Greyhead

I’ve done the exhaust tests and the results are very promising. The clamp has held the extension in place and the silicone tube used as a seal has worked well. I’m using the AcroWot as a test bed and now I know that the basics work I’ll cut the silicone tube to the correct length and attach the exhaust extension well enough to fly with it to give the system a thorough test before fitting in the SE5a.



I tested the revs using 5 different props altogether, both with and without the exhaust extension; for scale models such as the Parnall Elf I have in the past used a 13x6 but I’m thinking of using a 16x4 for the SE5a


Prop 13x6 Revs without extension 9700 Revs with extension 9400

Prop 16x4 Revs without extension 7000 Revs with extension 6800



The revs have dropped somewhat with the extension fitted but not to any significant amount and although the revs are considerably less with the 16x4 prop the static thrust is increased. I have no way of measuring this but just holding the model it was clear that the “pulling power” with the larger diameter lower pitch prop was much greater. The theoretical flying speed will be less of course but then it will be better able to overcome drag, which the SE5a has in abundance, so the end result could be the same!

I’ll tabulate all the results in another thread (tutorial?) as it may be of interest to compare the effects of prop diameter versus pitch on engine revs.

“Tabulate” may be the wrong word because as I’ve just found out tables can’t be used in forum posts, hence the rather strange way I’ve presented the above!

rjwood_uk

you could always make the table in work/excell then just print-screen and upload the image?

Richard

Greyhead

My brother eventually made it “up north” so I assembled the SE5a so he could see it properly; he took some close ups, which I thought you might find interesting, so here there are.

Greyhead

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.

tigertc

Pictures of her flying please!!!!!

Bluewavestudios

Hi Grahame,

Nice Pics and she looks nicely weathered too, love the rusted exhaust on the engine. The Pilot looks happy and to be honest I would be too sitting in that plane.
Like Terry above says, Looking forwards to the flying shots once the engine is sorted.

Regards.......Mark.

__________________
I'm Only Here Coz I'm Not All There !!!

gilesfordcrush

Obviously I'm delighted to see the silver soldering greyhead is doing looks like mine! Most encouraging. Ho ho.

Am I right in remembering that you've used silicone tube as the seal between the Laser exhaust and your copper housing, as well as for the extension running to the bottom of the aeroplane? Isn't there a chance this silicone is going to go the same way as you Elf and melt/deteriorate in time?

Greyhead

Giles

Glad you feel a bit better about your silver soldering! I have to admit that the example shown above isn’t one of my best, it had previously been soft soldered which does cause some problems but it still worked and looked OK once it was cleaned up.

I have indeed also used silicone tube as a seal, after all Laser use rubber O-rings to seal the exhaust stub to cylinder head joint. Only time will tell if it’s up to the job, it's only early days as yet, but so far so good!

I do have my doubts about using silicone tube after my experience with the Elf but it that case the tube was between the engine and the silencer. Gasses cool as they expand so after the silencer, which is really just an expansion box with a restricted outlet, the exhaust gasses will be cooler and there will also be less pressure. That’s my theory anyway; but the whole system will get a thorough testing attached to the AcroWot before I decide whether or not to fit it to the SE5a.

Grahame

Greyhead

Positioning the RC switch is often not the simplest of tasks on a scale model because it needs to be easily accessible but at the same time we don’t want it to be visible; there are really only 2 alternatives, either hide it or disguise it.

The most practical way to hide the switch but still be able to easily operate it is to use a scale hatch and the SE5a does have one but it is behind the cockpit so not ideal, disguising the switch seems to be the way to go but how to do it?

Luckily earlier in the thread, when talking about the interrupt gear for the Vickers, Steve posted this photo. It shows the interrupt pump driven by the prop shaft, of course this isn’t included on any of today’s restored aircraft because the Vickers is inoperative. But it does explain why the front has such a large cut out below the prop shaft!



The switches, I’m using a twin power pack, 2 batteries with an electronic switch over for added security, are operated by pulling / pushing the pump gear wheel, from a defunct servo, which is connected via a “snake”.





Not only does it make the perfect “invisible” switch, it adds a bit more interest to the front end,

Graeme Brumfitt

Brilliant idea Grahame, I keep going over all your pics almost daily coz me loves em.
I shall be building her sooner than I thought, I was going over my copies of Flying Scale Models July 2007 as it has a feature and free plan of the old war bird.
While reading the article for the ? time, it dawned on me that there was a web page link to buy the laser cut parts, thought this would be easier than cutting them myself as it has been about 30 years since I've done any form of modeling never mind balsa n tissue, should arrive very soon.
Also bought a Revell 1/48 just to check detailed bits. So to start the ball rolling I've just got hold of a KeilKraft Hurricane (ebay) scanned the wood then printed so as I don't use the kit, it'll give me practice with my cutting n getting parts right for my bigger projects. That Sea Otter will get built
Enough rant shall close n wish you all the best.