Lear 35A Profile in SimBrief - Need to Discuss Issues With This Profile

Greetings,

I am assisting the developer of Flightsimware’s Lear 35 as a beta tester. I am a former Lear 35A pilot and flight/simulator instructor on the airplane. I have direct knowledge of the cruise performance data for the airplane.

The SimBrief profile contains the following options for normal cruise and descent profiles:
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These profiles are from the Lear 35A Pilot’s Manual for the FC 200 autopilot. The model that FlightSimWare is modeling is the Lear 35A with the FC 530 autopilot with the Rosemount pitot-static system. The FC 200 aircraft have a known issue where Mach Indicated (Mi) speed is significantly higher than Mach True (Mt) airspeed. Here is a Normal Cruise speed chart for the Lear 35A with the FC 200 autopilot:

At 13,500 lbs., Normal Cruise M = 0.77. For an ISA day, the True Airspeed is 432 KTAS with fuel burn of 1010 lbs./hour.

Here is the same Normal Cruise chart for the Lear 35A with the FC530 autopilot & Rosemount static pitot static system:

At 13,500 lbs., Normal Cruise M = 0.75. For ISA day, the True Airspeed is 432 KTAS with fuel burn of 1010 lbs./hour. This is the same as KTAS and fuel burn for the Lear 35A with the FC 200 autopilot. The discrepancy between the two Mach speeds is because in Lear 35As with the FC 530 autopilot, Mi = Mt, while in the FC 200 autopilot airplanes, Mi is 0.02M greater than Mt.

In the Simbrief profile for the Lear 35A, you might be converting the Mach Indicated Normal Cruise Speed of M0.77 into a KTAS based on outside, which is commonly done by the professional flight planning systems. We can see from a flight today, that Simbrief computed a True Airspeed of 447 KTAS based on a Mach of 0.77. However, M 0.77 is the Mach Indicated, not Mach True for the FC 200 autopilot airplanes. In the Simbrief profile, the KTAS should be 435 KTAS for the Mach Indicated of 0.77.

Since the FC 530 autopilot and FC 200 autopilot Normal Cruise charts are identical except for the Mach Indicated speed to be flown (M 0.75 for the FC 530 autopilot verses M 0.77 for the FC 200 autopoilot), an easy fix is for the Simbrief profile is to change the cruise speed drop down box from M 0.77 to M 0.75. Also, the KTAS calculation has to be changed to use M 0.75 instead of M 0.77.

Also, the Descent Profile in Simbrief needs to be changed to 81/350/250 since Mmo in the Lear 35 with the FC 530 autopilot is M 0.81 as opposed to M 0.83 in the FC 200 autopilot airplanes.

Flightsimeware is modeling the FC 530 autopilot. These changes will help the user community match the airplane’s performance when they update the flight dynamics and engine modeling.

If needed, I can furnish Simbrief with a full set of current Lear 35 FC 530 autopilot climb, cruise, and descent performance data.

Please contact me directly if you have any questions about this request.

Thanks!

Rich Boll
Wichita, KS.