AS-365 Decrease in Fuel Flow with Increase in speed
 

Just cleaning up some old documents, and came across some technical information from Eurocopter on the AS-365 family. Fuel flow in cruise shows a distinct notch for all weights at about 240-280 kg/hr. For example, at maximum weight, at sea level, ISA, the curve increases normally until it reaches a point of 128KTAS, with a fuel flow of 278kg / hr, then as the speed increases a mere 2 knots, it suddenly drops to 270Kg/hr. This change is at a consistent fuel flow of 278kg, that then drops back to 270 kg/hr for all weights (obviously different airspeeds) with a 2 knot increase in airspeed.
At 5,000 ft, the change occurs at 240kg/hr, when it drops back to 233 kg/hr for all weights with a 2 knot increase in airspeed. Much the same sort of thing happens at 10,000' when the fuel flow goes from 206kg/hr to 199kg/hr
This appears to fly in the face of common sense and previous experience.
Is there a change in rotor RPM somewhere here? Or something else????

Could that be the point at which the bleed valves close fully?

-Stan-

Bleed valve ought to be fully closed for normal flight conditions as depending on N1/Ng, but I am only familiar with RR and P&W products.

Fuel Flow

I think it caused by Fenestron. Fenestron takes less power in cruise flight.

Power absorbed by tailrotor. Classical tailrotor vs. Fenestron

Hover (IAS 0) 15% - 30%
Climb (IAS 75) 12% - 15 %
Cruise (IAS 135) ~10% - 2%!!

as you can see in hover parameters the Fenestron is not the best choice to hoist (Hover) operations. This not the answer, only comment...

Hostile:ok:

Arriel engine - bleed valve closing.

Same on all Arriel powered aircraft.

Some are electric controlled via speed sensor, 1B, 1C etc, some are pneumatic 1D, 1S .........

Dusting off the grey matter - best range in 350B, BA was with bleed valve just closed, so long as you weren't exceeding Q limits. Sometimes not possible on variants with fat engines.

The graphs may say that but in real life - more power selected more fuel used. We use 280kg/hr as a standard fuel planning figure which produces accurate fuel figures for N Sea/Lpl bay operations which are generally flown at 3000ft and below.

THe only 365N2 "trick" I have used is to increase speed as much as possible and then back off the Tq a few % and she will sometimes hold the increased speed with the reduced tq and fuel flow.

HF

Does anybody have a AFM for the 365? Prefferabley an N1. Cheers.