3-blade propellor for an 0-320?

[seagull]

Hi Gents,

I intend to power my Piel Diamante with a 160 hp Lycoming 0-320. I'm trying to investigate the pro's and con's of fitting a metal or wood 3-blade fixed pitch prop. I'm not interested in a CSU or otherwise variable pitch prop, just a fixed pitch.

Has anyone out there fitted one to their 0-320 project? Is there an off-the-shelf prop that would do the job? Or would I have to get one made specially?

I would welcome any comments.

Cheers

Barry

EAA #144680

Auckland
New Zealand

[hmanvel]

Yes, try www.cattoprops.com/ (http://www.cattoprops.com/)

[Dave Prizio]

As soon as you say "3-blade" you limit yourself to wood or composite props by smaller prop manufacturers. There are no metal fixed 3-blade props made for the O-320 engine that I have ever seen. And I don't believe Sensenich makes a 3-blade wood prop for that engine, although they might be willing to give it a go. That pretty much eliminates off the shelf as an option.

Catto makes some great composite (fiberglass over wood core) props, and they will custom make one for your particular airplane/engine combination for a fairly reasonable price. Whirlwind may also be able to help you, as can a number of smaller prop makers.

Dave Prizio

[seagull]

Mastazero - greetings backatcha!

hmanvel - Thanks for that - I've had a look - very good!

Dave P - I think you are right, metal would not likely be an option. I'm very impressed with the Catto props and this may be likely the way I go. What I'm looking for is a simple to operate/fly 2-seat touring aircraft. The Diamante is a 2+2 seat (or 2+1 if the passenger in the back is an adult size). I intend building mine as a 2-seater with ample baggage capacity. The published power option range for this design is between 100-180 hp, so a 160hp 0-320 would be a good mid-range fit, and from my experience is a pretty trouble-free all-round reliable engine. I'm looking for a respectable cruise/take-off performance compromise as I intend operating from some short-ish grass strips, but do not wish to incur a weight penalty from fitting a CSU. A CSU is also something else to check, maintain and possibly go wrong so a fixed pitch falls right in line with the 'KISS' principle that guides me - e.g. fixed gear instead of retractable, etc. I feel the 3-blade would give me better figures than a 2-blade for the same power. Also looks nicer.

Thank you for your comments,

Cheers

Barry Gillingwater

[Jim Hann]

Barry,

First, another vote for Catto, I know both pushers and pullers using his three blades, all have good words to say about Craig and his props.

Second, are you on the Emerauders list on Yahoo? Contrary to the name, it is open to any Piel designs. Give it a look!

http://asia.groups.yahoo.com/group/Emerauders/

[seagull]

Hi Jim,

I think you're right. the more I read about Catto props the more impressed I am. I'm pretty sure he's going to get my business.

Yes, I'm already on both the 'Emerauders' and the French Piel Avions site too.

Cheers

Barry

[Bob H]

Just a side note to prop material-
Should you operate in an environment where a prop strike might happen, a wood prop will shatter upon contact and limits the energy transmitted back into engine. It's like a fuse.
A metal or even a composite prop under same contact conditions will transmit more energy and has higher likelihood of producing engine damage.

[seagull]

Hi Bob,

Yes thanks, I'm aware of that. A couple of guys I know have got wooden props on their warbirds for that reason. It would probably cost them more than my house is worth if they had to tear down or replace a Merlin! The reported handling characteristics of the Diamante or Emeraude series are pretty docile with little or no tendency for nosing over (although you never know with the right wind conditions). All I can do is go with the wood/composite prop and do my best to keep all three wheels on the ground when taxiing and try not to bump into things too often.

Thanks for the advice,

Barry

[skybolt]

Hi Barry, I have been using a Warp Drive 4 blade ground adjustable prop for about 120 hours now, and I am quite pleased with it so far. I have it mounted on a Lycoming O-360 180 hp powering a Steen Skybolt. This combination is working well for y needs. Bill R. I hope this helps.

[Bill Greenwood]

You say "better figures" for the 3 blade prop vs 2 blade. Not necessarily so. I don't have much experience with plane of that size and power and speed range, but at least for those more like a Mooney, the 2 blade prop is usually faster than the 3 blade one. Climb is about the same, may even be a little better for the 3 blade. With only 160 hp you don't need more blades to handle the power, but you may for ground clearance.

Looks are of course a personal taste, but to me if you can get a true 2 blade wooden prop with the grain showing like a Sensenich one on a Cub or a Stearman, it sure beats those fiberglass ones.

