Tuesday, January 5, 2016

An early jet I didn't know existed

I knew about early experimental jet aircraft such as the British Gloster E.28/39 and the German Heinkel He 178, but I didn't know that Italy also developed a "sort-of-jet" aircraft - the Caproni Campini N.1.  Wikipedia describes its propulsion as follows.

As designed by Campini, the aircraft did not have a jet engine in the sense that we know them today. Rather, a conventional 900 hp (670 kW) Isotta Fraschini L.121 RC.40 12-cylinder liquid-cooled piston engine was used to drive a three-stage variable-incidence compressor, which forced air into a combustion chamber where it was mixed with fuel and ignited. The exhaust produced by this combustion was to drive the aircraft forward. Campini called this configuration a "thermojet," but the term "motorjet" is in common usage today. It has also been described as a ducted fan.

Here's film of the Campini N.1's development and trials.

There's only one prototype still in existence, in an Italian museum.  I'd love to see it sometime.



Rusty Gunner said...

When I was flying sailplanes in the 1970s, Caproni made a glider with a little turbojet for auxiliary power, the model was the A21J. I think there are some videos of it on YouTube.

David Lang said...

This isn't a Ducted Fan because they added fuel to the airflow and burned it for increased thrust.

This is a jet, but using a piston engine instead of a turbine in the exhaust to power the compressor stage.

Thinking about it, this isn't even an unreasonable thing for those days. The early jets had a really hard time starting, and throttle response was very poor (adding fuel didn't cause the engine to spin faster immediately, think really horrible turbo lag). Using a traditional engine to run the compressor stage gave them the ability to start like a traditional aircraft, and should have given them throttle response similar to traditional aircraft.

They don't say what the final output of the engine was, that would be interesting to learn.

Anonymous said...

The video seems to show that the aircraft's tail was removed for engine starting, then installed for flight. ("Hey Vito, make sure you get all those bolts!")

Don in Oregon

Will said...

I'm not sure that that was implied by the film. Doesn't make sense, anyway. The only thing that is needed to start on the ground was the piston engine. I'm wondering if those flames were actually the exhaust stacks from the IC engine, and that it is dumped into the compressor/tailpipe. Unless running a turbo, the exhaust is wasted energy, and as rich as the mixture tended to be on that vintage of aircraft, adding it to the compressor stream would be useful.

It wasn't clear in wiki if the performance numbers were just with the IC engine alone, or with the compressor lit off. I suspect it was just engine only, as the numbers are similar to the distance mail run that was flown as just a ducted fan.

I'm guessing that dealing with the heat developed in the compressor/tailpipe assembly was what kept them from continuing with the design. If the Germans couldn't get the exotic metals needed, I'm sure the Italians were in the same boat.