Supercharger Development in the U.S. During the Inter-War Period Part 3 - Developments in the U.S.

Developments in the U.S.

Fig. 3.  Miller supercharger designed by Dr. Moss. An unusual feature is the small impeller installed in the intake nozzle. (Courtesy Miller/Offenhauser Society)

Dr. Sanford A. Moss (1872 – 1946) made the turbocharger practical, advanced the cause of gas turbines, and ended his long career by pressurizing civilian airliners. Earning a doctorate from Cornell in 1903, he was immediately hired by General Electric to head up their turbine research facility at West Lynn, Massachusetts, where he would remain until retirement in 1938. Some idea of his thinking comes about from his habit of asking prospective employees if, as a child, they had ever taken a clock apart to see how it works. For “A young fellow who never took a clock apart can never become a mechanical engineer.”

Supercharger Development in the U.S. During the Inter-War Period Part 2 - Types

Types

After the First World War supercharger development concentrated on gear-driven centrifugal compressors and turbochargers. NACA was almost alone in the pursuit of the Roots blower.

Fig. 1. British supercharger drive, circa 1920. Engine oil provided lubrication on this example.  German designs often used a separate reservoir and dedicated oil pump.

Fig. 2.  Centrifugal clutch patented by Heron and Green.

Gear-Driven Centrifugal Blowers

A centrifugal compressor consists of an impeller and a diffuser housed in a helical casing, or scroll. The diffuser, sometimes called the stator, occupies the annular space between the impeller and scroll. Passages created by the diffuser vanes open wider as they approach the discharge throat. Vanes on the impeller wheel are arranged radially and may be straight or curved. The use of curved vanes came relatively late in the period and improved efficiency.

Air enters at the impeller hub, rotates with the impeller and, under the influence of centrifugal force, moves outward in a path defined by the impeller vanes. Upon contact with the diffuser, the air expands and slows, converting much of its kinetic energy into static pressure.

Because the impeller cannot be allowed to make physical contact with the shroud, there is always some leakage between the vane tips and the scroll. The seal consists of air, an elastic medium. At low rotational speeds the impeller merely flays about delivering little or no output. As tip velocity increases, the air seal becomes more positive and the compressor begins to pump. Unlike Roots blowers that move the same volume of air per revolution, centrifugal compressors are dynamic machines, whose output increases as the square of speed—double the speed and the output theoretically quadruples.

Inertia

Work on aircraft superchargers began in Europe around 1915 with the intent of normalizing output at high altitudes. Initially experiments were carried out with a variety of pumps, but within a year or so the French settled on the Rateau turbocharger. The Royal Aircraft Factory

Supercharger Development in the U.S. During the Inter-War Period Part 1

This paper describes some major developments in aircraft superchargers that took place in the United States between 1918 and the Second World War. Emphasis is on the supercharger itself. Other developments that contributed to the success of the technology—doped fuels, reduction gears, variable-pitch propellers—will have to wait for another time.

Rationale

Engines induct air by volume, but consume oxygen by weight. As the atmosphere thins at high altitudes, fewer oxygen molecules are available for combustion. A naturally-aspirated engine loses about half of its rated power at 20,000 ft. Forced induction is a merely a way to increase the density of the charge.

Normalized Boost

Initially researchers viewed superchargers solely as a means of altitude compensation. The aim was to restore lost power by maintaining, but never exceeding, sea-level manifold pressure as the airplane climbed. As Dr. Stanford Moss put it, a normalized supercharger “kidded the engine into thinking it was a sea level.”[1] Brake mean effective pressure (BMEP), exhaust temperature and the heat lost to the cooling system remained within design limits.

The ability to operate with impunity at high altitudes resulted in increased speed and slightly more than anticipated engine power. The rarified atmosphere reduced drag on the airplane and backpressure on the exhaust. The loss of lift could be compensated for by greater angles of attack.

Ground Boost

The Rolls-Royce W2B/23 Welland

This turbo-jet was the first British production engine. The prototype F.9/40, DG202/G, powered by Rolls-Royce 1,700 lb W2B/23 engines, was flown by Michael Daunt, from Barford St. John airfield on July 24, 1943. In November this aircraft was delivered to the Rolls-Royce base at Hucknall for Welland development.

Two Rolls-Royce Welland turbo-jets were installed in the first production Meteor Mk.1, EE210/G, which was test flown by Michael Daunt on January 12, 1944. This Meteor was then sent to the United States in exchange for a General Electric J31-GE-powered Bell YP-59 Airacomet, RG362/G. The Meteor was first flown at Muroc AFB by John Grierson on April 15. Several test flights followed. By December, the Meteor had been shipped back to the U.K.

