My next poser may stump most aircraft historians, perhaps. Three-part quiz.

!. What documented single registered production aircraft used a Kimball Beetle K engine for test and development purposes?

2. What kind of engine was the Beetle K?

3. What was an odd distinguishing feature of this engine and what was its cubic inch displacement and horsepower?

Bonus question-What was the price of this engine crated at the factory?

13 days later

Wilbur R Kimball and the Kimball Aircraft Corp., Naugatuck, CT don't appear to be particularly well known in England. Despite my best efforts I have been able to ascertain the following information only.

The Beetle K was a 7 cylinder, air cooled radial of 135 hp. It weighed 378 pounds, had a bore and stroke of 4.500 x 5.500 and a compression ratio of 5.0. It could idle at 235 rpm but I don't know if this was unusual.

All the information I can find on Kimball relates to earlier projects such as the helicopter with 20 rotors that had an area of 320 sq. ft. and his Tailess design.

They did produce another engine, the 25 hp., 2 cylinder single ignition motor called the Gnat. How successful this was I don't know.

I can find no reference to the Beetle K powered aeroplane and look forward to the answer when available. Nevertheless I learnt a lot about Kimball's projects around 1908 - 1910 and also found out about the Cairns Aircraft Co., also of Naugatuck. I wondered if the Beetle may have powered one of their aircraft.

This is what makes these posers fascinating. I learn something new every time.

Bob

Thanks for your considerable diligence, Bob. My source gives the Beetle K engine weight as 380 lbs. dry, less hub and starter-close enough.

There is an oddity about the radial engine that is required for correct answers to this tough quiz, and of course the one test aircraft is needed. I am glad you enjoy these "hunts" and please keep trying. I have also received a private email about the quiz, but no all right answers. A Beetle K engine apparently sold on Ebay, I am informed.

22 days later

Five hundred views and no fully right answers, so here are the answers.

1. A Kreider-Reisner K-34 three seat biplane application by the Kreider-Reisner Division of Fairchild considered a Kimball "Beetle K" engine for possible use in the KR-34 at Hagerstown, Maryland after 1929. The tests were not deemed successful and the "Beetle K" engine was not incorporated in production KR-34s. (The KR-34 had formerly been known as the Challenger C-4). The actual K-R test aircraft with the 135 Hp "Beetle K" engine was a sole KR-32 Serial #148 registered to Kimball Aircraft Corp. as -5015 for test and development.

2. The Kimball "Beetle K" was a seven cylinder air-cooled radial-type engine.

3. The odd feature of this radial engine was it's F-head makeup. The intake was a side-valve built into the cylinder head and the exhaust was a valve-in-head operated by a push-rod. The timing sequence of each valve was operated by a cam disc. Both the cylinder head and the cylinder were liberally finned for air cooling.

The "Beetle K" was a large engine displacing 535 cubic inches and at 580 pounds dry less hub and starter was heavy for its horsepower. It was rated 135 horsepower at 1,800 rpm. The engine crated at the Kimball Aircraft Corp. factory in Naugatuck, Connecticut was to sell for $2,900.

Of interest, the unorthodox Caminez four-cylinder radial engine was also tested, but did not power any production Kreider-Reisner Challenger-series biplane. Does anyone know of any other even-cylinder (per row) radial aircraft engines? And please don't suggest a two cylinder engine, as that would be an opposed, as distinct from a radial engine. Nobody said this was easy!

Thanks to all who participate in these quizzes.