Quote from Hangar45 Admin on December 14, 2017, 9:45 am

(Original thread started on 03-09-10) by Jaap)

This is about the max altitude for the Lear45. I know it's ceiling is 51,000 feet, right? Since I mostly do short flights and seldom go higher than 30,000ft, I never came across this issue before. Yesterday I decided to make a flight of about 4 hours and set my cruise Alt. to FL500. Up to about FL380 everything went fine but when I came above that, the whole plane started to act weird. It started to sway from left to right. Slowly at first, but as altitude increased, it got worse up to the point where a crash would be unavoidable. At the moment it starts, my airspeed is around Mach0.7. I didn't have much time to look at the airspeed later because I wanted to save my flight but I imagine it has not been too low at any time. The Air File I use is from Per Alm and the Plane is ,apart from a repaint, FS9 original.

 

Idea's anyone? Does anyone fly at or around ceiling altitude? Anyone ever experienced this before?

 

(Posted by Eric Tomlin on 03-09-10)

Hi Jaap! Good to see you here in the Hangar.

 

Real-world: The Learjet 45 is certified up to FL510 but it is a rare occasion to fly that high. To get there, you need to have a light load (few passengers) and have burned quite a bit of fuel. Once you get there, you will stay there for just a little while and while you are there, the difference between MvO and your minimum safe airspeed is a very thin margin and has to be monitored often. This is due to the thin air and small wing of the LJ45. It's the same for the CitationX as well as the LJ60. This information regarding the LJ45 comes from talking with the crew of the LJ45 I visited a couple of years ago and the rest comes from various reading I've done in the past from real-world biz jet pilots. I should also mention that the real aircraft has no problem climbing direct to FL410 which is an optimal cruise altitude above nearly all commercial traffic as well as much of the weather.

 

FS-World: You have some of the very same issues as above, but it's compounded by what I have been told through reading that the FS engine has a hard time with the modeling of the extreme flight levels in FS and thus you get the dutch roll, yawing, etc. To get there, try a minimum amount of fuel and weight loading, but I'm guessing that you will find it still a bit unstable. I found with Per's modified airfile that I could fly up to about FL390-410 and then it was flying nose-high (although that was greatly reduced at lower approach speeds).

 

I just found some interesting information at the Eaglesoft forum that I read a few days ago that goes along with what I was saying:

 

"From flyultimate:

I started flying the CitationX (the real airplane) in 1998. Since 1998, I have flown at FL510 9 times. All but one time was with only the crew on board. Each time, my fuel load was less than 4,000 pounds, and the temperature was less than ISA +5. FL510 and the CitationX get along, but not very well.

 

You have to be very careful about transitioning to this altitude, in all jets. If you are heavy, and if ISA is too warm, the airplane will not make FL510. On one maintenance test flight out of Wichita, with three people on board, 3,700 pounds of fuel, a 21,700 pound empty weight, and ISA +6, the highest I could reach was 50,300 feet. She just would not go any higher. And, what Cessna promotes about the CitationX is that she will make FL410 at max takeoff weight straight away.

 

This is a FL390 to FL410 airplane. It likes this altitude range. And, this is where you will obtain your best TAS and Mach. You will get 0.92M almost all of the time with a 2,150 PPH average fuel burn. And, you will be above almost all of the weather with a smooth ride.

 

Common sense will tell you that if the airplane isn't performing very well at a selected altitude, i.e. about to stall or weaving to and fro erratically, that you probably have reached the limit for this particular flight. Additionally, take a look at some performance numbers concerning weight and temperature before asking ATC for a higher altitude.

 

I also am currently flying the Lear60 as well. And, Lear certified this airplane to FL510. But, any pilot worth their weight will realize that this is a No More Than FL430 airplane. While the manufacturer certified the airplane to FL510, getting there with the short wingspan of this plane can turn into a ride that you won't find at Six Flags.

 

Getting to FL510, with the incredibly beautiful 50 degree swept back wing, is great. The view is splendid, the ground speed is slow, the fuel burn is low and about the only thing you can hear is the hour meter clicking away the minutes."

 

(Posted by Jaap on 03-09-10)

Hmm, FL510 is awfully high indeed, but I just wanted to try it and see how it goes. However, there is still quite a bit of difference between the altitude I reached and FL510. The relation between weight and altitude is very logical when you think about it, but I never expected these wild reactions at FL380. The mentioned ideal Cruise altitude of FL410 was never to be reached in that flight, without severe problems. The part where flyultimate talks about sixflags is very accurate to what I experienced! Although it's "just a sim", I was glad to be back at FL350! I wouldn't want to experience that in a real world flight without a Pilot who knows exactly what he is doing! Nice story from flyultimate by the way.

 

I'm still curious as to what altitude I can reach. I wish I had some more time to put in my sim, but this is one on my list. I will try to get as high as I can with no Pax and little fuel. You said you did up to FL410, let's see if I can do that too! It will take a while until I can find the time, but I'll let you know in this post!

