The Model (Phase 4)

#41
I didn’t take any pictures of the tailwheel structure installed but I do have the CAD renders and a shot of the parts which you can see below. I’ve tied the axle structure into the keel beam using 3mm carbon plate. We have a 1mm thick carbon fairing that then goes over this as pictured so it all looks like the full size.

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by Alex Jones, on Flickr

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by Alex Jones, on Flickr

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#42
While on the subject of wheels...

The original concept was to have the aircraft ingress/egress the water via a slipway under its own power and independent of any ancillary equipment. The first SeaDart tested had a tailwheel and two fixed wheels in the aft portion of the skis.

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by Alex Jones, on Flickr

This worked well, however, the twin skis caused severe vibrations as the ski flexed between the forward and aft ski attachment points. Interestingly when testing their scale models this wasn’t present (fingers crossed). On the second SeaDart the fixed wheels were removed to concentrate on the ski hydrodynamics, this is the best SeaDart twin ski variant from a hydrodynamic perspective, also the only SeaDart to go supersonic and the aircraft we have chosen to model. This variant kept the tailwheel but had a beaching dolly. The wheels sat under the aft section the skis and fixed forward with bars onto the forward ski mechanism. Divers were used to remove and attach the dolly once the aircraft was in the water.

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by Alex Jones, on Flickr

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The third SeaDart went back to having wheels on the aft of the skis but these rotated through 90 degrees when in the water...

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by Alex Jones, on Flickr


I suppose this is a good point to share our plans in this regard... We have designed a dolly for the model which can be converted into a scale dolly by removing all the aft section rear of the wheels. So this will look very similar to the above pictures. The model can then sit on its own and move under its own power if desired.

For maintenance and testing purposes before we put the model in the water the dolly can be used to support its full weight using the full length non scale version. Ski retraction and oleo extension can be tested and we can also run the engines with the model sitting on the dolly. Our model is large and heavy so it’s important that it can be moved around easily and hopefully this will achieve that. The dolly uses disc brakes on the main wheels with a steerable wheel at the back. Below is a CAD render of our dolly designed by our engineering partners Performance Engineered Designs. Along with the dolly PES also helped work through the ski retraction system and scan the original pattern for us. They have shown great enthusiasm for the project and sponsored much of the design work so a bit of a shout out to them for all they have done so far. :) It helps when the MD and and Technical directors are aircraft enthusiast :)

Our Dolly hasn't been built yet but all the design work and engineering drawings are complete.

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by Alex Jones, on Flickr

Cheers, Alex
 
#43
The Elevons are constructed from carbon skins, carbon ribs and a Rohacell core. This is cold bonded in the CNC’d tooling cradles to ensure they keep the correct shape. The pattern had a little reflex built into the elevons and wing tips. The elevons are incredibly strong by design as they will take some punishment being on the water line. They attach with a 2mm steel wire which runs the length of the elevon and the pivot blocks are correct in number and location as per the original aircraft. Thanks to Steve for pointing me in the right direction with regard to sleeving for the 2mm wire. :)

The construction and finished components.

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The main issue we’ve had is the elevons are impossible to balance in themselves and the actuation is on the pivot so there is no moment arm to help the servos. We didn’t want servos in the wing due to the the bottom of the wing sitting on the water and we didn’t like the idea of having them in the top of the wing. I originally planned on two Ditex servos ganged together actuating the elevon from within the fuselage. It was immediately clear that this was problematic, it works in CAD but just didn’t feel right once installed. It’s one thing to look at the numbers on the screen but there is no substitute for actually doing it and deciding. I used one servo to test the geometry with the telemetry feedback from these servos proving very useful. I had never been entirely happy with the set up so it didn’t come as much of a surprise to see the servo struggle. Just to hold the elevon neutral required 7kgs of torque. There are arguments that the static flight loads on the servo will reduce when neutral etc... when your sentence starts with “it will probably be fine” you know it’s time to go back to the drawing board. :) To move the elevon at any speed to full deflection was causing the servo to peak at its maximum torque. Even with two ganged together theoretically halving the required torque it still didn’t fill me with any confidence. There was discussion around using larger servos with the same geometry but this doesn’t solve the underlying problem so it was decided that the actuation needed to be re-designed.

The torque requirements of the surface aren’t outrageous considering its size. A deflection of 40 degrees at 100kts and 12 degrees at 250kts requires around 1000ozin of torque but our new set up will far exceed this. The full size had a maximum elevon deflection of 40 degrees up and 29 degrees down.

Talking with the Phil and John at Fighteraces we came up with a much better way of doing things. The one thing we are not short of with this model is space in the fuselage. This allows us to counterbalance the elevons inside the fuselage. We then decided on using two SP50 servos per elevon mounting them over the CG and using carbon pushrods to the pivot arm. These servos are powered separately and at 8.4 volts produce a combined torque of 183kgcm (2540ozin). By mounting the two servos in an orientation that allows a plate to be fixed between the two servo arms we can cut a slot in one of the fixing points to the servo horn allowing the elevon a degree of freedom even if one of the servos failed in a fixed position. This is nothing new and used in large models without issue it’s just now we can see a way to integrate that principle into the SeaDart. I’ll post some pictures once I’ve finished the design as the above might not make much sense. At least this is a modification which can be installed into the complete airframe without much issue.
 
#44
We’re at the stage where we can start to do the prep work ready for painting. There is a huge amount of work to do in preparation for paint, far more than I had hoped for. This is the airframe we’ve used for all our development work and aesthetically it is in need of some work. We could just shoot a layer of primer and paint without doing any remedial work on the aesthetics but that isn’t in the spirt of this project. We want things to be as good as possible.

