Some initial observation on flight dynamics, mostly good!

[AngelOfAttack]

Did my first full flight, and here is what I have observed, I'm a NG/MAX instructor but never on classic so don't hold much credit then....

Taxi: Seems need a lot power to get moving, over 40% is quite high IMO but not sure if it's true on these old engines.

T/O: I made a improved climb with BPS data, the runway is almost gone, 15% of margin seems about correct (maybe a little short, and I'm using ATM it should have more margin then). However the rotate feels very nose light and I almost feel I have a tail strike (if it's on -800)

CLB: climb rate seems right, seeing the record about 10nm/2min longer than FPPM data, good enough.

CRZ: Compare to realworld cruise table, the N1 and FF is almost spot on!

DES: VNAV actually works mostly fine, and the descent rate matches FCTM data quite nicely.  On final N1 and pitch all looking good.

Flare: In contract to T/O, the nose is very heavy, kinda like most airliner port to XP12 or XP11 EFM without proper adjustment...(for example some A350 is almost unable to flare...)

Landing roll: Factor out my short flare distance, the landing roll distance is almost the same as the number I got from realworld data with Autobrake1, very impressive!

Over all, it feels believable and could flown by the book, The main problem seems with in XP12's new ground effect scope, feel both noes light on TO and nose heavy on landing (weird). and also maybe engine is a little bit under powered? I mean I'd love to have 22K engine then...but compare to 20K data it still feel a little bit short.

I might push it harder to test it against the "Flight With Unreliable Airspeed/Turbulent Air Penetration" chart! Not many high-end add-ons can pass that!

[Litjan]

9 minutes ago, AngelOfAttack said:

I might push it harder to test it against the "Flight With Unreliable Airspeed/Turbulent Air Penetration" chart! Not many high-end add-ons can pass that!

Please do so - it is what I have used to tune performance ;-)

I agree on the ground effect thing - it does strike us seemingly more than the default 737-800, might be a geometry thing. If I make the nose more "heavy" on rotation you would be unable to pull it past 10 degrees until out of the ground effect - the landings one can get used to, but you need to be ready for the nose wanting to drop (more than on the real aircraft).

I might take this up with Austin, but got him busy on the N2 acceleration during engine start for now ;-)

Try taxiing again on a verifiably flat area - I find that even a bit of slope plays a huge role. The 737 starts rolling on my side at idle power up to 50 tons of weight, as it should.

Cheers, Jan

 

[Morten]

Hi guy's, been a long time

Regarding rotate feeling light, this is mostly an XP issue (at least in XP11 that i knew well).  In short, the 737 has a supercritical airfoil (NASA term, or "aft loaded" airfoil as Boeing calls it).  One of the differences between conventional and aft loaded airfoils is (as the name implies) that the aft loaded airfoils have the center of pressure further aft.  Meaning also the center of lift is further aft than on a conventional airfoil.

XP does not model this very well, and as far as I know has its center of lift at the 1/4 chord.  So this means XP airliners have their center of lift too far in front which cause problems in the transition phase between ground and flight.  Should be a fairly simple fix for Austin. There are some temporary "hacks" one can do, but it's a can of worms...

Good to see the old girl in the XP12 skies - great work Jan and Tom

Edited September 19, 2023 by Morten

[Litjan]

Hey Morten, great to see you chime in!

I will take this up with Austin in a little bit, right now we are on his case to fix the too rapid N2 rise after fuel is injected. You know him, it is better to feed him stuff one after the other ;-)

All the best, Jan

 

[AngelOfAttack]

After few more flight I can say the rotation (both TO and LD) issue is the most annoying one, even the LVII bug I can get around, and all other bugs I can make a flight condition that get avoid, but only this one....

even with anticipation, the muscle memory on my home setting is hard to replace, explically when all other flight going smoothly so I almost forget these 2 kinks.

[Litjan]

@AngelOfAttack I have identified and fixed the reason for the weird pitch during takeoff and landing. It will be fixed in the next version, so dont get too used to the effect ;-)