Rob Tothill Posted July 30, 2017 Share Posted July 30, 2017 Hi all, I was lucky enough to be gifted a Seagull Yak 54 kit from someone who was giving up the hobby. A while ago I purchased a second hand Laser 120. I think it's from the early 90s as it has a Super Tigre carb and a single screw fixing the rocker cover. I'm at the stage of fitting the engine, and have found that the silencer wants to be in the firewall as there's only about 5 1/4 inches from the firewall to the front of the cowl. I'm not sure what the best way around this is. I have considered trying to find an aftermarket silencer/flexible pipe, cutting out a section of the firewall and reinforcing around the gap, or moving the whole firewall back (I'm not so keen on this option as I feel it may be less resilient than the current firewall fixing which was reinforced by the original owner). What do people think is the best way to deal with this? Quote Link to comment Share on other sites More sharing options...
Don Fry Posted July 30, 2017 Share Posted July 30, 2017 Laser do an inline exhaust, which fits on a flexiextension. See accessories on their website. Quote Link to comment Share on other sites More sharing options...
Gordon Whitehead 1 Posted July 30, 2017 Share Posted July 30, 2017 Hi Rob Looking at the dimensioned drawing of the 120 on the Laserengines.com website, Your 120 measures 139mm from prop driver face to the back of the silencer. Also from the drawing, it looks as if the carb projects almost as far back as the rear of the silencer. The Yak manual http://images.salsify.com/image/upload/s--ECEXDMaq--/qtnpp4xx03wzjrene7p4.pdf has the distance from prop driver to firewall as 140mm. So even if you could achieve this measurement, the carb won't get much air in. There's a pic on page 17 of the manual which shows a Saito FS mounted, but the Saito's carb arrangement allows it to fit OK. From studying the Saito mount pic, I'd suggest that you could just saw about 1/2in or so off the front of the mounting box, add a new 1/4in birch ply firewall recessed, 1/2in back, gusseted, pinned, glued and glassed, and you'll be good to go. Recess the firewall into the box sides, set back about 1/2in, glue 1/2in triangle round perimeter in front to of firewall as a gusset to help stop it pulling out forward, and drill holes through sides into firewall to take 1/8in dia dowel pegs, or even screws as belt and braces. I had to ensure clearance from the firewall for the carb on my 155 in the Krier Great Lakes I'm building and ended up with some unexpected surgery around the carb to ensure a good flow of intake air but got there in the end. I note the engine is angled 45deg in the Yak. You'll need the same setup to ensure a decent relationship between carb height and tank position. I did the same in the 'Lakes. Cheers Gordon Quote Link to comment Share on other sites More sharing options...
Gordon Whitehead 1 Posted July 30, 2017 Share Posted July 30, 2017 From what Jon at Laser told me, Laser don't stock the flexi pipe now. Mick Reeves models have it, together with a Laser exhaust adaptor on the end. Gordon Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 30, 2017 Share Posted July 30, 2017 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 30, 2017 Share Posted July 30, 2017 hmmmmm look at that, what a fine and lovely looking engine.... Anyway, you beat me to it. Chop the firewall off, move it back a smidge, glue back together. And Gordon is sort of right about the flexi pipe. The company we get it from has decided that they are now going to impose a minimum order quantity of 300m of pipe on all orders. As we only get through about 20m a year you can see why we didnt jump with excitement and buy more. I will argue with them about it eventually, but to be honest its a job better suited to my boss as he has been dealing with them for 30 years and hold the purse strings so i cant really achieve much. Alas he dosent seem to see it that way so its in my pile of things to do that arent as important as the other pile next to it. Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted July 31, 2017 Author Share Posted July 31, 2017 Thanks for your replies Donald and Gordon. I did see the fkexipipe on Mick Reeves website and was consideeing it. I think Gordon makes a good point about the carb being close to the firewall too, and the potentially restricted air flow. It looks like I shall have to move the firewall back. I think it will actually be stronger with gussets in front and dowel pegs I am planning to. Put the engine in at 45? as you say Gordon, to get the carb in the right place. Thanks for your advice. Rob Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted July 31, 2017 Author Share Posted July 31, 2017 Thanks too Andrew and John. I'm definitely going to hack in to the firewall. I will need to measure the amount chopped off carefully to retain the built in thrust angles. I think I have the same mount as you've shown Andrew. Does it have a fitting for a steerable nose wheel? There is room to move the engine forward around 1" so there should be plenty of space once fitted. The box may need some extra reinforcement as it's made of 1/8" lite ply, which seems a bit flimsy to me. I am surprised how lightweight the construction is in these models. I have only built the Wots series of planes and an Oodalally and they are much more robust. I can't see it being repairable after any heavy "arrivals", so better get a bit more stick time in before the maiden! Thanks again for your help. Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 31, 2017 Share Posted July 31, 2017 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 2, 2017 Author Share Posted August 2, 2017 Hi Andrew, my mount says Anderson on it, it is about the same length so should do the job. I have removed the firewall and will glue it back in in the next few days an inch behind its original position. I haven't fitted a mount to an artf before, they've always been fitted when I have received the model. Does the thrust line go through the centre of the hole on the firewall? The hole is central laterally, but about an inch above the centre of the fuse vertically, and above the centre line of the wing. I was planning to do some trig to offset the mount to get the back plate to line up with the centre of the hole. Is that correct Quote Link to comment Share on other sites More sharing options...
