Mass Moment of Inertia

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Re: Mass Moment of Inertia

Postby taildrgfun » Wed Dec 17, 2014 12:01 am

Lonnie did tell me that the MMOI on my 82-38 was 3300. I don't know yet what my 80-42 MMOI is yet, but it certainly doesn't feel and heavier than the longer prop.
Steve Henry, Wild West Aircraft
(the Dead Stick Take-off Guy)
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Re: Mass Moment of Inertia

Postby FlyerChief » Wed Dec 17, 2014 1:59 am

Hi Steve,
If it's not too much trouble, there are a lot of guys hoping you will take the time to test the MMOI on your prop. You have a very large following and a lot of guys sitting on the fence waiting to buy props but need to get an idea of the MMOI on the longer Prince props. The guys really trust your opinion on performance, but don't want to risk unnecessary gearbox repairs. It's a pretty quick and easy exercise to do it using the Rotax instructions. Just hang a couple of 72" safety wires from the rafters 12 inches apart, hang the prop using a small wood block and set it oscillating. Count the time for 30 full oscillations and use the graph to get the MMOI.
Thanks,
Dan
Highlander #241
When everything seems to be going against you, remember that the airplane takes off against the wind, not with it. ~Henry Ford
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Re: Mass Moment of Inertia

Postby taildrgfun » Thu Dec 18, 2014 8:54 pm

Dan it would be interesting to do my own in MMOI test but finding the time right now is kind of a problem for me. Has anyone checked the Catto props?
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(the Dead Stick Take-off Guy)
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Re: Mass Moment of Inertia

Postby levyland » Thu Dec 25, 2014 3:43 pm

Yes an important discussion. As previously mentioned my Prince 80 x 38 has increased my ground speed ten knots (78-79 knots) and a significant (not pull tested) increase in climb performance than the Catto. My static runup is 5450. I have ordered a Prince 80 x 40 with the hopes that it increases my cruise a wee bit (3-4 knots) without too much sacrifice in the climb performance. Steve Henry and I have discussed this at length and we believe (and hope) that the 80 x 40 is the ultimate fixed pitch combination for he 912 ULS. He has ordered one for one of his customers as well. Before I install mine I will do a MMOI and report the numbers as well as the performance. At the end of the day form follows function, and to me climb performance is the most important factor followed by cruise. The Catto revolutionised climb but no one cruised faster than 69 knots. The Prince is equal to or better than the Catto in the climb department but blows it away in the cruise (adding ten knots). Now obviously none of this is worth it if we are overreaching in the gearbox limitations, but at this stage Lonnie is saying we are not and I have no reason not to believe him. Watch this space sport fans.........
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Re: Mass Moment of Inertia

Postby FlyerChief » Thu Dec 25, 2014 4:22 pm

Thanks for the follow up and the promise to post your MMOI numbers. I believe there are a lot of builders/owners waiting to see how what MMOI numbers are on the longer props. Just to clarify though... 80 x 40 may end up being the best combination for maximum climb enthusiasts. I think my 74 x 51 Prince may be a better combination for those of us wanting a higher cruise speed and still have great short field performance. There are likely a wide range of diameters and pitches that will work very well on the Highlander and SuperSTOL. I doubt we will find one size that works for all flight profiles, but maybe there's a happy medium out there yet to be determined. Once Lonnie has the right combination(s) he can put the design on the CAD and crank them out a lot faster.
Regards,
Dan
When everything seems to be going against you, remember that the airplane takes off against the wind, not with it. ~Henry Ford
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Re: Mass Moment of Inertia

Postby levyland » Fri Dec 26, 2014 3:50 pm

Et all.....
Not to be an expert of the subject of props (because I am not) but one thing is for sure. Each engine (912uls versus 914) or aircraft Highlander (Highlander versus Super Stol) or variation thereof requires a different prop length and pitch. I am focusing on my prop/engine/airplane (912ULS) which is important to me of course, but I would believe to be the largest configuration of builders as well because of the significant added cost of the 914, not to mention the complexity of turbo's and electric feel pumps. Not to say the 914 is a bad choice, in some ways I wish I had gone that route, but the jury is still out in the cost of owning one and I wanted simplicity. SS owners with 914's are reporting 90 knots cruise, but they are relying on the IAS not a GPS cross grid so at this stage the jury is out in my book. With all that said, I know I am very close with the Prince prop at 80 x 38 . I am almost having second thoughts on ordering the 80 x 40 as the 80 x 38 is an awesome prop prop but it is worth trying the 80 x 40 to try and get that additional cruise without having to sacrifice too much in climb. What I would like to ask the builders is if you do buy a a prop from Prince to mention to Lonnie that you want it purchased through Steve and myself (as we are dealers) and that will help us in buying these props for testing. All this stuff takes time and money and Steve and I both love it, but again it takes time and money. Cheers, John
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