Tirpitz and Graf Zeppelin 1941

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Tiornu
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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Mon Jul 11, 2011 2:11 am

It would have to be a small strike. How many launches could the catapults perform before they had to be recharged?

delcyros
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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Mon Jul 11, 2011 12:58 pm

Neither the Ju-87C nor the Fi-167 were dependent on catapult launch. The Bf-109T was the purpose of the catapult trollies, allowing the Bf-109 to retract it's landing gear during catapult launch. I doubt that it was dependent on catapult, either.

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Re: Tirpitz and Graf Zeppelin 1941

Postby lwd » Mon Jul 11, 2011 2:13 pm

Tiornu wrote:It would have to be a small strike. How many launches could the catapults perform before they had to be recharged?

From previos discussions I believe it was 20-30 or about half her airgroup and then it was something like an hour and a half before she could have launched the rest. Success in arial attacks on ships seemed to depend on surprise or overwhelming the foe. A small strike group is going to have a harder time even with isolated targets. Also don't forget operational losses. The Me109 was rather infamous for those wasn't it? Operating on a carrier it would have been even worse, indeed an accident while landing can potentially impede further air ops for a considerable period of time.

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Re: Tirpitz and Graf Zeppelin 1941

Postby lwd » Mon Jul 11, 2011 2:16 pm

delcyros wrote:Neither the Ju-87C nor the Fi-167 were dependent on catapult launch. ....

But the catapults were raised significantly above the height of the deck making them potential obstacles for not catapult launches.

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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Mon Jul 11, 2011 3:31 pm

Neither the Ju-87C nor the Fi-167 were dependent on catapult launch. The Bf-109T was the purpose of the catapult trollies, allowing the Bf-109 to retract it's landing gear during catapult launch. I doubt that it was dependent on catapult, either.

That misses the point, doesn't it? Obviously these planes could take off without a catapult; they did so, all war long, from land bases. But the German concept of carrier warfare dictated that they use this contraption exclusively. Only people who didn't know what they were doing would come up with such a ridiculous system. This was one of the items that would have kept GZ out of action until 1943. The catapults would have to be removed and reinstalled flush with the deck. The Germans were perfectly capable of making a catapult that didn't protrude above the deck, but they chose to do otherwise. Hopefully they would have discarded the trolley system entirely.
It is unknown what other flight deck changes they would have made. We know the Americans thought the equipment was inefficient and unsafe.

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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Tue Jul 12, 2011 8:36 am

Ok, I get it. You seem to expect that no launches could be made without catapults due to obstacling rails. I beg to differ. Altough the idea was clearly to operate half of it´s airgroup, the fact that GRAF ZEPPELIN was a lone carrier designs (and Träger B slowed to get more experience from Träger A services) required that operationally, the ship had to conduct launch and recovery of airplane simultaneously instead of a pair of carriers operating launch and recovery in succession. This at least was the reason for the catapult system. The sophisticated pre-heaters were to economise avgas for increased practical range of the airplanes, bypassing their warming up period.
All planes could be launched without catapult, however. the rails were spaced off the centerline distant enough that You could launch two each Ju-87 or Fi-167 without obstacle creation of the rails much the way they would take off from runways.

The most strange system among the catapults were the trollies and the compressed air operating system, though. I don´t wonder why they did use trollies, the system was found to be effective aboard cruisers and battleships and trials conducted with GZ´s system in 1939 also concluded with good results (doubtful if this would have been mirrored onboard services). But compressed air? This is a potential hazard and the postal catapult ship SCHWABENLAND operated in 1934 already steam catapults feed by the main machinery boilers.