Gordon Whitehead 1 Posted August 2, 2017 Share Posted August 2, 2017 Hi Rob The hole is merely to support the tank bung and locate the front of the tank. This might locate the tank too high for the Laser carb however, and will need blocking as you move the tank aft and lower. Drill 3 separate holes in the firewall for the silicone tube fuel filler, feed and overflow pipes to pass through. One way to centre the prop is to screw the engine, without the carb and silencer, to its mounts. Then support the fuz vertically nose-up and place the engine+mount on the firewall. Add the cowl, then position the engine with propshaft central in the front of the cowl. Remove the cowl without disturbing the engine, mark the mount position on the firewall, then drill the holes. If the cowl snags on the engine cylinder, leave the cowl in place and try to mark the mount screw hole locations with a pencil on which you've carved a long slender point to fit through the engine mount holes. BTW, Laser sells injection-moulded Tee mounts, which I'm using on the 'Lakes. Gordon Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted August 2, 2017 Share Posted August 2, 2017 Be very interested to hear how it flies Rob....I've fancied one of these for a while but is the 1.20 four stroke enough to make it really perform....? Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 2, 2017 Author Share Posted August 2, 2017 Thanks Gordon. I will arrange it so the the prop shaft is central then. I have a bit more gluing to do yet, but I'd like to fit the blind nuts before gluing the firewall in position to save a fiddly job, now that there isn't easy access from the top of the box. I'm not sure how it will perform with the engine Steve But I think the biggest issue will be pilot skill rather than lack of power! I will let you know how it goes once I've had a few flights. Another club member has just got one too, and has fitted a 20cc DLE. Would that have a lot more power?He's a very good pilot so I'll let him fly mine too so that he can judge the performance.Edited By Rob Tothill on 02/08/2017 23:44:17 Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 3, 2017 Share Posted August 3, 2017 the dle 20 is about equal to our discontinued laser 150. our current 155 will outpace it especially on bigger props. the 120 wont match the dle but is no slouch and a 15x6 would be my start point for this model Quote Link to comment Share on other sites More sharing options...
