The Design (Phase 3)

The research was complete enough to start making a decisions regarding our approach to the model.

Many scales were discussed and after weighing up all the options we enthusiastically went with 1/4 scale which makes the model over 4 meters (157 inches) in length and 2.5 meters (98 inches) in span.

Helped along with a suitable budget it was decided that the model’s scale fidelity be put before all other considerations. So everything from this point is done to achieve that goal regardless of the more traditional constraints to such a project. This is probably as far from a traditionally built model as one could get.

The models whole philosophy dictates a different approach to its creation. There are seven companies and hundreds of people involved in it’s design and fabrication. All the companies are based here in the UK which was important to us and range from small businesses to multi million pound engineering firms. Parts being built alongside orders for Aston Martin and the top Formula One teams is really exciting. Its been a real privilege meeting the various companies around the UK and to see people so excited and engaged with the project is heartening. Although they do often add they think we are completely insane... which I think is part of their attraction.

The further along we get the more confident I become at this projects eventual success but there is still a risk over and above a ground based scratch build. To discard this or not be honest with ones self would be foolish. With this in mind our approach to everything is with reproduction in mind.

Initially two models will be built, the first a pure prototype whereby we can try our design ideas with the second used for the implementation of the designed solution. Both models will be built concurrently with the obvious need for a slight offset in build stages.

The project has been broken down in five distinct phases. History, Research, Pattern, Model, and Testing.
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Although the budget allowed for a full CNC’d pattern we were keen that this model have as much of the character as the original. Often very large models are impressive only due to their size but lack any real depth of character. By involving professional modellers in the production of the pattern we can build in the modellers touch, add every rivet (over 100,000), every panel line and every bowed or warped panel to create something very believable. This is all possible straight from CAD but felt we could better achieve the desired character of the aircraft by doing the detail manually, after all... the original was built by hand so we felt it would be fitting that the pattern is also built in this way.

This decision was helped along with the fact that we still had some holes in the research and areas of the model would need to be done with reference to photos alone, we believed an experienced team of professional modellers would have more success with this approach and have a sound understanding of whats required in a large complex model such as this. The SeaDart pattern is built purely by hand using scaled original drawings taken from the Convair Archives. All drawings were painstakingly digitally cleaned then enlarged to exactly 1/4 scale giving very good resolution and a decent start for making the pattern.

SeaDart Drawing1
by Alex Jones, on Flickr

Our other custom composite jet projects will involve both CNC’d patterns and hand crafted external detail which offers a good solution for the manufacture of Carbon LTM tooling suitable for repeated use in an Autoclave.

Initial CAD drawings were produced for the Wings and fin by FighterAces using the original aerofoil sections. The Little Jet Company then rendered the 2D drawing into three dimensional CAD work. Lift characteristics for the SeaDart delta wing are not impressive. These are symmetrical airfoil sections with a mean aerodynamic thickness of only 3.83%. The L/D is low at high angles of attack. I had a long conversations with the client regarding this and in the spirit of the project it was decided to go for a completely scale wing with blended aerofoils from root to tip using NACA-0003.30-65(Mod) and NACA-0004-65(Mod). The fin is very similar but uses NACA-0003.5-65(Mod) at the root. These are the exact aerofoils used on all five SeaDarts that were built. This is one of the very first supersonic delta wings designed and flown. Convair learnt a great deal from this and put this knowledge into some of their other iconic supersonic deltas.

SeaDart drawing 3
by Alex Jones, on Flickr
This moves us neatly over to phase three of the project which is the internal design and pattern build. Having looked at numerous professional pattern making firms it became clear we needed someone who understood model aircraft and there is only one company here in the UK that I would trust with producing a pattern with the level of detail and accuracy that we require for this project.

The team at Fighteraces run by the the very talented Phil Clarke (Pictured) was commissioned to build the pattern. We’ve worked with Fighteraces in the past so I was confident they could produce a stunning pattern to our very exacting standards.

by Alex Jones, on Flickr
For those of you that haven't heard of Fighteraces take a look at their website here.

They have produced some of the best piston engined scratch built models in the world and its a privilege working with them on the SeaDart.

After months of solid research it finally begins... Lasercut parts for the fin using aerofoils NACA-0003.5-65(Mod) and NACA-0004-65(Mod).

