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Jon Matcho

Choosing a Prop for Your Project

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Here's a free article from Kitplanes magazine titled Firewall Forward: Choosing a Prop for Your Project.  Of course you can just ask other flyers what they're using to help decide.

I bought a prop-stricken TriQ-200 that had a high-cost MT constant speed electric prop (on a 100HP+ Continental O-200).  The refurb cost to that was just shy of $7,000 a few years ago, which led me to plan for changing over to a fixed pitch.  Speaking with the original builder, he told me he would have never put the constant speed prop on if he had first installed the high compression pistons for a few extra horsepower.

Later, realizing I'd be changing the aircraft, I decided to bite the bullet and keep the existing configuration with the MT to keep the configuration as-was.

Flip-flopping still to this day, I would go for an alternative lightweight electric constant speed if I could find something in the $5,000 range.  Then again, this thread on the Pilots of America forums makes a good case for moving back to fixed pitch.  Just going through this writing exercise has me back in the fixed pitch plan, so thanks for listening!

 


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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These look interesting. Not sure of the price, but apparently they are light and effective?

 

But if you're only going to operate from good sized runways and don't mind trading off a bit of climb rate, the fixed pitch is probably the way to go.

On the other hand, if you want to be able to utilize the engine's full potential across a wide range of speed and altitude, fixed pitch cannot deliver that. I'd been doing some simulations with my Cozy, and using a fixed-pitch setup that works at acceptable RPM when cruising high and (really) fast, take-off and climb performance is quite poor for the installed power, and the pitch is very coarse. With a constant speed prop, the cruise is the same, but the acceleration and climb is stunning! For a 100hp Tri-Q, the difference is probably much less though.


Aerocanard (modified) SN:ACPB-0226 (Chapter 8)

Canardspeed.com (my build log and more; usually lags behind actual progress)
Flight simulator (X-plane) flight model master: X-Aerodynamics

(GMT+12)

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I was looking at those SprintAero props earlier today.  A suped-up O-200 is just about worthy of their SP20a, maybe.  I'd also have to move to NZ to make it worthwhile, which wouldn't be the worst thing I could imagine!

I know a TriQ-200 pilot flying a ground-adjustable Warp Drive propeller which is reasonably priced so that's an option.  I'm also looking at Prince and Catto options which are popular with those flying Q2/200s.  I am settling on getting max HP (expecting a touch over 100) with a fixed pitch due to budgetary constraints.

Thanks for the feedback!


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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I can understand CS props on airplanes that burn 20-50 gph or cruise above 200 kts but for airplanes burning 8-10 gph or cruise <150 kts I don’t see how the tiny fuel savings or small boost in speed can justify  CS.  

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Depends on the CS unit in question. If something like an MT, I would be very much inclined to agree with you, Kent!

 

I should call into the Sprint Aero facility sometime and see what's what. In fact, I think I walked right by it 2 weeks ago while hunting for interesting aircraft at NZRT (found a V8 powered Mk26 Spitfire - boy did that sound great taking off!).


Aerocanard (modified) SN:ACPB-0226 (Chapter 8)

Canardspeed.com (my build log and more; usually lags behind actual progress)
Flight simulator (X-plane) flight model master: X-Aerodynamics

(GMT+12)

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43 minutes ago, Kent Ashton said:

I can understand CS props on airplanes that burn 20-50 gph or cruise above 200 kts but for airplanes burning 8-10 gph or cruise <150 kts I don’t see how the tiny fuel savings or small boost in speed can justify  CS.  

Yes, I understand the motivation was for takeoff performance.  The tradeoff is weight and dollars escaping your wallet.  With all this in mind I am locking in on fixed pitch.  I would never have thought about constant speed if it weren't already on the plane.  

19 minutes ago, Voidhawk9 said:

I should call into the Sprint Aero facility sometime and see what's what. In fact, I think I walked right by it 2 weeks ago while hunting for interesting aircraft at NZRT (found a V8 powered Mk26 Spitfire - boy did that sound great taking off!).

 

I'm curious as to how aviation got so well-established in New Zealand.  It's one of those pockets in the world where there's a lot of activity.  Similar story with Brazil and France.


