Convair YF2Y-1 Sea Dart

[Phil Clark]

Incredible Phil, you need to nclude some tickets to florida, go look at the sea dart there, purely for research, of coarse, should take about 2 weeks?

Been there, done that Alan......at least the client & Alex from TLJC have.......see 2 of several hundred photos taken of the aircraft posted earlier in the thread.

P

[Phil Clark]

Hi Phil

Do I understand it that you will be making the patterns that will eventually be used by someone else to make a full composite model or are Fighteraces going to be involved all the way through to fitting out (and flying) the finished model (s) ?
John

At this stage, we're making & detailing the pattern. This will then be passed on to a tool making company & then to a 3rd company who will manufacture the final 'flying' composite parts. Being a jet specialist, Alex @ TLJC will then be building the 2 development models. This is quite a long way off yet and at this stage I don't know what if any involvement we'll have at this stage. We already have a number of other projects lined up from next spring onwards that will keep us busy for a good 18 months, 2 years after that, so it may be we simply won't have the capacity. The client will obviously have the flying duties, but it's hoped we'll have at least some involvement during the 'water' based testing/development stage.

Phil

[Phil Clark]

Interesting subject Phil, this may sound a daft question, will the finished model be flown off water as per the real one ?

YES......

It doesn't have wheels (other than small taxi wheels on the tail & rear end of the skis that allowed it to taxi up and down a slipway), so there will be no means of flying the model off land other than fitting it with a non scale undercarriage.

Phil

[John Greenfield]

Hi Phil

Do I understand it that you will be making the patterns that will eventually be used by someone else to make a full composite model or are Fighteraces going to be involved all the way through to fitting out (and flying) the finished model (s) ?
John

At this stage, we're making & detailing the pattern. This will then be passed on to a tool making company & then to a 3rd company who will manufacture the final 'flying' composite parts. Being a jet specialist, Alex @ TLJC will then be building the 2 development models. This is quite a long way off yet and at this stage I don't know what if any involvement we'll have at this stage. We already have a number of other projects lined up from next spring onwards that will keep us busy for a good 18 months, 2 years after that, so it may be we simply won't have the capacity. The client will obviously have the flying duties, but it's hoped we'll have at least some involvement during the 'water' based testing/development stage.

Phil

Thanks Phil. I do like models that push boundaries and are unusual.

[Phil Clark]

Thanks John......it definietely tick both boxes!!

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]

With a root chord of almost exactly 8ft, 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

[Phil Clark]

With the st/bd panel framed up, skinning (2mm lite ply) stats with the elevon. Not clear in the 1st 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.

1mm wide cut line between wing panel & elevon is clearly visible in the 2nd photo.

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]

This shows the three Petrausch Modellbau wing tubes nicely + the balsa capped shear spars in the centre section........note the balsa caps still to be added to the outer panel.

The bench mounted 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 image shows my build colleague John with the wings complete & 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]

This fuselage presents a particular challenge to the Fighteraces team as our only accurate drawing shows two elevations with eight cross sections spread over a 4.5 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.

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

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.

Alex Jones - TLJC

[Phil Clark]

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 on 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]

Forward fuselage with upper section 1/4" sq stringers & 1/8" balsa sheeting added. The removable nose cone is also started + the flat base for the canopy hatch.

[Phil Clark]

To ensure a perfect fit of the canopy hatch in the forward fuselage, after the flat base on the fuselage was glassed, this area was tape covered before a thick 1/16" base of epoxy glass was laid up that the canopy hatch would be built onto..........being as the base of the hatch is moulded over the flat base of the fuz, a perfectly mating surfaces are assured.

[Phil Clark]

With construction of the forward fuselage complete down to the hull area (which would be finished once the main rear fuselage is built & the 2 sections could be mated together).......work starts on the large rear fuselage sections. As per the front, a 8" sq ply box is built (with the wing centre section integral to it) that the rear fuselage will be built around.

Here she is outside for one of those all important motivational shots.......John giving an idea of just how big the Sea Dart is.

