The Northrop Turbodyne (XT37)
New Cost Plus Fixed Fee Contract, 21 May 1943

21 May 1943. BuAer produced a scope of work for the proposed new CPFF contract, along with several Engineering Production Planning and Detailed Scheduling enclosures:
  1. Jack Northrop letter dated 10 Apr 1943
  2. Power Plant memorandum PM-1
  3. Strength Requirements for Gas Turbine Power Plant for Class VPB Flying Boats dated 20 May 1943
  4. Strength Requirements for Gas Turbine Power Plant for Army Bomber Airplanes

A) Army-Navy Specification SS1A
B) Detail Specifications 1731502.4 Aviation Navy 1943 Subhead XI

Services and materials as necessary to study, design, construct and test two (2) internal combustion gas turbines for the purpose of aircraft propulsion as follows:
   1. Design data and drawings of two (2) complete intermal combustion gas turbines in accordance with Navy Aeronautical Specifications E-46-G (3 sets). Submit five (5) copies monthly progress reports and other pertinent data showing in detail project progress during the preceding month.
   2(a). Construct and furnish for ground test one gas turbine complete with starting mechanism and reduction gears. Submit five (5) copies monthly progress reports and other pertinent data showing in detail project progress during the preceding month.
   2(b). Construct and furnish one gas turbine complete with starter, accessories, reduction gears and control. Submit five (5) copies monthly progress report and other pertinent data showing in detail project progress during the preceding month.
   3(a). Conduct performance tests on the item in 2 (a) in accordance with specifications outlined herein and furnish five (5) copies of complete test reports.
   3(b). Conduct performance tests on the item in 2 (b) in accordance with specifications outlined herein and furnish five (5) copies of complete test reports.
   4. Conduct 100 hour endurance test on either Unit 1 or 2 as designated by BuAer. Furnish five (5) copies of complete test reports.
   Total estimated cost = $1,483600
   Fixed fee = $59,344
   Total = $1,542,944

Item 1: At BuAer
Item 2: At contractor's plant by INA, El Segundo, California, or BuAer representative.
Item 3: To be witnessed by INA and reports to be inspected by BuAer.
Item 4: Detailed Specifications

