Convair YF2Y-1 Sea Dart

[John Greenfield]

Phil
A long tube will have a more dramatic effect on the CG as the water drains than a short tank.
Fantastic project that has really got my interest.
Please keep the build info coming.
J

[Peter Siggins]

Thanks for the explanation Phil - sure is pushing the boundaries

Pete

[Phil Clark]

John....et al.....

Thought I'd post this e-mail I received earlier today from the Sea Dart client......(further food for thought)

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Phil Hi

I read John Greenfields comments in the LMA thread. I’m glad its getting the creative juices flowing as we want everyone to enjoy this project and its challenges!!!

Here is a thought. If I am right the flow rate of water lifted by 30cm in a tank through a 10cm exit pipe would be 18kg per second….Lifted by 20cm it would be 15kg per second. at 10cm rise we can lose 10kg per second. Check out this flow calculator….If this is correct we could probably evacuate the internal 30kg tank within 5 seconds if the aircraft rises slower to begin with....

http://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

Now consider the extraordinary nature of the Sea Dart and its take off run. Throttle is applied at the beginning of the run. 60kg of thrust is available. The hydro skis are fully extended for un-porting (The front of the skis breaking the surface of the water). This will be the point of maximum drag of the skis and hull in the water. The skis begin to lift the nose almost immediately and at this point the CG is of no critical importance. The Hydro skis are then set to the intermediate position to reduce hydrodynamic drag, and acceleration begins with the tail and two skis touching the water and lifting the fuselage in a stable triangle. Water will be exiting rapidly & as speed increases the fully extended ski position is selected, and it is at this point that the water tank should be dry. The pitch of the aircraft is now controlled around the CG which has been set up over the contact points of the hydro skis at take off speed in order that the airframe can rotate to the necessary angle of attack (17 degrees) for a delta wing take off. The aircraft is sharply rotated from the horizontal and........ in theory flies

It is worth noting that a normal take off run for an RC jet is 9 or 10 seconds from brake release. This aircraft could be longer…but the real aircraft could do it in 2300ft on calm water. We will just have to see.

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Phil

[John Greenfield]

Good formula for flow rates but remember that the head will be diminishing as the water is expelled (and shifting the CG) so the actual discharge rate will vary. (boy, I do love this stuff).
Having heard the proposed explanation of the take off run I do wonder of the effect of choppy water on the pitch of the model at the various stages of the take off and the effect on the water in the tank.
Fantastic project pushing the boundaries. Hats off to all involved, keep at it.

J

[David Brown]

A thought on expelling the water, would it be possible to put a flexible diaphragm / bladder in the tube about half way down and using air drive the water out during take off which would also guarantee total evacuation of the water to guarantee c of g on take off. I have seen similar use of this in engineering but on a larger scale, similar to blow pots.

Dave

[Phil Clark]

.....more from our Sea Dart client.

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I hope that the following photos show the various stages of the take-off run for everyone's reference.


John thank you. You are right of course. Just exactly what the process does to the aircraft is conjecture. There are quite a few variables. Firstly just how fast does the hull have to be moving to commence lifting at the rear. Secondly how much effect does the high mounted engine thrust have. The aircraft sits static with the wings touching the water at the rear. This supplies huge amounts of buoyancy as the water rushes to the rear probably limiting a dip as water moves back and attempts to find a constantly changing level. Based on my experiences as a waterskier I know that this is going to occur at low speed. On the real aircraft ski unporting occurred at 8kts (see pictures) I personally don’t think a large actual distance will be covered during this emergence process. A bit like a Saturn 5 coming off the launch pad, as the water is expelled the process will speed up as Hydrodynamic lift increases and weight decreases.

Dave I like the way you are thinking. It would certainly control expulsion. We will put the idea in the file and address it if the natural gravitational process (Plan A) has to be ruled out. Thanks

We will be taking the finished “Pattern” to be scanned into CAD so that the internal structures can be designed very accurately, and I am sure that Alex and Phil will show screen grabs on the two forums from Solidworks as the design progresses. The first Sea Dart will be built to test the Hydrodynamics and systems to provide us with a stable platform from which we can progress to flight. The second aircraft will be an exact scale model of aircraft 135762, the Sea Dart that went supersonic in 1954.

[Phil Clark]

Unporting at 8kts

[Phil Clark]

Now at around 15kts with the skis still in the fully extended position......

[Phil Clark]

Skis retracted in to the intermediate position for the main acceleration phase.

[Phil Clark]

The rear rams are then extended again which now allows the tail to fly and raise up out of the water (spray)

[Phil Clark]

A better side on shot showing the tail high out of the water approaching rotation speed.

