I tried this in our P-47D...it didn't work

[flakbait]

The following story taken from "The Smithsonian Book of Flight"...

"The Jug in New Guinea
Edwards Park


I work standing up. When people ask why, I murmur something about my back. The real reason goes back to December 1943, when the Pentagon rediscovered our long-forgotten fighter squadron in New Guinea's Ramu Valley, and gave us P-47s.

We had been flying P-39s, dicey by nature, and growing more so with advancing age. So my first memories of the Thunderbolt are tinged by obvious contrasts: it seemed huge to pilots used to the tiny '39. "Hey, we got Cadillacs," one colleague remarked-- and searched the spacious cockpit for a golve compartment.

Seated in elbow-spreading comfort, we checked out. Takeoff? You checked mags, set trim tabs, cracked flaps, locked the tailwheel, poured on the coal and the plane did the rest. It obeyed every whim--climbing steeply, abruptly winging over and diving-- without a sign of p-39 hysteria. On landing it simply sagged impassively, straight onto the runway. Unused to 16,000 pounds of airplane, we sometimes climped it on a little hard. "I just dropped eight tons on the Nadzab strip," a fellow pilot once ruefully reported, "And I was in it!"

No matter. The P-47 was built like a boulder. I ince saw one touch water on a low pass, and fly home with a foot of each propellor blade curled neatly back. Another colided with a P-38. Both got back, the Lightning with half a wing, the Jug with scratched paint. It flew another mission that afternoon.

Those missions were far longer than any we had ever flown before: four, even five hours. But these missions weren't long enough for the Southwest Pacific. So Charles Lindbergh, representing Pratt & Whitney, briefed Fifth Air Force Thunderbolt pilots on long-range flying. I remember gathering in a lantern-lit mess test one evening, and being introduced en masse to the god-figure of all pilots everywhere, tall, slender, familiar. Someone whispered that he had shot down an enemy plane that afternoon. Of course, he never mentioned it. In his soft Midwestern voice, he told us to try a high throttle setting and only 1,400 RPMs. Our propellors would grind along, taking great bites of air.

We stirred uneasily at the heresy, and Lindbergh read our thoughts. "These are military engines, built to take punishment," he said, "so punish them." The he added that if we felt uncomfortable about flying this way, we shouldn't do it: " You're the captains of your own ships. You must make the decisions. After all, you know more about flying your planes than I do."

At that we burst out laughing. And we began flying eight-hour missions. We'd return so numb we'd taxi standing up, feet on the rudder bars, massaging our buttocks with both hands.

Oh, yes. The P-47 was wonderfully forgiving and brutally tough. And thanks to it, and Charles Lindbergh, I now work standing up."

I tried doing just that: a high throttle setting with 1,400 RPMs. Our beloved Jug didn't fly, it fell! Although filling out graves registration papers for those sheep will stop me from doing it again. How come we can't cruise that long and far in AH?

Flakbait

[[Sg]ShotGun]

because we cant override prop pitch.

what lindbergh wanted was for the pilots to have the 'high' throt setting, but to use the pitch control to achieve 1400 rpm indicated.

by increasing the pitch of the prop at hi thot setting, u take 'great bites of air'.

in out AC, the pitch control is still auto matic...

[SFRT - Frenchy]

I'm not sure i understand... the pitch control is the + - keys right? So it's not automatic.
Usually high manifold pressure and low RPM puts heavy stress on the engine, it's not good for longevity. That's why when decelerating u lower manifold first then RPM, and when accelerating u increase RPM first and manifold pressure.
In non turbocharged planes, when cruising at high alt and decending u have to take care because ur MP increases as the air gets more dense and u end up with a HI MP, low RPM and overstressing the engine.

I met a guy who used to fly his twin at 30MP and 1700 RPM in cruise (quieter), it was ok because he had a 'gear box'.

As far for the P47, I don't know his systems so I can't tell how the supercharger affects his prop setting. I just know they had a light and they used MP as required not to keep the Turbo light blinking, not steady red.

[flakbait]

Nope, "+" and "-" vary RPMs, not prop pitch.

Flakbait

[niklas]

i have absolutly no problem to fly level with 1400rpm. I don´t even need 100% thrust. I can hold a P47 level with 1400rpm @ 180MPH

[flakbait]

Well, all we need now is manual prop pitch and we can get that last 40 mph out of it. When I tried it I climbed first to 25k, then pulled RPMs back to 1,400. The Jug fell like a rock at 140 mph indicated. Since they cruised at 220 mph with those settings, we're only 40 mph off!  

