forgottenfiberglass.com-the 1953 paxton phoenix brooks stevens designed steam car fiberglass bodied...

8/11/2019 Forgottenfiberglass.com-The 1953 Paxton Phoenix Brooks Stevens Designed Steam Car Fiberglass Bodied Prototype

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The 1953 Paxton Phoenix Brooks Stevens Designed

Steam Car Fiberglass Bodied Prototype

forgottenfiberglass.com/fiberglass-car-marques/one-offs/the-1953-paxton-phoenix-%E2%80%93-brooks-stevens-designed-steam-car-fiberglass-bodied-prototype/

Geoffrey Hacker

Hi Gang

Experimental motive power, world-class

designer, innovating disappearing / sliding

hardtop, fiberglass body.how much

intrigue and interest can you put into just one

car?

Well if you did, the best car that would fit thisbill would be the Brooks Stevensdesigned

Paxton Phoenix cover car of Road &

Track Magazinein April 1957.

Lets see what John Bondhad to say about

the history of this significant car in his 1957

Road & Track Cover story.

The True Story of the Paxton Phoenix

By John Bond

The dream of every dedicated automotive designer is to start with a clean sheet of paper,

unhampered by the necessity of using this or that component part which was used the year

before. Sometimes such a dream actually happensas in this case. Our story begins in 1950.

In that year Robert Paxton McCulloch decided that he would fulfill a long-time ambitionto

design and possibly to produce a true luxury car for the discriminating motorist who could

afford the best.

As a manufacturer of two-cycle engines and related products, he had been extremely

successful and could afford such a venture. His McCulloch Motors Corporation, founded in

1946, had expanded to the point that over 1500 persons were employed. His gasoline powered

chain saws, though not the cheapest on the market, were out-selling his competitors on the

basis of performance and a reputation for durability. Other activities included the manufacture

of target plane engines, the aviation Divisions helicopter and two newly acquired divisions;

Rhodes-Lewis (aircraft accessories) and Pacific Optical.

An engineer himself, Robert McCulloch was, and is, a firm believer in engineering and

development. Already he had surrounded himself with some of the best engineering talent, and

with this force to draw upon the Paxton Division was formed (in 1950), headed by an

engineer/general manager, John C. Thompson. The Paxton Division was to be the advanced

design department for many varied projects, but its biggest assignment was the car.

Remarkably enough, the concept of the Paxton car was very similar to a later car whichultimately came to be known as the Continental Mark II.

However, the Paxton was originally planned to be relatively small in size (115 wheelbase) in

keeping with the already noticeable impact of expensive imported sports cars. Although not a
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sports car, it was to give very high performance, seat four people, and incorporate a hard top

which would retract. Unwilling to rob other divisions of engineering talent, McCullochs

progress on the car was slow in 1950. The chassis design was entrusted to an experienced and

independent Detroit firm: Hoffman Motor Development Co., owned by Roscoe C. Hoffman.

This company was well known for its ability to

design and build experimental cars; they had

built a front wheel drive car in 1930, pioneered

designs with independent suspension of all 4wheels, and built prototype cars for several

large manufacturers. At least one vehicle had

a rear-mounted engine.

Body styling was turned over to Milwaukees

well known Brooks Stevens Associates, while

the actual design of mechanical components

were the province of the Paxton Division. No

expense was spared at any time, and after a

succession of beautifully modeled cars (3/8

actual size), Brooks Stevens came up with a

very successful body design which met all the

basic stipulations and which was acceptable to the management.

The prototype bodies were to be made of fiberglass, and the first step was to build a full size

clay mock-up of the car exterior. When completed late in 1951, the clay model was mounted on

wheels, painted and photographed. (See bottom of page 13.) Even before the full-size clay

mock-up was finished, work began on a super-accurate plaster model.

Despite an earthquake, which cracked the job when it was almost completed, the first

female molds were taken off, and finished panels were ready for assembly by August of 1952.This rate of progress may seem slow, but was actually quite remarkable in view of the small

body engineering crew and the fact that complete and accurate production drawings of every

contour and every detail, including the power-operated top mechanism, had to be made.

