Curtiss Jenny Restoration

Welcome! We hope you enjoy following the restoration process of a 1918 Curtiss JN4D Jenny. Once completed, the aeroplane will be flown and displayed at the Candler Field Museum in Williamson GA (30 miles south of Atlanta). You can contact me below by clicking on "VIEW MY PROFILE"

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Location: Peachtree City, Georgia, United States

Friday, August 09, 2013

Wires and update

During my last trip, I had a few hours in Seattle and ran over to the Museum of Flight.  Looks like they have the wings back on the Jenny and displayed properly.  I always loved the wood work on a Jenny!

In one of the displays about pioneer Alaska pilot Noel Wein, I noticed something interesting.  Look how the mechanic is tightening the Hisso prop nut!  He is using a big ol' pipe wrench.

While I was away at work, Brian made the right lower drag wire.

 As you can see, this wire goes from Station 1 to the bottom of strut number 2.

Brian also re-made one of the flying wires.  The first one had three threads showing and we decided to make a better one.

Lastly, Dave Trojan sent me this neat article he wrote.  I hope you find it as interesting as I did!

Radio Telephone Success in Airplanes during WWI

By Dave Trojan, Aviation Historian

SCR-68 Radio Telephone System in operation

Before the United States entered World War One, little had been done to adapt the radio telephone for aerial use. Although aerial radio work had been closely studied as far back as 1910, it wasn’t until after the U.S. committed to the war that development progressed at a fast pace. The US Army pushed for better aerial communication technology to gain the advantage in World War One.

The SCR-68 was the first complete radio telephone system that was US manufactured and developed specifically for aircraft communication between aircraft in flight and with a ground station. The Western Electric Company developed the SCR-68 radio telephone system to meet U.S. government specifications. Before the SCR-68 system, there had been other aerial radio telegraphs, transmitters and receivers, but the SCR-68 system brought a number of different components together.   Most of the technical challenges of radio telephony were overcome prior to WWI; it was just a matter of adapting the equipment for aerial use. Some of the problems that were solved were: overcoming of the noise and vibration from the motor; reducing the weight of the apparatus; avoiding hazards from the electric current; and making it simple enough for the flyers to operate.  

One of the hardest obstacles to overcome during development was convincing pilots to fly with the bulky apparatus. The early pilots were fussy about what was loaded into the planes they were to fly, and they disliked the trailing wires which served as antenna. It took a lot of maneuvering and diplomatic jockeying to get the apparatus aboard and into the air.

Test flights began as early as October 1917 using equipment installed on modified JN-4 Jenny airplanes. These test flights proved the concept successful and afterwards it was just a matter of selling the idea to influential military leaders.

In early December 1917, a decidedly skeptical crowd of admirals, generals, foreign representatives and technical experts gathered at South Field, Dayton, Ohio to witness a demonstration of the aerial communication apparatus. Upon arrival, the attendees were shown the apparatus in the planes and explained what it was expected to do. Many in the crowd had doubts that the apparatus would work.

Representative from the Western Electric Co and military officers watch an early aircraft radio test.

An eyewitness account from one of the men who helped set up the demonstration:

"They went to our little station on the hill, where we had rigged up a loud-speaking receiver connected to the wireless apparatus so that all could hear without the use of headsets. The planes left the ground and after what seemed an interminable length of time we got the first sounds in the receiver which indicated that they were ready to perform. The spectators were only mildly interested and some seemed a bit bored.

Suddenly out of the horn of the loud speaker came the words, 'Hello, ground station. This is Plane No. 1 speaking. Do you get me all right?' The bored expressions immediately faded and looks of amazement came over all their faces.

Soon we got the same signal from No. 2 and the show was on. Under command from the ground the planes were maneuvered all over that part of the country. They were sent on scouting expeditions and reported what they saw as they traveled through the air. Continuous conversation was carried on, even when the planes were out of sight, and finally upon command, they came flying back out of space and landed as directed. From that moment, the radio telephone was sold."

The Western Electric Company developed several components which became the SCR-68 radio-telephone system.  The SCR designation originally stood for "Set, Complete, Radio" but later signified "Signal Corps Radio”. The observer or gunner managed the radio system in the open cockpit aircraft by receiving and relaying messages for the pilot. The system also worked like a private telephone line because the pilot and observer could use the system to communicate with each other.  

The SCR-68 Radio System components

Wiring Diagram of Airplane Radio Transmitter and Receiver Set with interphone, type SCR-68, Signal Corps U.S. Army

The type SCR-68, basic component, BC-11, Radio Receiver/Transmitter was at the core of the system and was the circuit apparatus that was used for receiving and transmitting messages. It was housed in a suitcase shaped box that measured 17 inches by 10 inches by 7 inches and weighed 21 pounds. Dials were used to control the frequency of the radio and flip paddles switched the radio from receive to transmit and vice versa. The transmitter section used two type VT-2 tubes as oscillator and modulator.  The switch at the top and the knob at the bottom determined the receiver frequency.  The SCR-68 system operated between 600-1500 kHz. Three windows allowed the filaments of the three VT-1 tubes in the receiver section to be observed while in operation.  Below the windows was a switch which controlled the receiver audio level.  The receiver consisted of a non-regenerative detector, and two stages of audio amplification.

