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?
Edward