Convair YF2Y-1 Sea Dart

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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » November 28th, 2015, 11:26 pm

The complete fuselage is now glassed and a coat of Reface filler primer has been sprayed & fully flatted with 120 grit ready for the 1st coat of Klass Kote epoxy primer.
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Dart_LMA_87.jpg
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Dart_LMA_85.jpg
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maurice northcott
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Re: Convair YF2Y-1 Sea Dart

Postby maurice northcott » November 29th, 2015, 1:42 pm

Phil,
Really stunning.... Thanks for sharing.

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 1st, 2015, 7:29 pm

Thanks Maurice........

More progress with the fuselage. After sanding the Reface with 120, the 1st coat of epoxy primer was applied before wet sanding with 240. A 2nd coat followed with a final rub down with 400 (wet). This has left a surface we're pretty happy with so we can now start the mammoth task of apply all the surface detail..................
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Dart_LMA_88.jpg
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Dart_LMA_90.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 5th, 2015, 5:41 pm

At a recent workshop visit for the Sea Dart team, we took the opportunity to assemble the complete pattern for a few motivational photos for the 1st time since various components were complete. The photo below gives a good idea of the size of this 1/4 scale model with myself & my building colleague John alongside Alex from TLJC & our client Ben.

----------------

Visiting Phil and the team at Fighteraces is always a pleasure especially when the SeaDart pattern is so close to completion. We receive lots of email and enquiries as to weather this model will actually fly off water. The intention is that this will only fly from water just as the full-size did. It will be an incredible sight especially with 60kgs of thrust hitting the water at 30 degree incline.

Desperate to see the model in its natural environment it was decided to take the pattern for a swim at a local lake in County Durham. It did also have a practical reason as we needed to do some buoyancy tests to get a good idea as to what sort of weight the flying model will need to be so it sits at the correct waterline. We have a good estimate with calculations but there is no better test than actually doing it........

Alex Jones - TLJC
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Dart_LMA_95.jpg
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Dart_LMA_91.jpg
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Dart_LMA_98.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 5th, 2015, 5:46 pm

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
Attachments
Dart_LMA_99.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 5th, 2015, 5:49 pm

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.

Alex Jones - TLJC
Attachments
Dart_LMA_100.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 5th, 2015, 5:53 pm

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…

So this brings us on nicely to floating the pattern…

The picture below shows the pattern exactly as seen sitting in the water at 42.35kgs. As you can see it is far too light and needs to displace considerably more water to get the correct waterline.

Alex Jones - TLJC
Attachments
Dart_LMA_96.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 5th, 2015, 5:56 pm

We added 37.5 kilos of sand making the weight as pictured here 79.85 kgs but we are still an inch off the scale water line. The total volume to be displaced of the pattern is 103 litres so 103kgs. If we subtract the patterns weight we get 60.65kgs that needs to be added to achieve the correct waterline. Subtract the additional sand weight of 37.5 kilos we are left with 23.15kgs which is what we should have added over and above the sand. This tallies with our estimations of the extra weight required to submerge the hull that extra inch.

If we remove the volume of the ski wells which are submerged we can shed 14 kilos so a final flying weight with the correct waterline would in fact be 89kgs. A flying model weighing 60kgs without a wet compartment would get close but we will try and get the correct buoyancy using the solutions outlined above.

Alex Jones - TLJC
Attachments
Dart_LMA_97.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 12th, 2015, 11:58 pm

Last of the construction jobs on the Sea dart are the various fairings dotted around the airframe.

Epoxy mouldings were taken from the underside rear of the hull + the underside of the wingtips & the side of the fin/rudder to produce bases for the various fairings to be built onto. This would ensure a perfect fit of the final mouldings when fitted to the flying model. From front to back we have the tailwheel fairing, the two underwing tip floats, the rudder control linkage fairing & finally at the front, the small 3 part fairing on the top of the wingtips that covers over the tip elevon hinge.

The elevon tip hinge fairing is made from Chemiwood. This is only around 4-5" long and will be used to take a silicone mould before casting in fast cure PU resin.

Phil
Attachments
Dart_LMA_101.jpg
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Dart_LMA_103.jpg
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Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 13th, 2015, 12:11 am

Tailwheel fairing?........the Sea Dart was capable lf taxiing on dry land, if not flying from it.

The aircraft had 3 wheels......one in the tail + 2 on the rear end of each ski that rotated through 90 degrees to allow taxiing. All of these features will be replicated on the model.
Attachments
Dart_LMA_106.jpg
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Dart_LMA_107.jpg
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John Greenfield
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Re: Convair YF2Y-1 Sea Dart

Postby John Greenfield » December 13th, 2015, 10:21 am

Fantastic project Phil. Thank you for sharing it with us, most inspirational. Keep the info coming.