For the prep and paint I can think of no-one better than Phil and his team at FighterAces. Thank you to Phil for taking on this project and spending so much time on it over the last few months. Delivery is planned at the beginning of October so what you see here will soon be the current state of the model. I’m sure Phil will chime in with his processes and answer any questions as I post the pictures.

To get the model to the level we specified will be around 6-8 weeks work, I’m sure it will be worth the wait! The first week in October will see the airframe painted and fully assembled for the first time, I can’t wait!!

On with the work…

Firstly all the hatches needs to be installed with catches and sealed from the water. This is no small task in itself. Secondly, all our development work has been done on this airframe so we need to build back raised panels, re-rivet areas, crisp up panel edges and generally get the model aesthetically up to the standard that is expected of this project.

The model spending its first day in its new home.

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by Alex Jones, on Flickr

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by Alex Jones, on Flickr

A weeks worth of priming, filling and panel work

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by Alex Jones, on Flickr

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I delivered the wings a week later, so a quick motivational shot with it assembled. From left to right, Graham, Phil, and John.

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by Alex Jones, on Flickr

Grahams fist look at the single piece machined aluminium main spar… perhaps a caption competition for this one :)

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by Alex Jones, on Flickr
 
#45
More work from the team at FighterAces, they have put a lot of hours in to get to this stage. Lots of attention being payed even to the smallest of details while they get the finish up to specification.

Blending the exhaust section into the fuselage and notice the exhaust with greater definition on the panels after a re-work. This was one section that was a challenge to mould, it required a 5 part tool and coupled with the temperature specification of the part meant we lost a lot of detail from the pattern. With some work they have recovered the finish nicely… In hindsight I would have made this part in sections as opposed to one piece.

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I’m really looking forward to seeing it all one colour!
 
#46
#47
Time for the guys to turn their attentions to the intakes. FighterAces made a silicon mould of the intake patterns and cast these with a tough resin. This area needs to be strong as I’m certain at some point someone will grab or hold the intake.

John de-moulding.

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by Alex Jones, on Flickr

No one has ever seen John smile so this is included as evidence that he does or at least a grimace while trying . :)

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by Alex Jones, on Flickr

The fuselage close to receiving its top coat.

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by Alex Jones, on Flickr
 
#48
We didn’t detail the ski well patterns originally so Phil spent some time adding the raised rivets in both the forward and aft ski wells. With this complete and the forward spray rails installed it was time for some paint. The different shades of blue are due to these panels being constructed from different material on the original so this has been replicated here.

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by Alex Jones, on Flickr

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by Alex Jones, on Flickr

This aircraft didn’t have many decals but the few that it does have are added using paint stencils.
 
#50
The wings prep and paint, hopefully the pictures should explain things, if not feel free to ask any questions and I’m sure Phil will chime in.

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The elevons are not installed or pictured as I want to makes sure that the new elevon system works and is fitted and bonded before these are painted. If the elevon is a slightly out then the stripes on it won’t look right as there will be a slight misalignment.
 
#52
We’re nearly there… An enjoyable few days spent at Fighteraces going through the paint work before we commit to clearcoat. The following photos do come with a caveat… The paint work and weathering aren’t complete so some areas need work but you should get a good idea of the progress to date.

The aztec pattern completed bar a few tweaks.

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by Alex Jones, on Flickr

The elevons aren't installed and the skis are only placed in the rough position but other than that I’m really happy with how its looking. More importantly the client is too. :) phew…. The elevons are huge so it doesn't look quite the same without them.

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The plan is to have the airframe delivered back down south by the end of this month ready for us to start the equipment installation.

Thanks once again to Fighteraces for all their work on this.
 
#53
The stripes on the back of the wings and vertical stabiliser were to help measure spray patterns and control deflections. The Elevons are missing in the above photos but continue the stripes seen on the rear of the wing. During the hydrodynamic phase of testing many more areas were yellow but our scheme is the toned down version from the press day in November 1954. The yellow was chosen for contrast but we don't know the significance of the Aztec type pattern. I can guess but we haven't found anything in our research that can tell us with definitively.

A picture of some of the guys involved. Left to right... Phil (Fighteraces), Alex (TLJC), John (Fighteraces), Ben (TLJC)

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by Alex Jones, on Flickr

An elevated shot from the front. The white fuselage in the background is a 1/4 scale SeaFury which might give it some scale to those that have seen a 1/4 scale SeaFury :)

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by Alex Jones, on Flickr
 
#54
While Phil and the guys at Fighteraces finish off the painting side of things I’ve been busy re designing the elevon mechanism. Using two PS-050 Tonegawa Seiko servos a side. These are running at 7.2v giving a combined output of 185kg-cm of torque. This far exceeds our flight requirements, however, with the elevons possibly bouncing off the water at 50kts we want to make sure the whole drive chain can take a significant pounding which we now believe it can. The initial design looked ok but when I put it together it just didn't feel right. Hard to explain... I just didn't like it so went with my gut and changed things.

We should get the components manufactured in time for the start of November when we start to concentrate on the installation. The elevon mechanism is first on the list of things to complete.

The below shot is just a computer render of the design work.

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by Alex Jones, on Flickr
 
#55
Thank you to FighterAces for all their hard work on the paint. Almost all the paintwork is now completed with just a few parts that need to be finished after the final installation. I can start completing some of the small installation jobs while I wait for the new elevon mechanism components, this really needs to be done before anything major goes in.

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by Alex Jones, on Flickr
 
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