Archived

This topic is now archived and is closed to further replies.

n4gix

Learjet won't reach advertised cruising speed without "Overspeed"

Recommended Posts

The Lear is advertised in the description in FSX as cruising at 450 something knots, but I get an overspeed warning at 335 at low altitudes and 250 something at high altitude. What's going on here. I am using it to cover ground quickly, but I can't get up to speed.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Check your groundspeed on the GPS, I think you'll be pleasently surprised at altitude...There isn't much use going above 35,000 or so unless winds are more favorable.Best Regards, Donald T.:-wave

Share this post


Link to post
Share on other sites

I wish I had fifty cents for everytime this same issue is brought up... I could take early retirement... ;)IAS (Indicated Airspeed) decreases as you climb as the air density drops...At flight levels you should be using Mach not IAS to manage your speed.

Share this post


Link to post
Share on other sites

>I wish I had fifty cents for everytime this same issue is>brought up... I could take early retirement... ;)LOL ...--

Share this post


Link to post
Share on other sites

Must be inflation.Back in the day ... you could only get 5 cents for such.

Share this post


Link to post
Share on other sites

The advertised speed is TAS (True air speed)Ie how fast it flies through the air (and them some hehe)

Share this post


Link to post
Share on other sites

These questions pop up because the more MS makes FS into a game, the less people will use it as a serious tool to learn the basics of aeronautics. Kind of like Call Of Duty 4, no one will attempt to learn battlefield tactics or fire discipline but instead many will simply run screaming at the enemy and spray as much ammo down range as possible in hopes of hitting something.The maximum airspeed of an aircraft, represented by True Airspeed (TAS) is not the same as INDICATED airspeed (IAS) of an aircraft. Your airspeed INDICATOR (ASI) shows speed as, you guessed it INDICATED airpseed. What's the difference?TRUE airpseed is the speed at which the aircraft is actually flying through the air. Because your airplane is not a car, it is NOT a ground reference speed. Indicated airspeed is the speed shown on your IAS which is calculated on the amount of air molecules hitting your pitot tube. At sea level, at a speed of 250kts IAS, your speed is around 250kts true airspeed because the air is dense and TAS and IAS are pretty close.At 35000 feet True Airspeed could be 450kts but your IAS will show 250kts because there are less air molecules hitting the pitot tube which is why to get an accurate speed reading at those altitudes you must transition to MACH number. The same applies to MACH number also where MACH 1 at sea level is NOT the same as MACH 1 at 35000 feet because there is less air resistance at 35000 than sea level. It is not unheard of for a 747 with a 100 kt tailwind to fly at 550kts ground speed (speed you are moving over the ground), which at sea level would only be 50kts shy of breaking the sound barrier but be flying at an indicated mach speed of .85 kts, IAS of 250kts or TAS of 450kts. What does this all mean? Your Lear jet will show 450kts on the IAS if you fly it at that speed at sea level (on a standard atmospheric pressure day @ 59f Altitmeter 29.92). At 35,000 feet 450kts is around 250kts IAS. There is nothing wrong with the aircraft if you understand what you are looking for.Take the time to learn and you will get much, MUCH, more out of FSX than buzzing yaks in Tanzania. TAS and IAS are basic concepts such as the four forces on your aircraft that allow it to fly (you do know what those are I hope?)HTH,Mike T.

Share this post


Link to post
Share on other sites

First, there is no need to be so snobby and assume I didn't do my homework. I first checked around online to find the correct cruising speed for a Lear 45 to make sure it wasn't something FSX did. Then I checked around forums to see of anyone had mentioned this before, and I found multiple threads (granted not on sim boards, because apparently google can't find any sim boards when searcing for FSX topics) that gave me answers like "maybe you need to be at a higher altitude to reach max speed..." which are obviously wrong and lead me astray. I even checked my ground speed via GPS and THOUGHT it said 400something kilometers per hour, which would be much less than 450 knots. However, from your explanations, it seems like maybe I misread the abbreviation after the ground speed on the GPS, and it was actually reading in knots. Anyway, it makes sense now that I understand how indicated air speed is measured and how that relates to altitude. The trips I was taking seemed to pass nearly as fast as I calculated when planing the trip using 450 knots as my cruising speed, so I obviously was doing just fine on speed.Thanks for the help and explanation. Perhaps it would help to have a stickied topic or section for novices with important info and FAQs, so you don't all get annoyed everytime someone asks this.

Share this post


Link to post
Share on other sites

>Thanks for the help and explanation. Perhaps it would help to>have a stickied topic or section for novices with important>info and FAQs, so you don't all get annoyed everytime someone>asks this.Just NEVER ask:1 -- What causes lift2 -- Is it throttle for speed and elevator for pitch, or throttle forpitch and elevator for speed3 -- To run lean or rich of peak....These are flight questions that might be argued for eternity, with no exact and clear answers. All the homework in the world will only get you farther confused! :-hah L.Adamson

Share this post


Link to post
Share on other sites

"The four forces that allow your aircraft to fly".That would be CPU, Graphics Card, Ram and Software, wouldn't it? ;-)

Share this post


Link to post
Share on other sites

>"The four forces that allow your aircraft to fly".>>That would be CPU, Graphics Card, Ram and Software, wouldn't>it? ;-)Correct!

Share this post


Link to post
Share on other sites

>Then I checked around forums to see of>anyone had mentioned this before, The question was asked and answered on 08/14/08, just two days prior. It was even on the same page then... ;)http://forums.avsim.net/dcboard.php?az=sho...id=452675&page=>and I found multiple threads>(granted not on sim boards, because apparently google can't>find any sim boards when searcing for FSX topics)That's odd, google typically will show posts made yesterday from here, flightsim.com, simviaton, sim-outhouse and a few dozen others...Make sure to enter your keyword(s) along with "flight simulator" and that should work best for you.

Share this post


Link to post
Share on other sites