Aircraft Carriers

[PR19_Kit]

This is the current system used by modern tricycle undercarriage jets (taken from wikipedia).

I think I said that a bit further up the page.........

This system requires the landing gear to be re-stressed to take forces from a different direction to that which would previously be the case. Older type aircraft would be stressed to take high vertical loads, relatively smaller lateral loads and longitdunal loads that would be mostly from forward to aft, to take the landing shock.

With the nose gear leg launch system they'd have to take much higher loads in the aft to forward direction as well.

[Old Wombat]

You did, Kit, which is why I included it as an example.

In all honesty the new system (I call it new but it's been in use since the mid-/late-70's, I think) is probably the simplest, most efficient system going but it requires 2 things that most WW2 fighters didn't have;
1) a tricycle undercarriage arrangement, &
2) jet engines capable of moving bomber-weight aircraft as fast as fighters.

Seriously, modern carrier fighter aircraft are so heavy that the weight of their seriously chunky landing gear is a minor element in their overall mass & is easily carried by their enormously powerful jet engines.

For the small, piston engined fighters & light bombers of WW2 every kilo of extra mass took a serious toll on their performance. So, the lighter the modifications required to the aircraft, the better.



Guy

[Logan Hartke]

For the small, piston engined fighters & light bombers of WW2 every kilo of extra mass took a serious toll on their performance. So, the lighter the modifications required to the aircraft, the better.

Yes, but it was the very fact that they weren't jet powered that generally meant that a catapult launch was unnecessary in the WWII timeframe.  The lower top speed of WWII piston-powered aircraft practically translated to lower take off speeds, too.  New jet aircraft were designed for higher speeds, especially the new aircraft with swept wings.  As a result, they weren't as good at low speeds.  Compounding the issue is the fact that early jet engines just couldn't give the same acceleration that piston engines could.  Once you got them going, they were great, but off the line, the early jets had trouble.  Combine that with the higher gross weights, and you can see why the steam catapult went from "handy in a pinch" to a "must-have".


An F6F Hellcat, for instance, could get off the deck at about 75 kts, whereas the F8U Crusader was closer to 135 kts and the F-14 Tomcat about 275 kts.  In the case of the Hellcat, if the carrier has turned into a wind of just 10 kts and is cruising at 30 kts, that 2,000 hp engine just has to make up the remaining 35 kts to get airborne.  In the case of postwar carrier planes, you still have 95 kts to go with a less perky engine and a higher gross weight.  ou can't make the wind go any faster and 30-35 kts is about as fast as carriers could practically go from 1945-present, so those weren't going to be any help either.  You can't make the take off run any longer, so what are the options?  JATO/RATO.  It could work in a pinch, but it had its limitations.  This was used to help P2V Neptunes get the extra oomph necessary to get them off the deck for a nuclear strike.



Other than that, catapults were really your only option to make up that 95-200 kt.

Cheers,

Logan

[NARSES2]

An F6F Hellcat, for instance, could get off the deck at about 75 kts, whereas the F8U Crusader was closer to 135 kts and the F-14 Tomcat about 275 kts.  In the case of the Hellcat, if the carrier has turned into a wind of just 10 kts and is cruising at 30 kts, that 2,000 hp engine just has to make up the remaining 35 kts to get airborne. 

Logan can I ask a possibly stupid question ?

I might be missing something but if a carrier turns into the wind which is 10 knts and is steaming at 30 knts then the speed is still 30 knts with a 10 knt headwind ? Means Hellcat needs to find 45 knts. ? As said I might be missing or miss-understanding something.

Cheers

Chris

[PR19_Kit]

I might be missing something but if a carrier turns into the wind which is 10 knts and is steaming at 30 knts then the speed is still 30 knts with a 10 knt headwind ? Means Hellcat needs to find 45 knts. ? As said I might be missing or miss-understanding something.

Something screwed with your maths there Chris......

If the carrier's doing 30 kts directly into a 10 kt headwind the WoD ('Wind Over the Deck') is 40 knots. The Hellcat needs a speed of 75 kts to get airborne so it only has to do 30 kts across the deck to get there.

[Spey_Phantom]

i think this can be used as an exsample:

http://www.youtube.com/watch?v=Temm5lI-zUI&feature=related

http://www.youtube.com/watch?v=F6E7sq91Gkw

in this case, the car represents the carrier.
if the car is traveling at 35kts, a plane needs 65kts to take off.
so 65 - 35 = 30kts.

so if you have a headwind of 30knots, ad that to the speed of the car, thats 65kts.

[Logan Hartke]

If the carrier's doing 30 kts directly into a 10 kt headwind the WoD ('Wind Over the Deck') is 40 knots. The Hellcat needs a speed of 75 kts to get airborne so it only has to do 30 kts across the deck to get there.

Well, the math isn't quite there (75-40=35, not 30), but yeah, you get the idea.

Nils, that's exactly the idea.  I'd like to see that same stunt pulled with a Crusader or Tomcat.  You'd need a very impressive Hilux.

Cheers,

Logan

[NARSES2]

I might be missing something but if a carrier turns into the wind which is 10 knts and is steaming at 30 knts then the speed is still 30 knts with a 10 knt headwind ? Means Hellcat needs to find 45 knts. ? As said I might be missing or miss-understanding something.