Body Features:

When finally assembled early in 1953, the one (and only) Paxton car looked exactly as shown

here and on our cover. The car stood only 52 high, and though designed over 6 years ago, it

can stand along side any 1957 product and still get favorable comment from unbiased viewers.

It incorporated a thoroughly studied seating layout for the driver, with a definite sports car

feel. The front seat would accommodate three adults in comfort and the rear seat providedfor two more with only slightly less knee room than normal convertibles.

The true convertible hard-top feature was certainly logical and long overdueagain, six years

ahead of its time. Its operating principle was based on a pair of small steel cables which are

concealed in narrow T-slots running along each side of the trunk lid opening. When

conventional windshield toggles are released an electric-powered winch pulls the top back and

over the rear deck panel. The top, of course, fits very closely to the deck when folded and is

scarcely noticed when painted the same color as the body and deck panels.

Because of this feature some compromises in top and deck contours are mandatory, and the

overall design problem from the stylists viewpoint is not as simple as it may seem. Particularly

where, as in this example, the rear passengers must have adequate headroom and a rear-

mounted engine must be able to fit under the rear deck.


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The Frame:

Back in Detroit, Roscoe Hoffman and his crew of designers had the difficult task of creating a

frame and suspension system for a body not yet finalized, for an engine not yet running.

Although this forced them to make many changes, a completed prototype chassis was built and

shipped to California before a powerplant or a body were completed.

The frame for the Paxton was of a unique type, described by aircraft designers as a torque-

box. In essence, a cross section through the floor looks much like an airplane wing with a

central tunnel or duct analogous to the wing spar. Stressed skin of light gauge, rust-resistant

steel forms both the floor and the underpan with gentle slopes as the floor/frame tapers from

4.5 deep at the center to 2.5 deep at the side rails under the doors.

The result was a very satisfactory frame, relatively light (about 160 lbs.) and adequately rigid for

use with an open-roof body which could contribute little or nothing towards resisting torsional

loadings. The central duct served to supply air to the rear-mounted engine, but additional

cooling air was also supplied by the stylist via an opening on each side of the body. Tests, both

on a rig and on the road, showed the frame to be adequateits torsional rigidity factor was

slightly better than 3000 ft-lbs/degree, measured over the length of wheelbase (118).

The Front Suspension

Long advocated and practiced by

motorcyclists, the independent front

suspension of the Paxton had banking front

wheels. As shown in the photograph (page 16),

the basic form of this i.f.s. is Porsche, or

double trailing arm.

Each arm had an effective length of 9 and the

lower arms drive conventional torsion bars

with serrated ends and vernier adjustment for

standing height. The ride rate was 78 lbs/in.

giving a periodicity of 66 opm in front.

A neatly fitted antiroll bar can be seen in the

drawing on page 17, and it is interesting to note that the two front torsion bar springs were

shot-peened and pre-stressed to avoid settling with use difficulties.

The banking feature was extremely ingenious and remarkably simple. All suspension points

were rubber mounted, and the upper trailing arms were rubber-bushed at the frame mounting

bracket in such a way as to allow both normal suspension action and also pivot when viewed

from above.


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An inboard extension of each upper arm slips over an eccentric cam which is keyed to the

respective dual (vertical) steering idler shafts. Therefore, as the wheels are cramped, they also

tend to bank. The usual i.f.s. of this type has its roll center on the ground, and normally

wheel movements are always exactly parallel to each other, and to the chassis.

However, in a corner, the cassis-frame-body tilts, and the wheels do likewise and in the wrong

way. With the Hoffman design, the banking feature tends to restore the cornering cars wheels

back to something near 90 degrees to the road (0 degrees camber), even though the classis-

frame and body are rolling. There are limitations to this scheme, since a chassis roll angle of5 degrees or more is common in a .5g corner, and the banking feature restores only 3 degrees

at full lock. Also, deflections in both the rubber mountings and in the trailing arms tend to

cancel all the potential gains.

Summed up, the net result of this scheme appears to

be two-fold. First, a strong understeer effect is set up,

both by the loss in cornering power when the camber

angle changes, and also by the weight transfer effect of

the anti-roll bar.

Powerful understeering from the front wheels appears

essential in a car with a weight preponderance on the

rear wheels (in the Paxton, 42/58). Secondly, the

banking feature allows extensive use of rubber without

getting a horrible camber angle change when the ride is

ultrasoft and the roll angle is considerable.

