and loops. If you still have an old beater plane around, use it.

Russell Shaffer · « **Reply #7 on:** June 06, 2013, 08:32:32 AM »

Dick, something that has helped me when I've been off for a while - try spinning around with a handle in your hand. Start slow and work up, but do it in the back yard or living room, not in front of the house. I have particular problems with the old time pattern where you do some very high laps. Do hold something in your hand with your arm out - it does make a difference. Best of luck.

Balsa Butcher · « **Reply #8 on:** June 06, 2013, 10:42:57 AM »

Another tip is to walk around in a circle rather than spin in a circle. As far as props go, I like the APC 10.5x4.5. With a ground RPM of about 10,600 it gives good line tension and not excessive speed. While a good prop in my experience the TT prop you mentioned puts too much load on a B-40 (other's experience may differ). I don't know what lap times you are flying but longer lines will give slower lap times.

Bill Little · « **Reply #9 on:** June 06, 2013, 10:48:42 AM »

Quote from: Dick Pacini on June 05, 2013, 10:50:30 PM

Which prop would give a slower lap, a Cyclone 11X4.5 or an APC 10.5X4.5? Application is a Brodak 40 on a P40 ARF on 60' lines.

Hi Dick,

A WAG, but maybe an APC, or similar, 11-4 will be even slower. Just off hand I would say the 11-4.5 Cyclone would be slower than the PAC 10.5-4.5 since it has more diameter and may not let the engine spin up as much in flight.

BIG Bear
RNMM/AMM

55chevr · « **Reply #10 on:** June 06, 2013, 04:19:26 PM »

Quote from: C.T. Schaefer on June 06, 2013, 06:45:26 AM

Joe, Are you the the same Joe from ECTA etc. If so, you will know me from there. (PRT BSA's). We are still going in circles out here in NJ! Instead of trying to get the planes faster, we are slowing them down some so we can keep at it.

One in the same ... In fact leaving in an hour for Ohio to race the motorcycles ... haven't gone in circles in 25 years but intend to do so next week.

Joe

Steve Helmick · « **Reply #11 on:** June 06, 2013, 05:44:41 PM »

The TT Cyclone 11 x 4.5 is about max load for a typical B.40...with the big stock venturi, the later muffler, and 10%N. Great prop, tho, and definitely worth trying IF the engine is thoroughly run-in. If you want to run 5%N, then it'll probably be too much .

Most everybody around here has abandoned the B.40 in the last couple of years. Inverted, it's very finicky to start (on the wheels). The .46LA is just friendlier, cheaper, easier to get, easier to get parts for, more powerful...and it'll work with a wider variety of cheap props and assorted mufflers. And then, there's the Aero Tiger .36...nicest of all.

Steve

Chris Wilson · « **Reply #12 on:** June 06, 2013, 08:47:09 PM »

Quote from: Dick Pacini on June 05, 2013, 10:50:30 PM

Which prop would give a slower lap, a Cyclone 11X4.5 or an APC 10.5X4.5? Application is a Brodak 40 on a P40 ARF on 60' lines.

Since diameter = thrust and pitch = speed, and you are only increasing diameter in a fixed system the equation balances out with a decrease in speed - at least that's how I see it.

Brett Buck · « **Reply #13 on:** June 06, 2013, 10:26:40 PM »

Quote from: Chris Wilson on June 06, 2013, 08:47:09 PM

Since diameter = thrust and pitch = speed, and you are only increasing diameter in a fixed system the equation balances out with a decrease in speed - at least that's how I see it.

   Huh? I don't quite follow the first part. Take two otherwise identical props - a 12-6 and a 12-4. Which one has more static thrust if you spin them both at 10,000 rpm? Same question, which one has more static thrust if you set them to whatever RPM it takes to get the same inflight speed? At the same inflight speed, which has the most inflight thrust in level flight? Extra credit, which one is developing more shaft HP?

One of these is sort of a trick question, by the way.

