PA34-200T Engine Handling?

[Simon150]

Just started my first twin rating (first hour) and am finding the engine handling to be a bit 'interesting'.

Take off and (for example) stall recovery thrust requires an MP of 39inches. Any higher than that is prohibited because it is possible to overboost the engine, but it is possible if you full open the throttle. I understand that its an issue with turbocharged engines that don't have a wastegate!?!?! All the aircraft I have flown so far use full throttle for take off/stall recovery etc.

Anyway, with the dual needle MP gauge, I found it very difficult to set take off power during the take off run, and had particulary difficulty getting 'full (29 inches)' power during stall recovery. Even moving the throttles together seemed to result in the dual needles of the MP gauge going off on their own. This seems to be made worse by the significant lag that the turbo has on the MP. On the Arrow, the throttle was very easy to set, and very direct, but that was normally aspirated.

The basic problem is that it seems to need a lot of concentration and throttle twiddling to get full power, when during this stage of flight (take off, go around etc) eyes should be out of the cockpit.

Basically, from those that have flown this aircraft, any tips? On go-around etc, when workload is particularly high do you accept that the power setting may overboost the engine for a short while if you don't get it spot on (orange light comes on), or does this really kill the engine?

Any tips would be useful.

Thanks, Simon

[csa99s]

I did my twin training on the 220T Seneca III and when I first started I thought I'd never be able to get the hang of the throttles.

The problem is the wastegate is fixed, so at full throttle at sea level you are pushing too much exhaust gas through the turbo, and subsequently overboosting the engine. The higher you go, the less dense the air and the more you can open the throttle. For the model I flew you couldn't fully open the throttle below FL110 without causing the lights to come on and full power at sea level was about half way open.

Baring in mind how little in the way of engine instrumentation you get in a Seneca, its probably a fair assumption that when the orange lights do come on bad things will eventually happen to your engines. Also, a point worth considering is that during my training I was told that I could illuminate the overboost lights twice during my CPL for a short period (ie, go around or stall recovery), so long as it wasn't much above 40 inches, without failing, any more than that and it would be a partial. So, even if it doesn't trash your engines its not a good way to pass a flying test!

What I found was that after about 10 hours of flying I developed the necessary muscle memory to be able to consistently set 40 inches most times. It just comes with practise - in the go around, whack the levers up to where your arm knows 40 inches is then leave it and wait for the turbo to kick in. Don't be tempted to readjust the throttles too quickly, the turbo lag always takes longer than you think, and if it felt right when you set it, it probably is.

The preferred method for stall recoveries was set the throttle for about 40 inches, bring the flap up, sort out the pitch, roll, etc, then go back and readjust the throttle if the MAP was either less than 39 or the orange light was on. It was understood that the power was difficult to set and you had more important things to do at the time, so a certain leeway was granted, the important thing being that you set about the right power.

Anyhow, enjoy the Seneca, one day you will line up on the runway, ram the throttles up and exactly 40 inches will appear on both sides, on that day you will feel like a king!

[A and C]

It's not quite as bad as is made out, the overboost lights come on at 40in MP but there is a safety valve in the inlet system that "blows off" at 42in MP however this valve won't re-set untill the MP is below 38in MP.

A little practice is all you need with the engine and you will get up to speed.

[Simon150]

Thanks for the feedback. I am having fun so far with the Seneca and will try some of the suggestions.

[No Country Members]

Not only will perfection come with practice, as posts above indicate, but if you go onto turbine engines next this will stand you in good stead, as same applies, you have to set the power and watch the needles for the corrrect torque or N1 speed. It's tricky at first, but comes right eventually.

[Kempus]

As previous posts it just takes time to adjust, just wait till you get hold of a turbo fan and you need to adjust all over again!

Been a while since I flew the PA34 but setting 33" initially would give 36" once the lag was over(we used reduced take off thrust) and like wise during stall recovery, go for 25" then fine tune!

figures may not be correct but you get the idea??:

kempus