A Fix for the Bouncing B-52H

[JerryH]

I'm not the first one to say this, but my hat is off to Bonzonie (Kotaro Akikawa) for his marvelous B-52H design for FS2002.  Behind this work of art is a huge amount of technical data and, not surprisingly, a few problem areas.  Needless to say, beta testing doesn't always catch all of the problems.

During the past year, I've read about (and experienced) the "Bouncing BUFF" problem in FS2002.  For me, it occurs on the ground at partial fuel loads of about 60% or less.  During the landing roll or the start of takeoff, the tail of the B-52 will bounce high in the air, over and over, with the aircraft often ending crosswise with the runway with its nose on the ground and the fuselage in the air.  Not a pretty sight.

The problem is in the contact_points section of the Aircraft.cfg file.  The contact point for the Rear main gear is missing.  This missing point is not visually obvious because the aircraft looks normal on the ground.  However, the aircraft is actually only supported by the Front main gear and the two outriggers.  At lighter fuel weights, the center-of-gravity apparently shifts enough to cause this "tripod" arrangement to become unstable.  That, I believe, is what has happened and why it was not easy to discover.

Because of concerns over ownership, I contacted Kotaro by email on June 10 with my description of the problem and the proposed solution.  In his response he stated that he would not be able to verify my findings due to some PC issues.  He also said he would be pleased if I would post the fix and share it with the community.  I appreciate his confidence.

The fix shown below is rather easy, but if you're unfamiliar with file editing be sure to back up the original file before trying to do any revisions. Any text editor should work. I use Notepad.

    Open the Aircraft.cfg file with your text editor.
    Locate the [contact_points] section near the end of the file.
    Copy all of the data for point.0 and paste it just after the data for point.6.
    Edit this new line so   "point.0=1.000000,16.000000, . . . . . . . ."
                                  now reads   "point.7=1.000000,-34.000000, . . . . . . . ."
    Save the file.  The new contact point should read as follows:

point.7=1.000000,-34.000000,0.000000,-12.083333,3750.081701,0.000000,3.941352,41.520000,0.861471,2.500000,0.916691,10.000000,10.000000,0.000000,0.000000,0.000000

That's it.  This fixed it for me and made the BUFF usable again.  It now rolls normally regardless of the fuel load.  I hope this fix works as well for anyone else who tries it.

Cheers,
JerryH

This message will also be posted on other FS2002 forums.

[snazm]

Thanks for the info  :D

Maybe you should make a copy of this in his Wireframe forum below?

[WebbPA]

Thanks Jerry,

I can't wait to try this out.  I've experienced the ac flipping over and my only previous solution was to take off with full tanks and dump some fuel before landing.  I mean trying to land.  Not very thrifty or environmentally friendly.

There is also a known fix for autopilot problems here http://www.avsim.com/pages/0202/b52_rev ... eview.html.  I never experienced the ap problem because I applied the fix before I ever flew.  So I guess it works.

Now if we can just get that panel from Tipster ...

[WebbPA]

I've applied this fix and it doesn't work for me.  I want to make sure I did it right.  I now have a new line:

[contact_points] ...
point.7=1.000000,-34.000000,0.000000,-12.083333,3750.081701,0.000000,3.941352,41.520000,0.861471,2.500000,0.916691,10.000000,10.000000,0.000000,0.000000,0.000000

(Cut & pasted from the .cfg file)

Tested at 25% and 50% fuel and various flap configurations (50-100% extended)  the ac nosedives into the runway at about 125 kts.

Anyone else?

[JerryH]

Jim,

I'm as disappointed as you are.  Yes, your new contact point is identical to what I have.  Having the rear gear added was like night and day for me which is why I shared my find with you and others.

I'll go back and flight test some more conditions to see if I can duplicate your problem.  Incidently, I am not affiliated with Kotaro or his beta testers.  Just a stubborn retired Boeing guy who knew there must be an answer for a misbehaving B-52.

Regards,
Jerry

[JerryH]

Jim,

I just remembered another thing that I learned during my detective work.  Fuel consumption is carefully managed for this aircraft.  In other words, 50% fuel remaining doesn't mean all nine tanks have 50% fuel in them.  Fuel is drawn from the tanks in a specific sequence in order to control the position of the center-of-gravity.  I flew the aircraft for many hours (in slew mode to save time), stopping every half hour or so to note the status of each fuel tank.  My numbers for each tank are shown below for a total fuel load of about 50%:

Left Aux        0%
Left Main   41%
Center 1   100%
Right Main  41%
Right Aux    0%
Center 2    100%
Center 3         6%
Right Tip    100%
Left Tip         100%

You might try these to see if it makes any difference.

Good luck.  Looking forward to hearing some better news.

JerryH

[WebbPA]

Jerry,

I have been starting flight with all tanks set at the same percentage of fuel.

I know that in-flight consumption is not uniform, as you can see from the gauges (extreme upper right).

But I thought your fix was for takeoff, so fuel  consumption should be irrelevant.

Since you haven't duplicated my problems I'm going to reinstall a backup of the aircraft and apply, first, only your fix, then the autopilot fix.  If I can taxi and take off the ap fix shouldn't be the problem - I see that you have already applied it without ill effects.

Two more factors to consider:

I have only flown the first ac that pops up in the window (2nd Bombardment Wing), and

I've tweaked the panel.cfg file.

I can't see than either of these would make a difference but you never know.

[WebbPA]

Jerry,

I think I have an "ID Ten T" error.

I should have seen it when I saw your fuel configurations.

I had been changing the first 5 tank levels, never bothing to move the slider to see that there were 4 more tanks.  Leaving C2 and C3 at 100% seem to account for my problems.  And this may account for some or all of my landing problems.

In my defense I note that there are only 5 gauges visible in the panel.

I'll post a copy of this at AVSim.

Thanks for your help.

[JerryH]

Jim,

You got me on one thing; I've never noticed the fuel gauges!

I tried two takeoffs at 50% fuel, first with 50% in all tanks then with 50% distributed "correctly".  Didn't make too much difference.  Aircraft lifted off tail first (not unusual) and I had to pull back on the stick to lower the tail and get the nose pointed in the right direction.

At 25% fuel in all tanks, aircraft lifted off in a level attitude.  Looked good.

Please keep me informed, either here or at AvSim.

Regards,
JerryH

[WebbPA]

Jerry,

After noticing and correcting for the "extra" 4 tanks everything worked fine.

That was also the cause of my landing problems (try landing some time with C2 and C3 full!).

No need to worry about the panel.  Our failthful FSTipster is working on a new one (hint, hint).

Again, thanks for the fix.

[JerryH]

Jim,

You're very welcome.  Glad it worked for you.

And thank you for the final report.  I'll sleep better tonight.

JerryH