Air starts

Well I did a little more research on this subject, and I find it quite interesting…

The sound in the clip is indeed probably a diesel unit, the whine seems to be characteristic of such devices as screw or vane pumps. It kind of reminds of root blower sound.
But there is very little info on such devices.

I wish there was more interest on aviation history on WWW.

For many years BA used air starters for any type needing it as well as Concorde as it has no apu fitted,the air starters were nicknamed Trident Transit’s as they had the Garret apu’s on the back and boxed in,all the apu’s were removed from retired Trident’s ,here is a photo of one the units.

So, this whine we hear in the clip, is that from one of those diesel+compressor units or gas turbine units?

Most airfield based air starts have a compressor driven by a very large diesel engine. Houchin, Hobart & Stewart Stevenson are common makes. Lighter weight units consisting of a small gas turbine engine are sometimes used.
I don’t think they have changed much from the 707 DC8 days, nowadays they are only needed when the aircraft apu is inop, because of this when you do need one the battery is inevitably flat!:rolleyes:

Now that I’ve watched it with what you said in my mind, I see it makes sense. At 1.18 the whine “struggles” a bit, which would indicated that this is the point when the air cart is first loaded by the resistance of the actual engine of the DC8

About that whine from the ASU, then….what kind of engine would make that kind of whine? Doesn’t sound like a regular jet engine at high rpm. Is that some kind of alternative kind of compressor or what?

Is there a specific popular brand (any names to remember?) of ASU’s back in the days of 707 and DC8 that most airports used or were those custom solutions by every airport?

Having listened to the clip I would say that the sound heard at 1.03 is the Air Start accelerating to the ‘Jet Start’ condition. At 1.18 the note changes as the first engine start valve opens & the air flows to the engine starter.
On the JT3D’s in the 707 & DC8 the fuel went on at 15% N2 (HP Compressor), this probably took less than a minute to reach, starter cut off on most jets is approx 45% N2. Best practise on the large fan engines, JT9 PW4000 CF6 etc is to reach max motor speed approx. 21% before introducing the fuel. The PW 4000 is the slowest engine to reach starter cut off that I am familiar with, I’m not sure of the actual time but it seems to take an age.

Thanks everyone for their answers…

What about the sound in that clip, the whine, is that what a huffer cart sounds like, or is the low-rpm N1 sound?

Welcome to the Forum Trilex9 with an interesting question and perhaps a belated welcome to opssys, not a prolific poster but maybe an avid watcher!:)

VC10, B707, DC8 etc all needed ASU for Starts, also on Hot Days and if one was Available ACU as well. A Long Haul Jet of that era could have a lot of kit around it for the last 30 Minutes,
GPU, ASU, ACU, TUG Connected, Bowser expectng a final top up, Loading Vehices at forward and Aft Holds, plus some light Vans from Engineering, Catering, Ramp Dispatch (hopefully all neaatly parked), Passenger Step Units forward and Aft.
From memory the target was doors to close at STD -7 minutes (later -5).

With modern APU being so reliable, on the rare occasions the APU becomes U/S, it would not surprise me to find that the available ASU(s) were also U/S!

I think the OP was talking about old engines here. I remember ASUs being plugged into Aer Lingus B707s at Turnhouse back in the early 1970s but I couldn’t tell you exactly when things started to happen

On the 737, depends on the APU 😉

If an aircraft requires an ASU, surely its because the APU is U/S?

I think depending on the type of aircraft, normally does’nt take that long for them to spool up. Im sure a pilot on here could tell you better as im just a grounds man judging by the sound of them starting!