F-35 landing gear

linkomart · by **linkomart** » 04 Nov 2016, 18:13

johnwill wrote:Good points about different Navy requirements. One added requirement is tip-back resistance. On a carrier deck, the airplanes are often pushed backward with the tow truck and abruptly stopped near the deck or elevator edge. If the main gear is too far forward, the airplane may tip back and go over the side into the drink. Land based carrier suitability tests include demonstrations of tip back resistance at different weight / CG conditions.

What I was trying to say in my earlier post, but clearly one of us has the better ability to express oneself.
Thanks for your insights and ability to share. It is much apreciated.

Regards

spazsinbad · by **spazsinbad** » 10 Nov 2016, 14:10

"Description A U.S. Marine Corps Lockheed Martin F-35B Lightning II (BuNo 168059) on the runway during the first short take-off and vertical landing mission at Eglin Air Force Base, Florida (USA), on 24 October 2013. The milestone training mission was flown by Major Brendan M. Walsh of Marine Fighter Attack Training Squadron 501. Walsh qualified in vertical landing operations at Marine Corps Air Station Yuma, Arizona (USA), in preparation for this mission. Date 24 October 2013 Source U.S. Air Force photo 131024-F-oc707-001 from the Eglin Air Force Base website
Author U.S. Air Force photo by Samuel King PHOTO: https://upload.wikimedia.org/wikipedia/ ... B_2013.jpg (2.1Mb)

Source: https://commons.wikimedia.org/wiki/File ... B_2013.jpg

spazsinbad · by **spazsinbad** » 15 Nov 2016, 19:09

Super Hornet F/A-18E/F 'tipback' angle info from a large PDF F/A-18E/F Configuration Baseline 02 Apr 1991: 130Mb

http://www.filefactory.com/file/26rjl6h ... DPI%29.pdf

BELA · by **BELA** » 15 Nov 2016, 21:24

Ok, thats another term that is new to me...."tail down angle" are they referring to the anhedral of the tail? .... or incidence?

linkomart · by **linkomart** » 15 Nov 2016, 21:59

BELA wrote:Ok, thats another term that is new to me...."tail down angle" are they referring to the anhedral of the tail? .... or incidence?

Tipback angle is the angle when, balancing on the maingear, the Aircraft will tipover backwards and land on the tail. Tail down angle is the angle when, balancing on the maingear, the tail will hit the ground. Note:
Tipback is measured with landinggear in normal loaded position (approx 2/3 compressed is normal) Tail down is with gear fully extended.

linkomart · by **linkomart** » 15 Nov 2016, 22:05

The angle is measured with the centre of gravity in the rearmost position....

count_to_10 · by **count_to_10** » 15 Nov 2016, 23:46

Interesting, particularly given the F-18's noted difficulty getting it's nose into the air. I wonder if it would pay to make the main gear capable of moving backward while taxiing or parking, but forward for takeoff.

BELA · by **BELA** » 16 Nov 2016, 00:09

linkomart wrote:
BELA wrote:Ok, thats another term that is new to me...."tail down angle" are they referring to the anhedral of the tail? .... or incidence?

Tipback angle is the angle when, balancing on the maingear, the Aircraft will tipover backwards and land on the tail. Tail down angle is the angle when, balancing on the maingear, the tail will hit the ground. Note:
Tipback is measured with landinggear in normal loaded position (approx 2/3 compressed is normal) Tail down is with gear fully extended.

Ok got it. Thanks again Linkomart

spazsinbad · by **spazsinbad** » 16 Nov 2016, 01:31

"...F-18's noted difficulty getting it's nose into the air..." info on change to nose strut to follow from same source above.

spazsinbad · by **spazsinbad** » 16 Nov 2016, 02:46

Attached 19 page PDF showing content above and then very detailed drawings which can be Zoomed to see detail below:

http://www.filefactory.com/file/26rjl6h ... DPI%29.pdf (130Mb)

johnwill · by **johnwill** » 16 Nov 2016, 05:55

count_to_10 wrote:Interesting, particularly given the F-18's noted difficulty getting it's nose into the air. I wonder if it would pay to make the main gear capable of moving backward while taxiing or parking, but forward for takeoff.

