Learjet siren >335 knots?

[Guest Nismo35]

I've been flying the Learjet lately after many hours in the Cessna and Beech 58, and at 335 knots a siren comes on. At first I thought that may have been max speed, with doubts, but saw in the plane's tech info that cruising speed is 464 knts, I think. I don't know if altitude is affecting this as I've only been up to 20,000 ft in the Learjet. It would be nice to cruise 425-450 in this plane if possible. So, why is the siren going off at 335?Thanks for any replies.Todd

[Guest JSPuonti]

That 335 is probably your Indicated Airspeed, which "drops" the higher you go as the atmosphere around you becomes thinner. That is, your IAS might be 335 at 20,000 feet when in fact you're cruising along at the equivalent of 425 knots at sea level.You can try this by flying at 20,000 feet, noting the indicated speed and then opening Aircraft -> Realism Settings and selecting "Display true airspeed" under "Instruments and lights". Once you click OK your speed should jump to well over 400.

[Guest JoeInCT]

If you have a good add-on aircraft like the LDS 767, you will see the "barber pole" on the airspeed indicator (which indicates the max speed) goes down as you gain altitude. This is not because the max speed (over the ground) is actually less as you go higher, but rather, it is because the speeds displayed on the airspeed indicator is lower than actual. This is because there are less air molecules to hit the pitot tube as you go higher into the atmosphere. This causes the airspeed displayed on the airspeed indicator to be less than the aircraft's actual speed.A good way to get an idea how fast you are really going is to open the GPS (SHIFT 3 I think) and look at the ground speed (GS). A headwind or tailwind will throw this number off a bit, but you will see the ground speed is almost always faster than the speed displayed on the airspeed indicator.When I first started flying, I would notice that I could seemingly "fly faster" (according to the airspeed indicator) at lower altitudes before I got the overspeed warning. I wondered then why airplanes would fly at high altitudes at all when they can fly faster at lower altitudes before getting an overspeed warning? The answer is because the airspeed displayed on the airspeed indicator is not true relative to the airplane's speed over the ground. There airspeed displayed on the airspeed indicator is only a measure of the number of air molecules hitting the pitot tube and there are fewer air molecules the higher up you go.Another interesting related topic is with regard to temperature. As you go up, there are fewer air molecules to "bump into" a thermometer. Temperature is actually the measure of the speed of air molecules. At sea level, there are more molecules to bump into the thermometer. If you take the thermometer higher, there are less molecules. There are areas of the atmosphere that are hundreds of degrees, but would actually feel cold to you and me (and a thermometer) -- all because there are less molecules of air the higher you go.Less air molecules = strange readings on thermometers and airspeed indicators.

[Guest PPSFA]

Max indicated is around 300-310kts depending on alt. The 400+ numbers you are referring to is TAS not IAS.

[Guest Nismo35]

Thanks guys for the explanation. Makes sense. I'm on vacation and will check the indicated vs. true air speed when I get back. Slowly learning how to use the GPS and will pay more attention to all the info supplied there. Todd

[Icon 22 11]

Todd,There is a great addon in the library for the Lear. Among other things it adds a barber poll to the Lear.