Prop Selection

[22LD]

I've been doing some research online on propellers. If you go to Hartzell's site and look at there recommendations for the Bearhawk they call out a CS 2-blade 84" for the O-540 (250hp / 2575rpm) but a CS 3-blade 84" for the IO-540 (260h / 2700rpm). I am installing a 260hp IO-540 DA45. Does that mean I will HAVE to have a 3-blade or is this just a recommended engine/prop combo. I'd would really appreciate any feedback, input or suggestions of prop choices. Thanks.

[Mark Goldberg]

The two blade 84" prop will work just fine. We can help you buy a new Hartzell when the time comes if you like. Mark

[22LD]

Thanks, Mark.

[nichzimmerman]

Lets continue this thread for the purpose of generating a resting place of useful info regarding prop selection. Prop manufacturers are a good source of determining compatibility for NEW props, but those of us who are shopping the used market must rely on certified aircraft TCDS or a friend's recommendation, which don't address all the possible combinations.

So answer me this: What engine/prop combination are you using? How did you determine these were compatible? What resources are you aware of for others to check compatibility? What generic "groupings" of engines can use similar props (i.e., are all O-540-_ _ _ 5's the same from a prop standpoint)?

And I'll drink a cold one in your name if you can tell me what 2-blade 82+ inch Macs/Hartzells are compatible with an O-540-A1D5.

Thanks in advance!
-Nic

[Helichicken]

Nic asks a lot of good questions. I’d also like to know what combination everyone is using on the O-470. I’m contemplating putting a O-520 on during the rebuild. Unless someone talks me out of it.

[Mark Goldberg]

Two comments on the above two posts. First, a O540-A1D5 does not have the counterweights on the crankshaft to allow use of the modern Hartzell compact hub prop. If you do not place the counterweights on the crank - you would need to use a McCauley or alternately a composite prop. I have an A4D5 which does have the counterweights.

Second Mr. Helichicken - a 520 is way heavier than what Bob recommends as a max engine weight. If you do that you will find your empty weight CG too far forward and have to compensate. A Cont 470 is already 30 lbs heavier than a Lyc 540. A 520 is even heavier. I would not recommend a Cont 520 for that reason. But it is your airplane and you can do what you want. Mark

[Helichicken]

Thanks for the reply mark.... forward cg is definitely an issue and one of my biggest concerns. I hope the 470 crank is serviceable .... if so I’d like to use all of the lightweight accessories and a lighter prop to try to combat the forward cg concerns. Like Whee said .... Pponk it. I believe I’d still be adding weight with the tsio-520 cylinders that are required for the conversion.

[Bcone1381]

Can we dedicate this thread to Lycoming O/IO-540 engines? I'd like to ask about O/IO-360 engines but feel it would not help organize information for future builders.

[whee]

The McCauley B2D37C224/90RA-4 86" prop can be used on Maules with 540W and J series engines. If I had known about this prop when I started building I would have given serious consideration to a low compression 540 with the appropriate counterweight arrangement. Only reason it is not used on the other 540 variations is the higher max RPM for prop noise considerations.

Helichicken, Depending on your 470 model I'd look to what the Cessna 180 guys are using. I would have gone with a long C203 Mac. I think an 88" is going to be pushing the limits on ground clearance on the BH so 86" may be more appropriate. Pponk that 470!

Just a note on engine weights for anyone that is looking them up: The weights listed on the TCDSs from Lycomings and Continentals can not be directly compared. Continental includes every thing but oil. Lycoming does not include the alternator, starter and oil. The Lyc tech rep I talked to said the standard starter and alternator weigh 15lbs each. He also said if your using an engine that came from the factory with parallel valve cylinders but has been swapped to angle valve cylinders you need to add 5 lbs per cylinder.

[Helichicken]

I’m in the process of checking to see if my 470R crank has the 4 counterweights. The fellow at Pponk said some later model 470R’s have them. If I don’t , then I’d have to buy another crank to be able to Pponk it. 6500.00 for a crank that would work and 8200.00 for cylinders ... not sure how much $$ to have the carb reworked by ly-con. I’d love to do it. My head is spinning with all of the options I have. I sure do like the experimental world.

[svyolo]

I heard props bigger than 84" get really loud really quick. Engine weights seem to be proprietary/secret handshake/who knows how to compare.

[rodsmith]

My neighbor has a Cessna 185 with a 2 blade MaCauley. I can't remember if it is 86 or 88" but it is very loud, don't have to look to see who is taking off.

[Bdflies]

A quick note about C185's; They use a Continental IO520-D, which makes 300 hp @ 2850 rpm, with 5 minute rating. Doesn't seem like much, but that extra 150 rpm makes a big difference on takeoff noise!

