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Slingsby Petrel 3.4 metre designed by Chris Williams


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The above pictures are of Chris Williams version of this fabulous glider as I haven't even started mine yet!. I have been building and organising my new workshop illustrated elsewhere in these pages so have not been able to make a start on this until now. I have already built a Flamingo which flies elegantly, but cannot cope with winds less than 8mph in reality, which is when I tend to get these old timers out, whereas the Petrel was described in RCM&E to be just such a glider. 

 

The construction of the 2 gliders follows a similar path favoured by Chris, so, apart from the shape of the fine and the All Moving Tailplane, this should go together in a familiar way, though it is about 2 years ago when I built the Flamingo.

 

First thing I did was examine the plan. Sure enough it is the same as the cut down version which appeared in RCM&E. I wanted a full size plan which I could put down without cutting and taping together. I also always have an extra plan printed for reference whilst the plan is pinned to the building board. The magazine version is on A3 so handier to look things up.

 

I have the magazine article which recommends starting with the wing, which is what I did.

 

I also considered what finish I should go for. Whilst I like Chris's red finish, I think a bit more white together with the Hobby King Matt see through film would be my favoured look. I love the matt semi transparent film, which one has to order from the Far East. I found a finish I like on the Old Gliders website. They produce a 5 metre version in a kit. This is their logo which I am going to use. There were very few of these gliders actually built so, one can arguably produce whatever colourway one desires.

 

 

petrel-ulotka-Kopia.jpg

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Well for a change I have started with the wings. As you can see in this picture the ribs towards the tip have no backs on to make way for the aileron spar and separate inset aileron. The problem was, how do I make sure they are all lined up with each other to take the dummy leading edge and aileron spar. I used a cut off piece of 3mm square to rest on the top and the engineer square to line them up. I used CA and acclerator to make sure they stuck fast all the way along the wing.

 

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This shows the whole left wing which was really quick with CA. Once this is dry it will be jacked up on the wing supports - watch this space.

 

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One omits R2 in order to make way for the ply wing joiner box supports. Once the brass box is inserted coming out through R1 one closes it with ply and webbing for support.

 

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At the bottom of the picture you can see that in order to get the inboard ribs to lie flat, the trailing edge has to be packed up by 9mm - a piece of 6mm and another of 3mm which will be removed when the wing comes off the board soon.

Edited by Peter Garsden
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I know this is out of order but I didn't do a shot of the wood kit which is bulging and good value for just under £300. It's a while ago but I think it was £279 from Sarik as a short kit including plan, canopy, and extra wood pack. 

 

Unlike the Flamingo wood pack this one has cut outs in 6mm for the gull wing supports which is very helpful. No cut out however for the aileron spar or the false leading edges.

 

People spend hours watching YouTube videos of unboxing kits. Personally I would rather watch paint dry. So if it turns you on then here is a bit of kit porn.

 

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I also have a copy of the story when it  appeared in RCM&E as a free plan which helps a lot. I am going to scan it in and can send it to anyone who needs it. Just PM me. Don't overreact when you see this now.

 

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Edited by Peter Garsden
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Good luck Mike with your build.

 

Rule No 1 - follow the instructions despite what the build sequence was with the Flamingo. I did not add the 2 false leading edges of 2.5mm and 3mm thickness before taking the wing off the board, nor the aileron spar which was clearly the instruction. This ensures that the ribs stay in line with each other before bending it over the under wing jigs, so I pinned it back down and added these. It produces a much more solid structure.

 

I then pinned down the under wing angled gull wing jig and bent the wing over it.

 

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One has to add cross pieces to the jig for support

 

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One can see the doubled R11 rib in 6mm which I cut out from the scrap indent, and the 1.5mm gusset to reinforce the corner. Next job is to add the top spar. This makes the joining of the false leading edge and the top sheeting easier.

Edited by Peter Garsden
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Hi

 

Thanks for the advice.  Have you found the build photo sequence that Chris Williams references in the magazine article.  Should be on this site somewhere but I can’t find them ?

 

The more photos the better.  This will be the biggest model I’ve built.

 

Cheers

 

mike

Edited by MikeQ
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30 minutes ago, MikeQ said:

Hi

 

Thanks for the advice.  Have you found the build photo sequence that Chris Williams references in the magazine article.  Should be on this site somewhere but I can’t find them ?

