This link is for maintenance engineers on the PT6, but has some useful background, especially on how many different PT6 models are out there.
http://www.unitedturbine.com/pdfs/PT6%20Training%20Manual.pdf [ local copy 14MB ]
Normal SOP is that you want to see more than 24.4v on each battery before starting. Being a free turbine you gain on some bush pilot robustness what you might lose on efficiency. You also disconnect the batteries for overnight stops.
They take time to cool down, so you need to ‘motor’ them to bring TIT below 120 o, even after half hour to one hour turnaround time on the ramp. Low batteries, and failure to ‘motor’ during a start when they are warm probably accounts for most hot starts.
Yes, finding the people would be the hardest thing of all.
In general, people join syndicates because they cannot afford to go it alone. So, by definition, these people are on the limit of their finances – otherwise they would not be in a syndicate!
This is why many/most syndicates have difficult political problems. Basically everybody (in this case) is in it to get the most out of it. And in many syndicates you get a dominant member who takes the p1ss but because he is a forceful personality nobody else wants to fight him. One example is a member who keeps doing short foreign trips (out of the UK) and pockets the fuel duty drawback, so he gets a free flight, paid for by the other members. Then you get arguments about maintenance… Also some people go into homebuilt syndicates to get maintenance done by somebody else because they can’t do it and the alternative would be to pay someone which then defeats the point of a homebuilt (which is sure to p1ss off the other(s) – I can probably think of two cases).
Anyway, we have had numerous threads about why syndicates have problems. But it’s all relevant to even a TBM, especially if you want to be doing owner assisted / freelance engineer maintenance and not throwing tens of thousands at a company to tick 3000 boxes.
But not everyone goes into a syndicate to minimise money spent. Some will go into it because they would not fly enough to make good use of the (expensive) plane. And some will do it so they have reasonably assured flying partners. These people will have more money kicking about than they need for their share, and that is vital because you don’t want arguments over money.
RobertL18C wrote:
They take time to cool down, so you need to ‘motor’ them to bring TIT below 120 o, even after half hour to one hour turnaround time on the ramp. Low batteries, and failure to ‘motor’ during a start when they are warm probably accounts for most hot starts.
Indeed. Turbojet engines are far quicker to cool down. Hot starts should never happen but I had Cessna doing some work a few weeks ago and they had plugged in a avionics GPU during the day but had seemingly not quite pushed the plug in so had actually just run the battery down. In going to start with them in the plane I had 21 volts. Easy to not look when you are used to the plane and the battery. Called for a GPU and all was good. Even though the FADEC should have stopped the hot start I would prefer not to test that part of the software.
More common Peter is a TQ exceedance which is really a non event (if a small one). Easy to happen in non-FADEC (ie all PT6) engines on takeoff as the airflow picks up and the TQ rises during the takeoff roll. There is a mechanical torque limiter which prevents something really bad. Setting that limiter involves deliberately going past the torque limit on the ground runs.
On the PT6 installation I am familiar with you have to learn by experience the torque setting for the start of the take-off roll, because it rapidly increases as airspeed increases. It is very easy to overtorque the gearbox.
So, what prevents every TBM700 getting buggered very quickly?
During takeoff, one is not very likely to be looking at engine instruments. Well, not the whole time.
Peter wrote:
So, what prevents every TBM700 getting buggered very quickly?During takeoff, one is not very likely to be looking at engine instruments. Well, not the whole time.
Part of training on them is learning how to deal with it. It isn’t that hard but you do have to glance at the instruments during the roll. The best way as Neil says is to know the approximate TQ that works. As these are very powerful engines you are better being a little underpowered on the takeoff roll by say 20-40ftlbs than generating an exceedance.
That’s why on the Meridian is was flying, I used to said the owner to put 1200ftlbs on take off and I was adjusting the power during ground roll…
Never had a exceedence that way…
Romain
Hot starts don’t have to cost anything more than the inspection, if nothing was damaged. Best case scenario. A really hot one will probably mean replacing most of the stuff after the compressor.
One thing to keep in mind is cycles. Case in hand – my right engine needs a hot section inspection in about 450hrs. But, because one of the turbine wheels only has 137 cycles left (because they put in a used wheel with less cycles last HSI) , I’ll have to “open” up engine when those cycles are up. A cycle counts as a start, flight and shutdown. With lots of shorter flights, the plane cycles out before the hours do. This would be something to consider in a group where perhaps half the members use it for just shorter flights – the cost will go up. Turbines are not ideal for just bimbles.
Unpopular fact, but a Garrett twin will be cheaper to maintain and feed, than a PT6 single in most cases. Just something to keep in mind. There is of course the higher weight of a twin to consider, which will affect enroute and landing charges etc.
A really hot one will probably mean replacing most of the stuff after the compressor
Doesn’t it mean that on a real Hot Start the pilot did not watch the rather rapid EGT rise and cut off fuel in time?
Another scenario with axial compressor engines leading to a hot start could be high wind speeds and their direction before starting, i.e. the compressor is windmilling in reverse. If you do not realize this and reposition the plane you can easily get too hot conditions.
This would be something to consider in a group where perhaps half the members use it for just shorter flights – the cost will go up. Turbines are not ideal for just bimbles.
What I am thinking of would use the plane purely for long trips; say 1hr minimum and probably 3-4. At 270kt (economy cruise for a TBM700) that’s quite a long way. I cannot see anybody using a TBM for local messing about; the windows are too small and it’s hard to get half decent photos out of any of them (thickness, etc). It cannot be risked on grass unless you are extremely confident (or it’s somebody else’s – Air Touring used to do demos on grass) and frankly you would not want to risk it to some hard runway places I’ve been to because they are covered in rocks.