 

One more question to you as a die-hard FS9 adept: do you have experiences with FSX, and if yes, in your opinion is it really better? And that's not so much about the scenery itself (you won't see it anyway at FL410 ), but more about the handling of the aircraft, and most of all: the aircraft systems. Thanks for your answers, they're appreciated!

 

(Posted by Eric Tomlin on 03-09-10)

Hey Jaap, you're welcome! Well, I don't want to step on Per's work in any way, but as I said before I found that his model had a few issues around FL360-FL390 so I would encourage you to try the default model up to FL410.

 

Regarding FSX, I have a very strong lean toward FS9 for several reasons but I did fly FSX yesterday for the first time in about 2 months. It is 'okay', but that's about it as far as I'm concerned. The very pretty nice high resolution ground textures are nice at low altitudes, but I cannot tell hardly any difference when at cruising levels PLUS to me the FS9 textures (when used with Ultimate Terrain FS9 and Ground Environment FS9) are a much more realistic color. Add in REX 2004 and it looks like FSX, but with much better performance. The only time I see the nice ground textures of FSX anyhow are when I'm landing because when I'm climbing out from takeoff I can barely see the ground anyhow. I get okay performance, but I still prefer FS9 *even though* I have almost all the same scenery packages or FSX equivalents installed. One item that I repeatedly get annoyed at is the auto engine start issue within FSX that I cannot fix and is a suspected bug within FSX. One last thing, I hate the popping in and out of autogen within FSX. It annoys me greatly and so this is a nail in FSX's coffin for me.

 

Some of you may not know this either, but Scott Wegnar has left FSX for his new 737NG sim by the way as far as I know. He found that with all the add ons I'm running (which also includes the ENG series bloom plug in) that it really does not look too far from FSX.

 

(Posted by Alaxus on 03-10-10)

Hi Jaap, I had the same issue with Per's air file as well. I was even worse with the PM MCP. In any case I am using a air file that I found some where on Avsim, with a few of my own tweaks thrown in. And yes. I still use FS9.

 

(Posted by Jaap on 03-10-10)

Thanks for your kind answers and suggestions. I have again downloaded Per's Airfiles, and I don't know whether I had a very early version, or he updated it in the mean time, but this time it went better. I started out with 600Kgs of fuel and two passengers. I didn't even bother to taxi to the runway, but took off straight from my parking spot at Schiphol. Went right through a couple of buildings, but hey, it's a test flight.......

 

I initially set the autopilot for 2200 ft/min climb rate, and because I couldn't wait too long I accelerated the Sim speed to 8x. This took me very quickly up to FL350, and from there I went back to normal Sim speed. This time nothing happened at FL380 (!?), not even at FL410! So I kept climbing (climb rate 700ft/min). Then suddenly at FL480, the plane started swaying, slowly at first but gradually more erratically, so I decided to cut off the AP, and fly by hand. That way, the plane was reasonably controllable.

 

By the way Alaxus, I set the PM MCP to Boeing 777 instead of 737 maybe that had something to do with it too! And I still kept climbing, Airspeed at Mach .60 and dropping, while slowly decreasing the climb rate to barely nothing, I reached FL528. And then the Stall Warning kicked in! At that point it was not a comfortable flight anymore! But, I did it! Even beyond the specs! Next time on a longer flight I will go to FL410, and see if the problems are really gone! This was fun, and I guess I set the unofficial record for now!

 

(Posted by Alaxus on 03-10-10)

The code behind the 777 and the 737 are practically identical, so I don't think it makes that much difference. If you bump up the power rating in the cfg file you can get even higher, until coffin corner gets you.

 

(Posted by Mark Speechley on 09-17-14)

Hi all, It turns out Jaap attained an impressive height of FL528 but was using FS9 and was way back in 2010.

 

So not to be outdone for a fun challenge I had a go on a stock standard LJ45 using P3D V2.2. Whether it matters FSX or P3D, not sure. This was also done on clear sky. Can anyone beat mine or Jaap's ceiling? Good luck. Can tell you very curly flying at that height with increased angle of attack.

 

Here is a picture of my screen. P3D V2.2 FL527 Good luck!

 

(Posted by Eric Tomlin on 09-17-14)

Nice Mark. What I'm more impressed by is that you got high enough with that much fuel loaded on. Also, I do not recall ever seeing the N1 limit all the way to 100%, but that could be just bad memory. Finally, do you remember what your ground speed was?

 

(Posted by Mark Speechley on 09-17-14)

That's a good question,regarding ground speed. To be honest at that height trying to fly is really difficult as it just wanted to 'stall'. So didn't take note. If I can emulate it again I'll take more notice.

