Douglas TBD range needed

[Markus Becker]

I´m gathering info on various US carrier a/c. From 'The First Team' I found out an SBD had a combat radius of 170 to 220nm depending on the bombload and that it could make a 300nm search, presumably with a 500lb bomb?

The Wildcat´s combat radius is at least 125nm but up to 200nm was mentioned once.

The TBD has totally eluded and confused me. At Coral Sea torpedo armed TBD were send against a target -Shoho- that was reported 200nm away. Cruise speed for a TDB with a fish is 100 to 110 knots. The strike departed at 9:45, the attack began at 11:05. That 80 minutes. TBD could cover 140nm in that time, not 200. Ok, the inital report was wrong, a second place the Shoho 30nm away from the first but that would still be at least 170nm.


Anyone having some info or an idea where else to look?

[Larry deZeng]

Performance

• Maximum speed: 206 mph (179 knots, 331 km/h) at 8,000 ft (2,400 m)
• Cruise speed: 128 mph (111 knots, 206 km/h)
• Range: 435 mi (700 km) (378 nmi, 700 km) with Mk XIII Torpedo, 716 mi (623 nmi, 1,152 km) with 1,000 lb (454 kg) bombs
• Service ceiling: 19,500 ft (5,945 m)
• Rate of climb: 720 ft/min (3.7 m/s)

Just Google Douglas TBD Devastator - Wikipedia has all the specs on it.

[Markus Becker]

Hmm, that´s wiki and what do they mean by range? One way or a return trip? Probably the former. I also noticed the huge difference between nominal range and combat radii of various planes.

[Graham Boak]

From a recent discussion on J-aircraft.org, it was shown that the USN combat radius (example SBD) was one quarter that of the range. Normally one third would be considered a reasonably assumption, but carrier aircraft have a need for greater allowances. This suggests a combat range of around 110 miles, or about one hour travelling. Given the quoted cruise speed, this would be consistent with an the quoted 80min interval between launch of the first examples and beginning an attack.

Range is always considered one way, with no combat or (usually) other allowances. It is a measure of the extreme capability of the aircraft. There is an accepted formula known as the Breguet Range Equation.

[JoeB]

Originally Posted by Markus Becker

I´m gathering info on various US carrier a/c. From 'The First Team' I found out an SBD had a combat radius of 170 to 220nm depending on the bombload and that it could make a 300nm search, presumably with a 500lb bomb?

The Wildcat´s combat radius is at least 125nm but up to 200nm was mentioned once.

The TBD has totally eluded and confused me. At Coral Sea torpedo armed TBD were send against a target -Shoho- that was reported 200nm away. Cruise speed for a TDB with a fish is 100 to 110 knots. The strike departed at 9:45, the attack began at 11:05. That 80 minutes. TBD could cover 140nm in that time, not 200. Ok, the inital report was wrong, a second place the Shoho 30nm away from the first but that would still be at least 170nm.

The USN quoted aircraft ranges in statute mile, not nautical miles. It seems strange, since speeds for a/c, like ships, were quoted in knots, but it's clear in original documents, and a cause of confusion in books. Just glancing back at Lundstrom, he quotes a/c ranges as simply 'miles', and in some cases he quotes official figures, so I'd assume he means statute miles.

As on previous thread, the range of SBD can be benchmarked for SBD-5 (with no external tanks and otherwise pretty similar to the 1942 model SBD-3) from "Aircraft Characteristics and Performance" sheets dated June 1 1944: range with 1000# bomb=1115 statute miles, radius 240, same nominal range but 260 mile radius with 500# bomb. The assumptions are given in detail. Any quote of a practical range that differs can be compared to this.

Again for types not still in service ca. 1943 there don't seem to be official USN statistics for combat radius. The numbers on Wiki for TBD are also quoted in Barrett Tillman's "TBD Devastator Units of the US Navy", 435 mi with Mk13 torpedo, 715 miles with 2*500# bomb. He describes these as 'tactical ranges' so might be different from the still air max range in the 1944 document for SBD; might include some reserves or margins, I don't know. Also as mentioned last time, it wouldn't necessarily work to use the same % of range as radius for a 1115 range SBD as 716 (assuming it's comparable) TBD, because certain reserves are a constant, so reduce the % for the shorter legged a/c under the same assumptions. 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

[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.