Bill

[Helichicken]

A friend of mine just bought a 185 two weeks ago and it’s got a long seaplane prop on it. Boy is it loud. He’s flying it a couple hours everyday because he likes it so much. I was in my basement yesterday and I heard a loud plane flyover. I knew it was him by the sound of it. I sent him a text and asked if it was him to see if I was right. His reply was simply .... LOL

[rodsmith]

This was an issue I struggled with. Wanted an MT 3 blade but had a 2 blade Hartzell budget. I nearly bought a 2 blade 82" hartzell used, but looking it up realized it had a recurring AD on the hub and the seller was trying to hide that fact. So do due diligence when buying used. I did fill out a performance sheet with MT and sent it in they said I needed a MTV-9-B/210-58. That is a 3-blade 82.5" prop and the cost shipped from Germany was about $13,000, couldn't do that. Shortly after getting that quote I was looking at props on barnstormers. Couldn't believe it when I saw the exact prop being sold by Found aircraft in Canada. It was 5 years old, had never been installed, and they had just had the seals changed. After some negotiating I got it for $8000 plus $500 shipping with the spinner and governor. More than a new Hartzell but it was what I really wanted. My engine started life as an O-540B4B5 off a Cherokee 235. When overhauled it will be experimental with higher compression pistons, 2700 rpm limit, airflow performance injection and cold air induction. I'm figuring 280HP, that was the specs I gave to MT. George Himmeroder put the exact same prop on his plane and called me some very bad names when he heard the deal I got on the prop :>)

I should add that I was very interested in MaCauley's, thinking 86", but I had a terrible time trying to find out info on which prop models would work with which 540s etc. They don't seem to have much interest in the homebuilt market.

[JimParker256]

The formula for tip speed is pretty straight forward. Take the length of our "generic" prop in feet, multiply by the value of pi (3.14159...) to get the circumference in feet. Then multiply the circumference by the RPM to get the "static" (no forward velocity vector to complicate things) in ft/hour, then divide by 60 to get ft/min... For an 84" prop (7 ft) turning 2700 rpm, the "static" tip speed would be 7 x 3.14159 x 2700 / 60 = 989.6 ft/sec. Then you compare this to the speed of sound (Cso), with the "rule of thumb" for the older-generation of propellers stating that "static" max tip speed should not exceed 80-85% of Cso in in standard atmospheric conditions. So how does our 84-inch prop compare to that?

Cso at sea level (standard conditions) is 1116.4 ft/min. But temperature affects Cso pretty dramatically, with Cso dropping down into the 1080 ft/sec range in "winter cold" conditions (about -10^oC). So our generic 84-inch prop would have static tips speeds well above what the rule of thumb would recommend. At 88.6% of Cso (889.6 / 1116.4 = Mach 0.886), it would already be close enough to the speed of sound to have shock waves developing just behind the blade tips as they rotate through the air. This is because the air flowing over the cambered "lifting" surface is accelerated enough to enter the trans-sonic region, even though the air on the other (flat) side of the blade has not yet reached Cso. Those shock waves manifest as smaller "sonic booms" that are quite loud – just listen to a C180 with a large prop take off! They actually reduce the efficiency of the propeller, because of the disturbed air flow created by the shock waves.

And THAT is why the "rule of thumb" propeller selection guidelines call for max static tip speeds to remain below 80-85% of Cso at standard atmospheric conditions. (Leaving some margin for reduced Cso in colder temps, and for forward speed – see next paragraph.)

What's interesting (and what I didn't realize until I was reading through some material on prop selection) is that the "mach effect" is compounded when you factor in the forward speed of the aircraft as it begins to accelerate on the propeller tip speed. Below about 30-40 mph, there is little measurable impact, but as the airplane reaches 50-60 mph, the forward velocity increases the effective tip speed by about 1%, moving it just that much closer to the trans-sonic region, and increasing the probability of experiencing the noisy shock wave phenomena. That's why the C-180s seems to get even louder just about the time they rotate... Their older, high-camber blade designs exacerbate the shock-wave phenomena. Going even further, at Bearhawk cruise speeds (150-160 mph), if you were still turning 2700 rpm, the effective tip speed is increased by a little over 3%. At 91.6% (Mach 0.916), the blade tips (and a portion further inboard of the tips) are well into super-sonic airflow, and the shock waves are pretty massive. The sound would be highly objectionable – likely overcoming even a good ANR headset – and certainly very "loud and obnoxious" to observers on the ground.

