Helicopter rotor blade scintillation

Discussion in 'Weapons, Equipment & Rations' started by IndependentBoffin, May 11, 2010.

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  1. Hi guys,

    I was reading an unclassified MoD document pertaining to glowing helicopter blades in dusty environments, particularly during take off/landing.

    Have any of you personally observed the phenomenon?

    Do you guys have any pictures of it? I'm particularly interested to know if it also affects the tail rotor and other rotors, like turboprops.

    Do you have any anecdotes of at what RPM you observed HRBS to occur, and on which helicopters (actually I just need the rotor diameters to calculate the tip velocities it starts at)?

    Some dumb questions but when the phenomenon occurs, does the air smell any different? Do you find you discharge static electricity on objects more readily when in the rotor downwash?

    I'm designing a laboratory test rig to replicate HRBS in a convenient setting and wanted to know if I need to be aiming all the way for sonic blade tip velocities, or can start seeing the phenomenon at say 100m/s.

    Yeah I've tried asking the contact in the document but haven't gotten a response yet.
  2. msr

    msr LE

  3. IndependentBoffin, pm me.

    (are you working for or with Dstl btw?)
  4. Thanks for the link. RIP Kopp, Etchells, Hale and the other dead British and Allied men & women. :(
  5. I find it a very interesting clue that HRBS disappears when helicopters are landed.

    Does anyone know if helicopter pilots tend to reduce the lift of their landed helicopters by their decreasing their collective, or by reducing rotor RPM?

    Any personal accounts however trivial they might seem are most welcome (here or by PM).


    P.S. If the research proposal I am submitting to the MoD gets funded I vow to make a sizeable donation to a nominated source (which we will vote on) in support of our servicemen/women.
  6. Doesn't seem to know much about aircraft for a boffin........
    Obviously not realising that when an aircraft has landed it is grounded/earthed... Doh
  7. Ultimately they reduce RPM and angle of attack (collective pitch) but the collective pitch is reduced first.
  8. Whats the differance between sintilation and St Elmos fire as I thought they were the same thing,ie visible static electrical discharge
  9. Scintillation only appars on helo blades, AIUI.
  10. Got you, then I have seen somthing like it on a Scout flying under a Q-nimbus in Ballykelly the weather was crap and he tried to fly under it along the coast to get back to Aldergrove, when it returned the disc was glowing and we thought it was St Elmos, hadn't heard of sintilation then, I also saw it in El Adam on an RAF Wirlwind of 1564 SAR flight, Is it weather induced as on both occasions there were Q-nimbs about and the weather was really awfull
  11. Sympathetic_Reaction

    Sympathetic_Reaction LE Book Reviewer

    Could be interesting to see if there is a corrolation between blade design and effect, i.e. effect of metal v composite, leading edge strip material, rotor hub design (material composition of hub).

    Other factors may be under carriage design (wheels v skids) which may affect grounding resistance, particle size and ambient humidity.

    Looks like a fun thing to investigate, although if it isn't causing any problems why bother...just take photos and admire the sparkly lights.

  12. Thanks for your constructive criticism but my line of reasoning is that there are two things which happen when a helicopter has landed and its ramp goes down: lift drops (which may be due to collective or RPM decrease) and the helicopter is electrically grounded.

    You are assuming that electrostatic discharge is the cause of HRBS.

    There is no definitive consensus in the scientific community as to the cause.

    If collective is decreased but RPM is the same when landed then it is a strong indicator or electrical discharge being the cause of HRBS. If RPM is decreased then it suggests that blade erosion, triboluminescence or chemoluminescence may also be at work.
  13. AIUI it is making helicopters easier to locate and target for insurgents.
  14. Can you say if the helicopter's RPM is above the speed at which HRBS is observed to occur at the stage of takeoff/landing in these images:


    In this photo as people are near the helicopter I'm guessing that the pilot has reduced RPM to idling and the collective to the minimum so that there is minimal downwash.


    In the last photo as the helicopter is just about to take off I'm guessing the pilot had RPM to max and was slowly increasing collective, but I could be wrong.

    Or is all this really quite dependent on the pilot's style?