Slingsby Petrel 3.4 metre designed by Chris Williams

[Peter Garsden]

 

Next add the light ply 1.5mm ply All Moving Tailplane joiner supports into the space between Fin 4 and Fin 3. You can see that the holes have already been cut out for the back and front tail pivots. I have also temporarily inserted the aluminium tailplane horn. I am trying to work out how to get the tube that spans the slot in. There is a tube which glues to the horn then a concentric larger tube which glues to the fin, then a rod inside which fits into each tailplane.

 

 

 

Note the overlap of balsa sheet beyond the trailing edge of the fin to act as shrouds for the rudder hinges - 6mm.

 

Also I fitted and glued one side at a time. After the 1st side is glued, I made holes in the balsa to mark the limits of the ply internal supports then cut all the balsa out. I then glued on the 2nd side using these clamps, and when dry I will make holes in the other side. Not too big again so the AMT is importantly a tight fit.

[Peter Garsden]

I ummed and awed about the All Moving Tailplane crank as it consists of 2 concentric tubes, the larger of which is epoxied to the bellcrank, and the other smaller one fits inside and is epoxied to the fin. The problem was, how to avoid contaminating one tube with glue from the other which would jam up the mechanism.

 

So first of all I epoxied the larger tube to the bellcrank and ran a fillet round its circumference.

 

I made sure that it was the right length to fit snugly between the ply walls inside the fin to avoid wobble. 

 

Next I cut the smaller tube with some overlap which can be trimmed off later with a dremmel and inserted it through the fin and the bellcrank in position making sure that the correct hole goes to the correct bits ie the back takes the other tailplane pivot wire. I then applied epoxy and moved the tube in and out to coat the inside of the hole in the fin.

 

 

Not too many microballoons to the mix

 

 

 

Smaller tube shown through the middle and out the other side ready for epoxy

 

 

Again ready for glue

[Peter Garsden]

 

And so to the Rudder. This is the trailing edge formed with cyano over the plan. It consists of a lamination of 1.5mm ply with laminations of 3mm balsa. Very handy to have the laser cut parts as it consists of many interlinking pieces. Also put the pins in the correct position to take overlay of balsa. 

 

 

The glue in R6 to take the trailing edge

 

 

Then attach the trailing having attached the laminations of balsa on both sides.

 

 

Then you can slide in the ribs which fit very well. Also fillings of block balsa at the bottom to take the  carbon tube for the rudder horns, and some 6mm for hinge support and the  block balsa at the top and front to complete the build.

[Peter Garsden]

The All Moving Tailplane - tricky to line up of course, and keep rigid, as the nature of the beast predicts so care is needed with this.

 

The first step is to glue the 2off 4.5mm leading edge pieces together and pair them down from 9mm to 6mm at the tips. I did this carefully with my rotating disc sander - so much easier than trying to plane it. I first of all held in place the 1.5mm spar to act as an indicator to draw lines, then glued it on afterwards.

 

Next one glues on the root end T1 rib with some epoxy as this will take some load.

 

 

I drew a line down the middle to ensure T1 is central. I also laid the tailplane flat on the bench, again to make sure there is no twist in the tailplane half.

 

 

The tubing I have cut to size with an overlap for later trimming with a Dremmel. Needless to say the tube has to be fashioned at the ends with a file so as to remove any burrs. The tube supports are also glued in using epoxy and microfibres mix, first having filed some abrasion to the tubes to act as a better base for the glue.

 

Edited September 1, 2022 by Peter Garsden

[Peter Garsden]

Next job is to assemble the tailplane over the plan at least each half at a time. As it is symmetrical one does not need to worry about which hand is which.

 

First of all one makes up the trailing edge which consists of a middle piece of 1.5mm birch ply with 3mm balsa laminated each side. First one glues the inner ply together then the top piece of 3mm balsa. One then takes it off the plan, turns it over and applies the other side so that one has a ply sandwich with 3mm each side. The 3mm is sanded down to follow the profile of the tailplane/stab

 

 

One can see the sandwich of the trailing edge in this photo. In order to line up the balsa in the correct position I used pins to follow the curve.

 

 

When the trailing edge is complete - I used cyano - I pinned the leading edge blank to the plan and attached the trailing edge, then the tip rib T8 then the  ribs in between also with cyano and finally the tip balsa.

[MikeQ]

Hi Peter, good progress.

 

one thing, i guess as the LE of the tailplane tapers from 9mm down to 6mm at the tip, with a tapering spar too, is there a risk of building in a warp, or at least unintentional dihedral, if you build flat to the board so to speak.  When you flip the second tailplane over the effect will be magnified.  Depends how youve set your tubes i guess.  Just wondering if youve taken that into consideration looking at the pics?

 

not sure ive explained that clearly 😀

 

 

Edited September 3, 2022 by MikeQ

[Peter Garsden]

Good point MikeQ. I am simply following Chris's instructions in his RCM&E article. He says taper down the LE blanks before adding the rest of the structure. Not being a Physics major, I don't think I can reason this one through, but looking at it simply, the support tubes are at right angles to the fin so I presume that the taper will be equal top and bottom towards the tip of the tailplanes? If I am wrong then yes there would be a problem with each half but as the taper is equal both sides, I don't think it will matter?

