fixed pitch props

[matt]

i was thinking about the wooden fixed pitch props on some of the old '20's and '30's era racers and i can certainly understand the change to pitch changable props but wouldn't a composite prop optimized for full throttle efficiency have less weight and better balancing?

[AAFO_WSagar]

Re: fixed pitch props

Originally posted by matt
i was thinking about the wooden fixed pitch props on some of the old '20's and '30's era racers and i can certainly understand the change to pitch changable props but wouldn't a composite prop optimized for full throttle efficiency have less weight and better balancing?

I may be all wet on this but don't the IF1's run with a fixed pitch?

One of the reasons that Jon Sharp used to always be slow out of the gate was that the prop was optimised for once he got going fast, so it took him a long time to get there.

I believe you are correct Matt, but the convenience of having a prop that is able to "change gears" when needed will probably always outweigh he potential advangate in outright speed.

Wayne

[52eme]

Re: Re: fixed pitch props

Originally posted by AAFO_WSagar
I may be all wet on this but don't the IF1's run with a fixed pitch?

they do, it is mandatory.
however i believe some racers tried using scimitar blades but apparently with limited succes..


IMHO using a fixed pitch on an unlimited would resut in marginal take off and go around performance..

-
Matt, I'm down to 35lbs with that thing i was talking about the other day. may be usable after all.

[gsbloom]

bad idea...

You are at 450+ MPH, 40 feet above the ground and bang...your motor loses a cylinder. Now your fixed pitch, speed groomed prop is more like a barn door than a propulsion device. You trade airspeed for altitude...making things worse....

Shall I continue?

[Unregistered]

Just the opposite. At high speed the prop is in "high pitch/low RPM", so the blades are more aligned with the relative wind as the aircraft moves forward (assuming the engine has lost power). In fact, when a propeller is feathered it is aerodynamically aligned as closely as possible with the relative wind for minimum drag. The barn door effect is when the blades are flat to the relative wind (low pitch/high RPM).

Now then, before someone climbs all over me about "high" and "low" pitch, think about it. Pitch is measured as inches of forward progress as the screw (propeller) rotates thorugh one revolution. Therefore, the lower the pitch number the less the pitch, and the less the screw moves forward per revolution. Of course, the opposite is true for high pitch.

[AAFO_WSagar]

You guys are both right, sort of... In the case of the IF1's they have to go with a fixed pitch for both weight and rules (I think that is in the rules) Some go with a flatter pitch for a better start, others, like Nemesis, go/went for a more high speed setting on the fixed. This makes for a slow start, as the engine labors to turn the screw, like taking off in third gear. (Why Nemesis always seemed to have a slow start)

For sure tho, if your engine quits, being able to feather would be far superior to not, or worse, going into full flat pitch as happened to Hannah in Voodoo a few years ago.. An attention getting event to be sure!

Wayne

[Unregistered]

For sure tho, if your engine quits, being able to feather would be far superior to not, or worse, going into full flat pitch as happened to Hannah in Voodoo a few years ago.. An attention getting event to be sure!

This also happened with the RB-51 (Griffon/contra-rotating props/six blades flat to the wind). Talk about "high-drag".

[AAFO_WSagar]

Originally posted by Unregistered
This also happened with the RB-51 (Griffon/contra-rotating props/six blades flat to the wind). Talk about "high-drag".

That was my first year at Reno (*actually in the stands that is*) and it was amazing how rapidly that airplane decended with those six blades in flat pitch!

I think it remains today one of the great miracles in aviation history that Steve Hinton survived that landing! (yes, it was a landing, because he did survive)

Whittington also dropped out of the sky in Precious Metal due to the same problem, which, according to Ron Buccarelli, is now controlled in some way so that he has the means to feather in an emergency.

MAII also had a backup feature that would allow them more than one feather cycle, independant of the engine, in the case of an emergency.

If I'm not mistaken, properley counterweighted props will "autofeather" in the event of an emergency... much better to fail into the wind than against!

Wayne

[GWB]

That was my first year at Reno (*actually in the stands that is*) and it was amazing how rapidly that airplane decended with those six blades in flat pitch!

Well...... if my memory is better than your memory , he flew a long way out over Hoover's Gulch during the 180 back to the runway. He still had a lot of energy when he crossed the finish line, and the engine was still running - sounded sick, but was still running. I don't recall a great rate of decent until the latter part of the approach when he disappeared below the rim. That he survived owes more to luck than anything else. Not that I could do any better, but them rocks are hard!!

