Turbocharger Thrust

[Zipper730]

I flew every 747 type except the XP

Sutter's Balloon...

The main change between the 200 and 400 series besides engines, avionics, nav capability and on and on was what I believe was a change in the angle of incidence of the wing

I never knew that, I knew they reshaped the wing, extended the span, added winglets. As a general rule a lower AoA in cruise means you have more available lift -- nice touch I'd say.

The 200 always felt doggy in cruise and the 100 very much so.

When you say doggy, do you mean it as underpowered or sluggish?

 

[fliger747]

100 was way under powered, 200 somewhat underpowered. The -8/Intercontinental I would describe as "leisurely". With the 400 with enough fuel to fly Sydney to Shanghai (10 hrs +-) with full reduced power takeoff we could climb to 41,000' in 11 mins. North of Tiawan is a waypoint named Bulan which had a min crossing altitude of FL 290. In a fully loaded 200 Taipei to Anchorage making this crossing alt was a chore, then you spent a hundred miles trying to accelerate back to cruise mach. In a 400 one could generally climb right to FL 330 with a heavier load.

All the 747's are very elegant airplanes to fly, smooth, very responsive.

Sorry for "flying" off into the weeds here... : )

 

[BiffF15]

100 was way under powered, 200 somewhat underpowered. The -8/Intercontinental I would describe as "leisurely". With the 400 with enough fuel to fly Sydney to Shanghai (10 hrs +-) with full reduced power takeoff we could climb to 41,000' in 11 mins. North of Tiawan is a waypoint named Bulan which had a min crossing altitude of FL 290. In a fully loaded 200 Taipei to Anchorage making this crossing alt was a chore, then you spent a hundred miles trying to accelerate back to cruise mach. In a 400 one could generally climb right to FL 330 with a heavier load.

All the 747's are very elegant airplanes to fly, smooth, very responsive.

Sorry for "flying" off into the weeds here... : )

Are you saying a 747-400 with a lot of weight will climb at 4K FPM all the way to FL410 from takeoff?

 

[fliger747]

As with most planes you have your choices as to what you want to emphasize for a given task. Most planes, including this one, don't all at once be able to carry max load, get max altitude and max range. In the Sydney example maybe we took off with 130 thousand Kilos of fuel but not a lot of cargo, China doesn't buy a lot of goods from Australia. Empty, full of fuel I have flown non stop 18 hours with normal reserve on landing. Every bit of payload adds to the hourly fuel burn. With a full payload (120,000 Kg approx) at max tko weight, 12 hours with reserves would be typical. Normally the 400 would do sprightly climb to FL 330 after a max weight tko. Light over China at altitude I once did a rough fuel burn per mile, came out about 3.5 gal/mile, which isn't too bad. But boy, takeoff and initial climb really expend a lot of heat! We would go up to FL 450 on rare occasion, not much advantage climbing too far above the troposphere. Not too many traffic conflicts... TAS for a given Mach number generally decreases with altitude so at a given weight there would be an optimum altitude where best AOA and Best Mach would coexist. Planned range would be dependent on appropriate step climbs to sea near optimum altitude.

The Intercontinental-8 had a max takeoff of just 30 k pounds under a million pounds. I'll describe it as a bit more leisurely. Boeing snuck in a little "fly by wire, there was a "flare assist". Not sure what defect it was covering up for but if felt like the other 747's.

