Douglas TBD range needed

[Graham Boak]

Originally Posted by JoeB

OTOH if longer and shorter legged a/c operate alongside one another, there would be pressure to allow lesser margins for the shorter range planes to extend the radius of the whole air group as much as possible.

The same book gives the radius of the TBD strike v Shoho as 170 miles and again I would assume that means statute miles.

Joe

Such pressure would be resisted as grossly unprofessional and downright dangerous. The margins are there for good reasons determined by hard experience. In war there is always the suicide option, but it would not be planned for by the USN.

[JoeB]

Originally Posted by Graham Boak

Such pressure would be resisted as grossly unprofessional and downright dangerous. The margins are there for good reasons determined by hard experience. In war there is always the suicide option, but it would not be planned for by the USN.

No, history clearly shows otherwise. Note again I'm am speaking of the specific margins given in the 'A/c Characteristics' sheets of ca. 1943-44, as benchmark, such as I quoted for the SBD-5. The relatively long ranged (compared to its early stablemates, F4F and TBD) SBD was used in practice in 1942 at radii around equal to the those official 43-44 numbers, or only a little less. OTOH the F4F for example, -4 minus drop tanks, had an official radius in the '43 documents of only a little over 100 miles, but was used out to at least 170-200 in 1942, with, in some cases, heavy fuel exhaustion losses.

Another example is the strikes in the Philppine Sea Battle in 1944. It was well known the SB2C's had less margin than the TBF/M's and escorting F6F's but the strike was launched anyway. The military goal was important enough to risk some a/c, and OTOH not all the a/c would be at great risk. The SB2C's suffered heavy fuel exhaustion losses on return.

I think your point would be valid now in peacetime or even 'war' operations (but where there's often little risk of enemy action to a/c) where the planes cost a fortune and take years to replace. USN operations now would vitiually never violate cast in stone NATOPS safety standards for particular a/c even in quasi-'combat' scenario's. But it wasn't the case in WWII. The benchmarks in those ACP sheets were theoretical guidelines, and shorter legged planes operating alongside longer legged ones were demonstrably more likely to be asked to exceed them and accept more risk of running out of gas, if the mission goal was viewed as justifying it.

On the original point of the thread, if we got all the details of TBD fuel capy and consumption and calculated the radius on the same basis as 1944 document for SBD, it would pretty obviously be well under 170 miles, but that was the range of the strike on Shoho, one in which the SBD's were operating well inside their range equally conservatively calculated. More agressive risks were taken with shorter ranged a/c.

Joe

[DuncanM]

The prewar TBD pilot's manual states air miles/gallon as ~4.2/~4.8, loaded/unloaded at 105 knots IAS.

The TBD could carry 180 gallons of fuel, so the theoretical, still air range would be (less 10 gallons for warm-up, TO and climb to minimum altitude) 170 x ~4.5 or 765nm. However, if we subtract a total of 29.5 gallons (10 + 19.5) for a 50min reserve, we would get 677nm, still air range, and a radius of 338.5nm with a 50 min reserve.

However, there are a number of problems with these numbers:
a) they seem to be based upon 9300lb gross weight (TBD with torpedo and 96 gals of fuel and partial oil), when gross weight with full fuel and oil = 9850lb, prewar, so consumption would be higher than stated.

b) wartime TBDs had added armour, armament and avionics. Gross weight was probably at least 10,400lb, for a further increase in consumption.

c) wartime performance figures seem to be much less than in the prewar manual:

I noticed another TBD approaching me from the stern. It was T-3. He signalled his radio was out of commission. The fuselage of his plane was covered with oil and his engine apparently pumping oil badly. He joined on me and we proceeded on our return. At this time I became aware of the fact that my port fuel tank had been pierced - there was also a leaking fuel line inside the cockpit. On checking, I had only ten gallons of fuel left in the port tank. I immediately switched to my port rank, using fuel from the port tank until it was empty. I had lost about 55 gallons of fuel. The engine performed satisfactorily throughout the operation. During approach and retirement, I was using full throttle, turning up 2050 RPM at 35 to 37 inches of mercury. Realising I had about 30 to 35 gallons of fuel, I leaned my mixture to the minimum and throttled back to 23 inches of mercury, speed about 85 knots indicated
. (This is from the combat report of Lt Esders of Yorktown's VT-3.)

statements by other TBD pilots, such as Laub (VT-6) and Clark (VT-3) indicate a maximum low altitude speed with torpedo of only 120 (Laub) knots and 130knots (Clark).

The TBD engine/speed chart has no speed information on 2050 rpm at 35-37" HG.

At 9000lb it shows full throttle as about 36" HG at ~2300rpm, for a maximum speed of 164 knots at SL.

2050rpm at ~31" HG would equal about 148 knots at 9000lb at SL according to the charts.

At 7600lb it shows full throttle as about 36" HG at ~2300rpm, for a maximum speed of 169 knots at SL.

2050rpm at ~29" HG would equal about 148 knots at 7600lb at SL according to the charts.

Thus we can see that the weight and drag increases of the TBD exceeded the data range of the 1938 pilot's manual. Extrapolating from these figures, I would expect maximum speed at SL and ~10400lb to be 159 knots at ~2300rpm with ~36" HG. 2050 RPM and ~36" HG might give 150 knots at standard temp and pressure and a reduction to 130 knots, given increases in drag and tropical conditions would not be unlikely.

At 7600lb, 23" HG and 1800rpm (the minimum on the chart) = ~115 knots, so we see a 30 knot variation from Esders report to the figures in the prewar manual, and the minimum cruise speed on the fuel consumption chart is 105 knots at 7600lb for a 20 knot variation.

