Pulse Jet engine for CAS aircraft?

[davebender]

Rhone 14M 14 cylinder radial engine.
410 kg Dry Weight.
700 hp.
?? Cost.

Argus As 109-14 Pulsejet.
153 kg. Weight.
800 lbs. Max Thrust.
?? Cost. Dirt cheap.
An entire V1 cruise missle cost only 5,090 marks.
For comparison purposes. 12,400 marks for a BMW132 radial engine.

Did anyone consider powering Hs-129 CAS aircraft with pulsejet engines? The Argus As 109-14 engine was so cheap that you could throw them away after a single mission. No need for engine maintenance. No need for aviation gasoline either. Pulsejet engines will run on low octane gasoline or even kerosene. Power to weight ratio is outstanding. Fuel economy isn't good but most CAS missions take place at short range.

 

[Shortround6]

You just needed solid rocket boosters to get thing up to minimum operating speed. While the engine may run while stationary it may not produce enough thrust to get airborne. Vibrations was also a huge problem, See Me 328.
Trucking in replacement engines to the Russian front may cost more than the engine it self.

 

[tyrodtom]

Could the pulse jet be thottled ? Would the engine even stay together 1 hour ? It's range was just over 200 miles, and it's speed was about 390 mph, meaning it only ran a little over 30 minutes. It wasn't a terrible relieable engine, it didn't have to be . It had a about 1 in 5 launch failure rate, but that due to all causes, all failures couldn't be tied to engine faults.

To be used in a manned aircraft, it would have to be re-engineered with better materials, and workmanship, that would radically change the cheapness equation.

 

[davebender]

Perhaps so but not radically better if required service life is only 3 hours.

 

[Shortround6]

Even at 3 hours you could use up a set of engines in a day, You probably need 4 engines minimum per aircraft for flight if not 6. A 16 plane squadron could suck up 64 engines a day even at 3 hrs each and 4 engines per plane. cheap is one thing, getting several hundred engines per week to a single squadron requires too much logistic effort.

There were cases (not often) of close support aircraft not even turning engines off or refueling between sorties, just rearming, taking off and striking again.

 

[tyrodtom]

Germany didn't even seem to have enough high tempreture alloys to supply their needs when it came to conventional jets, let alone pulse jets. One of the things that made pulse jets so cheap was they used no exotic metals, but that's also why they were destroying themselves from the second they started.

Plus pulse jets need speed to open the front flaps. This inablility to be throttled means every landing would be without power.

The Luftwaffe was desperate, after all they tried the Me 163, which might have killed more German personnel than Allied.

 

[tyrodtom]

It appears i'm wrong about the pulse jets ability to run at low airspeeds, it can run at zero airspeed with very low static thrust.

But I also found out it has a very high fuel consumption. The V-1 had a 150 gal fuel tank, and with that it flew, about 1/2 hour.

I wonder where you could put the 600 gals of fuel required for 2 Argus pulse jets, for just 1 hour of flight, on a HS-129

 

[davebender]

I would not expect a pulsejet powered CAS aircraft to equal the capability of a piston engine powered aircraft. This would be strictly a war emergency project. Just as the inexpensive Marder series AT guns were an emergency substitute for more capable tanks and StuGs.

 

[Shortround6]

The Marder's actually had some capability, they also were NOT substitute tanks and Stugs. They were self propelled AT guns which is a weapon of a different tactical class. They were also a way to use exiting tooling.

The Pulse jets didn't have enough life to make them worthwhile for a plane that would be used for more than a few flights. they had horrible fuel efficiency which cuts into payload. They vibrated horribly causing airframe problems and they had other problems. It is one thing to make a weapon system that that is less than perfect or even less than what is desired. It is quite another thing to make a weapons system who's only advantage is that it is cheap. Engines that cause horrible vibration, suck fuel (even cheap fuel) 3 to 4 times worse than a regular piston engine (reducing bomb/gun load even for short flights) and need to replace every couple of flights for a plane that might fly 2-6 times a day is not just less capable, it is a massive drain on resources that no air force could afford. As a power plant for a 1/2-1hour one way flight with a crash at the end they were acceptable.

 

[bobbysocks]

i think if it was a viable option for aircraft..then germany would have exploited it to the max. like tyrodtom said, i dont think it could be throttle controlled. so it would be running balls out...unless you can turn it on and off like some of the ww1 fighters had to do with their engines. did find a nice website years ago when i was looking at these...

Home made jet pulsejet engine

 

[davebender]

if it was a viable option for aircraft..then germany would have exploited it to the max

Not necessarily.

The outstanding R4M FF rocket was a viable option for German combat aircraft from the late 1930s onward. Panzerfaust light anti-tank weapons were also viable using late 1930s German technology. Probably the StG45 assault rifle too. But you still need a bright engineer to put the design together and a manager willing to fund the project.

 

[Rivet]

Someone above mentioned the Me-328, the nazi concept for a cheap interceptor. This turkey highlights some of the debits of the use of pulsed combustion as an airframe powerplant.

For a greater than puerile understanding of this powerplant read NACA TM-1131. This document is internet accessable.

 

[phatzo]

But I also found out it has a very high fuel consumption. The V-1 had a 150 gal fuel tank, and with that it flew, about 1/2 hour.

I wonder where you could put the 600 gals of fuel required for 2 Argus pulse jets, for just 1 hour of flight, on a HS-129

I have a small 30lb pulse jet, it sucks fuel like crazy.

 

[davebender]

What do you use for fuel? Any reliability issues?

 

[Rivet]

Germany developed a coal-tar based fuel specifically for the Argus pulsejet engine.

The flame front of the operating wave seperates from the wall during yaw (turns). Occasionally a CAS vehicle might want to make a tight turn. Vibration and confusion of the waves to the point of stall possible.

The altitude at which the pulsejet engine will operate is a limiting factor. These engines breath from both the front and the rear. At some critical reduction in atmospheric pressure they cease to function, the intake from the rear provides the compression necessary to maintain an operating cycle.

The petal or reed valves used to seal the front of the engine fail from fatigue. The Argus engine was built to last 1/2 hour.

Regards

 

[Shortround6]

What powers the auxiliary services?
Like the fuel pump and ignition for starters, battery?
What would you power the landing gear and flaps?
How do you get a power take-off on a pulse jet?
If there is no generator or hydraulic pump you are going to need a lot of electric motors and a BIG battery

 

[davebender]

altitude at which the pulsejet engine will operate is a limiting factor.

WWII era CAS aircraft typically operate below 1,000 meters.