PM 38 Why the difference in prop length

[Cadet]

Re: PM 38 Why the difference in prop length

I'm not disagreeing that the airplanes speed and condition have been greatly improved. It's obvious that the crew has made great strives in the right direction. I'm not attacking the crew or the airplane, I simply disagree that you can make a direct comparison from this year to last. And I don't think that there is any solid numbers proving the new course is actually slower. Does anyone know what kind of power Strega ran last year during qualifying compared to this year?

[RAD2LTR]

Re: PM 38 Why the difference in prop length

Twice!

That really is pretty impressive. I remember a couple years ago when I think it was Cloud Dancer and September pops were photographed showing just how much larger the Sea Fury was.

Still, you can see how much larger the Buick is in this shot.


There is something to be said about the fact that there was that much dirty air coming off PM.


These guys rock and I'm thrilled to see PM finally getting sorted out and becoming the contender it should have been a decade ago.


Will

[Big_Jim]

Re: PM 38 Why the difference in prop length

and becoming the contender it should have been a decade ago.


Will

A decade ago? Try 25 years ago...Whittington was the guy who had the bottomless pit of money to throw at it.

[Paynts]

Re: PM 38 Why the difference in prop length

I've mentioned this before, thinking to myself how nice PM would look with a 5 blade Rotol on
So the question is is the Shakelton prop better for reno than a Rotol 5 blader, or is it just as good, or we dont really know? or is it just too expensive to get hold of a Rotol?

be interesting to know the crew chiefs thoughts

Ps Im a massive PM fan, I have always romantically liked the idea of a Griffon Mustung being the ultimate inline racer even if a Merlin one seems invicible at present!

[Wild Bill Kelso]

Re: PM 38 Why the difference in prop length

I've mentioned this before, thinking to myself how nice PM would look with a 5 blade Rotol on
So the question is is the Shakelton prop better for reno than a Rotol 5 blader, or is it just as good, or we dont really know? or is it just too expensive to get hold of a Rotol?

be interesting to know the crew chiefs thoughts

Ps Im a massive PM fan, I have always romantically liked the idea of a Griffon Mustung being the ultimate inline racer even if a Merlin one seems invicible at present!

The nose cases and prop for the mk 74 Griffon are getting very rare and expensive. I would sure hate to convince our owners to spend the money and have it not work. Also if we had to cut the blades down for proper tip speed at race rpm I don't think you could because that is a wood core prop.

And I do want to know one thing. Could Cadet please tell us who you are and your background? I only ask because you opinions seem to lack what most the teams already know. The more constant and higher g's the airplane pulls the more it will bleed off speed. Therefore this course is slower. It's shorter so the speeds we saw in 2012 may not reflect average speeds too much because it's a shorter distance covered over time. We all set base settings for qualifying. I'm pretty sure they ran the same settings in 2012 as they did in 2011. During races they got out front and only used as much power as they needed to stay in front. That's how you run a good race program. PM did the same. We wanted to stay in front of Dread and only used enough power to do so.

[RAD2LTR]

Re: PM 38 Why the difference in prop length

I've mentioned this before, thinking to myself how nice PM would look with a 5 blade Rotol on
So the question is is the Shakelton prop better for reno than a Rotol 5 blader, or is it just as good, or we dont really know? or is it just too expensive to get hold of a Rotol?

be interesting to know the crew chiefs thoughts

Ps Im a massive PM fan, I have always romantically liked the idea of a Griffon Mustung being the ultimate inline racer even if a Merlin one seems invicible at present!

I've wondered the same thing. The last of the Spit and Seafires ran the 5 blades, the Sea Furies ran the 5 blades, it would seem that if the counter rotating props were the answer they would have used them. I wonder if the 5 blade props are A) hard to find, and B) prone to seal leakage like some of the P-51 props or D) loose their efficenecy at the rpm required for racing? I'd love to hear the thoughts from the people who know more than I.

Will

[Wild Bill Kelso]

Re: PM 38 Why the difference in prop length

I've wondered the same thing. The last of the Spit and Seafires ran the 5 blades, the Sea Furies ran the 5 blades, it would seem that if the counter rotating props were the answer they would have used them. I wonder if the 5 blade props are A) hard to find, and B) prone to seal leakage like some of the P-51 props or D) loose their efficenecy at the rpm required for racing? I'd love to hear the thoughts from the people who know more than I.