[seagull]

Thank you Bill R & Bill G,

I hear what you both say. My basic understanding is that 3-blades tend to damp down some of the vibrations slightly, give less noise and as you say, a smaller diameter arc so less (sorry that should read 'more') ground clearance. And I agree that for a small aircraft like this with only 160hp the diffences may be negligible at best. But some fliers seem to swear by them and my personal taste is the 3-blader looks better. 35 years ago when I joined EAA we didn't have much of a product choice (at least in my country) so now I have a lot more options to evaluate with this, my retirement project. The choice is exciting! - So I am keeping an open mind and checking things out as best I can. I must be getting quite ancient 'cos I just dislike the modern square glass panel screens on principle. Yuck! - much prefer the old analog instrument displays I was brought up on. Who cares if they are proven to be more efficient - they're just not right. Back to the project - I'm trying for good take-off performance out of some short strips in the hills. Hopefully not too overweight with my bag full of NZ Rainbow Trout.

Cheers

Barry

PS - Here's a baby we had to throw back - undersized!

1738

[Bob H]

I fly from a relatively high altitude airport at 6800' with density altitudes reaching close to 10K' during summer. To accomodate operations, I have a wooden GSC ground adjustable 2-blade prop, which allows custom tweaking of pitch for the conditions. Works well and is inexpensive. Plane is a Pulsar and engine is Rotax 912 with high comp pistons at around 90 hp max.
Props have to absorb all the power the engine can produce without lugging the engine down with too much pitch or having insufficient pitch and over speeding and not developing full power. In general terms, you want the largest dia blade to move a high volume of air but also need proper pitch for power absorbtion and maintaining engine rpm within power band. The Prince Prop folks have a good formula for computing prop dia at cruise;

Dia (inches) = 125[ [HP/ (RPM^3 x mph)]^.2] for 2-blade. Multiply the 2-blade dia by .933 for 3-blade, and .891 for 4-blade.

[seagull]

Thank you for the formula Bob, I hadn't seen that anywhere else. As for the 'hills' I intend flying it to the highest I would mostly go to are around 4,000 feet density altitude even on a hot day, and that would be for a venison trip where my companions and I would likely hire a chopper to get us in and out. Most of my intended excursions flying myself in would be in the lower 'rough country' where the best trout streams are, not the real high stuff. It's more important to me to get the power development for a short take-off than a very fast cruise speed, although exactly what that prop compromise might be is possibly too early to tell.
Thanks again for your interest

Cheers
Barry

[Dave Prizio]

There seems to be a glitch in the prop diameter formula. I keep getting answers in the range of 1". Someone else try it and see if it is me or the fomula. I used a GlaStar with a 180 hp engine, 2700 rpm, and 160 mph speed. I got an answer of 1.1.

Dave Prizio

[spungey]

Agreed. Something seems amiss. Here's some results from dumping it into a spreadsheet. ... Transcription error?



rpm
Rpm^3
times mph
180 / rpmstuff
fifth root
Times 125


2700
19683000000
3149280000000
5.71559213534522E-011
0.0089415384
1.1177


2550
16581375000
2653020000000
6.78472080873872E-011
0.0092535078
1.1567


2400
13824000000
2211840000000
8.13802083333333E-011
0.0095962987
1.1995

[Bob H]

I got 66".

Take the quantity 180/(27 X 160)=.04167
Raise that to the 0.2 power which equals .529
Multipy that .529 by 125 and result = 66.2"

[Snowflake]

Take the quantity 180/(27 X 160)=.04167
Raise that to the 0.2 power which equals .529
Multipy that .529 by 125 and result = 66.2"
Yeah, but that's a different formula. The formula in Post #13 says RPM^3, not RPM/100.

[Max Torque]

seagull - recommend you get together with Jan at JC Propellers www.jcpropellerdesign.com (http://www.jcpropellerdesign.com) . He offers an excellent prop design program that is well worth the price and he is extremely knowledgable about propellers. 2-blade or 3-blade depends upon many things. I'm designing a prop for my direct-drive Corvair and the rpm dictates a 3-blade prop for what I want it to do for the plane it's going on.

[seagull]

Thank you for the contact Max - I'll go and check them out.

Cheers

Barry

[Max Torque]

My bad - Jan's website is actually www.jcpropellerdesign.com (http://www.jcpropellerdesign.com)

I also highly recommend getting a copy of Jack Norris' book: Propellers - the first and final explanation http://www.propellersexplained.com/ Different writing style, but an informative book.