Detailed Specifications, Item 1
The design data and drawings shall be of the complete internal combustion gas turbine, which shall meet the following specifications:
  1. Sea-Level Performance, Normal Operation
    • Forward Speed = 0 to 500 mph
    • Turbine Inlet Temperature = 1,450°F
    • RPM = 10,680
    • Shaft Brake Horsepower = 3,000
    • SFC with 18,932 BTU/lb Fuel = 0.51 lb/hp/hr
    • Exit Jet Velocity (axial) = 5,000 ft/sec
  2. Sea-Level Performance, Military Operation (5 minute rating)
    • Forward Speed = 0 to 500 mph
    • Turbine Inlet Temperature = 1,600°F
    • Shaft Brake Horsepower = 3,800
    • SFC with 18,932 BTU/lb Fuel = 0.48 lb/hp/hr
  3. Weights and dimensions, including reduction gears, engine accessories, controls and starter
    • Weight ≤ 3,215 lb
    • Length ≤ ?
    • Diameter ≤ 45"
  4. Design load factors: The unit should be able to withstand accelerations and velocities required by Navy specifications, reference (c), for Navy patrol bomber or by Army specifications, reference (d) for an Army bomber, whichever results in the more critical design condition.
  5. Spark plugs, fuel nozzles, fuel and oil strainers shall be easily accessible for allowing quick change (≤ 2 hours for a complete change)
  6. Engine accessories to be supplied as part of the unit shall include the following: propeller reduction gear, starter, oil pumps, fuel pumps, tachometer drives and tachometer generator, ignition system (except for generator and battery), overspeed protection device, overtemperature protection device, engine controls and regulators (including fuel flow control altitude compensator), torquemeter.
  7. Drives and pads shall be provided on the unit for the following accessories: Generator Type I(a) round, Dwg AND 10002; Vacuum Pump Type II Dwg. AND 10001; Hydraulic Pump Type II Dwg. AND 10001.
  8. At sea level military power condition the propeller shaft speed shall be between 1,000 and 1,200 rpm. The gas turbine and reduction gears shall be designed for a contra-rotating propeller with variable pitch controls in accordance with Army-Navy specifications. The unit must be designed such that the hot gas exhaust shall not interfere with the operation of a normal propeller.
  9. The unit shall incorporate a torquemeter suitable for the measurement of shaft power output in ground tests and in flight.
  10. The starting system shall be capable of starting the unit sufficiently rapidly so that the speed of the unit can be brought from standstill up to the 10,660 rpm design speed within two minutes.
  11. The controls supplied by the contractor shall provide a smooth and stable system for controlling the speed and power output of a unit. Automatic altitude compensation be furnished so that a given control lever setting will correspond to a fixed turbine rpm.
    1. The stress analysis of the unit shall be based upon:
    2. Design load factors of sections (ld) in conjunction with normal operating conditions of the unit.
    3. Overspeed condition at 110%of military power rpm at sea level.
    4. Yield and ultimate strengths of materials based upon best existing data. Strengths at elevated temperatures should be based upon stress-rupture tests at elevated temperatures (at least 300 hour test for the normal design condition and at least 15 hours for the military design condition).
  12. There shall be no natural frequencies of bending or torsional vibrations of the rotor that coincide with the operating range rpm between minimum rpm and 110% of military operating rpm. The minimum rpm shall be defined as 5,000 rpm.
  13. The compressor shall be free of pulsation over the entire military operating range (from 5,000 rpm to 110% of military operating rpm, forward speeds from 0 to 500 mph, altitude from sea level to 50,000 ft). In case this design condition cannot be met, the contractor shall provide devices or mechanisms for avoiding or eliminating pulsation.
The design data and drawings shall conform to Navy Aeronautical Specifications E-46-G. Three (3) complete sets shall be furnished. Design data and drawings shall include the following:
  1. Drawings
    1. Preliminary assembly, detail and layout drawings of the complete gas turbine unit. Drawings to be submitted as they are completed. Reduced size Photostats are acceptable provided they are legible.
    2. Final complete detail and working drawings to be submitted upon acceptance of the unit.
  2. Structural Analysis and Tests
    1. A stress analysis giving factors of safety shall be submitted for all highly stressed gas turbine components. Each component's stress analysis shall be completed before it is constructed. All assumptions should be clearly stated.
    2. A deflection analysis shall be submitted for all components that are critical in regard to clearances or deflections. This analysis shall be completed before undertaking construction of such critical components.
    3. Vibration analysis and test. An analysis of the rotor critical speeds in bending and torsion shall be submitted. This analysis shall be completed before undertaking construction of any large rotor components. Tests shall be made to determine the natural frequencies of the compressor and turbine blades (without centrifugal force). These natural frequencies shall be corrected for the effect of centrifugal force and compared with the major existing frequencies in the operating range. An analysis of these tests is to be submitted to BuAer before operating the gas turbine.
  3. Performance Tests and Analysis
    1. Aerodynamic Analysis. A complete aerodynamic analysis shall be furnished including predicted performance curves. Reports shall be furnished on the theoretical methods used to design the compressor and turbine. Complete reports shall be submitted on all aerodynamic tests of individual stages, lattices and the completed compressor.
    2. Cycle analysis. A thorough cycle analysis shall be carried out on the unit's operation based upon the assumed compressor and turbine characteristics. This analysis should be completed before the design is frozen. After completing performance tests on the ground, the performance at various forward speeds and at altitude should be deduced from the ground tests and presented in the manner recommended in reference (b).
    3. Combustion tests. Complete reports of the combustion tests shall be furnished.
    4. Performance tests. The contractor shall furnish a schedule for the proposed test for the completed gas turbine.
    5. Temperature analysis. Temperature analysis shall be made of the components subject to high temperatures. These calculated temperatures shall be sued for the purpose of estimating thermal stresses and deflections and the factor of safety for the stress analysis.
Detailed Specifications, Item II.
  1. Furnish one complete gas turbine (Unit 1) according to the specifications of Item I, except that fuel pumps, oil pumps and ignition system may be separately driven. Automatic overspeed and overtemperature limiting devices may be omitted provided that a tachometer and thermocouples recording turbine inlet temperature are installed. Automatic altitude compensator may be omitted. The starter may be any starting device useful for ground tests and need not necessarily be the same as for the flight installation. The drives and pads for generator, vacuum pump, and hydraulic pump need not be provided.
  2. Furnish one complete gas turbine (Unit 2) according to the specifications of Item I.
Detailed Specifications, Item III
The contractor shall carry out complete performance tests on the Unit 1 gas turbine of item 2. It is suggested that a variable-pitch propeller be used to absorb the power and the engine torquemeter to measure shaft power.
  1. Performance tests of Unit 1
    Measurement of the performance characteristics over the entire rpm range from starting to a maximum corresponding to a turbine inlet temperature of 1,600°F. Measurements shall include airflow through the unit, fuel flow, rpm, shaft power, oil inlet and outlet pressures and temperatures, static pressure, total pressure and temperatures in the following locations:
    1. ahead of the unit
    2. at compressor entrance
    3. at compressor discharge
    4. at turbine inlet
    5. at turbine discharge
    6. behind the outlet nozzle.
    7. Observation and measurement of the starting and acceleration characteristics
  2. Acceptance Tests of Unit 2
    1. The contractor shall carry out the following acceptance test on Unit 2 including all engine and aircraft accessories driven by the unit. A generator, vacuum pump and hydraulic pump will be furnished by the government for this test.
    2. One hour acceptance test including 5 minutes in each of the ten speed ranges specified in Item 4 between Ndesign and Nminimum and two runs of 5 minutes each at a turbine inlet temperature of 1,600°F, at military power.
    3. Ten starts (using the engine starter) and acceleration to normal design speed. Observation and measurement of the starting and acceleration characteristics.

