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Hartzell 3 blade Aluminum Prop

walker172

Active Member
Hey guys/gals,

First time builder on the RV-10 and I’m just about at the tailcone attach phase of the build. A question for all of you about weight and balance and propellers. I bought a recently overhauled IO-540 C4B5 for my project and it came with a brand new Hartzell 3 bladed aluminum scimitar prop. I haven’t weighed it just yet, but does anyone know what kind of weight difference it would have compared to the 2 blade option Vans sells? And would anyone be willing to plug that weight difference into their W and B numbers to see if the forward c of g limit would become a pain to manage?

I’ve been doing a fair bit of reading about the issues removing the lower cowl with a 3 blades prop, and some of the heavy nose concerns in the 10 with only front seats occupied. Do you think this prop would practically usable in my 10, or am I better off selling and going with the standard Vans 2 blade option?

Thanks in advance for your wisdom,

Mike
 
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I'm biased to the 3-blade props so I would keep that. There's solutions to make it easier to take the cowl off such as using a RamAir unit, or you could easily make the stock scoop removable as well.
 
Removable scoop

Hi former hangar neighbour,
If I had to do it over again I would have modified my cowling to make the intake scoop removable on my stock cowling. A friend here in Calgary has done it with his and it works well.
Taking the lower cowling off even with a 2 blade prop is not particularly easy, especially by yourself.

As for the weight, I wanted all the useful load I could get with mine. Every extra pound steals from it and I didn't want to go without the nice Aerosport interior and other amenities that make this a jaw dropping airplane. However, I wanted to keep it in a range to still carry 4 adults and full fuel. You can easily turn the rv-10 into a 3 person airplane if not weight conscious. I, apparently, am still a growing boy and it is (shamefully) easier to remove weight from the airplane than it is from me. I went with the lightest CS prop I could find (2 blade whirlwind RV-10) and put an EarthX battery on the firewall (instead of a lead acid battery behind the baggage bay) to keep the CG around what it would have been with the factory recommended configuration. These 2 changes saved nearly 50 pounds IIRC. Lots of ways of building it, everything is a compromise.

Have you weighed the prop to see how heavy it really is compared to the 2 blade? It may not be as bad as you expect...or maybe it's worse.
 
I haven?t weighed the prop just yet. I guess that?s the next step. I?m just concerned about a heavier prop up front, with a lighter (earth x) battery in the back. I?m worried about forward c of g when it?s just me, or me and one of the kids flying in it. I know some fly with ballast in the trunk for those types of flights, but I?d like to avoid it if at all possible.
 
I built as light as I could (1607 lbs bew) and ended up with a slightly forward cg when solo. For solo flying, I carry a 2.5 gal plastic water jug in the back. When carrying a heavy load, I just pour the water out. I think you’ll find most -10’s are limited by cg, not weight. So having to carry a bit of ballast when solo is a plus.
But, back to your question: the three blade has some nice things (smoother, more ground clearance) but will most likely cost you a few knots in cruise.
 
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Second the comments on weight and CofG. I don't know if it is actually possible to exceed the front limit. I guess if you had a very forward empty datum, one light pilot and full fuel, you might just do it. However, everything else you put in and fuel you burn takes the CofG aft.

There is also no doubt that it handles better with the CofG back, especially on approach where you can start to run out of trim. But any of these problems are only going to manifest themselves lightweight so there is absolutely no issue with carrying a few pounds of ballast in the baggage compartment.

So my advice would be - build as light as possible and get the empty CofG to the forward end.

As for the 3 blade argument, a "few" knots slow in the cruise is, I think a myth put around by the 2-blade fraternity :D I was air-racing last year following a 2-blade -10 for about an hour. We tried everything to overtake him but we were just too well matched. In the end, he JUST crept away from us - maybe 1/2kt...........
 
