Propeller questions

[Devil 505]

2. Why did The P-51 and P-47 have 4 blade props, while P-38, P-39, P-40 and the blue planes have three blades?

Remember that the P-51A uses an Allison engine, same as the -38,-39, and -40. All have 3 bladed props. I'd say the reason had to do with available horsepower.

[BigKev03]

So far as I know, all of our planes have constant speed propellers.  Your throttle sets manifold pressure, your RPM control (whatever you use!) sets the propeller pitch at that particular moment, and the propeller automatically adjusts its pitch to maintain that RPM as you do things like climb and dive.

- oldman

Thanks!  I was just curious.  I do adjust manifold pressure and rpm's but I had no idea it was factored into the propeller pitch.  Good to know info as an FYI.

BigKev

[caldera]

Remember that the P-51A uses an Allison engine, same as the -38,-39, and -40. All have 3 bladed props. I'd say the reason had to do with available horsepower.

What about the 2,000 hp P-47 (4 blades) vs the 2,000 hp F6F and F4U (3 blades)?  All three had the R2800 IIRC.

[SIK1]

What about the 2,000 hp P-47 (4 blades) vs the 2,000 hp F6F and F4U (3 blades)?  All three had the R2800 IIRC.

I've always wondered about that as well. Specially with the F4U-4 swinging a four bladed prop. Wouldn't the earlier corsair marks have benefited from a four bladed prop?

[drgondog]

So far as I know, all of our planes have constant speed propellers.  Your throttle sets manifold pressure, your RPM control (whatever you use!) sets the propeller pitch at that particular moment, and the propeller automatically adjusts its pitch to maintain that RPM as you do things like climb and dive.

- oldman

All Mustangs (and I'm pretty sure most a/c using any variation of Hamilton Standard Constant Speed Prop systems) had a manual overide capability to vary between Coarse (aft) and Fine (forward) Pitch.

The P-51 pitch control was automatically moved forard with a forward movement of the throttle, but the pilot could maintain high boost and then manually (left hand directly under the throttle control) move the pitch control back toward Coarse.

[colmbo]

All Mustangs (and I'm pretty sure most a/c using any variation of Hamilton Standard Constant Speed Prop systems) had a manual overide capability to vary between Coarse (aft) and Fine (forward) Pitch.

The B-17 and B-24 have Hamilton Standard props...all we could do was select RPM with the prop control.  The only pitch control we had was to feather the prop.

The P-51 pitch control was automatically moved forard with a forward movement of the throttle, but the pilot could maintain high boost and then manually (left hand directly under the throttle control) move the pitch control back toward Coarse.

When I flew Crazy Horse it didn't work as you described.  It worked as any constant speed prop I've flown with..RPM is set with the prop control (then governed by varying the prop pitch).  I can't see why you'd want the pitch to change with throttle change except to prevent overboost, but then at times that you're likely to push the throttle up you've already increased prop RPM since you're wanting more power.

[hitech]

All Mustangs (and I'm pretty sure most a/c using any variation of Hamilton Standard Constant Speed Prop systems) had a manual overide capability to vary between Coarse (aft) and Fine (forward) Pitch.

The P-51 pitch control was automatically moved forard with a forward movement of the throttle, but the pilot could maintain high boost and then manually (left hand directly under the throttle control) move the pitch control back toward Coarse.

Yes and no, fine pitch is really just increasing rpm, coarse pitch low rpm. I do not know of any wwii planes that had any other system then this one. The control just sets the rpm on the Governor. It then changes the pitch.

Most pilots use the term interchangeably, pitch control is the lever that sets RPM, but it is indirectly controlling pitch.
So if a plane sais it has pitch control,or prop control, just assume it is an normal rpm setting.

When doing my checks, I always call the lever prop. I.E. Prop,Mixture ,boost pump, gear down and bolted, tank on the fullest.

Same with start, prop forward, mixture ritch, boost pump to 20 and off, hot start, thottle full mixture ideal cut off, crank until fire or 3 secs.Wait 10 and repeat. Then do the fun mixture throttle shuffle while pinching the stick between your legs.

Cold start is easy, mixture rich thottle 1/8 inch ,crank for 1 blade and watch it fire.

HiTech

[MiloMorai]

hitech have you flown a P-51? Iirc drgondog has about 50 hrs in the P-51.

[hitech]

hitech have you flown a P-51? Iirc drgondog has about 50 hrs in the P-51.

Yes, have 1 hour dog fighting Bob Shaw.



Is a photo taken by Bob of me coming threw the vertical a formation loop.

HiTech

[Tyrannis]

Yes, have 1 hour dog fighting Bob Shaw.

(Image removed from quote.)

Is a photo taken by Bob of me coming threw the vertical a formation loop.

HiTech

who won?   

[Ardy123]

who won?    

they collided, but only Bob got the message and damage  

Jokes aside, I bet it was fun as fk!!, I'm tottaly jealous. From what I hear, Bob is a compact built guy, I bet he can handle more 'g's than most people.

[hitech]

they collided, but only Bob got the message and damage  

Jokes aside, I bet it was fun as fk!!, I'm tottaly jealous. From what I hear, Bob is a compact built guy, I bet he can handle more 'g's than most people.

Thats why we call him mouse.

One day we were flying my RV together and decided to go find 6g corner speed. Bobs flying from the back. Anyway we start at about 8k. After about 1 min I finally go lights out.

The same day we found min loop speed of about 112 knots.

Did I mention he also broke my plane 1 day?

HiTech

[Stoney]

I see what you mean.  I was thinking of the 109K-4 and its wider than normal 109 prop.  I had always thought that they increased area to make up for less air up high, but your post suggests to me that they widened the blades to give it a better climb rate with all that extra HP.

This is why the P-47 was changed to the "paddle-blade" prop.  When originally designed, the prop was optimized for high-altitude cruise performance.  In wartime service, the need to increase the climb rate was realized, and they added the broader chord prop to increase the rate of climb, which actually knocked a few mph off the top speed.

Generally speaking, the fewer blades and the larger the diameter the better, but then you run into all the other design problems previously mentioned--keeping tip speeds subsonic, ground clearance, power absorption, etc., you sometimes need to add blades, make them shorter, or have thinner or thicker chords. 

Propeller theory is pretty mind-bending when you get into the more technical/advanced aspects of it.  It is probably a bigger example of "everything's a trade off" in aircraft design than some of the airframe issues.  And unfortunately, without some very in-depth discussion, its very difficult to boil down into simple, generalized statements.  Its one of the reasons computing thrust equations on propeller aircraft is so difficult.

[Tupac]

How did he break your plane?

[Ardy123]

Did I mention he also broke my plane 1 day?

HiTech

sounds like an expensive date...