No . 138 The Trusty Servant
The Lavochkin model
to work . In those post-war days ex-military stocks were still available from specialized shops , and one such shop , in the Edgware Road near my parents ’ house , had a length of four-inch diameter duralumin tube of minimal thickness : perfect for our needs . The “ Allbon Dart 0.5cc ” engine was removed from the Lavochkin . We made a new impeller fan to suit the diameter of the dural tube , which involved a sheet of dural and much sawing and filing . It was duly shown to Bryan , who for once seemed impressed . The Allbon Dart was then remounted in the duct tube .
A copper tube was connected to the duct , just aft of the impeller , leading from a small tin fitted with a bicycle valve . A needle valve in the copper tube would control the amount of fuel supplied . Fill the tin with fuel and it would be pressurized by a few strokes of a bicycle pump . But what fuel ? David and I discussed the matter . Paraffin would be easier to get hold of , but we didn ’ t think it would vaporize at low temperature . Petrol would be much more likely to give exciting results . serious obstacle . The garage refused to sell to him until once again Bryan was consulted . Bryan later described his feelings : “ I used to lie awake at nights , terrified that you were going to set fire to Mill and burn the place down . But foremost in my mind was the advice to Winchester Dons that our mission was to encourage men in ALL their interests , and that certainly was what I was doing .” So , the garage was mollified , and David returned with a large tin of the right stuff .
Of course , just about everything that could go wrong with our device then occurred : the pressure system kept springing a leak ; the fuel ignition system ( the element from a gas stove lighter mounted in the tube - David ’ s idea as I recall ) would burn out or its battery would fade ; the diesel engine would fail to start . No doubt a good deal of petrol was spilled on the floor of the ‘ model aeroplane building room ’ of Mill . But no fire broke out . And one day a whining , roaring sound echoed from the walls , as our tube belched an orange flame . That , however , was as far as it went . I am not sure whether the ‘ afterburner ’ produced any more thrust than
the fan on its own . And the contraption looked a long way from being something that could actually be mounted into a practical flying machine .
Once again , in our reckless schoolboy way we had done something that felt rather daring and splendid , and it had worked . We were able to boast that we had “ built a jet engine ”. But the fun was now over , and other interests emerged : notably , gliding at Lasham .
I was able recently to ask Bryan a bit more about his work on low-speed aerodynamics . He told me about the Thwaites Flap , a remarkable idea , which has never been put to practical use , although it was proposed at one point by NASA as a solution for the Mars Lander . The lift coefficient of a wing can be multiplied many times : a most useful feature in ultra-thin atmospheres . It would not be beyond the scope of a group of Winchester Scholars to build a model drone able to demonstrate this effect , but are there 21 st -century Thwaiteses , Du Boulays or Winkworths who might have the sheer effrontery to try ?
So David , who was a more practical sort of chap , was deputed to buy a gallon of the stuff . Here we met our first
The Allbon Dart 0.5cc diesel engine
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