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massive gyroscopic twisting on simmo and a hard landing

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my friend had his very short first flight last week, he is fine, a bit sore but ready to get back on the horse as soon as this issue is sorted. the video will explain what happened. on testing afterwards it was noticed around half throttle onwards the unit wants to violently twist you to the left. its a simo mini 2 with 22cm prop. He is a big bloke so able to fight the twist to a point. on previous attempted launches he would be running then suddenly flip to the left and fall, we thought he was tripping but evidently not.

any one got any ideas as to why this should happen?? normal torque should be to the right


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Looks like there is Right-Brake being pulled from 0:01 to 0:07 and then again at 0:15 until he hits the deck.

That's the only obvious thing I can see from the video. :?

Glad to hear he's ok. And kudos to him for not being put off by that experience.



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When the prop disc is perfectly perpendicular to the direction of flight then the torque effect on the Simonini will give you a steer to the right because more load is placed on the right risers than the left. If the prop disc is angled (watch him swing back when he lifts off the ground in the video) then the same torque now has a horizontal component which twists him to the left. Now there is a side thrust pushing him left and the wing into a right hand turn from which he is locked out.

These are just the basics before we even consider asymetric blade thrust and the effect of precession with the sudden aft rotation.

This is the result of not doing a proper hang check and getting him set up with his equipment. Was any hang check done before flight? Who is instructing him?

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Hi Cobra,

Starts off great nicely centered under wing.

Pilot commences takeoff run adds power,

Engine now starts to move round right side of pilots body (harness too loose) thrusting pilot to the left (still on ground at this time. (pilot no longer centered under wing.)

Leaves ground - lots of power, (worse) engine has now twisted completely round right side of pilot. This is pushing the pilot out to the left while the wing is trying to fly to the right. ('lock out' effect) more power at this stage will not convert to climb because the thrust is not pointing in the direction the wing likes to fly making the situation worse.

At this point the perfect solution is POWER OFF for a nice safe landing. Pilot will centre back under the wing once power off and face same way as wing.

Tighten up all harness straps to not allow engine to twist around body. Hard hang points reduce this twisting lots.

You can get away with some of this twisting by moderating the power, getting enough height to get right back in the seat. If the engine is right round the side like this though best to land and sort the harness. Also check both caribiners are level if they are adjustable on that harness.

Once your fully in the seat with your back against the machine it cant twist much like this. The thrust line is then pointing forwards and the pilot is pushed nicely out centered infront of the wing for a climb out.

Unfortunately more power makes it worse. Similar principle to 'lock out' when towing a paraglider.

Just my thoughts/ experiences, hope it helps, what do others think?

Hope you don't mind me not using the technical terms, I'm not very good at understanding them.

Safe flying,



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That's right... he is initially running with the prop cage angled (appears to be leaning forward even) so there is a horizontal component of torque. The direction of the horizontal component of torque reverses when rotating from a leant forward position to a leaning back one making its effect even more sudden. There is scope to remove some slack from the harness but a well suspended harness can be flown surprisingly loose. The set up must not cause rotation when it lifts. The more excess of thrust you have then the more this snatching rotation can cause problems.

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Makes sense really. You could undo the straps on mine, whilst in flight, as they are doing absolutely nothing. Only the shoulder straps are tight when running and all the leg straps seem to do is stop the unit swinging side to side and pull the seat under you when you take off.

Looked a scarey crash. Hope he's ok and I'm sure he'll cut the power if a similar event should occur. Once he starts to build faith in the wing he'll probably lean back more on the run out and that should sort the problem anyway.


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Ouch! that looked painful I hope he's ok.

I have seen a similar thing before on a first flight.

That was caused by an excessive amount of power being used and a very old wing, when he went to full power it almost twisted him right round.

Hopefully your friend will not be put off by his very scary first flight!

Tom :explode:

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A good point.

It's a difficult call as its hard to see the angle of the pilot but looking at just the wing... you may well be correct with that one.

Although I do hate to comment on accidents that I did not see first hand leads to all sorts of BS.

(JUST LOOKED AGAIN) on full screen, and I would have to agree that little to no attempt was made to bring the wing back with the left brake.


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