[billy]

this is a very cool thread.
thanks

[Big Dog]

There is a company now building full-size replicas of the German ME-262 jet fighter. Very pricey. They are using the GE J85 engines, so the engine failure rate of the old WWII jets is corrected and they are safe to fly. Very impressive! Had the Germans built the ME-262 in greater numbers a couple years earlier, with reliable engines - our bomber fleets would have been decimated. And of course, Dolf screwed it up too insisting on using them as bombers themselves! Much of our success in WWII had to do with his stupidity and misuse of resources.
"Wonder weapons" aren't so wonderful when they are used wrongly.

[Clem321]

The original engines for the Me-262 had about 1500 lbs of thrust and were good for a grand total of 25 hrs. The J-85 has about 3000 lbs of thrust and lasts much longer. A 262 with twice the thrust could be really cool, but in the article I saw, the guys building them were only going to build about 5 or 6 total. I guess we missed out.

[TXplt]

J85's are still used on our T-38's and have proven a very good engine albeit a wee bit fragile and sensitive to Foreign Object Damage/Ice (they were originally designed for a type of cruise missile). They are of first/second generation axial flow jet development though and are in any case an older turbojet (and quite thirsty at low altitude)--but they are a reliable and good engine. If you could get over the fuel consumption I think they'd make a decent engine for use on a fighter remake. I think surplus/civilian versions were used on the mother ship for Rutan's Starship 1/Spaceship 1 but might be wrong. We had the good fortune to be parked next to it (and speak briefly with the pilot--a true gentleman) on an unexpected divert into Madison due to storms on the way to Oshkosh in 2005.

[ottawa rogue]

ok Txplt, you got me on the ramjet

Man, i would love to have a sturmvogel replica, i thought those were the coolest looking aircraft.
and as far as being ahead of their time, don't forget the Arado Blitz bomber the germans had

[Clem321]

Quote:       Originally Posted by TXplt

J85's are still used on our T-38's and have proven a very good engine albeit a wee bit fragile and sensitive to Foreign Object Damage/Ice (they were originally designed for a type of cruise missile). They are of first/second generation axial flow jet development though and are in any case an older turbojet (and quite thirsty at low altitude)--but they are a reliable and good engine. If you could get over the fuel consumption I think they'd make a decent engine for use on a fighter remake. I think surplus/civilian versions were used on the mother ship for Rutan's Starship 1/Spaceship 1 but might be wrong. We had the good fortune to be parked next to it (and speak briefly with the pilot--a true gentleman) on an unexpected divert into Madison due to storms on the way to Oshkosh in 2005.

The T-38 has afterburner. The T-2 also used the J-85 but didn't have burner. Imagine a 262 with the J-85 with burner? Really cool! 5000 lbs a side.

[Big Dog]

The J85 was used first in the little Ryan Firebee drone. We used them at Tyndall AFB for interceptor training.
They usually had surviving Firebees parachute into the Gulf, if they weren't shot down. Then they used some Sikorsky H3 helicopters modified with hooks to catch the Firebee and pull it into the back of the helo while in flight! Bet the recovery crew felt a bit nervous with a live jet coming up behind that open rear door!

I believe the J85 was somewhat smaller and lighter than the original Jumo engines the ME-262 used - so more power and lighter weight - bet that is one FUN aircraft to fly!

At Tyndall, I worked on the old Lockheed T-33A trainer with it's old Whittle-derived J33 centrifigal flow engine - we could stand in the intake at full throttle - no problem! Try that with any later jet fighter!

[PAPA G]

Quote:       Originally Posted by ottawa rogue

i could be totally off the mark here, but that don't strike me as a true jet engine seeing how the compressor is driven by a piston engine instead of the exhaust turbine. anyone have any thoughts on this???

he needed an auxillary source to run the compressor, since his was not like a turbofan engine as self susaining compression.

by the way what gives a turbofan the initial spin on start up???

[Clem321]

Quote:       Originally Posted by PAPA G

he needed an auxillary source to run the compressor, since his was not like a turbofan engine as self susaining compression. by the way what gives a turbofan the initial spin on start up???

Jets use air impingement starting, from either an auxiliary kart or an on-board jet start unit. As the jet start units keep getting smaller, even fighters are getting them.

[Big Dog]

Many jet fighters and trainers use electric start, via an external 'start cart'. Basically, we would plug the wheeled cart's generator into the aircraft, the pilot would start the engine, we (the crewchief) would then disconnect the cart once the engine was wound up and running.
Some older jets like the Martin B57 Canberra used a powder-fired cartridge, similar to the system used in old radial engines. That was always fun to watch! Sometimes took a few 'Bangs' to get it going.
The current use of APU's means less equipment needed on the runway or parking areas. Easier to have the tactical aircraft in remote locations too.

[TXplt]

Quote:       Originally Posted by PAPA G

he needed an auxillary source to run the compressor, since his was not like a turbofan engine as self susaining compression. by the way what gives a turbofan the initial spin on start up???