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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Tue Jul 12, 2011 3:12 pm

You could build a small castle on the flight deck, and the Fi 167 could take off over it, I think. But it would be ridiculous to build a small castle on the flight deck, and it was ridiculous to foul the front end of the flight deck with protrusions of any sort. With them there, the distance for rolling take-offs by the 109 (as officially specified) would put the plane back as far as the aft elevator. That would make for an interesting attempt at simultaneous launch and landing. And where exactly is the flight deck crash barrier? (If the Germans foresaw two-carrier teams launching and landing in succession, that's further evidence of their limited understanding.) The Germans were perfectly capable of making a catapult that was even with the deck; after all, they actually did so on other ships. GZ's catapults were closely spaced, the distance between them (including their side slopes) being less than the wingspan of a plane. These are the sort of things that the Germans would have found necessary to change before GZ would enter operational service.

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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Tue Jul 12, 2011 3:48 pm

The centerline axe distanc between the two rails was 14m, the distance between their inner sloped covers was 10m. You are right that this is less than the span of a plane but it doesn´t matter. The wings do have enough clearence to the runway AND to the catapult rails so that they cannot touch them, save an emergancy case. Important is the track not the wingspan. 10m is enough space for two each Ju-87 or Fi-167 to start side by side intersected much like the japanese did:

http://www.history.navy.mil/photos/images/g100000/g176150.jpg

(there isn´t enough deckspace to park three type0´s side by side on the flight deck, but they did)

The portrusions were carefully studied in windtunnel tests and the creation of vortexes was ruled out as a result of these studies. As I mentioned previously, the catapults were there to start & recover planes simulaneously. If You drop the requirement of simulatenous operation You have the entire deck length to launch aircrafts without catapult.
Rolling take off speed of Bf-109T was pretty low actually and significantly lower than Bf-109F, -G or even -E or Seafire derivates. Rolling take off distance was specified without wind component and few carriers in this period could operate their fighters without headwind factor at all. The take off speed is 68kts at max gross weight and 63 kts at normal gross weight (clean fighter configuration) with the carrier alone capable of doing 30 to 35 kts. Add 10 kts wind and the Bf-109T only needs to accelerate 20 kts before lift off. Since acceleration is related to thrust/wight ratio´s and thrust is related to propellor size, pitch, blades and horsepower You will see that the Bf-109T had a superior power/weight ratio compared to it´s period naval opposition and hence a superior acceleration. Both the Ju-87 and the Fi-167 had a less favourable power/weight ratio but this was more than offsetted by the lower take off speed of these planes. The Fi-167 had a lower take off speed (=32kts) than the top speed of the carrier was predicted to be capable off (33-35kts). This is fully equipped, landing speed was specified with min. 20.5 kts (=38km/h). Consequently, the Fi-167 didn´t required catapult use at all and could be launched on the deck in front of the rails or (...with the gear track...) in between them.

The catapult compressed air capacity was sufficient to launch all 10 Bf-109 and 13 Ju-87 but not large enough to additionally launch the 20 Fi-167 of the original airwing size. But You have to reckon that the Fi-167 was not to be catapulted in the first place.

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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Tue Jul 12, 2011 5:16 pm

You are correct that the catapults effectively restrict the forward end of the flight deck to a mere 10m or so. You are incorrect that the wingtips are not a matter of concern, unless the Germans unerringly lift both wheels from the deck simultaneously. We can ignore the requirement of simultaneous launch and landing because it would have worked its way out of consideration quickly enough. That doesn't obviate the use of catapults of course, nor does it obviate the need for a crash barrier. But it's my contention that such things would be corrected during the period when the ship was being made operational. Perhaps some of the work would be done while the ship was having its hull form fixed. By that time, the Fi 167 is out of a job.
The catapults could not launch ten 109's and thirteen Stukas; they could launch only eighteen aircraft before needing 50 minutes to recharge. If the catapults were rightly recessed into the flight deck, the first eighteen planes could be catapulted, which would probably leave sufficient deck space available for rolling take-offs by the remaining planes.