I think that the 3 blade in aluminum is going to make you a little nose heavy. My RV-10 had the two blade Hartzell and had dual PC680's in the per plans tail location. Since I have short legs and had the seat full forward when I flew, that did not help either. I flew mostly alone and had ballast in the baggage compartment to lighten up on the nose. A removable scoop is a no-brainer for removal/installation of the lower cowling with a three blade prop,,,especially by yourself. MY W&B:

N959RV Weight & Balance Data
Empty Weight: 1703 lbs. (8 qts oil & Wheel Fairings @ #3.75 lbs. each
Gross Weight: 2700 lbs.
Datum: 99.44" forward of wing leading edge
CG Range Limits: 107.84" - 116.24" aft of Datum
Fuel: 108.90" Aft of Datum
Pilot/Front Passenger: 114.58" Aft of Datum
Rear Seat Passengers: 151.26" Aft of Datum
Baggage: 173.50" Aft of Datum
Right Wheel: 688 lbs., arm 123.85", moment 85209
Left Wheel: 685 lbs., arm 124.15", moment 85043
Nose Wheel: 330 lbs., arm 49.90", moment 16467
Total Weight: 1703 lbs., moment 186719
Empty CG: 109.64" (moment divided by weight)
 
Appreciate the feedback and information from everyone. I?ll weigh the prop and compare to the 50-55 pounds quoted by vans for the 2 bladed alternatives and see where I am at.
 
Weights:

About 75lbs for the 3 blade; about 62lbs for the two blade (same as the MT 3 blade).

Make sure the prop is designed for the RV-10. Other props won?t be set up for that airframe.
 
Actually, if you start out close to the forward cg limit, burning fuel moves the cg more forward. With the 10 you must always check cg at the expected landing configuration.

You're right, of course, at very forward CofG. I'd just never operated in those regimes - things like my mobile tool kit, tie-downs etc in the baggage compartment have always meant that my CofG is aft of the fuel datum so the CofG moves back as it is burnt. With rear seat passengers, the aft movement as fuel is burnt can become critical and the zero-fuel situation can be limiting.
The good news is that the fuel datum is close to the forward limit so it doesn't move forward much in the forward CofG situation - and it can always be solved with a bit of ballast (or tie-down kits ;)) in the baggage hold.

Apologies for the error..... :(
 
About 75lbs for the 3 blade; about 62lbs for the two blade (same as the MT 3 blade).

Make sure the prop is designed for the RV-10. Other props won?t be set up for that airframe.
The 3 blade MT prop is much lighter than the Hartzell 2 blade.
Vans shows it at 43 lbs. It is a very nice prop except for the lower cowling removal.
 
Absolutely. I just happened to get a Hartzell 3 blade aluminum prop with my engine when I bought it. That was the reason for my post.
 
As for the 3 blade argument, a "few" knots slow in the cruise is, I think a myth put around by the 2-blade fraternity :D I was air-racing last year following a 2-blade -10 for about an hour. We tried everything to overtake him but we were just too well matched. In the end, he JUST crept away from us - maybe 1/2kt...........

I think that what is fair to say is that plane to plane variations, resulting in different speeds, will usually hide the speed difference attained by different propellers on different airframes. The (few) tests I know about - where different props were put on the same airframe - always showed the 3 blade as a bit slower in cruise, compared to a 2 blade.
 
I think that what is fair to say is that plane to plane variations, resulting in different speeds, will usually hide the speed difference attained by different propellers on different airframes. The (few) tests I know about - where different props were put on the same airframe - always showed the 3 blade as a bit slower in cruise, compared to a 2 blade.
Bob is correct. The amount of loss varies by actual prop model and airframe.
Mooney, being obsessed with marketing speed numbers, tested a lot of props, and for awhile offered their Ovation with a 2 blade prop on IO-550 engine. Later, they decided the speed penalty of perhaps 3 kts was worth the shorter takeoff run and better climb with the 3 blade. The speed loss is more noticeable on lower powered engines with older design props. The choice on six-cylinder engines is mostly personal preferences. Aluminum 3 bladed props are not recommended on 4 cyl engines because it is difficult to achieve acceptable balance, and blade spacing will never match up with 4 cyl firing sequence. Composite blades are better at absorbing that vibration and may be okay on 4 cyl. engines.
 
"3 for show and 2 for go"

I have a three-blade Hartzell for my IO-540-C4B5 on a Rocket. There has to be enough blade area to absorb the engine HP, which is why the two blade is longer and the paddles are broader than the three-blade. There is definitely a slight speed reduction with three blades because the additional blade also creates additional drag, but for my money the extra ground clearance, climb performance and awesome looks make it a no-brainer decision .. and that's on a tail-dragger. The reduced ground clearance on an RV-10 would be even more compelling, for me, to help avoid stone chips.
 
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