to prevent a hot start!?

[tigerpic]

another question on this forum reminded me of something i have been wanting to know.

so far in my career after maybe 500 turbine starts (not many) in both b206 and as350, i have not yet experienced a hot start. i have had several incidents where the following happened:. .1. weak battery, 15%, introduce fuel, tot took off like a rocket, closed the throttle. .2. uhm....ok....throttle in ground idle, pressed the starter, heard it light right away, chopped the throttle. .3. weak battery, 12%, introduce fuel, tough longranger to modulate, tot 8.5 sec in transient, closed throttle. .4. introduced fuel too early/too much, t4 exploded, pulled throttle back

in ALL the scenarious, the tot/t4 did not exceed the limitations stated in the pilot operating handbook, and no tot light was ever illuminated (where fitted).

in which cases is it possible to get a hot start? i have heard pilots say "you must be sleeping to get it" and "it was impossible, because the tot/t4 came up so quickly".

[ 28 February 2002: Message edited by: tigerpic ]</p>

[Hughes500]

Tigerpic. .To answer your question I am assuming you are starting an Allison:. .1. Battery flat or weak = a) just get to 12 / 13% this will mean you will get a light off and will have to watch the 927 degree limit. More likely due to a knackered battery turning the engine as well as heavy 206 blades you will exceed the 10 second limitation. Remember there is the second stage accleration around 52% on start up. I have found on a 206 that if the battery struggles to get to 12 / 13 % you are going to have to watch things pretty closely.. .2. Starting with throttle open is careless and asking for a hot start, unless you act very quickly you will have molten metal.

3. Most other start up problems are mechanical not pilot induced <img src="wink.gif" border="0">

[aspinwing]

Another one to watch for is residual T4 - only shut down for a few minutes when pax comes back and says, "Plans have changed, let's go!" or pax arrive just as you shut down. You better crank it until the temp gets down to 150, preferably 100 before introducing fuel. <img src="cool.gif" border="0">

[Helinut]

I have been following the threads on hot starts with some interest. In general, I think it is difficult to sensibly do anything other than what the "good book" says i.e. the flight manual. Allison and Bell probably know more about their engine in their helicopter than most other people.

My experience of the Allison 250 (mainly JetRanger) is that if you do not get in excess of 12% out of the battery, you will almost certainly get an aborted or hot start, and you almost certainly will not get an engine that you can go flying with. There is a bit more scope for modulation with a Ceco system.

[tigerpic]

ok, let me clarify a thing or two:

i wanted to know how it is possible to GET a hot start. maybe i wasn't clear enough. i have never had one, because i was quick enough to understand that something was about to go wrong.

how is it possible to get a hot start? not how it works, that you will get an iron clad or an engine ready for inspection, but how is it possible to get to that point? has there been tot/t4 needles that was impossible to stop???? that is my question!

[finalchecksplease]

Tigerpic,

I believe it's a bit like a gear up landing in an fxdwing a/c some people say there are those who done it and those who will.

If you make sure the N1 get high enough (enough juice in the battery) and monitor carefully the chances you get a "hot start" are slim, but (there is always a but) if you get distracted, get overconfident or for some other technical reasons it might happen!

So I would never point my finger at somebody who’s had one, we are humans after all and make mistakes (some we get away with some we don’t) but by being professional we try to eliminate them.

[tigerpic]

thanks for the reply, all of you! i got a good answer! there is always a possibility of terminating a hot start, unless a mechanical problem. :)

[Nick Lappos]

In 7500 hours of tubine helo flying, I never had a hot start, mostly because I never pushed far enough to get one. Flat accel from a dead battery, or poor start behavior (perhaps due to dirty nozzles) are detectable prior to things getting out of hand. Unless there is something wrong with the fuel control, the engine will not jump to crazy temperatures unless you let it hang, or open up the throttle with too little N1.

[jayteeto]

I have had a hot start with a squirrel, my 3500 turbine hours were worth diddley....... .The T4 went up and I closed my motorbike's throttle....... only it wasn't a motorbike. Cognative failure maybe a reason?????

[paulgibson]

For those who may not be aware, an engineer has 2 points on a Bendix Fuel Control Unit to adjust the fuel scheduling. One controls the light-off and the other is only effective above 33%N1.. .. .Infomation passed on re start problems should include: OAT, residual TOT, light off %, first and second temp 'peaks' (TOT and N1) and 'time to idle'. This will give the best possible chance of speedy and accurate maintenance response.. .. .I was always taught that having the attitude that every start will be a 'hot one' will keep you alert to the most often early signs of impending disaster.....