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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CS, maybe not. But in-flight adjustable options are getting better. IVO Prop and Airmaster have been known around here for a while. There are also a lot of props coming out of Ukraine and Russia these days. Their thing is mostly ground-adjustable props for <130hp and they seem to be marketing their products more toward the STOL guys so I haven't paid them much mind, but if you look at this link (http://www.airtrikes.net/propellers.shtml) you can see that one of the companies, calling themselves Kool has an in-flight adjustable option. If you go this way though, it's worth making sure that they understand that you'll be using a direct-drive engine. Apparently they're not as common outside North America and there have been some blade failures over the misunderstanding. Ground adjustable models run about 1200 USD, in flight adjustable models go for 1800.

Another option, sure to stir up some controversy, is the Aeromatic propeller. It was a precursor to the modern constant speed propeller and was kind of a thing for a while on certified aircraft in the post-war era. Air pressure against the blades pushes the pitch toward fine, but centrifugal force on a set of counterweights in the hub as the prop speed increases forces the pitch toward coarse, ideally finding an equilibrium. Univair quit making them I think in the 60s, and the propeller went out of style, but a guy named Kent Tarver revived them a few years back. Reviews are mixed to say the least. Some people love them, saying they're the next best thing to a CS prop at half the price, and others say they hate them and would never fly behind one but I can never find much specificity to the haters issue. I have turned up that the prop hubs will leak a little oil, and that in certain flight regimes the prop will seem to "hunt" back and forth rather than settling on a pitch for the RPM it's at. Used ones don't seem to be easy to come by, but no telling if that's good or bad. Tarver used to make claims like "60+ years without a single AD" or something like that (the first ones were built in 1946 and some are still flying apparently), but I haven't seen that in a while and the claim is gone from his website. It also seems he got tired of wrestling with the FAA and gave up on the certified market. I haven't seen any crashes or anything relating to the failure of one of these things, but it also looks like they were never all that popular, so who knows? If you want to see what all the fuss is about a new one will cost you about 5400 USD.

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11 minutes ago, Jon Matcho said:

I'm curious as to how aviation got so well-established in New Zealand.  It's one of those pockets in the world where there's a lot of activity.  Similar story with Brazil and France.

 

Two contributing factors, I think. First, we were a pretty good source of military personnel in WW2, training thousands of pilots (and other kinds of soldiers of course) and sending them off to Europe (mostly). Second, being a rugged country of low population density, using aircraft made a lot of sense for travel and other applications in decades past. Both still apply in a broad sense, though the government is making things more difficult and expensive over time.


Aerocanard (modified) SN:ACPB-0226 (Chapter 8)

Canardspeed.com (my build log and more; usually lags behind actual progress)
Flight simulator (X-plane) flight model master: X-Aerodynamics

(GMT+12)

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8 minutes ago, Quinton Oliviero said:

CS, maybe not. But in-flight adjustable options are getting better. IVO Prop and Airmaster have been known around here for a while. There are also a lot of props coming out of Ukraine and Russia these days. Their thing is mostly ground-adjustable props for <130hp and they seem to be marketing their products more toward the STOL guys so I haven't paid them much mind, but if you look at this link (http://www.airtrikes.net/propellers.shtml) you can see that one of the companies, calling themselves Kool has an in-flight adjustable option. If you go this way though, it's worth making sure that they understand that you'll be using a direct-drive engine. Apparently they're not as common outside North America and there have been some blade failures over the misunderstanding. Ground adjustable models run about 1200 USD, in flight adjustable models go for 1800.

2

I know someone flying a Warp Drive propeller behind an O-200 on their TriQ-200, which is ground-adjustable.  I look at the IVO mechanism and I'm just not comfortable with it (whatever that's worth).  At most and for my needs (it's crowded here in north-central New Jersey USA and long runways aren't all that common) ground-adjustable may be the next option if I need it.  I probably will put on whatever is economical for first flights.

The KOOLprop looks like an IVO, but might have different mechanisms.  I don't know.

