TECHNICAL REPORT
|
HEADQUARTERS
|
VI. Appendix I/1
a. Pilot's Operating Handbook
b. Maintenance Handbook
First in this category of Junkers airplanes was the JU-88, which has been credited with twenty-two different functions in the German Air Forces, including fighting, bombing, dive-bombing, night-fighting, and reconnaissance. Similar in many ways to the JU-88, the JU-l88 may be regarded as a subsequent development and was used for essentially the same purposes. The JU-288 was a completely redesigned aircraft, not related to either of the first two in this series - the purpose of it being an attempt to combine firepower with a large bomb load.
The JU-388 was the latest of the "88" series to reach the production stage. It was first test-flown in l943 and was included in the restricted production program that was in force when hostilities ended. Although various subtype were found in Germany after the capitulation, the JU-388 L-l version was found to be the most representative model, and this model was selected for examination and analysis.
The JU-388 aircraft is a modification of the JU-88 series and retains many of the salient features of the JU-88 and JU-188 aircraft. It is a twin-engine, low midwing airplane fitted with BMW-80l-TJ engines and exhaust-driven turbosuperchargers integrally mounted in the nacelles. Air led in through the air scoop located underneath the engine, flows through the compressor side of the turbosupercharger to the engine-driven supercharger on the accessory section, from there passes through a ring-type intercooler to an annular manifold, and is led into the cylinders by intake pipes.
The landing gear is hydraulically operated, incorporating an emergency air system in case of failure of the hydraulic system. Bomb-bay doors and flaps are also hydraulically operated. Electrically-actuated valves are an unusual feature of the hydraulic system in that conventional designs maintain one system rather than a combination of two.
Two outboard wing tanks, two inboard wing tanks, one forward fuselage tank, and one rear fuselage tank are installed for a total capacity of 1020 U.S. gal. Increased range is obtainable by substituting drop tanks for external bombs. The fuel and oil tanks are the leakproof type.
For flight testing, the armament was replaced with equivalent ballast but it merits description in passing. The remotely controlled tail turret (2 x MG 13l/13 mm) has a radius of action of 45 from the horizontal up or down and l80 in azimuth. There is one control for azimuth movement and one for elevation - the latter being a small joy stick that can be depressed or elevated. The control mechanism consists of two cylinder servos that operate two small gears. These gears turn rods that are connected by universal joints to the turret proper, one rod causing changes by mechanical transfer to a worm gear.
The crew of three includes pilot, observer, and radio operator/gunner. Each member is provided with electric plug-in boxes for heating flying suits.
The JU-388 L-l was fitted with the latest radio equipment and considerable radar was installed for interception of night fighters as well as for protection.
The cabin-is pressurized from a turbosupercharger. An air scoop is located in the nose of the aircraft for ramming air into the cockpit up to the 28,000-ft level, to diminish the load on the mechanical blower system.
De-icing for the wing is provided by hot air fran The engine exhaust, and the horizontal tail is similarly de-iced by a heater located in the fuselage. The propellers are fitted with conventional slingers for ice prevention.
(1) Dimensions
|
Span |
72 ft 2 in. |
|
Length |
48 ft 10 in. |
|
Height |
15 ft 5 in. |
|
Wing Area |
602 sq ft. |
(2) Weights
|
Normal all-up |
30,450 lb |
|
Maximum take-off |
32,350 lb |
(3) Power Plants
Two BMW-801-TJ air-cooled, 14-cylinder, radial engines with a take-off
rating of 1810 hp at 2650 rpm. "Kommandogerat" units were incorporated for
automatic adjustment of fuel mixture, propeller pitch, and supercharger shifting.
(4) Performance
The maximum speed is 383 mph at 40,300 ft, and the range with maximum fuel load of 1020 gal is 2160 miles at 36,000 ft.
To forward pilot's comments on handling characteristics of JU-388.
(1) Introduction.
The German JU-388 is a three-place, all-metal, midwing, twin-engine, high- altitude, reconnaissance airplane. The JU-388 power plant consists of two BMW-801-T-l-L engines rated at 1750 hp each. Supercharging is provided by an exhaust-driven turbo and a gear-driven, two-stage impeller.
A total of ten hours was flown in the airplane by various flight-test pilots to determine its handling characteristics and to obtain the pilots' com- ments.
On the first flights, some trim and weight and balance difficulties were encountered, although these were finally eliminated, and subsequent flights were accomplished with little difficulty.
The majority of pilots agree that the JU-388 does not have handling characteristics equal to the JU-88. In general, the stalling speeds are too high, the controls have excessive play and the power-off approach angle is too steep to afford a good flare for landing.
(2) Weight and CG Information.
Flights were made with a take-off weight of 27,835 pounds and a CG location of 26-7/l0%.
(3) Flight Characteristics
(a) Cockpit Layout - The cockpit of the JU-388 is built to accommodate three crewmen: one pilot, one observer and a radioman navigator. Entry to the cabin is made by climbing up a ladder mounted on the access door in the cabin floor.
The pilot's seat is located on the left side of the fuselage and the observer's seat which is stowed behind the pilot's seat, swings out and down - locking into position to the right side and aft of the pilot's seat. The radio- man's seat is located aft of the access hatch.
Due to the cramped space and awkward seat location, the crewmen have some difficulty in seating themselves; once seated, however, little difficulty is encountered by crew members in handling the controls and otherwise carrying out their duties.
The pilot's seat is adjustable fore and aft in flight, although the rudders are adjustable only before take-off. All engine controls and primary engine instruments are located on a control panel at the pilot's left side, and the flight instruments are suspended to the right and in front of the pi lot approximately at eye level. The temperature, pressure and fuel gages together with the wheel and flap control, are located on the right wall of the fuselage opposite to and within easy reach of the pilot.
