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Weight difference: alum vs comp props

SabreFlyr

Well Known Member
Sponsor
Planning on using the Hartzell blended airfoil 74" aluminum prop on my -14. However, I would like to consider a composite prop but want to make sure that I don't create a CG problem. Where can can I find the weights of the aluminum Hartzell and the Whirlwind and Hartzell composite props? I'm planning on moving the ELT to just behind the aft baggage bulkhead but not sure how much more I'd have to move (or what) to maintain the same CG. I seriously doubt the ELT move will come close to matching the CG shift caused by the prop change.
 
I think the aluminum Hartzell vs the Whirlwind is something like 55 vs 42 lbs. I know there are a few 14s out there already flying with the composite Hartzell and Whirlwind props.
 
Props

We love our Hartzell composite prop, and I have flown many other ones before we decided on it. It is very smooth, the climb is fantastic and the CG could not have worked out any better if we planned it. The spinner that you need for it is beautiful, long and sleek. The only downside I can think of is the cost. You get what you pay for. Buy it, you will be pleased. Good Luck
 
Prop weights

Ray,

I have been exchanging e-mails with Matt Van Voorhis at Hartzell about prop weights. Here is some info I received recently from him in an e-mail:

"The most common 2 blade blended airfoil prop is the F7497 blade model. That propeller weighs about 58 pounds. The most common Van's composite propeller would be either the N7605 blade or the NC8301 blade. Those propellers weigh 43 and 41 pounds respectively."

Matt's e-mail is: [email protected]
 
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Carl, Oly, thanks for the information. Very useful in my planning.

Carl, you mentioned the spinner. I found it curious that the second-hand QB kit that I bought included a spinner but I didn't ask about it. I would have presumed that would have come with the firewall forward kit. I only have empennage, wings and tail. Did you buy your spinner from Hartzell?
 
Ray,

I have been exchanging e-mails with Matt Van Voorhis at Hartzell about prop weights. Here is some info I received recently from him in an e-mail:

"The most common 2 blade blended airfoil prop is the F7497 blade model. That propeller weighs about 58 pounds. The most common Van's composite propeller would be either the N7605 blade or the NC8301 blade. Those propellers weigh 43 and 41 pounds respectively."

Matt's e-mail is: [email protected]

What concerns me other than PRICE on the Hartzell composite prop is that Van's website says "Extended hub composite 2-blade".

It they mean extended hub like the old Twin Comanche, that would be a deal breaker for me. If it is the hub that works on Van's standard cowl, then that works for me.
 
Carl, on your great website you have your w&b posted prior to paint. Any chance you can update us on what you paint job has done to the cg and weight of your plane?

Thanks
 
Thanks for pointing that out, Gary. Definitely needs to be checked out.

Ray:

I did email Matt to ask about the extended hub. Will report back if I learn anything.

It appears that the hub listed on Van's website has the same Type Certificate Data Sheet. P-920.

The confusing part is that C in the hub model: "Identifies basic design ? C denotes no integral shaft extension" on the above linked TCDS.

That is why I emailed Matt to learn more.
 
I am currently planning to follow Carl and Rafael's lead with the Hartzell composite prop. What is the concern about the extended shaft? Doesn't a Twin Oomanche have O-320 engines?
 
I am currently planning to follow Carl and Rafael's lead with the Hartzell composite prop. What is the concern about the extended shaft? Doesn't a Twin Comanche have O-320 engines?

The O-320 Comanche extended hub prop is NOT a combination that one can do acrobatics with.

Not sure but I believe that all extended hub props have a recommendation of NO Acrobatics.

Another thing, the extended hub prop will not fit the standard cowl that we now use.
 
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Here's my two cents.

I went to SnF with the task of getting an engine and a prop. I was smitten with the Hartzell composite as Carl and Rafael have on their 14A; it is gorgeous and the spinner adds to it's beauty in spades.

With regards to weight differences between the Hartzell blended aluminum and the composite.
A 'rumor' that I investigated was that MT (or other prop manuf) did an analysis between a composite (lighter prop) and an aluminum (heavier prop) on a 4 cylinder engine with electronic ignition. The suggested conclusion was that with elec ignition on a 4-cyl engine the bigger bang that occurs at each cyl firing puts a little bit of additional strain throughout a 4-cyl (as opposed to 6-cyl); and that because the composite prop is lighter, the bigger bang does not have to overcome the inertia of the prop as much as it does with a heavier prop. Don't know if this 'rumor' has any basis of fact. The presumption was that the 6-cyl engines have more mass in the engine which absorbed this bump at each firing better than do the 4-cyl's.

