Lockheed Model 89 Turbosupercharger Selection
Turbosupercharger Comparison
Compiled by Kimble D. McCutcheon
21 Jun 2025

Overview

4 Mar 1944. W.W. Merrill released Lockheed Report No. 4651, Comparison of Turbosupercharger for Model 89. The U.S. Navy had requested that Lockheed study installing a current model turbosupercharger in place of the General Electric Type BT units that had been studied. The GE Type B-133 had too small a capacity, limiting the high power performance. The Turbo Engineering Corporation (hereinafter TEC) Type P-15B capacity was too large, giving more than ample high-power performance but limiting the low power cruise regime due to surge limitations. The proposed GE Type BT adequately spanned both power extremes and seemed ideally suited to maximum Model 89 performance and economy.

The TEC P-15B-3 turbosupercharger increased the aircraft gross weight by 1,929 lb in order to maintain the same range and payload capacity as with the GE Type BT. Of this weight increase, 1,022 lb was empty weight increase and 907 lb was additional fuel required to carry the turbosupercharger weight and overcome the larger nacelles' increased drag. Lockheed estimated that an additional 4 – 6 months of engineering time would be required to redesign the nacelle to accommodate the TEC unit, delaying nacelle completion.

Introduction

Lockheed compared three turbosuperchargers for use on its Model 89, and concluded that a new-design "cruising turbo" was necessary. The units considered were the GE Types B-133 and BT, and the TEC Type P-15B-3. The Type BT was a new turbosupercharger under development by GE for the Lockheed Model 89. The TEC Type P-15B-3 was the brain child of Rudolph Birmann, founder of Turbo Engineering Corporation, and developer of a mixed-flow compressor impeller that was claimed to be more efficient than the pure centrifugal ones available from other sources. Birmann turbosupercharger designs were the darlings of several proposed aircraft designs, but despite their claimed advantages, never saw production.

The three units' compressor capacities were examined, along with the installation weights and problems. The sole purpose for Model 89 turbosuperchargers was to achieve maximum fuel economy for long-range cruising. They maintained sufficient carburetor deck pressure at high altitude so that cruising powers could be used at engine speeds and manifold pressures conducive to minimum fuel consumption. Unlike fighter aircraft that needed military power levels at high altitude in order to achieve a safe rate of climb, the Model 89 turbosuperchargers.

TEC Type P-15B-3 Turbosupercharger Installation

Fig. 1	Fig. 2. TEC P-15B-3 Installation	Fig. 3. GE BT Installation

TEC turbosupercharger (hereinafter turbo) installation required a frontal area increase as shown in Figure 1. This was primarily due to the larger P-15B-3 diameter as compared to the GE Type BT. The lower nacelle contour was dropped 9.25" to accommodate the bulkier unit. The turbo's vertical nacelle location was limited by clearance between the turbo casing and coolant air ducts leaving the intercooler. These ducts were located as high as possible so that the exit openings were just below the wing leading edges. Moving the turbo aft gave better clearance between it and the intercooler ducts and allowed it to be raised 2.5" until it just cleared the horizontal floor supports above. However, the rearward turbo location was then limited by the exhaust heat exchanger, which was already as close to the firewall as nominal clearance allowed. The exhaust pipe sections between the turbine and exchanger were only long enough to allow a transition from a round section at the turbine exhaust to a rectangular section at the heat exchanger. The transition pipe also included an expansion joint and the waste gate bypass pipe junction. As a result the turbo was in the highest and most rearward location possible.

The Type P-15B-3 turbo exhaust gas inlet ports were located at the turbine casing periphery, and in accordance with TEC specifications, the pipes must enter these ports in a tangential direction; this resulted in a minimum 9" bend radius for the pipes, resulting in longer exhaust pipes than were used on the GE Type BT installation. The pipe entering the turbine left side followed a tortuous path in order to enter at the required angle. The increased Type P-15B-3 length and complication contributes to the increased installation weight.

The GE Type BT induction system arrangement has the compressor scroll discharge ports directed forward, while the Type P-15B-3 compressed air was discharged radially from two ports on the scroll periphery, making them slightly longer in order to make the additional bend from the scroll case forward. Unlike the Type BT, the Type P-15B-3 had no special compressor discharge port for cabin supercharging. However, the cabin air line could be taken from one of the scroll discharge ports as shown in Figure 2.

