Learjet 24B Flight Dynamics Issues (FSX)

[tatfsn 2]

Hi all--

 

I recently purchased the Lionheart Learjet 24B (for FSX).     

 

It's a beauty, and a real hot rod (I knew the early Lears were fast, but had no idea that they were THAT fast!).

I was also thrilled with its interior and cockpit, and the requirement that specific procedures be followed in order

that the aircraft be flown correctly and safely.    The level of systems depth is something that, up to now, has

been lacking in most of the payware bizjets out there for Flight Simulator.

 

The downside is that I experienced, in FSX, a couple of very vexing flight dynamics issues with the Lear that

initially made it virtually unusable.

 

The first is that at speeds above about 215 to 220 KIAS, the airframe would begin shuddering notably.   The shudder

and vibration would persist, even after I reduced the airspeed.     I had to abandon a number of flights almost immediately

after takeoff.    This happened a number of times, despite many attempts on my part to head it off with different flight 

procedures (and yes, I made absolutely sure that the yaw damper was on immediately after I became airborne).

 

The second, and most troubling issue was that the autopilot's altitude hold mode did a marginal, at best, job of holding

altitude, especially in turns.    In straight and level flight, it would porpoise for sustained periods over 100 feet above and

below the set altitude; at some flight levels the behavior would even itself out only after a very long wait.

 

If not for the fact that have a bit of knowledge of FSX's aircraft.cfg file, I would have had to abandon using the plane.  

Thankfully, after numerous trial and error adjustments to the Lear's cfg file I was able to eliminate the shudder/vibration.    

I've also managed to get rid of much of the porpoise behavior, but not completely (testing continues).   

 

My understanding is that Lionheart's project, while compatible with FSX, was developed primarily for Prepar3D;

in fact all of the YouTube and Air Daily X footage of it takes place in Prepare3D and in that platform, everything seems

to work perfectly.

 

FSX users, though, should be prepared for some possible aircraft handling issues and be willing to spend some time figuring

out solutions.   The plane's a beauty, and I hope that Lionheart is able to address the issues I've mentioned (I e-mailed them

as well) so that no future buyers have to do anything but fly and enjoy it.

 

 

 

 

 

[Les Parson 99]

 I also have the LHC LJ24B for FSX in lieu of Prepare3D. On the FSX forum there is discussion about the aircraft being overpowered as it relates to N1 RPM and IAS. Even though this aircraft/engine combo is known to be a real hotrod, the question remains if the model is still considerably overpowered.

 

In any case, I would be interested in which specific changes you made to the aircraft.cfg to effect the changes  you speak of. I would think the issue (s) I raise would require a FDE or .air file changes rather than aircraft.cfg. I think the former (.air) is more complex and difficult to adjust. It would be helpful if actual performance data/tables could be located.

 

Hopefully, LHC can chime in with more info at some point. I don't understand why more folks don't use this dedicated forum.

 

Les Parson

[tatfsn 2]

Hi, thanks for the feedback.

 

I initially tried recalculating the bank, yaw, and pitch MOIs, but that only made the problem worse.

 

I then changed nearly the whole [airplane geometry] section, using the Lear 35 as a reference;

it occurred to me that for whatever reason, the actual control surface area values for the Lear 24

were not sufficient to sustain stable flight in the FSX platform, given other factors in the cfg file 

(many of which I don't really understand).   

 

That all but eliminated the vibration/shuddering issue, and some of the porpoising behavior that

happened when I had the altitude hold engaged.

 

I've been tinkering with the [flight tuning] section, specifically the elevator effectiveness and the

elevator trim effectiveness values, as well as the [autopilot] section (pitch acceleration and max

pitch velocities).   Dampening the former and the latter values a bit has thus far eliminated much

of the porpoising at low altitudes, and virtually all of it when I did a trial at 15,000 feet.    At 7000

the issue is still pretty evident, though it is better.

 

I haven't yet found the right combination of values to completely solve the problem, and I haven't

tested the changes I made in all the flight regimes I have in mind, but will continue to work on

it.

 

To date, I've received no reply from Lionheart, which is disappointing.    Until that happens (if that

happens), I'll continue experimenting.

[Jimmy RFR 406]

Interesting.

 

However, I've flown it a few times in FSX with none of the issues you've spoken of here.  Hand flying, and I've even forgot to turn on the yaw damper.  Goes very, very fast, but I've really had no noticeable handling issues at all.  The only issues I've had is trying to force a landing where I was going to high and too fast (was struggling with the approach mode on the AP) and the aircraft didn't like me trying to force it down... I ended up having to do a go around, which would of been absolutely essential anyways.

 

I don't feel everything is perfect with this release, but it's pretty darn close (to me).

[tatfsn 2]

Thanks for the feedback.

 

In fairness to Lionheart, they've now replied to my e-mail and also said that they had not experienced the

issues that I'm talking about.    Since you have not either I'm all the more perplexed as to what's going

on.    The vibration issue is something that I experienced several times, and consistently, until I did the

tweaks to the cfg file that I talked about.

 

Regarding the porpoise behavior, they had some suggestions about the way I set the autopilot, and

that I may have had more than one vertical axis set, though I don't believe that I did.   I'll follow up.

They had no idea about the vibration/shudder, as they were unaware of any such occurrences.

 

For the record, I like Lionheart, and I'm really pulling for this product, but I'll have to do some more test

flying with it.

 

 

 

 

[Jimmy RFR 406]

 

 

Regarding the porpoise behavior, they had some suggestions about the way I set the autopilot, and
that I may have had more than one vertical axis set, though I don't believe that I did. I'll follow up.
They had no idea about the vibration/shudder, as they were unaware of any such occurrences.