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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Wed Jul 13, 2011 12:41 pm

I do think that we have different data to base our conclusions on*. The compressed air reservoire of the DKW catapult was designed to allow launch of eighteen airplanes, specification called for 5 ts gross weight and 36m/s take off speed, thus requiring the aequivalent of 64,152 mt total power compressed air power. The 13 Ju-87 at full loaded gross weight (4.33ts with one SC-500 and four SC-50 at a take off speed of 38m/s) required 41,923 mt from the reservoir, roughly 2/3 of the reservoire. The Bf-109T1´s MTOW was 3ts, thus catapulting ten Bf-109T1´s would require an additional 21,660 mt from the compressed air reservoire. After that the reservoire was almost empty (569 mt remaining), and I don´t think this is a coincidence. It´s a design feature allowing GRAF ZEPPELIN to catapult all of it´s fighters and dive bombers in within 11 minutes and 30 seconds with the twenty remaining Fieseler making rolling starts (= STOL, depending on the carriers speed and headwind factor, a vertical take off would be possible but not from a safety point of view). Note that the Fieseler did not participate in catapult trials (which the Ar-195, the Bf-109 and the Ju-87 did!) and I have yet not come across a single photograph showing trollie attachment points in any of the Fieseler prototypes. -they didn´t required them.

* I offer my sources:

Breyer, S., Flugzeugträger "Graf Zeppelin" (Marine-Arsenal vol. 4), Friedberg, 1988.
idem, Der Flugzeugträger "Graf Zeppelin" (Marine-Arsenal Special vol. 1), Wölfersheim 1994.
Israel, U. H.-J, Einziger deutscher Flugzeugträger "Graf Zeppelin", Herford 1994.
idem, "Flugdeck klar!" Deutsche Trägerflugzeuge bis 1945, in: Fliegerrevue extra 2 (Berlin 2003).

You are incorrect that the wingtips are not a matter of concern, unless the Germans unerringly lift both wheels from the deck simultaneously.


As I mentioned above, I don´t think so. The vertical part of the rail coverage extended only about a ft above the fligthdeck with the sloped and part extending another feet. The lower wingtips of the Fieseler Fi-167 do not touch these areas unless the plane takes off with a roll in excess of 20 deg, by which we have to talk about an accident, irregardless of whether or not the aircraft manages to take off:

Image

I doubt that the stability figures of GRAF ZEPPELIN were worse enough to allow for a roll of 20deg in seaconditions which would allow for flight ops. Roll periods not in within quarters of seconds, either. I doubt that this would have a notable effect. A case could be made that the gears could crash on the rails but then again, looking more carefully this wouldn´t easily happen because the deck is slightly sloped towards the rails and a pilot not able to controll direction of his take off has no buisness on a carrier, either. You have 10m wide track to lift off. From my personal experience, it´s not to difficult to precisely take off from much narrower strips with worse turbulent air and side wind factor, but admittently on a solid ground and not from a floating platform. The rails offer points of easy to recognize reference lines to the pilots view out from the cockpit, which is a nice thing to have for planes with limited forward downward visibility during take off (meaning the Bf-109T here).
The clearence of the wingtips to the ground by the Ju-87 is even larger. I think that the Bf-109T had the lowest clearence. Thus, the "obstacle" theory isn´t well founded in my perspective. The Fi-167 was not dropped from the proposed airwing before the complete revision of the design in mid1942.

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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Wed Jul 13, 2011 5:09 pm