 

[BiffF15]

As with most planes you have your choices as to what you want to emphasize for a given task. Most planes, including this one, don't all at once be able to carry max load, get max altitude and max range. In the Sydney example maybe we took off with 130 thousand Kilos of fuel but not a lot of cargo, China doesn't buy a lot of goods from Australia. Empty, full of fuel I have flown non stop 18 hours with normal reserve on landing. Every bit of payload adds to the hourly fuel burn. With a full payload (120,000 Kg approx) at max tko weight, 12 hours with reserves would be typical. Normally the 400 would do sprightly climb to FL 330 after a max weight tko. Light over China at altitude I once did a rough fuel burn per mile, came out about 3.5 gal/mile, which isn't too bad. But boy, takeoff and initial climb really expend a lot of heat! We would go up to FL 450 on rare occasion, not much advantage climbing too far above the troposphere. Not too many traffic conflicts... TAS for a given Mach number generally decreases with altitude so at a given weight there would be an optimum altitude where best AOA and Best Mach would coexist. Planned range would be dependent on appropriate step climbs to sea near optimum altitude.

The Intercontinental-8 had a max takeoff of just 30 k pounds under a million pounds. I'll describe it as a bit more leisurely. Boeing snuck in a little "fly by wire, there was a "flare assist". Not sure what defect it was covering up for but if felt like the other 747's.

Fliger,

I'm an airline guy currently and a retired military pilot. I've flown F15, B757 767, A319 320, plumbed the DC-10, DC-8, and the 727. I've come out of Osaka in a light load heavy fueled DC-10-30F with initial pitch at 22+ degrees ANU. It would not get anywhere near 4K per minute up beyond high teens. I would be surprised if a clean (no external stores) F15 without afterburner would do too much better up to FL410.

Impressive that a 747-400 could climb so well.

Cheers,
Biff

 

[fliger747]

One of the cautions we had was a 22 deg deck angle. This due to possible uncovering of boost pumps! And yes on a min fuel go around one would see some of the low pressure lights come on! The plane climbed best with lots of speed! 4000 fpm at 350 kts is less than 9% climb gradient.

I always heard the 757 was a real sky rocket!

Cheers: Tom

 

[rinkol]

A turbocharger is going to hurt thrust, this assumes the non-turbocharged engine had an efficient exhaust system in the first place..

Thrust is the weight of the exhaust gases times the velocity of the escaping gases. The weight will stay pretty much the same for a given engine and manifold pressure. The velocity of the escaping gases will depend on the air pressure in the system (higher altitude means lower pressure which means higher velocity) and how long it takes to get the exhaust to the nozzle/s.

The exhaust gas pressure also depends on temperature, as the gasses cool they shrink in volume and have less pressure. Long pipes between the exhaust port and the nozzle with give room for the gasses to expand and drop pressure and the exposure to the cooler pipe walls will lower the temperature/pressure.

As the gases go through the turbine of the turbocharger they do actual work and drop in temperature, this could be several hundred degrees F. It is one way the turbine works, higher pressure on the inlet side of the turbine vs lower pressure on the exhaust side. Exhaust temperature can be hundreds of degrees lower at the discharge of the turbo (with the consequential drop in pressure/velocity) than the exhaust gas temp/pressure at the end of a short (6-8in) stack.

The R-4360-51 engine with the Variable Discharge Turbine represented a post-war effort to maximize the use of exhaust energy to drive the superchargers and produce jet thrust.

See The Last Gasp For Large Piston Engines : Atomic Toasters

Robert

 

[fliger747]

Designed by German Engineers and scientists smuggled into the program to see what level of complication could be reached? The additional thrust potential is the same principal as was to be used in the Nuclear Powered airplane, which though flew the reactor never got to the thrust utilization stage.

Steam turbines used a high and a low pressure turbine, Uniflow Marine Steam Piston engines used three pistons of increasing size and modern turbine powered electrical plants using GE's CF6 (same as 747-400) engine use heat exchangers to extract steam for extra generation. All laudable attempts to utilize more of the heat cycle for propulsion or energy.

Fascinating! Thanks.

 

[wuzak]

I believe VDT was under development during the war. Even played with VDT for the R-2800.

There was a V-1710 with turbocompounding that ran during the war (V-1710-127/-E27).

The Rolls-Royce Crecy had a turbocompound unit developed for it, and it may have actually ran. The turbine for that was a scaled version of the Derwent V's turbine.