[AAFO_WSagar]

Originally posted by GWB


Well...... if my memory is better than your memory , he flew a long way out over Hoover's Gulch during the 180 back to the runway. He still had a lot of energy when he crossed the finish line, and the engine was still running - sounded sick, but was still running. I don't recall a great rate of decent until the latter part of the approach when he disappeared below the rim. That he survived owes more to luck than anything else. Not that I could do any better, but them rocks are hard!!

What I *remember* and that was a long time ago

He went by the finish line, pulled up abruptly, made a left climbing turn with the intent to get it back to the runway... as he approached the "bluff" at the east end, it became apparant that the bread and butter were not going to mesh at the right time and he turned across the bluff, rather than hitting it head on. Could he have made the field at that point? Obviously, to Steve, it must have looked as though he could not so the turn to 90 degrees across the runway heading was appropriate but also guaranteed an off airport landing.

I do remember that once he turned back toward the field, his decent rate was sickeningly high, even though his airspeed appeared to be equally high. If memory serves me correctly, he appeared to be going down at about the same rate as ahead..

Luck, skill or blessed.. after seeing the crash pix and seeing it happen. It remains one of aviation's greatest miracle "landings" in that Steve lived through it... and had children... if you've ever seen pix of that seat pan, you know what I mean.... (ouch!)

Wayne

[FightinBluHen51]

Originally posted by AAFO_WSagar
That was my first year at Reno (*actually in the stands that is*) and it was amazing how rapidly that airplane decended with those six blades in flat pitch!

I think it remains today one of the great miracles in aviation history that Steve Hinton survived that landing! (yes, it was a landing, because he did survive)

Whittington also dropped out of the sky in Precious Metal due to the same problem, which, according to Ron Buccarelli, is now controlled in some way so that he has the means to feather in an emergency.

MAII also had a backup feature that would allow them more than one feather cycle, independant of the engine, in the case of an emergency.

If I'm not mistaken, properley counterweighted props will "autofeather" in the event of an emergency... much better to fail into the wind than against!

Wayne

Explain something to the new guy, do contra-props have fixed pitches?? or can they adjust them as well?? What advantages do the contra vs single props have??? Thanks guys

[AAFO_WSagar]

Originally posted by FightinBluHen51


Explain something to the new guy, do contra-props have fixed pitches?? or can they adjust them as well?? What advantages do the contra vs single props have??? Thanks guys

I'm far from an expert on the subject but for sure, the contras have variable pitch prop blades. The advantage of the contras is spreading the power of the engine out over more blades. With the contras, you also get the advantage of each blade set countering the torque of the other set. The pilot can apply a lot of power early and will have the control authority to fly the airplane. With a very high power engine and single prop set, enough airspeed has to be developed so that the controls will have enough air over them to counteract the engine/prop combo's will.. which can, in some cases even flip an airplane on its back. Or at the least, send it skittering across the runway at a sickening angle and off the pavement into the weeds..

For those at Reno a few years ago... Can you say.. YAK!!!

Wayne

[FightinBluHen51]

HP and cubes?

What kind of power are these unlimited motors making?? What kind of displacement and RPMs do Merlin and Griffon motors turn?? Well ok, RPMs on the merlin, and both for the griffon.

[gsbloom]

Re: HP and cubes?

Originally posted by FightinBluHen51
What kind of power are these unlimited motors making?? What kind of displacement and RPMs do Merlin and Griffon motors turn?? Well ok, RPMs on the merlin, and both for the griffon.

It is more a question of power rated in manifold pressure. Stock Merlins can pull 60 inches of "war emergency power" off the standard 50" max. (From the P-51 flight manual) Which is about 1500 HP.

The manifold pressures I have heard of range up to 160 inches. Maybe more. That equates to about 3000-4000 HP (from what I have been told).

Either way...it is a lot more than stock.

[First time Juke]

fixed pitch props on twins ?

Hi,

Before I develope any further idea of my new twin of non-category racer with fixed pitch props....I want to know if there is anyone flown a twin with one engine of this kind with fixed pitch on props ?



Dave Morss,

Did you try the 2/3 scale P-38 on one engine ?


best regards,

Juke