So an 84-inch prop turning 2700 RPM would seem to be turning static tip speeds well above the recommended values, thus we would expect it to be making a lot of noise at full RPM, and losing some efficiency as well. But a lot depends on the camber of the blade, it's aspect ratio, and the actual shape of the tips themselves. The Hartzell Trailblazer, for instance, has swept tips that reduce the formation of shock waves at max RPM. The same is true for the latest-generation of Whirlwind and MT props designed for use on "bushplanes". As a result, the manufacturer's recommendations should definitely override the "generic" rule of thumb guidelines when using these newer-generation props.

As an interesting example of the impact of all this "tip speed" stuff, I used to fly a Rockwell Commander 114 with a 77" older-model Hartzell prop. At high altitudes (cold temps, so lower Cso) and at high cruise speeds (180 mph+), I could technically run the engine at 2700 RPM (turbo-normalized, so altitude was no issue). But if/when I did so, the airplane was noisy, and there was some noticeable airframe / engine vibration that made me uncomfortable until I pulled the RPM back to below 2600 or so. At 2500 things got really smooth. In hindsight, I now realize that with the colder temps aloft lowering Cso, at 2700 rpm that prop was well into the trans-sonic region, and the vibrations I was feeling were probably the result of the shock waves impacting the prop and airframe. Reducing the rpm to 2500 brought the prop back below the Mach 0.85 range, where the shock waves wouldn't yet be forming...

Live and learn!

[Gerhard Rieger]

Thanks Jim, very enlightening article, I have a IO540 E4A5 2700 rpm with a 76 MTV14 4 blade prop also max 2700 rpm. With traditional round tips. I should be ok at altitude at 2500 rpm

[Bcone1381]

....Engine weights seem to be proprietary/secret handshake/who knows how to compare.

The Type Certificate Data Sheet for Lycoming engines gives specific weight/CG for each engine variant. Here is a link to the TCDS for a Lycoming IO360. https://goo.gl/DsN9J5

See note 7 on p.13. It specifies what is included and what is not. Like Jon said, no starter or alternator.

[svyolo]

Dry engine block weight is easy, especially when comparing a Lyc to a Lyc. But installed weight is a lot different, especially when comparing different manufacturers and auto conversions. Even a O-360 vs a O-540 is not that easy, as the 540 has 4 more quarts of oil, 2 more exhaust pipes, spark plugs, wires, baffling, etc. The installed weight of a 540 is a LOT more than the difference in dry weight advertised by Lyc.

[Battson]

Well, at this risk of boring avid readers, I will re-write-up my prop selection process highlights here.

We ended up with a Hartzell Trailblazer 83" carbon fibre two blade prop. We really like it so far.
Following a lot of research, talking to as many people as possible who have composite props, we decided to try the newest offering on the market. I chose this over the major competitors (MT, Whirlwind) for a range of reasons, including Bearhawk relationship with Hartzell.

Combining the research and our subsequent experience operating the prop, we like the:
- testing by Hartzell which shows it produces 18% more thrust than their standard metal prop offering for a Bearhawk,
- sharp price offered through Bearhawk Aircraft,
- reduced vibration compared to a metal prop,
- lighter weight compared to metal,
- reduced inertia compared to a metal prop, meaning it responds a lot faster,
- shape and width of the blade aesthetically,
- reduced risk of engine damage in the event of prop strike.

We felt the biggest risks with a composite prop were largely the same for all manufacturers:
- stone damage to the carbon fibre; although carbon can be repaired unlike metal, a stone does a lot more damage to carbon,
- chips to the nickel leading edge from stones (same for aluminium really),
- higher cost of replacement blades,
- lower knowledge base in the maintenance shops compared to metal.

Overall we are really happy with the prop so far, but we haven't picked up a stone chip yet....



Now for the negative feedback.

Originally we wanted to get another MacCauley, but wow what a difficult company to deal with. I loved their props, but their "customer service" was bad enough to put me off. They literally would not sell me a factory new prop to mount onto an experimental Lycoming IO-540-D4A5 engine. That, and they were going to charge me 50% MORE for an inferior metal prop, than the Trailblazer cost me.

Most surprisingly, over a dozen people contacted me after my post on BCP about experience with composite props. All the people were unhappy with their Whirlwind or MT props (sorry rodsmith!!). I also had lots of public posts in support of MT. Most people with composite props on Lyc/TCM engines have MTs. A popular and wide-spread prop will always have some issues and detractors. The common complaint was damage to the leading edge causing a blade write-off and need to a whole new balanced set of 2 or 3 blades. Expensive returns to Deutschland for repairs, instability of the composite material itself (warping) which MT said was just visual (not structural), and aesthetic finish breakdown (paint cracking) also came up.

[svyolo]

Thanks for the info, again.