[Buitenzorg]

On the B206 I've encountered 4 main factors causing hot starts:. .- pilot technique/just not paying attention;. .- weak battery;. .- bad fuel control;. .- faulty bearing in throttle linkage causing a very stiff and hard-to-move twistgrip.. .. .With a little experience in type a weak battery will be obvious when you push the starter button from how rapidly the igniter clicks and how fast the engine spools up. Also a good sign is the fuel pressure gage: if fuel pressure drops to almost 0 as soon as you hit the starter, that's a sure sign of a weak battery. JetRangers with their small batteries have problems than LongRangers (both NiCad types). NiCad batteries aren't meant to sit for long periods in charged state, so if your battery was serviced (deep-cycled) a month ago, charged, and then fitted in the aircraft that then didn't fly for a month, it will be in poor state.. .. .A bad fuel control with cause high TOT peaks during the start sequence, and the only way to find that out is to start it. To avoid a hot start under these circumstances set some hard limits for yourself and follow them. For instance, on the C30P LongRanger (modulated start) I start backing off the throttle when the TOT climbs above the yellow, and abort if it goes over 823C. A long way from the absolute limits I know, but at $15,000 for a new turbine wheel I don't get many complaints. Eventually the fuel control will have to be replaced.. .. .A certain bearing in the throttle linkage, I can't remember exactly which bearing it is, tends to go bad, which will make the twist-grip very stiff and hard to move small amounts - a real problem on a modulated start. Mechanics with some experience on the B206 will know which bearing to replace.. .. .The key to avoiding hot starts is to know the limitations, set your limits, watch that TOT/T4/ITT/whatever like a hawk, and don't be afraid to abort the start. Oh yes, and be nice to your mechanics. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[tigerpic]

there is something i do not quite understand. isn't it bad pilot technique if a pilot gets a hot start because of a weak/bad battery? was the pilot paying attention? no, i don't think so. yes, the ticking should give you a hint, but also how fast (!) the needle increases after introducing fuel (a little earlier for cold weather turbomeca operations). also, having flown the machine before, it should give you a hint that something MIGHT be wrong?????

[robik1]

Hi!

I have a problem during start with one B 206 jetranger III the TOT went to 850 degress celsius for 5-6 seconds , last saturday 8 of 10 starts had this high TOT no mather it was first start with cold engine or warm engine after 20 minutes cooling. We have anoither three B 206 they dont have so high TOT during start. I said this to our maintenance guys and the told me that this normal. This high TOT were in outside temperatures from 15 degress celsius to 40 degress celsius


Is this normal or????????????

Thanks!

[mfriskel]

Is it a C20R engine?

[nouseforaname]

if it peaks at 850 you don't have a problem probably could get reduced one click to make it cooler, but peaking at 850 no problem it shouldn't hang there though.

I've found that engineers and engine shops all have a slightly different opinion. Some say hot (ish) start means start is faster meaning less thermal stress on the engine. Some say high start peaks torch the back end over time meaning that when you do your hsi you will probably need new 3 or 4 wheels. Most of our starts peak about 810 think it's a happy medium. Not saying that is 100% right though.!

Remember magic number is 927 deg c get beyond that your in for some serious $'s

[Hughes500]

take the battery out of one of the other 206's and use in the " hot " machine and see what happens, most lead acid battereies only last a couple of years

[Savoia]

This ship is also touching 850 on its start.

As said, not that unusual but, the fact that it was cooler and is now hotter may warrant further investigation:

JBXryrtENE4&feature=related

[P1DRIVER]

This ship is also touching 850 on its start.


Which gauge are you looking at ???? I only see it get to 750 throughout the start sequence.Slightly cold if you ask me. I was always told Hot and Fast. ( bit like my favourite pastime )

:ok:

[Saint Jack]

P1DRIVER is correct, 'hot and fast' is the correct way to start a 250 series engine. There is a CEB/CSL (sorry, can't remember which) addressing this issue. Some, but not all, FCU's have adjustments to control light-off temperature and the acceleration - don't get them confused. When making these adjustment you MUST have; a) an experienced engineer, b) an experienced pilot, c) a good, preferably external, power supply and, d, this is the one a lot of people forget, position the helicopter into wind.