Turbo dial & throttle combinations

[Alfredson007]

Hello forum.

Finally bought the Accusim B17, eventhough big planes usually arent my thing.

I think i can fly the plane pretty nice already dispite having it only for a day now, but one thing bugs me. It's the manifold pressure selector. I was left with the image it was making this plane easy, but it's causing me some headaches. I've read the manuals, but haven't found the answer to this.

While on a high altitude cruise it makes perfect sense. (well, i am aware this plane probably was designed to be high altitude cruiser...) I advance full throttle, take off, reduce MP selector, then when levelling off to an altitude of let's say 20kft i reduce it some more and it has done pretty much it's magic: kept the MAP stabile etc, having no need to touch with the throttles. When i descent from cold, high altitude conditions though, i feel i must keep the turbo running and reduce the throttles in order to keep Carb Air warm. (co-pilot takes care of my intercoolers)

The question goes: Does such an action (mediocre turbo, lowish throttle) do any damage on the engine? or create any other risks? I know the manual states that in carb icing that should be done, but... i use it as a precaution. If i fly slow and low, should i use no turbo, and reduced throttle, or can i keep some turbo with reduced throttle? I know the manual states that i should first lower turbo setting, then throttle, then prop then mixture, but do i need to reduce the MP selector all the way to zero prior to lowering the throttles?

Thanks so much!!

[MTFDarkEagle]

Hi,

For decent do this, and you should be good:
cruise rpm;
turbo dial @ 8 (this is to prevent carb icing);
auto lean mixture;
adjust throttle to keep about 26-27 inches MP.

This setting gives good decent performance, and doesn't damage the engine in any way.

Hope this helps,

[Alfredson007]

Hi,

For decent do this, and you should be good:
cruise rpm;
turbo dial @ 8 (this is to prevent carb icing);
auto lean mixture;
adjust throttle to keep about 26-27 inches MP.

This setting gives good decent performance, and doesn't damage the engine in any way.

Hope this helps,

Yes, it helps. I thought those parameters were meant for final landing approach only. But thanks!

If you'd tell me the proper settings for low altitude cruise with 140-150ias then i'd be 100% satisfied. So, no turbo and reduced throttle, or with (some?) turbo and even more reduced throttle for proper MAP. Thanks! Low altitude don't tend to freeze my carb so badly so i could idle the turbos. (in the summer anyway). Manual states 5000ft cruise to be flown with little less than 30" and 1500-1600rpm but doesnt tell me the turbo/throttle combination. So does it really matter how i create the MAP?

[MTFDarkEagle]

For low level flying I tend to keep my turbo selector between 4-6, depending on OAT and the speed that I want to fly in. Keep your RPM at around 2200, mixture auto-rich if you want to do some manouvering. Adjust your throttle to keep manifold pressure. I don't know by hard what setting for the manifold pressure you have to keep to get around 150. I think it's around 25-30 inches.

[Alfredson007]

For low level flying I tend to keep my turbo selector between 4-6, depending on OAT and the speed that I want to fly in. Keep your RPM at around 2200, mixture auto-rich if you want to do some manouvering. Adjust your throttle to keep manifold pressure. I don't know by hard what setting for the manifold pressure you have to keep to get around 150. I think it's around 25-30 inches.

Yes it's roughly there, the MAP is so low anyway that "4-6 and full throttle" as the checklist states for level flight won't work. (when low), that would make me go pretty darn fast with huge MAP load.

Thanks for your answers.

[Norforce]

Or use the settings that are near the 1 & 2 MP gauge

38 and 2300rpm are climb settings MP @ around 5
Cruise 2200rpm MP 34 or 2100rpm and MP 31

[MTFDarkEagle]

..text and picture...

True, but OP was asking for settings at low level, and I believe there are no "ready-to-go" power settings for that.

[r4y30n]

So does it really matter how i create the MAP?

For fuel economy, yes it does. On gas engines whenever the throttle plate isn't fully open it acts as a flow restriction that the engine has to fight against (diesels do not have throttle plates), thus, the more throttle you can use to achieve a given power output the less fuel it'll burn at that power. The advantage of turbos combined with low pressure or no superchargers (the P-47 has a standard pressure supercharger) is that it's much easier to achieve optimum fuel economy at pretty much any power level and altitude you want since you can pretty much always leave the throttles wide open and just tweak the turbos. To respond to your initial post, no, it is not detrimental to the engines to use a mixture of throttle lever and MP knob settings to make the power you want, it just isn't the most efficient way to do it.

Now when making the descent from cruising altitude, I usually don't find it necessary to mess with the MP knob from it's cruise setting, I just start killing power with the throttles to keep the carbs warm and once on final I kick the mixture into auto-rich in case I need to abort the landing. Another thing you can do to keep the carbs warm on descent is to engage the air filters early (the manual states that they can be engaged as high as 15,000 feet).

Finally, in regards to the order of operations for reducing/increasing power, the important thing to remember is that so long as MP is in the green zone it's okay to use auto-lean, regardless of MP knob and throttle settings.

[Alfredson007]

Thanks r4y30n for your great answer!

BTW. Has anyone done or found checklists for the B17 that are printer-friendly? Accusim checklists lack the information of shutting down the plane etc. Original WW2 era checklists aren't perfect for my printer.