So wartime performance is much less, and the implication is that pilots were running the engine at much higher power settings even during a 105-110 knot cruise.

If we use the prewar fuel consumption at 140 knots as indicative of wartime consumption at 105-110knot we get 2.9/3.3 loaded/unloaded AMPG or 3.1 AMPG average.

A 50min reserve now requires 28 gals, additional allowances for 15min combat at full throttle would require another 23 gals for 51gals reserve and 129 gallons now gives only 400nm range, or a radius of ~200nm

[DuncanM]

The weight of the TBD is also a bit of a mystery. Some sources give an empty weight of 6182lb and some state 5600lb.

Using 5600lb empty weight we get the following:

aircraft:5600lb
fuel : 1200lb
Crew: 600lb
Torpedo: 2200lb (additional weight for fairing)
9600lb (full fuel and torpedo.)

9862lb is often given as the loaded weight.

However if the empty weight = 6182 lb, then max TO weight with full fuel and a torpedo rises to 10182lb and coincidently most sources state a max TO weight of 10176lb to 10192lb. However, if we add 300lb for armour, plus extra weight for additional avionics and armament, then a mid 1942 gross weight with full fuel might be 10600+ lbs. When we consider also that these were all high time airframes, probably with high time engines, then the pilot's reports of abysmal performance and very poor ceiling begin to make sense.

[Bill Walker]

"Empty weight" is sort of like "range". You need to know the definition of an "empty" aircraft before you can make a meaningful comparison. Depending at what point in the life of a US military airplane this weight is reported, it may (or may not) include:

crew
GFE (government furnished equipment, like radios, bomb racks and guns)
oil (engine and hydraulic)
unusable fuel
etc.

[Mark E Horan]

The numbers you are quoting are theoretical ranges of new aircraft with new engines flown by top (i.e. test) pilots flying in excellent weather off a land-base without the need to follow combat doctrines under combat conditions. Another words, they don't apply in reality. Speaking of 1942 specifically:

1. Aircraft range was unimportant. The critical range was the squadron's range - which was that of the most wasteful plane in the formation. This was invariably the tail-end plane(s).

2. Squadron aircraft were not equal. Senior pilots received the newer, better maintained planes. Those same pilots, as leaders, flew the squadron and division guides. In theory they had considerably more experience in maximizing engine performance for fuel economy and thus used far less fuel..

3. The aircraft ran their engines up under power to fully warm them up and then they remained under idle power for unplanned periods because of problems on other aircraft during launch.

4. Squadrons departed in reverse order. Thus, the inexperienced junior pilots took off first. Their aircraft were older planes with more tired engines. They had less experience maximizing performance for fuel economy. They orbited more forming up. They had to jockey in formation on their leaders throughout the flight.

5. The squadrons landed in formation order, lead planes first. Thus the planes in the worst position in regards to fuel needed to remain in the air longer. These same pilots, more likely to be more wasteful of fuel due to less training were also more likely to be less accurate in their navigation were they to unable to form on a division leader during withdrawal, (wasting more fuel) needed to orbit the ship for far longer before landing.

6. The planes were much more likely to operate at full power during the high-speed approach, attack, and subsequent withdrawal for periods longer than prewar estimates. Also, if the ship needed to steam away from the enemy during launch and recovery an additional additional fuel (up to 50 miles worth) would be required for the distance covered during launch and recovery.

7. Prewar figures available for the TBD, SBD-2/-3 and F4F-3/3A/-4 available to the fleet did not include the combat equipment (dual .30 free guns, and extra weight for armour and self-sealing tanks).

8. Allotment needed to be made for the distinct possibility of weather related issues and a large reserve was needed for navigational issues, the chance that damage to the ship would require further flight time, crashes might halt flight operations during recovery, and the ship might not maintain its option course.

9. At ranges beyond 200 miles the navigation issues of finding the target and getting back home were much more serious. Homing becons were new and most pilots did not understand how they worked and thus were disinclined to rely on them.

10. The Pacific Fleet carriers through Midway were still developing wartime doctrinal modifications. Lexington SBDs carrying 1,000 pound bombs still followed the pre-war book requirement that they drop off 22 gallons of fuel. Both the Enterprise and Yorktown Air Groups rejected this doctrine from the first raids on. None the less, all three carriers (Enterprise, Lexington, Yorktown) adopted the same general guidelines in regards to range:

TBD: 200 miles with torpedo and two crew
SBD: 200 miles with 1,000 pound bomb
SBD: 275 miles with 500 pound bomb
F4F: 175 miles

By 1944 the SBD-5s were going 325 miles with more power, more fuel, more pilot training on fuel economy, and doctrinal changes that emphasized economical formation flying, including not climbing to 20+ K feet.

Thus, the limiting factor was the range of the fighter escort, NOT the TBDs.

That said, the navigational problem of departing a moving base to locate a moving target and then return to a moving base was daunting enough that at ranges beyond 200 miles prewar and early war experience showed that the chance of not locating enemy warships was significant enough that it was not worth launching at those ranges if the target was not a stationary enemy base.

Additionally, it is worth noting that every single Enterprise SBD and TBD that returned to the ship from the morning launch on 4 June was in the air from 5.2 to 5.5 hours - considerably longer than the book values for either plane's endurance - and no plane came aboard with more than 10 gallons of usable fuel remaining. The pilots did this by adjusting their engine settings for maximum fuel economy from immediately after takeoff without regards to minimum "book" settings, accepting possible engine wear as a by product of getting home safely.

So, based on extensive interviews with the pilots doing the flying, those book figures were worthless under combat conditions. They were just as worthless in 1944.

Hope this is of interest.

Mark E. Horan

[John Beaman]

Mark, thanks for that dose of succint reality!