   If you have two props, both with the same pitch and differing diameters, assuming the same inflight RPM, the larger one will go faster because it will be more efficient and move forward further for each rotation. OR, alternately, it will have to spin more slowly to get the same speed. Typically the larger prop will have to be set much slower on the ground to get the same inflight speed, because in addition to needing less in-flight RPM, it will also unload more from the ground to the air.

   Brett

Chris Wilson · « **Reply #14 on:** June 07, 2013, 12:00:44 AM »

Quote from: Brett Buck on June 06, 2013, 10:26:40 PM

Huh? I don't quite follow the first part. Take two otherwise identical props - a 12-6 and a 12-4. Which one has more static thrust if you spin them both at 10,000 rpm?

Hi Brett,
I did say "in a fixed system" - as in the same amount of power is fed to both props, so how do you spin them both at 10,000 rpm?

And since there was never any mention of anything changing other than the props, that's what I assumed.
Can you get a non tuned pipe engine to spin 10,000 with an 10x4.5 and then, with no other changes still get those rpm's with an extra inch in diameter?

Surely the greater diameter will spin more slowly, give more thrust and less forward speed as a result (unless we introduce other variables.)

Dick Pacini · « **Reply #15 on:** June 07, 2013, 12:18:00 AM »

Quote from: Brett Buck on June 06, 2013, 10:26:40 PM

If you have two props, both with the same pitch and differing diameters, assuming the same inflight RPM, the larger one will go faster because it will be more efficient and move forward further for each rotation. OR, alternately, it will have to spin more slowly to get the same speed. Typically the larger prop will have to be set much slower on the ground to get the same inflight speed, because in addition to needing less in-flight RPM, it will also unload more from the ground to the air.

Brett

Thank you Brett. You have answered my question. I will start with the smaller prop.

Phil Bare · « **Reply #16 on:** June 07, 2013, 08:24:54 AM »

Six inches of pitch is six inches of pitch, no matter if the prop is eleven inches in length or twelve inches in length.
Turn both props at the exact same RPMs in the air and the speed will be the same.

<The purpose of a propeller is to convert power (delivered by a rotating shaft) into thrust. It does that by accelerating a large mass of air to a higher velocity. The effectiveness with which a propeller performs this conversion is known as "efficiency".

As you already know, a propeller blade is a sophisticated whirling airfoil. At a constant RPM and aircraft true airspeed, the speed of the air over any portion of the airfoil varies with the distance from the center of rotation. The maximum velocity occurs at the point of maximum thickness out near the tip.

Therefore, in an effort to provide an ideal angle of attack all along the blade, the blade has a "twist" to it which varies the pitch angle of the blade from root to tip. The pitch angle of a blade (β) is typically the angle measured at 75% of the radial distance from the center of rotation to the prop tip.

As aircraft velocity increases, the angle of attack seen by the prop blade of a fixed-pitch prop will decrease. That effect limits the maximum efficiency of a fixed pitch prop to a single airspeed at a given RPM, as shown by the following plot (ref-4:13:149) of efficiency at different blade pitch angles (β) shows.

http://www.epi-eng.com/propeller_technology/selecting_a_propeller.htm

Brett Buck · « **Reply #17 on:** June 07, 2013, 08:43:11 AM »

Quote from: Phil Bare on June 07, 2013, 08:24:54 AM

Six inches of pitch is six inches of pitch, no matter if the prop is eleven inches in length or twelve inches in length.
Turn both props at the exact same RPMs in the air and the speed will be the same.

OY! Turn both props at the same rpm in the air and the larger diameter prop will pull the airplane faster. It will travel further for each revolution than the smaller prop. The only point at which they will be acting pretty much the same is when the pitch x rpm = the forward speed. In level flight this would imply an airframe drag of ZERO because each prop would be providing zero thrust. This is pretty much the definition of pitch.

It's also showing that the strange rule of thumb that Chris was using above was incorrect, because you can get a given amount of thrust by changing the pitch AND diameter presuming you have unlimited power (which for the most part, we do).

