Of the four unrelated things talked about, the last is an unlikely scenario... How would you restart an engine in flight if you had no power to the starter? Well... let's think about that for a minute.
Maybe someone else has already said this. For the CFM56-7B engine ground start, fuel is added at no less than 25% N2 or up to the maximum motoring speed of the starter. Under specific conditions, fuel may be added at 20% N2 and for emergencies only, fuel can be added at 15%. Adding fuel before 15% will nearly certainly cause a hot start. I know there is a pilot quick reference handbook procedure for windmill starts which requires a small range of true air speed to make it work. I don’t recall that procedure off the top of my head however.
Great video, great perspective. On bolt torque--I just use the old fashioned US Midwestern technique--tighten it 'till the head rips off, then back it off a half turn. ;-)
I enjoyed this question and answer. It came across my mind too while watching a video on air Canada 143 but would not have helped. I did not know about the rpm requirements for starting so thank you for covering that.
low torque bolts coming loose begs the question, what was the engineer trying to do? The torque on the bolt creates a clamping load that is a portion of the bolt's ultimate strength. So if the value is low, did the engineer feel that a large amount of bolt strength was required to do other things? Other things like managing engine output forces, dynamic vehicle forces, resisting flex of a component resulting from forces applied or changes in temperature. Can you measure the bolts that came loose to see if they are stretched?
I have also seen ban manuals with torque tables, so I made new ones using something that will stay put. Counterweights on a excavator can be 400 foot pounds for the bolts.
I was assuming there must be some kind of hi tech, space aged, unobtainable by mere mortals, thread locker compound for the problem you've been talking about. Really deep and intelligent response. Regarding torquing and not being sure it was already done or to have to re-torque fasteners which had thread locking compound and the confusion that could cause, I had never thought about. Lots to learn in this episode. Thank you...!!
I was looking for an Email for you to send a link to a developer on the SR71 engine build. You may be interested in. Although you may have already seen this. It's called( The Pratt & Whitney J58 - The Engine of the SR71 Blackbird )
Some additional info: The whole video was started with emergency situation when engines are lost only emergency power is available from Ram Air Turbine or from batteries. Yes all this emergency scenarios are designed into the airplane systems BUT it never ever happened. For example during operational the histroy of the Airbus A320 the RAT never had to be extended anytime during a commercial flight. Even during the Hudson Landing the RAT was not activated because AC power was available from the main AC busses because the APU was started. So this what if scenaraios are totally out of reality. Nice to analyze it as an engineer but never happen in real life.
Bravo,Agent Jay Z,greetings from Greece!My question is:When,why & under which circumstances will these engines from the '40s '50s & similar age stop to be efficient, effective,productive, economically viable or even unserviceable due to lack of parts?When a turbojet engine stops to breathe hot gas for ground use?what is the next choice for industry & other "grounded" use?Thanks a lot for your great effort to educate us,be well!
FYI: The engine manufactures establish inflight rellte envelopes (altitude/airspeed) for both assisted and windmilling restarts. We do this typically on a dedicated test aircraft such as a flying test bed (FTB). Windmilling starts do not require bleed air from either another engine or APU. I was a flight test engineer at Honeywell in Phoenix and we performed over 1,200 air starts (assisted and windmilling) during the development/certification of the AS900 (HTF7000) turbofan. The correct restart fuel schedule must be determined by test. Note that FADEC controls are self powered by PMAs (permanent magnet alternators), one for each FADEC and do not require aircraft power to control the start. Typically the windmill envelope is between 250 and 300 knots and less than 30,000 feet (each model will have its own specific envelope). I believe that during flight testing we were able to successfully start an AS900 above 35,000 feet. I hope that helps. Thanks for posting.
