Board index FlightGear Support Flying

747-8i bank angle crash.  Topic is solved

Controlling your aircraft, using the autopilot etc.

747-8i bank angle crash.

Postby gray1 » Wed Jul 01, 2020 1:48 pm

Hello ,
I have this very annoying problem. I have no problems flying the 747-8i to any destination. But as i prepare for landing, the aircraft always banks & plummets to the ground. This happens with both autopilot & manual control. I cannot control it, & my other aircraft do not exhibit this behaviour.
My MSI Apache Pro has a Nvidia 1070 GTX GPU. The CPU is Intel Core I7 7th gen. So i have the power & a frame rate of between 50 to 90 fps.
Has anyone experienced this problem & did they find a solution?
I love this aircraft, but it's almost pointless when you know it just loses all flight control about 10 nm's before landing.
I have at a guess over 1800 hours in all 777's with no problems at all . My hanger includes the 747-8i, 777's, 757's, A380, and the A320 series . All are absolutely fine.

Thank you everyone.
Gray.
gray1
 
Posts: 12
Joined: Wed Jul 01, 2020 1:27 pm

Re: 747-8i bank angle crash.

Postby tdammers » Wed Jul 01, 2020 6:43 pm

The FG 747-8i uses a YASim FDM, and a typical aspect of that is that it produces a somewhat unrealistic stall response, namely, this exact one-sided wing-dropping behavior - AFAICT, the FDM basically decides that "the" wing is stalling, and introduces drag, kills lift, and introduces a banking moment (and I think it's generally to the left). I've encountered this numerous times in the Twin Otter, when trying to golf for an extra short landing, and I've also experienced it in the CRJ700, another YASim aircraft. JSBSim, the other main FG FDM, has more subtle and accurate stalling behavior; here, if you stall the aircraft with the wings level, the stall will develop on both wings, and you'll just sink, but there will not be a strong banking - unless there's also a yaw, or you're stalling in a banked attitude. JSBSim models, if done well, are also better at modelling stall recovery - in a YASim model, once you're in this deep stall where one wing drops, there's no way you can recover.

However, I successfully land the 747-8i all the time. You just have to be mindful of your Vref during the approach (and have the correct value to begin with). Same for the CRJ, really. Fly fast enough, and you'll be fine.
tdammers
 
Posts: 327
Joined: Wed Dec 13, 2017 10:35 am
Callsign: NL256
IRC name: nl256

Re: 747-8i bank angle crash.  

Postby tikibar » Wed Jul 01, 2020 6:46 pm

What's your airspeed, weight, and flap condition when this happens? Of the aircraft you listed in your hangar, the 747-8 has the highest approach speed at 150 kias (compared to 137 kias for the 757-200). To be safe, you'll want to keep your speed at or above 155 with full flaps, especially if you're close to max landing weight. If you're landing light, you can get away with lower speeds and sometimes even 25 deg flaps. For this particular FDM, the stall is pretty unforgiving. I think it's a little bit mellower for the 747-8F, but the approach speed is 159 kias.
Boeing 747-8 (rename folder to 747-8i)
Boeing 757-200/300 (rename folder to 757-200)
Boeing 767-300/ER (rename folder to 767-300)
User avatar
tikibar
 
Posts: 525
Joined: Mon Mar 05, 2012 6:05 am
Location: Los Angeles
Callsign: CHT0009
OS: Ubuntu 14.04

Re: 747-8i bank angle crash.

Postby tdammers » Wed Jul 01, 2020 6:50 pm

The approach and ref speeds depend on landing weight. But yes, the 74 wants to land fairly fast, the usual "110-130" range is way too slow.
Last edited by Johan G on Tue Jul 07, 2020 6:56 am, edited 1 time in total.
Reason: Please, do not quote the entire post directly above your post.
tdammers
 
Posts: 327
Joined: Wed Dec 13, 2017 10:35 am
Callsign: NL256
IRC name: nl256

Re: 747-8i bank angle crash.

Postby gray1 » Wed Jul 01, 2020 9:03 pm

Thank you so much for this information regarding the 747-8i bank angle crash.
This is for both tdammers & tikibar.
I'll try an ILS flight from Heathrow to Schipol in the morning.
I think you may have solved this, my landing speed has been too slow at 140 kias using full flaps on final approach.
I always check my gross weight & set this at around 70% max landing weight.
But you guys have been great & I thank you so much.
gray1
 
Posts: 12
Joined: Wed Jul 01, 2020 1:27 pm

Re: 747-8i bank angle crash.

Postby gray1 » Wed Jul 01, 2020 9:05 pm

PS: I will let you know the result.
Thanks guys.
gray1
 
Posts: 12
Joined: Wed Jul 01, 2020 1:27 pm

Re: 747-8i bank angle crash.

Postby Alant » Wed Jul 01, 2020 11:05 pm

Alant
 
Posts: 980
Joined: Wed Jun 23, 2010 5:58 am
Location: Portugal
Callsign: Tarnish99
Version: from Git
OS: Windows 10

Re: 747-8i bank angle crash.

Postby gray1 » Thu Jul 02, 2020 2:53 pm

Thank you guys,
tdammers & tikibar (also Alant).
You were absolutely correct with your info. I used kias 159 for touchdown & it went superbly.
I now have my aircraft back!! And i love it.

Enjoy your travels because you've made mine great again.

Best regards,
Gray.
gray1
 
Posts: 12
Joined: Wed Jul 01, 2020 1:27 pm


Return to Flying

Who is online

Users browsing this forum: No registered users and 1 guest