F-35C Lands at Lakehurst For Testing

[spazsinbad]

The photo of the A4G painted in VC-724 tail colours for their 'RamJet' Aerobatic Team for an air display at NAS Nowra in the late 1970s is one of the best A4G photos around. Sometimes VF-805 would go on a cruise with A4Gs taken from VC-724 at the last moment because they were serviceable whilst the one perhaps painted in any VF-805 paint scheme was not serviceable for embarkation. Anyway the photo shows the hook catching one of the five wires set out where No.4 was the target wire although more often than not only 4 or a minimum of three wires were set due to unserviceability. If four wires set then No.3 was the target wire same same USN. Aim is to plonk the hook midway between No.3 & No.4 wire if No. 4 is target.

We cannot see the 'AoA lights' in the port wing root but judging by the leading edge slats that A4G is a little slow perhaps (meaning a higher angle of attack slightly - hence exaggerated landing attitude slightly). Which means the hook is now lower than usual, hence more easily able to catch a wire perhaps if the geometry is OK and there is no 'hook slap' or other contretemps. Always best to land at Opt AoA, in the middle of the Glideslope and lined up - nothing else will do. The LSO knows all though and there is no fooling the LSO. A good old school LSO Utube movie is here: [the movie will explain A Lot I hope)

F-570 The Landing Signal Officer 24 min Video

http://www.youtube.com/watch?v=7vRstczn-yw

"Uploaded by sdasmarchives on Oct 12, 2011
A United States Training film on the Landing Signal Officer. From the archives of the San Diego Air and Space Museum http://www.sandiegoairandspace.org/research/
Please do not use for commercial purposes without permission."

[spazsinbad]

navy_airframer, sorry for delay but in the middle of computer OS rebuilding so sometimes things are slow here. I guess the F-35C HOOK testing has to include every conceivable situation including ashore for both long and short field arrests, not just onboard. From what I have read in that report the fix may be easy but then again - who knows.

The F-35C will have an Optimum Angle of Attack (known from an LSO newsletter elsewhere on this forum) which ensures the same thing. The hook tip will be slightly below the main wheels when 'on speed'. As explained about the A4G it is slightly slow (in the photo illustration) thus exaggerating the 'nose up' landing attitude which puts the hook tip even lower than required - not always a good thing. For example in the USN the minimum 'hook to ramp' vertical clearance was 6.5 feet whereas HMAS Melbourne had a 6 foot clearance, hence landing slightly longer on the shorter deck to No.4 of 5 wires (in the Sea Venom era there were 6 wires).

[navy_airframer]

Is the hook point for the A and B the same as the C model? Aren't field arresting gear elevated off the runway?

[spazsinbad]

No. There is a thread about the A model 'emergency hook' which is not as robust as the C model (link to follow) and the B model has no hook. Yes field arresting gear is elevated usually (although may not be if not working properly). Tramping is an issue for sure and not just for carrier capable aircraft. Latest field gear wires can be lowered into the runway so as to be invisible to ordinary aircraft but raised on request as needed.

Arresting F-35s & Brake Testing Scroll down

http://www.f-16.net/index.php?name=PNph ... ncy+arrest

http://attach.high-g.net/attachments/f_ ... um_289.jpg

[spazsinbad]

alloycowboy, you would be pleased to know that parts of BONAVENTURE lived on slightly elongating the 100 foot catapult to 110 feet approx. in MELBOURNE. Then they went to CHINA for study.

Another thing about the two Skyhawk photos. The first one with the civvie white A-4 side on is not at optimum AoA but fast probably at around 180 KIAS I estimate. The leading edge slats started to crack open just below the landing gear max speed of 225 knots. At Opt. AoA the slats are open by about 1/4 to 1/3 depending on who is looking at them (pilot or outside observer such as the LSO). However as indicated in the olde LSOe movie the Optimum Attitude is gauged by the LSO in a way appropriate to his viewpoint.