This reduces ride harshness without the need for

sloppy tire pressures. On the subject of tires, the

Paxton personnel were unanimous in specifying 6.00-

16 tires, and the cries of all the tire vendors were mostamusing.

If the car had gone into production, it would have been necessary to pay a considerable

premium per tire in order to get a carcass and a tread design of the latest improved type as

used only on e.l.p. tires with 15 rims.

The Rear Suspension:

Although the original plans called for independent rear suspension (virtually essential with a

rear-mounted engine), there were many changes before the design was finalized.

Ultimately, Hoffman designed a diagonal-axis i.r.s. which as somewhat similar in geometry to

the scheme used at the time in the Lancia Aurelia. However, the prototype chassis used

concentric torsion bars instead of the leaf springs shown on the early 115 chassis layouts.

The roll center was at ground level, but cornering roll was employed to give a slight rear wheel

steer in an understeering direction. (see photo on page 16).

Design work was also instituted at Paxton towards the building and testing of a deDion type

rear axle, but this was never completed. Work was also in progress on special brakes, light-

alloy wheels, etc., this being mentioned merely to show that the Paxton car would have been a

truly advanced automobile in every detail, if it had been produced.

The Automatic Transmission:

The disposition of the engine and differential (on different levels) required some form of a

transfer case and a special feature of the unit was a design to include the duties of ratio


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changing. As strange as it may seem (at first thought), the automatic transmission/transfer

case used V-belts.

Extensive experimental work with a conventional 100 bhp, 3000 lb. car showed that such a

transmission had possibilities, and further tests showed that 4 belts would do the job.

Eventually the test car (American) was supercharged, and with the cooperation of the belt

manufacturers (Gates, in particular) satisfactory durability was obtained.

Ratio changes were effected by sliding the sheaves on their respective shafts, and with a 5.38axle ratio the overall ratio could be varied from approximately 10:1 for starting to 3:1 for high-

speed cruising. The complete transmission is shown on page 18, enclosed in an aluminum

housing (primarily for dirt and water protection) and located forward of the differential. The unit

weighed less than 100 lbs. or approximately half the weight of a typical automatic transmission

as used on our cars today.

The Powerplant:

At Paxton, work progressed rapidly on a

radical new power-package to be mounted in

the rear. The original layouts called for a two-cycle engine, of course.

It was fully understood by all concerned that a

rear-engined car would only be a practical,

drivable vehicle if something less than 60% of

the total weight under the worst condition of loading could be attained at the rear wheels.

The weight of a conventional engine-transmission-differential assembly would be far too much

to meet this requirement, especially in a car which was to have a curb weight of under 3000 lbs.

Since the engine constitutes the biggest percent of the power-package weight, it was decided

to carry on with some earlier experimental work and design a two-cycle engine with three

cylinders, opposed pistons and two crankshafts.

Air-cooling and supercharging were logical corollaries to this high-power, low-weight

hypothesis. This engine was very compact and was placed directly over the differential with

the two crankshaft axes parallel to the ground and to the cars fore and aft centerline. The

usual type of transfer case mounted behind the engine brought the power down to rear axle

pinion level, and also served as an automatic gearbox.

As the engine design progressed, the first hints of a horsepower race became evident and with

it the need for 200 bhp instead of 150. So it was that the engine ultimately had four cylinders

instead of three, and eight pistons instead of six. Also, the time schedule required a revision in

engine location to behind rather than over the differential, primarily a temporary expedient. A

view of the 4 cylinder engine appears on the cover and also on page 18.

Complete details of this engine are not available, but it is similar in principle, to one designed

by Causan in the early twenties. The combustion chamber is formed predominately by the

piston crowns as they meet (nearly) at the top dead center. Ignition is by conventional spark

plugs, and as the power stroke progresses, the exhaust ports at one end of the cylinder are

uncovered by the exhaust-side piston. Shortly thereafter, the opposite intake-side piston

uncovers the intake ports.


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This gives what is termed uniflow

scavenging, and by causing the exhaust side

of the engine to lead intake ports are closed.