The answers to my questions are:

1 The 12-6 has more static thrust than the 12-4 at the same RPM, substantially more (not 50% like you might be tempted to thing, but a lot more). The amount of power it takes to spin the 12-6 at this speed is also substantially more (easily 50% or more)

2 The 12-4 at around 12,000 RPM needed for proper in-flight speed has A LOT more static thrust the 12-6 at the 8500 it needs for the same in-flight speed. This is tremendously more, something like a factor of 2.5 more. We actually did this case, it was 80 oz of thrust VS 32 oz with a Rev-Up 12-4 and 12-6. The HP is correspondingly higher for the 12-4 case. This is very close to a completely practical case, these are about the launch RPM for the same airplane with a ST46/12-6 and a 40VF/12-4.

These two together definitively disprove the "diameter"= "thrust" and "pitch" = "speed" homily.

3 Both props/engines are putting out exactly the same thrust, by definition. The thrust has to equal the drag, the drag on the airplane is the same at the same speed. Note that this also means that the power being provided to the airframe is identical, in fact, its the thrust*speed with some scaling factor to get it in the right units. This was a sort of trick question.

4 The engine with the 12-4 is generating much more shaft HP. That's because for the same thrust there is much more parasitic drag meaning that the faster it is turning the less efficient it is when turning shaft HP to thrust HP.

These are all critically important things to understand about stunt prop selection. There are still plenty of people still trying to figure out how to stick the biggest prop on the airplanes and then bragging about it. This while one of the most successful combinations ever used a 11.5" prop that you could turn with a strong Fox 35 at least fast enough to get it up to speed.

Brett

Derek Barry · « **Reply #18 on:** June 07, 2013, 09:07:03 AM »

Quote from: Brett Buck on June 07, 2013, 08:43:11 AM

OY!

Brett

Phil Bare · « **Reply #19 on:** June 07, 2013, 09:38:59 AM »

Again. six inches of pitch is six inches of pitch no matter if one prop is eleven inches long and the other is twelve inches long.
If the pitch is identical and both props are turned at the exact same RPM in the air, the speed will be the same.
There is no magic that changes the slip stream velocity off the twelve in prop versus the eleven inch prop, only a change of pitch can do that.
The larger prop will have more prop disc area and more static thrust than the smaller one but thrust does not equal velocity.

Mark Scarborough · « **Reply #20 on:** June 07, 2013, 10:15:04 AM »

Quote from: Phil Bare on June 07, 2013, 09:38:59 AM

Again. six inches of pitch is six inches of pitch no matter if one prop is eleven inches long and the other is twelve inches long.
If the pitch is identical and both props are turned at the exact same RPM in the air, the speed will be the same.
There is no magic that changes the slip stream velocity off the twelve in prop versus the eleven inch prop, only a change of pitch can do that.
The larger prop will have more prop disc area and more static thrust than the smaller one but thrust does not equal velocity.

Phil, if you read what Brett wrote,, you would see this is not true,,

for me, the simplest reality is On my LA 25,, going from a 9x4 apc to a 10x4 apc,, the lap times dropped like 3 tenths,,
what you are saying is analogous to saying John Forces funny car will still do 4 second quarters if you take the slicks off,, and put on the same outer size, but narrower tires,, its about traction. The bigger diameter prop will get more "bite" in the air, and at the same rpm, it will fly faster even with the same pitch,,

now, keep in mind,, prop airfoil, blade planform shape, undercamber, all kinds of things contribute to affect this as well,, however ghoing from the 9x4 to a 10 x 4,, both APC, and both appear the same except for diameter,, and the plane DID fly faster,, a bunch,,

Brett Buck · « **Reply #21 on:** June 07, 2013, 10:28:06 AM »

Quote from: Phil Bare on June 07, 2013, 09:38:59 AM

Again. six inches of pitch is six inches of pitch no matter if one prop is eleven inches long and the other is twelve inches long.
If the pitch is identical and both props are turned at the exact same RPM in the air, the speed will be the same.
There is no magic that changes the slip stream velocity off the twelve in prop versus the eleven inch prop, only a change of pitch can do that.
The larger prop will have more prop disc area and more static thrust than the smaller one but thrust does not equal velocity.

