SE5a CONSTRUCTION BEGINNING TO . . .

[Greyhead]

To clarify things, when I said "now is the time to change the title of this thread by substituting "END" for the last 3 dots" I meant I’ve finished the construction section of the thread, not that the thread itself has come to the end. From now on, as well as the more mundane task of actually fitting out the model ready for flight, I’ll be adding / improving some of the detailing that I didn’t bother with earlier. Then of course there’s the flying!


The Lewis gun is very prominent, mounted as it is on top of the wing, so I thought that the magazine strap, which I’d made from masking tape, let the job down a bit. I still had some of the "thinned down" leather I’d used to make the cockpit edging so I decided to make a leather strap, complete with brass buckle.





The buckle was very easy to solder up from thin brass rod, but I think it really finishes the job off and was well worth the little time and effort it took. It was so easy in fact that I did the same thing to the "spare" magazine, which is just about visible through the fuselage window if you look very carefully.

[wonwinglo]

The whole model has been a delight Grahame from when the first few tentative parts were cut out,to your latest shots with all of that wonderful detail,I think you have done the subject more than just credit,thank you for taking the time to record what you have achieved along the way.

[Greyhead]

I’ve added a bit of “bolt head” detailing to the wings but nothing of note, however, a couple of other things may be of interest.


I attached "looped" tails to the rear flying wires that thread easily through the lower wing stubs and into the fuselage; these are pulled tight and held by a pair of aluminium clamps. When prepared for flying the tails will be positioned down the side of the servos to ensure that they can’t snag the elevator or rudder controls.





With all the flying wires under tension the wings no longer need the grub screws, which lock onto the wing pins, to hold them securely to the centre sections, but a bit of extra security never goes amiss so I’ll still use them!


One major drawback of having a fully enclosed engine is that regular checking / maintenance is awkward and the temptation is to stretch the times between checks. For this reason it is important to make sure that the fuel tubing can’t slip off the tank tubes etc. and the best way I’ve found to do this is to solder a ring of thin wire around the ends of the brass tubes.





To make doubly sure a commercially available fuel tube clip can also be used but I haven’t found this necessary in the past.

[Greyhead]

The “plumbing” on most scale models is somewhat more involved than on sports models; with the engine being fully enclosed it’s not easy to get at the fuel pipes and we don’t what to have erroneous holes in the cowl or pipes protruding where they shouldn’t.


My preferred method is to have the filler pipe going to the bottom of the tank so that it can also be used to empty the tank, this means that to prevent the fuel siphoning from the tank the filler pipe has to exit the fuselage somewhere above the top of the tank and my original intention was to use the radiator cap to hide the filler pipe. This idea was abandoned because it would have made the fitting and / or removal of the cowl very awkward, other openings also presented problems and I was beginning to think that I’d have to resort to removing the cowl for filling and emptying the tank.


The answer was in fact blindingly obvious; it just took me a long time to see it!


The top of the tank becomes the bottom of the tank when the model is upside down and, as I have to invert the model to de-rig it, I simply have to wait until that time to empty the tank. The filler and vent pipes both go to the top of the tank and are accessed through the prop shaft opening just below the crankcase


.


Both pipes face forwards to provide slight positive pressure in the fuel tank and are set back somewhat into the fuselage so will be very unobtrusive.





I’ve not as yet decided how I’m going to do the exhaust. The standard silencer fits inside the cowl, of course the outlet will have to be extended to exit the fuselage via one of the many holes in the bottom pan but I’ve had problems with silicone exhaust tube in the past with my Parnall Elf.


To be fair the silicone exhaust tube in that case was fitted between the engine and the silencer so had to deal with more pressure and a higher temperature than normal





Or I could use flexi pipe to a custom silencer mounted under the engine plate similar to the method I eventually used for the Parnall Elf.





Obviously using the standard silencer is the easier option but it might be “spoiling the ship” etc.; I’ll see.


The tank has been sealed to the firewall using “bathroom” silicone sealant to ensure no fuel / oil gets into the fuselage innards; when I came to seal the tank in place I realised that had in fact prepared the wrong tank (see the photo in my previous post!)

[wonwinglo]

There is a lot to cram in there Grahame,but you are getting there with the plumbing etc.

I have used that flexi pipe myself in the past,this is very versatile material.

[Guest]

Where do you get the flexible pipe from? I think I might use that with my V twin as I have silicone tubing at the moment - which might melt!

Giles

[Greyhead]

Giles


I bought the stainless steel flexi exhaust pipe direct from Laser Engines but I understand that they have had problems with the quality and recently stopped supplying it. Whether or not they’ve managed to sort out the problems I don’t know but it’s worth giving them a ring, I’ll certainly ask when I order my new engine later this week. Otherwise DB Sport and Scale sell some but what the size is like to fit Laser engines I don’t know but I’m sure they will!


Grahame


If at all practical I do prefer to use the standard silencer rather than make my own because the manufacturer has tested it so you can be sure it will work as an efficient silencer and also won’t have a detrimental effect on the engine’s performance.


The standard silencer fits OK inside the cowl but extending the outlet is not straightforward as it involves a tight 90º bend which could cause a heat / pressure build up and possible failure of the silicone tube.


To eliminate this bend I’ve made a 90º connector using standard copper pipe fittings silver soldered together; a 15mm Tee and 15mm to 10mm Fitting Reducer. I’ve removed as much copper as possible from both fittings in order to save weight and sealed a one end of the Tee with a flat plate. I used a “solder ring” Fitting Reducer because the ring formed to hold the solder makes a nice lip, which will help to retain the silicone tube.





By good fortune the silicone tube is just the right size to form a flexible, gas tight seal when the connector is pushed onto the silencer outlet. Thanks to Alan I can tell you that the silicone tube is exactly 15mm plus a gnats whisker less than a smidgen!





