Forum: F-35 milestones

"The strap, although curved with no load, assumes a perfectly straight shape when loaded to 65,000 lb." Does it stretch at all?

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Putting my stress analysis hat on, I can make a pretty good ballpark guess how much it stretches (all structure stretches when loaded in tension). Let's say the average max stress (s) on the strap is 50,000 psi and the modulus of elasticity (E) is 30E6 psi. That means the unit strain (e) is s/E = 1700 E-6 in/in. So for every inch of strap length, it will stretch .0017 inches. If the strap is 70 inches long (WAG), it would stretch about an eighth of an inch. But it won't stretch that much for very long, only as long as it takes for the entire cable to start moving, about a tenth of a second. The biggest hook load is to accelerate the cable to airplane speed. The actual roll out load is much smaller.

Question for John, isn't there a shear bolt for lateral loads that is replaced after each hook use? I seem to remember some such follow-on maintenance after high power restrained engine runs?
Thanks.
fisk

Last edited by spazsinbad on Jan 28, 2012 - 12:44 PM; edited 1 time in total

I thought this was interesting: http://www.aerospaceweb.org/question/pl ... hook-3.jpg

From: http://www.aerospaceweb.org/question/planes/q0295.shtml

"...Landing or takeoff emergencies requiring the tailhook are generally rare, but perhaps a more common use for the tailhook is during routine engine testing on the ground. Many Air Force bases feature facilities called hush houses and trim pads where planes are tied down to the ground while the engine is throttled up for post-maintenance checks. The tailhook is often used to secure the aircraft to the ground and prevent its motion during these high power tests...."

There are photos of the F-35C (I think) being restrained during a hi power engine run by the hook attachment point (but not the hook itself).

Here it is but it will have come not from this place but LM originally most likely:
http://i531.photobucket.com/albums/dd35 ... urner1.jpg

The Sea Vixen seems to have a short distance between main wheels and hook point - with a twin boom tail. I wonder what that looks like exactly side on (not quite in this photo: http://upload.wikimedia.org/wikipedia/c ... an1970.jpg

U-2 AIRCRAFT CARRIER TAIL HOOK AND "Q-TIP" May/14/2009

"...Project Whale Tale fitted a few U-2s with arresting hooks like the one on display here. The hooks would snag cables strung across aircraft carrier decks and "capture" aircraft, bringing them to a quick stop. The small black plate on the shaft shows that this hook was used in five landings, and could be used up to 20 times...."

http://www.nationalmuseum.af.mil/factsh ... sp?id=9171

Wowee. Here is the U-2 Hook: (see previous pages on this thread for info):
A brief history of tailhook design
http://www.f-16.net/index.php?name=PNph ... p;start=15

http://www.nationalmuseum.af.mil/shared ... 4P-016.jpg

"DAYTON, Ohio - U-2 aircraft carrier tail hook and "Q-tip" on display in the Cold War Gallery at the National Museum of the U.S. Air Force. (U.S. Air Force photo)"
&
http://www.nationalmuseum.af.mil/shared ... 4P-015.jpg

"The U-2 was studied for use aboard aircraft carriers to extend its range, but this idea was not used operationally. Here, a U-2 lands on a carrier using an arresting hook. (U.S. Air Force photo)"

fiskerwad wrote:

Question for John, isn't there a shear bolt for lateral loads that is replaced after each hook use? I seem to remember some such follow-on maintenance after high power restrained engine runs?
Thanks.
fisk

fisk, you maybe right, I simply don't remember. The hook swings wildly on off-center engagements (up to 50 ft in F-16 tests), so if there is a bolt there, it would easily be sheared.

One of the believable subject matter experts on Pprune has this to say today.

'Engines': 2nd Feb 2012, 00:55 More delays for the F-35

http://www.pprune.org/military-aircrew/ ... -a-14.html

"...I worked with the team designing the hook and can confirm that the design they came up with (after a number of changes) was fully approved by the many US Navy subject matter experts from NAVAIR who conducted a string of reviews. (The US specification does not, as far as I know, specify a minimum distance between gear and hook - it does specify around 30 other parameters, all of which the design met).

The whole business of getting arresting hooks to work is actually highly complex and difficult. The USN make it look easy because they are extremely good at it.

LM are trying a redesigned hook point and a new damper to regulate hook bounce. If those don't work, they are going to have to design some form of extending hook or move it aft - and that could be a real problem. However, they are not there yet...."

Ideal No.3 CDP Arrest EA-18G VIDEO

http://www.youtube.com/watch?v=BqZWXuRFX6Y
_______________

How to get an Ideal No.3 CDP Arrest EA-18G VIDEO

http://www.youtube.com/watch?v=MZ6ECPe7VRI

Lockheed Official: Tailhook On Navy F-35C Won't Be Lengthened

http://insidedefense.com/index.php?opti ... gxLmh0bWw=

"Lockheed Martin has no plans to lengthen the tailhook on the Navy carrier variant of the F-35 Joint Strike Fighter despite a Defense Department report that indicated the aircraft was failing to reliably catch the arresting cable on a carrier deck, Steve O'Bryan, Lockheed vice president for F-35 business development, told Inside the Navy Feb. 29."

Perhaps someone with a subscription to above website can elaborate please? Thanks. To me it seems a non issue if LM have said only the hook tip was going to be modified (in hope that that change would work as elaborated on this thread and others on this forum).