It depends on the particular engine. For the J-85 (or the J79 which were used on the F-4, or the TF-30's used on the F-111), it is an air start cart which provides moderate pressure high volume air to get the engine spinning to about 20 % of its rated RPM at which time fuel and ignition are turned on. Connected to the engine (in the case of the TF-30 at least--never flown anything with a J 79) is a small air turbine which is geared to the main engine (clutched usually to drop out around 50% rpm) and this is what the air from the cart spins and gets the main engine spinning.

Smaller engines (and most turboprops) use a geared motor/generator which is connected to the accessory drive case and starts the engine spinning (as a motor) via the constantly connected reduction gearing (reducing the engine RPM from very high to something managable) -- when the engine reaches somewhere between 12 and 25 % (depending on the type of engine) once again fuel and ignition are introduced into the hot/burner section. Once the fire is lit it is self-sustaining--not unlike a blow torch--and starting fuel and ignition are turned off. Ignition and the motor are typically turned off around 50 % RPM (it seems everything I've flown has some form of "50 % switch" including the 747) and the motor then usually becomes a generator.

The F-15 and F-16 use a device called a "Jet Fuel Starter" which is a miniature engine started (in the F-15 at least) by compressed air and powered by ships' fuel in the case of the F-15 and hydrazine in the case of the F-16. This JFS provides some electrical power through a small generator and when the start lever is raised connects mechanically through a clutch to the engine being started and starts it spinning (fuel/ignition introduced again around 25 % and the JFS drops out around 50 % after the engine is lit and spinning up).

Most everything else uses bleed air and a dedicated air turbine starter (connected to the engine through a clutch and gearing) to get the engine spinning. On a commercial airliner electrical power and air are provided on the ground by an Auxiliary Power Unit -- APU -- usually located in the tail. This is a miniature jet engine (started electrically as previously stated) which runs a fairly large electrical generator as well as provides quite a bit of air (this is usually what powers the air conditioning packs on the ground and why they cut out when the engines are started--the air is going to the engines). All the air from the APU as well as air "tapped" from the compressor sections of the engines when they're running goes to a main manifold and is used for all kinds of things including heating/ air conditioning/pressurization, engine start, water tank pressurization, reverser movement power, wing and nacelle anti-ice and in some cases leading edge flap power, etc. Usually the APU is only used on the ground (then engines provide plenty of air from the compressor sections once started) but can be used airborne on some types of aircraft. Additionally, sometimes the packs are turned off (you can usually hear this as a bump in the air conditioning) prior to takeoff to improve takeoff performance on hot/high/heavy conditions. Anyway, when a start switch on an engine is pulled air flows backward from the main manifold to the engine starter (a little air turbine geared thru a clutch to the engine) and starts it spinning -- at a certain RPM which varies with the engine type starting fuel and ignition are added and the starter cuts out around (again) 50 %.

If the APU isn't working for some reason the main air manifold can be connected to an external air cart (and external power) and an engine started at the gate. Once an engine is started there is usually plenty of air and the aircraft can be disconnected from external air and power and pushed back.

During start, the temperature of the engine is carefully monitored because if something goes screwy it can do great damage to the hot section of the engine. Some engines do this automatically and have an "autostart" feature which introduces the fuel and watches the engines automatically (but this is always backed up by the pilot).

Airborne it depends -- if the engine is spinning fast enough just fuel and ignition can be provided--not unlike getting a car with a dead battery rolling and then popping out the clutch to start the engine. If it's not going fast enough (depending on the aircraft type) speed can be increased or a "crossbleed" start can be done where air from the operating engine (s) are used to power the air turbine starter. Most aircraft have an altitude/airspeed envelope where the engine can or cannot be started so it might have to drift down from cruise to get a relight in some cases--usually this is somewhere in the mid to high 20's but varies by engines.

On some "cold war" aircraft (B-52, F-111, F-4) the air turbine could be powered by a "Cartridge" -- a coffee can size thing of solid rocket fuel ignited by an electrical charge from the battery. We would sometimes use these when air carts weren't available. It usually kicked up some spectacular smoke and worked quite well (the cart was only on the left engine but would fire if EITHER throttle were advanced above cut-off and battery power was on which could lead to some buffoonery). Once the left engine was started the right was started with crossbleed.

With all due deference to my British cohorts (and the RB-211 has been a fine engine) it is really amazing how airplanes have well developed over the past century and most of it has been due to good old Yankee ingenuity and a bold "CAN DO" attitude. It really shows what kind of progress we can make if we put our mind to it and I think most Pilots' Pilots would recognize America as the leading aircraft designer and producer from the infancy of Aviation through the golden era of Aircraft design and well into the 21st Century. It's really something we have done well and today's airliners and military aircraft are better than ever. I really mean it when I say we could take stock of this as proof we CAN do things well when our thoughts and minds are pointed in the right direction and away from the wacky malaise and self-persecuting attitude which seems to waft from the present regime and the malcreants we have inside the beltway. Like a Cancer, they seem on a mission to destroy America's greatness--our aircraft history shows proof positive we as America are better than this and it doesn't have to be that way.

