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The Seagull has landed

Seagull Yak 54 - 90 size - SEA53B

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Gary Manuel17/05/2018 15:31:12
1788 forum posts
1507 photos

I have been looking for an airframe to replace the Slipstream MX-S I destroyed at last years DVMFC open weekend. It had a lovely Saito 150 engine in it which was crying out to go into another model.

I've had my eye on the Seagull Yak 54 - 90 size for a while as they look great and all seem to fly well. The Saito 150 might be a bit on the large side as the recommended 4 stroke engine is a 125. Better too large than too small though and the weight / physical size difference is minimal.

This is the little beauty that will be going in to the model. The Dubro Soft Mount is already drilled and tapped for the Saito engine so I'll be using this.


The model cowl fitment requires the engine to be mounted such that the measurement from the engine box to the spinner backplate is 140mm. I measured mine ......


..... and it's 166.5mm. Obviously a problem with this mount, but this is the challenge I'm happy to face. 26.5mm (166.5 - 140) needs to be removed from the front of the engine box


I could have just about got away with using the supplied mount with a bit of trimming. This would have given the required 140mm and avoided the problem, but would have resulted in the throttle lever being very close to the firewall. I'd rather spend a bit of time and effort to get more accessible controls and less vibration due to the Dubro Soft Mounts.


Edited By Gary Manuel on 17/05/2018 15:32:28

Gary Manuel17/05/2018 15:42:43
1788 forum posts
1507 photos

Line drawn 26.5mm from the front face of the engine box.


Razor saw used to cut along the line.


New firewall made from good quality ply. I'll fit a piece of lite-ply over the hole later.



Firewall epoxied in place to make a nice strong engine box.


Reinforced internally with triangular stock......


.... and pinned externally using barbecue skewers.


Rich too17/05/2018 16:16:48
2875 forum posts
1046 photos

nice one Gary, sub'd yes

cymaz17/05/2018 16:25:25
8268 forum posts
1144 photos

Excellent work as always young Gary......I’m in and watching cool ( btw....very pleasant here in Hurghada at the moment....34 and sunny hothotcocktail)

Edited By cymaz on 17/05/2018 16:27:03

Gary Manuel17/05/2018 16:38:24
1788 forum posts
1507 photos

Use plenty of sun screen Cymaz.

Must admit - I had to look where Hurghada was blush

Rich too17/05/2018 16:41:07
2875 forum posts
1046 photos
Posted by cymaz on 17/05/2018 16:25:25:

Excellent work as always young Gary......I’m in and watching cool ( btw....very pleasant here in Hurghada at the moment....34 and sunny hothotcocktail)

Edited By cymaz on 17/05/2018 16:27:03

We had our 3rd trip there this Easter. yes We didn't make it but the new marina is supposed to be worth a visit. And not the best location, but I can recommend the food at the Hard Rock Cafe wink

Edited By Rich too on 17/05/2018 16:41:40

cymaz17/05/2018 16:44:22
8268 forum posts
1144 photos

I’ve sidetracked Gary for too long now......back to the coal face lad !

Gary Manuel17/05/2018 17:39:30
1788 forum posts
1507 photos

The cardboard wing tube liner looked a bit fragile, so it's has a couple of layers of glass cloth. The dark bits are where the resin has soaked in but the light coloured bits aren't dry. They must have had a thin coating of glue which has stopped the resin from soaking in


Nothing special about the hinges. They are the standard furry cyano type, which are perfectly up to the job. T pins used to centralise the hinges between both surfaces.


All sufaces are now hinged, with the exception of the bottom rudder hinge, which will by glued later when the fin is joined to the fuselage.


john stones 117/05/2018 17:49:16
10181 forum posts
1475 photos

Cracking model, soft mount ? bit rattley Saitos then crook

Had 120 in mine your 150 will be perfect. yes

Giz a go.face 1

Biggles' Elder Brother - Moderator17/05/2018 19:05:23
15748 forum posts
1460 photos

Nice Work!

It's always a bit "heart in the mouth" isn't it when you take the saw to the brand new out-of-the-box expensive model!! Well done for resolving to do the job properly and not bodge it because its easier in the short term.


Edited By Biggles' Elder Brother - Moderator on 17/05/2018 19:05:59

Gary Manuel17/05/2018 21:37:24
1788 forum posts
1507 photos

Yes BEB.

It's definitely a case of "measure many times and cut once". Makes it worse when doing a live blog. Nowhere to hide if I've got it wrong.

Gary Manuel11/06/2018 18:40:43
1788 forum posts
1507 photos

Crikey - where has the last month gone?

I can't believe how long it is since I did any work on my Yak 54. Can't complain though. It's because I've been making the most of the nice (flying) weather.

The barbecue skewers on the shortened engine box have been trimmed flush.


I know that my shortened engine box has exactly the same thrust angles as the original, because I cut 26.5mm from all 4 sides, so I don't need to worry about this. What I do need to take into account is that any thrust angle on the firewall will affect the engine centre line when calculating the engine mount screw positions.