   Thrust certainly does relate to velocity! The steady-state speed is where the thrust equals the drag. A typical 40-60 sized stunt plane has a little less than 2 lb of drag at a typical in-flight speed of 80 fps. To get there, you have to have 2 lb of thrust from the engine. This means that a larger diameter prop, everything else being equal, will pull the airplane faster, or require less RPM to go the same speed. Less RPM means less HP, meaning that the prop efficiency is higher.

   BTW, I can probably think of cases where raising the pitch REDUCES the speed. Replace a 9-6 with a 9-12 on a stunt plane, and see what happens.

   Note that "more efficient" is not necessarily synonymous with "better" for a stunt prop.

   Brett

RandySmith · « **Reply #22 on:** June 07, 2013, 10:28:23 AM »

Quote from: Phil Bare on June 07, 2013, 09:38:59 AM

Again. six inches of pitch is six inches of pitch no matter if one prop is eleven inches long and the other is twelve inches long.
If the pitch is identical and both props are turned at the exact same RPM in the air, the speed will be the same.
There is no magic that changes the slip stream velocity off the twelve in prop versus the eleven inch prop, only a change of pitch can do that.
The larger prop will have more prop disc area and more static thrust than the smaller one but thrust does not equal velocity.

Phil

No it isn't..as far as pulling an airplane, if that were true you could take 2 exact same 12 x 6 props, use one as is, then cut the other one down to 5 inch diameter, and it is STILL 6 pitch, try running that on a plane and see if the speed is the same at the same RPMs. It WILL be much much slower, the efficiency has just been killed off on the 5 inch prop, by trimming the diameter.
Simple exercise if you really want to see.

Regards
Randy

Howard Rush · « **Reply #23 on:** June 07, 2013, 04:16:16 PM »

Everybody's a f****** aerodynamicist. There is a way to calculate what a prop will do, but I don't think the above stuff will get you there. Mark had the obvious answer, particularly if a person not susceptible to dizziness can be recruited to do the experiment.

Steve Helmick · « **Reply #24 on:** June 07, 2013, 05:20:22 PM »

I recall Mike Haverly telling me that he used the 11 x 4.5 Cyclone on his B.40, but had not used it on the Magnum XLS .36 when I got it from him. But that's what we first tried on the KISS! profile, and tho I tried some other props, none worked as well. I asked about the 10.5 x 4.5 APC and he said it'd be too fast, so I never even tried that one. Yes, I probably should have, but didn't. My guess was that he had tried it on that engine when he had it in his Oriental (classic). Pete Peterson often used the 11 x 4.5 Cyclone on his B.40 powered Venis (sic), but also used the 10.6 x 4.5 Phelps CF prop quite a bit.

My conclusion is/has been that you need to find a prop that is the right amount of load to make the engine happy. Too much load, resulting in "runaway" is not good. I believe the 11-4 APC will prove to be more load than the 11 x 4.5 Cyclone. The only time I recall running the 10.5 x 4.5 APC was flying the Forunner in Reno with Larry Richards. I had my proven MACS Muffler setup (10% and 11.5 x 4 APC, launching at 10.2k. It wouldn't pull enough rpm, so I had to choose between going to 20%N. or a smaller prop. The 10.5 x 4.5 got the nod, and it was a sweet combination. Altitude just under 5,000 ft ASL.

Tho not all of this really applies to the B.40, I have a lot of experience with using the Cyclone, and given that the engine is well run-in, I think it will work better. If the engine is not fully loosened-up, then the APC should do the job. I'd suggest launching at 9.5-9.7k with the Cyclone, if you decide to go with it.

Steve

Brett Buck · « **Reply #25 on:** June 07, 2013, 05:53:35 PM »

Quote from: Howard Rush on June 07, 2013, 04:16:16 PM

Everybody's a f****** aerodynamicist. There is a way to calculate what a prop will do, but I don't think the above stuff will get you there.

