Learjet 35A IAS mode

[richjb2 195]

Thanks Al!

That's a problem with after-market conversions by STC.  One STC does it one way, and another STC does it another way.  Both ways could be right depending on who's STC you purchased to install the GTN 750.  

I've been lucky the last 20 years and have not had to deal with aftermarket modifications, except for passenger Wifi….for which I repeat the above! 🙂 

Thanks for the heads up on the F1GTN file switch!

Having fun with this simulator!  It brings back memories!

Rich 

[capceo 117]

I should probably have been more specific when I mentioned that the ADCs were connected to the Mach meters. The Learjet RVSM STC that uses the IS&S altimeters (like the FSW Lear now has) installs dual ADCs which are capable of reading the indicated Mach from the airspeed indicator, as well as determining Mach speed on their own through the UNS-1. I don’t recall exactly why they derive airspeed data from the indicators, but if I recall correctly, they do. 
 

Al, as far as VNAV data being presented on the GS indicator, this is actually fairly common. As we’ve discussed, the UNS-1 installation in the LR35 will provide VNAV data, but won’t couple to the autopilot. What it will do, however, is display vertical track deviation on the GS indicator, as long as the FMS/NAV source selector is in FMS. If you switch to NAV mode, or “green needles”, the GS indicator will only provide indication of a glideslope. 

[ark 1,288]

1 hour ago, capceo said:

Al, as far as VNAV data being presented on the GS indicator, this is actually fairly common. As we’ve discussed, the UNS-1 installation in the LR35 will provide VNAV data, but won’t couple to the autopilot. What it will do, however, is display vertical track deviation on the GS indicator, as long as the FMS/NAV source selector is in FMS. If you switch to NAV mode, or “green needles”, the GS indicator will only provide indication of a glideslope. 

Thanks Joe, didn't know that. Looking forward to getting the UNS-1 in the Lear to try it out since I don't have any FMS experience.  As an aside, when you had the Garmin GTN750s installed in the C414, was there an install option to use the GS needles for VNAV deviation?

Al

Edited November 3, 2019 by ark

[richjb2 195]

16 hours ago, capceo said:

I should probably have been more specific when I mentioned that the ADCs were connected to the Mach meters. The Learjet RVSM STC that uses the IS&S altimeters (like the FSW Lear now has) installs dual ADCs which are capable of reading the indicated Mach from the airspeed indicator, as well as determining Mach speed on their own through the UNS-1. I don’t recall exactly why they derive airspeed data from the indicators, but if I recall correctly, they do. 

Thanks Joe!

That makes sense.  I only saw the IS&S altimeter in the Lear 35 simulator in Wichita when I rode copilot a few times on the side. it looks like a great system.

A story I heard about the Lear 20s when the installed the same system to meet RVSM requirements was that it improved the autopilot performance in cruise.  The Lear 20s were notorious for not holding altitude well when an altitude hold mode and for having some quirky air data performance, which was replicated in the simulator.  For example, you could rapidly but smoothly pitch the nose up and down and get the altimeter and VSI moving in opposite directions. The Lear 35 with the FC200 autopilot was the same since it shared common pitot static system.  The FC200's Lear 35's MMO is .83M, but the true Mach MMO is .81M.  The FC530 fixes the pitot static issues with the earlier Lear's.

Everyone thought that the Lear 20's 1960's autopilot was the issue with the altitude holding problems.  After the put the RVSM compliance altimeters and air data systems in the Lear 20s to meet RVSM, the autopilot altitude holding issues all but disappeared.  Turned out it was bad air data all along and not the autopilot.