As in other German airplanes, the automatic engine control and the push button system for operating the flaps, wheels, trim, etc., are incorporated in the JU-388 and contribute greatly to its convenience of operation.
(b) Taxiing and Ground Handling - The JU-388 is somewhat difficult to taxi due to very poor brakes and the lack of a steerable tailwheel. Directional control can be maintained only by using a combination of power and brake application. Much discomfort was experienced by the crew members due to excessive cabin temperatures, especially in ground operation. Take-off and initial Climb - The take-off run is short and directional control is not difficult to maintain. Initial climb is fair; although most pilots found that the longitudinal trim changes rapidly after take-off. The gear and flaps retract rapidly, but necessitate rapid trim correction.
(d) Climb - The JU-388 has a good rate of climb and gives the pilot no difficulty of control or restricted vision.
(e) Handling and Control at Various Speeds - The controls are fairly effective at most speeds. Control feel is good and forces are well balanced except for the rudder forces, which seem somewhat light for this type of plane.
(f) Trim and Stability - Trim changes are easy to accomplish, although when lowering flaps or wheels it is found that the electric stabilizer trim device is not rapid enough to compensate for resulting trim changes. Ample trim control is provided by aileron, rudder and stabilizer trim devices located on the pilot's control panel. In addition to the manual stabilizer trim control, there is an electric trimmer switch on the pilot's control stick. Stability of the JU-388, as nearly as could be determined by pilot observations, was found to be satisfactory.
(g) Stalls and Stall Warning -The airplane has a gentle stall, characterized by relatively little warning before the stall and by an abrupt pitching moment following the stall; recovery from stalls in any configuration is rapid with little loss in altitude.
(h) Maneuverability and Aerobatics - The Ju-388 was round to be quite maneuverable and it displayed desirable flying characteristics for its particular type.
Although no aerobatics were attempted, it was evident that the airplane has a good rate of roll and a relatively short turning radius.
(i) Control on reduced Number of Engines - although no tests were made with one propeller feathered, it was obvious from flying with one engine idling and the other at cruising power that the JU-388 has excellent single engine performance and handling characteristics.
While flying with the conditions at stated above, it is possible to trim the plane to fly hands-off, and control in turns, etc., is easily maintained.
(j) Changes in Trim when Operating Landing Gear, Flaps, etc. though trim changes resulting from the operation of landing gear and flaps, or changes in power are excessive, the aileron, rudder and stabilizer trim controls provided are adequate to restore the airplane to a stable trim condition.
(k) Noise and Vibration - The noise level of this airplane is somewhat less than is found in the JU-88, due to the sound deadening effect of the pressurized cabin and the sponge rubber insulation provided.
Vibration of the power plant and airframe is at a minimum in flight; however, while idling the engines on the ground, an excessive amount of power plant vibration and control shake is evidenced.
(l) Comfort - In general, the crew members experience little discomfort in operating the airplane. Seats are well designed and located; although somewhat small by our standards. Ample shoulder, head and leg room is provided all crewmen.
(m) Vision -Vision is excellent downward and forward, although somewhat restricted laterally and to the rear. The web members of the "Greenhouse" type cabin obstructs the pilot's vision to an undesirable extent, although only slight distortion is caused by the many double surfaced windows incorporated in the "Greenhouse" structure.
(n) Approach and Landing - This airplane displays poor power-off approach characteristics in that its angle of descent with power off is so great that a complete flare cannot be accomplished at normal approach speeds. It was found that by using a slight amount of power throughout the approach and a very shallow flare just before touching down, good three point landings can be made.
Directional control after landing is easy to maintain even in a fair cross wind.
(4) General Functioning.
(a) Power Plant and Associated Equipment - The BMW 801 engines functioned well throughout all flights and most pilots expressed utmost confidence in the power plant and its accessories.
It is believed that the unified engine control, which automatically selects the correct propeller pitch and fuel mixture for any power settings, is well adapted to the power plant, and is a desirable feature since it relieves the pilot of individual attention to these items.
(b) Hydraulic, Pneumatic and Electric Systems - Operation of the electric-hydraulic flap- and landing-gear systems was very satisfactory; however, the hydraulic brake system left much to be desired.
The automatic electric fuel transfer system gave some trouble on one flight when it failed to transfer fuel properly. Other electric systems functioned satisfactorily.
(c) Emergency Systems - An emergency handle is provided to jettison the top hatch of the radioman's compartment. The floor entrance hatch is provided with a hand operated hydraulic system which may also be used to open the bomb-bay doors, and lower the wheels and flaps. All emergency systems operate satisfactorily.
(5) Performance
None obtained.
It is believed that the JU-388, while possessing fair performance characteristics for a reconnaissance type, is somewhat deficient in excellent handling traits so necessary in this type. It is assumed that the excessive trim changes and the light rudder forces would be more detrimental at operational altitudes of 35,000 to 40,000 ft.
None.
(l) As far as ease of maintenance is concerned, this aircraft is on a par with comparable American aircraft.
(2) The extreme compactness of the engine and turbosupercharger instal lation retards servicing but does provide for quick nacelle changes- estimated by the Germans at one-half hour for three or four men.
(3) The "Kommandogerat" or "master control" units functioned well throughout testing and point up the need for further American development along the automatic control idea.
(4) The remotely-controlled, twin-gun tail turret is a novel feature in that it is mechanically controlled by servo motors unlike the electronically controlled remote turrets of the AAF.
(5) An overall analysis of the airplane leads to the conclusion that it could be employed well in its design function of long-range reconnaissance.
This report is broght to you by courtesy of William A. Medcalf and is now part of
Back to main page...
Zurück zur deutschen Hauptseite...