F1J/F1P engines

by Martin Gregorie

This is a personal view of the F1J and F1P engines that I have used or been told about. They are grouped roughly by power under the headings of Low-power, Mid-range and Hot. Production of engines under these headings overlapped: the appearance of the Hot engines did not cause production of the lower powered types to be abandoned. The engines under each heading are arranged in the approximate order in which they were produced rather than alphabetically.

Unless otherwise stated, all rpm measurements were made by me using fuel containing 50% methanol, 25% synthetic oil and 25% nitromethane. I used a Galbreath Ultratach audio tachometer to measure rpm.

A final section containing Mystery engines deserves a little explanation. These are all little known engines and in most cases the source of them is unknown. The entry for each of them contains what little we know. They have been included in the hope that anybody who is familiar with any of them will pass on what they know to benefit the Free Flight community at large.

This note originally appeared on the FFML in January 1999 but has been extensively revised since then. All pictures were taken by myself unless otherwise credited. Corrections and additional information are welcomed: I hope this page will remain a work in progress.

Low powered engines

Engines in this group will work with relatively small light weight models. Ideally these will be built down to the F1J minimum weight of 160g (5.65oz) and will have a relatively small wing area of around 16 dm2 (250 sq.in). Many classic 1/2A designs, if built down to weight, would be competitive during the rounds though they may struggle during fly-offs.

These engines are likely to be under powered for F1P with its higher minimum weight and relatively large minimum projected flying surface area.

Mid-range engines

Engines in this group should be suitable for entry-level F1P models.

The larger 1/2 A designs (1/2A Train, Maverick) are probably OK for F1J but will generally be under area for F1P. They will be lively with these engines and may be difficult to trim without VIT and auto-rudder. These engines should also suit the classic 1.5cc (.09) designs as well as light weight F1J designs such as Bruce Augustus' Northern Light and Gil Morris' POP-UP.

Hot engines

Engines in this group have outputs similar to the F1C engines available in the late 1960s prior to the introduction of the Super Tigre G.15. This makes them unsuitable for small or light models because they will tend to over power anything smaller than 22 dm2 (350 sq.in) projected wing area. They should suit models up to the size of the late 60s F1Cs built to a flying weight of 285-300g (10 - 11 oz). Experience with 1/2A models of various layouts suggests that the classic 1/2A or 1960s F1C layout with a moment arm of less than 4 wing chords and a 35% tailplane will transition perfectly well with VIT and auto rudder and is unlikely to benefit from bunting. Conversely, models built like modern F1Cs with a moment arm of more than 5 wing chords and a 20% tailplane or less will require bunt to transition at all.

There should be an advantage in making F1P models powered by these engines larger and proportionately heavier than the class minimums.

Apart from obvious power trimming difficulties the main disadvantage of a model that is too small is that it is throwing away overall performance. A very small model will benefit from using a larger wing because the improved glide duration will outweigh the resulting reduction in climb height. Even with the two minute max a 10 second engine run is only 8% of the flight time, which suggests that optimising glide performance may be a good idea. Of course, if you live for the adrenaline buzz that only a supersonic climb can give, your priorities may dictate a rather smaller model....

Mystery engines

Mystery engines? No mystery engines round here!