In effect the first photo (hook up) shows a fast approach and the second photo shows 'a little slow - nose cocked up' (perhaps) at the ramp, in the wires but probably safe. Only the LSO has the correct criteria (what the pilot thinks doesn't count).

[spazsinbad]

Because A-4s were used to illustrate a point I'll continue to use them. The rear quarter photo below shows a USN Skyhawk about to arrest with hook point below main wheels. Similarly this photo shows the Super? Hornet hook:

http://upload.wikimedia.org/wikipedia/c ... an2007.jpg

And to add to Opt AoA example the last photo shows (I think) the correct landing attitude of a Skyhawk (note LE slat position) at Opt AoA (sadly no hook).

And lastly an illustration of Carrier Glideslope Geometry from: http://www.dtic.mil/cgi-bin/GetTRDoc?Lo ... =ADA087012

[spazsinbad]

Excellent Slow Motion Carrier Catapult and Arrest Video especially for the Approach / Arrest at end here:

VFA-137 Cruise 2010-2011 'Music Video'

"Uploaded by aophil on Apr 13, 2011
Compilation of a Tanking Mission around the boat (CVN-72) on Cruise 2010-2011. I used a Samsung point and shoot with for the slow motion, and a ContourHD helmet camera for the 'over the shoulder' in-flight video."

http://www.youtube.com/watch?feature=pl ... OA8#t=192s
_____________________

Photos illustrate some aspects of hook/wire/arrest forces:
http://www.villanova.edu/artsci/assets/ ... imized.ppt
__________________

Last photo series from InstaPinch who may be off the air now, anyway I'll look again later to see if there is any extra info: http://instapinch.com/?p=2280

InstaPinch Text from the photo/.gif graphic below:

“The wire itself is, understandably, rather stiff and inflexible when laying in repose upon the wire brackets that support it between 2 to 5.5 inches above the flight deck. This is to ensure there is room for the aircraft tailhook to grab the wire. If it were laying flush on the deck, the tailhook would be unable to grab a’holt of it.

A split second later the steam hits from the friction of the tire on the deck and the reaction of the wire hitting the deck in such a rude manner!

So, now that we’ve gone through how absolutely intense these crossdeck pendants have to be and how robust and manly and strong and all they are, THIS pic is all the more amazing. I had the trusty Canon 50D set to the fastest shutter speed possible and had it snappin’ pics at the 10 frames per second (or whatever it is). What you are seeing is the instantaneous deformation of the CDP by the nose gear of a Hornet as it lands and passes over the wire at 135knots.

And a split second after THAT….the wire-b-gone as the tailhook snatched it!”
http://instapinch.com/?p=2280
_________________________

Lucky Last Photo shows wheel smoke point (perhaps indeterminate) but nice action photo anyway.

[alloycowboy]

@spazsinbad...... Nice pictures and it's intersting to know that the wire is suspended above the deck, I always wondered about that. So the worry with the F-35C is amount of time the wire has to straighten back out once the main gear roll overs. Gee, that would be neat to see in high speed camera.

[spazsinbad]

alloycowboy, apologies, I thought that the arrestor wire is suspended was well known. I guess not. No worries. One reason why istarted on the 'How to Deck Land' and the A4G in RAN FAA (plus their other fixed wing) PDF was to help explain all these details. The USN calls their Naval Aviation stuff different names often which I am not so familiar with nor do I use. For some reason 'the wire' as I call it is named the 'Cross Deck Pendant' CDP. Which is fair enough. The Septics - Septic Tanks - Yanks probably rail at the OzRAN/UKrn usage also for various items. So for the life of me I forget what the 'springs' are called in the USN but they raise the wire some inches above the deck for arrested landing ops. Once complete these springs lower the wire to deck level. Otherwise they are quite hazardous when left raised (easy to trip over etc.).

