Any flight tested figures for the B-25 later model take-off and landing dista. Please do not post flight manual data as I have that plus the data does not really jive with the fact of the Doolittle Raid (if the manual figures were absolutely true, no way could it have taken-off from any carrier). Www.wwiiaircraftperformance.org has B-26 reports, but no B-25 reports.
B-25 later models take-off and landing data tested
- Thread starter Trilisser
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FLYBOYJ
"THE GREAT GAZOO"
I suppose they had great pixie dust! Why don't you post that data and show us what you're talking about?
Snautzer01
Marshal
- 46,292
- Mar 26, 2007
Because both do not discribe the pixy dust. That was most secret and could not get in a plain manual ment to fly the thing.
- Thread starter
- #5
For a very simple reason: E.g. the data given in the P-39 pilot manual differs very greatly from the what was achieved in tests. For the P-39 the tested data at approximately 7300 lbs was 660 feet ground roll and 1060 feet to clear 50 ft. obstacle. Pilot manual gives at 7400 lbs a ground roll of 1350 ft. and to clear 50 ft. obstacle 2150 feet. In other words, nearly 100 % higher figures. So do not ask why I don't trust the manual.
For the B-26, British official data sheet gives a 50 ft. obstacle clearance a distance of 1500 yards at 37,000 lbs. In American tests at 35,100 lbs the same distance was only 770 yards. It is very clear that the manual figures are very conservative.
fubar57
General
Snautzer01
Marshal
- 46,292
- Mar 26, 2007
FLYBOYJ
"THE GREAT GAZOO"
I wonder if there is another guy in an alternate universe that thinks the Flight Test data is overly exaggerated?
Maybe you should just pick some numbers that you are happy with and enjoy the day.
- Thread starter
- #10
Well, if one checked an x number of pilot manuals and discovered that the data given in all of them is greatly in disagreement with data obtained from actual tests, it is quite logical to assume that the same applies to the B-25 manual as well. Second, it is clear that if the manual was absolutely correct, the Doolittle Raid would have never taken place as none of the B-25s taking part would have been able to take-off (yes, I have added the effect of the carrier's speed)! So what more do you need to prove the manual data wrong?
- Thread starter
- #11
Are you perhaps one of those guys in a universe that thinks pilot manuals are 100 % accurate? Maybe you should just pick up a phone and call a doctor to seek a brain surgery to remove that pile of manure within your skull.
FLYBOYJ
"THE GREAT GAZOO"
Show us SPECIFICALLY what you're talking about? Pages, numbers, charts.
Think about this though - an aircraft carrier going 20 knots into 30 knot winds, 500' run, aircraft accelerates to about 80 mph, crank in full flaps (there may not be charts developed for the take off configuration the Doolittle Riders used) and it's very do-able.
Feb 1942, this was actually demonstrated aboard the Hornet.
Here's a good discussion on this; B-25 Takeoff Distance
Lastly PBJ-1H's have taken off and landed on aircraft carriers after the Doolittle raid.
Since we're talking about take-off lengths for the B-25 and the Doolittle raid, I have taken the time to see if taking off from the carriers' deck was possible or not if, as you wrote, "the manual figures were absolutely true ".
I have done a quick calculation of the lightened B-25B's gross weight with a 2000 lb load. By using the weights listed in p.34B in "The Pilot's Manual for B-25 Mitchell" and taking a look at what equipments were removed from the aircraft (removal of lower turret, radio, norden bomsight, etc.), and also considering the addition of the auxillary fuel cells, I have found a gross weight at take-off of 31,000 lb (let's take 32,000lb to stick to the pilot's manual).
The speed at which the Hornet and Enterprise were sailing (20kt while heading 270° at 8 AM when Doolittle took off) and the relative head-wind of ~26 kt (from WNW) should also be taken in account, giving us a total headwind of roughly 42 kt (or 48 mph) with some sidewind (data from Enterprise's Log of 18/04/42). At p.44 of the pilot's manual, the takeoff run of a B-25 loaded at 32,000 lb on a hard surface is stated to be 1400 ft for a headwind of 40 mph (I'll take 1200 ft for the head wind of 48 mph). The takeoff length of Doolittle's aircraft was 467 ft (this would leave a length of aprox. 800 ft for the last aircraft to take off), leaving ~730 ft (or 500 ft for the last B-25) where the aircraft could potentially crash in the ocean.
The catch here is that all these figures are given for a takeoff with flaps lowered down to 20° (see p.30 of pilot's manual) and gently raising the nose, and on a runway that is at ground level where you can actually hit obstacles. In the case of a takeoff from a carrier deck, there is an appoximate height of 70 ft above water which can leave a margin for the aircraft to gain speed before ending up sleeping with the fish. Also, photos taken from the deck of the carriers and other ships show that the bombers lowered their flaps to 40° and took off with a high angle off attack (see attached pics), which both significantly increased the lift produced by the wings, and thus shortened the takeoff run by a wide margin. Taking these parameters in consideration, the takeoff run could potentially be shortened by 33% (only a guess on my part), which would give a necessary takeoff distance of only 800 ft, leaving only 300 ft and 0 ft for the first and last aircrafts taking-off to gain enough speed to not end up splashing down in the ocean. This means that such takeoff was theoretically do-able even with the more or less conservative values I have taken. And as FLYBOYJ said, history has clearly showed us that is was indeed possible.
