1. #1
    Hanglands's Avatar Banned
    Join Date
    Sep 2006
    Posts
    672
    Hi,

    I read a book recently (maybe it was 'Tail End Charlies'?), which at one point described fatigued, or inexperienced and frightened bomber pilots feigning technical problems and making early returns to base.

    One of the means of doing this, accoeding to the book, was to induce magneto drop on one engine.

    I have a couple of questions on this.

    First, what is magneto drop exactly? I think it might be to do with fouling of the sparking plugs perhaps?

    Second, if it was fouling of the plugs, how was it induced? Running an engine on a high fuel mix for too long?

    Third, were genuine cases of magneto drop a valid reason for an early return? (I expect the answer might be 'yes' for twin engined bombers, but not sure about four engines).

    And finally, what other technical/mechanical faults were 'engineered' to force an early return?

    Many thanks for any help.

    Regards.<div class="ev_tpc_signature">

    Share this post

  2. #2
    Hanglands's Avatar Banned
    Join Date
    Sep 2006
    Posts
    672
    Hi,

    I read a book recently (maybe it was 'Tail End Charlies'?), which at one point described fatigued, or inexperienced and frightened bomber pilots feigning technical problems and making early returns to base.

    One of the means of doing this, accoeding to the book, was to induce magneto drop on one engine.

    I have a couple of questions on this.

    First, what is magneto drop exactly? I think it might be to do with fouling of the sparking plugs perhaps?

    Second, if it was fouling of the plugs, how was it induced? Running an engine on a high fuel mix for too long?

    Third, were genuine cases of magneto drop a valid reason for an early return? (I expect the answer might be 'yes' for twin engined bombers, but not sure about four engines).

    And finally, what other technical/mechanical faults were 'engineered' to force an early return?

    Many thanks for any help.

    Regards.<div class="ev_tpc_signature">

    Share this post

  3. #3
    Aircraft engines have two ignition systems for safety. The magnetos generate the very high voltage needed for the spark plugs.

    When both systems are running the engine will run just a bit faster, around 50-100 rpm, due to the extra spark. Before take-off the engine is run up a bit and run on each magneto independently. If the rpm drop from both mags to a single mag is more than the engine specs, then the flight should be aborted.

    I can't see why anyone would actually do this in flight though. It's not like your crew chief is in there with you so it's easier and safer to just lie about it. If you have a co-pilot you can't fake it b/c he would see you turn off one of the mags so once again, it's just easier for the both of them to lie about it.

    If a magneto actually FAILS in flight, I guess it would be up to the discretion of the pilot(s) as to continue or not. In lots of cases it would probably be safer to stay with your group, depending on how far away you are from a friendly field.

    "Engineered" faults (those that aren't lies) would be very dangerous and I doubt if it happened very often. That's like cutting your brake lines and then starting off to work. Sure you could make it home using the emergency brake and then call your boss BUT, you might also get in a wreck. It's easier to just call your boss and lie.

    --Outlaw.
    Share this post

  4. #4
    Taylortony's Avatar Senior Member
    Join Date
    May 2002
    Posts
    8,557
    Ok Mag drops............. On an aircraft engine losing a plug or even a mag and hence a complete cylinder or a total engine failure would be bad news, so to prevent this you have 2 plugs and 2 mags, so if one fails there is a back up....... the advantage is you now have 2 sparks and a more efficent burning rate to your fuel, if for some reason a plug fails in a cylinder the burning efficency is reduced so you get what is in effect a mag drop where you get a large drop in rpm, or a really rough running engine when that mag is selected. that is why you check the mags. if you have one plug out on say the left system, selecting left the engine will run rough as on a 4 cyl eng as an example it would be firing on 3....... the reason you check them is to ensure both systems are running correctly. on a flat 4 two top plugs on one side and 2 lower on the other are on the same mag and vise versa, this is because the lower plugs tend to foul easily, this often can be a whisker of carbon shorting the plug and can often be cured by leaning the mixture right off..... this in effect makes the cylinder run hot due to an engine naturally being set to over fuel to aid engine cooling....... leaning it gets the carbon hot and burns it off the plug.

    various things can cause a plug to foul, slow running will, also running rich or low temps can as well as well......... a badly fouled engine that you cannot clear would definately be a return to base case, if you had probs with the other you would be up sh*t creek without a paddle so to speak.

    engineered faults could be caused by simply leaving the cooling gills closed and cooking the damn thing, but the rest of the crew would be in the know.... I have seen it in the past for real whilst in the RAF but for other reasons...... I have also witnessed pilots reporting snags that no one else had had on the same plane......... you tend to get blas'e to these, or I did when one pilot repeatedly snagged an engine for slow to accelerate, no one else had............ we put it on the detuners and ran it at full power doing slam checks when the sh*t hit the fan, or should i say the turbine spun out the ar*e end and buried itself into the detuner,.... damn thing seized in about 2 revolutions.......... and the whole airliner tried to rotate about its axis.......... now i listen to em all.
    Share this post

  5. #5
    Sergio_101's Avatar Banned
    Join Date
    Dec 2005
    Posts
    1,095
    Mag drop/mag check is simple.
    After reaching about 180 deg cylinder head temp
    or roughly the same oil temp (it'd been over 30 years, I may be off a tad)
    the engine is brought up to around 1600rpm, depending on the engine.
    At that point both mags (4 mags for a late R-4360)
    are on.
    One mag is then shut off(Two of them on a R-4360).
    There should be no perceptable change in RPM or
    smoothness on a Prat, there is a standard drop number
    but I do not recall.
    On Wrights the rpm drop is substantial.
    On Prats it's more like, if the RPM drops then something is amiss.
    If you pass a mag check, it's green light for
    a power check and takeoff.
    Two mags for a R-2800
    Four mags for a late R-4360.
    Early R-4360s had seven mags, never worked on one, don't ask!
    All the late series R-2800 and R-4360s I was around had low tension mags.
    The plugs had booster coils.

    I was limited in my exposure to recips, I worked Jets
    primarily Boeing B-52 and KC-135. But we worked on in transit planes
    often. By 1976 it was rare to see a piston plane.
    In 1972 it was VERY common and most were R-4360 or the odd R-3350
    or R-2800.

    By the way, we were taught and indeed required to
    believe the flight crews verbatum. If they said there
    was a problem, then there is a problem, find it and correct it!
    Much perfectly good hardware was changed because
    of that.
    That was the flip side. If we could not find a problem, change
    the engine, generator, mag, radio, etc.....

    By the way, Mech breakdown happens because
    of crews getting cold feet, or in some cases
    it's geographical. We were told that Hickam AB
    in Hawaii had the highest rate of mechanical failure on earth.


    Sergio

    Share this post

  6. #6
    Hanglands's Avatar Banned
    Join Date
    Sep 2006
    Posts
    672
    Very informative, thanks for that

    Regards.<div class="ev_tpc_signature">

    Share this post