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Thunder Tiger 35% Extra 260 Build Blog


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I couldn't resist buying this from Kings Lynn Model shop at a much reduced price.

They are apparently old stock that KLMS bought from Thunder Tiger as a job lot. The fuel tubing has perished as you will see later, but other than that it looks good.

It comes in two huge boxes. I've got to build it straight away because the boxes are taking up a lot of space.

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This is the fuselage unpacked from the box. It looks well built with no signs of damage.

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Removing the canopy reveals masses of space inside.

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Rudder servos (2) are supposed to go here, but I'm planning on mounting them at the rear end depending on where the CoG finishes up.

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It comes complete with pre-installed fuel tank and plumbing, including a side mounted fuel dot. The perished fuel tubing is obvious.

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I have some Tygon fuel pipe, so this will all get renewed, including inside the tank.

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This is what's going in it.

DLE111 twin petrol engine.

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Twin MTW canisters.

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MacGregor MG5921HV Servos all round. These are 20Kg / 0.12 seconds at 8.4 volts.

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Two x 2 cell 2200mAh LiPo's for the receiver / servo power.

One x 2 cell 2100 LiFe for the ignition.

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JR RD922 Powersafe receiver.

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A few other bits and bobs still in the post.

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First job is to decide how much to shorten the engine box by i order for the prop / spinner boss to be just clear of the cowling.

It's a lovely 2 piece cowling .....

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.... with built in baffling for a twin engine.

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The engine cylinders are slightly staggered, so one side of the baffling will need trimming and the other side building up a bit. This is about how the engine will sit inside the cowl. I'm hoping that the only cuts I will need to make in the cowl are for the exhaust pipe outlets, choke lever (maybe) and for access to the needles.

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Engine length and cowling depth measured to allow calculation of the firewall position to be made.

It needs to be 14mm behind the front face of the current engine box.

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These angle brackets are designed to wrap around the 2 sides of the engine box once the firewall is glued in the required place and the surplus material from the bottom and sides has been trimmed flush. I won't be doing it like this though. I have a better (?) idea.

The angle brackets are conveniently the exact size that the firewall needs to be moved back. Here they are clamped to the inside front of the engine box to act as a guide for positioning the firewall.

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Here is the firewall being epoxied and clamped in place, using the angle brackets as a guide.

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Angle brackets removed whilst epoxy is still wet.

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Clamps removed and the two angle brackets screwed into the INSIDE corners.

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View from the outside. Note that I will be leaving the overhang in place and NOT trimming it flush. This will allow a wooden fillet to be glued between the overhanging edge and the firewall all the way round for added strength. I might also drill through the side of the engine box into the firewall and add wooden dowels.

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This is where I could do with a taller shed!

 

Fuselage hung from the rafters ......

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..... to allow the engine to be test fitted and adjusted by sitting it on the firewall with the bottom half of the cowl in place. It's catching on the baffle at the moment.

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Left hand baffle marked and cut to allow the engine to slide all the way into place.

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Once the engine is in place, the top half of the cowl can be added.

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Clearance at the front looks just right. Looks like I got the calculations right smiley

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Position of engine adjusted by trial and error and using a MIRROR held against the ceiling to position the spinner in the centre of the cowl opening. Position of engine mounting hole centres marked once I was happy.

Note that this is not the final spinner back plate. That is on it's way from China.

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Edited By Gary Manuel on 20/01/2017 19:03:34

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Posted by john stones 1 on 20/01/2017 20:10:18:

Looks very nice Gary

What size is tank/prop ? looks like plenty thrust on engine or an optical delusion ? and are there cutouts hidden under the covering as an option on rudder servos ?

No corners cut on the gubbins, can't fault that man yes

John

Tank has no capacity marked on it, but it's about 100mm x 70mm x 150mm, which is about 1 litre (35 oz).

Prop is on order. Menz S 27x10 Red Beech wood.

Right thrust is built in. Zero down thrust. As long as you take the same off both sides when positioning the firewall, the thrust angle should be correct. No need for calculations the way I did it but for the record:

RHS of engine box = 167mm. LHS = 175mm, Width = 189mm.