This was probably more than you wanted to know

[PAPA G]

Quote:       Originally Posted by TXplt

I really mean it when I say we could take stock of this as proof we CAN do things well when our thoughts and minds are pointed in the right direction and away from the wacky malaise and self-persecuting attitude which seems to waft from the present regime and the malcreants we have inside the beltway. Like a Cancer, they seem on a mission to destroy America's greatness--our aircraft history shows proof positive we as America are better than this and it doesn't have to be that way. This was probably more than you wanted to know

excellent point, no telling where we could be if the gummint, and the naysayers would get themselves out of the business of progress, and thanks for the little tutorial on jet engine starting

[ottawa rogue]

Yes, great tutorial, and +1,000,000 on the other comment!

[Clem321]

I flew F-4s in the Marine Corps. We always had to use an external start cart to start the J-79s. Air Force F-4s had cartridge start capability, but they didn't use it if they could avoid it. The cartridges put out colorful products of combustion which would cause corrosion if left untreated.

[Cyrano]

Quote:       Originally Posted by ottawa rogue

ok Txplt, you got me on the ramjet

Are we talking about the same thing here? My understanding is that a ramjet will work only above Mach 1 and has no moving parts. Fuel is just injected into the combustion chamber and the sheer pressure of the air compresses the air-fuel mix to ignition point. (Oh, all right, I think there's a glow plug in there somewhere, but that's not a moving part, if you see what I mean.)

The other World War II-era jet engine was the pulse-jet used on the V-1 Doodlebug. It also had no moving parts, just an air intake with hinged shutters on the inside, a combustion chamber and a pipe to direct the exhaust gases out the back. It was set off by a spark plug. It's kind of hard to describe the combustion cycle; it's not like a diesel or a gasoline engine.

At the start of the cycle, the airflow would have the shutters open and pointing inward. Fuel is injected into the combustion chamber through an atomizer to create the air-fuel mixture. When the spark sets off the fuel-air mix, the resulting explosion pushes the shutters at the forward end of the combustion chamber closed. This forces the explosive gases out the rear of the chamber via the exhaust pipe. As the gases exhaust out the back, the pressure holding the shutters closed drops and the airflow pushes them open again. More fuel is injected and the cycle repeats. The constant starting and stopping of combustion is what gave the Doodlebug it characteristic growling stutter sound.

The great advantage to the pulse-jet is its simplicity. As I said, there are no moving parts in the engine itself. It's simple and cheap to make; there are actually people who have adapted go-karts to run with pulse-jet engines. Apart from the manned prototype versions of the V-1 made to find the solution to the V-1's control issues, I don't believe the pulse-jet was used in piloted production aircraft.

[Clem321]

Ram jets use the slowing down of the air to compress it. It requires about Mach 2.5 for it to work. One place where you see it now is in Surface to Air missiles like the Russian SAM-6.

[nathangdad]

You are so on target concerning Germany's collosal failures to promote
emerging science/technology after Hitler came to power in 1933.

Although I am glad it did not happen I do wonder what would have happened on opening day of the war with England had Germany hit London with several thousand of the V type rockets.

Of course, an early Manhatten type project for jet fighter aircraft would have made Germany generations ahead of Russian/Allied fighter aircraft
by 1939.

So, I sometimes take in conversations about WW2 that it was truly a
wonderful thing for world history that it was Hitler who came to power as opposed to someone with his thought processes plus a keen scientific mind.

Naturally, it would have been much more wonderful for world history if
Germany would have charted a peace loving, democratic path after WW1
mated to a vibrant, growing, strong economy.

[PAPA G]

Quote:       Originally Posted by nathangdad

Naturally, it would have been much more wonderful for world history if Germany would have charted a peace loving, democratic path after WW1 mated to a vibrant, growing, strong economy.

post WWI Germany was forced into what happened. Germany had no help in its recovery, many bans on manufacturing, and import/export restrictions. the D/M collapsed...not even worth the paper it was printed on. massive unemployment, massive unrest. meanwhile the Allies tightened the screws to defeated Germany. it was general desperation that German people supported Hitlers initiatives.

this was not repeated following WWII, the Marshall plan made sure that Germany would not follow extremist by supplying funding and initiatives to become self governing and productive in a positive way.

[Big Dog]

Quote:       Originally Posted by Cyrano

...I don't believe the pulse-jet was used in piloted production aircraft.

The Japanese had the manned Bakabomb, but I disremember whether it was rocket powered or pulsejet?

[PAPA G]

Quote:       Originally Posted by Big Dog

The Japanese had the manned Bakabomb, but I disremember whether it was rocket powered or pulsejet?

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