Gas Turbine Development Questions

[Zipper730]

1. Why was Edgar Buckingham's research used against anybody proposing any form of jet engine?

His idea revolved around…

1. A piston engine with a supercharger blasting all it's exhaust out the back as thrust instead of spinning a propeller
2. A required pressure ratio of 15:1 to be useful
3. A velocity of around 5280 feet per second

… on an aircraft expected to achieve 250 miles per hour

Early gas turbines generally were…

1. Not piston engines
2. Self-driving turbochargers
3. Required pressure-ratios of 4:1 to be useful
4. Had exhaust velocity of around 1700-1800 feet per second, or 1/3 that of Buckingham's engine which is better for propulsive efficiency

… on aircraft expected to achieve 500 miles per hour or greater.

While he claimed that jets had no prospect whatsoever, they were premised on a top-speed of 250 miles per hour…

1. By November of the same year he wrote his report (1923), that speed was exceeded
2. By the 1930's, race planes would already exist capable of exceeding 400 mph and proposals would exist aimed at 500-550 mph

2. Why was there a continued obsession with jet-engines that more resembled the Caproni-Campini system than gas-turbines in NACA?

3. Why was there an attitude that Gas-turbines were rather heavy?

 

[Shortround6]

3. Why was there an attitude that Gas-turbines were rather heavy?

Because gas turbines had been built for industrial use, like powering air compressors for powerplant boiler rooms or mine ventilation or for supplying large quantities of air for industrial processes.
ANd all of these gas turbines had been very heavy, close to 10lbs per hp.
And sometimes had trouble keeping themselves running let alone actually perform useful work (supply the compressed air) for a fuel use that compared with conventional engines.

 

[Zipper730]

Because gas turbines had been built for industrial use, like powering air compressors for powerplant boiler rooms or mine ventilation or for supplying large quantities of air for industrial processes.

I guess they didn't consider that a version for an aircraft would be much smaller...

ANd all of these gas turbines had been very heavy, close to 10lbs per hp. . . sometimes had trouble keeping themselves running let alone actually perform useful work (supply the compressed air) for a fuel use that compared with conventional engines.

Did Alan Griffith's work make it over the Atlantic? From what I remember the problem was that the blades were running stalled...

 

[Fighterguy]

Lets not forget the use of steam turbines. The concept of the gas turbine engine for aircraft relied on the ability to produce turbine, and in some cases, compressor blade, materials, that could withstand high temperatures, along with circumferential and axial loads, while remaining lightweight enough. The processes of metallurgy to meet these demands had not yet been developed, mainly because the need hadn't arisen. Then there's the issue of control mechanisms. Internal combustion engines used rudimentarily simple fuel-air mixing principles. Gas turbine engines require a fine tuned ability to automatically adjust to variations in air temperature, density, and speed, throughout the continuous intake, compression, ignition, and exhaust sequence. At the time, the ability to test theories didn't exist, so engineers and scientists had to rely on what they currently knew, or technology currently available. Like the incredible rise in aircraft design and construction abilities experienced during WWI, WWII similarly drove the need.

 

[XBe02Drvr]

Why was there an attitude that Gas-turbines were rather heavy?

Because they were. The J34s we had in mech school and the RR Darts we had at the airline were both examples of 1940s gas turbine technology. They were full of heavy castings reminiscent of '40s radial engines, with very little of the high tech high temp sheet metal that characterizes today's gas turbines. Our SD30s had PT6s that were within 150 HP of our F27's Darts but weighed half as much and burned half the fuel.
Cheers,
Wes

 

[Zipper730]

Lets not forget the use of steam turbines.

True, the origin of gas-turbines came from turbochargers and steam-turbines together.

Because they were.

Looking at some figures I've found online, they seem to have both weighed around 1200 pounds, which is actually lighter than the V-1710 (1395 pounds) and Merlin 61 (1640). The J34's 3000-3700 horsepower figure would be poor compared to a jet at low altitude but by 375 mph it'd be about the same as a 3000 HP engine.

 

[XBe02Drvr]

Looking at some figures I've found online, they seem to have both weighed around 1200 pounds, which is actually lighter than the V-1710 (1395 pounds) and Merlin 61 (1640). The J34's 3000-3700 horsepower figure would be poor compared to a jet at low altitude but by 375 mph it'd be about the same as a 3000 HP engin

Where'd you get those figures? 1200 pounds sounds awfully light for a Dart. We used to haul them up to Montreal to the RR shop for overhaul, and occasionally Customs would insist on weighing the truck. After all the corrections were made for fuel, oil, the truck, etc, the Dart in its shipping cradle came out to about 1 1/4 ton. The cradle itself weighed 350-400 pounds, so that leaves the Dart at a shade over a ton. And just to make any comparisons more fair, a Dart comes out of the aircraft as a bare engine, leaving the accessory section behind in the plane. Almost all other turbine engines come out with their accessory sections attached.
3000 HP from a J34 sounds pretty optimistic to me, too. Better quote your sources. The reserve squadron P2V7s at NAS Memphis where I went to school (and got a ride in one) had a pair of 3000 HP piston pounders and a pair of J34s and when they turned on the jets it certainly did NOT double the power. It did, however, give the pilots enough control authority to overcome the violent swerve that would occur if they lost one of the main engines during takeoff or climbout. Boy, the view from the nose "spotter's" seat is some kind of awesome, especially cruising the "Mighty Mississip" at low level!
Cheers,
Wes

 

[Zipper730]

Where'd you get those figures?

Wikipedia

We used to haul them up to Montreal to the RR shop for overhaul, and occasionally Customs would insist on weighing the truck. After all the corrections were made for fuel, oil, the truck, etc, the Dart in its shipping cradle came out to about 1 1/4 ton. The cradle itself weighed 350-400 pounds, so that leaves the Dart at a shade over a ton.

2100-2150 pounds.

And just to make any comparisons more fair, a Dart comes out of the aircraft as a bare engine, leaving the accessory section behind in the plane. Almost all other turbine engines come out with their accessory sections attached.

How much does that add?

3000 HP from a J34 sounds pretty optimistic to me, too.

I made an error, that's 3000-3700 pounds of thrust, which at 375 miles an hour becomes 3000-3700 horsepower.

The reserve squadron P2V7s at NAS Memphis where I went to school (and got a ride in one) had a pair of 3000 HP piston pounders and a pair of J34s and when they turned on the jets it certainly did NOT double the power.

As a general rule of thumb propeller thrust is around 2.5 x horsepower, so basically you have 7500 lb/thrust an engine.

 

[XBe02Drvr]

How much does that add?

Don't know. When I was there we never took an accessory gearbox out of a plane, just swapped out the various components mounted on them.
Cheers,
Wes