Guys
I've never flown a turbine but one thing that has always intruiged me is when you hear pilots talk about planning ahead for the amount of response time from the stick movement to the actual response from the plane. I remember hearing Terry Nitsch talk about it being 4-5 seconds years back. I'm assuming it's gotten better since then. But my real question is why is there a lag time between the stick movement and the actual airplane responce? Maybe you guys could educate me on this and if modern technology has made it better.
Thanks
Tom

This link might present some useful information to you with regards to flying turbine powered R/C aircraft:

http://www.jetpilots.org/Turbine%20Awareness1.htm


Cheers,

Tom,

To answer your question more directly, yes, the turbine throttle lag has gotten better - although its still there. Its fairly easy to deal with, but can be critical in two areas. First, on takeoff, when you get to full throttle, if the airplane goes astray (wondering off the runway due to steering problems or a crosswind, for example), the second or two it takes the engine to wind down can be enough to drive the model hard into an obstacle. That is one reason you see jet guys tend to advance the throttle somewhat slowly on takeoff - to get the jet moving in a direction aligned with the runway before pouring on the coals. Second, on landing, if you get slow with the throttle at idle, the one to two seconds (or more) it takes to get power can be a long wait some times and can lead to trouble if you box yourself into a corner.

One of the more important throttle skills though, I think, is throttle management. That is, knowing your aircraft and its ultimate limits and pulling the throttle back, or even off, at the right times to keep the model within those, and safely in control. This activity is more important, IMHO, and somewhat independent from, dealing with throttle lag.

Bob

Hi Tom, I'm relatively new to turbines but here goes.Yes the engines have gotten better in throttle response time. But with a turbine there is only so much you can do.Unlike a piston engine you can't just dump fuel into it and expect it to run up the RPMs. Fuel flow must be carefully metered both in acceleration and deceleration. If to much fuel is added on throttling up ,you get a rapid temperature increase and if fuel is decreased to quickly on throttling down engine will flame out. It's the micro proccessor that makes these mini turbines a reality today. If you take into account also that the jet engine is not putting out alot of static thrust at lower speeds and the fact that there is no prop wash over you flying surfaces you kind of get the picture. Get yourself a flight simulator , the lag in response time is built into the turbine aircraft program. Hope I helped , Doug

If you look at the physics of it..getting a piston engine from idle (say 4000 RPM) to full power ~ 12,000RPm only has to gain 8000 RPM

A large turnbine will idle around 33,000 RPM and full power is in the neighborhood of 120,000...so you are looking at adding some 90,000 RPM, and no matter how fast you dump fuel in the combustion chamber, it is going to take some finite time to get there...same thing on the way down. The smaller turbines have a range of 120,000 RPM (or more in some cases) difference between idle and full power........

Key point by dbateman. Even with instant throttle response you don't get more air moving over the surfaces until you pick up speed, which takes time.