 

Regarding the vertical axis on the autopilot - it is definitely possible to 'confuse' the autopilot by having multiple modes set.  I had an issue where I thought I was arming an approach... nope, I had the plane trying to hold altitude and heading, as well as lock the glide slope.  To be fair, the manual clearly states that you have to un-select modes before setting others.

 

I hope you get your issues sorted!

[Les Parson 99]

What about the "engine overpower" as it relates to the FDE and N1 RPM?

 

Is the general feeling it's accurate as is?

 

As you may be aware, this was one of the earlier discussions on the FSX forum shortly after the initial release.

[Glynn 405]

 

 

They had no idea about the vibration/shudder, as they were unaware of any such occurrences.

 

Are you using Ezdok by any chance ?

[~Craig~ 10]

Are you using Ezdok by any chance ?

I was thinking along the same lines .......... or Accu-Feel ?

 

If the VMO / MMO (max speeds) are set incorrectly in Accu-Feel, you get nasty vibration above those speeds.

 

 

Also.......... 

 

 

 

(I knew the early Lears were fast, but had no idea that they were THAT fast!).

 

...sorry but no matter how many people tell you they are that fast, they're not.   Climb rate referenced to N1 (with weights taken in to account) is all wrong in this model.     The Lionheart Epic and Kodiak were similarly highly over-powered on release.

[tatfsn 2]

Everyone--

 

I really appreciate the level of response and the feedback.    Negative on Accu Feel, and EZdok. 

 

I put aside the experimentation I've been trying with the aircraft.cfg file and restored the original one, to give

everything another try and a fresh look.

 

I did some more test flights, taking pains to ensure that I had followed Lionheart's guidance.   I made three

takeoffs, with the autopilot set to 4000 (no other axis set).    I took pains to keep the speed from getting away

from me (which is a challenge with this bird), and kept my rate of climb below 2000 fpm.     I then engaged the

autopilot well below the desired altitude.  

 

Still the same vibration/shudder once I neared 250 KIAS (a little later than previous times), that persisted

until I had the thing down to under 200 KIAS.

 

The autopilot might as well have not even been engaged, though it was.  The plane muddled to 4100, and

then drifted down below the desired altitude; on one flight it kept descending past 3500, and was on the verge

of going into a dive when I quit the flight.  

 

I'm at a loss as to what's going on, given that other FSX users have had no such issues.

 

I've had no choice but to resume my experimentation with the aircraft.cfg file if I want to continue to use the

airplane (which I really want to do).

[vgbaron 3,510]

Just as a FYI, I fly it in P3D2.3 and have none of the issues posted. Yes, it appears overpowered but once alt is established it is rock steady unless ASN weather bounces it around.

 

Vic

[tatfsn 2]

All,

 

I've managed to resolve most of the handling issues; just did a test in the pattern with the GS capture

mode of the autopilot and it worked great.   Still more testing to be done, but all is looking good.

 

Even better, the Lear remained rock solid in its attitude and rate of descent when I disconnected the

autopilot (which is a totally different situation from that I've experienced with other FS aircraft I've

flown!).   

 

I'm coming to truly LOVE this bird, and the 1.1 upgrade is like manna from heaven!    I think she's

going to be a keeper. 

[Mike62 29]

Do any of you have issues with fuel management after 1.1.  I did not take long enough flights with version 1 to know if the issue was there also.   After the tip tanks are depleted it is not using the fuel on the wing tanks, the engines just shut down on my system.  Am I missing something, do I need to select the wing tanks with the knob in the cockpit?  I have sent an email to Lionheart, hopefully I am doing something wrong.   Sorry if this is somewhat off topic but I consider this a flight dynamics issue when my aircraft wants to fall from the sky do to fuel starvation.

 

Thanks,

Mike Cameron

[William J.S.S 173]

The speed thing is a hard one to figure out.

I have no idea why, but I have done more reading on history of this plane than any other I have an addon for save the Q400. While this thing is a fighter jet, yes....I am still unsure about the N1 needed for correct takeoff power. I can lift off out of KSSI at 60% just fine and that does not seem right to me.

 

BUT, reading from SPEC on the engines, and from RW pilots that flew these, they are nothing short of a long fighter jet. They can climb to the point of throwing you out of your seat and bust ALT restrictions at the same time. YES...they can over-speed on one engine. If you read up on these engines....wow. Just wow.

 

Rate of climb: 6,800 ft/min

 

Maximum speed: 545 mph (473 knots, 877 km/h) at 31,000 ft (9,450 m)

 

• Powerplant: 2 × General Electric CJ610-6 turbojet engines, 2,950 lbf (13.1 kN) each
• The engines are pure stage 2 turbojet engines, as opposed to most modern jets today, which are powered by turbofan jet engines. Pure turbojet engines are not very fuel efficient, especially at low altitudes. But, the power behind these fighter-like engines is incredible. In fact, the Air Force's T-38 has this same engine.

[ray hughes 165]

^{I am also having issues with vibration of the Lear above 230 knots (in FSX) very consistent and very annoying. If you go to the outside view you can see the Tail elevators juddering}  

 

^{I would love to know what you did to resolve this matter ??}

 

^{I find the gear sound now way too loud. Kicks in at around 110 knots ... love to tone that back down.}

 

^{I have other issues with the Lear also regarding blowing out my VAS causing a quit to desktop when trying to look at the map view. I have talked to Bill about this and his recommendation would be to downscale my scenery or disable ORBX  - I am reluctant to do this. I really do like the Lear Jet but am considering hangering it until a lower res version comes out. The other option is a complete reinstall of FSX and with all my add-ons that is waaay down the list.}