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Carb Heat

Old 6th Dec 2021, 22:03
  #61 (permalink)  
 
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And yes, you can really get a turbine start wrong. I have seen it from right seat! A few turbines I have flown have very strict procedures about clearing fuel after a failed start.
And it should be with light aircraft piston engines. This is where I think it should be. Mandatory placards: 1. 'Over priming may cause an engine fire'. 2. 'Caution: the engine must be clear of residual fuel prior to priming'.

The effective fuel clearing procedure should be detailed in the Flight Manual/POH and with expanded explanations.
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Old 7th Dec 2021, 07:01
  #62 (permalink)  
 
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I was sitting in the cockpit while my friend ( who owned the aircraft) was starting the engine on a Taylorcraft. A continental, can't remember if it was 65 or 90 hp. It was being very reluctant to start, lots of cursing, mags on and off, sucking in, priming, the usual hand swinging stuff. Eventually we thought we were getting somewhere when it decided to cough a couple of times, so "one more prime" he says "mags on" and another swing.
Which was when it caught fire.
He informed me of this fact, quite calmly, so I did the obvious thing and got out. I then sacrificed what had been a perfectly good hat to stifling the not very impressive flames.
The aircraft didn't seem to take any great harm from this, which is more than I could say for the hat, the only flat cap I have ever owned that was comfortable with a headset.
OTOH, I once managed to start an O-360 straight out of the hangar, -15c, mixture idle cut off, fuel and mags off, (keys in my pocket) four blade prop, by pulling it through prior to what I anticipated would be a difficult start. Good job we had a standing rule at that club to always chock the wheels when parked. Yep, hot mag.
Things like that just don't happen with cars, do they?
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Old 7th Dec 2021, 13:43
  #63 (permalink)  
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'Caution: the engine must be clear of residual fuel prior to priming'.
One airplane I flew, a Siai Marchetti 1019, had just about this placard, it was even more severe; something to the effect that if you found the fuel control out of the cut off gate, you must do a dry run before a start attempt. But, this is uncommon in GA planes (and the SM1019 isn't really a GA plane anyway).

In general, placarding is a subject of varied certification discussion. It's possible to bury critical information as a placard, by surrounding it in many important information placards. Sometimes, it's an AD or the lawyers which require a placard, otherwise, it's those of us who certify the aircraft design. There are so many things I can think of which merit placarding, but there is no panel space. In an ideal world, the pilot would be so well trained and current on type, that no placards would be needed at all, the pilot would just know. So how much can we accept a pilot "forgetting" little things?

But, as I reminded my boss, and the certifying authority, for the five years I worked in GA airplane starter design and approval; if you can't get it started, it's really unlikely the plane will be at risk of an accident. The only time it was a discussion point was restarts in flight in twins. So, failures to start and unsafe conditions during start are way down the list of hazardous flight conditions. Sure, a carb fire is a bad thing, but the plane has a firewall, and exiting it is pretty straight forward. A start fire is the least possible safety of flight risk of things a pilot can get wrong. The only reason that the SM1019 had the start warning placard is the risk to the $150,000 engine of a hot start!

And, with placards, as flight manuals, we really try to quantify things, rather than subjective words like "over" [priming], or "must be clear of...", which are very difficult for the pilot to measure or confirm. I so dislike assembly instructions which advise for screws and bolts: "do not over tighten". What a silly thing to say. My wife can't turn it tight enough, but I could strip the hole tightening. If it matters, state a quantity, and a way to measure it if needed.

It's a real balance as to training verses flight manual information verses placarding. A lot of thought goes into what information where during approval. I encountered this philosophy while I was receiving type training on the turbine DC-3 (a very technique sensitive airplane!). The flight manuals, both Douglas original and Basler STC, are very brief. My mentor explained that for that airplane type, the main customers were airline and military, so training top heavy. Verbose manuals were less necessary, as you weren't flying it without a lot of training. But you go and buy a Caravan from Cessna, which is only a little less complex than the DC-3T, and you get a 500 page flight manual - because Cessna knows that a wealthy low trained pilot can buy a Caravan, and choose to fly it home with little or no type training, so they hope that pilot reads the manual (and they heavily placard the cockpit, so at least you read the placards when you're bored during a long flight!).

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Old 7th Dec 2021, 14:23
  #64 (permalink)  
 
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Originally Posted by Fl1ingfrog View Post
The effective fuel clearing procedure should be detailed in the Flight Manual/POH and with expanded explanations.
I agree, but I'm sure you are familiar with the brevity of the Cessna 150 POH.... I mentioned earlier that this particular school (it is not operating anymore) would have their students fly dual flights on a C152, then switch them to a C150 for their solo flights. They were suddenly confronted with a different flap system, an ASI in mph rather than KT and a different engine and they were often on their own for this experience. I'm still very glad we only had a few carb fires, it could have been a lot worse.
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Old 7th Dec 2021, 15:36
  #65 (permalink)  
 
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Pilot DAR, I haven't quoted you because I agree with all that you have written in your last post.
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Old 8th Dec 2021, 16:55
  #66 (permalink)  
 
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Originally Posted by Pilot DAR View Post
Yup!

I hadn't realized, though should have, that I had failed to clear fuel, and created a hazard for myself. My point is that you can put a lot more fuel into the airbox faster with several throttle pumps than several primer strokes. If I bungled it using the primer, I would have really got it wrong pumping the throttle for the same intended outcome.

And yes, you can really get a turbine start wrong. I have seen it from right seat! A few turbines I have flown have very strict procedures about clearing fuel after a failed start.
Pilot DAR, when you say turbines do you mean turboprop or turbojets?
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Old 8th Dec 2021, 17:42
  #67 (permalink)  
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P.A., In this context, I mean turboprop and turboshaft engines. The engine with the start warning to which I have referred is the Allison C-250, when installed as a turboprop in a Siai Marchetti 1019. I have flown the same engine as a turboshaft in a number of different helicopters, for which there is not a similarly worded placard.

I am a turbojet and turbofan neophyte! 'Never flown a jet.
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Old 9th Dec 2021, 01:41
  #68 (permalink)  
 
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Pilot DAR I'm on the flip side, I have never flown a big piston but it's on my bucket list to do that some how. The biggest thing that I noted going from pistons to Jets is Jets are more sensitive in pitch than props...
also, if you wanna go have real fun try to get a hold of any of the Learjet 20 series because they are fun and a little mischievous. Also, I'm sure you know about Handling The Big Jets...reading DP Davies you will realize that Jets aren't more difficult than props, just different in some ways Jets are easier than props.
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