By Tommy H. Thomason

Wednesday, December 12, 2012

Making It Harder Than Necessary?

Designing a carrier-based aircraft means dealing with several constraints that don't have to be addressed by designers of land-based ones. These affected folded size, weight, strength, takeoff and landing performance, etc. and varied by carrier class. However, in general, the designer was required to accommodate the most onerous. One across-the-board standard was the number that could be parted in the first 200 feet of an Essex-class carrier deck.

In the years following World War II, there were four basic U.S. aircraft carrier types:

Note that the elevators, deck width, and landing areas were roughly the same size. The major difference in size was total deck area with the escort carriers, CVEs, having the least. They were also much slower than the others, having a top speed of a bit less than 20 knots versus more than 30 for the bigger carriers including the CVLs.

The speed difference had a major impact on landing and takeoff performance requirements, since wind-over-deck was critical and the most that a CVE could generate in no-wind conditions was its own top speed. Because lift varies as the square of speed, that meant that the benefit of wind-over-deck in no-wind conditions was not about 30% less but more than 50% less.

In the early 1950s, due to budget and other considerations, only a few CVEs were deployable. However, many more were mothballed and available for recall if necessary. As a result, design requirements for new programs like the S2F and even the A4D jet attack airplane required operation from CVEs. Northrop proposed an early version of a lightweight fighter to the Navy in the early 1950s, without success, that was specifically focused on operation from CVEs.

Block Island was among the last of the escort carriers to deploy as such (some went to sea later as aircraft transports or communication relay platforms). Here CVE-106 is operating AF Guardians in the early 1950s as an ASW carrier.
It was put into reserve on 15 January 1954.

Having to deal with the lower wind-over-deck capability of the CVEs did provide naval aviators with extra margin when operating from the faster carrier classes. It also meant that the A4D Skyhawk could be successfully qualified to operate from former Royal Navy Colossus/Majestic-class aircraft carriers that had been modified with an angled deck, more powerful catapults, and stronger arresting gear like Melbourne, shown here alongside Kitty Hawk.


Aerospace test equipment | AvionTEq said...

Carrier-based aircrafts are just some of the attractions that I loved when I visited the U.S Air Force Museum.

Michael Kaintoch said...

Now, what I'd really like to know: Has the A4D ever been actually tested on a CVE, i.e., could it be launched with the H-4C catapults?

Tailspin said...

I don't know about a CVE/L evaluation per se (although the H-4C was similar to the Essex-class catapult that was used to launch A4Ds initially). Wind over deck may have been a problem with CVEs.

The Skyhawk was qualified for operation from HMCS Bonaventure and routinely operated to and from HMAS Melbourne, both Majestic-class carriers that were on the order of CVE/CVL class in size. However, they had been reequipped with steam catapults albeit with very short strokes.

Michael Kaintoch said...

Thank you for the reply.

The catapults are indeed the tricky part. The background is that I'm wondering whether the angled deck CVE design as depicted in Friedman's 'U.S. Aircraft Carriers: An Illustrated Design History' (->[url][/url]) would have been able to operate the Skyhawk in the CAP role. If built, that particular design would have been equipped with H-4B catapults, and Friedman claims that steam catapults would have been required to operate jet planes.

Well, to my best knowledge Antietam performed the canted deck trials in 1953 with her original catapults, i.e., H-4B. The tests were, amongst others, conducted with the Banshee which was a much heavier plane than an early Skyhawk. Therefore I fell it should have been possible, even with less wind above the deck. But that's just my personal guess...

Tailspin said...

The critical metric is wind-over-deck. According to the Service Trials report on the A4D-1, the H-4B generated end speed for a Skyhawk with full internal fuel only and no external stores was about 85 knots. At that weight (which wasn't very useful from a mission standpoint) it needed about 20 knots wind-over-deck, which a CVE could almost generate, no wind. With two 150-gallon external tanks and a Mk 7, the A4D-1 weighed about 17,600 lbs and required 124 knots wind-over-deck. For an H-4B launch, that would require about 40 knots total from wind and the carrier itself, which could contribute about 32 knots.

Michael Kaintoch said...

The 32 knots, however, apply only for an Essex, not for a CVE. I have only numbers for the initial SCB-43 proposal, which was designed for 26.5 kts. That angled deck alternativ, in particular, is even smaller and less capable. Therefore, I'd estimate its top speed rather to be about 20 kts, which leaves another 20 kts for wind speed above ground.
Hmmm... that's not exactly what I'd like to rely on to operate one fifth of my already limited air group... I guess that has been it for the Skyhawk.

Thank you very much for your detailled answer (and sorry for my delayed reply)!
Michael Kaintoch

I guess

SpazSinbad said...

Apologies for an extremely tardy reply. Being an A4G pilot in VF-805 on cruise late 1971 then early 1972 I can attest the A4G Skyhawk worked well onboard HMAS Melbourne. At that early time (ops started in 1969) we had only 8 A4Gs & 2 TA4Gs (which could not operate from MELBOURNE short deck - not enough deck length to get the trainer nose up again during touch and goes or bolters, this is especially critical at night). The original steam catapult stroke was 100 feet then with the aid of an add on strop catcher lengthened approx. 6-10 feet (after a collision with USS Frank E. Evans at night during flying operations in 1969 - first A4G cruise) during subsequent refit/repair.

The A4G reached the end of that short stroke in less than two seconds. It felt like someone had punched you in the middle of your chest with all their strength. We were told the G was from about 5 to 6. The steam catapult could fling the A4G even at very heavy weights in nil wind in the tropics. The Skyhawk family was stressed for 9G in the lateral direction (direction of catapult) while we were told that a 'warshot' could get us off the deck at max. take off weight in nil wind in the tropics. However to our knowledge this was never practiced with the A4G in those actual conditions.

When alongside in Sydney Harbour the catapult was tested with water filled tanks on a wheeled sled, so I'll guess this is how the capacity of the steam catapult was known.

SpazSinbad said...

"...The Board noted that HMAS MELBOURNE's records show that there had been 8,834 A4 Skyhawk launches since 1969..." Sentence from a summary of the Board of Inquiry into the loss off the catapult (engine failure) of A4G Skyhawk 875 - pilot ejected / rescued OK. BOI approx. Oct 1980

This catapult was one of the last - a few weeks later the last A4G catapult was a cold one - aircraft fell over the front with pilot ejecting / rescued OK. That was it for the A4G with the last cruise for HMAS Melbourne the next year - 1981 - being without any A4Gs onboard with the catapult & arrestor gear deemed NOT OK for A4Gs.

SpazSinbad said...

I'll guess there are any number of A-4 catapult videos with few as good as these slow motion A4G catapults with new strop catcher plus slow motion arrest videos.

SLOW MOTION Catapults A4Gs 886 & 889
see new strop catcher at work

A4G Arrest HMAS Melbourne & Hook Runner Slow Motion

A4G 885 Cold Catapult Ejection - Pilot OK - Compilation
last A4G catapult - ever....