Many of the unlimiteds are running engines that produce double, or even more HP than stock, but it looks like most of these planes are running stock propellers. How are they able to use all that additional power without going to either a larger diameter prop, or going with wider blades?
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Re: Question about power and props
They have enough pitch to use all that extra power? That's a lot of pitch!Originally posted by ChrisMX105 View PostComment
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Re: Question about power and props
If you look at pictures of them on the course it is rather impressive. They set the RPM they want to run and the governer adjusts the pitch of the blades to keep the RPM where it needs to be.Comment
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Re: Question about power and props
In some cases, very different props are used than were stock. Bearcats and Sea Furys didn't come with Skyraider props originally. In that case the power to the prop really isn't all that far beyond what the prop was designed for- at least not a factor of two in most cases (Dreadnought, 232, Bear being notable exceptions that do approach a factor of two). The Mustangs do use stock props (with some profile modifications in some cases) and they do have way more power going into the Hamilton-Standard cuffed prop than a stock Merlin ever put to it.
I think there's good evidence that props are an area where a lot of energy from the powerplant is being wasted. The props can keep the engine from running away by going to incredibly aggressive pitch (look at high-speed shots on the course, and those things look nearly feathered), but they're probably way off in the corner of their effective operating envelope and not working at peak efficiency. A prop blade is a wing and running that much pitch is the same thing as a wing at a constant high angle-of-attack. However the job of finding a suitable prop to modify or the cost of starting from scratch is very high, and past attempts haven't paid off all that well. Computational modelling has come a long way down in price since those days though, and its becoming something that's much more likely to succeed and not break the bank. Look at what the PM team did last year by improving the aerodynamics of the prop alone! Of course it could be argued that the airfoil of the Griffon's contra-prop setup was one of the ones farthest behind the curve to start with, but still...Comment
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Re: Question about power and props
The P3 Orion prop that was on RB for a while always made me think; while it had very wide blades, it was also down one compared the stocker and I wondered if it was more or less efficient...kinda figured with as much power as it was making it could've used 4 blades like those on the P3 prop...maybe that would've been too much prop?Comment
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Re: Question about power and props
The 3-blade prop was heavier than the current one so my uneducated guess would be that 4 of the P-3 blades would be too heavy.
JarrodComment
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Re: Question about power and props
Do the math and change as needed. Propellers are the next leap.Comment
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Re: Question about power and props
It's not usually the horsepower that's the structural limitation on a propeller, rather the RPM. The centrifugal forces keep the blades from bending due to high lift production. Just look at a flimsy helicopter rotor. Bends easily until RPM's are
applied...
Propeller blades are generally much stronger than necessary because they need some kind of airfoil, which in turn increases the structure of the blade itself. The hubs will fail long before the blades. Most propellers can be over sped by 20% or more before an inspection is even required.
That being said, we are limited in how high we go in RPM due to helical tip speed. If the Mach number is too high, we create too much drag. So no use in increasing RPM beyond a safe range.
And there's a lot yet to be learnt about propellers and their black magic...Comment
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Re: Question about power and props
Thank-you Thom!
I'm sure your head has been in the books in recent year(s) on this subject!
Congratulations on the success of 'Metal' and her new blades.. Anxious to see what they really will do, with more power...
Long live the Griffon!
- JosephComment
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Re: Question about power and props
ding it; havin' a senior moment here. I seem to remember a pic somewhere about an experimental prop that had like 7-8 blades and the blades were extremely curved. I think they called it a Scimitar prop or some such thing. I do remember it was mounted on an unlimited (I wanna say Tsunami). And what about the props on later model C-130's? Certainly not for speed, but maybe more for short-field performance/lifting improvement?
Help an old f*** out here, will ya?Comment
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Re: Question about power and props
The blades on current turbine airliners like the atr and j model 130s are of scimtar design, the curved shape of the blades if i remember right help the airflow around the blades and cause later airflow break up, which in turn allows a higher rpm. Tsunami had a composite prop that wasnt raced, and i thing tiger had one designed for stregarace fan, photographer with more cameras than a camera storeComment
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Re: Question about power and props
After the prop people talked it up "Tiger" tried it on "Strega" but it didn't perform that good. I'm sure someone has a photo to post with it on.
Lockheed BobComment
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Re: Question about power and props
The Tiger Claw prop is what you're talking about on Strega. US Propeller Service built that prop. It was tested in two different configurations in 1995 and 1996, but was never really put through the ringer. Kerch says that he thought that with enough testing it could have been made to work with some really positive results...but...things going the way they did, it never happened and as I recall it's still sitting in the hangar at Minter Field.Originally posted by Lockheed Bob View PostAfter the prop people talked it up "Tiger" tried it on "Strega" but it didn't perform that good. I'm sure someone has a photo to post with it on.
As for the scimitar prop that was mentioned in a previous post, that was the infamous Montagne "Sky Prop". It was supposedly built as a 'demo only' model, and was dry fitted onto Risky Business in 1989. Jack Sandberg bought it to run on Tsunami and did some taxi tests with it at Minneapolis in the spring of 1990. But when they put it in the test cell and put moderate power to it, one of the blades failed, and the imbalance let the others fail and all that was left was carbon stumps on the hub. Montagne, the builder, claimed it was only intended to be a demo model and that the foam core had been crushed during build-up. Sandberg claimed he had bought an airworthy prop. Was a moot point a year later when Mr. Moneybags crashed.
Tsunami in 1991 used something of an imitation scimitar prop--T-28 triangluar blades that had the leading edge tapered. It was used in qualifying and during the Friday and Saturday heat races after the race prop was oversped in practice. But on Sunday the stock prop was back in place.
Howard Pardue also tried a similar 'shaved' prop on Fury in the mid-90's, but that didn't last long.Comment
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Re: Question about power and props
In my only foray into anything like aero design (civil & structures are my area) I designed a VERY low aspect ratio "propeller" to trail behind a sailboat and run a generator. We built it as designed then ended up tweaking it by the TLAR (That Looks About Right) method to get what we wanted for performance. Granted I was way out of my expertice, but following all of my studies, I could have done it in less time by just winging it! Of course, computers were not around then...And there's a lot yet to be learnt about propellers and their black magic...
I can understand why it has not been an area easily tackled and I give Thom and PM "props" for going there!Comment
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