On a runway ashore the long or short field gear (or long field emergency arrest) is permanently raised on rubber grommets. New fangled arrestor gear wires can be hidden under the runway to alleviate the problems for some civilian aircraft not able to 'trample' over them quickly either during takeoff/landing or during taxi. Often these aircraft will land beyond the short field gear for example.

And yes sometimes these wires can be flat on the deck or runway but this is a worst case and not likely. With the exception being the situation highlighted in the F-35C hook report as described (caused by trampling by main gear before hook arrives). But the fix is in and some of us hope it works.

For 'alloycowboy': BTW some ex-Canuks transferred to/joined the RAN (some had also served in the RN during wartime). One such was LCDR Fred Goodfellow ex-Banshee pilot also AEO (Air Engineer Officer) on VC-724 back in 1968-9. He did not fly that often then being just about to retire he had a serious accident landing in a Vampire with a thunderstorm near the airfield. In those days we did not know about microbursts so it is likely one slammed him into the ground. He was in a wheelchair permanently subsequently.

[alloycowboy]

spazsinbad.... as usual your a walking naval aviation encyclopedia, thanks for the info, learning a lot. I left some new pictures on the other thread. Check them out let me know what you think. Cheers!

http://www.f-16.net/f-16_forum_viewtopic-t-16554-start-45.html

Oh wow, just checked the wiki on the Banshee the plane was a widow maker for Canada. They lost 30% of them in service.

http://en.wikipedia.org/wiki/McDonnell_F2H_Banshee

[spazsinbad]

This TA-4J 'moment before arrest' photo is a classic and can be found on Wikipedia and the US Naval Aviaton/DOD website I think. One can see the long hook on deck well before main wheels. Angle of Attack at Optimum looks correct from this perspective.

Anyway it is also or used to be here: http://www.skyhawk.org/5e/g158073/html/158094p.htm

A-4 Association have changed their website recently with new URLs for stuff. Photo taken on 02 May 1998 aboard USS J.F.K.

"Description: right front view of Eagles Skyhawk BuNo 158094, A-700, with the hook on the deck 2 feet before 3 wire while 700 is still in the air."

[spazsinbad]

Yes landing any jet aircraft on a small fleet carrier in any kind of sea was exciting as they say. Must have been horrendous in the North Atlantic. Flew with Fred on a test flight in a Venom in the right hand 'observer' seat (no flying controls there) just to get a look at it before going solo. Fred went on to have a very successful career in Canberra as a lawyer.

We were puzzled by events that day (I was not at the airfield but out in the bush on a survival exercise; being drenched by same thunderbumper). Learning about microbursts and other unknown hazards then - later - helps explain a lot. Of course there is a lot more detail not revealed but Fred sure was unlucky but lucky that day so to speak.

Have commented about the F-35 pics/movie at that link:
http://www.f-16.net/f-16_forum_viewtopi ... rt-45.html

[spazsinbad]

ON PAGE 3 of this thread 'alloycowboy' cited a very old but very good PDF about designing 'arrestor hooks and damping them satisfactorily' from 1954. Yes a lot of water under that bridge since then but a good insight into the difficulty as 'alloycowboy' correctly suggests. Usually all arrestor wires are held inches above the surface either by 'fiddle bridges' (on carriers) or 'rubber grommets' (on runways). However the weight of main wheels trampling the wire down flat before the arrestor hook arrives can be an issue as discussed in the recent F-35C report about that. Anyhow I thought it useful to excerpt some text from the old PDF document:

http://naca.central.cranfield.ac.uk/rep ... m/2980.pdf (3.3Mb)

A Study of the Aircraft Arresting-Hook Bounce Problem
By J. THOMLINSON, Ph.D. May 1954

http://naca.central.cranfield.ac.uk/rep ... m/2980.pdf

SUMMARY: The kinematics of an arresting-hook unit are studied in order to determine, within the limits of the assumption of a perfectly rigid hook unit, the damper force necessary to control hook bounce. The necessity for a smooth deck and the desirability of small trail angle for the hook unit are demonstrated from several aspects. The design requirements for a hook damper unit are discussed in all their functional aspects and methods are given for determining the up-swing motion of an arresting hook unit immediately following engagement of an arresting wire. The behaviour of arresting wires after being depressed by the passage of aircraft wheels is also outlined.

