Taxi RPM increase

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severniae
Senior Airman
Posts: 191
Joined: 04 Jul 2009, 10:43
Location: England

Taxi RPM increase

Post by severniae »

Hi Guys,

Was wondering if anyone could help me nail down if this is correct behavour, or a bug... I'm using Prepar3d 3.2.

When I'm taxiing out, I like to use the two inboard engines (as suggested in the manual) - so I set the RPM on engines 1 & 4 to around 1000, and then select the inboard engines on the engine selector. I'm using two throttle levers - set up for engines 1&2 and 3&4 using the input configurator.

What happens - as I'm taxiing out, as the aircraft speeds up (around 10 - 15 knots) the RPM of the outboard engines seems to increase to around 1500RPM, and then makes the aircraft accelerate more. It gets quite annoying having to constantly re enable the other throttles to lower their power so I can have finer power control during taxi.

Is this normal, or have I found a wee bug? I checked for conflicting prop pitch assignments, there are none. I have RPM selector set to a button on my throttles (saitek) and that is the only configured RPM/Pitch selector in either the P3D config, or FSUIPC.

If anyone can give me an answer, that would be much appreciated.

Best,
James

joers182
Senior Airman
Posts: 118
Joined: 27 Mar 2016, 17:13
Location: United Kingdom

Re: Taxi RPM increase

Post by joers182 »

It's the same for me, I don't know why it does it or if it is correct though.
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CAPFlyer
A2A Aviation Consultant
Posts: 2241
Joined: 03 Mar 2008, 12:06
Location: Wichita Falls, Texas, USA

Re: Taxi RPM increase

Post by CAPFlyer »

I can't tell you for sure if it should be picking up 500 RPM, but it's normal for an engine to "unload" and the RPM increase as airspeed increases. This is because you're below the governed range of the propeller and as speed increases, there is less "drag" on the engine as it is "helped" through the air by forward movement and thus for the same power, it will spin faster without the prop pitch increasing to keep it the same, but because the power is below the governed range, the prop won't change.
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Piper_EEWL
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Posts: 4544
Joined: 26 Nov 2014, 14:14
Location: Germany

Re: Taxi RPM increase

Post by Piper_EEWL »

Could it also be that the engines speed up a little when they warm up? This is definitely a real world effect that the engine rpm will creep up a little as the engines warm up. What temp do you start taxiing out?
B377&COTS, J3 Cub, B-17G, Spitfire, P-40, P-51D, C172, C182, Pa28, Pa24, T-6 Texan, L-049&COTS, Bonanza V35B

Artur
Staff Sergeant
Posts: 306
Joined: 12 Jun 2015, 08:37

Re: Taxi RPM increase

Post by Artur »

I was going to start topic about it.
I don't know if that is realistic, but rather annoying as i have troubles to keep constant taxi speed.
Other A2A planes like B17 or Comanche do not behave like that, or at least effect is not such big as in Connie case.

severniae
Senior Airman
Posts: 191
Joined: 04 Jul 2009, 10:43
Location: England

Re: Taxi RPM increase

Post by severniae »

I can't tell you for sure if it should be picking up 500 RPM, but it's normal for an engine to "unload" and the RPM increase as airspeed increases. This is because you're below the governed range of the propeller and as speed increases, there is less "drag" on the engine as it is "helped" through the air by forward movement and thus for the same power, it will spin faster without the prop pitch increasing to keep it the same, but because the power is below the governed range, the prop won't change.
I thought it might be something like that, but somewhat over-exaggerated... Hopefully someone from A2A will chime in and let me know if I've found a wee buggie!

Sparky69
Airman
Posts: 23
Joined: 14 May 2010, 19:15

Re: Taxi RPM increase

Post by Sparky69 »

Hi there,

This happens to me as well. One thing I thought it might be is the FE trying to sync/match the RPM's of all 4 engines. It seems to follow your throttle positions up and down, albeit very slowly.

Just my thoughts.

Has anyone tried to taxi with the FE off?

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