First JATO Flight in the USA Anniversary

[MIflyer]

12 Aug 1941 was the date of the first JATO flight in the USA. A group in the 1930's, at Cal Tech, GALCIT had been interested in rocket propulsion and as a result received a contract from the National Academy Of Sciences for Jet Assisted Take Off research. Meanwhile, Capt Homer Boushey, Jr, had been promoting the idea of rockets for the US Army Air Corps at Wright Field and was assigned to be test piolot fro the program.

Unlike rockets used as armament, JATO rockets had to deliver smooth thrust for an extended period of time rather than a very few seconds. They eventually succeeded in producing a rocket motor that weighed 10 pounds and would produce 28 pounds of thrust for 12 seconds.. It was relatively reliable but did have a tendency to explode if it was fired too long after it was cast. The answer was to cast the motors early in the morning and then rush them to the test site for use that same day.

An Ercoupe 415C was selected as the test airplane, since its broad aluminum center section would not tend to catch fire, unlike most fabric covered light aircraft of the time. Initial tests were conducted with the aircraft in level flight and they did experience one exploding motor. March Field was the test site. Test flights were began on 6 Aug 1941, intially using three rocket motors under each wing.

On 12 Aug 1941 all was ready and the first JATO take off was accomplishd. A Porterfield Collegiate did a drag race with the rocket boosted Ercoupe. The Ercoupe's takeoff roll was cut from 580 ft to 300 ft and takeoff time was reduced from 13.1 sec to 7.5 sec.

On 23 Aug 1941 twelve rocket motors were installed and the Ercoupe's propeller was removed. Capt Boushey hung onto a tow rope hooked to a truck until the airplane reached 25 mph, then ignited the rockets and took off under rocket power only before gliding back down to the runway.

As a result the Jet Proplusion Laboratory was formed and the USA became the world leader in solid rocket technology.

 

[EwenS]

With the emphasis on "in the USA".

In Britain, interest in what was known as Rocket Assisted Take-Off Gear (RATOG) started in 1939 with proposals and calculations for the non-projectile rocket use formulated by the end of that year. I have a book with an MoD copyright photo dated April 1941 of a Blackburn Shark with RATOG being boosted into the air at Farnborough.

In Britain the focus was on shortening the take off run of bombers from what at the time were still largely grass airfields. As part of RATOG development at the RAE there were successful experiments with Whitley bombers in 1941. And they then moved on up to the Stirling. 2 jettisonable rocket packs each with 12x3" rockets secured under the wings between the engines. On 18 August 1941, in front of many important visitors & brass hats, it taxied out for its first trial. Due to a cock up in the preparation, all 12 rockets fired all at once instead of serially in groups of one or two pairs at a time. The rockets and their carriers detached the aircraft, carrying parts of all 4 props with them, and cartwheeling back over the wing! In the ensuing emergency shutdown and evacuation the aircraft was wrecked! That seems to have been an end of plans to the regular use of RATOG on heavy bombers. There is a story of a B-17 being recovered from a muddy field with RATOG assistance later in the war.

Interest from the RN continued and by 1944 it was in regular use on escort carriers.

 

[ThomasP]

Cool stuff, guys.

 

[MIflyer]

By the way, the question of why the motors blew up after being allowed to sit for more one day was answered. The "plasticizer", the material that kept the solid fuel grain soft and pliable, tended to vaporize and float off as it sat, just like as occurs with paint. As a result the dried-out propellant tended to fracture and break up when ignited, and the greatly increased burning area resulted in overpressurization of the case. This problem was not completely solved for about another 40 years, and even today older solid rocket motors are viewed with more than a little suspicion. Asphalt was an ingredient that helped with the problem and was added soon after WW2. The addition of aluminum powder was another big development and improved propellant mixtures became a major focus of solid rocket motor development.

And "the wing of a convenient aircraft" described in the second photo is rather obviously the Ercoupe used in the test. The airplane was later sent to a USAAF technical school where it was used to teach student mechanics about aligning the aircraft compass.