Something screwed with your maths there Chris......

If the carrier's doing 30 kts directly into a 10 kt headwind the WoD ('Wind Over the Deck') is 40 knots. The Hellcat needs a speed of 75 kts to get airborne so it only has to do 30 kts across the deck to get there.

It's not my maths it's my understanding  If you are doing 30 kts then you are doing 30 kts regardless of the headwind. What I can't grasp is how can a headwind, which is traveling in the opposite direction to the ship, add to the forward speed of the Hellcat ?? Now if WoD is different to forward speed then I might be getting there.

I get the impression that this is one of those things that will need to be explained to me at Telford by some kind gentleman with a large sheet of paper whilst I have a pint in my hand. I can just see the faces of the waiters in the Chinese when all the table stuff is being moved around in order to explain it 

[Hobbes]

Yes, WOD is different from the forward speed of the ship. WOD consists of 2 parts:

1. the true wind speed and direction, i.e. the wind you would measure if you were standing still.
2. the speed and direction of the ship.

The WOD is what you measure when you stand on the deck with an anemometer. When the ship is lying still, you're measuring the true wind speed. Crank up the speed of the ship, and you have to add [1] and [2], taking into account their directions.

If you sail the ship into the wind, the two factors are in the same direction, so you can add [1] and [2] to get 10 + 30 = 40 knots.
If you were to sail in the opposite direction, you have to subtract them: -10 (because this part of the wind is now coming from astern) + 30 = 20 knots. 

This is why ships turn into the wind before launching.

[Logan Hartke]

It's not my maths it's my understanding  If you are doing 30 kts then you are doing 30 kts regardless of the headwind. What I can't grasp is how can a headwind, which is traveling in the opposite direction to the ship, add to the forward speed of the Hellcat ??

Because what matters is the relative speed of the air that's traveling over the airfoil (wing).  To maintain lift equivalent to the aircraft weight, it has to be X kts (different for each type of aircraft).  For the Hellcat, X is about 75, so it needs air traveling at 75 kts over the wing.  If you're on a runway with 10 kts of wind blowing into your face, that's 10 kts of air over the wings.  Not enough.  If you drive your runway into the wind at 30 kts, that's 30 MORE kts, for 40 total.  That means that you just need to find a way to make up the remaining 35 kts.  In the case of the Hellcat, it used an R-2800 turning a 13 ft propeller.  That did the trick.

If you need more kts, for whatever reason (carrier is dead in the water, no wind, tail wind and carrier can't turn into it for operational reasons, or--most likely--the plane needs a higher take off speed), then you need a quick boost, like a catapult, JATO/RATO, even a bit of help from gold ol' gravity because you set your flaps wrong.

Cheers,

Logan

[Old Wombat]

Logan, I'm quite aware of the usual method of carrier launch in WW2 but this conversation was triggered by the post quoted below & the German carrier posts leading up to it.

i see, but still i have one thing that doubts the carriers lauch capability.

while the british, japanese and american carriers had the aircraft take off, one by one, from the deck under they're own power, the Germans planned to lauch they're aircraft by pairs with the catapults. but these catapults were the same as they used on battleships/seaplane tenders to launch seaplanes, with the aircraft mounted on a collapsable cradle. i thinking, to launch those aircraft, it had to be very time consuming to mount them on the cradle first?

http://en.wikipedia.org/wiki/Graf_Zeppelin_class_aircraft_carrier#Catapults

Basically I was saying that there are better methods available, & even were at the time.

Now, while I know the Germans had a tendency to over-engineer things, I'm pretty sure that they would, eventually, have adopted a simpler & faster catapult launch system than the battleship/cruiser rail-&-cradle system prior to production.



Guy

[NARSES2]

Thanks Hobbes and Logan....I get it now 

Chris

[Logan Hartke]

Basically I was saying that there are better methods available, & even were at the time.

Now, while I know the Germans had a tendency to over-engineer things, I'm pretty sure that they would, eventually, have adopted a simpler & faster catapult launch system than the battleship/cruiser rail-&-cradle system prior to production.

Yes, but as you pointed out, better and simpler wasn't always the German way.  Germans were relative newcomers to the world of carrier aviation, so I think it would have taken some years of service to work out the kinks.  I've always thought the Graf Zeppelin was neat, but the more I've studied it, the less impressed I've been.  That having been said, I think the Ju 87C and Bf 109T would have been perfectly serviceable carrier aircraft.

Cheers,

Logan

[Mossie]

Found an old Popular Mechanics article showing a colour illustration of the Skyhook submarine concept.  It's similar to the pic GTX posted on page 12:
http://www.whatifmodelers.com/index.php/topic,9868.msg362968/highlight,skyhook.html#msg362968

Original article here, I spliced it together from seperate pages:
Popular Mechanics Vol 162 No.4 April 1985

[PR19_Kit]

The Skyhook plan is becoming more and more attractive in my mind. I think a diorama with a SHAR or SHAR2 suspended in mid-air is becoming quite a good idea. Mind you, what I use to build the 'hook' bit would be a bit of a problem.........