Lockheed Martin Confident F-35 Tail Hook Problem Resolved (DEFENSE DAILY 02 MAR 12) ... Mike McCarthy

http://www.hrana.org/news.asp#LockheedMartinConfident

"Lockheed Martin is optimistic it has successfully redesigned the tail hook for the carrier version of the F-35 and believes testing can resume later this year, the company's top executive for the program said yesterday.

Tom Burbage, the vice president and general manager for the Joint Strike Fighter, said company officials met with the Pentagon's F-35 program office on Wednesday and was told the meeting "went well."

Lockheed Martin had to rework the tail hook design after it failed to snag the arresting wires during testing at Lakehurst Naval Air Station, N.J. The tests failed because of a problem with the mechanism, or "damper,” responsible for keeping the tail hook down and stable. [That is news - if it was the only cause (given what is otherwise outlined in this thread for potential 'easy' fixes - we'll see I guess.]

Asked whether the redesign has resolved the problem, Burbage said: "We think so."

Burbage said the company is waiting for the new parts and believes a new round of testing can begin this summer...."

Lockheed could accommodate UK reversal on F-35 variant By Craig Hoyle

http://www.flightglobal.com/news/articl ... nt-369443/

"...Meanwhile, O'Bryan says Lockheed has performed a preliminary design review to address an issue with the F-35C's arrestor hook design, after concerns were raised over its performance during previous trials. An improved system with a redesigned hook point and "hold-on damper" will undergo testing at the US Navy's Patuxent River site in Maryland later this year. The F-35C "will go to the boat in 2014, as scheduled", he adds."

Lockheed Martin Awaits UK F-35 Decision Aviation Week's DTI | Robert Wall | March 13, 2012
This article first appeared in Aerospace Daily & Defense Report.

http://www.military.com/features/0,15240,242692,00.html

"...Meanwhile, O'Bryan notes that efforts continue to address JSF test and development issues. A revised tailhook for the F-35C model is due to undergo trials at NAS Patuxent River, Md., during the summer. Boat trials may slip into early 2014 as a result of the design changes, which include a shape redesign to better capture the arrester wire and a fix to the hold-down damper to add pressure...."

Looking for news about F-35C arresting tests came across this old gem. I gather the 'land' tests for the A-7D would be relevant in part today? Anyway the report gives an idea of what goes into testing for land-based systems anyway.

A-7D/Arresting Systems Compatibility Tests
Technical Report No.71-32, July 1971

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0888969 [11Mb PDF]

ABSTRACT
Seventy successful arrestments of A-7D, S/N 67-14583, were made on two operational Air Force aircraft arresting systems, the standard BAK-12 and the BAK-13. Thirty-three arrestments were made with the BAK-12, and 37 with the BAK-13. As a result of six approach end engagement arrestments, changes in the Flight Manual approach end engagement procedures were recommended. Runway centerline engagements were made at aircraft weights up to 42,000 pounds. The maximum engagement speed was 167 knots at an aircraft weight of 33,000 pounds. Off-center engagements were also made up to 50 feet from the runway centerline using a 190-foot span between the runway edge sheaves of the arresting systems. Aircraft control problems were not serious except for 50-foot off-center engagements with the BAK-13. Test data indicated that the design limit hookload would only be approached at engagement speeds in excess of 190 knots for both arresting systems. Four tests resulted in missed engagements due to a combination of poor hook shoe attitude and poor cable dynamics. A change in hook shoe design was recommended. The cable dynamics problem occurred with the rail type arresting cable supports when the A-7D main gear passed between the rails. Further testing of polyurethane rails was recommended to determine optimum~spacing for use with the A-7D. Except for the aircraft hook shoe design, the A-7D proved compatible with each aircraft arresting system using donut type cable supports. There were no failures of the standard BAK-12 or the BAK-13 arresting systems. Although not tested, the extended runout BAK-12 was also considered to be compatible with the A-7D aircraft based on results of this test program.

...SYSTEMS DESCRIPTION Aircraft
The test aircraft was an A-7D Corsair II, S/N 67-14583, (A-7D production No. 2). The aircraft was equipped with a production arresting hook subsystem which consisted of a stiff shank hook, replaceable hook shoe, a hydraulic snubber to keep the hook on the runway during use, and an operational hydraulic/pneumatic actuator system to allow the pilot to raise and lower the hook from the cockpit (figure 1). The hook assembly, P/N 215-44020-1, had a design tensile strength limit of 116,000 pounds, and the hydraulic snubber actuating rod end had a design compressive strength of 21,500 pounds. The ultimate strength of the hook was 187,000 pounds."...

spazsinbad,

Thanks for posting the report link. The A-7D test was very similar to the F-16 test I worked in 1979. Not only is the test procedure similar, but the results are similar. Not so much the test speed limits, since the A-7D was heavier than the F-16, but the airplane response was similar, especially to off-center runs. One big difference in the test was the necessity to monitor landing gear loads on the F-16. Being designed for carrier operations, the A-7D gear was of no concern.

The F-16 test had one missed engagement out of 94, as I recall, but might have been more. The A7-D had 4 misses out of 74, and the report provided some insight about the misses, including photos of the hook point. Amazingly enough, I thought I was reading about the current F-35C problem with missed engagements. The hook point photos look exactly like the F-35C points. There was no mention of any changes recommended to improve engagement reliability. I'm going to forward the report to my friend on F-35C landing gear to see if he has any comment or might forward it to the hook improvement team.

Forum: F-35 milestones

F-35C Lands at Lakehurst For Testing