So I asked a rep at the Hartzell booth at SnF about this 'rumor'. The guy was Brian and he said that this area of analysis was right up his alley at Hartzell. His duty at Hartzell was focused on analysis of the engine/accessories/prop (e/a/p) package as a system, i.e. how a modification or adjustment with one part of the system affected the rest of the system. He said that his analysis found the opposite between a light prop and a heavier prop. This because the heavier propeller has been absorbing more of the cyl explosion firing jolt through it's greater mass and that when a lighter prop was installed into a e/a/p system other pieces of the system had to make up that dampening effect. One thing they found was that the shafts and some elements of the accessories (alternator/cam shaft/crank/etc) were showing signs of increased stress. Take this all with your own grain of salt.

When I left the Harzell booth I immediately ran into Sean Tucker (world class aerobatic pilot) who has the Hartzell composite on his airplane. I briefly gave him the gist of both rumors and asked for his opinion - he asked 'Are you going to being doing competition aerobatics in your airplane?' The answer is 'No.' His response to that was that I did not need the composite. What he liked about the composite was that it gave him incredible climb performance - he called the prop the "CLAW" for it's climbing ability.

The composite is about twice the cost of the alum blended and the gorgeous aluminum polished spinner alone is a bit over $1300.

I ended up ordering the Lycoming Thunderbolt 390 and the aluminum 74" prop. A part of the savings of the alum prop went towards the higher price of the Thunderbolt - for me, that was a good compromise.

According to a Lycoming rep, the aluminum spinner (for the composite) will fit the Harzell aluminum blended prop assembly on the 14A if I ever want to give myself a Christmas present.

All of this should be considered food for thought as I am not as expert in the analysis of e/a/p systems.

Av8rRob. The Cummins spinners are worth a closer look.
 
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Response to my questions

Here are the answers that I have been looking for and will now say that the Hartzell Composite is what I want to use on my RV-8 project.



"The ?G? extension is one inch longer than the ?C? extension and it was made because Van?s operators were having issues with the blade contacting the cowling. Compared to the F7497 blade, the N7605 blade has a much wider chord which could cause the blade to contact the cowl if using the ?C? extension. The spinner you use may correct for the inch extension that is used on the ?G? extension hub and fill the gap between the prop and the cowl.

The prop with the ?G? extension is used by Team Aerodynamix so there are no issues with performing aerobatic maneuvers with this extension. The spinner that Van?s sells is required with the G2YR/N7605W-2X prop to close the gap between the prop and the cowl when using the ?G? extension.

Hartzell does not have test data for the N7605 prop being used with electronic ignition. From prior experience with testing other propellers, electronic ignition alone doesn?t make much of a difference to the prop. If you are using higher compression pistons or other modifications that will respect to the prop."


I hope this helps others make their decision.
 
From prior experience with testing other propellers, electronic ignition alone doesn?t make much of a difference to the prop.

Not entirely true Gary.

In fact it was during some propeller testing being done at Van's many years ago that some surprising results were discovered while testing with one of the electronic ign. systems still popular.

That is likely the reason for this document, but they have others (that I couldn't find at the moment) that issue warning for use of there props with variable timing electronic ign. systems.
 
Scott, thanks for the reminder. I saw this a while back and had forgotten about it.

The prop recommendation letter implies that there may be something about the composite propeller that should be considered on a 4-banger with elec ignition. The letter seems to be a summary of findings; the details would be interesting if they were understandable by a layman.

Do you know if there has been any further published information that is relevant to the IO-390?
 
Wt FP vs C/S

Ray. FWIW, The wt difference on my IO-360, all items included, was a whopping 1 pound. Removed Sensenich FP and installed Whirl wind C/S. Love the WW... J
 
FWIW, The wt difference on my IO-360, all items included, was a whopping 1 pound. Removed Sensenich FP and installed Whirl wind C/S. Love the WW... J

Well, that's apples to,oranges, Jerry. My comparison is between Hartzell alum CS and Hartzell or WW composite CS. I think I've already received some good information. Thanks, anyway, and interesting comparison, at least.
 
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