[Phil Clark]

Work complete on the jet pipe pattern.......

[Phil Clark]

The main rear section of fuselage following application of it's 2nd coat of gloss colour. The texture & depth added to the surfaces by the rippled panels and all of the raised panel edges showing up well.............

........once cured, the lengthy flatting/polishing process of the complete pattern begins

[Phil Clark]

Forward fuselage, canopy & nose probe - FINISHED

Having left the Klass Kote to fully cure for a week or more, everything was flatted (wet) with an 800 grade foam backed flatting pad, followed by the same with a 1000 grade pad. Two grades of 'Farecla' rubbing compound were then used before a final polish with T-Cut. A LOT of work, but work that should pay off in a surface quality of the final moulded parts (& ease of release from the moulds).

[Phil Clark]

Today was D-Day for the Sea Dart project. Work is now 100% complete on the pattern & Alex from TLJC has collected the pattern & delivered it to the scanning team who will be 3D scanning the pattern to create the basis for the CAD work that will be used to design the internal structure for the flying models.....................

Alex being a far better photographer than me has taken a series of fantastic photos of the complete pattern which I receive soon, so in the mean time.....a little sneak preview.

Phil

[maurice northcott]

Marvellous project and a beautiful representation of the original Phil...... Congratulations from all at the North London Club.

Do you think you will do any further work on it, or is your work fully completed?

[Phil Clark]

Thanks Maurice

Alex & I have spoken & we may have further involvement. Depending on how time goes, we may have some involvement in the final build of the 2 prototypes to get them done to fit into the time frame Alex has set down with the client. There is also the possibility of some static display examples being built for museum use (Alex has had enquiries about this), so there may be 1 or more non flying examples to be built as well.

.......time will tell.

Phil

[Phil Clark]

The Sea Dart patterns are now 100% finished. Alex from TLJC was with us for 2 days last week and took delivery of the patterns before delivering them directly with the 3D scanning team. Scanning is due to take place this week before the pattern moves again to the tooling company who will be making all of the moulds. Not only will the 3D scan data be used to help design all of the internal structure, wing spars, wing/fin attachment methods etc.....for the flying models, but it will also be used to help design the multi part tooling, parting boards etc......

There is still a long way to go but it is hoped the 1st test airframe will be ready to enter the water in late May, early June.........in the mean time, I'll endeavour to keep updates coming as and when I get any info through from the various companies who'll be working on this project now it's left Fighteraces.

The small 600pxl limit on photos doesn't help here........you really need to view the full resolution images to get a real idea of the work that's gone into the pattern.......but here's the small versions to give you an idea.

Thanks for watching in.......

Phil

[Alex Jones]

Phil and his team at FighterAces have done an outstanding job on this pattern. I just hope I can do it justice as the project moves forward. Great Work Phil... Thanks

Alex
The Little Jet Company

[Alex Jones]

The project should move quite swiftly now as we hope to get a basic prototype complete for May. This can be evaluated here in the UK ready to send abroad for flight testing although we are still in talks with the appropriate aviation authorities as this model breaks almost every rule in the book in most countries. I consider myself lucky to have such a good large model scene here in the UK. This is run by the LMA on behalf of the CAA which allows us to do almost anything with the correct oversight, inspections and flight tests. So a quick thank you to everyone involved in the LMA.

With phase 1 & 2 completed on schedule we can now move forward with the composite design. The next few months won’t actually see anything physical being built except the tooling. The time will be spent in CAD designing the internal structures, ski mechanisms and lay up designs etc… To facilitate this we are in the process of having the pattern scanned using blue light technology. There are many advantages to this that justify the significant expense of the process especially considering the resolution required to capture every rivet and panel deformation in the pattern.

Ordinarily on a project like this you would start with a CAD model, CNC the pattern and take the tooling from this. We don’t have the luxury of a CAD model which is where the scanning comes in. With the scan data we can accurately design all the internal structure but not only this we can now accurately determine the weight of the model before its built. This will significantly speed up the design process as weight it critical in determining how the model presents on the water. CG, ballast tanks, component position and many other areas of uncertainty can be designed in from the outset. Undoubtedly there will be changes in the design as there nearly always is but this allows us to get much closer to a finished model first time out.

The team at PES Scanning gave me a quick work flow run through of how they will scan the pattern along with a short demonstration starting with the photogrammetry. The scanning team have been very helpful through the whole process and I’m looking forward to seeing the results.

_DSC9626 by Alex Jones, on Flickr

_DSC9637 by Alex Jones, on Flickr

_DSC9643 by Alex Jones, on Flickr