DC-3 high pitch whine before engine startup

[b377]

When I was a kid I flew frequently on well equipped 'corporate' DC-3s.

Just before starting up #2 I would always here a series hi pitch whines and buzzing coming from what appeared to be the equipment rack located on RHS immediately infront of the cabin/cockpit bulkhead.

I presume these were gyros comming to life in sequence after CBs were made or power supply dc-dc converter vibrators (although I have wondered if engine starter motros were responsible for the whine).

Any other suggestions?

I don't suppose all DC-3s make this noise as most are just flying tin pots poorly kitted out with a bare minimum of avionics.

[stevef]

There are generally whines and groans from the fuel booster pumps which are located under the forward cabin floor. The hydraulic system gurgles, knocks and sings in varying degrees.
I don't know much about 'corporate' DC3s but the noises you describe might well be inverters.
It's very rare to see a standard electrical or avionic layout on Daks/DC3s in my experience.

[Daysleeper]

Could it be the winding up of the flywheel on the impulse starter, My memory is going can't remember the proper name, basically you spin up a lump of metal till it's going really fast then engage it with the engine and it gives enough impulse to turn it over a couple of times.

They'd all gone to clutched starters by the time I got on them so it's a bit fuzzy.

After you've been on them a week you couldn't hear any of that stuff anyhow as you were deaf. :}

[stevef]

Inertia starters, Daysleeper? Always liked that system for the sound and technique. Haven't seen them for a looooong time.

[barit1]

Inertia starters usually had a side shaft that a crank could be fitted to (assuming the oil tank wasn't in the way :} ). Thus a dead battery could be overcome with some manual windup. The BT-13 "Vibrator" was so equipped.

[Daysleeper]

Inertia! That's the one :ok:

[b377]

Note that the whine persisted after the engines started which makes me think it came from the power supply vibrators and/or gyros.

Were intertia starters used into the 60s & 70s? AS I said these planes were well looked after and fitted with modern refinements like weather radar so the latest in starter technology was most likely in use. Mind you on a few ocasions one or the other of the motors had to be started with a rope wrapped round the prop hub and pulled by a truck. Bet none of you have had to do that!

[Eric Janson]

I have had to do this once on a DC-3 when the left starter failed.

Surprisingly straightforward.

Now how about hand propping a DC-3 - anyone done that?

[Jimmy Do Little]

hi pitch whines are generally the pilots complaining about salaries, working conditions, etc!

[Capot]

Now how about hand propping a DC-3 - anyone done that

No, but I have been involved with starting one with a Landrover and a piece of rope when a starter failed; indeed the engineer in charge said that the prop boss was specifically designed like a very protuberant nipple for that purpose.

It worked well, after a bit of practice with the speed to drive away at, and optimising the number of turns round the boss. (It was quite slow; just enough to turn the engine over at the same speed as the electric starter.)

But I noticed that the passengers, who watched the performance from the departure lounge, walked quite slowly to the aircraft as we stood round congratulating ourselves.

[stevef]

I rather think your engineer might find that the prop dome was built that way purely to contain the pitch change mechanism. :) In those design days, the hand-start inertia system was available for when the electrical motor was inoperative.
B377 - inertia starters were in common use (in the UK at least) until the mid eighties. Then all overhauled engines came with direct drive starters. Sometimes a block of wood and a lump hammer was needed to wake them up and the pax reaction was as Capot describes. :eek:

[MarkerInbound]

I'd vote for the fuel boost pumps if the sound started just before engine start and continued. They were fairly noisy.