 

[Jugman]

This might be of interest to some people.
Design of nozzles for the individual cylinder exhaust jet propulsion system

 

[Jugman]

I thought they used some of the exhaust thrust to also help lower the pressure on the aft side of the radiator and produce downforce too?

The Caproni-Campini design. From what I was told it wasn't a new idea, but the problem was that it wasn't a real substitute for a jet-engine

1. You're burning fuel twice instead of once: First to drive the piston engine and propeller (which acts kind of like a compressor), followed by additional combustion in a dedicated combustion-chamber (which was really more of an afterburner).
2. A jet only burns fuel once: In the combustion chamber, the turbine extracts power leaving a surplus to push the plane along, and driving the compressor, repeats the cycle

Which would amount to a little under 219 to a little bit over 234 pounds (a pound of thrust is greater than a horsepower at higher speeds), which comes out to around 7.3-7.8% thrust to horsepower at 400 mph @ 40,000 feet, and a horsepower addition of 8-1/3%. It's way better than the XP-47J but looking at the Hurricane IIB's (mentioned by Shortround6) 342 mph maximum speed: You would be left with around 187-204 pounds of thrust (about 6.23-6.81% thrust/hp) and around 170.6-199.7 horsepower (around 5.69-6.66% horsepower addition), though this presumes you're at 40,000 feet; go down to 20800 feet (the Hurricane IIC's critical altitude), you'd end up with about 77.9-85.1 lbf (around 2.6-2.84% thrust/hp), with 71.1 to 83.2 horsepower (2.37-2.77% horsepower addition) roughly produced.

With the R-4360's 3000 horsepower output producing roughly 10-12 percent thrust/horsepower you'd see 300-360 pounds of thrust which would correspond to around 262.5-337.5 (8.75-11.25% horsepower addition) horsepower at 342 mph provided it was geared for a critical altitude of 20800 feet.

Which means that for the same horsepower, the supercharger is more efficient because of the exhaust augmentation. At high altitude you would basically see a 20% boost in thrust/horsepower which means that using a well-designed twin-stage supercharger and exhaust system, using the R-4360's horsepower figures and the Merlin's high altitude performance figures

1. Horsepower levels are approximately
   • Military Rated: 3000 in low blower / 2540 high blower
2. Horsepower and thrust additions to come for it (altitude/supercharger-setting/horsepower/thrust/thrust-percentage)
   • 0'...........Low-Blower...3000...300.0...10.0%
   • 5000'.....Low-Blower...3000...360.5...12.0%
   • 10000'...Low-Blower...3000...436.5...14.6%
   • 15000'...Low-Blower...3000...531.8...17.7%
   • 25000'...High-Blower.-2540...683.6...26.9%
   • 29800'...High-Blower.-2540...848.4...33.4%

Based off of the NACA report I posted we can figure the thrust. As a minimum we will assume a mass flow of 21,600lb/hr. and a nozzle area of 4 sq/in. per cylinder. We get a thrust of 307lb at sea level and 494lb at 30,000ft. For a maximum we well assume 23,000lb/hr. and 2.7sq/in. This gives us 407lb and 565lb respectively.

 

[wuzak]

I thought they used some of the exhaust thrust to also help lower the pressure on the aft side of the radiator and produce downforce too?

Current cars have an exhaust location designed to limit the aerodynamic influence of the exhaust, though it is not completely eliminated.

The last generation engines had exhausts positioned to give more downforce. First by exhausting into the diffuser, and when that was banned they used the Coanda effect to direct exhaust flow over the top of the diffuser, to help extract more air from under the car and create more downforce.

Blowing the diffuser was not new in F1. Through the '80s and '90s cars blew the exhaust through the diffuser. In 1998 Ferrari started using "periscope" exhausts out the top of the bodywork, enabling more stable aerodynamics. After a few years all teams went that way, until Red Bull started blowing their diffuser in 2009 (IIRC), using the engine management system to keep airflow to the diffuser, even when the driver was not on throttle.

