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F2D Engine Cowl
How to improve speed by reducing parasit drag
First published: 15/5 2012 - Last update: 16/6 2012

Fly fast and win at combat!

Speed is an advantage in combat. If your model is a little faster than your opponent's you will be able to dominate the match. All pilots try to fly faster by optimizing engines and propellers. Many pilots are good at optimizing the speed and it is very difficult to find the extra power that will make a difference.

Another approach would be to reduce the drag on the model. Some of the drag on a model comes from parts exposed to wind. Parts as engine, muffler, engine mount, streamer hook and swing arm shut-off systems will curse a lot of parasitic drag. They are located in the slipstream of the propeller and will typically be exposed to an air speed much higher than the model flying speed.

A reduction in the parasite drag will leave more power for flying faster. Not much attentions have been paid to this fact before but now the Lithuania pilot Vytaustas Rimsa (nickname: "Killer") have designed and manufactured a faring or cowl to reduce the parasitic drag from the engine mounts and the lower part of the engine.

The cowl is made from vacuum formed plastic sheet and the weight is only 5.2 gram.
The cowl is fixed to the model with tape and can easily be removed if it is damaged in a hard landing.

The cowl was first presented on the Russian FAS forum (Translate to English) and was first used at the World Cup competitions in Kiev, Ukraine earlier this year.

The cowl should reduce the time for 10 laps by 0.5 seconds.
To reduce the time for 10 laps from e.g. 24 seconds to 23.5 seconds the speed must be increased by 2.1%. To get this extra speed from engine power only you would need a 6.4% higher power output from the engine since the power consumption will rise as the third power of increase in speed.

You can make more calculations on drag and engine power with the Control Line Calculator

A cowl is a simple and effective way to improve your flying speed. The cowl will make it more difficult to change the bladder during a match. Without a cowl you will save a little time if you have a problem with the tank but you cannot win by reducing losses.
For a winning strategy you must go for the maximum speed. You must go for the cowl!

/Henning Forbech

The cowl on a model with an MS engine and a Rastenis swing arm shut-off

Audrius Rastenis presenting a model of Vaclovas Cyzas with the "Killer Cowl"

The cowl was first made as an CAD model using some of the free models that can be found here

For more information contact Vytaustas Rimsa
Phone: +37068781128

Vytaustas "Killer" Rimsa winner of the 2010 World Cup in Sebnitz, Germany