View Full Version : Single Throttle question for Twin TP drivers

16th Jan 2017, 13:56
Dear fellow PPruners,

Just brainstorming as usual.....

I was thinking: what if the engine Control System was smart enough so that you would not need THREE different throttles for RPM/Torque and Fuel but only ONE ? Would you consider this as a very strong advantage ?

And even more crazy......:
What if, for a TWIN turbo-prop aircraft (a la King Air for example), you would have ONLY ONE throttle for BOTH engines ?

When would that be an advantage and when would that be a disadvantage ?
For pilots in the whole spectrum of experience and in all conditions (Weather, Single Pilot Operations, etc...)

Thanks for your inputs !


16th Jan 2017, 15:00
On the DH8, there are power levers, governing mostly engine torque (but at their extreme positions also assuming control over prop RPM and reverse in various ways), and condition levers, governing the propeller RPM and the fuel on/off selection for startup and shutdown.

This is a rather well working setup. The operating range of the power levers is from 1000hp rated reverse power to Ground Idle (actually a mild reverse), flight idle (the lowest setting allowed in flight, but way too much power for taxiing), the rating detent (putting the power lever into it will result in the engines being demanded power in accordance to a selected maximum rating), and beyond that the overtravel region, in which the engines will deliver maximum transient power and the propellers will be set to max RPM irrespective of condition lever position. The condition levers have 5 positions: Fuel off, Start/feather (the gas generator runs but the propeller is in feather and not producing thrust), and then 850, 900 and 1020rpm. They are only touched for startup, for setting climb and cruise power, once pushed forward during the final approach (but the RPM may keep locked on 850 if desired, it will only automatically increase when the power lever angle passes a certain value) and then for shutdown of the engine.

Sounds complicated, maybe, but itīs usable rather intuitively.

In normal operations, you move both power levers together and they might indeed be connected. But let us look at failure cases. If You have one lever per engine, you can move that lever and see how the individual engine reacts to this. During an inflight shutdown (often performed by memory on my type), itīs not only required to have both pilots verify the correct lever to be moved, itīs also a most wise idea to move the selected lever at a moderate speed to see if the systems reaction is as desired and You are not attacking the good engine.

By contrast, if you only have a button to push in this case, reversing the selection if you find it to be wrong is way less easy.

Or assume situations in which you cannot demand rated power from the engine but like to keep it running if only to provide hydraulics, electricity and/or bleed air. Some overtemperature, be it oil or ITT, or something else. With the normal, proven setup, You just retard the affected engines power lever to the required setting and use the other engine normally. How are You going to do this with only one power lever for both engines without resorting to highly complicated switching?

Taxiing. This is often done with one engine shut down or running in start/feather to save a cent or two for the company. With only one power lever, how will this be accomplished? Also, You remove a LARGE cue for the crews: should they forget to startup or unfeather the other engine for departure, with the current setup this will be easily spotted from the wrong lever settings and also immediately felt as soon as one grabs the throttles: intending to push them to the takeoff setting, but finding only one in ones hand is a slight clue of something being not as it should be. With Your proposed change implemented, expect corresponding incidents.

Mark me highly unconvinced. I strongly prefer the current setup of having separate controls for each engine to Your suggestion.

17th Jan 2017, 05:38
The FW190 had one lever combining throttle, prop and fuel control and this was in WW2 !

Alpine Flyer
20th Jan 2017, 23:45
Porsche built an airplane engine in the 1990s that used a single throttle which was briefly available in a Mooney and as a retrofit.

Some modern piston aircraft engines use single lever control as well.

While a single lever control is feasible there are a lot of reasons why pilots might want to be able to control propeller RPM independent of actual power demand.

IMHO the Dash 8-400 setup was chosen to allow for maximum similarity with the Dash 8-100/200/300 arrangement. The condition levers are not really necessary as demonstrated by the Fokker 50 which had power levers and small ON-FEATHER-OFF selectors resembling a jet layout. Power Rating and Propeller RPM setting were controlled by pushbuttons (TO, CLB, CRZ, MCP, GA).

21st Jan 2017, 04:21
The latest TBM 900 has single lever control on its PT6. The Dassault Rafale twin jet fighter has a single lever (throttle/thrust) which controls both engines. The old de Havilland Heron had four throttles, mixture and pitch being taken care of automatically.

21st Jan 2017, 05:52
That is an unusual arrangement on the Rafale and I don't see the advantage of
one thrust lever controlling both engines, simpler for the Pilot perhaps but there
are times you'd like to be able to modulate thrust separately.

Seems like you're taking away one of the advantages of a multi engine aircraft.
Perhaps someone can explain Dassault's thinking ?

21st Jan 2017, 10:23
The Dassault Rafale twin jet fighter has a single lever (throttle/thrust) which controls both engines

The Rafale has three thrust levers. The main thrust lever, plus two small auxiliary levers (so called "mini-throttles") -- one for each engine.

21st Jan 2017, 13:19
That is an unusual arrangement on the Rafale and I don't see the advantage of one thrust lever controlling both enginesI'd assume because of the switches necessary for the HOTAS functions. Bit difficult if you were to have throttle mismatch for whatever reason. As peekay4 says there are mini throttles for each engine.

Alpine Flyer
21st Jan 2017, 22:03
And with almost centerline thrust asymmetric thrust is probably less of an issue (and doesn't help a lot with maneuvering on ground).