There does not appear to be any right thrust or down thrust built into the firewall at first glance, but a bit of careful measuring using the two opposite sides of the fuselage, reveals that the front face of the 130mm wide engine box is offset by 2.75mm. This gives an angle of arcSin(2.75/10) = 1.2121 degrees. Not much, but I want to try to get the engine prop shaft exiting the exact centre of the cowl if I can.

I will need to offset the holes from the fuselage centre line by 166.5 Tan(1.2121) = 3.5mm.

Here's the firewall marked and pilot drilled .....


..... and drilled ready for the engine mounts.


Engine mounted .....


..... using 5mm bolts and captive nuts - partly tightened.


The position of the hole for the throttle pushrod marked but not drilled yet - I'll wait till I've mounted the throttle servo.


Engine removed and the engine mount screws fully tightened with full strength epoxy between the captive nuts and the firewall.


Steve Hargreaves - Moderator11/06/2018 21:13:41
6689 forum posts
185 photos

Really fancy one of these myself Gary so watching with interest...thumbs up

Gary Manuel13/06/2018 18:29:08
1788 forum posts
1507 photos

Turnbuckles are provided for tail struts. I've never had a model with tail struts before. I'm not sure whether they are functional or just cosmetic. The instructions ask for the tail to be glued to the fuselage well before the struts are added, so they are certainly not used for adjusting the geometry. Maybe just to add strength?


The tailplane is symmetrical top / bottom before the turnbuckles are added. Adding the turnbuckle defines this as the bottom of the tailplane.


Elevator controls horns ......


...... fitted to the bottom of the tailplane, with a coating of epoxy applied to the thread / pre-drilled hole between the two washers.


Slightly longer Aileron control horns ......


..... fitted to the wings in a similar way to the elevator horns.


Gary Manuel13/06/2018 18:41:04
1788 forum posts
1507 photos

I had a bit of a problem here!

The rudder control horn is described in the manual as being a 60mm length of 3mm threaded rod. There was no such piece in my kit, but there was a spare aileron pushrod, which is 60mm long with a 3mm thread on each end and a slightly narrower plain rod in the centre. When the nuts are screwed all the way onto the pushrod, they become loose where the thread runs out, and just slide freely along the plan rod. The length of the plain rod is long enough to span both washers, nuts and the rudder, making it impossible to tighten the washers onto the rudder.


Fortunately, I had a short length of 3mm threaded rod available, so I cut 60mm from the end to replace the missing rudder control horn.


This appears to have sorted the problem. Again, epoxy was smeared onto the thread between the two washers.


Gary Manuel13/06/2018 18:57:42
1788 forum posts
1507 photos

The epoxy within the aileron control horn is now set, so I'll fit the wing servos and controls next.

First job is to make up a short servo extension lead.


Secure the plug / socket with "unbreakable" thread.....


..... and heatshrink.


Then protect the wiring with 3mm spiral-wrap. Then thread the wire down the wing using my trusty length of waxed string with a large nut weight on the end.


Servo holes marked, drilled and hardened / strengthened with cyano.


Servo and controls fitted. Supplied clevis keepers (fuel tube?) and 3mm lock nut fitted but not applied at this stage, as I expect that I'll be making adjustments later. The short HiTec servo arms provide well in excess of the recommended aileron throws, with the clevis on the second longest hole. There is plenty of aileron movement to allow this to be increased later, or decreased as required. The servo and control s have been centred and tested for full movement using a Turnigy servo tester.

Note the 3mm screws are positioned on the central narrow part of the rod, where they are free to slide as described in the rudder problem in my previous post. They will be lid onto the threaded part and tightened up to the clevis after I have finished my adjustments.


john stones 113/06/2018 19:08:53
10181 forum posts
1475 photos

Well I'm gobsmacked, where's the endoscope ?surprise

Gary Manuel13/06/2018 20:10:47
1788 forum posts
1507 photos
Posted by john stones 1 on 13/06/2018 19:08:53:

Well I'm gobsmacked, where's the endoscope ?surprise

I don't think it's the right tool for a smacked gob, unless you want to view it from the inside.

Geoff Sleath13/06/2018 20:57:56
3188 forum posts
247 photos

I must admit to using thread to keep extension lead connectors in place - or I have used heatshrink tubing but never both! I thought I was a belt and braces type but this is belt, braces and elastic And none the worse for that!

I've not put a lot of ARTFs together but the bit I like least is marking out and drilling the firewall which is something I do on a kit or plan build before it's glued into the fuselage. Gravity always seems to win on either pencil or the ruler


Gary Manuel13/06/2018 21:16:53
1788 forum posts
1507 photos

To be honest Geoff, the heatshrink is for neatness rather than strength. I'm not sure that heatshrink alone would prevent the plug from pulling out of the socket if the wiring was given a good tug. I think the wire would pull out of the crimp before the unbreakable thread gave way.

I acquired a roll of it from my mother's sewing box when I was in my mid-teens. I've been using it for all sorts of jobs for the last 45 years and it's still going strong but the roll is getting thin now. I've tried to find more of it but I can't find anything nearly as strong / thin as this stuff.

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