Evidently that is an unnecessary complication. The combined effects of inward deflected rudders, swept horizontal tails, and nose gear compression are enough to force the nose up. Of course, the NG compression is effective only for catapult takeoffs. What really hurts them is the forward CG location, since they never took full advantage of the aft CG capabilities of the fly by wire system. The E/F CG was moved back a bit, but is nowhere near the aft CG of the F-16.

Thanks to spaz for posting the E/F development .pdf. Some very interesting content. Notice the inlets are simply enlarged A/B/C/D round-ish rather than the eventual E/F rectangular ones. Similarly, the LEX looks like an enlarged version of the original rather than the much larger production E/F version. Interesting also is the -414 engine is the same as the -412 planned for the Navy A-12 Dorito plus an afterburner.

spazsinbad · by **spazsinbad** » 16 Nov 2016, 07:29

'JW' was wondering if something like what is happening with the F-35C nose gear is happening on the Super Hornet NG?

Complex & Robust
Flight International F-35 Special ? 2014? Magazine

"Mark Ayton explains the highly complex landing gear systems used on the F-35...

...The nose gear of the CV variant is a dual stage gas over oil cantilever strut with a staged air curve that provides a source of high energy, which helps the aircraft to achieve adequate angle of attack when released from the catapult during take-off from the aircraft carrier....

...There are two reasons for having a staged shock strut for the nose gear on the F-35C CV variant.... The second is to store energy gained from the compression of the strut under the high pressure effect of the catapult. When the catapult lets go of the launch bar, the energy is released, providing a rotation that helps achieve the angle of attack necessary to get off the deck.

Similarly when the aircraft hits the deck on landing the strut is compressed and energy is stored to help rotate the aeroplane and get it back off the deck if the arrestor cables are missed and a ‘go-around’ or ‘bolter’ is required. Bolter is the term used when the aircraft’s tail hook misses the arrestor cables on the carrier deck forcing the pilot to go around for another landing...."

Source: No longer available at former URL - download available here: download/file.php?id=23692 (PDF 1.44Mb)

johnwill · by **johnwill** » 16 Nov 2016, 08:06

Exactly the same functionality for both airplanes. As far as I know, all Navy catapult launched airplanes that use nose gear launching use the same process. Bridle launched do not, because they do not compress the nose gear. Even the F-111B I helped test 48 years ago had the same compressed strut design.

Notice the launch bar is connected to the shuttle at a 45 deg angle, so when the the bar pulls on the gear it is pulling forward and down. Look at the F-35C videos and you will notice the airplane nose drops abruptly and oscillates a couple of times as the airplane starts to move. The strut has compressed the air/oil in the cylinder until it hits bottom, then the tire is compressed and causes the oscillation. When the shuttle releases the launch bar, the tire expands and the shock strut is extended, both of which force the nose of the airplane upward to get the desired AoA.

spazsinbad · by **spazsinbad** » 16 Nov 2016, 08:09

OK - thanks 'JW'.

spazsinbad · by **spazsinbad** » 16 Nov 2016, 13:37

Aha. More on the nosewheel lift off issue - caused by unrealistic tipback requirements 4 page excerpt attached:

F/A-18 Flying Qualities Development
25 Mar 1983 J.M. Abercrombie; McDonell-Douglas Corporation

"...Nosewheel Liftoff
Figure 1 illustrates the first problem encountered in the flight test program which was experienced on the first flight: poor takeoff rotation characteristics -- high rotation speed and, as a result of a very brief time between nose gear liftoff and main gear liftoff {not much time for pilot reaction} a characteristic that was described as "explosive". The cause was two-fold. First, a main gear well aft of the center of gravity (to satisfy the unrealistic tip back requirement to be able to apply full brakes rolling backwards downhill on a 5 degree sloping deck without bumping the tail on the deck). Secondly, a horizontal tail that was virtually stalled at full airplane nose up deflection at takeoff attitudes. This problem was anticipated by us in the flying qualities business (as a matter of fact, our pre-first-flight simulations were virtually identical to actual flight experience) but it was decided to await flight verification before making any major changes...."

Source: http://aviationarchives.net/F-18%20Flyi ... opment.pdf (8.6Mb)