http://www.pponk.com/HTML%20PAGES/propellers.html

Thrust developed may not tell the whole story but it is something that can be easily tested and compared. Ponk's website shows thrust figures for several 2 blade and 3 blade configured McCauley props. Looks like a considerable difference between the 82" 2-blade at 940 lbs and the 86" & 88" 2-blades at 1016 & 1019 pounds respectively. Doesn't say what engine but this is at 2600 rpm which is where mine is redlined.
He shows a similar difference between the 80 & 86/88" 3-blade props. In both cases, there's little to no difference between the 86 & 88 inch props. Seems like it's better to start at 88", then if need be ("oops!") you can trim her down to a still good 86-1/2 inches.

From the calculations , at 20 deg C (68F) and colder is noisier. .90 being best speed
2600 rpm 86" .867 V good
2600 rpm 88" .89 V good
2700 rpm 86" .90 perfect (lost thrust at lower temps)
2700 rpm 88" .92 too long, lost thrust
2850 rpm 86" .95 Way too fast and long
2850 rpm 88" .97 Stupid

Lets sound less annoying for the majority and we may all enjoy flying longer.

I know you have a 2 blade hub Hotrod, but what pulls harder, an 86" 3 blade or 86" 2 blade? I have an 84" 3 blade Hartzell on my 180 and it seems to pull hard. But this is the only 180 I have flown and have nothing to compare it too.

Barnstormer wrote:

CamTom12 wrote:Props are a 3d airfoil.

I'm not a quantum physicist but I'm fairly certain everything in the physical universe (not considering time) is three-dimensional.

Yuk yuk yuk...

I was talking about the thrust (lift) distribution. 3d (you're right to read this as "real") airfoils generate very little of anything at their tips except shed vortices and their associated drag.

A1Skinner wrote:I know you have a 2 blade hub Hotrod, but what pulls harder, an 86" 3 blade or 86" 2 blade? I have an 84" 3 blade Hartzell on my 180 and it seems to pull hard. But this is the only 180 I have flown and have nothing to compare it too.

I have no idea. There's "disc area" but then there's also blade area. Seems to me that a 3-blade prop is a way to get more blade area without exceeding max diameter and so busting mach and creating inefficiency and noise. Maybe another way to approach things would be two extremely wide chord blades?
I don't wanna pony up for another prop, but since my C203 is supposed to be a good one I figured the most cost-effective upgrade would be a set of longer blades for it: same hub, same spinner, etc.

Ya, I agree that it is definitely most economical for you to just get new blades.

A copy of an article published in 2011 by the founder of Flight Resource on this exact subject.

The 3-Blade MT prop STC kit is priced at $14,450 plus assy, crate, frt. Money back satisfaction guarantee...so you can buy one with full confidence. John.
-------------------------------------------
The Myth of High RPM
by Larry Schlasinger (Founding Partner – Flight Resource, LLC)

The first time I pushed the throttle forward on my newly acquired Cessna 185
I noticed something strange. Instead of the tach going to the expected 2850
RPM it went all the way to 3100…wow.
Since I had no experience with 185’s or their engines I decided to seek the
advice of a friend that had been flying them for years. He asked where it had
come from, and when I answered Alaska, he started to laugh and said
“figures”. I inquired as to what was so funny and he stated “those guys up
there will do anything to increase the performance, whether it’s approved or
not”. The increase in RPM will increase the horsepower and reduce your
takeoff…just don’t let an inspector see that as it should only go to 2850. His
explanation seemed to make good sense and I started to make takeoffs with
the RPM at 2850 unless I thought I needed the extra performance. Anytime I
was heavy or it was hot the prop control went in to the panel and the prop
screamed and away I went. It did seem to have better power…and a lot
more noise. I flew this way for many years and I never thought much about
the RPM…just high for more power and less when I didn’t need it.
Then I was introduced to Gerd Muhlbauer, the President and Chief Engineer
of MT Propeller. I was negotiating to be his U.S. Sales Rep when the subject
of high RPM and specifically the Cessna 185 came up. I wanted to STC the
MT 3 blade propeller for the 185 and I wanted a long prop that could be
turned at least 2850 RPM. Gerd started to laugh (sound familiar?) and told
me a story about Horsepower vs RPM vs Thrust. He gave me a good lecture
about what makes a plane fly and how power is converted to thrust and it is
thrust that really counts. He stated that my idea of more RPM making more
power was correct, but when the prop is turned beyond about .9 mach (the
speed of sound) it starts to become inefficient. When this happens, the
propeller is converting power to noise instead of thrust and real performance
decreases. I found this hard to believe (why should I believe one of the best
propeller engineers in the world?) as I had been flying with the RPM turned
up for so long. Gerd saw the doubt in my face so he decided to prove to me
his point.
He set up a digital thrust testing scale and attached it to the stinger on my
185. We then proceeded to measure the static THRUST applied at full power
and RPM starting at 2400. To my chagrin, he was right. We saw an increase
in thrust up to about 2600 and then it started to DECLINE after that. We
could only get 2800 static, but the thrust was considerably less than the
2600 reading. I can just imagine what 3000 would have been…much less.
After this testing session, I invited some of my other seaplane friends to
come to a propeller comparison/testing clinic. We assembled several
propellers suitable for the 185 including: a standard metal 86” 2 blade, a new
86” metal 3 blade, a 82” MT 3 blade composite and also an 82” MT 2 blade.
We ran all the props on the same plane, on the same day, in the same
conditions. Everyone there (except me) was really surprised by the results.
ALL the propellers produced more THRUST at lower RPM’s (all around the
2600 mark) and the 83” MT 2 blade produced the most. The 78” MT &
McCaulley 3 blades were about the same and the 82” 2 blade McCaulley was
the least. The MT 2 blade was also almost 40 pounds lighter than the metal
3 blade…that combined with titanium gear will reduce the weight of your
plane almost 100 pounds.
So what does all this mean? It means that I’ve flown under a misconception
for all these years and made my neighbors mad at the same time. The only
advantage of the high RPM scenario is a really great buzz job at camp, but to
sacrifice takeoff thrust and engine life for this isn’t real smart. I find it better
to fly a little lower on my camp buzz jobs and keep the RPM where it does
the most good. It also means that when someone with as much expertise
and experience as Gerd Muhlbauer tells me something, I’ll be more inclined
to believe him.
------------------------------------
Larry Schlasinger is the Founding Partner of Flight Resource. Today they are
the worlds largest volume distributor of MT Composite propellers and own
several STC’s to install the MT props on thousands of aircraft. Larry is an
award winning airshow pilot with A.C.E. credentials, an A&P with IA and
thousands of hours flying singles and twins on wheels, floats and skis all
around the world. MT Propeller - Germany contracted with Larry, through
Flight Resource, as a North American Distributor. STC’s to replace stock
metal propellers were developed and approved for hundreds of popular
models of Cessna, Piper, Beech, Mooney, Aviat and many others.