1. Introduction. The operation of deck landing depends to a large degree on the ability of the aircraft arresting hook to engage a cross-deck centre-span. of an arresting gear. It is most desirable, for many reasons that the hook upon coming within reach of the deck shall engage the first centre-span which crosses its path; or expressed another way, the hook on reaching the deck shall not bounce, or if this ideal is unobtainable then the bounce (in terms of clearance between the deck surface and the underside of the hook) shall be measurable only in fractions of an inch. If this objective is achieved then the arresting wire will be engaged by the hook before the aircraft wheels touch down and disturb the arresting wires, since a hook installation is usually designed so that the hook lies some 2.5 ft or more below a line which is tangent to the underside of the main wheels and parallel to the deck or ground, when the aircraft is in its approach attitude. If, however, the hook, having failed to engage an arresting wire before the main wheels touch down, is then confronted by a wire which has been disturbed by the aircraft wheels, then the chances of the hook engaging such a wire may be greater or less than that of engaging an undisturbed wire (see Appendix V). In the case of a nose-wheel aircraft with its main wheels on the ground or deck, the chances of engaging a wire are greater when in a nose-up attitude than when in a nose-down attitude, because in the nose-up attitude the hook suspension is trailing at a smaller angle with respect to the deck, than when in a nose-down attitude, with a result that the hook is in a more favourable attitude for engagement with the wire, since the small trail angle is less conducive to hook bounce. This condition is one of first importance when considering arresting gears as an overshoot safety measure on land runways.

One has only to witness a few deck landings of aircraft fitted with hook installations having, alternatively, good and poor anti-bounce properties, in order to appreciate the existence of a problem having a fundamental bearing on the safety of deck landing operations. However, the factors which contribute to this bounce phenomena are not at all obvious, and realistic theoretical treatment becomes most intractable....

...Fig. 1 illustrates a typical layout of a hook installation and shows the parts with their names as will be used in the subsequent text. The element known by common usage as the hook damper, is not necessarily a damper in the strict mathematical sense, and in the U.S. Navy is known by the more lengthy but more exact title of: Arresting-hook shock absorber and hold-down device....

...It is clear therefore that the bounce properties of an arresting hook during landing cannot be explained in terms of the simple percussion examples described above, these effects, if any, making only a small contribution to the hook bounce behaviour. The next section shows that the initial hook bounce is caused by a wedge action between the hook suspension and the deck, the ‘wedge’ being the angle between the deck and the descent path of the aircraft....
__________

...Finally, a plea is made for simplicity of design with due regard for ease of servicing, maintenance and inspection, bearing in mind that with the aircraft in a static attitude, whether it be a nose-wheel or a tail-wheel layout, the hook in the ‘down’ position is not at the limit of its travel, particularly with a tail-wheel aircraft....

...During arresting proof strength testing, when the aircraft is taxied at speed into an arresting gear (on a land installation), an indication of the effectiveness of the damper can be seen during the taxying run with the hook down. However, under these conditions it is usually not possible to get the hook into its fully down position, since the wheels must be clear of the deck or ground to achieve this.....

...11. Conclusions:— With the ever increasing approach speeds of successive generations of deck landing aircraft and in consequence of this, the reduced area of touch-down following on which satisfactory arrested landing can be made, it is imperative that arresting hook bounce shall be reduced to an absolute minimum in order to insure engagement with an arresting wire within this limited area. A critical and searching examination of the hook bounce problem shows gaps in the knowledge of the fundamentals of the problem.