Type SCR 68, BC-11, Radio Receiver/Transmitter

Inside the type SCR-68, BC-11, Radio Receiver/Transmitter

Early radio equipment mounted in rear cockpit

The SCR-68 Radio Telephone Set was mounted in the rear cockpit of several different types of biplanes. The antenna reel was mounted to the left. The filter box was screwed to the fuselage floor, under the forward seat or placed in the cockpit under the instrument panel. The pilot’s interphone set box was mounted where the operator could reach it.

The type SCR-57, basic component, BC-10, Airplane Interphone unit was the first airplane interphone and it was used in conjunction with the type SCR-68, Receiver/Transmitter. The Airplane Interphone unit was essentially a portable intercom switching station that allowed the pilot to communicate with his gunner or observer during flight or switch to communicate with the ground. The interior of the box contained condensers, coils and wiring and a tray for batteries that supplied the current for the carbon microphones in the headsets.  The box measured 10-3/8 inches x 6-3/8 inches x 2-5/8 inches. There were a total of 3,978 type SCR-57, Airplane Interphones produced as of Nov. 11, 1918.

Type SCR 57, BC-10 Interphone Box on display at the Hamilton Field Museum CA

Inside the type SCR-57, BC-10 Radio Interphone box

The generator GN-1 was a wind-powered device that used a miniature propeller. It was located in an aerodynamically shaped pod fitted on the braces of the landing gear so that it would not hinder any other parts of the aircraft. The generator was used to gather adequate wind power and convert it to electrical power for the aerial radio telephone system. The generator provided a plate voltage at 300 volts and a filament voltage at 30 volts. The voltage output was regulated by a General Electric type TB-1 vacuum diode which controlled the amount of current flowing through the generator field winding.  The wind-powered generator was not very efficient because it required the airplane to travel at fast speeds in order for it to work properly.

 GN-1 Generator installed on a Jenny

GN-1 generator

Inspecting the GN-1 Generator used for the wireless telephone system

There were two types of antennas used for the system. The single trailing antenna type A-21 was used for straight away flying. It comprised a 4 foot length of cord made fast to a reel at one end and tied at the other end to a 300 foot length of antenna wire. The observer used a hand-operated reel to extend and retract the antenna while in flight. The antenna was made of copper wire and weighed 19.5 pounds including the two pound weight shaped like a fish at the end of it to stabilize the wire in flight. The second type of antenna was the double trailing antenna type A-23. It was used for airplanes flying in formation. The length of the copper wire on the type A-23 was 130 feet.   

Double trailing antenna type A-23 diagram

Other equipment in the system included the two leather flying helmets, type HS-1 which were fitted with a microphone and headphones. They were designed to fit snugly in order to eliminate most outside noises in the open cockpits.   Either one of the two single-button carbon microphones could be used for transmission. 

Testing the Wireless Telephone system on the ground before flight
The Army Signal Corps type SCR-68 Radio Telephone communication system was designed for short ranges and was reliable up to five miles. However, during one test under ideal conditions, the system received and transmitted messages up to eighteen miles to radio equipment on the ground.

According to the Signal Corps Pamphlet #29: “Type SCR 68 presents no special difficulties when simple rules are remembered”

  1. Do not forget to inspect the set before each flight.
  2. Do not forget to plug in the telephone transmitter and receiver plugs.
  3. Do not forget to throw the receive transmit switch.
  4. Do not talk rapidly.
  5. Do not have the telephone transmitter away from your mouth.
  6. Do not cup the hands over the telephone transmitter
  7. Do not shout into the telephone transmitter.
  8. Do not become impatient if you do not hear signals immediately.
  9. Do not expect satisfactory operation over more than five miles.
  10. Do not touch any un-insulated parts while the switch is on transmit.
  11. Do not tinker with the set. 

By the late summer of 1918, approximately 3,000 complete type SCR-68 units were manufactured and distributed to the US Army and most were mounted on De Haviland DH-4s. Conversations between airplane crews and ground stations by means of the radio telephone became routine and they were used during the closing months of the war. For the first time it was possible for ground observers to talk to pilots in the air miles away. Furthermore, Commanders of aero squadrons could also voice warnings to all their pilots as to the movements of enemy aircraft. Squadron formations of all sorts could be maintained in the air as easily as infantry units on the ground. It was reported on November 23, 1918 that squadrons of American airplanes fighting in France were maneuvered under vocal orders transmitted by radio telephone and its advantages were proved in actual air combat. 

Shortly after the end of the war, Major General George O. Squier, Chief Signal Officer of the U.S. Army, in an address before the American Institute of Electrical Engineers extolled the merits of the radio telephone system. He stated that the radio telephone enabled American squadron commanders to direct and control by voice the movements of individual units, who in turn helped allied artillerymen to silence the German guns.

Due to its many problems, primarily its inability to communicate with other types of radios and its very limited range, the SCR-68 radio system quickly became obsolete after the war and was replaced with better systems. Nonetheless, the SCR-68 system was one of the first steps towards developing more effective messaging between pilots, crewmembers and commanders on the ground. The success of the aerial radio telephone was one of the greatest achievements of WWI. 




Anonymous Stan said...

You have done an amazing job of of documenting the progress. I am building a1/6 proctor kit and plan to use your a/c as the subject. Thanks for posting such great pictures, and I hope you will fully photograph the completed project for us modelers and fans.

7:19 AM  

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