Convair YF2Y-1 Sea Dart

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Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 7th, 2019, 11:35 am

Thanks guys, We're glad you're enjoying following along.

Antenna position is something we've thought carefully about. We have four 2.4Ghz antennas and two 900Mhz antennas as a tertiary backup. The entire fuselage monocoque is glass although as you say we do have aluminium and carbon structure. The antennas will be placed in the nose, tail and central in the fuselage. We have telemetry on each antenna which will be reviewed after each flight and actively monitored during the flight. I'm putting together the test schedules at the moment... This certainly isn't a model to just stick in the water open up the throttles and hope for the best :) There will be several weeks of ground testing both in and out of the water here in the UK before it's committed to flight. Test flights won't be in the UK... we're still trying to finalise with the relevant authorities as to the exact location but most likely this will be a military testing area with requirements for range officers, fire fighting provisions etc... I've digressed slightly mainly to emphasize our approach to testing. However the ground testing antenna reception will be monitored closely. One of the first things to do is range test with the aircraft in all the possible worst orientations for signal strength etc... We'll see how we get on and change antenna positions as necessary. The idea is that at least two antennas are visible with a line of sight not obscured by anything that will attenuate the signal. This is where our CAD model becomes very useful.

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 7th, 2019, 1:53 pm

Hi Guys,

As I mentioned in my last post several design modifications were required. Starting with the actuators, these had been checked in CAD and the lengths required were 60mm. In reality this stroke length worked as designed but we never allowed for any slop in the system. The stroke needed to be extended by 5mm so the mechanism could lock. This applied to the rear rams and the forward ram. I also wanted to use a larger diameter ram on the rear actuation as the pressures involved with the 25mm ram currently installed were increasing up to 10bar to get a smooth retraction. We can get a similar level of force at 6bar with a 32mm diameter ram. Changing the rams required a redesign of the mountings. There is a lot of force going through these so we used a 6mm carbon former to mount 4 CNC’d brackets which secure the rams. A ‘U’ shaped 6mm carbon former was installed to transmit the load into the fuselage via the forward spar box. Below shows the new mountings although I still haven’t bonded it all to the side of the fuselage yet.

ImageIMG_0309 by Alex Jones, on Flickr

ImageIMG_0313 by Alex Jones, on Flickr

The actuation for the front has been tweaked and now uses 6mm carbon. The front ram works both skis. If there is a failure we want it to be symmetrical this is particularly important at the front.

ImageIMG_0314 by Alex Jones, on Flickr

This hopefully solves the issues internally, we now need to address the problems in the external mechanism and main pivots.

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 13th, 2019, 1:29 pm

The next issue to address is the unacceptable amount of mechanical play in the mechanisms. If we take each individual pivot point and test it for play we might be forgiven for thinking it seems a good fit. But put those same 17 pivots together and ask them to move at the same time, suddenly it becomes more of a problem as the play on the small moments is amplified significantly. By the time you get to the bottom of the ski the whole thing can move to a level that causes us concern.

The first issue was the PTFE IGUS bearing bushes we had used on every joint. We had a meeting with their rep before committing to these and explained the application etc… All our components were designed at the correct tolerance, however, they just had too much play. I was expecting a nice tight fit and was fairly annoyed at the results. The only option left to us was to design our own bearing bushes. For this we used Phosphor Bronze PB102 and set about designing every bush in the mechanism. Using a set of callipers on our machined components we designed the bushes to have H6 and G6 tolerances which are within 9 & 14 microns (0.009.0.014mm) respectively. This will cure the play between all the pivot shafts and their bearings. Overall I think there are about eighty of these phosphor bronze bushings installed in the mechanisms.

Not the most exciting picture I know but you should get the idea.

ImagePB102 Bushings by Alex Jones, on Flickr

Alan Cantwell 1131
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Re: Convair YF2Y-1 Sea Dart

Postby Alan Cantwell 1131 » February 13th, 2019, 5:10 pm

Using a set of callipers, really? :D Hmm,

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 13th, 2019, 7:20 pm

Well that and the post production inspection reports and some CMM :) But I still do like my calipers.