These structural changes increased weight by about 564 lb, as shown in Table 1.

GE Type BT and TEC Type P-15B-3 installed weights were compared in Table 1, which shows the weight increase of various power plant components when the P-15B-3 replaces the BT turbo. The P-15B-3 turbo weighed 255 lb compared to 155 lb for the BT. In addition to this basic weight increase, the P-15B-3air and exhaust ports were arranged so that longer and heavier ducting to an from the unit were required. P-15B-3 power plant controls were lighter because the regulator was weight was included with the unit's weight, but was a separate item with the BT.

The increased turbo and ducting weight amounted to 516 lb per airplane. Another 306 lb was added due to the increased nacelle diameter, bringing the P-15B-3 total weight increase to 822 lb. Finally, the power plant lowering necessary to accommodate the P-15B-3 lengthened the lower engine mount supports attached to the wing underside and increased the mount support weight by 200 lb per airplane.

The total aircraft empty weight increase due to the P-15B-3 installation was 1,022 lb. Because of the empty weight increase and larger nacelle frontal area a greater amount of fuel must be carried in order to maintain the 5,000 mile range with the 17,500 lb payload. This additional fuel increases the takeoff weight by an additional 907 lb, for a 1,929 lb takeoff weight increase for the P-15B-3 equipped aircraft versus the GE BT.

Breguet's Range Formula

Fuel Weight Required to carry 1,022 lb 5,000 miles

From Breguet's formula shown above the Range, R, and the ratios (L / D), (Ŋ / C) and (W_o / W₁) were unaffected by the weight empty change. The new initial weight, W_o, was determined from the new final weight W₁ and the ratio (W_o / W₁).
     (W_o / W₁) = (184,000 / 136,200) = 1.35 (From Lockheed Report No. 4289)

The fuel weight for the airplane with GE BT turbos was: 0.35 x 136,200 = 47,800 lb

The increased fuel weight due to the heavier P-15B-3 turbo installation was: 0.35 x 1,022 = 358 lb

Additional Fuel Weight Required to Overcome Increased Nacelle Drag

     Nacelle frontal area with GE BT turbo = 27.6 ft²
     Nacelle frontal area with TEC P-15B-3 = 32.0 ft²
     Nacelle form drag coefficient, CDπ = 0.067
Increase nacelle drag coefficient increase: ΔCD = (4 x ΔS_nacelle x C_Dπ) / Swing = (4 x (32.0 -27.6) x 0.067) / 3,610 = 0.000327

Original airplane drag coefficient for maximum range flight = CD
     CD = CL / (L / D) = 0.66 / 21.69 = 0.0304 (Data from Lockheed Report No. 4289)
0.35 x 136,200 = 47,800 lb
The increased fuel weight due to the heavier P-15B-3 turbo installation was 0.35 x 1,022 = 358 lb.

Additional Fuel Weight Required to Overcome Increased Nacelle Drag

     Original individual nacelle frontal area was 26.7 ft²
     Frontal area with the P-15B-3 turbo was 32.0 ft²
     Original nacelle form drag coefficient = C_Dπ = 0.067.
Increase in airplane drag coefficient due to nacelle drag:
     ΔC_D = (4 x ΔS_nacelle x C_Dπ) / Swing = (4 x (32.0 -27.6) x 0.067) / 3,610 = 0.000327

Original airplane drag coefficient for maximum range flight = C_D
     Maximum lift / drag ratio = 21.69
     C_D = C_L / (L / D) = 0.66 / 21.69 = 0.0304 (Data from Lockheed Report No. 4289)

Drag coefficient with P-15B-3 turbo:
C_D1 = C_D + ΔC_D = 0.000327 + 0.0304 = 0.0307

Lift / drag ratio with P-15B-3 turbo = L / D = 0.66 / 0.0307 = 21.48

With the ŋ / C unchanged by weight increase, Breguet's formula implies:
ln (W_o / W₁) ~ 1 / (L / D)

The weight ratio with additional drag due to the P-15B-3 turbo installation: (W₁ / W₂) = anti-log (ln (184,000 / 136,200) x (21.69 / 21.48)) = 1.354