 

Just thought I would throw this one in as we are all busy building and forgetting the end game. My sim is in pieces at the moment redoing wiring so when I'm installing it all into the shell it will be a lot easier on the back & neck! Hopefully will be back in the competition soon. I really was trying to see FS9, FSX and P3D whether the envelope was similar. I know lots of variables but a bit of fun.

 

Tip:  When you get to FL510 or thereabouts, make sure you save the flight otherwise will have to start again.

 

(Posted by Randy Buchanan on 09-28-14)

The challenge you present sent me over to the web and YouTube where there are real planes flying at FL510 and 100% with 2000lbs of fuel. Eric I could not see the ground speed. I agree with Ron as to no fuel and I will have to get back to you after I fly higher than you and run out of fuel. Then the challenge is to find an airport and land with engines off. Maybe over Edwards Air Force base as it has some of the longest wide runways in the world.

 

How am I doing so far. Check this out:

 

So at this altitude I am at 95% power (full throttle) and about an airspeed of 154 knots. I think the definition of a service ceiling is "that altitude at which the plane cannot climb at a rate of more than 100 feet/minute" so it looks like I could go higher. Anyone else going to take Mark's challenge?

 

(Posted by Mark Speechley on 10-15-14)

Hi Randy, awesome job! I found flying at this height very unstable as you had to keep the nose at the right attitude and not stalling. You've given me an incentive to beat that now that you have the record. I was interested though if there was a difference between FSX and P3D. We are using the same flight model but wondered if the weather detail between the sims affected the planes envelope, assuming you chose 'clear'. When I put the MIP back together, game on! Are you migrating to Prepar3D?

 

(Posted by Randy Buchanan on 10-16-14)

When I fly I start by getting the real weather using REX plus HD and then start FSX using "Fly now". You are right about unstable, but at 157 knots I am not very close to stalling. I don't use the autopilot either. I do use the trim tabs a lot. Are you migrating to Prepar3d ? Are you thinking the P3D might be treat the plane performance differently? I have not done that and if I did it would probably be because of your recommendation to do so. I am not sure other members of the club have had much experience with P3D to say one way or the other. Ron has said he will. What does Wills fly? Game on is right and I think I can go higher so watch out!

 

(Posted by Mark Speechley on 10-17-14)

Randy, I have been using P3D since they started. I have P3DV2.4 update, but have the sim in bits, so have not had the opportunity to upgrade. The last few updates have not taken and so I have had to do a clean install which means re-install all the ORBX and other 3rd party add-ons. A mammoth task that can take days.

 

Migrating to P3D is a matter of time for you FSX chaps as it is the FSX code. It is FSX updated 8x so why wouldn't you? I didn't know if the performance varied but was interested enough to have this little competition to try it out. You have done well as I was flying with AutoPilot on for that height and I was pretty close to my limit. You have done really well. As I have mentioned earlier Jaap attained a height of FL528, well you have smashed that record, so look out, game on good buddy.

 

I have some Air Force cadets 'impatiently' waiting for the sim to be up and going again, so under the pump to get it going. Aiming for FL550. As for Will S., he his focused on the hardware, so he uses FSX but is close to upgrading to P3D.

 

(Posted by Ron Rollo on 07-21-15)

This is not a record but at least my personal best so far:

Randy, your FL544 will be hard to beat!

 

(Posted by Randy Buchanan on 08-08-15)

What a fun competition. I now can try for some record with P3Dv2.4. I have been doing some flying with it now and I do find some cool differences. Or maybe. One thing is the plane seems take longer to slow down. Plan ahead and according to one manual, a speed of 160Kts was recommended at about 25 miles from the destination airport. With FSX this seemed too slow, but now it works better. I do a lot of flying without using the autopilot. I think I am a better pilot for this practice and P3D seems to work me a little harder than FSX.

 

Maybe in the future we could have an IFR approach competition showing a little video of DU1.

 

(Posted by Ron Rollo on 03-09-16)

Greg and his friend Chris came down from Savannah Georgia a few days ago and we did some flying. We got a little side tracked and found ourselves trying to get the Lear45 as high as it would fly. We dumped all our fuel and headed north into some very cold air. We nearly hit 56,000 feet as we were running out of time. I do believe this is a new Hangar45 record!

 

(Posted by Mark Speechley on 03-09-16)

Wow, Having tried a few times I really know how hard this height is to achieve. Well done. At the Hangar Day 2016, I might pick your brains for a few more pointers!

 

(Posted by Ron Rollo on 03-10-16)

Actually it was more Greg and Chris coming up with the magic formula to get that high. Here are a few pointers:

 

1. Weight is key. Get rid of all your passengers and baggage in your settings.

2. Drop your fuel down to less than 10%.

3. Pick a really cold place to fly.

4. Decrease your rate of climb to 100 FPM once you get up around 45,000.

5. Burn your engines by going into in APR, (Auxiliary Performance Reserve).

 

Try this and see what you get. AT least 55,000 would be my guess.