Lightning T5 Starting System
The Lightning is a T5 variant, based at Cranfield, maintained by a team of volunteers and fast taxi run on various dates during the summer months. More info can be found at: lightningt5.com.
Lightning engines were originally started using an IPN monopropellant starter, but this is expensive, difficult to find and the group have replaced that with an electric starting system running at approx 160 volts DC. Presently, this is derived from 6 x 28v NiCad aircraft batteries, wired in series for starting and individually charged offline. The ongoing maintenance, uncertainty about charge state and ageing of the batteries has made it difficult to guarantee reliable starts. Another engineer designed the 160 volt starting panel, but has moved on. I’m new to the group, but have been asked to find a more robust long term solution. The group have a 25Kva Houchin GPU, which could be used to charge the batteries at start of day, between runs and augment the battery power during starting, but this requires some means of converting the 208v 400hz 3 ph output to a more suitable dc level.
I'm proposing a two track approach:
1) Buy in a 25 kVA 400Hz transformer and build a 160v dc transformer rectifier, in parallel with the batteries for starting and with constant current control when charging. I have two quotes for a suitable transformer thus far, but the price is not far short of astronomical.
2) Find 6 off surplus 208v 400Hz 3ph -> 28vdc, 200-300 amp transformer rectifier units (TRU's).
Tru's are a standard fitment on a variety of a/c and have a couple of smaller 50 and 125amp units in my own collection, but we really need higher output types and 6 of them, so we can allocate one per battery.
Background here is electronics and can build new or modify surplus kit, but not sure what has been used where and on what a/c. For example: What sort of TRU's / power systems were used in older (scrapped) commercial aircraft that might be pressed into service ?. Some RAF types used a 112v dc bus for the heavier loads and would assume that they used large tru's to generate that voltage, rather than dc generators. Perhaps the same for commerical a/c. To sum up, we're looking for large kVA 400Hz transformers, TRU's, or other high power a/c power systems that might be pressed into service. Ideally, this needs to be up and running by mid to end of May this year. Suggestions, ideas, sources etc would be appreciated...
Chris