Right thrust angle = arcTan (175-167)/189 = 2.42 degrees.

There are no cutouts at the rear - it's designed for the rudder servos to go at the front. Because I'm putting twin MTW silencers up front though, I'm expecting to have to move some weight rearwards. I have a cunning plan though .....

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Posted by Gary Manuel on 20/01/2017 22:31:42:
Posted by john stones 1 on 20/01/2017 20:10:18:

Looks very nice Gary

What size is tank/prop ? looks like plenty thrust on engine or an optical delusion ? and are there cutouts hidden under the covering as an option on rudder servos ?

No corners cut on the gubbins, can't fault that man yes

John

Tank has no capacity marked on it, but it's about 100mm x 70mm x 150mm, which is about 1 litre (35 oz).

Prop is on order. Menz S 27x10 Red Beech wood.

Right thrust is built in. Zero down thrust. As long as you take the same off both sides when positioning the firewall, the thrust angle should be correct. No need for calculations the way I did it but for the record:

RHS of engine box = 167mm. LHS = 175mm, Width = 189mm.

Right thrust angle = arcTan (175-167)/189 = 2.42 degrees.

There are no cutouts at the rear - it's designed for the rudder servos to go at the front. Because I'm putting twin MTW silencers up front though, I'm expecting to have to move some weight rearwards. I have a cunning plan though .....

It involve Turnips crook

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Posted by Rich2 on 20/01/2017 22:14:44:

Excellent Gary, subbed. I am particularly interested as I have a similar sized future project with the same motor yes

It does make you wonder why we don't use better material for fuel tubing!

Indeed.

I'm not sure what material has been used. Some of it seems to be quite tough still. Other bits can easily be cut with just finger nails! It will all get renewed regardless.

The bung is black. I assume that it's petrol proof but I'll not risk it. I'll put a red DuBro one in to be sure. I'll also put a felt clunk in if it doesn't already have one.

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Posted by cymaz on 20/01/2017 22:44:11:

Rudder servo? How about one of these?

That's where the cunning plan comes in.

I looked at them (several times). They are designed for multi servo per control surface to prevent servos failing and also give some control in the event of one of the servos failing. This is effectively a simple escapement mechanism.

I would find it difficult to justify the cost of one of these, when I could make something like this which will do the same thing. This was my original plan before considering moving them to the rear.

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Then I started to think to myself - "why would a rudder servo fail without this escapement". The answer is - if they are not set up correctly, a pair of servos operating the same control surface directly could be fighting against each other and one of them could stall and possibly burn out. It would then be a matter of time before the other one burnt out also. The key phrase here is "if they are not set up correctly".

I am planning on mounting one servo on each side of the fuselage, DIRECTLY operating a threaded rod control horn on the rudder (similar to pull-pull) via short push rods with ball joints at each end. Each servo will have a dedicated receiver output and I will go to great lengths to make sure the geometry and transmitter are set up so that the servos are working together rather than against each other.

I'll explain in detail as I'm doing it and hopefully it will work. If it doesn't work for any reason, I'll have to look at some form of escapement.

I'll have a similar issue on the Ailerons, which have two servos per control surface.

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I've had a quick look at my Tranny (JR DSX9 Mk2).

Unfortunately, it doesn't do what I thought it did. I thought you could set ANY channel as Master and any other as Slave. Not the case - it's only AIL, RUD, EVE and FLAPs that can be duplicated. Looks like I'll be saving up for a Powerbox sad.

Wouldn't have had this trouble with a Taranis.

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That's a so & so Gary. They come up on Ebay now and again. I usually buy my PowerBox gear direct from source in Germany. There are very good to deal with and ship stuff promptly.

I have just found a photo of my old TT 28% Katana which found a new home to a guy in Essex as a result of a previous hanger clearance.

p1020753.jpgShe flew pretty well and despite being a 50cc plane I had a 33cc gasser in it which was good enough as the power/weight ratio was very favourable.

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