[MikeQ]

Haha ... im probably overthinking it.  But you could end up with a small amount of washout on one and washin on the other.  Not sure it makes any difference on models like this?

 

I used to fly a lot of FF power duration competition and 1/32” warp could make a big difference ... not sure same at this scale and speed range.

 

 

[Peter Garsden]

I get it now. I think the answer would have been to trace the tailplane outline onto the other side of the plan and make a left half - too late now. I know Chris Williams follows this blog so maybe he can comment. Never could answer physics questions on leverage correctly at school.

Edited September 4, 2022 by Peter Garsden

[MikeQ]

Hello

 

been playing with a new toy and re the bellcrank, i drew up and 3D printed a unit on an SLA printer.

 

Very much a prototype but seems pretty solid.  Means you can have the unit all in one piece.  Asking the 3D guys if they think SLA is durable enough for this application.

 

Long way round for a shortcut but knowing my luck I would glue all the tubes together.

 

cheers

 

mike

 

 

Edited September 4, 2022 by MikeQ

[MikeQ]

Haha .. i bow to the wisdom of CWs design ... wheres that ali sheet?

 

 

[Peter Garsden]

Oh dear Mike. How disappointing. I think I have used plastic bellcranks available, I think, from SLEC before but of course they are a different matter. I just happened to have some spare 1mm Aluminium Sheet knocking around. Like the comments on the other blog it is a critical piece of kit unlike a pilot, which a friend of mine - Andy Meade -  has printed to the correct scale and which I need to paint etc - more of which later in the build.

 

Incidentally, I have looked at the instructions from Chris again. One is not meant to glue the bellcrank in at this stage. First one makes the tailplanes then lines up the bellcrank against the root rib of the tailplane in order to get the hole for the activator wire absolutely in the correct position, so that each tailplane is in the correct position ie lined up both in plan view and front view. I am going to get round that problem by lining everything up in situ as it were. Doh!

Edited September 5, 2022 by Peter Garsden

[MikeQ]

Yep ... ill stick with convential wisdom on his one.  Its quite tempting to use new techniques.

 

For simple parts like the bellcrank you dont really need much more than schoolboy technical drawing skills and the software does the rest.  You use maybe 5% of the functionality if that.  Maybe a pilot or ejector seat needs a notch or three or undoubtedly more above that.

 

Keep up the good work.

 

mike

 

 

Edited September 5, 2022 by MikeQ

[Zflyer]

Maybe you could test it with a mock up and a good hairdrier, just for future reference.

I have printed servo horns using PLA and so far no failures.

 

[MikeQ]

Hi

 

thanks ... maybe didnt give it enough exposure time.

 

https://www.chitubox.com/en/article/support/indepth/troubleshooting/45

 

saying that, it was more of a fracture across the piece rather than what looks like layer separation.

 

Either way, i think ill go native on this one and use ali and brass tube.

 

cheers

 

mike

 

PS not meaning  to hijack your thread Peter.  Happy to talk to anyone who knows back on the 3D printing forum 😀

Edited September 5, 2022 by MikeQ

[Chris Williams]

On 03/09/2022 at 07:24, Peter Garsden said:

Good point MikeQ. I am simply following Chris's instructions in his RCM&E article. He says taper down the LE blanks before adding the rest of the structure. Not being a Physics major, I don't think I can reason this one through, but looking at it simply, the support tubes are at right angles to the fin so I presume that the taper will be equal top and bottom towards the tip of the tailplanes? If I am wrong then yes there would be a problem with each half but as the taper is equal both sides, I don't think it will matter?

As the AMT section is NACA 009, which is symmetrical, both AMT halves are identical, allowing for variations in any hand-built structure. I don't seem to have many pics of the process for the Petrel, but here's one from the 1/4 scale Rhonadler, which is identical. As you can see, once the root and tip ribs are in place, followed by the TE, you can eye up the TE to see that it is parallel, before fitting the remaining ribs off the board...

[Peter Garsden]

Thank you for that Chris. That is how I  should have built the tailplane like the fin, but I don't think it will make much difference.

 

So to the fuselage servos. Unlike the Flamingo whose rear cockpit slopes acutely backwards, the Petrel is more upright, which does not give any room for screwing down the servo screws and horn central screw whilst in situ, so the ply tray should be removable. I am sure there are many ways of doing this but I opted for 2 blocks of balsa block, shaped to the sides of the fuselage which is tricky due to the curve topped off with a piece of 1.5mm ply to hold the screws, which I put in at an angle to give access for a screw driver.

 

 

You can see that I used a shaping tool to trace the curve of the fuselage once I had measured and cut the servo tray. Tricky because one has to make allowances for the side 3mm spruce rail, and the formers. There is room for the large old faithful Futaba S3003 which are only £8 each.