Flakbait

[SFRT - Frenchy]

Flakbait, a contant prop RPM is acheived by changing the prop pitch via the prop RPM lever. I change the prop pitch lever, the fly weights feel an overspeed or underspeed due to centrifugal forces. When the fly weights are moving, it sends more or less oil to the prop hub, the change of oil quantity affects the pitch of the prop. Low RPM is high pitch angle, high RPM is low pitch angle.

Did I missunderstood something there? Are we talking of the same thing? what is the prop pitch for you?

[flakbait]

Prop Pitch: The angle at which the propellor blades meet the air, creating thrust. More pitch [up to 45.5º] creates more thrust, while fine pitch [down to 0º] creates less. Prop RPMs only vary the rate at which the propellor rotates, not the angle of the blades. In theory, you could set the pitch at 10º and RPMs at 30,000 and actually get high speed flight. It's much more simple to set the pitch at 45.5º, lower the RPMs, and reduce the manifold pressure to create long distance flight. Plus Texico won't charge you $12,000 for gas

We can currently vary the RPMs, or rate at which the propellor rotates. What we can't do is vary the angle of the prop blades. If we could, you could fly all the way across the map and half-way back on a single tank of gas.

Flakbait

[funked]

Flakbait, AH models a constant speed prop.  When you change RPM with +/- you are setting the speed that the regulator tries to achieve.  The regulator controls the prop pitch to keep the RPM at the value you set even if there are changes in throttle setting, airspeed, altitude, etc.  This is how it worked on nearly every WW2 fighter and this is what HTC are trying to simulate.

[This message has been edited by funked (edited 07-20-2000).]

[SFRT - Frenchy]

Flakbait... are WW2 planes different on setting up the props as it is on the planes i teach my students to fly? (Mooney, Arrows, Seminoles and others constant speed propeller small general aviation aircrafts).

If they are, then please enlight me, do they have levelers for manifold and prop RPM and 'prop pitch control'? How does that work?

In the planes I fly, I have manifold and prop RPM, prop RPM is set via the propeller pitch who is adjusting himself depending on how much oil is traveling to the prop hub. (Like I explained earlier).

[SFRT - Frenchy]

I went to see some old timer fellow flight intructor and inquired about a separated 'pitch control' lever else than prop RPM.

According to him, he never eard of that. He told me about some old planes having a propeller with a pitch control not being a constant speed prop. You could adjust two pitch settings only, 1 for climb and 1 for cruise.

Airplanes using a gear box obeys the same prop hub rule as a constant speed prop (fly weight/prop hub/blade pitch angle). Just the gear box allow to supress the stress to the engine when flying high manifold and low RPM (like the transmission on a car).

Changing the prop RPM (thus the blade angle) should not necessary mean that you should achieve faster airspeed. For each 'flight configuration altitude' there is only one efficient setting, given by the performance chart.
Let's say u are flying level at a constant RPM setting at prop "full foward" (High RPM, low blade angle). Your prop is not very efficient because it's spining 'too fast'.When u start lowering ur RPM, u take a bigger bite of air, allowing to increase your prop efficiency till you reach the optimum efficiency for this 'fly configuration/altitude'. When u pass this point and keep lowering ur RPM, the added lift on the prop blade also induce more drag and your plane starts to loose airspeed.

If we do an analogy with a car, it's like changing gear, except that a car as a transmission thus u can achieve superior airspeed as long as the drag of the car is inferior to the BHP of the engine.

Flakbait, I think you miss-explained your thinking, or I didn't get it right. Can you find me a reference of your 'prop pitch control' in a book or web site. As a new flight instructor, I'm always happy to extend my field of knowledge and learn new systems.

Have fun all!

------------------
Olivier "Frenchy" Raunier
     


[This message has been edited by SFRT - Frenchy (edited 07-20-2000).]

[Toad]

Yep, what Funked and Frenchy said.

Now, sorta back on topic, try THIS in your F4U-1D (taken from _The Jolly Rogers_ by Tom Blackburn <VF-17 CO>, ISBN 0-671-69493-6,Chapter 10)

"The Vought people proved as good as their word. As soon as Bunker Hill arrived at Norfolk, the new Hogs <note: these were the first of the operational F4U-1A's -  Toad> were picked up at Floyd Bennett Field. As I was making my check hop in the first of them-my new Big Hog-I got a radio call, "Corsair out of Floyd Bennett. This is LaGuardia Tower. Over."

"This is Big Hog. Go ahead La Guardia."

