Absolutely, positively, categorically NOT THE K-80.

I refer you to the table in the back of any recent RCJI mag. The K-80 tested did rather poorly in that department, nevermind that it weighs nearly a POUND more than some of it's competition. There are claims that the oiling system has been revised to lower the fuel consumtion since that time. Could be so. Perhaps Shok is flying a newer variant which is vastly improved over the engine that Kingtech supplied to RCJI for testing?? Although the K-80 is very inexpensive, and the $$ saved at purchased will buy lots of kero, I'd want to see some independent data before making that leap. I'm also very wary of "average use" numbers because there are simply too many variables.

Get a copy of RCJI mag and read the stats. You will find several engines which offer 10-25% better tested fuel efficiencies and weigh a LOT less. This means lower gross weights and/or longer flight times. I assume that any of us spending crazy $$ on toys are interested in fuel burns as related to weight/performance issues rather than economy?

Take a look at the Wren SS and Merlin 90 in particular. The Merlin 90 is higher than your thrust range inquiry at 21+ pounds but still weighs only 3 lbs vs the K-80 at 3.9. It sips fuel, burning 1/10 of 1 ounce (!) more fuel per minute than the K-80 tested, while producing 3.5 pounds more thrust.


ABSULUTE fuel burn per min is not the measure you want. What u want to know is the fuel burned per unit of thrust. RCJI's efficiency index gives you that number so that u can more readily convert an apples/oranges comparison into an apples/apples comparison. It allows you to estimate how much a more powerful engine would burn if throttled back to equal the thrust rating of a lesser one, for instance, as opposed to just looking at what they will all do flat-out.

These ratings allow me to compare, for instance, my guzzling P60 to the Merlin 90. At first glance, since the 60 burns 9.5 oz/min @ 13 lbs thrust, compared to the Merlin 90's 11.9 @ 21.5, it seems as though the 60 "burns less". Nope. The efficiency index numbers indicate that the 90 burns 25% less fuel at comperable thrust settings. The 90 burns 25% less fuel at the P60 13 lb thrust rating, or it makes 17 lbs of thrust on P60 gas. Take ur pick. I have a scratch-built/kit bash jet with a P-60 which averages 6 oz/min on a normal flight and 8 when the hammer is down. In theory, then, a 10 minute fuel load would weigh approximately a pound less if I switched to a Merlin. Hmmmmmmmm.

Here are some interesting efficiency ratings. The lower the #, the better:

Merlin 90 (.050)
JetCat P80 SE (.051)
Wren SS (.055)
K-80 (.059)
P-60 (.066) :-(

A close cousin of the Merlin is the Jet Central Rabbit. They share a lot of common parts and have similar performance, but I have not seen independent tests.