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View Full Version : 109 Leading edge slat "snatching"???



XyZspineZyX
09-07-2003, 10:33 PM
I've read about aiming in turns being difficult in 109s due to automatic deployment of the leading edge slats. Is this modeled in FB? Maybe I've spent too much time in the 109 now and just don't notice it.

XyZspineZyX
09-07-2003, 10:33 PM
I've read about aiming in turns being difficult in 109s due to automatic deployment of the leading edge slats. Is this modeled in FB? Maybe I've spent too much time in the 109 now and just don't notice it.

XyZspineZyX
09-07-2003, 10:46 PM
I used to fly a bit in a Koliber which is a polish built Robin and that used the very same system, you never used to notice them bar the damn things winging in and out in your periferal vision, oh and as for Robins, they should have been strangled at birth and to allow the poles to build them just compounded the issue.

XyZspineZyX
09-08-2003, 03:56 AM
First, LE slat snatch and aileron snatch is not modelled.

But what is snatch? In the case of Bf109 LE slats it's when the things bang open or closed unexpectedly, suddenlly changing lift and drag on that wing. The slats are spring loaded and generall tend to open at a fixed AoA, but more often you'll have them open a little unevenly, making the plane a little squirrely until you're back to having both open or both closed.

Also, the things had no dashpots or rubber bumpers to keep them slamming shut with the full force of the springs. Suppose you're in a slow steep climb when you bump the stick forward a bit - BANG suddenly both LE slats slam shut as you've removed the suction over the top of the leading edge that kept them open. This can be doubleplus ungood if you're slow enought that shutting the slats means stalling.

"Snatch", however, generally refers to ailerons, not the LE slats. When you're flying at high AoA the air tends to detatch over the upper surface of the wing, making the ailerons less effective. LE slats baning open and shut can exacerbate aileron snatch tendencies as well, since open LE slats help keep the air attached over the wing (making ailerons work properly). If the slat bangs shut, bang, the ailerons turn to mush (or worse!) Slat bangs open... bang, suddenly your aileron response gomes back. It can be pretty tricky.

On some aircraft (LA-5/7 for instance) the aileron stick force will even REVERSE if you try a hard roll at high AoA. It's like, you're flying a tight barrell roll when suddenly the control column gets sucked sideways in the direction of the roll and you have to PULL it back to center to stop it rolling. It's a very ginchy feeling, and even if the force feedback in the game did simulate this it would not simulate how freaked you will feel the first time it happens. And if you think that's bad, the I-16 supposedly suffered from ELEVATOR control force reversal at high AoA, and that's in addition to the whole lack-of-trim, forward-push-on-the-stick-while-cruising stuff. Whee, ain't flying fun?

XyZspineZyX
09-08-2003, 05:04 AM
The slats in the 109 were operated soley by aerodynamic pressure, therefore, there were no springs that would suddenly snap them open or closed unexpectedly. They opened during low speeds or in turns. There was a clunking sound that could be heard and according to Dave Southwood, who flew a restored 109 G2, also felt. To quote him:

"One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis."

I have also read accounts of LW pilots reporting a clunking or banging sound when the slats extended. For example, Oberleutnant Erwin Leykauf said that younger, inexperienced pilots would be frightened by the sound, thinking they had been hit. "For us, the more experienced pilots, manoeuvering only started when the slats were out."

I should add that Leykauf was referring to his experience in a Emil during the Battle of Britain.



Message Edited on 09/08/0308:41AM by Chadburn

XyZspineZyX
09-08-2003, 05:45 AM
Thanks for the correction! http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif So the Bf109 slats have no springs. They just move open or shut according to air pressure and suction.

If i'd been a luftwaffe mechanic back then I might have tried installing little oil or pneumatic dampers on the slats to slow them down a bit... just enough to keep them from banging so harshly. Failing that, maybe try to rig a way to lock them in the open position with a cockpit switch, to make landing a little frendlier.

XyZspineZyX
09-08-2003, 06:08 AM
" also read accounts of LW pilots reporting a clunking or banging sound when the slats extended. For example, Oberleutnant Erwin Leykauf said that younger, inexperienced pilots would be frightened by the sound, thinking they had been hit. "For us, the more experienced pilots, manoeuvering only started when the slats were out." "

Funny, when they deploy ingame I usually find stalling to be the manuvering result (-:

There seems to be some issues with slat equipped planes and the patches over original FB, slats deploy, planes fall to ground in spin (-:

XyZspineZyX
09-08-2003, 05:48 PM
yep air does it, as the wing reaches near stall the low air pressure of the Centre of pressure approaching the leading edge sucks them out. as it retreats and the airpressure increases they slam back in