Turbo lag?

PanJet

PanJet

Well-Known Member
Lately I've gotten back into flying and teaching in a Piper Turbo Seminole, and there's one thing that I noticed and was reminded of about that plane that always was peculiar. Whenever you go from really low power settings to high power settings too quickly (i.e. go-arounds, power-off stall recovery, etc), the engines shudder and don't really respond as quickly as most planes I've flown. I was wondering if it has something to do with a sort of turbo lag or just simply the fact that they're not fuel injected. Do most turbocharged aircraft respond this way?
 
The Seneca II I fly does this on takeoff. One turbo will kick in before the other, requiring rudder input to correct.
 
I owned a PA-28-201T Piper Turbo Dakota and experienced the same thing. A mechanic told me that the turbo wasn't activated below something like 27" MP. Above 27" you could hear the turbo "scream" and feel a power increase.
 
meritflyer said:
I owned a PA-28-201T Piper Turbo Dakota and experienced the same thing.
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I infer from the OP that the power during a go-around is below what he would have experienced in a non-turbo aircraft. A delay between normal power and any extra turbo power would be understandable.
 
I am sorry, I am only familure with jet lag..............I'll let myself out, thank you!:D

BTW, Are you at Accuwings?
 
tgrayson said:
I infer from the OP that the power during a go-around is below what he would have experienced in a non-turbo aircraft. A delay between normal power and any extra turbo power would be understandable.
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Actually there is plenty of power, it's just that it reacts slower than all of the non-turbo aircraft I've flown, and is often accompanied by a bit of a shudder in the engines. I guess the good part is it's kinda like doing a go-around in a turbine aircraft. With the lag you have to plan ahead. ;)

CirrusMonkey, if you were asking me, no I'm not at Accuwings. I'm at a small private university in SE Washington state.
 
I have noticed something similar flying a Bonanza B36TC (Continental TSIO-550) Although its injected, when you add takeoff power (if you do it too quickly) the engine will power up to 30" fine but will have a slight delay as the turbo spools up for the full 40" of M.P. After it spools up you better be ready for the fright train though.. :-)
 
The compressor wheel, in a lagged situation, becomes a huge obstruction in the intake path. Hesitation is normal due to lag, but stumbling or shuddering means you're adding power too fast.
 
PanJet said:
Lately I've gotten back into flying and teaching in a Piper Turbo Seminole, and there's one thing that I noticed and was reminded of about that plane that always was peculiar. Whenever you go from really low power settings to high power settings too quickly (i.e. go-arounds, power-off stall recovery, etc), the engines shudder and don't really respond as quickly as most planes I've flown. I was wondering if it has something to do with a sort of turbo lag or just simply the fact that they're not fuel injected. Do most turbocharged aircraft respond this way?
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Turbos are not instantaneous power, they always take a few seconds to spool up, usually considered inefective below around 1200 RPM. but the shuddering is not usually caused by the turbo. As an A&P, if I got that write up, I woould first check the mixture, and if that checks good go to the timing..... then go from there...... partially blocked fuel injector, etc. Do you notice a slow climbout, or what is your max RPM on the Run-up, what is the mag drops?
 
make smooth increasing power changes. if you go too fast you'll flood the engine and it will die. this is especially true to the new columbias and others with a dual turbo on them.
 
I do not have much experience with turbo airplane engines but I have a good amount with turbo car engines. In a car if you are in a high load/low rpm situation the engine will bog down and shutter if you try and go full throttle all at once. In a car this is partially due to the load of the transmission. I would assume that the same sort of load is placed on the engine when going full throttle by the prop changing pitch and taking a bigger bite out of the air.

One draw back of a turbo engine is they tend to be higher compression compared to a naturally aspirated engine. This decreases their low end torque in favor of high end horsepower. If you Compare a Supra Dyno sheet to a Mustang GT dyno sheet you can see the difference.

Supra
dyno.gif



Mustang
8780-2001-Ford-Mustang-Dyno.jpg


The mustang has almost peak torque from a very low RPM. The Supra needs to wait for the turbo to spool to get the torque you are asking for. The shuttering you feel is the engine struggling to spin the props.

You can stop the shuttering and actually get the power you want sooner by adding throttle in slightly slower but steady pace rather than all at once. When you go full throttle it causes the engine to fight itself. It is dumping fuel in thinking it is getting more air, which actually cools the charge going through the hot side of the turbo. Since turbos rely on the expansion of hot gases you are reducing its efficiency which takes the turbo longer to spool which makes you wait longer for the power you want.
 
Baronman said:
I agree with other posters about smooth application of power....Don't just "jab" the throttles open.
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This is what I've learned as well. A smooth and steady application of power works very well, and I've gotten quite used to it myself. It's a bit different trying to teach students who've never flown in a turbocharged aircraft and are used to jamming the throttle to the wall on a go-around or stall recovery, etc. It's also different because the Turbo Seminole does not have automatic waste gates, so you have to watch the students like a hawk so they don't try to blow up the engines on a go-around. At about 1200 ft. density altitude, (approx. alt of our airport), redline manifold pressure is maybe 1/3 to 1/2 forward on the throttle quadrant.
 
PanJet said:
.....students who've never flown in a turbocharged aircraft and are used to jamming the throttle to the wall on a go-around or stall recovery, etc. It's also different because the Turbo Seminole does not have automatic waste gates, so you have to watch the students like a hawk so they don't try to blow up the engines on a go-around. At about 1200 ft. density altitude, (approx. alt of our airport), redline manifold pressure is maybe 1/3 to 1/2 forward on the throttle quadrant.
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makes you wonder just how many times its gone past redline....
 
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