In this way it becomes practical to supercharge

the engine without recourse to troublesome

rotary valves. A special feature of this engine,

not previously mentioned, was its full

utilization of aluminum alloys.

It weighed less than 300 lbs. with all

accessories. Several other types of engines

were given consideration including a two-

cycle, air-cooled V-4, and a four-cycle V-8.

The latter was designed by Hoffman and

weighed 430 lbs. with all accessories. However, without a doubt, the most interesting

powerplant was the Doble-designed steam package. This unit will be described by Mr. Allan F.

Bell, Paxton project engineer.

The Steam Powerplant:

The experimental steam power plant selected for use in the Paxton car was designed to be of

maximum efficiency and to attempt to make use of the most modern advances in materials and

techniques. One of the leading authorities on steam automotive power systems, Mr. Abner

Doble, was engaged as a consultant. His designs, the results of many years of practical

experience in designing and manufacturing steam vehicles, were used as a basis for the steam

power system in the Paxton car.

Of prime importance, of course, was the steam engine itself. This engine was a 6 cylinder

engine of the compound type. The three low pressure cylinders were bored in line in the low

pressure block casting. The high pressure cylinders were placed at the head end of the low

pressure block, and each high pressure piston was connected to the low pressure piston below

it by a round piston rod operating through a seal.

The low pressure pistons in turn were connected by automotive type connecting rods to a

crankshaft with three throws 120 degrees apart. In the compound type of steam engine, steam

at a high temperature and pressure is first expanded in a high pressure cylinder. Then it must

be efficiently transferred into a low pressure cylinder and allowed to do the remainder of its

work on the low pressure piston. In a well designed engine, such as the one used in the Paxton

car, the amount of work done in each of the cylinders should be very nearly equal.

On the up stroke, the high pressure piston did the work, and on the down stroke the low

pressure piston took over, and it can readily be seen that although the crankshaft had only

three throws, there were six very smoothly delivered power pulses developed per revolution of

the engine, and only in a 12 cylinder configuration can a 4-cycle internal combustion engine

come anywhere near to matching this smoothness of power delivery.

To continue with the description of the Paxton

engine, poppet valves were used to control the

admission of the steam to the high pressure

cylinder and its transfer to the low pressure

cylinder. Steam was normally exhausted from

the low pressure cylinder through a series of

unaflow ports near the end of the piston

stroke.


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For operation in long cut-off conditions, an additional poppet valve was employed to insure

that all of the steam was exhausted from each low pressure cylinder before it received its next

charge from the high pressure cylinder above it.

Perhaps it would be well to say a few words of explanation concerning the term cut-off as

used in steam engine practice. During periods of starting and acceleration, when maximum

torque is required from the engine, the inlet valve is kept open during almost the entire stoke of

the piston, resulting in a tremendous force being exerted on the piston rod through its full

travel.

This long cut-off operation results in spectacular engine and vehicle performance, but is very

wasteful of steam. Therefore, for normal moderate speed operation, it is necessary to shorten

the cut-off and admit steam during a relativesly short period at the beginning of the piston

stroke. The thermal energy in the steam allows it to continue to expand and do work on the

piston after the valve is cut-off or closed, but the amount of force decreases as the piston

nears the end of its stroke, resulting in a reduced delivery of power.

Short cut-off operation is far more economical, so an automatic control was provided on the

engine to continuously adjust the cut-off to give maximum economy for any condition of

operation and also to instantly shift the cut-off to long cut-off whenever the throttle was

opened for a burst of acceleration. The Paxton steam car was probably the first vehicle ever to

use this fully automatic valve control system.

The engine was designed to accept inlet steam at temperatures as high as 1200 degrees F. and

1800 psia pressure, and the exhaust was to be into as high a vacuum as could be maintained by

the vehicle condenser and vacuum pumps.

By efficiently utilizing this highly superheated steam, the engine and power system could

approach or exceed the overall thermal efficiency of a modern ohv internal combustion engine,


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and when one considers that low priced gasoline or even kerosene could be used to fire the

boiler, the advantages of this propulsion system can be appreciated.

The boiler used in the Paxton car was of the flash type. It consisted of a highly efficient

carburetor type burner and stainless steel fire box, surrounded by literally hundreds of feet of

steel tubing. The hottest point in the firebox contained some inconel tubing where the steam

received its final superheat before passing into the engine. The combustion air was blown

through the burner at high pressures, resulting in a heat release as high as 1.5 million btu per

cubic foot of fire box space.

