Throttle and Manifold pressure
We just purchased a 1979 Piper Dakota Turbo. We are used to flying Cessna's. We noticed that at 41 MP we are only halfway to firewall. Is this normal? How do you deal with a go around procedure where the your supposed to go full throttle if you need to be watching your throttle position in an emergency? Is it possible our MP gauge is wrong? Is it normal that the 41 MP is achieved at only half throttle or so?
I don't mean to sound preachy so I apologize if this does. Any question is a good one. But in this case, the best thing to do is start with your POH and see what it says.
Before engine start your MP gauge should indicate what the Kohlsmann window on the altimeter indicates when set to field elevation. The Kohlsmann window is the little window on the altimeter face.
As Jeff said, start with the POH for proper takeoff power settings and proper climb settings then fly with a CFI to obtain high performance training and the associated endorsement.
"How do you deal with a go around procedure where the your supposed to go full throttle if you need to be watching your throttle position in an emergency?" Firewall does not mean "full throttle." You stepped up to an aircraft that requires the skill and diligence to set precise power settings on takeoff, climb, go around and abnormal situations with the associated engine instrumentation.
You must understand this before you fly without proper training again or you just may push six pistons out the sides of your cowling.
Your statement "In an emergency situation you should be able to full throttle the plane without blowing your cylinders" is not entirely true with many high horse power engines. They cannot be "full throttled" without consequences of over boosting, possible damage or at a minimum, internal stress occurring. Many of those engines will have a max continuous power setting below the takeoff power setting, above the climb power setting and well below the "full throttled" position. As max continuous implies, it is an engine limitation that must be adhered to. Your maximum take off power, GA power, and max allowable climb power as you climb is also equally restrictive to achieve engine longevity.
Correct quote terminology
> It's like comparing an axe wielding lumberjack to a
> concert violinist. If you are "playing" your aircraft
> correctly,there are no abrupt inputs to power, you
> are ahead of your aircraft at all times and know
> where "max" is on the throttle quadrant
> instinctively and don't go near it.
I like that.
There is nothing wrong with your airplane, engine or gauge and there has been nothing deficient in your training. In fact, that you noticed one of the Turbo Dakota quirks and had the good sense to ask about it shows you have good judgment.
The Turbo Dakota is a quirky plane. Piper went cheap in put a fixed wastegate instead of automatic wastegate (controlled by an absolute pressure controller). As a result, the only time the throttle will be "firewalled" and get 41" is at "critical altitude" which is about 12,000' density altitude. Anything lower and you'll reach 41" before the throttle is fully opened. There is an overpressure pop-off that shouldn't allow the MP to exceed 42" but I wouldn't bet my engine on it functioning properly. 1/2 throttle at sea level is about right.
The POH does give procedures and limits but it's a bit lacking in some of the finer details like what to expect as far as throttle position vs. density altitude.
I doubt that you'll find many CFIs familiar with the T-Dakota's idiosyncrasies as Piper made less than 100 and that was over 30 years ago. You might find one who knows the Turbo Arrow as they share the same engine. In fact, the Turbo Dakota is far more like a Turbo Arrow than a Dakota.
The technique I use is to initially set the throttle based on fuel flow. At the beginning of the T.O. roll I set 20GPH on the FF. As the turbo spools up and MP rises, it will get to about 40" and 100% FF. I check the MP just before I rotate for any minor adjustments.
Yes, this "system" (or lack of it) does increase pilot workload but don't be afraid to "firewall" the throttle in a true emergency as the pop-off valve should prevent any damage to the engine.
Ignore the sanctimonious preaching in some of the previous posts, nothing you've said leads me to believe that there is anything wrong with your plane or your technique. It's just that the Turbo Dakota has a few quirks that will take getting used to (like MP will decrease, not increase with RPM reduction).
> Before engine start your MP gauge should indicate
> what the Kohlsmann window on the altimeter
> indicates when set to field elevation. The
> Kohlsmann window is the little window on the
> altimeter face.
Sorry GM, that's not correct.
The Kohlsmann window (and we all know what that is) will indicate the same as the MP gauge when the altimeter indicates sea level, NOT field elevation.
>> Sorry GM, that's not correct.
> The Kohlsmann window (and we all know what that
> is) will indicate the same as the MP gauge when
> the altimeter indicates sea level, NOT field
Yes that is correct, and to clarify the original point, to verify the accuracy of the MP instrument before engine start, subtract the normal average one inch per thousand feet and it will pretty much coincide with your field elevation.
It was about Turbo Arrows but everything that applies to them (except landing gear issues) also apply to T-Dakotas. Catch it early and it's no bid deal, let it go too long and you're looking at $17,000+.