home    Nederlands

A Selfcontrolled Chainreaction (the V1½)

Slideshows        V1 flying bomb        V2 rocket        Rolls-Royce gasturbines

Why V1½?

The selfcontrolled chainreaction is nicknamed V1½ or V1.5 after the V1 and V2 weapons launched by Nazi-Germany during WWII, which were completely different beasts as is explained below and can be seen in the Discovery Channel documentary
https://www.youtube.com/watch?v=ro4ApX7EhJw Wings of the Luftwaffe (44m07s)

A very incomplete history of gas turbines is added.


V15_files/V15-layout.jpg Heating a flammable liquid to its boiling point and using the heat of the burning vapour to evaporate even more of the liquid can obviously lead to a chainreaction. We give the values for ethanol (85%).
In first appoximation Q(t)=Q(0) for t ≤ t0 and for t ≥ t0 dQ(t)/dt=Q(t)* η C/E
Where t0 is the moment the boiling sets in (78.5 °C) , η is the efficiency of heat transfer, C is the calorific value (6000 cal/g) and E the heat of evaporation (approx. 260 cal/g) .
So with only 9 % feedback we have an exponentially growing heat output Q(t) ≈ Q(0)*exp( η tE/C) on a time scale of ½ second. In other words a spectacular flame leaping from the chimney.
As with every exponential growth, non-linear effects restrict the chainreaction.
• Very soon the internal flame get choked. Despite the chimney effect, not enough air can reach the outpouring vapour and most of the action is outside the apparatus. This is however a temporary effect and after a few seconds the next blast will emerge.
• It may take upto 5 minutes before the show starts, but in a couple of seconds all fuel is consumed and the apparatus is left to cool down.

Safety precautions

Spectacular as a demonstration is, there have been half a dozen public demo's, it is not dangerous provided a few safety precautions are taken into account.

• Perform the demo outdoors on a free and flat stone platform.
• Keep a safe distance once the preheater is ignited and the chimney is placed. • Never look into the chimney, for instance when you think the apparatus is failing.
    Wind may extinguish the preheater, but a windscreen can prevent that.
• Do not use other fuel than 85% vacuum distilled ethanol (*).
    This will burn safely and leave no residue.
• Do not scale it up.
    I use 60 ml ethanol and the same amount in the optional afterburner.
• Soft solder can not be used in the construction.
    I used stainless steel and hardsoldered brass.
    Tin cans for the chimney can be reused.
• The internal diameter of the C-shaped pipe should be large enough to prevent
    pressure building up in the fueltank.

(*) Approximate values for other fuels:
fuel C E C/E
unit kcal/g cal/g dimensionless
ethanol(85%) 6 260 23
ethanol(100%) 7 200 35
kerosine 11 60 183
hydrogen(liquid) 34 110 309

The demonstration

V15_files/V15-modules.jpg V15_files/V15-stack.jpg V15_files/V15-burning.jpg
The design of the apparatus is modular. This allows easy variation of aeration and chimney height.
An ethanol flame is barely visible in daylight. Applying a bit of grease to the inside of the chimney solved that "problem".
Note the blue flame from the afterburner.

Using a fan

V15_files/V15-fan.jpg V15_files/V15-fannedflame.jpg
With an electric fan we can more or less prevent the choking effect.
The result is a hissing flame and a shorter burning time.

NAC 2011 festivities

To celebrate the 90th birthday of Prof. Kees de Jager http://www.cdejager.com/ the chainreaction was, after a short explanation, demonstrated during the 'Nederlandse Astronomen Conferentie 2011' on the island of Texel on May 19 2011.
V15_files/slideshow.jpg V15_files/thumbnails/IMAG0031-cropped.jpg V15_files/thumbnails/IMAG0034-cropped.jpg V15_files/thumbnails/IMAG0035.jpg V15_files/thumbnails/IMAG0036.jpg V15_files/thumbnails/IMAG0038.jpg V15_files/thumbnails/IMAG0039.jpg V15_files/thumbnails/IMAG0043.jpg V15_files/thumbnails/IMAG0047.jpg V15_files/thumbnails/IMAG0048.jpg V15_files/thumbnails/IMAG0049.jpg V15_files/thumbnails/IMAG0050.jpg V15_files/thumbnails/IMAG0051.jpg

Birthday party

To celebrate the 65th birthday of Els Wegdam LinkedIn the chainreaction was, after a short explanation, demonstrated in front of Cultuurhuis Stefanus in Utrecht on June 22 2014.

V15_files/slideshow.jpg V15_files/thumbnails/uitnodiging_Els_65_jaar-cropped.jpg V15_files/thumbnails/Panasonic1.jpg V15_files/thumbnails/Panasonic2.jpg V15_files/thumbnails/Panasonic3.jpg V15_files/thumbnails/Panasonic4.jpg V15_files/thumbnails/Panasonic5.jpg V15_files/thumbnails/Panasonic6.jpg

Click on Start slideshow . Every image will be shown for 6 seconds. Just click in the image to skip to the next image.
Or view the individual images by clicking the thumbnails. Click in the large image to return to this page.
You can also view the original images by clicking on JPG .

The V1

The V1 was a flying bomb powered by a pulse jet engine. The fuel in flight was gasoline.
    Click in the picture for the full resolution version (2096x1156).