Alan Cantwell 1131
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Re: Convair YF2Y-1 Sea Dart

Postby Alan Cantwell 1131 » February 13th, 2019, 8:52 pm

Cmm is more like it, calipers are only good for .1mm. Looking good though,

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 13th, 2019, 9:48 pm

Thanks Alan, we're getting there but slower than I would like, although that probably applies to everything :(

The other area of concern was the main pivot on the rear mechanism. This had been designed in two parts consisting of the SS shaft with one o-ring seal groove and a SS clevis. This holds the main arm which connects to the oleo and moves it along the slide bar. The two slide together and lock using a keyway. This keyway had a small amount of play but even this amplified to an unacceptable level by the time it got to the oleo, compounded by the IGUS bush installed into the pivot block. Unfortunately I was unable to get this out without risking damage to the block.

Original pivot and clevis

ImageIMG_0333 by Alex Jones, on Flickr


We re-designed this whole area and included what the original had to support the main pivot externally. We increased the shaft diameter to match that of the IGUS bush and combined both original components into one single machinable component while reducing all the tolerances.

Re-designed pivot and clevis

ImageIMG_0356 by Alex Jones, on Flickr

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 21st, 2019, 9:49 am

As I said in my last post we decided to support the main pivot externally which is exactly what they did on the full size. I assume for a similar reason. We tried to keep it as scale as we could within the confines of actually having a functioning part. The top hat is removable to allow the main pivot to slide out if required for maintenance. Like before all the tolerances have been reduced and it the top hat runs on a PB bush. This works as expected and removes all play in the pivot.

Image_DSC8171 by Alex Jones, on Flickr

ImageIMG_0379 by Alex Jones, on Flickr

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 21st, 2019, 4:08 pm

After all that work here is a video showing the final iteration of the skis and mechanism working as intended... yay :)

Ski Retraction Video

maurice northcott
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Re: Convair YF2Y-1 Sea Dart

Postby maurice northcott » February 21st, 2019, 8:41 pm

Fantastic posts on a fascinating Project Thank You Alex ....... I don't say much but have been looking forwards to your next posts throughout. This aircraft intrigued me from the first time I saw it way back then.......and I look forward to seeing further posts and eventually the first flights of the model..... Thanks for keeping us informed.

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 25th, 2019, 10:31 am

Hi Maurice, Thanks, I'm glad you're are enjoying following along. I'm looking forward to getting into the water although I can't say I'm looking forward to the first flight! :)

With the relief of finally having two functioning skis we can turn our attentions elsewhere. Part of the brief was to get realistic in cockpit footage to try and recreate what it might have been like to fly this aircraft. There are three separate camera angles, one behind the pilots shoulder, one looking up from behind the rudder pedals and a head camera on our pilot. With the brief in mind we decided on a fully functioning animatronic pilot. We’re using servo driven flight controls that will move the pilot. The below images show the mechanics of this.

Flight Control Stick

ImageIMG_0293 by Alex Jones, on Flickr

ImageIMG_0294 by Alex Jones, on Flickr

Thrust Levers

ImageIMG_0332 by Alex Jones, on Flickr

Everything mounted in place including the mechanisms for the rudder pedal movement.

ImageIMG_0334 by Alex Jones, on Flickr

Parts are a mixture of 3D prints using SLS and CNC’d Aluminium. We had to make a few changes form our initial designs which included larger servos and some reinforcement but after this it all works nicely.

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » February 26th, 2019, 8:45 am

Time for some of the fun stuff… Starting the scale work on the cockpit…

ImageIMG_0301 by Alex Jones, on Flickr

ImageIMG_0304 by Alex Jones, on Flickr

Timothy Huff
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Re: Convair YF2Y-1 Sea Dart

Postby Timothy Huff » March 1st, 2019, 2:19 am

Hats off to you sir, for some beautiful engineering, and a very courageous and unusual choice of subject craft.
Some questions if I may:

Have you had to make provision for keeping water out, and if I can't be, how to keep it away from electronics etc? When landing, I presume you have to design for the eventuality of a capsize and or sinking at some point. If so, it is possible to incorporate some facility for flotation and or self-righting, again with the view of protecting the model from water-damage?

The reason I mention this is that a little-known feature of the Wellington was internal flotation bags in the "roof" of the bomb-bay. These bags could be inflated before impact with the sea, but also had immersion-switches to self-inflate on ditching, so far as I'm aware the only aircraft of that era that possessed them. I don't know much at all about the sea-dart, but one would think that some provision for flotation was provided...?

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » March 4th, 2019, 11:02 am

Hi Timothy,

Thanks for the encouragement and your thoughts, the closer we get to water trials the more worried I become!

