Simviation Forum - Throttle question for Twin Pilots

May 25^th, 2011 at 12:30am

snippyfsxer Offline
Colonel

Posts: 404

I have 2 Saitek throttle quadrants side by side. No matter what I'm flying multi-engine in the Sim, I'm always having a heck of a time synchronizing my throttles. Even if I have my throttles, Mixtures, or Props perfectly lined up, I always have some assymetric thrust. It isn't by much, but enough that I sometimes pull myself to one side as I'm retarding the power for landing.

Now looking at this picture that -Crossfire- posted http://205.252.250.26/cgi-bin/yabb2/YaBB.pl?num=1305011349 (the cockpit picture), I'm seeing that his levers are actually at quite different positions in order to produce the same thrust from each engine. Much more so than I ever imagined, making me think I've been trying too hard to get my simulator throttles exactly symetric. For instance, on my Cal profile for the Turbine Duke, I got it so that when my throttles were lined up, I could get about a symmetry of about 2 percent (95 n1 from #1, 97 from #2) I previously thought that was somewhat imprecise, but now that I see that picture...

So my question is this: How much difference is considered "acceptable". If I have to push one throttle an inch farther forward then the other, that is considered okay in the r/w???

If so, do you have ever have problems in the landing approach or especially during the landing flare as you pull your power back?

Back to top

IP Logged

Reply #1 - May 25^th, 2011 at 1:00pm

Strategic Retreat Offline
Colonel
Wish people were less
idiotic as an average

Posts: 603

I start this declaring I'm no twin pilot... nor pilot at all, if not of simulators, sadly, for matter of money... Sad

...but it's quite a renown fact that IRL there is no engine that is perfectly 100% similar to another. Between two very same model of engine, built in the same factory, in about the same timeframe, and kept efficient in the very same manner, you'll find ALWAYS operational differences, and these differences translates in very rarely having throttle axis lined up, like so very often happens in the various sims.

And if you keep in mind that prop governors and carburettors are similarly NOT 100% similar one to the other of the same kind, just like engines, props and mixture controls follow the same rule.

There's no really "acceptable differences" written on paper that I know of (and if there is, it is expected it should change between a plane and another). If an engine begins straying too much from the expected parameters, it simply means it needs to overhauled, but unless you use some complex payware with very complex damage modules that work per engine, I don't think you need to worry about this.

The various simulators for PC (all of them) give often a very unrealistic response to single axis throttle commanding multiple engines, like so often happens when using a joystick with a small throttle controller like mine, but being non professional softwares, consistency is often preferred over perfect simulation (and it makes the coding easier too). Consistency that IRL rarely, if ever happens.

Of course in YOUR case, you may fall straight into the rule that no throttle control is perfectly 100% similar to another of the same kind (yes, the rule is valid for PC throttles too Tongue

), and using two different throttle levers to command an engine each, you have surely a more realistic response than... than me, for example. I wouldn't really begrudge that, was I in your shoes. Wink

There is no such a thing as overkill. Only unworthy targets.

Back to top

IP Logged

Reply #2 - May 25^th, 2011 at 2:50pm

snippyfsxer Offline
Colonel

Posts: 404

Strategic Retreat wrote on May 25^th, 2011 at 1:00pm:

There's no really "acceptable differences" written on paper that I know of (and if there is, it is expected it should change between a plane and another). If an engine begins straying too much from the expected parameters, it simply means it needs to overhauled, but unless you use some complex payware with very complex damage modules that work per engine, I don't think you need to worry about this.

I frequently do use complex payware with individual engine modelling. The A2A airplanes come to mind. You have the individual engines having a slightly different response to the throttle position, plus, then you have a different turbocharger for each that has its own set of adjustable potentiometers, within the sim, so its sometimes difficult to determine whether you are dealing with a cranky engine being simulated or just that your crappy throttle quadrants needing to be re-callibrated.

There must be some standard in which the pilot goes to the maintenance guy and says "hey, tighten up those throttle cables". Again, it surprises me to see a real world picture in which one throttle needs to be a thumbs-width different than the next.

I have to say that it helps to have a dedicated flight engineer, however.