Well then I suppose you can calculate the information we need and publish it here for all of us lesser mortals to see.

Brett

Howard Rush · « **Reply #26 on:** June 07, 2013, 10:23:47 PM »

I posted here several times a link to a paper that tells how. Namely the Adkins and Liebeck thing. You need to input airfoil data, too. It's nontrivial. As Chris Machin said, a propeller is not a screw going through cheese. As with most stunt topics, you're better off experimenting than theorizing.

Phil Bare · « **Reply #27 on:** June 07, 2013, 10:33:10 PM »

Lots of 'magic' in stunt props, isn't there?

Brett Buck · « **Reply #28 on:** June 08, 2013, 01:12:53 PM »

Quote from: Phil Bare on June 07, 2013, 10:33:10 PM

Lots of 'magic' in stunt props, isn't there?

  It's less magical than most people think, and it's more magical than Howard thinks. In the former, it's reasonably predictable what the HP/speed/static thrust and to a lesser extent required ground launch revs might be - assuming that people are willing to use actual definitions of power and torque, and some knowledge of the general relationships of the parameters are. Given that 90% of the people who will read this are absolutely convinced they understand what power means and are nonetheless absolutely wrong, that's not a good start.

   In the latter, while it might be possible to calculate most of this stuff, it requires information that we will likely never have in sufficient detail to make it worth the effort. For instance it has been experimentally observed that doping a single layer of .2 oz graphite mat to the back of the prop can have a dramatic effect on the performance. To model that effect alone, you have to know the modified and unmodified flexible characteristics to an extraordinary degree. We will never know anything more than that vaguely one is probably stiffer than another. We don't even know what the airfoil is to any reasonable degree of accuracy and likely never will. Like virtually everything with simulations of real life, particularly in stunt, simulations might show you something useful about the general characteristics but will never ever be able to resolve the issue posited in the beginning of this thread.

   Brett

p.s. BTW, I never even addressed the original question (only the comment Chris Wilson made). That's because Mark Scarborough got it on the first response - try it and see!

Phil Bare · « **Reply #29 on:** June 08, 2013, 03:04:30 PM »

Brett, yeah, Mark nailed it, take a handful of props and switch them out until you get what you like.
When I ordered a cruise prop for my Taylorcraft BC12D with a Continental A 65 from Senssenich Propeller Company, they sent me a 72 X47 to replace the 72 X 42 climb prop with. They did not send me a 78 X 42 ..............................

Phil

Steve Helmick · « **Reply #30 on:** June 08, 2013, 09:00:39 PM »

Dave Gardner showed up at our Fun Fly today with a new plane (Veco Chief), powered by a Byron Barker tuned Magnum XLS .36. With a .270" venturi, .156" spraybar, home brewed equivalent of 10-22, various CF props were tried, with mediocre results.

The last prop tried was a Thunder Tiger Cyclone 11 x 4.5...I suggested launching at 9,600, and ol' David was a happy camper. He also learned to put the plug in the tank overflow. I learned not to pinch off the rubber ducky to kill the engine when the overflow isn't plugged when using muffler pressure!!! I guess I could say "I wet myself". Isn't that a song by "The Divinyls"?

Steve

Mark Scarborough · « **Reply #31 on:** June 08, 2013, 10:17:45 PM »

one relevant fact to remember,, every airplane, engine, tank, lineset, and prop is a system,, and as with every system there is an optimal combination,, change one thing and it all changes,, so remember,, every prop is creating a new system of interactions that need to be sorted,,

but then, thats what makes this silly event so much fun,, ya never get bored,,

Howard Rush · « **Reply #32 on:** June 09, 2013, 01:45:11 PM »

Quote from: Brett Buck on June 08, 2013, 01:12:53 PM

In the latter, while it might be possible to calculate most of this stuff, it required information that we will likely never have in sufficient detail to make it worth the effort. For instance it has been experimentally observed that doping a single layer of .2 oz graphite mat to the back of the prop can have a dramatic effect on the performance. To model that effect alone, you have to know the modified and unmodified flexible characteristics to an extraordinary degree. We will never know anything more than that vaguely one is probably stiffer than another. We don't even know what the airfoil is to any reasonable degree of accuracy and likely never will. Like virtually everything with simulations of real life, particularly in stunt, simulations might show you something useful about the general characteristics but will never ever be able to resolve the issue posited in the beginning of this thread.