I’ll extend the connector with either a short length of silicone tube then flexible stainless steel or silicone tube all the way to the exit.





I’ll soon be ordering a new Laser 70 for the SE5a so I’ll use the running in period as an opportunity to thoroughly test the system before committing it to the model.

[Guest]

Grahame, when you say soldered do you mean silver solder or lead solder?

I would be a bit cautious with lead solder because if that plate was to come adrift in the engine compartment and allow the hot gasses inside it could cause a disaster.

I also think from a gas flow point of view that the "T" with a dead end is going to cause a bit of a back pressure and so affect engine performance. As you say the manufactured silencer has been tested and proven without the added restriction you have put on the outlet so if you must you really need to get the flow as smooth as possible.

I would suggest that you go for a simple single piece copper plumbers elbow which would help with both issues. If you cannot get one of the correct diameter then bend a piece of copper pipe to give you the 90 degrees you are after. Plenty of annealing and use of springs or sand should get you a fairly sharp curve.

[Guest]

I'll give Laser and DB a call tomorrow - and I'll have to post a picture on my build showing how my exhaust is working at the moment.

I agree with Bunkerbargethat your 90 degree turn will cause backpressure. However, my early tests with extended silicone pipes of my V-twin showed an increase in maximum revs with the additional backpressure - so you might well benefit from the same. Could I suggest doing a before and after test with a rev meter? It is possible that Laser wanted to have more backpressure on these engines but had to compromise and our set ups are now allowing a little more pressure. Just a thought.

Are you going to let the gasses out from the bottom of the engine bay? I thought the exhaust of the Laser could be pointed straight down and therefore all you need to do is extend the way the outlet is pointing?

[Greyhead]

Richard

Although the fittings are designed for soft soldering I used silver solder, the copper needs to be a dull red before it starts to melt and the resultant join is in fact stronger than the copper itself so I have no fear that the end plate will be “blown off”. I agree with you about probable poor gas flow but unfortunately the bend is too abrupt to use a standard elbow joint, I tried one of them first!

If, when I test the system whilst running in my new engine, I find that it does adversely affect the engine performance too much I’ll have to make a remote silencer and use flexible stainless steel pipe to connect the engine to it.

Giles

You could well be right about the backpressure, Laser engine are very forgiving about extensions to the silencer, I’ve never had any problems. The silencer has to be angled inwards at the top to fit in the cowl as in post 589 and as the engine plate hardwood bearers are attached to the fuselage sides I can’t extend the silencer straight down.

Grahame

[Guest]

Hi Grahame. I used a stainless steel extension with the factory muffler on mine. I took the threaded coupler and cut off the threaded ends with about a 1/2" of pipe. I cut a groove around the smooth pipe and attached them into the ends of the flex pipe with JB Weld.

Steve

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[Greyhead]

Steve

That’s a very neat set up, I bet as an added bonus it keeps your bomb release well oiled!

I hadn’t thought about using flexible stainless steel to attach to the standard silencer mounted under the engine plate. Lasers being made form aluminium might cause a bit of a problem though.

Grahame

[Greyhead]

The exit pipe once again uses a 10mm copper pipefitting and in this case also some 10mm brass tube; all silver soldered. The exhaust will exit via 2 of the holes in the engine under pan, not the scale exit points but at least I’ll have 2 exhaust trails following the model.





The complete exhaust system.





I ordered a new Laser 70 today so it shouldn’t be too long before I can start to test everything. If all is OK then I’ll trim the ends of the exit pipe to be inline with the under pan when attached to the model so in practice they will not be seen.


If the system isn’t satisfactory then it’s back to the drawing board!

[Greyhead]

My new Laser 70 has arrived and of course it ran flawlessly after starting “first flick”, not that you’d expect anything less from a Laser. I should point out at this juncture that I have no commercial interest in Laser engines; it’s just that they are such good engines that I can’t stop “singing their praises”!


Although the excuse for getting this new engine is the SE5a, in fact I’ll use one of my older, well run, engines. This one will free up one of my other Lasers by being mounted in the AcroWot and have a good few flights, first without the cowl to ensure really efficient cooling then after a couple of hours flying time with the cowl fitted. A fully enclosed installation such as the SE5a isn’t the place to bed-in a new engine.


I have modified the crankcase breather on all my Lasers to make it easier if the engine is mounted close to the firewall. A short length of brass tube is soldered to the nipple; without it the fuel tubing extension would have to make a sharp 90º bend, which has a tendency either split of restrict the breather.





I make it a “T” so it’s just as good if the engine is upright or inverted, the extension tube is fitted to the appropriate side and the other is blocked off.


I ran the engine both with and without the SE5a exhaust extension and the only difference I could tell was that the exhaust note sounded a bit quieter with the extension fitted. One thing that I did find out was that I’ll have to incorporate some form of strap because when I opened the throttle above about half way it blew the extension off. Before I do any more testing I’ll run a few tanks of fuel through the engine to get it settled down and fit the strap.


For the next tests I will get more “scientific” results on the effect of extending the exhaust by using a rev. counter, which I don’t own, but I know a man who does!

[Greyhead]

Although I’ve not yet done any “scientific” tests, I should be getting a loan of a rev. counter next week, I have carried on with the installation of the exhaust.


Having run the engine both with and without the exhaust extension I applied my usual method of decision making; if it looks / feels / sounds OK then it most probably is OK! (apologies to Peter).


I silver soldered mounting brackets to the exhaust and squashed the ends of the pipes somewhat to fit through the holes in the under pan. 2 hardwood blocks epoxied to the fuselage sides to screw into completed the installation.





I trimmed the pipes so that with the under pan fitted the exhaust doesn’t protrude and isn’t visible when viewing the model normally.