The probable use of arresting gears on airfields again makes it essential that the understanding of the hook bounce problem shall be developed to as high a standard as possible.

Two clear-cut conclusions emerge from the present study, namely, that the trail angle of the hook should be as small as is reasonably possible, certainly not more than 65 deg if possible, and that the surface of the touch-down area shall be free from obstructions. Both these factors have become self evident in a qualitative manner, particularly the latter, from experience during the past years, and the present study, it is considered, enables quantitative values to be established for the purpose of design and general assessment. The study also demonstrates that even though the above two conditions are met to a high degree, the absence of bounce can only be assured if high damper loads are employed.

No conclusions are submitted here concerning the effect of the flexibility of the hook suspension....
_________________

...There is a danger with contemporary aircraft and arresting-wire layouts that the time of recovery of the arresting wire maybe longer than the time for the hook to reach the wire after the passage of the aircraft main wheels. Under such circumstances the hook will only engage the wire if the hook is in contact with the deck (which demands good anti-bounce characteristics) and even then only if the traiI angle of the hook is small. Fortunately this latter condition is fulfilled in a tail-down landing but not so in the case of a nose-wheeled aircraft rolling on all three wheels. This last point is of importance when considering arresting gears as overshoot preventers at the ends of runways.

In order to ensure recovery of the cable before the arrival of the hook–for a given engaging speed–it is obvious that the cable tension should be as high as possible; the distance between rope supports as small as possible; and the wheel track and wheel axis to hook distance as big as possible. Practically all these requirements are in conflict with requirements in respect of other considerations. Thus the only recommendation which can be made with certainty, in the case of a carrier landing, is to ensure engagement with a wire before the wires are disturbed by the aircraft wheels. The hook suspension is usually of a sufficient length to ensure this happening providing the hook does not bounce after first contacting the deck. Hence a further emphasis is placed on the requirement of a ‘no bounce’ hook installation.

A tail-wheeled aircraft having its arresting hook aft of the tail wheel is a common configuration of special interest. If the tail wheel is rolling on the deck and depresses the wire then engagement of hook and wire is only possible if the hook is in such an attitude that the hook beak is able to ‘scrape up’ the cable off the deck. There are contemporary aircraft where this is not possible, but the occurrence of the tail wheel depressing the wire before hook engagement is considered to be so rare with conventional layouts during deck landing that it can be neglected; the aftermost position of the hook installation being most desirable in its ability to prevent excessive pitching during the subsequent arrested motion. Nevertheless when considering an arresting gear for runway overshoot conditions the hook position aft of the tail wheel is undesirable and may be unacceptable unless the hook suspension tail angle is sufficiently small."

[spazsinbad]

Post from elsewhere on this forum repeated here for illustration purposes....
To continue with the Skyhawk theme here is an RNZAF A-4K Skyhawk short field arresting at NAS Nowra NSW Australia where No.2 RNZAF (Skyhawk training) was based for a decade from 1991-2001. Anyway perspective is a little odd because the runway (21) goes downhill steeply from threshold viewpoint. Gear would have been BLISS BAK-9 AFAIK (runway arrestor gear has been upgraded in last several years).

RNZAF NAS Nowra A-4K Skyhawk Short Field Arrest Demo

http://www.youtube.com/watch?v=5MdtnzNv ... 4Z-VgVUpmd

"Uploaded by SpazSinbad2 on Sep 8, 2011
Aircraft probably from No.2 Squadron RNZAF lands further down runway 21 at NAS Nowra (NSW Australia) than usual with hook extended to engage the short field arrest wire (with a much longer pullout than A-4Gs experienced onboard HMAS Melbourne - 1000+ feet compared to 250- feet)."

[alloycowboy]

Hey Spazsinbad.....

After the F-35 main landing gear rolls over the cross deck pendant (cable) it is the spring rate of the these leaf spring "risers" that may ultimately determine whether the F-35 traps or not.