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr
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The fin is progressing well having the first half sheeted and a picture with Phil holding it so you can get a sense of scale.

by Alex Jones, on Flickr

It's worth noting the structure pictured is purely for the pattern and not necessarily representative of the flying model.

Alex, TLJC

"The double rib marks the joint on the top of the fuselage.......the lower section will sit on top of the wing inside the fuselage (with a wing section shaped packed on it’s root end). This internal section will be cut down in chord.......the front rib sections will be removed back to the front face of the front spar.....the rear to just behind the rear tube."

Phil Clark, FighterAces
"Initial construction starts with the vertical tail fin. All ribs have jigging tabs which were tack glued to the bench to ensure perfect alignment before the 1st skin was added.

Appearing maybe over engineered for a tail fin, but being a master pattern for a composite mould, weight is unimportant with this project whereas the structural stability of the finished component is the key. All laser cut parts are from 1/4" birch ply and the skins are 2mm liteply.......the finished fin is HEAVY but immensely stiff so ensuring there is no distortion during the mould making process.

The double rib marks the joint on the top of the fuselage.......the lower section will sit on top of the wing inside the fuselage (with a wing section shaped packed on it’s root end). This internal section will be cut down in chord.......the front rib sections will be removed back to the front face of the front spar.....the rear to just behind the rear tube.

Three tubes are fitted, 10 mm at the front, 20 in the middle and 16 at the rear. These are purely for alignment & fitting purposes only. They are unlikely to be used on the final flying version simply because they do not pass far enough up into the fin due to the thin section. Double if not triple full section blade type spar/joiners are likely to be used on the flying model.

The shear spars are all cut approx. 2 mm under size & they are faced in balsa that is easily sanded flush to the ribs. The LE is a section of hard 1/8” balsa notched onto the ribs......this gives the skin something to bond to at the LE + a larger base for the hard balsa LE block to bond to."

Phil Clark, FighterAces
More progress from FighterAces on the SeaDart fin with the start of the glassing.

by Alex Jones, on Flickr

A peel ply layer which you can see folded back for demonstration only. Epoxy to come... Phil uses the excellent L285 skinning resin which I can highly recommend having used it myself on several projects.

by Alex Jones, on Flickr

A link to materials the Fighteraces team are using for the glassing etc...
"More progress with the fin following completion of the 2mm liteply skinning + hard balsa LE & tip blocks. Glassing is done with my favourite L285 skinning resin + a close weave 4oz cloth (as mentioned, weight not an issue, but component stability is). With the glass on, a layer of peel ply is then added (shown here partially removed post cure). This is wetted out with a 2nd application of resin but with the 1st layer + cloth still wet. The resin wets out the peel ply and once cured, the ply is ripped off leaving a beautifully smooth lightly textured surface that's ready for a light rub down & a 1st application of primer."

Phil Clark, FighterAces
The wing panels are build identically to the fin.....1/4" ply ribs & shear spars, again with the spars cut 2mm underside so they can be faced in balsa to be easily levelled with the ribs prior to skinning.

Rib 4 has a duplicate as this is the break point between the removable outer panel & the centre section that is to be built into the fuselage.

With the scale section, we have a max root thickness (including the upper & lower 2mm skins) of only 70mm.......this means the ribs are quite flexible especially towards the top, so the jig tabs (glued directly to the bench) are vital to ensure a true panel is built.

Phil Clark, FighterAces
"Not clear in the photo, but the elevons have the 'scale' 2 degrees reflex built in progressively from '0' at the root to 2 degree (TE up) at the tip. The elevon LE & false TE are built into the wing panel 1mm apart so the sheeted elevon can be cut off after the underside is sheeted. Also note the wedge shaped packer position centrally between the front & rear jig tabs to prevent sagging of the ribs when the top skin is added & weighted down to cure. All skin bonding is done with foaming PU 'Gorilla Glue' plenty of working time & an excellent bond between ribs & skin.

Three wing tubes are used for alignment purposes as per the fin.......2 x 25mm and a smaller 20mm tube at the front. These pass as far out into the panel as is possible before breaking through the edges of the ribs at the tip end of the tubes. The 3 root rib bays will be mated to the corresponding 3 from the other panel to form a centre section that will be built integral to the fuselage."

