Minor issues with laser cut JP parts?

[Phil Cooke]

Although the Jet Provost plan has been well proven in the 8 years since its initial publication, via a number of successful builds in the UK, the laser cut woodpack is brand new and despite our best efforts, perhaps unsurprisingly, a couple of minor issues have been found with the first sets of parts.

When found, the laser cutting programme has been altered immediately in manufacture by the guys at Traplet who have been very supportive, but inevitably those woodpacks already delivered will need fettling by the builder. This section will help builders pick up on any issues we've found upon receipt and alter any effected parts they have prior to their use in assembly.

As a rule, because the plan is proven and deemed correct, its always advisable to lay the laser cut parts out over the part drawn on the plan to double check its form prior to assembly.

 

 

ISSUE 1. Wing Tip laminates.

Having received one of the very first kits, it was found that the third inboard wing tip tank laminate was missing its aerofoil section shaped hole to enable the wing tip to pass through it.

The plan (below) clearly shows the wing tip passing through the inner 3 balsa laminates and push fitting upto the central tip tank 'spine'.

But when the first parts were checked, only the inner 2 laminates were machined with the aerofoil clearance hole. Traplet were notified and the laser programme was altered immediately, so we believe only the very first few woodpacks were effected in this way.

If you, like me, have to cut out the aerofoil into the 3rd laminate then this is best marked up when the parts are still attached as shown, by drawing a straight line just touching the 2 LE and TE extents on the other 2 laminates - this will then enable you to position the tip rib profile.

 

 

ISSUE 2. Former F1

Former F1 has been found to be missing the 2 recesses (positioned on either side of the battery box) to accept the fuselage side extensions. The plan for F1 is a little complicated here as it has been drawn with a lot of dotted lines representing the soft balsa sheet that will eventually form the front nose section. The F1 former profile is shown as a SOLID line, and you can see the 2 recesses required at the 3 o'clock and 9 o'clock positions. These have been missed in the early woodpack kits.

Again, Traplet have responded with an immediate update to the woodpack machining programme, but the first 40 or so kits will be effected in this way.

The liteply is easily cut with a scalpel so the 2 required recesses should be added before F1 is glued to the battery box assembly.

Edited By Phil Cooke on 18/01/2014 14:45:12

[RedBaron]

Thanks for that Phil,

If I could add another minor comment on the wing tanks:

When the laminations are held together the width of the stack is about 3mm wider than indicated on the plan. This no doubt due to material usually being of nominal size.

Do nothing and you will have an oval tank or you will have a lot of extra shaping to do. The quick fix for me appears to be to leave out the central 3mm lamination.

Anyway it is worth each builder checking this out before gluing, that is unless you like shaping and sanding

Regards

RedBaron.

Edited By RedBaron on 18/01/2014 16:05:17

[RedBaron]

PS to the above, the "draw straight lines on the laminates whilst in sheet" may not quite be exact as the LH and RH parts are not arranged completely symmetrically on the sheet.

My best idea so far is to stack the three parts that need cutouts exactly as per plan and each other (except one left and the other right hand). Pin the three laminates and using a fine felt tip pen mark out the third cutout by putting the pen through the two already done. With care one can then cut just inside the line to get the shape right.

Rgds

RedBaron

[Phil Cooke]

Many thanks RedBaron,

Appreciate the update - you are leading the way with your build already underway so please keep adding to this section if you do find any more build issues (related to the woodpack definition)

Watching your build blog with interest!

Phil

[Andy Blackburn]

Posted by RedBaron on 18/01/2014 16:04:32:

<snip

When the laminations are held together the width of the stack is about 3mm wider than indicated on the plan. This no doubt due to material usually being of nominal size.

Do nothing and you will have an oval tank or you will have a lot of extra shaping to do. The quick fix for me appears to be to leave out the central 3mm lamination.

My two penn'orth, FWIW;

The "normal" tip-tank extra width is about 1 mm; if yours happens to be 3 mm because of some thick wood then leaving out the central 3mm lamination might be an approach - provided that the two laminations each side are the same size (I haven't got a wood pack to hand so I can't check, but the parts are slightly different to what was originally designed). However, I don't really see that it's a lot of extra work to remove 1.5 mm from each side - maybe a couple of minutes with a razor plane and another couple of minutes with a coarse Permagrit block?...

A.

[William Corbin 1]

I've had my Traplet wood pack for Andy's Jet Provost on the shelf for ages- (I think I'm probably too late for the 2014 mass build!) - but I'm now (at last) starting to build!

I think I must have one of the earliest packs, because even though the tip tank sections have the aerofoil aperture omission rectified the former F1 still has no fuselage side recess cut .(Easy Fix)

However, when doing the"check all parts against the plan" evolution I have encountered two unidentified pieces, both in 3mm balsa,

1. A piece measuring 150mm long and tapering from 10mm down to Zero.

2. A piece measuring 128mm long - 20mm wide at one end and 14mm at the other with the whole slightly angled beyond 90 degrees at the 20mm end.

There are 2 of each piece.

HELP!

Any advice appreciated

Bill

[Andy Blackburn]

Um...

I have to admit to being initially baffled but I have a dim memory of the fuselage sides being made from multiple parts in the usual traplet manner - is it possible that they're additional bits to be added to the fuselage sides to get the correct shape? That should be easy enough to check?

A.

[Andy Blackburn]

Yep, I've just been into the loft (at great personal risk, I might add) and checked with my original traplet wood pack - both mystery pieces are on the same sheet as (and are next to) the fuselage side pieces; the triangular section fits on the top of the rear piece and the other bit fits at the bottom of the front piece. Put them all together over the plan, and it should be obvious.

[William Corbin 1]

Hi Andy,

Thanks for that. All now becomes obvious! It's the oft repeated phrase isn't it? "when all else fails...........etc."

However, I think "the other bit" fits on top also - it looks like the lower side of the cockpit. It certainly fits anyway.

Many thanks again. Sorry to have put you in peril climbing into the loft!

Bill