Ferrari 156-85 of Stefan Johansson at 1985 Monaco Grand Prix by racing is life, on Flickr

 

[Zipper730]

This might be of interest to some people.
Design of nozzles for the individual cylinder exhaust jet propulsion system

It's around 5:50 AM over here and I have bad insomnia: Some of the math described seems beyond my pay-grade at this time. That said, isn't k-constant the relationship of horsepower/mph^3? Unless you're measuring the exhaust speed and not the aircraft, I'm not sure how to even put that number into the equation.

Based off of the NACA report I posted we can figure the thrust. As a minimum we will assume a mass flow of 21,600lb/hr. and a nozzle area of 4 sq/in. per cylinder.

I'm not sure how one is able to determine the mass-flow and nozzle area?

We get a thrust of 307lb at sea level and 494lb at 30,000ft. For a maximum we well assume 23,000lb/hr. and 2.7sq/in. This gives us 407lb and 565lb respectively.

I was basing the numbers on atmospheric pressure changes and the ratio of speed to horsepower. From what I remember, 1 lbf = 1hp at 350-375 mph, and the increase/decrease from that is proportional to the increase in speed. So it was a lot of guesswork.

Regardless, that produces around 10.23-13.57% at sea-level, and 19.45-22.24% at 30,000 feet. That seems to be quite impressive regardless.

 

[Benjdragon]

I remember reading an article where during WW2, they installed flame dampeners on the exhaust of planes like the Mosquito to make them less visible at night. It resulted in the loss of 10-20 mph of speed because it disrupted the thrust from the exhaust.

 

[fliger747]

Also from parasitic drag. There is an interesting short USN study with regards to the drag from small items on the F4U, even something minor like the walkway on the wing for "boarding" was good for 6 mph.

 

[chuter]

There seemed to be considerable effort expended in the early days of the P-38 program to get directional turbo exhaust hoods to work without any success. Lockheed persisted for some time with this before giving up as it appeared Republic had the hood working on the P-47 (where if it didn't the turbine might've been exposed to potential FOD). What the residual exhaust thrust was for the P-47 installation and what was expected for the P-38 I really don't know.

 

[Shortround6]

Things changed during the war, Turbos got better. during the early part of the war keeping them cool might have take precedence over trying to get exhaust thrust.
Some P-38s were equipped with armor plate to shield the pilot from a an exploding turbo or thrown blades. Part 245437 for the left hand engine and part 235436 for the right hand engine, Diagram says B-2 turbo so perhaps later P-38s with later turbos did away with the armor?

 

[fliger747]

Turbochargers during the war had two main problem areas; the actual turbines dealing with temperatures and RPM's, and even more difficult, successful regulation. Turbo's have a problem with "boot strapping", increase the throttle a little, the engine puts out a little more power, adds some more power to the turbo which wants to increase the engine power more, and then there can be ram effect which also contributes to this.

Various schemes were implemented to control the Turbo via Waste Gate which would bypass the turbo. All well and good with the trusty flight engineer keeping track of this in a Bomber and maybe a bit more distraction in a fighter.

 

[Zipper730]

Turbochargers during the war had two main problem areas; the actual turbines dealing with temperatures and RPM's, and even more difficult, successful regulation. Turbo's have a problem with "boot strapping", increase the throttle a little, the engine puts out a little more power, adds some more power to the turbo which wants to increase the engine power more, and then there can be ram effect which also contributes to this.

I call that a positive-feedback loop...

 

[fliger747]

For the rather primitive (read simple) turbo's that I flew at one point one eventually got a feel for setting a throttle position taking into account the boot strapping, or you could set it then nudge it back as needed. Might have made formation flying interesting? The F4U-5 had automatic cowl flaps which apparently made formation flying more difficult.