Fuel weight increase to overcome drag: ΔW = (1.354 x ( 136,200 + 1022)) – (1.35 x (136,200 + 1022)) = 0.004 (136,200 + 1022) = 549 lb

Weight Increase Summary

Additional Empty Weight for P-15B-3 Installation = 1,022 lb
Added Fuel to Carry Weight = 358 lb
Added Fuel to Overcome Drag = 549 lb
Total Weight Increase = 1,929 lb

Required Power Plant Performance

Fig. 4	Fig. 5	Fig. 6

Lockheed Model 89 specifications state that the airplane would carry an airline payload of 17,500 lb over a 5,000 mile range. In order to obtain this performance each power plant was required operate between 1,100 and 1,700 bhp at 25,000 ft (see Lockheed Report No. 4289, Figure 17). In addition, a power excess was required for climb and emergency operation on three engines, and still lower powers were required to provide the 7,400 mile maximum ferry range. As a result the turbosupercharger/engine combination was required to operate at engine powers from 900 bhp to 2,100 bhp at 25,000 ft. These requirements were shown graphically on Figures 4, 5 and 6, where power required is plotted versus altitude. The minimum power requirements decrease as the square root of the density ratio as the altitude decreases (constant indicated power). A maximum of 2,500 bhp was desired for climb at 20,000 ft and was probably available from any turbosupercharger operating with the engine running at 2,100 bhp at 25,000 ft. Takeoff power of 3,000 bhp per engine was required from sea level to 7,000 ft in order to assure a reasonable takeoff distance from any of the world's airports (The highest airport for regular operation was below 7,000 ft).

Superimposed upon the required performance lines were curves showing the maximum and minimum power available from the engine when working in conjunction with the GE Type B-133, GE Type BT and TEC Type P-15B turbosuperchargers. Each was working at its rated speed, which was noted on the figure. Data for construction of these lines was obtained from the manufacturers' performance charts for the three units under consideration (GE Type BT Curve P-1090988-1, GE Type B-133 Curve P1090841 and TEC Type P-15B Curve Y-171 and Y-172) and the Pratt & Whitney curve INST No. 3572 (revised 7 Dec 1943). Each compressor was required to deliver 30 lb/min of cabin supercharging in addition to the engine requirements. The curves showing GE Type B-133 performance (Fig. 4) indicate that its capacity was inadequate for the Model 89. Its operating range at 25,000 ft was intended for lower engine power than required for the Model 89, with the result that it provided only 1,600 engine byp while the requirement was 2,100 bhp.

The TEC P-15B-3 (Fig. 5) had adequate capacity for the high engine powers and could handle 2,660 bhp at 25,000 ft though only 2,100 bhp was required. The P-15B-3 surge limit (below which it could not operate) was 1,200 bhp while the airplane requirements show that 900 bhp was necessary to accomplish the Model 89's 7,400 mile ferry range. The fact that it could maintain engine powers in excess of 2,100 bhp at 25,000 ft was of little value in a transport airplane since such powers were uneconomical for normal operation in transport work. The engine intercooler and exhaust gas heat exchanger were both designed for a 2,100 bhp maximum power at this altitude and would restrict higher power operation by imposing excessive pressure losses on the induction and exhaust systems.

Figure 6 indicates the manner in which the GE Type BT compressor performance bracketed the requirements for a "cruising" turbosupercharger. Its operating range at 25,000 ft was broad enough to cover the required engine power span from 900 to 2,100 bhp with a safe margin on either side.

Conclusion

At the time this Lockheed Report No. 4651 was written the engineering of the Lockheed Model 89 with the GE Type BT turbosupercharger installation was sufficiently complete to begin construction. The GE Type BT met all Lockheed Model 89 requirements and it could be delivered in a timely fashion. Lockheed planned to construct and test a complete nacelle in the NACA Cleveland power plant wind tunnel, which afforded an opportunity never before available to test a turbosupercharger under controlled altitude, pressure, temperature and airspeed conditions in conjunction with the engine and all its component parts. Such complete testing was expected to be of great value to future transport aircraft.

[U.S. National Archives Record Group 72, Entry 145, Box 3. Lockheed Transport Model 89 Report No. 4651.]

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