Detailed Specifications, Item IV
The contractor shall carry out a 100 hour endurance test on either unit 1 or 2, whichever is designated by BuAer. Any time spent on performance tests may be included in these 100 hours. The operation shall be carried out over the complete range as follows:
   One hour – (12 runs of 5 minutes each at a turbine inlet temperature of 1,600°F at military power. This test shall be run after all other tests have been completed.
   Twenty-four hours – continuous operation at normal design conditions (turbine inlet temperature of 1,450°F).

2 Jun 1943. BuAer wrote MatCmd about Northrop Aircraft's requested contract change and forwarded copies of the correspondence, specifications, etc. BuAer wanted to proceed with the project and wondered whether MatCmd would still cover half of a new contract's $1,542,944 cost. MatCmd concurred on 18 Jun 1943, and also classified the project as CONFIDENTIAL without assigning a classified project number.
7.5 hrs in the speed range Ndesign to Ndesign - 0.10ΔN
7.5 hrs in the speed range Ndesign - 0.10ΔN to Ndesign - 0.20ΔN
7.5 hrs in the speed range Ndesign - 0.20ΔN to Ndesign - 0.30ΔN
7.5 hrs in the speed range Ndesign - 0.30ΔN to Ndesign - 0.40ΔN
7.5 hrs in the speed range Ndesign - 0.40ΔN to Ndesign - 0.50ΔN
7.5 hrs in the speed range Ndesign - 0.50ΔN to Ndesign - 0.60ΔN
7.5 hrs in the speed range Ndesign - 0.60ΔN to Ndesign - 0.70ΔN
7.5 hrs in the speed range Ndesign - 0.70ΔN to Ndesign - 0.80ΔN
7.5 hrs in the speed range Ndesign - 0.80ΔN to Ndesign - 0.90ΔN
7.5 hrs in the speed range Ndesign - 0.90ΔN to Ndesign - ΔN
Where
   Ndesign = rpm corresponding to normal conditions
   Nminimum = minimum operational rpm
   ΔN = Ndesign - Nminimum

Guarantee
The contractor guarantees that the unit will meet the specifications of Item I except that the performance guarantee shall be reduced compared to the design conditions in the following particulars.
Normal sea-level operation of the test stand (reduced to standard NACA sea-level atmospheric inlet conditions according to reference (b)).
   Forward Speed = 0 mph
   Turbine Inlet Gas Temperature = 1,450°F
   Shaft Horsepower = 1,800 bhp
   Specific Fuel Consumption (based on fuel having a 18,931 BTU/lb heating value) 0.70 lb/hp/hr
   The units shall demonstrate satisfactory performance by completing without failure of the major parts the following tests:
   Starting and acceleration: Ten tests (as described in Item 3(b)) Starts and acceleration from standstill to normal design speed in less than 2 minutes per test
   Endurance test (99) hours: As described under Item IV, except that the one-hour test at military power (turbine inlet temperature of 1,600°F) shall not be included in this guarantee.

Delivery Point and Date
Item (1) Copies of all reports shall be forwarded to the Chief of the Bureau of Aeronautics, Navy Department, Washington, DC as soon as completed.
Item (2)(a) To be delivered upon request by Bureau of Aeronautics, FOB, suitably crated at contractor's plant not later than 30 Dec 1944.
Item (2)(b) To be delivered upon request by Bureau of Aeronautics, FOB, suitably crated at contractor's plant not later than 30 Dec 1944.
Item (3) Reports of tests to be delivered to the Chief of the Bureau of Aeronautics, Navy Department, Washington, DC as soon as completed.
Item (4) Reports of tests to be delivered to the Chief of the Bureau of Aeronautics, Navy Department, Washington, DC as soon as completed.

Inspection
Item (1) at Bureau of Aeronautics.
Item (2) at contactor's plant.
Item (3) Tests to be witnessed by Inspector of Naval Aircraft, reports to be delivered to the Bureau of Aeronautics.
Item (4) Tests to be witnessed by Inspector of Naval Aircraft, reports to be delivered to the Bureau of Aeronautics.

Payment
Payment of the fixed fee shall be made in full upon completion of the contract provided that the contractor has satisfied the contract guarantees.

Allowable Cost
Cost incurred under contract NOa-85598 that have not already been paid by BuAer are to be included in allowable cost of this contract. In consideration therefore all equipment and material constructed or paid for by government funds under this contract and contract 85598 shall belong to the government and is to be relinquished upon completion of this contract.

Termination of Original Contract
The original contract (NOa-85598) shall be cancelled when this contract goes into effect.

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