Happy Christmas to all at Fighteraces.

John

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 17th, 2015, 9:54 pm

Thanks John.....

Work is now well advanced on the forward fuselage. The rippled skin effect has been replicated using a combination of primer build up and careful sanding. Panel lines have been scribed into the surface with the tip of a fine needle file + a number of other panels have been added as 'plants' to leave a slightly raised edge around access hatches etc.......

Rivets are applied using the tried & tested soldering iron & brass tube tip method before a final 800 grade flat back and the 1st coat of Klass Kote glossy sea blue. The gloss finish (being applied purely to air in mould release) is really highlighting the rippled skin effect........very similar to that shown in the Florida museum example below. The final flying model will have a satin finish more in keeping with the original aircraft back in the 50's so the effect will be more subtle on the finished model.
Attachments
Dart_LMA_108.jpg
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Dart_LMA_110.jpg
Dart_LMA_110.jpg (38.66 KiB) Viewed 12167 times

ian redshaw
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Re: Convair YF2Y-1 Sea Dart

Postby ian redshaw » December 17th, 2015, 11:16 pm

Bloomin' marvellous. That skin finish is perfection!!

Ian.

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 30th, 2015, 10:23 pm

Thanks Ian

.......work on the MUCH bigger rear fuselage sections seems never ending.......but light is at the end of the tunnel :D
Attachments
Dart_LMA_111.jpg
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Dart_LMA_113.jpg
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Alan Cantwell 1131
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Re: Convair YF2Y-1 Sea Dart

Postby Alan Cantwell 1131 » December 30th, 2015, 10:41 pm

Will the actual model be ballasted to the almighty weight mentioned, or will you have, in effect, ballast tanks, and dump the water on take off?

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 30th, 2015, 10:51 pm

Hi Alan

Yes, a system of tanks that flood upon entry to the water, and empty as the model planes up on the skis is the plan......the difference between floating & flying weight will be around 30kg's

Phil
Last edited by Phil Clark on December 31st, 2015, 10:37 am, edited 1 time in total.

Alan Cantwell 1131
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Re: Convair YF2Y-1 Sea Dart

Postby Alan Cantwell 1131 » December 31st, 2015, 8:50 am

:shock: Ruddy nora, Thats some ballast drop! And on the take off run as well, phew!

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » December 31st, 2015, 10:42 am

The intention is to use the water rudders at the rear as the water exit point. These will be cracked open to open the rear of the ballast tank as soon as the model starts moving forwards. This forward movement should automatically start the emptying process so it's a gradual thing as speed increases and the model lifts up onto the skis, hence it won't be one big 'dump' part way through the take off that would unsettle the model once it's already up one the plane.

....at least that's the idea.......much testing will obviously be required to prove the concept and make any design chances that may be necessary.

Phil

John Greenfield
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Re: Convair YF2Y-1 Sea Dart

Postby John Greenfield » January 1st, 2016, 5:19 pm

Hi Phil, Happy new year.
Been sitting here thinking about the water ballast system you have proposed and it has got the grey matter spinning. If you intend to dump the water from the rear then the CG will be shifting rearwards all the time as the water is discharged as during acceleration the water will want to move to the back of any tanks.
Also even at a discharge rate of 1 litre a second (which will require a huge opening to achieve) then it will take 30 seconds to discharge all the water which is a very long take off run.
I know you say there will be lots of testing to prove reliability but somehow at the moment the laws of physics don't seem to favour what is being proposed.
May be worth thinking of a "plan B" as a backup !? Have the water tanks full for static posing and then manually drain them before attempting to fly the model ?

Regards

John

Phil Clark
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Re: Convair YF2Y-1 Sea Dart

Postby Phil Clark » January 1st, 2016, 8:41 pm

Hi John

The 'hole' in the rear created by cracking the water rudders open is approx. 5" sq......I'm no wiz mathematician (others involved in the project are!!!), but I don't think it'll take 30 seconds to dump 30 litres of water through a 5" square hole, given that the flooded tank is proposed to be a long tube in the 'V' of the hull rather than a conventional 'tank' at the rear of the model.

I know those more heavily involved with the 'internal' design of the Dart have other options they are considering......the 'ingestion/dumping' of water was the 1st idea we came up with and is by the far the simplest.......if it doesn't or can't be made to work to our satisfaction, option B (& probably, C, D, E, F & G will be looked at as well!!!!)

Phil

Phil


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