15 minutes ago, Quinton Oliviero said:

Another option, sure to stir up some controversy, is the Aeromatic propeller. It was a precursor to the modern constant speed propeller and was kind of a thing for a while on certified aircraft in the post-war era. Air pressure against the blades pushes the pitch toward fine, but centrifugal force on a set of counterweights in the hub as the prop speed increases forces the pitch toward coarse, ideally finding an equilibrium. Univair quit making them I think in the 60s, and the propeller went out of style, but a guy named Kent Tarver revived them a few years back. Reviews are mixed to say the least. Some people love them, saying they're the next best thing to a CS prop at half the price, and others say they hate them and would never fly behind one but I can never find much specificity to the haters issue. I have turned up that the prop hubs will leak a little oil, and that in certain flight regimes the prop will seem to "hunt" back and forth rather than settling on a pitch for the RPM it's at. Used ones don't seem to be easy to come by, but no telling if that's good or bad. Tarver used to make claims like "60+ years without a single AD" or something like that (the first ones were built in 1946 and some are still flying apparently), but I haven't seen that in a while and the claim is gone from his website. It also seems he got tired of wrestling with the FAA and gave up on the certified market. I haven't seen any crashes or anything relating to the failure of one of these things, but it also looks like they were never all that popular, so who knows? If you want to see what all the fuss is about a new one will cost you about 5400 USD.

3

@Kent Tarver is on this forum as well, with a lively discussion of the goings on at Aeromatic in this thread.

@Voidhawk9  That makes perfect sense Cameron!  Same here in the USA as to why there are so many older pilots -- they all got trained during wars and planes were cheap after WW2 here as well.

Thanks for your feedback... I expect to be moving forward with a basic fixed-pitch prop before I invest in a Prince or Catto.


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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Oh, by the way, if you're planning to use the formulas from the article to calculate pitch don't be a weirdo. Please use knots, not mph. Why would you use mph for aviation? It bothers me, like when Europeans express altitude in meters. Don't even get me started on altimeter settings in millibars...

Anyway, the conversion factor is different for knots. Pitch is expressed in inches of forward motion per revolution of the prop, but we want nautical miles so: 6080 feet in a nautical mile, and 12 inches per foot is 72960 inches per nautical mile. Likewise RPM is per minute, and we want hours (for nautical miles per hour) and there are 60 minutes per hour.

72960 / 60 = 1216

so if you want to go speed V at rpm R, the desired pitch is P.

P = V x 1216 / R

or alternatively if you turn a prop of pitch P at rpm R  you will get speed V

V = P x R / 1216

where
P = pitch in inches
V = speed in kts
R = prop speed in rpm

Just be aware that these are what I would call "glossy brochure" numbers. You may not be able to achieve a speed of V because of drag, or an rpm of R because your engine doesn't produce enough torque. But it'll help you get a good sense of whether a prop is a good fit for your aircraft. Vne is 191 kts, so P = 191 x 1216 / 2700 gives you 86 inches at max power could theoretically rub just up against it. I'd call that the upper limit for a cruise prop.

There are, of course, other factors. That 86" pitch might not turn at a sufficient RPM (2200 at a minimum, I'd be more comfortable with 2400) at static to give you enough takeoff power. Rule of thumb I learned is that subtracting an inch of pitch will give you an extra 40 RPM at static. I've got no math to back that up though, so take that for what it's worth.

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20 hours ago, Quinton Oliviero said:

Oh, by the way, if you're planning to use the formulas from the article to calculate pitch don't be a weirdo.

Not being a weirdo might be a challenge for me.  I'll do my best to use knots.

I was wondering where the Diameter in your equation was so I reread the article and realized I skipped past the formula parts.  I'm collecting information on options to get the plane back in the air and will verify other flying props against the formulas and eventually report back.

Thanks!


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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On 4/12/2019 at 8:45 PM, Jon Matcho said:

I look at the IVO mechanism and I'm just not comfortable with it (whatever that's worth).

I took another look at the IVO prop design and found that my initial assumptions were incorrect.  It works like the neck adjustment for guitars, where adjusting a screw induces a bend in the neck of the guitar (a twist in the propeller blade in the case of the IVO).

I could imagine this being used nicely for infrequent ground adjustments, but not for frequent in-flight adjustments.  I am speculating, but I still don't care for the mechanism as a constant speed propeller solution.

For my situation, I have decided on a basic climb propeller for initial flights and can move up from there once the front landing gear proves itself (along with the pilot, me).


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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