[Phil Clark]

On my last visit to FighterAces we wanted to find somewhere close to the workshop to do the initial buoyancy tests. John seemed delighted to be volunteered to test the slipway out in a lake at Herrington Park or at least he was until he slipped! Its a good spot to just test the buoyancy against our calculations but I think we would probably get arrested if we tested the working model here not to mention multiple duck strikes! We'll hire a water sport lake here in Cambridgeshire for the taxi tests...

Alex Jones - TLJC

[Phil Clark]

I mentioned buoyancy in the previous post and its probably worth explaining why this needs to be tested. From the very first meeting with the client I expressed a concern as to how heavy we need to make the model so it sits at the correct waterline. To have it bobbing on the water like a bath toy just isn't acceptable. We are going to great lengths to assure scale fidelity and the sit of any model either on the ground or in the water is very important to the overall look and ultimately is part of the identity of that aircraft. We know from our research the exact waterline required which sits 0.46 meters (18 inches) below the root leading edge and flush with the back of the wing.

Alex Jones - TLJC

[Phil Clark]

We talked at length with Fighteraces about possible solutions and collectively came up with this basic plan.

With the basic principle that one liter of water is equal to one kilo in weight we can cut the hull along the scale water line to find the volume that we need to displace. This varies slightly with fuel state but not significantly. Having designed the hull in CAD while doing the ski retraction work we could easily cut across the water line and work out the volume. Assuming we make the Ski’s neutrally buoyant we need to displace 89 litres of water, hence the model needs to weigh 89kg (196lbs). We’d like the model to weigh 60kg (132lbs) as this gives an acceptable wing loading, any more and its starting to become a handful especially with our scale aerofoil sections. The reason for having the available thrust equal to weight is that scale models don't have the energy of their full size counterparts. With excessive power we can create the impression of energy using the thrust intelligently which allows us to fly the model in a scale manner.

We are now left with a model weighing 29kgs (63lbs) more than we would like. The solution with the obvious requirement for lots of tests is to build a 29 litre wet compartment into the hull. This would be shaped to distribute the water with regard to the CG. The tank would flood once the aircraft is sitting on the water and have several large openings concealed in the formers that the front and rear ski mechanisms will be mounted to. Its easy getting the water in but we now need to evacuate it during the takeoff.

Believe it or not the full size actually took on water, in one instance the ground crew forgot to remove the stoppers in the vents and the aircraft took off with over 1000kgs of water in the hull. The difference being is that the water wasn't wanted in the case of the full size but just accumulated from the open areas at the back near the jet nozzles.

Conveniently the SeaDart has a large water rudder at the back which doubles as a speed brake. The area available to evacuate the water from is large when the water rudders are cracked open so the hope is by the time the model has de-planed its skis the compartments water level should be in line with the current waterline of the model. We have lots of other ideas but this is by far the simplest so starting here seems the best choice, if this doesn't work we will move to the more complex ideas…

The initial plan is to float the pattern once finished bearing in mind we have to add 14kgs (31lbs) to take into account the lack of ski wells. So if we load the pattern to 103kgs (227lbs) with the correct CG then the waterline should be at the scale position.

Alex Jones - TLJC

[Phil Clark]

As per the forward fuselage, limited data was available for the rear fuselage sections. Of the 9 shown above, we only had drawings for 3 of them. Manual drawing techniques were used to generate the additional 6.........once in position, it was clear they were close but not perfect, so a little trimming & packing would been necessary to retain the smooth lines of the upper fuselage & air intake areas.

[Phil Clark]

The stringered areas that are inset form the basis of the access hatches for the turbines........these match up with access panels on the full-size (the rear panel in the B&W photo below). The panels themselves will be separate patterns allowing for 2 separate mouldings. The stringered sections are also separate structures (just pushed in position here) that will be bonded in once their surfaces are 100% finished which will allow us to face & finish the front & rear edges of the opening as well.

[Phil Clark]

More progress on the upper rear fuselage.......work here is very much trial end error as our only drawings refer to the early tail/jet pipe area for the non after burning engines.

[Phil Clark]

Further progress on the rear fuselage.....no drawings at all for this area so the former profiles are generated by good old fashioned paper & pencil with only photos for reference.