Dear ppruners
 

After posting the first message about the crash of the Cabri at Lelystad, it is interesting to see the reactions. In my opinion this community is to inform about the helicopter world, to learn from mistakes and not to burn down other people. Respect!!
Altough there are some posts removed ( from the pilot involved) it is good to read the answer from the designer of the Cabri . This is the power of this community and I am glad to be part of it.

rotordent.

p.s mastbumping was a bad transalation from me for tailboom strike

Low G with a carburetor
 

Any float type carburetor relies on gravity for the float to work.

If the float stays at the top of the chamber it will not replace the fuel used in the carburetor as the needle valve is shut.

Try it in a frame with the same engine that is allowed to operate at zero G i.e plank C172 for example.

It happens very quickly and a plank will restart due to windmilling (if you don't get too slow) a helicopter will not unless you restart it!

Maybe the rotor on the G2 is too good for the engine!

seems to me the information thus presented is confusing in the extreme.
"for some reason the engine did not respond"
"and who is prepared to explain"
"they decided to go around"

some people here talk of zero G causing a short term engine power loss?

did the zero G occur, if so where? from an auto commenced at fifty feet? or at commencement of the auto at some time above where the (what I would call a long term) decision to go around when a taxiway loomed up in the sights?

I.E. a momentary loss of power might have occurred as suggested but well before the decision to go around as presumanly the PIC knew at that time that the engine was running OK and therefore elected to apply power.

Therefore the auto commenced at a high height, high enough for even a slightly prolonged brrp brrp to have sorted out into a smooth running idle.

From my point of view the suggested certification flight test regimes would have included sudden throttle roll offs or more correctly, abrupt downward selection of the collective within the profile of maintaining allowable maximum RRPM and ERPM.
Those tests would have sorted out whether there was ever a momentary loss of power capable of being experienced in the engine. Is there such mention in the AFM? No? well it doesn't happen then!

I believe that unless you are flying a helicopter with negative pitch capacity that negative G will not occur in any auto unless one wound the throttle off during a low g pushover or perhaps a violent pushover. Who in their right mind would do that?

I do not think the engine suffered negative G. At all times during positive to flat pitch maneuvres the aircraft are usually assuming a not less than one G profile.

Therefore we have not had yet - an explanation.

It is said that the machine is fitted with an automatic carburttor heater.

It is not said whether the device was tested as functioning correctly.

In my view either;

the engine suffered a carby ice blockage which can be undectable until power on is selected.

However "the pilot acheived a very smooth level landing", means to me that if the engine quit suddenly at the go round decision height that the airraft was not then in a profile which meant a heavy landing would ensue.

or ;

the collective was selected downwards during the run on quickly enough for the M/R to touch the tail whilst the cyclic was selected rearwards to arrest forward run on speed.

I have done such myself in a '47, threw the collective down to arrest forward movement as a final resort to save the aircraft going over a very nasty drop in front. I was in a freewheel failure auto at the time with no choices about selecting a longer run on area.

The second scenario leaves conjecture about any problem of the helicopter or engine in the dustbin.

Rearwards cyclic can be selected to arrest forward speed, during practice autos but the collective must be right up or being lifted upwards at the same time.

In no strectch of the imagination could one suggest that the A/C 'crashed' during such an incident.
regards tet

I don't think it is all that complicated; EHLE has a 1250m long runway with on 1 side taxiways at equal distance which creates 4 grass segments. autorotation starts on final at 700 ft and normally ends somewhere on segment 3. It is normally a full auto with recovery into a running landing. They either ended at the end of segment 2 or at the end of segment 3 and tried to recover to go over the taxi way and land on the next segment. usage of the collective during the second flare, which normally starts around 100-120 ft is not necessary, at least I never used it in a flare and I did at least 100 auto's on a 3 bladed bird (H269). After the second flare we level ship at around 20ft or so and use collective only to cushion landing... It looks like the recovery did not work out with hard ground contact as a result, they pulled collective to pass the taxi way and then landed soft in the next segment. Question remains when did the blades hit the tail boom; after the first hard landing or during the second while giving aft cyclic to reduce speed while rotor rpm was already way too low....

@ torpendtorque:

dont get the accidents/incidents mixed up. The low-g i referred to, happened during one of these tryout flight were a passenger gets to touch the controls from the left seat. After the passenger applied too much aft cyclic, the instructor responded with forward cyclic to stop the climb. This low-g situation is the moment, the engine quit.
After entering autorotation, the instructor succesfully restarted the engine and flew back to base safely.

The other incident didnt involve low-g, but a sudden throttle chop in order to iniciate a practice autorotation. Again, the engine quit, though different machine.

All the above happened in Germany. Finally there is the accident this thread is actually about. In this case, no one mentioned low-g in the first place.

Anyone know why a thoroughly modern machine such as this has a 19th century technology fuel delivery system with the associated failure modes still present?

should be fuel injected, then also no ice probs :}