The Rolls-Royce Welland entered service with the RAF Meteor Mk.1 jet fighters EE211-229 and Meteor Mk.3/EE230-244. The first of these Meteors was delivered to No.616 Squadron RAF in May 1944, equipped with 1,600 lb thrust engines rated at180-hours between overhauls. Flying from RAF Manston, near the English channel, the Squadron first saw action against the V-1 flying-bombs en-route to London on July 27, 1944. The first of thirteen V-1s to be destroyed was on August 4, when Flying Officer Dean used his wing tip to tip a V-1 off its course and saw it crash onto open ground.

The Rover W2B

The W2B was the Rover version of the Whittle engine, ordered into production by the British Ministry of Aircraft Production in 1942. This “reverse-flow”, 43.5-inch diameter engine, featured a 19-inch, double-sided impeller, 10 “reverse-flow” combustion chambers and a single-stage turbine. Engine weight was some 850 lbs.

To improve the “surging” problem found at altitude, Maurice Wilks and his staff at Rover, Barnoldswick in Lancashire, developed 20-vane diffusers to Whittle’s design. With the thrust still at 1,000 lbs, Mr. J.P. Herriot from A.I.D. came to Rover and with improved turbine material, achieved a 25-hour test at 1,250 lbs in November, 1942.

From July 10, 1940, test pilot Jerry Sayer, was only able to make taxiing runs with 1,200 lb thrust Rover W2B/23 turbo-jets fitted to the first twin-engined Gloster F.9/40 prototype fighter, DG202/G.

The Rover W2B turbo-jet was first flown in the tail of a twin-engined Wellington test-bed, Z8570/G, from Hucknall, on August 9, 1942.

How to control Flying Radio Control I.C. Powered Model Aircraft ? The Receiver & The Battery part

The Receiver 

This is the small rectangular sealed box with a length of thin wire protruding from one end and a set of sockets and exposed pins at the other end. These sockets are provided to receive the plugs attached to the servos. Normally the sockets are marked with the appropriate designated function. The number of functions available will normally range from 4 up to 7 or 8 depending on the model purchased. There will also be another input socket designated for the battery lead.

There will also be a socket to take a receiver crystal. The crystal will normally be fitted in situ when a new system is purchased. Crystals are usually supplied in matched pairs designated Tx (Transmitter) & Rx (Receiver), the frequency value in MHz and/or the channel number. Never interchange the Tx and the Rx crystals.

Servos 

How to control Flying Radio Control I.C. Powered Model Aircraft ? The Radio Control System Part 2

Antenna
Batteries
Battery Meter
Crystal
Gimbals (Stick)
Handle
Power Switch
Trainer Switch
 The telescoping tube that transmits the signal
 The device that provides power to the transmitter
 The device used to monitor the strength of the transmitter batteries
 The device that sets the radio frequency of the transmission
 The device that allows the user to input desired control movements into the transmitter
 The device for carrying the transmitter
 The switch used to apply battery power to the internal components of the transmitter
 The switch used to allow an instructor to give control of a model to the student
Trim Lever  Slides used to adjust control surfaces during flight

How to control Flying Radio Control I.C. Powered Model Aircraft ? The Radio Control System Part 1

The Radio Control System 

There are many modern radio systems to choose from.  Each manufacturer offers a wide range of options from simple 2 - channel to computer assisted 8 - channel systems (and more!).  The choice is limited only by your financial budget. As a beginner you should discuss the choice of system with your intended instructor.  There are several good reasons for doing this, the primary reason being that the student's systems must be compatible with the instructor's system if a buddy box link is proposed.  This option will be covered in more detail later.
 
All standard radio systems consist of four (4) basic components.  Transmitter     - The unit that takes the control input from the pilot through the gimbal mounted sticks, encodes this input and sends it to the aircraft as a radio signal.
 Receiver - The unit that receives the signal from the transmitter, decodes it and  routes it to the appropriate servo.
Servos - These devices convert the decoded signals into a mechanical force that  is directed via a linkage to the appropriate control surface.
Batteries - The component that provides the electrical supply enabling the other  components to function.

How to control Flying Radio Control I.C. Powered Model Aircraft ? The Power Plant part

The Power Plant 

The most suitable engine size for almost all trainers is a 6.5cc. (0.40cu.in. or "forty") size.  When it comes to choosing an engine for your trainer, the choice is almost mind boggling.  So many manufacturers, each one offering several engines in the same capacity range.  So which do you choose?  You can buy cheap or you can buy reliable. "Reliable" means it starts, ticks over, runs and stops when it's meant to and will probably cost an extra £10 to £15 more than a cheap offering.  If you enjoy the challenge of getting an engine to run properly when it doesn't want to - buy cheap.  If you want to learn to fly - buy reliable.