Gordon Whitehead 1 Posted August 3, 2017 Share Posted August 3, 2017 It won't hang about with the 120! At 850sq in, 63in span and 10lb weight it's about the same size and weight as the early Brian Taylor Spit which he flew and won comps with using the original Laser 75. Its power to weight ratio will be about the same as a full size Fw 190. Ref fitting the blind nuts, as you're modding the box anyway, you can just cut an access hole in the top of the box, fit the nuts, then patch the hole with ply and glass. Gordon Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 3, 2017 Author Share Posted August 3, 2017 Hi Jon. That's good news as I have bought 15 x 6 props for this project, The stated maximum weight on the box is 4.5 kg. I recently built a Wots Wot from the kit which came in at 3.4kg. This has a Saito 82 fitted and has plenty of power for my skill level. I would think this would also be the case with the Yak as the increase in weight is less than the increase in engine capacity. Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 3, 2017 Share Posted August 3, 2017 at 10lbs it will not be a problem at all. My 63inch hurricane is about 9.5lbs and our 80 totally monsters it. You should have a really nice little combo there. If you find the model a little sluggish on the 15x6 try a 15x8 for a bit more speed. Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 3, 2017 Author Share Posted August 3, 2017 I'm pretty excited about getting the Laser fitted and running. I've not seen one run in person yet, although I've watched a few on YouTube. I have the 62" TN Hurricane to build after this, and I have bought an old Laser 90 that's never seen fuel to power it. It will probably take me a loooong time to get it built though, do could be a while before I get yo run that one. Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 3, 2017 Share Posted August 3, 2017 I dont want to be all doom and gloom but you will struggle to get the 90 fitted nicely in the hurricane as you wont be able to get the tank low enough for it to work properly. The 90 would also over do it somewhat when it comes to power as well. Irrespective of all that, given the age of the 90 i wouldnt go near it if im honest . It might be new in theory but its still 25 years old as a minimum and if the liner has rusted in storage, or you break anything or even loose the needle valve/exhaust then its scrap as i cannot replace any of the parts. In all honesty i would sell it as is in mint condition as i am sure a collector would love it. Then recycle the cash and pick up something newer for the Hurricane. This isnt meant as a sales pitch, its just that even if i removed my Laser hat and went back to being a modeller i still wouldnt recommend using an engine that no longer has any support or spares available. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted August 3, 2017 Share Posted August 3, 2017 Posted by Steve Hargreaves - Moderator on 02/08/2017 22:23:03: Be very interested to hear how it flies Rob....I've fancied one of these for a while but is the 1.20 four stroke enough to make it really perform....? Mine flew with an O.S 120 fs in it, good combination. Edited By john stones 1 on 03/08/2017 12:35:41 Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 4, 2017 Author Share Posted August 4, 2017 Hi all, I hear what you are saying Jon. Gordon previously mentioned that I would struggle with a laser in a hurricane because of tank positioning. So I guess I'd better find something else to put in. As a hypothetical question would it be possible to use a header tank to eliminate the problem of fuel syphoning to the carb, potentially with a uniflow system vented to the air? I read a little about this, but I'm not clear on whether it would work. I'm not sure about selling the 90, as I would rather see it fly than know it was sitting in a collection somewhere! I am aware that there's no support for it. When you say the liner could have rusted, do you mean inside the piston (I. E. It would be visible if I took the head off)? Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 4, 2017 Share Posted August 4, 2017 Hi Rob The tank position can be sorted with our 70 or 80 (I sorted it on my Hurricane, see photo at the bottom) but the 90 is likely to be too tall. As for the rusting the liner and ring could easily be in trouble but it would be apparent if you remove the head. Remember that if you loose the rocker cover screw I cant replace it, if you damage any of the head bolts (the rear one in particular) they cannot be replaced. While I am also of the mind that engines are supposed to run and not sit on a shelf I am just trying to warn you that you could end up with a great deal of hassle and end up with something that is broken and worth nothing, where as right now its 'perfect' and could be worth something to the right person. If you are prepared to take the chance then that's fair enough and fingers crosses the engine is in good condition. if it is then there is no reason it wont last 30 years, just don't crash it! Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 4, 2017 Author Share Posted August 4, 2017 Hi Jon, is the centre of the tank tank lined up perfectly with the centre of the carb, or is there some tolerance to them being misaligned? And if so how much? I thought that some of the bolts would be replaceable through model fixings, but are they something that had to be manufactured specifically for you guys, and wouldn't be stocked by anyone else? Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 4, 2017 Share Posted August 4, 2017 The rearmost bolt is a special as its drilled and tapped for the rocker cover retaining screw. As with all things its not impossible to replace it would just be a total pain and impossible unless you have a lathe handy. As for the tank position there is some tolerance but it is highly likely the 90 would fall outside it. What I suggest is plonking the engine on the plans and seeing how things work out. Perhaps start another thread dedicated to the hurricane build so we don't get so far off track here. Assuming anyone cares we wandered off? Quote Link to comment Share on other sites More sharing options...
Rob Tothill Posted August 5, 2017 Author Share Posted August 5, 2017 Thanks to everyone for all the advice. I'll do as you say Jon, and start a hurricane thread once I get the build started and check against the plans. Cheers Rob Quote Link to comment Share on other sites More sharing options...
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