Agusta 109C Generator / Starting Question

[chutedragger]

Can anyone tell me why a 109C, starts both #1 and immediately #2 on battery power...and then turns on Gen 1 and Gen 2 ?

Everything else seems "Bell" (engine #1 start, Gen #1 wait for green volts, and start #2) ...except for this difference.

Thanks,

Thanks

[GipsyMagpie]

Seems Augusta changed their minds on the E model. You have the gen ready to go as soon as each engine starts. Surprised the electrical installation is different.

[belldriver]

If you want to play it safe start no1 then engage generator to top up the battery when the load drops turn off the generator then start the second one and turn on both generators, this will give you the most power out off the battery to ensure a good start especially on the first start of the day.

[ShyTorque]

This procedure loads the battery very heavily for the second engine start, but it does prevent excessive loading of the "first" engine's generator during the second engine start. I suggest it's probably done that way to prevent excessive generator brush wear.

The later models (E & S) are started with the generators set to "ON", to come online as soon as the start cycle is completed, with the caveat that generator output is monitored and allowed to reduce below 160 Amps before starting the second engine. Presumably, the later models' generators are more substantial.

[John Eacott]

I believe this has been discussed before. The issue is the C20 series engine and the fragility of the generator shaft which has a history of shearing under excessive load.

Later A109E and others have different engines.

The AS355 is similar to the A109AII and 109C but the manufacturer has slightly different procedures. Generally you should not cross start a C20 and should use ground power or the battery, in order to prevent damage of the generator shaft of the running engine.

[spinwing]

Mmmmm ...

John might well be correct on this ....

... having said that never had an issue starting the Twin Squirell or the Bo105 with the same engines and the same generators (Lear Seigler) with I seem to remember the same generator drive shafts .... so perhaps it has more to do with the starter/generator cooling I have seen these starters melt down their commutators due to overheating during a prolonged start ...

:suspect:

[chutedragger]

Thanks guys,

Discussed with the DOM...and he confirms the above.

Cheers,

[John Eacott]

spinwing,

If you ever flew Bill's Taxi you would have been told in no uncertain terms: don't cross start!

I had at least one gen shaft failure on a 109AII that I operated when another pilot cross started, nowt to do with cooling. The 1 minute wait until switching on the gennie in a B206 is to allow cooling before turning the starter into a generator.

[timprice]

Personally start one engine give it a minute, then switch generator on after opening throttle to 70% wait until load below .5 on load meter, switch off gen on first engine then start engine two, like someone mentioned above the quill shaft has a built in weakness that can shear under excessive load.:ok:

[RVDT]

To add -

Most twins with C20 series are pretty old and archaic and hence simple.

Electrical systems were not so sophisticated and had no method of limiting the generator current. You just got the lot.

Where it became an issue was as electrical loads and batteries got bigger.

Exception to that may be late model 355F2's had a current limiter in the box and it was reflected in the RFM procedure.

[spinwing]

Mmmm ...

I'm sure John is again correct .... but I understand that the weak point design of the Starter Gen drive shaft was to allow it to fracture if the generator bearings were to seize and thus not drag the N1 section speed down (at least that is what I was told on various engineering courses I attended) ... these s/g's were of course as installed on Hu500s B206 & anything else with the Allison even before the light twins were developed .. and as RVDT pointed out the electrical systems were somewhat different to the more modern machines with respect to controlling overcurrent control ...

(John ... the 'Bills Taxi' days are history... I deleted those memories as my hard drive become too full and I need the space for more important junk !! :confused: )

[John Eacott]

spinwing,

Delete memories of Bill's Taxi: sacrilege! Who else could get an AS355 airborne from cold in under a minute.....

Re the earlier comment about the A109E and later models, cf the earlier A109A. Not only are the later aircraft fitted with completely different engines with FADEC there was also a major re-think of both the electrical and the hydraulic systems between the A109A, AII and C so the operating procedures tended to differ enough to catch out the unwary.

[that chinese fella]

The 1 minute wait until switching on the gennie in a B206 is to allow cooling before turning the starter into a generator

That has always intrigued me as the often forgotten caveat to the 1 minute cooling is its only required if the engine has been stopped for more than 15 minutes (in a 206 anyway…)

Never satisfied my curiosity as to why??

Any ideas anyone?

[Peter3127]

Particularly as there is a lot of heat-soak of the S/G going on under the cowls after shutdown ....