A good engine isn't necessarily a powerful one.  What you need in a suitable trainer engine is one that starts easily, is easy to set up and runs consistently.  When you're learning, most of the time you are unlikely to have the engine running at much more than half throttle.  Ask around at the club and watch anyone else learning to fly.  Notice how easy it is to get the engine started.  Does the engine run consistently throughout the flight - full throttle on take off then back to about half throttle?  Does it falter just after take-off or die in the air unexpectedly?

How to control Flying Radio Control I.C. Powered Model Aircraft ? Ease of Repair Part

Ease of Repair 

You have to accept that your first—and maybe your second—model could well be damaged in the course of your learning how to fly.  With this in mind, you should look for a trainer that has relatively few parts that can be easily repaired if they are broken.

Wood and foam are high on the easy-to-fix list; molded plastic, fibreglass or epoxy resins are more difficult to repair.  Cyanoacrylate (CA) glue (sometimes called ‘superglue’ or ‘cyano’) and epoxy are the most common adhesives used  for gluing wood parts together.  Aliphatic resin or special white glues available from your model shop are excellent for gluing foam pieces back together.

Parts availability Often it is easier to replace damaged parts than to repair them.  Try to select a model that has replacement parts readily available via your model shop from the manufacturer. Some model kits have extra wings supplied in case you damage one beyond repair.

How to control Flying Radio Control I.C. Powered Model Aircraft ? The Instructor & Choice of Model Parts

The Instructor 
It’s not completely unknown for individuals to teach themselves to fly model aircraft but more fail miserably than actually succeed.  Without the help and support of an experienced flyer, you are almost certain to destroy your pride and joy at the first attempt.

Gravity is a very unforgiving adversary in this battle and unless you are very lucky, you will loose the initial confrontations.  Even if you have a very commendable attitude and a determination to not be defeated, the encounters will empty your financial coffers quite rapidly.  Repairs or replacement aircraft, engines and radio equipment can be a major drain on finances.
Why make life difficult for yourself when, for the price of a meal out for two, you can have a full year’s club membership and the help of a qualified tutor at your disposal?  Most clubs provide free tuition for novice members.

A proficient instructor can be the best aid to your success in this adventure.  Most club instructors have been through a process of selection and special training to provide them with the skills they need to teach others.
Talk to each of the appointed instructors to find one you can relate to.  Bear in mind also that your instructor has to have your respect.  This relationship is very much a two way exercise and requires you to be receptive and prepared to obey instructions as required.  If the club appoints an instructor that you feel uncomfortable with, don’t be afraid to explain this to the training officer and find one you are happy with.  It is very important that you and your instructor have a strong measure of both trust and understanding.

Once you are happy with your instructor, take some time to sit down and have them explain the programme you will follow (they will probably do this anyhow).  This is important so that you know exactly what will be expected of you.  Not only this, but you will have some idea of the time frames required to fulfill the various stages of the programme.

Choice of Model 

How to control Flying Radio Control I.C. Powered Model Aircraft ? - Essential Considerations & Where To Fly Parts

Essential Considerations 
We are going to work only with fixed wing model aeroplanes powered by two stroke fuel engines.  The basic advice is also relevant to helicopters, as far as engines, radio and starting kit is concerned.  There are some basic fundamental factors you must accept and appreciate before you even start.

1) Where you are going to fly your model.
2) The necessity for you to be protected by third party indemnity insurance.

Both of these essentials can be fulfilled by approaching and joining your local model flying club.  Such organizations will, in most instances, have negotiated flying rights with a local landowner, council, etc. or even own their own flying field.

Most established clubs will be affiliated to the national governing body that controls model flying in your country.  As part of that affiliation they will have inclusive membership insurance at a fraction if the price it would cost you to insure yourself.  Not only does club membership carry these most useful benefits, there will almost certainly be a pilot training scheme for you to take advantage of.  Many clubs today even provide a suitable club trainer and control setup for you to ‘cut your teeth on’, so to speak.  If you haven’t already been put off your initial enthusiasm by the above reality check, then let’s move on to some further considerations.

a) Where are you going to learn to fly your model?
b) Who’s going to teach you?
c) What sort of model will you choose?
d) How are you going to power it?
e) What radio equipment will you choose to control it?
Let’s take each of these basic considerations in turn.

How to control Flying Radio Control I.C. Powered Model Aircraft ? Introduction Part 1

Where to Fly