Detailed Starter/Generator Questions

lolachampcar

lolachampcar

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lolachampcar
By chance do one or more of you have overhaul facility level knowledge of Starter/Generators? I'm looking for information on things like voltage v. rpm curves for unloaded units without field current and max load sensing/regulation (D load sensing with current fold back).

Thanks,
Bill
 
Just to be clear, are you wondering about s/g combo, or 1 of each?
 
SG combo....
I'm grafting a TFE731 to an experimental application. I've got an overhaul manual for the GCU and the RCR but it raises questions as to the exact mechanism and timing of the generator function coming on line. It seems like the GCU starts providing ("A") field current to permit forward potential such that the RCR will engage. Knowing more about the generator portion of the SG combination would help me understand exactly how things happen (and thus allow troubleshooting when the time comes).
 
lolachampcar said:
I'm grafting a TFE731 to an experimental application.
Click to expand...
Why not duplicate an existing DC control system from an aircraft with a 731 installed or with a similar ST/GEN installed? Preferably a single engine example to simplify the bus shedding requirement. It would be more plug and play and come with a schematic and troubleshooting chart.
 
Got all the WestWind, Hawker and the like documentation I need in addition to some overhaul manuals from CMMs. I'm just trying to understand the overall functionality so thus the desire to speak with someone that has first hand SG overhaul experience.
 
lolachampcar said:
I'm just trying to understand the overall functionality so thus the desire to speak with someone that has first hand SG overhaul experience.
Click to expand...
In that case, if you're looking for the theory end of the DC system then you may want to contact the GCU side of the business or an applicable airframe OEM tech support. The ST/GEN is a stand-alone component and a slave to the starter or generation circuits of the airframe DC control system. A ST/GEN O/H shop would not deal or test for the items you look for.
 
Pre-retirement, I was an engineer at a local company that built regenerative electric motors (ST/GEN) for the F1 race car industry. They could pack 100 + hp units in a package smaller than a football, but I recall it operated at 120,000 rpm max and had air bearings. Lots of RPM and rare earth magnets, those were the keys.
 
Bell,
I've got the GCU overhaul manual and have digested the schematic. Its analog so a bit out of my bailiwick but I was able to understand its functionality. I'm mostly curious as to the SG's output at idle in the absence of any additional field exception from the GCU. Is it sufficient to forward bias the RCR and permit even the slightest of battery charging? Questions like those and so narrowly focused on the SG that they would not be answerable by a GCU overhaul facility (which likely knows no more than the overhaul manual allows).

No worries...... It was a one in a million shot anyway. Thanks for helping out!
 
nrp,
I did not want to use the stock hydraulic pump on the 731 in this installation (it was Skydrol and not 5606 amongst other reasons) but preferred an electric pump pack so that the gear could be cycled without a mule and I could move the mass to fore-cg. I did not find anything remotely reasonable off the shelf so I ended up building one using the larger BLDC motors available in the RC world. Brushless motors have come a long way. I can not even imagine what they are running on todays F1 cars.
 
ok, I think we now have the right to know what you are cooking up!
What is this going on??
 
lolachampcar said:
I'm mostly curious as to the SG's output at idle in the absence of any additional field exception from the GCU. Is it sufficient to forward bias the RCR and permit even the slightest of battery charging?
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Yes on charging at idle: analog or digital systems. Some of the old analog systems with separate clunky relays could drop off line at idle but it was more a worn relay than system failure.

As for the RCR (reverse current relay?), most current aircraft systems the RCR is more static than dynamic in the system. In some older analog systems the RCR was directly biased to battery voltage which in turn would control the generator voltage at the bus. However, in general, most RCRs are only looking for 5-15A movement over a specific time (MSEC) and will simply drop another relay off line. A number of GCU/VREG use a Line Control Relay or contactor to read GEN voltage (>24v) and energize a GEN control relay which provides a path to the bus and charging.
 
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