 

 

This shows that the tray has to fit just where the 3mm spruce spar and the ply tab are so cut outs have to be made. One can also see that I have omitted the cross members to allow easier access to the space in between F4 and F5.

 

 

This shows better the  cross members that I left out until the servos are fitted.

 

 

You can just about see that I have drilled and screwed in the servo tray with 4 screws at an angle so that when the top plywood skin is on I can unscrew from outside so as to remove the tray in one piece.

 

 

[Peter Garsden]

A slightly tricky bit ahead - the bending of 0.8mm ply to suit the shape, and previous thereto the cutting of it to size.

 

 

First I taped together some pieces of A4 and roughly cut them to size for the top of the fuselage to the rear of the canopy. I drew a line down the middle to keep it in line.

 

 

I then used the pencil rubbing technique with a 4B along the hard lines of the edges where I could. For the mid join, I made marks at each end and drew a straight line with a metal straight edge. 

 

This I then laid onto the plywood and drew round it for cutting

 

Then when the ply was cut to shape, I drew another centre line so as to manoeuvre it correctly into position.

 

 

Then came out the steam kettle and rubber gloves which I ran up the middle of the ply. After it had softened and was pliable I stuck some masking tape across the edges to ensure it remained in the curve whilst I assisted it further. Then when it could go right the way round, I taped it into position with masking on the fuselage and left it overnight. In the morning, having thoroughly dried this shape was left. It will now be so much easier to glue into position with some aliphatic resin.

 

Why did I not glue it when wet? Because aliphatic does not stick well to wet surface and the plywood was soaked through from the steam.

[Alan Gorham_]

On 17/09/2022 at 23:27, Peter Garsden said:

Thank you for that Chris. That is how I  should have built the tailplane like the fin, but I don't think it will make much difference.

 

So to the fuselage servos. Unlike the Flamingo whose rear cockpit slopes acutely backwards, the Petrel is more upright, which does not give any room for screwing down the servo screws and horn central screw whilst in situ, so the ply tray should be removable. I am sure there are many ways of doing this but I opted for 2 blocks of balsa block, shaped to the sides of the fuselage which is tricky due to the curve topped off with a piece of 1.5mm ply to hold the screws, which I put in at an angle to give access for a screw driver.

 

 

You can see that I used a shaping tool to trace the curve of the fuselage once I had measured and cut the servo tray. Tricky because one has to make allowances for the side 3mm spruce rail, and the formers. There is room for the large old faithful Futaba S3003 which are only £8 each.

 

 

This shows that the tray has to fit just where the 3mm spruce spar and the ply tab are so cut outs have to be made. One can also see that I have omitted the cross members to allow easier access to the space in between F4 and F5.

 

 

This shows better the  cross members that I left out until the servos are fitted.

 

 

You can just about see that I have drilled and screwed in the servo tray with 4 screws at an angle so that when the top plywood skin is on I can unscrew from outside so as to remove the tray in one piece.

 

 

Pete those 2 servos in the Fuselage don't look like genuine Futaba S3003s to me. The shape and features on the case are wrong and the grommets are different to the genuine Futaba types. It's hard to tell but it also looks like you might have installed the brass ferrules into the grommets the wrong way up. The flared out end should be in contact with the top of the ply plate, not the mounting screw head. 

[Alan Gorham_]

This is what I think a genuine S3003 looks like. You can see the difference in shape. 

[Peter Garsden]

So with a lot of masking tape (wide) clamps, and pins, the top fuselage sheeting is no awaiting drying

 

[Peter Garsden]

7 hours ago, Alan Gorham_ said:

This is what I think a genuine S3003 looks like. You can see the difference in shape. 

So did I buy a fake then? Ooops! I think I have. heavans. Thought I bought it from a reputable supplier but it was an Ebay purchase. Let's hope it survives!

Edited September 28, 2022 by Peter Garsden

[Alan Gorham_]

Let's hope it doesn't crash the model or burst into flames... 

[John Wagg]

49 minutes ago, Peter Garsden said:

So did I buy a fake then? Ooops! I think I have. heavans. Thought I bought it from a reputable supplier but it was an Ebay purchase. Let's hope it survives!

I bought some Futaba S3003 off Ebay and they work but cheap enough to put them in the bin. Found the centering isn't precise. Use them where they won't do any harm if they fail. 

[Peter Garsden]

Because I mistakenly attached the elevator horn to the fin I had to have a method of lining up the tubes to the tailplane correctly. I thus made  copy in 1.5mm plywood. and lined it up with the rear tubes (alignment only) to make sure the wire would go through both tailplane halves, and the horn inside the fin - a bit of a fiddle. The slightest misalignment will cause problems later on. It was also difficult to get the holds in the dummy I had made in the exact same spot. Also the tailplanes have to be level with each other. Think I will sit down for a cuppa! 

 

Chris advises making the hole slightly bigger to enable correct alignment - good advice!

 

 

Obviously the correct way to do this is flat on the building board but due to the horn already being in the fin, I could do a mock up with the dummy ply horn, but not the final check as here in the photo.

 

Next job is to glue the fin in position.