Yes, particularly to answer the original question of this thread. Aeroelastics aside, you'd be nuts to try to model the airfoils, see what they do at the requisite Reynolds numbers, and calculate the prop characteristics when you can just fly them. My exasperation above was with bogus theorizing that purported to give you an answer quicker than you'd get by flight test.

If you are starting from scratch to make a prop and can make accurate NC molds, the real theory-- still simplified from reality, of course-- can give you some pretty good props, especially for stunt, where the flow is all subsonic. Stuart Sherlock in Australia and APC know how to do this. The hard part is knowing what to ask for.

Aeroelastics complicate prop design or analysis. I don't know how to analyze it. If the prop is sufficiently stubby and competently made out of carbon, that issue probably goes away. I don't think it was an issue with the carbon Y&O 8-8s I made. An all-carbon APC F2B Electric prop may still be pretty wimpy. Guys who really know what they're doing can probably take advantage of elasticity to make a prop that works better than a rigid one.

Chris Wilson · « **Reply #33 on:** June 10, 2013, 04:17:03 PM »

Quote from: Brett Buck on June 06, 2013, 10:26:40 PM

If you have two props, both with the same pitch and differing diameters, assuming the same inflight RPM, the larger one will go faster because it will be more efficient and move forward further for each rotation. OR, alternately, it will have to spin more slowly to get the same speed. Typically the larger prop will have to be set much slower on the ground to get the same inflight speed, because in addition to needing less in-flight RPM, it will also unload more from the ground to the air.

Brett

Hi Brett,
I don't mind being proved wrong at all but how do you ever assume the same inflight rpm with a differing load?

The only variation in the original post that I see is a prop change, as in fly with one - measure a level lap time, then change the prop and repeat.

And the 'homily' in fact came directly from the maker of 'those expensive Australian props.'

I am having trouble in seeing that a slightly larger diameter prop spun more slowly will ever have a fast a forward speed as a slight smaller one in level flight.

Anyway, been wrong before ..........

Thanks.

Mark Scarborough · « **Reply #34 on:** June 10, 2013, 04:50:19 PM »

Chris, while not an aerodynamisist person,, my only explenation,, every prop,, or airfoil, has inefficiency,, the bigger prop bites more air therefore the slippage if you will is less,, not a scientific explenation,, but its the only way I have to justify it
I can however prove it in real life,, explenation or not, I have done the exact experiment,,

Howard Rush · « **Reply #35 on:** June 10, 2013, 05:06:35 PM »

Golly, I have been using a 7.6" diameter prop on a Nelson .36 and it only goes 120 mph. Imagine how fast it would go with a 10" prop.

Howard Rush · « **Reply #36 on:** June 10, 2013, 05:14:05 PM »

But seriously, folks, if you want to get insight as to how props work without spending any money or doing any math, you might just fiddle with this: http://www.mh-aerotools.de/airfoils/javaprop.htm .

Mark Scarborough · « **Reply #37 on:** June 10, 2013, 06:10:45 PM »

Quote from: Howard Rush on June 10, 2013, 05:06:35 PM

Golly, I have been using a 7.6" diameter prop on a Nelson .36 and it only goes 120 mph. Imagine how fast it would go with a 10" prop.

Howard, imagine if your Nelson actually had enough power to spin that 10 incher at the same rpm,, now that would be a serious go fast setup there,, of course pretty sure the prop tips would be past supersonic at that point,,

Like I said,, I dont have the learnin,, just the observin,, and my "theory" may be flawed,, but the results by all indications are pretty real,, unless there are variables involved that I either dont know about, or missed,,

Author Topic: Which Is The Slower Prop? (Read 4834 times)

Rick_Huff