Odds and Ends (Alias Lines and Tubing)

By Alice Cotton-Royer

September 2006

Diesels (and shutoffs) in stunt

Hi Flying Line dudes and dudettes,

I have received some interesting email from those who have read my previous articles. Here is some information I received from Eric Clutton who responded to the diesel article with these words:

Date: July 30, 2006

"Dear Alice ... your recent forum on diesels was good but it missed the reason why diesels are so good for stunt. Maybe the crafty lot who gave you the info were holding back? If you examine similar capacity diesels and glows you will see that the intakes on the diesels are very much smaller than those of glows. This is because kerosene does not require the large amounts of oxygen to burn that alcohol does, and a secondary effect is that the diesel has very much superior fuel draw (lots of suck!). This also means that you very rarely need fuel pressure feed with diesels and it makes them virtually a one-speed engine, not caring whether they are going straight up or straight down! I have been amused to see some guys putting such a lot of effort into trying to make four-cycle glows do what diesels do naturally-- every time. Guys who fly diesel stunt will tell you that you need one quick test flight on the day to establish the settings for that occasion and then that is it. I wish there were other guys (or gals!) who fly stunt in this area. I have an O/T stunt Chief with a PAW .35 up front and it pulls my arm off on 68 to 70ft lines; also a Brit vintage stunter with an Elfin diesel, just like we used to fly back in the fifties!

Just to put the record straight, I have flown glow stunt over the (many) years and if the 2-4 break is your thing, then that is the way to go, but if you fly full throttle (better in a wind) then diesels are better by far.


I found this to be quite interesting so I wrote back with something that was bothering me from the last article:

Hi Eric,

I'm glad to hear from you. And glad to know you actually read the article. Your message makes a great addition to the whole diesel thing and I would love to include it in my next article in a couple of months. Is that OK?

Here is what a couple of people said about the diesel consistency problem....

"It is hard to get the same run twice in a row." Dennis Lein said he over-ran on a first flight at a CA contest and under-ran on the second both with a full tank of fuel. What do you make of that?


On Aug 1, 2006, at 7:47 PM, Eric Clutton wrote:

"Hi Alice ... If you fly diesel it is advisable to do one test flight on the day to establish the settings for that kind of weather (temperature, humidity etc). After that there will be no changes to the needle unless a prop change is called for. The compression usually needs an increase because heat and compression are interchangeable, so when cold it needs more, and as it produces heat, it needs less (that is why fixed compression diesels are not too good), but same compression setting for running each time is all that is required. They are certainly much more consistent than glows so someone is not doing it right! One of the little tricks we used to do with small (up to .19) stunters was to run the fuel line around the crankcase before plugging it into the spraybar. It also works on glows and give a small reservoir of extra fuel (a larger one for a diesel 'cos of the much lower fuel consumption). Feel free to use anything useful and if you or anyone has any questions I would be happy to answer them. ERIC"


On Aug 3, 2006, at 7:02 PM, Eric Clutton wrote:

Hi Alice.... Sounds like his (meaning Dennis Lein) tank is too big and on his second flight he had some crap in the fuel! It affects glows too! Might also be tank design, of course. Never use pressure. I have often wondered why the stunt comp guys never think of using a cut-off instead of just depending on tank size, especially with the length of run being so critical in a competition. ERIC.

I find this to be an exciting and interesting aspect of our hobby. Does anyone else have anything to say about diesel engines for stunt?

In answer to Eric's question about shutoffs for stunt engines, Pampa member Hube Start, a Canadian pilot, sent this to me when the question came up at a contest. The relevant section was found in a FAI publication and it reads like this:

FAI Sporting Code
Section 4 - Aeromodelling
Volume F2
Control Line
2006 Edition
Effective 1st January 2006
4.2.1. Definition of an Aerobatic Model Aircraft
Powered control line aerobatic model aircraft in which all aerodynamic surfaces (except for the propeller plus that/those surface/s used to control the flight path) remain fixed during flight.
4.2.2. Characteristics of an Aerobatic Model Aircraft
a) Maximum total flying weight (excluding fuel)    3,5 kg
b) Maximum wingspan (overall)      2.0 m
c) Maximum length (overall)        2.0 m
d) Permitted power sources shall include any power except rocket motors. Piston engine/s shall be subject to a total swept volume limitation of 15 cm3. Electric power shall be limited to a maximum no-load voltage of 42 volts. Gas turbine engines shall be limited to 10 N static thrust. A suitable silencer must be used on all piston engines. The noise limit set out at paragraph 4.2.6 c) shall apply to all power sources.
e) Wireless remote control (electrical, optical, or any other) of any control function of, and/or of any system in the model aircraft shall not be permitted.
f) The following exceptions to rule 1.3.2 of Section 4C of Volume ABR are allowed.
i Other controls may include, but are not limited to: landing gear operation and built-in engine starters. Such functions may be controlled by the pilot only via line/lines, or may function completely automatically. The frequency of any electromagnetic pulses transmitted through wires/cables to the model aircraft shall not exceed 30 kHz.
ii For piston engines (including "Wankel" rotary types), no outside control of the engine/s in-flight power output shall be permitted whether or not such control is direct to the engine/s or via propeller/s with variable pitch. For the purposes of this paragraph, the term "in-flight" shall mean the time between the release of the model aircraft for the Take-off Maneuver and the end of the Landing Maneuver. Active or dynamic automatic power output control based on flight parameters such as, but not limited to, shall also not be permitted: model aircraft speed; angular speed; centrifugal force; line pull; flying height; or any combination or derivation thereof. However, if not used for the purpose of active power and/or throttle control, the following shall be permitted:
-     Passive or static devices controlling rate of fuel flow or fuel pressure (for example "uniflow" fuel tanks).
-   Passive or static exhaust systems (for example tuned-length exhaust pipes to control engine rpm).
-       Provided they are used only to end a flight, the use of engine/s shut-off systems, either operated by the pilot or functioning fully automatically, shall be permitted, subject to the restriction at paragraph e) above.
g) For power sources other than piston engines, engine power controlling systems, whether pilot-operated or automatic, shall be permitted.
h)       Rule B.3.1. of Section 4B of Volume ABR does not apply to class F2B.

4.2.3.      Line Length
The minimum length of control lines shall be 15.0 meters, the maximum length 21.5 meters, to be measured from the centre-line of the grip of the control handle to the centre-line of the propeller. Where model aircraft with multiple power sources are used the longitudinal (fore and aft) centre line of the model aircraft shall be taken as the reference for measurement.
4.2.4.      Line Tests (to be made before each contest flight)
a)    The length of the control lines shall be checked before every contest flight.
b) Not less than 20 minutes and not more than 1 hour before every contest flight a test load of 10 times the total weight of the model aircraft without fuel shall be evenly and smoothly applied to the assembled control handle, lines, and model aircraft. The load used in this test shall be applied once only to the control handle in such a way that the test load is equally distributed between both flight lines/cables during the whole pull test.

To end things I have a photograph of one of our kids (Eric Fitzgerald), stunt pilot, who flew at the last Northwest Regionals contest. He came with his dad, David Fitzgerald (US world team stunt pilot). Eric was quite proud of his flights in Beginner. How cute is this...


If you have any information, e-mail Alice Cotton-Royer.

I hope to hear from you.

This page was updated Sept. 7, 2006

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