Dash 8, how to fly

[Guest]

Hi,first of all the dash 8 is a master art. Thanks so much.Now the question:Can someone explain the interaction of the rotor torque and the rpm.ThxTFT

[Guest jonpoint]

TFT,Torque vs. RPMThe Dash-8, being a turboprop, is slightly different to a 'normal' prop aircraft when it comes to prop settings.Firstly, please understand that you don't have a turbine RPM gauge so you cannot immediately see the result of increasing or decreasing throttle. FU3 doesn't provide turbine gauges for props :-(What you have to do is just make sure that the prop RMP is ~1060RPM all the time. This requires no input from you - it's automatic (assuming you have pitch set in 'Auto'). If the prop RMP is anything different (whilst flying), something is wrong :-(Beyond that, refer to the torque gauges to tell how much power you are delivering to the props - it's that easy ;)The reasons for the major difference to other aircraft is that turboprops generally use constant-speed props with an automatic pitch controller which adjusts pitch to keep prop speed constant. If you were to increase the throttle, just as the turbine (and eventually prop) begins to speed-up, the pitch controller applies more pitch until the RPM is back to the preset revs (1060RPM in this case).The reasons for constant-pitch props are many but in this case they include:1. It reduces strain on the entire drivetrain by not having the 'drive' part of the engine constantly changing speed.2. It provides a smooth method of engine control - jet turbines have a power output proportional to the square of the turbine speed. This is like a piston engine running 10x boost. Rev it a little and it 'takes off' and next thing you are at full power.3. The constant pitch controller prevents the turbines from over-revving by providing a braking force (via increased pitch).4. It provides better synchronisation to avoid the 'cyclic drumming' we are familiar with when flying twins.5. It allows for the use of anti-noise equipment. The Dash-8/Q-300 is renowned for it's computer-controlled noise reduction systems which give a much quieter ride than the old F27! Without constant-speed props, this last feature would be far less effective.The main thing you have to do when flying the Dash-8 is not worry about it. Leave the pitch in 'Auto' and use the throttle alone to make power changes. Try to use small increments of throttle to keep the speed constant. Also, due to the 'fiddled' engine settings, leave mixture alone (full rich).I hope this makes sense! Maybe someone has a simpler, better explanation. I have never had the opportunity to fly a turboprop in real life and I know a few here have ;):-waveJon Point*************************(effyouthree@hotmail.com)*************************

[Christopher Low 5,341]

You mean that you guys actually worry about what the gauges are telling you ? :-eekChris Low,ENGLAND.

[Guest]

Hi Chris,you do not worry of the fuel gauge in your car?:-eek If I know what tells me, I can easyer handle the plane.:-hah

[Christopher Low 5,341]

Well, I do check the altimeter, and the airspeed indicator, and the amount of fuel left in the tanks.....but as for the RPM indicator in the Dash 8......well, let's just say that I am not aware of this. I fly it entirely by "feel", so what the torque gauge indicates is rather irrelevant to me :-)Chris Low,ENGLAND.

[Guest R_Driscoll]

One useful gauge for me is an external one:undercarriage straight = good landingundercarriage bent = bad landingundercarriage in next country = very bad landingAs you said, Jon, this would be a great plane for Americans, where you could take slightly longer trips than in UK. Congrats again on this masterpiece.RobD.

[Guest Motormouse]

