Microlights and Looping

[Helicopterfixerman]

Can someone please clarify something for me.?

I am of the mind that the "typical" open cockpit, flexiwing microlight aircraft is incapable of performing a loop in normal circumstances. My rational comes from teh combination of: Lack of turning moment since there is no elevator placed "x" distance from the CofG, the aircraft itself is little more than a flying wing with a gondola "pod" suspended beneath it, any deflection of the wing, i.e. angle of attack, will merely alter the amount of lift the wing generates rather than alter the nose up or down attitude of the "pod" and so in effect the whole aircraft either rises or sinks, the thrust from the engine is insufficient to provide enough momentum to achieve the roll, and any dive manouevre perfromed to aid in the build up of speed and thus momentum would ask questions of the structural integrity.

I would also like clarification that it cannot climb vertically, mainly for lack of thrust.

Am I right?

If I'm in the wrong section of the forum I apologise.

Many thanks in advance

HFM

[chevvron]

I'm not too au fait with flex-wings which is presumably what you're referring to but:

Microlights are officially prohibited from any aerobatic manouevre in the UK, but I have heard stories of flex-wings being 'successfully' looped.
Some of them are over powered (eg 80hp Rotax 912)and can climb vertically

[Genghis the Engineer]

Like most aeroplanes, a flexwing could theoretically fly a loop - by diving as near to Vne as possible, pushing the bar out hard, whilst maintaining full throttle. You'd have to do the flight mechanics maths to double check that for a specific aeroplane, but I'm sure some could - indeed I've seen video of it. Similarly, I've seen film of hang-gliders looping.

Climbing vertically is a different issue - it requires a thrust:weight greater than 1 - I don't think that any microlight (or indeed the majority of fighters when at a warload) has that capability so any vertical climbing would be very short-term until you ran out of energy (a few seconds at most for the majority of microlights).

For some very good reasons why you shouldn't attempt to loop a flexwing, search on the terms "flexwing tumble"; if you really want to get into it, read this (http://bura.brunel.ac.uk/bitstream/2438/705/1/GrattonNewman_TumbleResistance.pdf) (5Mb pdf).

G

[Helicopterfixerman]

Thanks guys.

When you say a microlight and hang glider have looped, are we talking about a true loop, where the "circle" is completed or are we talking about a glorified tip over at the "top"?

[Genghis the Engineer]

By law, all microlights are prohibited from pitch angles greater than 30 degrees, which limits all but the most basic 'unusual attitudes'

Not quite true - CAP403, the display requirements limit microlights being displayed to ±30°, and quite a few types (mainly I think Mainair flexwings) also publish this as a hard limit - but it's not a legal limit.

Mind you, there is a legal 60° bank limit (although a few types have a stricter limit of 45°) - arguably at top of loop you have 180° of bank!


Any loop in a microlight, 3 axis or flex wing, would not be a true circle, as much due to the fuel starvation issue as the aerodynamic / mechanical design limitations inherent in the flex wing design.

Most loops should stay in positive g throughout, so there shouldn't be a fuel starvation issue.

G