Will

I already answered that. See last post.

[51fixer]

Re: PM 38 Why the difference in prop length

The nose cases and prop for the mk 74 Griffon are getting very rare and expensive. I would sure hate to convince our owners to spend the money and have it not work. Also if we had to cut the blades down for proper tip speed at race rpm I don't think you could because that is a wood core prop.

The mk 74 and mk 65 Griffons are similar but all the nose case gearing internal is different. The Nosecase casting as well as the the crankcase is the same for both models.
The 74 typically used a 4 blade prop of longer length and ran slower. The gearing was .451 to 1. Due to the cam drives being run off the large prop drive gears the gears that drive the cams and magneto are specific to that mk of engine. IIRC the mk 58 uses the same gear ratio to drive the cams and mag. The 74 is what was used on many Fireflies with alum prop blades.
The mk 65, 66 and 67 are what was used on the Spitfires running the wooden 5 blade props. The prop gears are bit faster turning at .510 to 1. Again all the gearing that drive the cams and mag are specific to that nose case gear ratio. The gear ratio was determined by the smaller airframe of the Spit as the prop shaft is closer to the ground. To avoid contact the faster turing 5 blade prop was developed to absorb the horsepower of the engine.
The 5 blade Rotol prop on the Spit has wood blades, (actually all wood with a resin covering and metal leading edge, not just a wood core) and they can actually be cut down a bit as there is a range of diameters allowable per the book. There are a couple companies, Hoffman in Germany and an Italian Company that will make blades. I'm sure they could be made up in any configuration of airfoil and length that can be figured out and engineered.
We actually have 5 Mk 9 style blades that were made as a mirror image on the Mk XVIII Spitfire I take care of. At the time Hoffman only had approval for the Mk 9 blades and could only make them in a left handed version for the Griffon powered Spitfires. That was the early 1980s. The normal Griffon blade has an enlarged cuff at the base of the blade.
The Spitfires that used the Contra Props back in the 40s had both wood blades and metal blades during wartime and right after. I'm not sure what the Seafire mk 47 had which was the last of the Spitfire types produced in any quantity. It had the contra props.

[wingman]

Re: PM 38 Why the difference in prop length

So this year's target was to stay ahead of Dreadnought -- next year you stay ahead of the Bear??

[Wild Bill Kelso]

Re: PM 38 Why the difference in prop length

So this year's target was to stay ahead of Dreadnought -- next year you stay ahead of the Bear??

Everyone!

[wingman]

Re: PM 38 Why the difference in prop length

Ah -- Good answer!

I like Race teams motivated and hungry...

I've always loved this airplane, and now more than ever!

Now the tech discussion can resume -- it's been interesting so far.

I just couldn't resist interrupting...

[Wild Bill Kelso]

Re: PM 38 Why the difference in prop length

Ah -- Good answer!

I like Race teams motivated and hungry...

I've always loved this airplane, and now more than ever!

Now the tech discussion can resume -- it's been interesting so far.

I just couldn't resist interrupting...

Notice how much trim is being used here BTW. Very little!

[Big_Jim]

Re: PM 38 Why the difference in prop length

Sorry for hijacking your pic, Neal....but what are we seeing here? Oil coming off the side of the doghouse? Something (spraybar) venting from the Oil Cooler bypass door? Or is it just the clouds in the background with an interesting placement?

[Wild Bill Kelso]

Re: PM 38 Why the difference in prop length

Sorry for hijacking your pic, Neal....but what are we seeing here? Oil coming off the side of the doghouse? Something (spraybar) venting from the Oil Cooler bypass door? Or is it just the clouds in the background with an interesting placement?

7.5 gpm of spraybar water got to go somewhere! Oil is coming from bottom of the cowling and the boundary layer just takes it everywhere. A small leak was draining a quart or so every flight. A little oil makes a huge mess.

[Dialtapper]

Re: PM 38 Why the difference in prop length

So this year's target was to stay ahead of Dreadnought -- next year you stay ahead of the Bear??

Ya, that could happen.

When monkeys fly out of your butt.