RC vs FLY BY WIRE

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By: pistonrob - 28th November 2011 at 21:30

why can a radio controlled model of an Eurofighter fly without "fly by wire" and yet a "real" Eurofighter fall out of the sky if the fly by wire system fails?.

as i believe the real aircraft is designed to be unstable and unable to fly without it...

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By: Moggy C - 29th November 2011 at 00:08 - Edited 1st January 1970 at 01:00

An RC model is generally not 'fly by wire' other than in the sense that wires are used to mechanically connect the servos to the control surfaces

Fly by wire in the full scale aircraft means that the control surfaces are connected to the servo (pilot) electronically, not physically, with a computer between the two (Three computers actually - they take a vote in the case of a disagreement)

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By: pistonrob - 29th November 2011 at 07:33 - Edited 1st January 1970 at 01:00

so if you ripped out the fly by wire stuff and you stuck a good old fashioned set of controls in the Eurofighter would it still fly though?. i would have thought so but i suppose its not the kind of thing we would ever find out unless someone made a real good flight sim of it

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By: Moggy C - 29th November 2011 at 17:34 - Edited 1st January 1970 at 01:00

I doubt we will ever know.

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By: Dave S - 29th November 2011 at 20:13 - Edited 1st January 1970 at 01:00

CG position.
If you move the CG back as far as the real ones are then you would not be able to fly it RC, when building large scale turbine powered models for competition, marks were lost in static judging because the under cart position has to be further forward on a model because of the forward CG or it would not take off

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By: Anonymous - 9th December 2011 at 07:56 - Edited 7th October 2019 at 08:47

This.
The CG on the real one is moved so far aft that it causes stability problems (this is done to reduce drag as far as possible to get the best speed from the power available). This reduced stability is what generates the need for the "fly by wire" system.
On an RC model, the performance is not so critical wheras the stability is (otherwise it would be impossible to fly) so the C of G is moved forward from the prototypical position.

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By: jbritchford - 9th December 2011 at 11:50 - Edited 1st January 1970 at 01:00

so if you ripped out the fly by wire stuff and you stuck a good old fashioned set of controls in the Eurofighter would it still fly though?

The Typhoon relies on it's computers to constantly make small adjustments in its control surfaces to keep the aircraft in the air, without them it would simply fall out of the sky.

As I understand it the Typhoon is negatively aerodynamically stable, a human pilot would simply be unable to compensate for this in flight, hence the computers. The benefit to this is that it makes the aircraft much more maneuverable.

By: Anonymous - 9th December 2011 at 12:33 - Edited 7th October 2019 at 08:47

The benefit to this is that it makes the aircraft much more maneuverable.

A common misconception. Actually it does not make it more manouvreable, it reduces the drag which increases top speed.

The impression of increased manouvrebility comes from the fact that as the C of G of an aircraft moves aft, the centre of gravity and the centre of pressure are closer together. Consequently, the size of the control input required to generate a given pitch rate reduces which leads to the impression of the aircraft becoming more pitch sensitive.