Phil Clark, Fighteraces
One half of the center section built in the same manner as the wing panels.

by Alex Jones, on Flickr

by Alex Jones, on Flickr

Jigs built onto the work surface to reverse the panel and sheet the underside.

by Alex Jones, on Flickr

The wing starting to take shape.

by Alex Jones, on Flickr

John from the team at Fighteraces rightly pleased with the results so far. Fin, wings, elevons and center sections now complete ready for surface preperation so its onto the fuselage.

by Alex Jones, on Flickr
"The first picture shows the three Petrausch Modellbau wing tubes nicely plus the balsa capped shear spars in the centre section. Note the balsa caps still to be added to the outer panel.

The jigs are simply mirror images of the ribs but with the 2mm skins taken into account so once skinned on top and flipped over, the panel is a perfect fit in the jig ready for the underside to be skinned.

With the underside skinned, the elevon is removed. The TE of the 2mm skins is chamfered down to a feather edge and 0.3mm Proskin is laminated in between the 2 to give a stiff but sharp TE to the elevon. The hard balsa tip block has 1/32" ply sandwiched between two 1/2" balsa sheets as does the LE block to ensure the LE retains a nice hard edge to it's radius.

The final shot with John shows the wings fully glassed. Quite a job in itself given it's 35 sq ft area so a combined 70 sq ft top & bottom. Glassing was done as per the fin with Fighterace's own L285 resin & a close weave 125g cloth + peel ply."

Phil Clark, Fighteraces
This fuselage presents a particular challenge to the team as our only accurate drawing shows two elevations with eight cross sections spread over a four meter model. Lots of information can be extracted from the drawing but the last quarter is completely different as the aircraft we are modelling has the after burning engines and this drawing shows the very first SeaDart with the J34 non after burning engines. As a result the top rear section of the aircraft is very different.

SeaDart Drawing1
by Alex Jones, on Flickr

This photo shows the difference when looking at the aircraft with afterburning J46 engines.

by Alex Jones, on Flickr

Fighteraces have a big task filling in the holes using our photographic research and some of the other drawing research to accurately re-create the second SeaDart built (YF2Y-1). The hull has been drawn in CAD using measurements from the Florida SeaDart to facilitate the creation of accurate former sections. The ski retraction mechanism is very sensitive geometrically so its critical the hull is built in accordance with the CAD work or the ski’s will not retract correctly into the ski wells.

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr
Of the 11 formers shown here, only 3 were shown on our drawings, so the remaining 8 had to be produced taking what information we could from the drawings + refering to the multitude of photos. We opted to break the fuselage at a prominent panel line a little ahead of the intakes + the formers spacing shown is approx. 4" which will give excellent support for the skin especially when a higher density than may be normal for a 'flying' model of 1/4" sq stringers are added as well.

There was nothing 'Hi Tech' about the production of the 8 new formers........good old paper & pencil & some old fashioned drafting techniques was all that was required (A set of French Curves were worth their weight in gold!!). To ensure the whole nose section remained true, it was built around an 8" square 1/8" ply box (which tapers off towards the nose). This in turn has a 1" aluminium tube running through it that can be supported at either end to facilitate easy 'finishing' of the nose when it comes round to glassing, surface prep & painting.

You can see a series of 5 holes on the rear face......these are 10mm I/D phenolic tubes that will take shorts 10mm aluminium alignment pins......the front former of the main rear fuselage will obviously have corresponding phenolic's to ensure perfect alignment of the 2 sections.

Phil Clark, FighterAces
Some more sheeting complete on the forward fuselage section and a start has been made on the large canopy section. The canopy will be fully functional like the full size as you can see in the historical image on my previous post. Another 8 inch ply box has also been made for the aft fuselage formers to keep everything true.

by Alex Jones, on Flickr

by Alex Jones, on Flickr
by Alex Jones, on Flickr
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Out in the sunshine for a motivational assembly of whats been done. Some imagination required but I'm sure you get the idea... Its a shame the photos can't do the size much justice as in person it looks colossal. Fighteraces are doing an excellent job and proving that they are among the best around for this sort of thing. I'm looking forward to posting some progress next week!

by Alex Jones, on Flickr

by Alex Jones, on Flickr