 

The more photos the better.  This will be the biggest model I’ve built.

 

Cheers

 

mike

 

Hi Mike, if you email him he will gladly send them to you. They are his photos rather than mine -  his email address is [email protected]

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Next step before removing the wing from the under wing supports is to glue in some webbing - grain vertical of course in 4 or 5 places to give the wing some strength. The plan does not show the webbing which sits in front of the spar rather than behind. I made a mistake with the Flamingo but only with 1 piece of webbing - not the end of the world.

 

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The tricky bit with the Petrel is sanding down the front temporary leading edge (2.4mm) and the front leading edge (3mm) to line up with the curvature of the ribs without damaging said ribs with the plane. I used the familiar technique of covering the edge with masking tape then using a combination of the David Plane and my Proxxon Shoe Sander - very effective.

 

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The plane cuts the masking tape before it damages the ribs.

 

 

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One of the most useful of tools in my bijou workshop is the long, flat sanding block. A sheet of 5 or 6mm balsa with 40 grit on one side and 80 grit on t'other. 

This is ideal for the task of sanding down the aileron spar on a wing and rendering it flush with the ribs. You needn't worry too much about slightly re-profiling the wing ribs: if they've been cut by hand (as mine always are) this will smooth out the inevitable slight differences...

P1070916 copy.jpg

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Again, follow the instructions which say that before one puts the wing back on a different jig - that for use when putting on the top sheeting - just attach the leading edge sheeting for under the wing, and the narrow strip adjacent to the aileron spar before putting it back on the jig to attach the top leading edge sheeting - why? Because if you attach the rest of the underneath sheet adjacent to the root, and next to the gull join, then the wing will be too stiff and not flexible enough to bend the leading edge top sheeting into shape. Even so we are advised to use water or steam.

 

You can see that I lashed out for some more pins - they are so sharp and go through spruce a treat, unlike round headed pins.

 

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Here you can see that I used masking tape to bend the sheeting round the leading edge. Note to self - with the other wing don't chamfer off the leading edge so much because it is difficult to get the sheeting to bend round the curve.

 

Also you have to take one of the spring clamp coloured flat pieces to get them to stick to the 3mm square spar.

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On 10/06/2022 at 21:45, Chris Williams said:

One of the most useful of tools in my bijou workshop is the long, flat sanding block. A sheet of 5 or 6mm balsa with 40 grit on one side and 80 grit on t'other. 

This is ideal for the task of sanding down the aileron spar on a wing and rendering it flush with the ribs. You needn't worry too much about slightly re-profiling the wing ribs: if they've been cut by hand (as mine always are) this will smooth out the inevitable slight differences...

P1070916 copy.jpg

Hear hear, I made one and it is brilliant. This great tip was in the Flamingo Build Article, I remember. Having made it, I use it all the time.

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If you look carefully you will see that I have now put the wing on a different jig for attaching the top D Box sheeting which goes on in one piece. The Flamingo had a larger gull dihedral so went on in 3 pieces. Because the Petrel uses one the balsa sheet needs wetting - I used a spray which I applied in copious amounts when the rear had been attached to the main spar.

 

You have to use aliphatic or PVA because Cyano would dry before it had been secured. This is a 3 dimensional bend so a lot of masking tape, clamps - only 3mm spar to grab, and Graupner pins. Before everything is pinned down apply the weights to persuade the wing into shape. It does not sit on the jig otherwise. When all the support is applied it is too late.

 

Oh and watch out for the exposed ribs near the root. I have broken and re-glued them 3 times! Everything will be fine when the cap strips and final sheeting go on.

 

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The masking tape does not stick to wet sheeting! So you have to wrap it round the back and attach it to the dry under wing sheeting! If you let it dry it will be too late. One could pre-bend the sheeting but it is such a complex 3D shape that it would be practically impossible to do so.

 

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This is the kitchen spray that I have refilled and marked water to stop people spraying it into their mouth after some cranberry juice in the hope it is vodka?

 

You can see that one has to pin down the mid points over the complex curve. I found these pins ideal because you can use them as clamps by pushing them all the way in.

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DISASTER ALERT

 

I have made some mistakes in my time building models, but none as serious as this one. I do have COVID which is no real excuse as this started before I caught it. No worries though, you can't catch COVID from this site unless you are sitting at my computer in the Study part of my workshop, and there is no one here at the moment, so I think we are safe???

