[AR] Re: Thrust augmentation?

  • From: Peter Fairbrother <peter@xxxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Thu, 11 Feb 2021 16:16:50 +0000

On 11/02/2021 09:38, Dr Edward Jones wrote:

In the early 1950s, Wilmot and Mansour of Jetex in Totten, near
Southampton UK, expanded their line of reloadable solid rocket motors
for aeromodels, with thrust from 1/2-oz up to 6-oz, burn times around
15-20 seconds. Jetex came up with "augmenter tubes" to fit around the
exhaust and increase thrust.

Per their reports: "Makers of Jetex offered two sizes of ‘augmenter
tubes’, which were formed from thin aluminum sheet; the forward end is
bell-mouthed and considerably larger in diameter than the Jetex engine
(one tube size was for the two 50 engines, the other for the
Jetmaster, PAA-Loader 150 and Scorpion 600), and the edge of the bell
is placed about even with the rear of the engine case."

"When the jet is operating, cool air is drawn into the tube mouth and
is expelled at the tail of the model along with the hot gases.  This
air not only cools the gases but contributes to thrust. Figures show
that the augmenter will increase thrust from 20 to 30 percent."

"Performance tests were made by Aeromodeller in January 1954. Results
were presented as two graphs and a table."

   https://archivesite.jetex.org/motors/motors-accessories.html

I remain skeptical of this thrust augmentation. What's your opinion?

The thrust increase was small but real. Hard to test though, as apparently it worked better when it was moving. However the increase in thrust was only about the same as the weight of the tubes, and less than tubes plus necessary extra structure - they were meant for use in aircraft, not rockets.

Being more into rockets than aircraft at the time, I only used them on the first stage of a two-stage rail launcher, as seen in the movie When Worlds Collide. Two augmented ?Jetmaster 100? motors on a balsa frame on twin OO model railway rails.

The thrust augmentation was undoubtedly less than the mass of the tubes, wheels and balsa; and the expensive Scorpion 600 powered second stage was lost on the first flight, so the motors and tubes were put back in their boxes and subsequently lost. :(

Ah, happy days.

Peter Fairbrother

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