Back to top

IP Logged

Reply #3 - May 25^th, 2011 at 4:25pm

Strategic Retreat Offline
Colonel
Wish people were less
idiotic as an average

Posts: 603

In Real Life every plane engine comes with a servicing history of every part it is composed of. Not only that, but a flight crew taking command of a plane WOULD have received some sort of warning from the crew going off duty about an engine misbehaving. It is quite simple, with this knowledge to glean where the fault of the system is more liable to be. Undecided

In the sims, usually you don't have a servicing history of your plane, or even only the engines... every time you start they are brand new, and similarly, you do not have a crew going off duty to tell you if the plane you're about to take up in the air has one or more faults. Tongue

Limitations of the system. We all have to accept them. Even your engineer, cute as it is, must make due with not having opposable thumbs. Wink

There is no such a thing as overkill. Only unworthy targets.

Back to top

IP Logged

Reply #4 - May 25^th, 2011 at 4:55pm

snippyfsxer Offline
Colonel

Posts: 404

Strategic Retreat wrote on May 25^th, 2011 at 4:25pm:

Limitations of the system.

I'm actually not seeing it is a limitation. It seems that my throttles might be better synchronized than is actually considered necessary in real life judging from -Crossfire's- picture, and a couple of others I've recently seen on Airliners.net, but I'm curious what the real guys have to say on the matter. I'm still wondering if they ever encounter an annoying yawing motion when setting climb power, or retarding the throttles for landing. Obviously in the Sim, that depends on how well asynchronous thrust has been modelled (and some planes, like the Milviz 310 are REALLY sensitive to even the smallest discrepancy...whether that is accurate, or overdone, I don't know, I'm just a lousy Computer Gamer

)

Back to top

IP Logged

Reply #5 - May 25^th, 2011 at 6:51pm

Brett_Henderson Offline
Colonel
EVERY OUTER MARKER SHOULD
BE AN NDB

Gender:
Posts: 3593

Awwwww.. that cat could be my males cat's twin brother

Quote:

There must be some standard in which the pilot goes to the maintenance guy and says "hey, tighten up those throttle cables".

From my expriences (even on singles).. the throttle linkage itself is capable of manipulating the carb/throttle-body, well beyond either extreme.. so it would be a matter of mechanically synchronizing the levers, and then the "stops".... But even that can only be "good" at certain power settings (as per individual engine traits).. the levers might be in-line at 21", but not 25" of manifold-pressure... and that doesn't allow for slight differences in the MP gauges Cheesy

(or tachs, for that matter)..

Then of course there's fuel loading imbalances, or passenger/cargo loading, that might need differential yaw (by either thrust or rudder trim).

So... just put it out of your mind and use differential thrust as just another tool.. I've seen it used on takeoff, instead of rudder, in a X-wind.. and of course it can aid in ground steering too Cool

As for the AccuSim 377.. my inboard engines get warmer on climb than the outboard.. so lower MP on them until a stabilized, cool, cruise..

Since I don't have FOUR throttles, it's VC mouse thing... Same at startup.. I mouse each engine, one at a time, up over 1000rpm, from the engineer's station.. until CHT and oil-temp are all in the green.

BUT, if for some reason between 100-hour inspections; you cannot achieve max-MP, or stable idle.. then yaeh.. go see the A/P guy .. Sad

Back to top

IP Logged

Reply #6 - May 26^th, 2011 at 3:59am

-Crossfire- Offline
Colonel
Northern Canada

Gender:
Posts: 954

In every twin I've flown, the throttles or power levers have not been perfectlly lined up while the engines are at the same power setting. Just slight differences in multiple different things, I guess.

As for landing, you do have to take it into consideration. In the BE10 I fly, I pull the right power lever back further with my index and middle fingers, while my other fingers are on the other power lever. It helps keep the torques balanced in the flare. And remember, thats what I do in the right seat... it's opposite for the captain. Wink

It's a different case in the BE20 thats in the picture. With 3-blade props, the powers are brought straight to idle in the flare... so the power levers are at the exact same place, right against the gate.

Back to top

IP Logged

Reply #7 - May 26^th, 2011 at 8:09pm

snippyfsxer Offline
Colonel

Posts: 404

Quote:

the levers might be in-line at 21", but not 25" of manifold-pressure

Quote:

In every twin I've flown, the throttles or power levers have not been perfectlly lined up while the engines are at the same power setting.

Thank you, gentlemen. Sounds like I've been spending too much time calibrating my controllers to achieve a symmetry that rarely exists in the r/w.

Back to top

IP Logged

	Search the archive: