or a few ideas on model engine construction.

Rob Metkemeijer and Enrico Flores.

1. Introduction.

The design and construction of the FMV took place from November 1976 until right before the 1978 World Championships and must be considered as a synthesis of ideas we took from quite a few years of teamrace-experience and espionage.
Flying experience taught us what we needed: A fairly powerful and economical engine and, far more important, one that would GO under all circumstances.

A teamrace engine is only worth for the number of laps it can run at top speed, and its capability to withstand wrong - especially lean - settings, and/or heavy races.
The once, and maybe still, superior Russian engines Onufrienko, Krasnorutsky, Maslov) were never more powerful than good Bugls or Rossi's.
They were just built into excellent models and had an amazing capability to withstand any setting in any type of race.

Some Bugls MK 1 and MK 11 and many Rossi's were probably more powerful, yet generally incapable of completing a race if set for maximum speed and economy. because very prone to sudden seizures.
So a "good" setting on these engines was a safe one, slightly rich and undercompressed, but slower with possible problems of range.
With the "discovery" of the Nelson l5D motor in the second half of 1977 it was clearly shown that contests could be won with an engine not any faster than the opposition but far more consistent. Its consistency in a race, rather than its power, impressed us deeply and we realized that Henry Nelson was on the right path.
We must admit that it wasn't very easy to find out the reason of its superiority. Moreover we had already lost two years, because in 1975 we had been so stupid as to judge this engine only by its appearance.

2. Distinctive features of a teamrace engine

A teamrace engine, is the only type of competition model-engine where power as well as fuel consumption matter. As everybody knows, diesel engines have a good reputation for economy, and that is why they are used in this racing class. Engines with with a low fuel consumption get very little internal cooling from the fuel, so they are at the mercy of cooling from outside, air-cooling because of weight.
In all other types of competition engines small mechanical imperfection's are reckoned with by simply opening up the needle, and therefore never recognized.
In TR-engines this solution is not acceptable. However, even the best TR-engines are unfavorably with the big diesels with respect to specific fuel consumption.

As every TR-mechanic knows there are settings with more compression and less fuel which make the engine running faster for a short while ...... and then a sudden stop follows caused by rise of internal temperature and/or friction and consequent pre-ignition. Because in competition flying the running conditions of TR-engines are very close to this limit we are convinced that TR-engines can teach us a great deal more than any other type of engine about the existing mechanical and thermal problems.

This, and the following articles, will describe general mechanical principles and thermal considerations on model engine construction and the way they were applied to the FMV. Hereby we trust that persons concerned with model engines achieve a deeper understanding of them and will hopefu11y become able to recognize and so1ve the problems they encounter.

Our approach can be summarized as follows:

• Prevent local sources of friction, and thus heat. (Excessive friction and heat are generally generated by vibration, wrong tolerances or deformation, wrong material combinations and lack of lubrication).
• Give cooling and lubrication to those places where necessarily heat is generated: combustion chamber, small end, ball races, piston and cylinder.
• Try to stabilize the system in such a way that, at rising temperature, friction in all moving parts does not increase (right material choice with regard to thermal expansion coefficient is extremely important. If by thermal deformation friction is increased, temperature will locally rise more, giving more thermal deformation etc. and the engines seizes).

With the limitations in all existing TR-diesels on the mechanical side, we think it is absolutely useless to do a lot of research by means of improved gasflow, as long as too much fresh gas is not wasted during the filling of the cylinder.
Quite a few experiments on cylinder timings and the shaping of ports taught us that you'll find all kinds of differences, but never a significant change in efficiency of the motor. The reason being that timing is a factor of power more than a factor of efficiency. The only wrong things was decreasing the differences between transfer and exhaust timing in the cylinder to less than 18°.
For a schnuerle scavenging layout all exhaust timings between 125 ° and 150 ° and many different portshapes seem to work.
Rotary vales opening at 45 ° ± 15° A.B.D.C. and closing 50° ± 15° A.T.D.C., worked as well
Experiments showed, that it is always possible to compensate for the above mentioned variations by changing propeller and/or venturi.