As the construction of the pulse jet engine is simple and well known, a number of people or groups have rebuild the engine for fun. However the original design was intended to bomb London and other cities in Southeast England. The lifetime of the inlet valves is limited to less than an hour (~100000 movements @ 45 Hz).

V1 on YouTube

There are numerous videos on YouTube about the V1, historical footage as well as post-WWII reconstructions.

• V-1 flying bomb. Original German technical instruction film in 6 parts.
https://www.youtube.com/watch?v=ffjdgVU_RMQ (part 1 4m34s)
https://www.youtube.com/watch?v=NXWSQ4clh7k (part 2 4m31s)
https://www.youtube.com/watch?v=HQccOvNG_ZY (part 3 4m43s)
https://www.youtube.com/watch?v=-XiRkk4zYtU (part 4 4m37s)
https://www.youtube.com/watch?v=sfN50qB6h8Q (part 5 4m39s)
https://www.youtube.com/watch?v=Kcup3W6uy_E (part 6 4m54s)

• Test runs of a rebuilt V1 pulse jet engine, note the details.
https://www.youtube.com/watch?v=Rdwbp6R2qM8 (3m50s)
    - Opening music @ 0m13s
    - Door opening at end of test @ 1m14s
    - Vortex ring @ 1m57s
    - Vague comments @ 2m34s

• V1 on skis in Sweden
    Preparation and testing https://www.youtube.com/watch?v=-O-JWddgagk
    The V1-sledge in action https://www.youtube.com/watch?v=pR0d6s-28MA

The V2

The V2 was a real rocket or ballistic missile. It burned a 74% ethanol, 26% water mixture with liquid oxygen.
    Click in the picture for the full resolution version (2000x1200).

Further development lead to the American space program.

V2 on YouTube

After WWII salvaged V2 parts were assembled and used for scientific masurements in the upper atmosphere in the USA.

V-2 stearing mechanism (Wright-Patterson Air Force Base)
https://www.youtube.com/watch?v=H65IIfXFMhs (1m42s silent)
Assembling V2 rocket from German leftovers and launch (1947)
https://www.youtube.com/watch?v=tIUxhTYsKBg (19m39s)
Assembly, launch and recovery of V2 rocket, White Sands Proving Grounds, New Mexico (1947)
https://www.youtube.com/watch?v=QjXwsj8kHT4 (19m49s)

Rolls Royce Derwent gas turbine (1943)

British engineers were succesful in building turbines, starting with marine steam turbines developed by Sir Charles Parson for the Turbinia 1894, top speed 34.5 knots (63.9 km/h), and later for the Mauretania and its sistership the Lusitania .

Before and during WWII gas turbines were developed in the USA, Germany and the UK which could be used for turbo-prop and jet-airplanes. The most elegant design is the Rolls-Royce Derwent gas turbine which powered the twin-engine Gloster-Meteor.

V15_files/1024px-Rolls-Royce_Derwent.jpg V15_files/GM-1024x767.jpg
V15_files/derwent-drawing-Dutch.jpg     Click in the picture for the full resolution version (8512x4896).
A drawing of the thermodynamics of the Derwent from A.J.C. De Lang & L.Suetens, Toegepaste technische warmteleer.
V15_files/derwent-tech.warmteleer.jpg     Click in the picture for the full resolution version (2476x1292).
• A: 4 inlet ducts
• B: impeller of compressor
• C: 9 diffusor channels
• D: 9 combustion chambers
• E: turbine, 48 fixed and 54 moving blades
• F: jet exhaust duct
• G: connection shaft
• H: cooling fan

More information from G. Geoffrey Smith M.B.E., Gas Turbines and Jet Propulsion for Aircraft, can be read here .


Hear the sound of the Derwent (wav).
       WAV        mp3
You hear:
• the clutch of the auxilary engine
• rotating at low speed by the auxilary engine
• first fuel injection
• speed up to full power
• the second half (17.6 s) is the reverse of the first half.

New records

On 7 November 1945, the official air speed record by a jet aircraft was set by a Meteor F.3 at 975 km/h (606 miles per hour). In 1946, this record was broken when a Meteor F.4 reached a speed of 991 km/h (616 mph). This record was again broken by testpilot Roland Beaumont in 1946 with a speed of 1047 km/h.

In 1947 the Soviet Union bought (with approval of the British government!) Derwent and Nene engines from Rolls-Royce. They were copied for the MiG-15 (Mikoyan-Gurevich) jet fighter aircraft (David Holloway, Stalin and the Bomb page 235).

Rolls Royce jet engines on YouTube

• The Derwent jet engine under construction (1944)
https://www.youtube.com/watch?v=uPkp3TaePY4 (10m09s silent)
• Destructive testing of an Airbus 380 engine
https://www.youtube.com/watch?v=j973645y5AA (14m13s)
At 2:08 to 3:20 showing the construction of a titanium turbine blade.
• A DIY gas turbine with afterburner. Do not do this at home!
https://www.youtube.com/watch?v=WHEHMFbEH8I (2m46s)
home (English)    Nederlands   
© COPYRIGHT: Harm J. Schoonhoven, Utrecht, 2011. version 2015-01-19. All rights reserved.