As I thought might happen the exhaust did get hot enough to melt the solder joints for the strap, which used soft “lead” solder. It didn’t affect the working of the exhaust but I decided to silver solder it to eliminate any chance of “metal to metal contact”, which could cause radio interference.
I’ve included this photo, which shows the work before any cleaning up, just for Giles to show that my silver soldering isn’t really that neat!
Well I was a bit hasty silver soldering the strap.
I took the AcroWot out today to test the exhaust in the air and basically everything worked OK but the strap broke so I’ll have to replace it with one made from thicker steel, I’d used tin plate and obviously the vibration proved too much. I only had 3 flights but the silicone tube used as a seal shows no sign of deteriorating and the reduction in revs had no noticeable effect at all.
I’ve decided to include all the prop size / revs data in this thread as it is relevant to what follows.
For the first 2 flights I used a 12 x 7 prop, which gives a theoretical top speed of 64 mph. I then tried a short flight with the 16x4 prop, being a new engine I didn’t want to run it for too long with such a large prop. With a theoretical top speed of only 26 mph I expected to see a vast difference but in fact there was very little difference when flying into the fairly strong wind, with the wind the difference was noticeable but not excessive. As the AcroWot isn’t a particularly “draggy” design I’m very surprised by this but it bodes well for using a 16 x 4 prop on the SE5a.