In parallel, I have fired up IL-2 1946 with a modified flight model of the B-25J (which I have extensively tested to ensure that I had the most accurate stall speeds in clean and landing configurations) and set up a mission with all the necessary weather conditions to simulate the doolittle raid takeoff. I have done a few tests, and I have managed to get off the deck without splashing down a single time. I don't know if it is relevent enough to my aformentioned estimations but it shows it is at least do-able in a simulator.
I have done a quick calculation of the lightened B-25B's gross weight with a 2000 lb load. By using the weights listed in p.34B in "The Pilot's Manual for B-25 Mitchell" and taking a look at what equipments were removed from the aircraft (removal of lower turret, radio, norden bomsight, etc.), and also considering the addition of the auxillary fuel cells, I have found a gross weight at take-off of 31,000 lb (let's take 32,000lb to stick to the pilot's manual).
The speed at which the Hornet and Enterprise were sailing (20kt while heading 270° at 8 AM when Doolittle took off) and the relative head-wind of ~26 kt (from WNW) should also be taken in account, giving us a total headwind of roughly 42 kt (or 48 mph) with some sidewind (data from Enterprise's Log of 18/04/42). At p.44 of the pilot's manual, the takeoff run of a B-25 loaded at 32,000 lb on a hard surface is stated to be 1400 ft for a headwind of 40 mph (I'll take 1200 ft for the head wind of 48 mph). The takeoff length of Doolittle's aircraft was 467 ft (this would leave a length of aprox. 800 ft for the last aircraft to take off), leaving ~730 ft (or 500 ft for the last B-25) where the aircraft could potentially crash in the ocean.
The catch here is that all these figures are given for a takeoff with flaps lowered down to 20° (see p.30 of pilot's manual) and gently raising the nose, and on a runway that is at ground level where you can actually hit obstacles. In the case of a takeoff from a carrier deck, there is an appoximate height of 70 ft above water which can leave a margin for the aircraft to gain speed before ending up sleeping with the fish. Also, photos taken from the deck of the carriers and other ships show that the bombers lowered their flaps to 40° and took off with a high angle off attack (see attached pics), which both significantly increased the lift produced by the wings, and thus shortened the takeoff run by a wide margin. Taking these parameters in consideration, the takeoff run could potentially be shortened by 33% (only a guess on my part), which would give a necessary takeoff distance of only 800 ft, leaving only 300 ft and 0 ft for the first and last aircrafts taking-off to gain enough speed to not end up splashing down in the ocean. This means that such takeoff was theoretically do-able even with the more or less conservative values I have taken. And as FLYBOYJ said, history has clearly showed us that is was indeed possible.
In parallel, I have fired up IL-2 1946 with a modified flight model of the B-25J (which I have extensively tested to ensure that I had the most accurate stall speeds in clean and landing configurations) and set up a mission with all the necessary weather conditions to simulate the doolittle raid takeoff. I have done a few tests, and I have managed to get off the deck without splashing down a single time. I don't know if it is relevent enough to my aformentioned estimations but it shows it is at least do-able in a simulator.
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FLYBOYJ
"THE GREAT GAZOO"
Great information! But I take simulator data (unless it's a full motion certified unit) with as much confidence as a perforated condom...
Me too, but I still wanted to see if an amateur like me could still pull it on his own
. Besides, I'm well aware of the shortcomings of such an old sim since I have had to fix so much eroneous flight models (I'm looking at you He-111).special ed
1st Lieutenant
- 6,588
- May 13, 2018
All B-25s had to taxi to the narrowest point at the island for takeoff, therefore all take off runs were the same. Also, one aircraft took off with out flaps by mistake.
To all: please respect each other. Personal insults are not tolerated!
GreenKnight121
Staff Sergeant
- 913
- Mar 16, 2014
Now, now... that was a special case - as that PBJ-1H was fitted with an arresting hook and catapult bridle attachment points, so those were arrested landings (2) and catapulted take-offs (also 2).
http://steeljawscribe.com/2007/10/0...om/2007/10/05/flightdeck-friday-more-oddities
Also, note the upward pitch of the bow of Hornet in the photo you linked... this was standard carrier practice for basically all nations - timing the take-off run so that the bow is moving upward as the aircraft leaves the bow. This gives the aircraft the same upward motion as does the modern "ski jump" bow - giving the aircraft more distance and time to reach a flight speed that will keep the aircraft in the air.
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FLYBOYJ
"THE GREAT GAZOO"
Good point but examine how much heavier these aircraft were compared to the Doolittle aircraft.
Wasn't that specifically mentioned in the movie with Van Johnson and Spencer Tracy about the Doolittle Raid?