Yes, the catapults were designed to launch a total of eighteen planes. I have the same sources you've listed, along with Whitley and the 2008 Warship International article. (I've got a copy of Hadeler's Fluzeugschiffe, but it's printed in Fraktur, and my eyes threaten to bleed every time I look at it.)
We agreed some time ago that take-off is no problem for the Fieseler, so I don't know why it continues to figure on the discussion. In any case, I claim the Fieseler would not have been on board anyway. It was declared obsolete, attendant to the decision to resume construction in May 1942, a declaration that would have come earlier if focus on carriers had continued uninterrupted. GZ herself could not have been operational before late-1941 even by optimistic timelines, so there doesn't seem to be much of a window for the Fieseler.
Regarding launches, my main concern is with the 109, but again, I contend this would not have arisen in action as the Germans would have corrected their mistake. The height of the catapult housing above the deck was not constant, so the hazard would vary. The flight deck had an exaggerated camber, but I'm not sure how that would affect things. The distance between the deck axis and the plane's axis would lower the wingtip, though the degree might be minimal. Since there was no reason to reduce the flight deck to an effective width of 10m, the Germans would have exercised the common sense to undo it. Did any experienced carrier navy encumber its launch path with such obstructions? Of course not. The idea that rails aid in take-off by providing a reference point is backward, to say the least. You can argue that a qualified pilot should not be troubled by such things; more reasonably, you can argue that the difficult task of carrier take-off was challenging enough without deliberately making things more difficult. The hazard of ship's motion comes increasingly into question for the carrier whose hull was improperly designed in the first place.

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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Wed Jul 13, 2011 10:06 pm

I am not sure if I understand You. Let me expand my thoughts.

You seem to be convinced that the Fi-167 wouldn´t be part of any airwing. I would like to know what makes You sure about this detail? Fieseler signed contracts to deliver them but stopped production after the preproduction models because GRAF ZEPPELIN´s fitting out was halted in May 1940 when ca. 90% complete.
The Fi-167 was taken out of consideration in late 1942, not earlier. And that was with the hope expressed of getting GZ service ready by late 1943. I suggest that You encounter three years difference here. These three years make up for quite a difference.
What are You going to supplement the Fi-167 with when You continue along schedule with the fitting out of the carrier? The Ju-87C couldn´t lift off a torpedoe. The Ju-87D could but this plane isn´t aviable before 1942. In my mind one should replace the Ju-87 entirely with Fi-167. The latter may not have been that fast but assuming a Db-60E rated to 1.42 ata (using C3-fuel) instead of a Db-601N and the difference in speed between a Jumo-211J driven Ju-87E and a db-601E driven Fi-167 is simply not justifying the preference of the Junkers.
The Fi-167 had a longer range, could dive bomb, carry a torpedoe (or big bombs), had better handling and a larger general flight envelope.
It´s true, it´s an odd looking biplane but does it compare unfavourably with -say an Albacore, a Stuka, a Dauntless or a Barracuda?
My strictly personal opinion was that -had the fitting out been continued then GRAF ZEPPELIN would have been completed during winter 1940/41 with most of the year 1941 spent working up, isolating and deleting problems and create useful deck procedures. It´s not unreasonable to see her ready for action in late 1941 and by that time the Fi-167 is the mainstay of this carrier. I do think that experiences in the working up period would also be favourable to the Fi-167, guessing from it´s benign flying and gentle stall charckteristics.
It was the only plane not intended for catapult action and thus GZ could entirely operate it´s full airwing without breaking for replenishing the compressed air reservoire. This would probably have played a role in the decision making process, too. With the airwing centered around Ju-87 and Bf-109´s, only one would sooner or later get rid of the whole catapult system because it couldn´t provide enough power to support them all and what´s the point in having an installation sufficiant for 50%? That would make for a big improvement in allowing rolling take off but it´s still in the future by that time.

Regarding launches, my main concern is with the 109, (...)
The height of the catapult housing above the deck was not constant, so the hazard would vary.

the "obstacle" was to low to play any significant role as mentioned in my post above and the gentle slopes allowed to roll over them:

Image

It requires about 20 deg roll to touch the rails with the wingtips. This is way to much to justify the term "obstacle". Contrast this with another, successfull carrier plane like the Fairy Swordfish:

Image

You see that it´s wingtips may touch the flat runway with only about 18 deg roll factor but here it´s not assumed to be a problem. The larger anhedral of the wings in combination with larger struts allowed the clearence to the ground -or in this case the catapult rails. I don´t think this really becomes an objection for rolling take offs of either Bf-109T, Ju-87C or Fi-167 on board GRAF ZEPPELIN.

