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:
Quote:
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.)
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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