An extremely clever system of automatic controls invented and developed by Mr. Doble insured

that the steam would be delivered to the engine at the proper temperature and pressure, and

that there would always be sufficient water in the boiler to make steam. Through the use of the

flash or continuous tube type of boiler, there was no hazard even if a control malfunction did

occur. At these very high steam pressures, a boiler burst merely meant a rupture of the tubing

inside the heavy aluminum boiler jacket and the only result would be the extinguishment of the

burner and gradual stoppage of the car.

Water was forced into the boiler by a set of

high pressure feed pumps which were in

operation whenever the vehicle was in motion.

Combined with the feed pumps was a

reciprocating vacuum pump whose function

was to exhaust any air that might be present in the condenser.

Since adding of water was considered to be unacceptable in a modern car, the hotwell or

water tank and the condenser were completely sealed from the atmosphere. All of the water

converted into steam at the boiler was, after being utilized in the engine, condensed back into

water and pumped again to the boiler for reuse.

To insure that the entire steam car operated at maximum efficiency under all possible

conditions, and was competitive with a modern gasoline automobile in regards to simplicity

of operation, a very elaborate overall control system was required. All the driver had to do was

to get into the car, turn on the ignition key and after a delay of possibly 20 seconds, be on his

way.

To accomplish all of this, automatic controls started an electric motor which pumped some

water into the boiler, started another electric motor which operated the boiler air blower, and

also put into operation, the burner ignition system and fuel pump.

As soon as steam pressure was obtained, theboiler control system adjusted the fire and

water supply to assure the proper operation

conditions. A large fan was provided back of

the condenser to insure an adequate flow of

cooling air through the core. At low car speed

this fan was driven by a shaft from the engine.

Under the conditions of rapid acceleration and

high speed operation, a steam turbine driven

by exhaust steam from the engine took over

the driving of the fan. In addition to the fan

drive, an additional mechanical connection

from the turbine speeded up the boiler blower.


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Thus, both additional condenser capacity and fire were provided whenever needed for high

performance, and steam which would otherwise be wasted was utilized by this exhaust turbine.

Some development work was also done on an electrical drive system for the auxiliaries,

condenser fan, etc. in an effort to arrive at the best and most modern control possible.

As the various parts of the steam power system were designed and the testing of prototype

units gotten under way, it began to become apparent that a tremendous amount of engineering

and testing would be required to come up with a vehicle which would be as simple to operate

and reliable as a modern gas automobile, and still be capable of being produced and sold at areasonable price, even in fine car brackets.

Steam power certainly has many intriguing possibilities, but an enormous amount of work must

yet be done to narrow the gap of fifty years of engineering effort poured forth on internal

combustion engine vehicles.

Conclusion:

In mid 1954, the entire Paxton car project was droppeddisappointing perhaps, but based on

sound economics. We asked Robert McCulloch the reason for this decision and he summed it

up neatly. In our words, it boils down to a problem of engineering man-power.

As everyone knows, there is a tremendous shortage of engineers in this country, and the car

program was taking trained technicians away from the multitudinous McCulloch projects in

other fieldsfields which, for numerous good reasons, the company feels will be more profitable

(and perhaps less risky) than the automobile manufacturing business.

So it was that the last dream of the steam-

power advocates died, not because steam-

power has no merit, but because no one will

risk the tremendous amount of capital required

to produce such a car.

And, in the final analysis, would you invest 50

million dollars (or more) to manufacture a car

that couldnt possibly be built and sold at a

profit for less than $10,000?

Summary:

Steam power never became a reality for the Paxton. Instead, the Paxton Phoenixkept the original

Porsche powerplant that had been installed for testing purposes. Recently, this very special car was

shown at the 2011 Milwaukee Masterpiece Concours d Elegance. Well feature photos of the

Paxtonat the Milwaukee Masterpiece Concours d Elegancein a future story here at Forgotten

Fiberglass.

Hope you enjoyed the story, and until next time

Glass on gang

Geoff * Click on the following link to view all stories

on: One-Off Sports Cars

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