A1Skinner wrote:I know you have a 2 blade hub Hotrod, but what pulls harder, an 86" 3 blade or 86" 2 blade? I have an 84" 3 blade Hartzell on my 180 and it seems to pull hard. But this is the only 180 I have flown and have nothing to compare it too.

Check the link I posted earlier to Ponk's website. His test chart shows 1016 lbs thrust at 2600 rpm for the 86" 2-blade, vs 1183 lbs thrust for the 86" 3-blade.

Thanks Hotrod. The ponk thing won't work on my computer. Not sure why.

Hotrod,

If you're thinking of changing to a PPonk engine in the future, keep in mind that the C203 prop is not certified on it.

Chris

I have a 86 inch-3 blade prop on my 185, it is noisy, (I don't care). People here accept airplanes and the noise they make, they are part of the package (a requirement to move people and freight), I assume Alaskans feel the same.

The first time I switched the 185 from wheels to floats, the plane had a standard 80 inch 3 blade prop, take-off was not impressive. At the first opportunity, that prop was changed out for a new 86 inch 3 blade. What a difference that made, money well spent.

Going along with the theme of prop RPM's, this is what I have noticed with my IO520, with the 86 inch 3 blade prop. It is quite noticeable if I take off with full prop RPM, clear the water, then back off of the prop RPM's (some), it is like kicking in the afterburners, the plane climbs noticeably better. The downside is I loose some of that sweet noise. Just my observation.

Steve

airChris wrote: Hotrod, If you're thinking of changing to a PPonk engine in the future, keep in mind that the C203 prop is not certified on it. Chris

This 180 is the first airplane I've owned with over 150hp, so the stock 230hp is enough for me, I think. I just wanna get the most out of it, therefore the idea of going to 88" blades.

hotrod180 wrote:
This 180 is the first airplane I've owned with over 150hp, so the stock 230hp is enough for me, I think. I just wanna get the most out of it, therefore the idea of going to 88" blades.

I certainly agree 88" blades are the way to go, especially on floats. I was just pointing out that if you are thinking about a pponk engine in the future, the C203 prop won't work. On the other hand, the C58 or C66 props would work, but they are so old that finding parts for overhaul is getting hard and therefore expensive. Furthermore, it might be hard to find a C58/C66 with 88" blades that have good meat left on them.

Chris

I know several guys with Ponked 180's and 182's-- I think every one of them is running a three-blade Mac. Seems like that (or an MT) is probably the way to go with the bigger engine.

hotrod180 wrote:I know several guys with Ponked 180's and 182's-- I think every one of them is running a three-blade Mac. Seems like that (or an MT) is probably the way to go with the bigger engine.

I should clarify my statement; a C401 or MT is definitely the preferred choice over an 88" 2 blade on the bigger engines. However, as I understand your circumstance, you are looking for a prop that will work on your stock 180. In that case, the 3 blade choices are out and the 88" 2 blade prop is the way to go (or the 2 blade MT is worth looking into but at much higher initial cost). So when choosing a prop for today, it might make sense to think about what will be compatible with an engine choice you make tomorrow.

Chris

Chris

Old thread I know, but I'm curious. All this talk about longer blades slowing the plane down. I'm curious what going from a 2 blade to a 3 blade will do for cruise speed? There is a lot of extra drag created by a whole other blade. So in theory, wouldn't this slow the plane down more then adding 6" of blade to a 2 blade?

A1Skinner wrote:Old thread I know, but I'm curious. All this talk about longer blades slowing the plane down. I'm curious what going from a 2 blade to a 3 blade will do for cruise speed? There is a lot of extra drag created by a whole other blade. So in theory, wouldn't this slow the plane down more then adding 6" of blade to a 2 blade?

I suspect a lot would depend on the particular airplane and its drag vs. available power. Back when I was regularly flying the Mooney 231, its owner thought it would "look nicer" if it had a 3 blade prop on it (he wasn't overly concerned about the cost). He asked me to look into it. At the time, the only choices were the factory 2-blade or the factory optional 3-blade. The clincher in his decision not to go for the 3 blade was that it would knock off something like 6 knots from the cruise speed. Whether there'd be that much loss of cruise speed on a relatively dirty 180/185/172, I tend to doubt, although a couple knots less wouldn't surprise me. But all that's merely a WAG.

Cary

In the highly specialized world of control line model airplane racing, single-blade props are the norm:

And the guy could still stand after that!!!

A Taylor J-2 Cub with a one blade prop: http://eaaforums.org/showthread.php?438 ... -propeller