 

DON'T FORGET TO ATTACH THE 3MM SQUARE SUB SPARS TO THE MAIN SPARS BEFORE YOU GLUE ON THE TOP AND BOTTOM D BOX SHEETING. Don't ask me how I know!

 

I attach a picture of DOOM

 

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You can see that I have cut a 15mm strip out of the sheeting so that I can get at the spar. I have done this already on the top. I will cut 3mm slots out of each rib and glue the sub spar to the main spar webbing - fortunately it does not run the full length and only to R22. I won't show you any more photos as exactly the same procedure is shown in my Flamingo Blog 

 

Very clever design by Chris here. It uses laminates of 2 pieces of 3mm Spruce with a 1.5mm piece of .8mm ply webbing in between to create a strong but light box girder cross section. I was tempted to miss the sub spars  out but the wing would have ended up too weak by some margin. To absorb stress loads the sub-spar is chamfered to nothing between R21 and R22.

 

I know we have all made errors but this is a very annoying one which required me to prise off the top sheeting with my chisel blade you can see in the foreground.

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Hello Peter

 

Bummer.  No doubt you’ll sort it.  Thanks for making my mistakes for me ?

 

My kit has just arrived today.  I need to get the PSS Canberra out of the way and then ill be making a start.

 

cheers

 

mike

 

PS ive made two right wings before.  Cant be worse than that ?

Edited by MikeQ
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Thanks Mike. All sorted now. The subspars make such a difference to the strength of the wing. It's like an I beam in the middle of the wing. And 2 left hand wings - I have made to left fuselages before, I suppose that is similar.

 

And a Canberra eh - I suppose you know I also have a Canberra which I fly regularly at PSS events. Great plane by Andy Blackburn. See my RCM&E blog for tips - I just looked and realised that I have followed your blog and you are aware of mine. Making your own canopy now that is ambitious.

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Im terrible for having lots of things on the go at once.  It might take 3 or 4 yrs for a simple model to come off the production line, although there are models coming off two or three times a year if you know what i mean.  Ive got a Loaded Dice 40S pattern model thats about to drop and its been on the go about 15yrs ?.  Freeflight, control line, radio ... i always finish a project, at some point in the nine specific future.  My buddy only ever builds one at a time.  Much more sensible.  Im clearing the decks for this Petrel though..  
 

 

Edited by MikeQ
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Yes I know people who have lots of things on the go at once. Andy Meade for example who is presently moving house and frantically trying to get rid of half finished projects!

 

Anyway, repair work done, mistakes corrected and on with the bottom sheeting. Also, to correct another error, I have to open up the top sheeting to insert the front R2, and the ply supports for the hooks that take the rubber bands which hold the wings together.

 

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Used some steam to bend the 6mm square over the curve of the wing, and glued with cyano.

 

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Here you can see the bend in the 6mm square which I did with steam to follow the curve of the ribs, also the boxed in 3mm brass tubing for the incidence pins which will be 3mm piano wire. You can just see where the end of the tube is nipped with snippers to create a stop for the wire. Also the 2 layers of 3mm ply for the rear wing hooks.

 

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Next are 5mm wide cap strips. I have been using an amazing 5 minute PVA which my builder gave me to try. It really does set that quickly. Quicker than aliphatic even. Also waterproof!

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So to the spoiler - not shown are the inside lengths of 6mm square balsa to line the hole into which the spoiler fits. It is made of 3 laminations of balsa ply balsa with cut outs for the hinges in the middle ply of the sandwich. Make sure your hinges fit into the slots and enlargen, trim as necessary. I used proper hinges as they have to raise to 90 degrees vertical. The hinge slots were cut at a 45 degree angle and the edges chamfered

 

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Underneath shows the space into which one mounts the micro servo with the horn (a cut off Futaba servo horn is glued into the middle to allow for leverage.

 

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Also I have fed some wire through before it is boxed off for the servos.

Edited by Peter Garsden
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Aileron Servo bay for the Corona Flat wing servo on spruce bearers. Note that it is positioned a right angles to the trailing edge but askew of the leading edge.

 

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And finally top sheeting weighted down to dry. Note that I have made a large hole in R1 to allow exit of the Multiplex Wing Servo plug in green.

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