Hartzell Whirlwind 300-77 or 79 3 blade for a IO540

[dmattmul]

Working on a project with an IO-540 and went to order a prop. WW says I can use either there 77 or 79" prop. These are telling me 77" is the most used but could not tell me why. Anyone out there using the 79 in. 3 blade 300 and why? Spec says they both weigh the same and WW confirmed this? BTW Hartzell has held pricing fairly constant since the merger.

 

[ewumnrr]

I purchased the 330 hub (recommended if you want same weight as stock prop, and also if you have more than 260 hp) together with 78 inch blades. In general, it's a trade-off between propeller efficiency and ground clearance. The efficiency of a propeller goes directly with the diameter. The larger the better. But the larger the prop, the more likely will you get a prop strike on soft runways or if you bounce.
My invoice says:
CS330-3B/78G-78 Propeller

 

[glider_rider]

The efficiency of a propeller goes directly with the diameter. The larger the better

Unfortunately it's not that simple. The larger the prop the sooner the speed of tips would approach the sound barrier and generate lots of drag.
Another thing is that from efficiency standpoint it's difficult to justify a 3 blade prop for RV10.

 

[dmattmul]

I purchased the 330 hub (recommended if you want same weight as stock prop, and also if you have more than 260 hp) together with 78 inch blades. In general, it's a trade-off between propeller efficiency and ground clearance. The efficiency of a propeller goes directly with the diameter. The larger the better. But the larger the prop, the more likely will you get a prop strike on soft runways or if you bounce.
My invoice says:
CS330-3B/78G-78 Propeller

Thanks, appreciate the input. The CG should be ok as most 10's need some added weight in the baggage area and a lighter nose should help and increase useful load (hopefully). Vans does recommend an 80" prop for the 10 and they are typically pretty conservative but good to understand ground clearances.

I assume you are using the 14 or 15" spinner for the 330? WW literature lists in some places both but I thought the 13" would not fit on the 330?

 

[ewumnrr]

Thanks, appreciate the input. The CG should be ok as most 10's need some added weight in the baggage area and a lighter nose should help and increase useful load (hopefully). Vans does recommend an 80" prop for the 10 and they are typically pretty conservative but good to understand ground clearances.

I assume you are using the 14 or 15" spinner for the 330? WW literature lists in some places both but I thought the 13" would not fit on the 330?

WW comes with a spinner ready to install, already primed, mine is 13".

 

[ewumnrr]

Unfortunately it's not that simple. The larger the prop the sooner the speed of tips would approach the sound barrier and generate lots of drag.
Another thing is that from efficiency standpoint it's difficult to justify a 3 blade prop for RV10.

yes, prop efficiency is worse the more blades you have.
IO-540 is designed for 2,700 max rpm and the stock prop is 80 inch, so no issue with speed of sound with a prop smaller than 80.

 

[rongawer]

I have the WW 330-3B-78" prop. It's a great performing prop. The 78" was designed for the 300-400 Hp range with the target airframe being the Socata Epsilon, but if you have an IO-540 260 Hp engine, the 330-73" is an ideal prop with plenty of ground clearance.

 

[lr172]

Thanks, appreciate the input. The CG should be ok as most 10's need some added weight in the baggage area and a lighter nose should help and increase useful load (hopefully). Vans does recommend an 80" prop for the 10 and they are typically pretty conservative but good to understand ground clearances.

I assume you are using the 14 or 15" spinner for the 330? WW literature lists in some places both but I thought the 13" would not fit on the 330?

Yes some 10’s, mine included need some weight in the back when solo, but this condition helps to insure that you can reach gross wt before the aft cg limit. I did this purposely. Reducing weight on the nose will mitigate the need for ballast when solo, but will eat into your ultimate carrying capacity due to aft cg issues when loaded. Better to require dead weight for solo that can be removed than to have to leave baggage at home due to breaching the aft cg.

I would argue the 10 does not need added weight in the back and doing so will reduce the ultimate utility of the plane. If you are using lithium batteries, the lower prop weight might balance this out.

 

[Desert Rat]

"...Vans does recommend an 80" prop for the 10 and they are typically pretty conservative but good to understand ground clearances..."

Regarding ground clearance; For a certified tricycle gear airplane, FAR23 requires 7" clearance with the nose gear at its max deflection. Since Vans tends to not re-invent the wheel with stuff like this, I'd imagine you have at least that with an 80" prop if that's what they're recommending.

 

[Pdp7427]

I went with smaller diameter for max clearance given that I plan to fly off grass. Will it really matter? Who knows.

 

[dmattmul]

Yes some 10’s, mine included need some weight in the back when solo, but this condition helps to insure that you can reach gross wt before the aft cg limit. I did this purposely. Reducing weight on the nose will mitigate the need for ballast when solo, but will eat into your ultimate carrying capacity due to aft cg issues when loaded. Better to require dead weight for solo that can be removed than to have to leave baggage at home due to breaching the aft cg.

I would argue the 10 does not need added weight in the back and doing so will reduce the ultimate utility of the plane. If you are using lithium batteries, the lower prop weight might balance this out.

Reducing 15 lbs. on the nose for me increased useful load 15 lbs. With added weight in the nose for a pad mount alternator and 2 Earth X batteries in the tailcone to reduce aft weight worked well. Would love to see examples of CG's with total gross weight of 2,700 or less loaded with 4 passengers and baggage, full fuel.

Obviously, we don't need to worry about tips going supersonic since that is calculatable for a 79 in prop at 2,700 RPM and not close. Besides Vans recommends an 80 in prop for the 10.

Anyone using a 3 blade 79" prop? That was the original question.

Appreciate the responses.

 

[lr172]

Reducing 15 lbs. on the nose for me increased useful load 15 lbs. With added weight in the nose for a pad mount alternator and 2 Earth X batteries in the tailcone to reduce aft weight worked well. Would love to see examples of CG's with total gross weight of 2,700 or less loaded with 4 passengers and baggage, full fuel.

Obviously, we don't need to worry about tips going supersonic since that is calculatable for a 79 in prop at 2,700 RPM and not close. Besides Vans recommends an 80 in prop for the 10.

Anyone using a 3 blade 79" prop? That was the original question.

Appreciate the responses.

I guess that battery weight reduction makes a big difference and that makes sense given the long arm there. Will try to post my cg data. I am 1635 empty with tools and fire ext. i can go to 2800 #s with moderate sized passengers in the back plus 100 lb of baggage and stay ahead of the aft cg limit, even at 5 gal of fuel. That said, i need 30-40 lbs of ballast when solo, as empty is fwd of the limit. 2 680s in the back. I can do it full or empty, but the empty state is what pushes the cg aft. Mostly any way.