"Big Hog, we've got very little traffic. Can you make a low pass by the tower? There are a lot of people who'd like to see that thing."

Would I! Do fighter pilots like girls! "This is Big Hog. Can Do. I'll come by downwind. I'll call you one minute out in case you need to wave me off."

"This is La Guardia. Roger. Standing By."

I pointed her down from 5,000 feet and came by, full bore, close aboard the tower at window level indicating 350 knots-403 miles per hour. I pulled up in a 45 degree climb, slow-rolled to the right, slow-rolled to the left, and leveled out at 10,000 feet from  the half loop and half roll of the Immelmann, which put me on a heading back over La Guardia.

"Big Hog, this is LaGuardia. Wow! I say again, Wow! Thanks."

"This is Big Hog. My pleasure. Any time. Out."

Impressive, eh? To quote Wil Smith in Indpendence Day, "Man, I have GOT to get me one of these things!"

Nice book too. If you read it, it will give you a different impression of Head-Ons with respect to what you hear around here. About half the engagements reported have a HO in them somewhere.

Of course, I'm sure Blackburn isn't an acceptable eyewitness. I don't think we can trust his reports...after all fighter pilots are known for exaggerating! He's probably part of the American Conspiracy anyway.

 

[This message has been edited by Toad (edited 07-20-2000).]

[Downtown]

Frenchy and Toad.

I am not a pilot, never had the money to be one.  I am an avid aviation enthusiast though.

My understanding is.

Constant speed propellors turn at a constant RPM.  A blade passes a certain point so many times per minute.

Constant pitch propellors have a fixed cutting angle, and you can controll speed and drag by varying the RPM of the Propellor.

Variable Pitch Propellors have motors that will change the cutting angle of the individual propellor blade.

Variable Pitch and Variable Speed Propellors you can very the cutting angle of the propellor blade as well as the speed that the propellor rotates (one blade past a given point, so many times per minute.)

I am reading "America's One Hundred Thousand" and it describes the oil through a gear box result you are describing.  According to Americas 100,000 all U.S. fighters had Constant Speed Propellors.  The only way Blade Count rotation varied was according to altitude, or run aways.

------------------

"Downtown" Lincoln Brown.
    lkbrown1@tir.com    
 http://www.tir.com/~lkbrown1
Wrecking Crews "Drag and Die Guy"
Hals und beinbruch!

[funked]

Downtown, the way that constant speed props keep their speed constant is by varying the blade pitch.

Also, with a constant pitch prop, the way you "vary the RPM of the propellor" is by changing the throttle setting.

Read the "America's Hundred Thousand" section on constant speed props again.  There were hydraulic constant-speed props as well as electric types.

[Toad]

OK, from the Pilot's Flight Operating Instructions for the Vultee BT-13 (450HP P&W w/"Ham. Standard, two blade, hydro-controllable, two position type, nine feet in diameter."  A pretty common WW2 set up.

"PROPELLER CONTROL.- The propeller control is located on the inboard side of the engine control unit. To "INCREASE" engine rpm (low pitch), move the propeller control forward; to "DECREASE" engine RPM (high pitch) move propeller control aft. (Figure 10.) The propeller is put in low pitch for take-offs, maximum climbs, approaches and landings. The hight pitch position is used for slow climbs, high speed, and before stopping engine."

In actual use, excerpted from the checklist:

"Climb:

1.Throttle back, as soon as a safe altitude has been reached, to 2100 rpm for continued climb in "INCREASE" rpm (low pitch).

Cruise:

1.Propeller control aft to "Decrease" rpm (high pitch).

2. Cruise rpm.
(a) Pratt and Whitney engine-1950 to 2000 rpm"

...and this one note in the Landing checklist:

"Note  In changing from high to low pitch on approach, move the throttle AFT to DECREASE engine rpm. THEN move the control to low pitch."

This is not a variable, but a two position prop (like some of the early fighters); you can see that moving the propellor control alters the pitch and throttle is used to then set desired rpm.  The note points to the fact that changing pitch incautiously can seriously over-rev the engine. If you have a lot of throttle in on approach and shove the prop back in to "INCREASE" rpm, the propeller will spin the motor up. This many not be a good thing.  

Another point is that in the operating charts, they never give a MP number. It's either "full" as for a take-off or "as required" for cruise.

(Although we use specific MP coupled with RPM to set cruise and such. Like 28" and 2000 RPM. Set 28" with the prop in "decrease" and ease prop in till you get 2000 RPM.)