 

[tyrodtom]

When I was in the USAF in the mid 60's and worked in munitions they had found a partial solution the propellant drying up and becoming brittle.
There was a weather seal on the nozzle, it was airtight and kept the propellant from drying up.
Used on every solid fueled rocket in the USAF inventory, 2.75 rockets, Genies, Jato units, even the first stage booster of the Minute Man ICBM.

At Hill AFB Utah I was on a crew that replaced faulty seals on mostly Minute Man boosters.
It involved cutting the old seal off , putting the booster in a enormous oven, big enough to drive a deuce and a half in, and baking out the moisture, letting the oven cool down to 140 degrees, then installing a new seal.
Not fun work, you had to work fast to install the new seal, and the booster was still hot.

They would at random take boosters out of storage and test them on fixtures that would test the thrust.
We would transport the booster to the area, then dispose of the used hulk.
So we were a few miles away on a ridge when the test was performed.
I wasn't on the crew the day they had a failure of either the hold done fixture, or the booster body.
The booster got loose and bounded across the desert until it went into the ground at a steep angle, stopped and exploded.

 

[gruad]

Weren't the Germans pretty advanced on RATO?

Seem to remember pics of He177 and Me321 Gigant using them???

 

[MIflyer]

A standard practice for testing older space launch rocket motors is to cold soak them in a refrigerator, followed by an X-ray. The cold would cause the propellant to attempt to draw away from the case and the idea was that if cracks were prone to form that treatment would induce them to occur.

"Nozzle Down Time" was an issue for many years because standing a rocket motor upright, with its nozzle down, would make the propellant tend to slump down into the center cavity. So motors were stored nozzle up and when they were mounted nozzle down that was a concern if they were older than 4 years or so. Eventually they developed ballistic missile motors that were capable of standing upright, nozzle down, for a decade or more.

One horrific mishap occurred with the first stage of a Peacekeeper ballistic missile in the Thiokol facility in Utah in the late 1980's . The large motor, 10 ft in diameter, was cast, nozzle opening pointed up. After the propellant had cured the next step was to withdraw the mandrel, the big plug that formed the center cavity of the motor. This was occurring with outside temperatures at well before freezing. As they withdrew the mandrel they realized they would have to lower it back down and start over. Know how when it is cold and with low humidity that you can make static electricity by rubbing a fabric like wool on plastic surfaces such as nylon? When they started withdrawing the mandrel the static electricty ignited the motor. The building was destroyed and everyone in it was killed.

Yes, the Germans used some JATO. An example is shown in the box top picture of the Ar234, which featured parachutes to enable recovery. They had one of those rocket packs on display at the University of Oklahoma. But the German JATO were liquid fueled and everyone else's rockets were no more than gunpowder packed into a tube. The GALCIT rockets represented a major leap forward in solid propellant technology.

 

[Shortround6]

Some of the German rockets appear to have been "cold".
The hydrogen peroxide was flowed through (badly stating this) a vessel containing calcium permanganate with the resulting chemical reaction producing superheated steam and free oxygen. It was only "cold" in regards to introducing a fuel to burn in the free oxygen.
The "cold" engines generated much less thrust than the engines that used fuel but perhaps as around 500kg of thrust?

 

[MIflyer]

Some of the German rockets appear to have been "cold".

Yes, the Me-163 used a "Cold" reaction and the V-2 used hydrogen peroxide to drive the turbopump, an approach used by the earliest US developmental rocket and space boosters such as the Jupiter C, Viking, and Redstone and is still used by the 11A511U Soyuz booster that is a straight line development of the Soviet SS-6 ICBM. For the Germans their desperate lack of nickle alloys made such lower temperature reactions preferable where possible.

 

[hawkeye2an]

View: https://www.youtube.com/watch?v=Nf7Lv4UwRP8

 

[marathag]

At the start of the War, the USN had Dr. Goddard working on liquid fuel JATOs, using Red fuming Nitric Acid and Aniline after his original fuels of gasoline and liquid oxygen were too troublesome for adding a take-off assist unit for PBYs.

These were 3000 pound thrust v 1000 pound solid fuel JATOs, more thrust over a longer duration. Despite the advantage of far less corrosive smoke that the asphalt/perchlorate solids produced, the solid fuel was so much easier to store, these became dominant in 1944