Hi, me again:-)"The reasons for the major difference to other aircraft is that turboprops generally use constant-speed props with an automatic pitch controller which adjusts pitch to keep prop speed constant. If you were to increase the throttle, just as the turbine (and eventually prop) begins to speed-up, the pitch controller applies more pitch until the RPM is back to the preset revs(1060RPM in this case)." ;)"In a turboprop engine output power is in eshp,(equivalent shaft horsepower) but is converted to a maximum torque figure (torque being the turning load applied to the propellor by the engine) for ease of use.The automatic prop pitch controller is basically just a flyweight/bobweight governor.Here's a more detailed description...The constant speed governor is based on standard centrifugal governor principles. The earliest application of this concept was made on a steam engine in 1788, by James Watt, the English inventor. The aircraft constant speed propeller governor is used to direct oil flow to and/or from the prop, thereby modulating blade angle (B.A.) A governor is an RPM sensing device It responds to changes in RPM by directing oil pressure to or from the propeller until the preset RPM is restored - governing RPM Basic configuration (components) A drive shaft - connected to engine; runs 80% to 110% of engine RPM, depending on gearing Oil pump drive gear co - located on drive shaft, and meshes with driven gear (operates exactly like engine oil pump, is a gear type pump). It boosts engine oil pressure to approximately 270-310 psi. And a Pressure relief valve - bypasses any unused oil to governor oil inlet. A Pilot valve (also called pilot spool) - located in the center of the drive shaft, directs oil through ports in the drive shaft, sending oil to or from the prop The Fly weights - adjust the position of the pilot valve. They are "L" shaped. During rotation centrifugal force exerts an outward force on the flyweights. As the fly weights tip out, the pilot valve is raised. A Speeder spring - located on top of the fly weights. It opposes the centrifugal force exerted on the flyweights. "On-speed condition"Fly weight and spring force are matched, and the pilot valve remains in the neutral position. Negligable oil pres. moves to or from the prop "Over-speed condition" Engine RPM is higher than governing RPM, so the centrifugal force acting on the fly weights is stronger than the speeder spring force, and the fly weights tip out, raising the pilot valve. Oil flows, either to the prop or from the prop as necessary to increase B.A. until engine RPM matches governing RPM "Under-speed condition" Engine RPM is below governing RPM. Centrifugal foce, acting on fly weights, decreases and speeder spring force causes the fly weights to tip in lowering the pilot valve. Oil flows to the prop or from the prop as necessary. This decreases B.A. until engine RPM matches governing RPM By increasing or decreasing speeder spring pressure being exerted on the fly weights, we can set the RPM at which the forces will balance each other, and thus center the pilot valve. This is called "governing RPM" And finally...."It allows for the use of anti-noise equipment. The Dash-8/Q-300 is renowned for it's computer-controlled noise reduction systems which give a much quieter ride than the old F27! " He-he thats' when it is working!!:-wavePete

[Guest jonpoint]

Thanks for that, Pete ;)I attempted to avoid a technical description but that is exactly what was needed. Thanks.On the noise-reduction system, I can agree that when they don't work 100%, they are worse than non-existent :-(I have been involved with a few industrial systems over the years. My original background was in communications systems and audio engineering so I understand only too well that for any cancellation system to function, a large number of factors must be balanced.To those unaware of how these systems work, basically, they 'listen' for noise then 'feed-back' the same noise but with opposing phase such that (supposedly) the two signal cancel out in the listeners ears. Due to reflections, phase delays, air movement (and listener movement...), cancellation is never 100% but, in controlled circumstances (i.e. a laboratory), a measurable reduction can be achieved.An aircraft cabin makes a reasonable 'lab' in that the acoustics can be controlled to a great degree and, in this case, the frequency of the offending noise is fairly constant (a 4-bladed prop @ 1060RPM gives about 71Hz). The only real issue is amplitude balance. In some parts of the cabin it will naturally be quieter than others - these parts require less energy for cancellation. However...Where all of this falls down is the fact that it relies on our brains to do the 'subtraction'. Our ears still receive the combined energy of the original source and the cancellation source :-( . This means we are actually being exposed to TWICE the signal level than if the system never existed. Have you ever stood in a noisy place and had someone close by yelling to you so loud it hurt - but you still couldn't understand what they said? This is the effect caused by these systems. Instruments will tell you it's working. Your ears will tell you it 'sounds' quieter because you cannot distinguish the sounds as well BUT, in reality your ears hurt, you can't understand the guy sitting next to you and when you leave the area, your ears ring. This is why they have a dubious reputation. Those systems that seem to work properly still annoy the cr** out of anyone within earshot. Or the poor residents who dwell a few km from an industrial facility - all they can hear at night is the whine of the cancellation system!Nice in theory though :-waveJon Point*************************(effyouthree@hotmail.com)*************************