A Jet Jeep?

[1fastneonrt]

Hey guys you have to check this one out. It's a pj powered helicoptor on display at the Wright-Patterson AFB. I must say it's a very intresting little contraption. The link should be posted below.

http://www.nationalmuseum.af.mil/factsh ... p?fsID=583

[Mark]

"However, the pulsejets produced so much noise that the Army found the aircraft unsuitable." Who would have guessed? ha

[Jim Berquist]

Man! Engine weight, 35lbs! What kind of stress did that put on parts? I bet the engine weight could be brought down to 1/3 that now.

I assume they was Pressure Jets?

[Mike Everman]

Naw, those are valvers.

[GRIM]

Very brave men , to take that to 7000 feet knowing that the valves are going to fail , just the same awesome machine , and nice touch for that museum website that you can download full size images

[Bruno Ogorelec]

Very brave men , to take that to 7000 feet knowing that the valves are going to fail , just the same awesome machine , and nice touch for that museum website that you can download full size images

Given that this was just one of three different helicopters powered by pulsejet tipjets that the company made, and that all three underwent serious testing, one would think that their valves did not burn out.

The engines look like Solars to me, but apparently the company made its own engines, rather than buying them from someone else. I wonder what they did to protect the valves.

I'd also love to see the details of their starting arrangements. Starting air was pumped through the rotor to the engines!

[Viv]

Man! Engine weight, 35lbs! What kind of stress did that put on parts? I bet the engine weight could be brought down to 1/3 that now.

I assume they was Pressure Jets?

Mike's right they are valved but to add to it they are 35 lbs thrust not weight from reading the text, I did not see mentioned how heavy they were though.

Viv

[GRIM]

quote from website text

the Jet Jeep was powered by two 6.75-inch pulsejets on the end of each rotor blade tip. Designed by American Helicopter, each of these pulsejets weighed 16 pounds and produced 35 pounds of thrust.

Yes it would indeed be very interesting to know how they managed to protect the valves or indeed what type of valve to achieve a reliable operating life

quote

TECHNICAL NOTES:
Engines: Two American Helicopter AJ-7.5-1 pulsejets
Fuel capacity: 50 gallons
Range: 135 miles
Endurance: Approx. 2 hours

[dynajetjerry]

Hi, Guys,
I just spotted this thread and decided to insert my 1 cent worth (my opinions are not worth 2 cents.)
At the time this helicopter was developed, American Helicopter Co. (AHC,) had not yet been acquired by Fairchild. Aeromarine Co. (Dyna-Jet,) got a contract with AHC to come up with a p-j that was suitable for their "jeep." We developed a twin-barrel design and tested it on the AHC-supplied whirl test stand in early 1952 (see attachments.) I don't remember all the particulars other than we never determined useful valve lives. However, the best sustained speed we attained was about 300 feet/sec., about 210 mph, much less than would be suitable for this application.

The p-js on the AF Museum's chopper were (apparently,) somewhat more efficient than ouur version, at 2.1 lbs. gas/hr. for each lb. of static thrust. For comparison, the D-J burns 2.5 lbs. and Aeromarine's 8 in. p-j was among the best (in 1952,) at 1.95 lbs. At operating speed, most valved p-js suffer from reduced efficiencies because thrust falls off but fuel consumption does not. Out big p-j was static tested for more than 12 hours of sustained operation, statically without valve failure. However, this duration was better than most similar p-js.

In my opinion, the relatively long AHC p-js would probaby distort during use because of the extreme g-stresses and 1500 F. temperatures.

To those able to visit the USN Air Museum in Pensacola, they might be permitted to examine Aeromarine's 8 in. and an early version of our helicopter p-js. I drove down there with them in 1996 and donated them, courtesy Patty Tenney. She is the widow of Bill Tenney, owner and CEO of Aeromarine.

Jerry

[Bruno Ogorelec]

Wow! Thanks for this, Jerry. Great-looking engines. I must admit I have never even heard of them. Good stuff!

[Jim Berquist]

Wow! clean looking little thing.

I would love to see the reed blocks on those. They seem to be short in length. Cool.

Questions:

Would efficiency been gained using a single engine in place of the twin set up?

Twin provides some redundancy in chase of reed failures?

[dynajetjerry]

Jim,
Aeromarine's helicopter p-j employed a "Siamese" combustion chamber and one set of reed valves but two separate tailpipes. Therefore, it behaved as one in that damage to any reed(s) affected operation of the whole assembly. What was unique about their 8 in. and the above p-js was the use of flat reeds and curved air passages. Most other p-j systems (except for copies of the Dyna-Jet,) use curved reeds and seats to permit straight through air passages. In either case, there are benefits from the addition of "turbulators" downstream of the reeds. This and other measures lessen the usual fall-off in thrust as such engines move at higher air speeds.
Jerry

[dynajetjerry]

Sorry, Guys,
Something funny is going on with the computer I'm using. It keeps telling me I'm using the wrong Username or password and the message won't be sent so I try again. My inputs ARE are correct and, by going back to the forum, I see that each message DID get sent. Go figure!
Jerry

[Jim Berquist]

Thank You Sir! Educated I are now!