DC-3 high pitch whine before engine startup
 

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.

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.

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. :}

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

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.

Inertia! That's the one :ok:

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!

You'd lose the bet
 

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?

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

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.

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:

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