You can argue that a qualified pilot should not be troubled by such things; more reasonably, you can argue that the difficult task of carrier take-off was challenging enough without deliberately making things more difficult. The hazard of ship's motion comes increasingly into question for the carrier whose hull was improperly designed in the first place.


I do not agree that qualified pilots do not require or are grateful for additional directional evidence if pilot view is obstructed. In fact signaling over the side was also done in many cases during approach conditions of past and more recent carrier deck operations.

I do not know why GRAF ZEPPELIN´s hull is improperly designed. But perhaps You can expand more upon this?

btw-do You have Hadeler´s vintage edition of Kriegsschiffbau?

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Re: Tirpitz and Graf Zeppelin 1941

Postby Tiornu » Wed Jul 13, 2011 11:51 pm

No, I have only the one Hadeler book.
Improper weight calculations caused GZ to have a natural list of 4.5 degrees. This was noticed only after the project had been restarted, and an asymmetric bulge was added to fix the problem. It also increased bunkerage, I believe, and enhanced torpedo protection, so all in all it worked out well.
According to Breyer (p 64 in my AJ Press edition), the Fi 167 was declared obsolete in May 1942, so there was no problem with the availability of a torpedo-armed Ju 87. Was the tail gear of the Stuka altered in any way when adapted for torpedo work? You don't need to convince me of the merits of the Fieseler. I think it's a fine aircraft, and I even like the look of it.
The "gentle slopes" of the catapult housing had side ridges 200mm high. That's an 8in bump while you're trying to take off from a pitching carrier deck. I don't know what pilot would rather have an obstruction on deck rather than paint. Any calculations that fail to show the varying height of the housing above the deck cannot be of much use.

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Re: Tirpitz and Graf Zeppelin 1941

Postby Byron Angel » Thu Jul 14, 2011 12:45 am

..... If I'm not mistaken, the Bf109T had an extended wingspan.

delcyros
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Re: Tirpitz and Graf Zeppelin 1941

Postby delcyros » Thu Jul 14, 2011 9:09 am

@ Byron:

This is correct. The Bf-109T received an inner wing filet section which increased the span to 11.08m. The picture above shows the Bf-109T frontally, not the -E, -F, or -G-derivates.


@ Tiornu:

Even with - it´s two years after the carrier was stopped and by this time they couldn´t make the carrier operational in within a few months. They based their decision upon more distant thread estimates, not about recent ones.
Had the carrier continued in fitting out in 1940 there would be zero possibility to take the Fi-167 out of the airwing. It would enter operational service with the Fi-167 as a mainstay aircraft. Before winter 1941/1942 the Ju-87D1 isn´t aviable either. And the Ju-87C cannot take torpedoes. Whether or not the Ju-87D1 could is an interesting question because this plane couldn´t dive bomb anymore (the principal reason it could be stressed to accept higher payloads).
The Ju-87E was estimated to be able to dive bomb, requiring further modifications to be made on the original Ju-87D airframe.

The "gentle slopes" of the catapult housing had side ridges 200mm high. That's an 8in bump while you're trying to take off from a pitching carrier deck. I don't know what pilot would rather have an obstruction on deck rather than paint. Any calculations that fail to show the varying height of the housing above the deck cannot be of much use.


There is no vertical "hump" on the rails. The small hump visible in the photos from the BA Freiburg are to be covered with deck planking as should the slopes but not the flat covers of the rails. The slopes extend for 800mm to 1000mm at 15 deg. The question isn´t whether or not a completely recessed catapult would be preferable -to this I think we both agree- the question is whether or not the choosen form of installation prohibits rolling take off -and to this question I disagree because -as shown above- there is no possibility to touch them with the wingtips unless an accident is happeneing and the interspace between the two rails is large enough to allow for rolling starts with the given gear tracks.


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