All hatches are above the waterline and have rubber seals which I hope will keep the water out. The intakes are completely sealed from the fuselage so you can spray as much water down these as you like and it will just come out of the other end. We have internal lights in the fuselage with cameras providing live feeds during testing to see how things are holding up. We've also considered a bilge pump although I haven't really considered a complete capsize until your post. I'll have a talk with the client and see if we can incorporate something as it's a good idea even if its only a temporary solution during initial testing until we're confident of the hulls integrity and the models handling on water. Food for thought... and thanks for pointing it out.

Cheers, Alex

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » March 4th, 2019, 11:03 am

I’ve always enjoyed building small plastic models although time constraints mean I haven’t done so for years but I do still have all my paints and weathering materials etc… many of the techniques used by the plastic modeller can be scaled up to suit our needs. I started by doing some subtle weathering to the floor and rudder pedals using several different enamel washes and pigments. Using a water based paint for the base colours you can then use an enamel wash and work this in using a brush wetted with sprit until you have the level of weathering you desire. Dry pigments used sparingly can add some depth. It’s subtle at this stage but when applied to everything in the cockpit I hope it will soften it and make it look more realistic. (Fingers crossed)

Before

ImageIMG_0318 by Alex Jones, on Flickr

After

ImageIMG_0319 by Alex Jones, on Flickr

Timothy Huff
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Re: Convair YF2Y-1 Sea Dart

Postby Timothy Huff » March 4th, 2019, 2:11 pm

I love the weathering/distressing of the heel-plates. The screws probably ought to be countersunk, as something that could arrest your heel when applying rudder would be undesirable from a pilot's point of view. Regarding the flotation etc. My guess is that a bilge-pump that can clear a lot of water quickly would be prohibitively heavy. On the other hand, trying to take-off with a keel full of water from a previous flight, migrating to the rear fuselage as it accelerates could "end badly", so it's clearly an important issue.

Do the skis have any intrinsic buoyancy themselves? I figure they must do to keep the fuselage clear of the water before takeoff.. If so, the answer may be to add buoyancy to the upper fuselage, and put electrics on the midline, so whether it's on its skis, or capsized, the batteries etc remain above the waterline in both cases. Now that I come to think on it, I think self-righting would be very difficult, in much the same way as righting a capsized sailing boat is difficult if the sail is under-water.

The other line of thought you might like to look at is provision for a removeable bag of a suitable dessicant, which would be removed before flight, which might mitigate corrosion within the fuselage of metal and electrical components. it could be something simple like a muslin bag of rice...

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » March 5th, 2019, 10:29 am

Hi Timothy,

Strangely those screws are exactly what the original had from our historical images. Like you I would have had them countersunk. :) If you are ever in Florida take a detour to the Sun 'N Fun Museum where they have one on display. It's built like a cruise ship rather than an aircraft and for a single seat interceptor the size is impressive.

I had thought of putting the electronics in sealed boxes, I can make very cheap SLS printed items with o ring seal groves and bolt clear lids down on top. It would be relatively simple to design a circuit that could detect water in the keel and mount sensors to send telemetry back to us. Our initial buoyancy testing in a swimming pool will certainly be interesting.

The skis are designed to be neutrally buoyant.

Cheers, Alex

Alex Jones
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Re: Convair YF2Y-1 Sea Dart

Postby Alex Jones » March 5th, 2019, 10:32 am

After a little weathering this is short video showing the movement of the flight controls. The flight controls drive the pilots movements hopefully giving the effect of the reverse once we tweak the speeds and throws etc... less is so often more.

https://www.youtube.com/watch?v=tH_QFpAnZyw&list=PL2xOSRvupovQGPXq9etwSY777nc7s3eJr&index=9&t=0s

Timothy Huff
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Re: Convair YF2Y-1 Sea Dart

Postby Timothy Huff » March 7th, 2019, 8:57 pm

Alex,

I've been watching the performance (and learning as I go)) of the full-size aircraft and thinking further about the model. One of the really critical aspects is going to be the relationship between the inertia of the model, and the movement-rate for a given force applied of the shock-absorbing oleos. If the latter are too stiff, and the airframe too light, then I instead of compressing the geometry of the ski's, it'll cause the nose to pitch-up and throw it in the air with low airspeed. Too soft and it'll do a passable impression of a submarine crash-dive!

How on earth will you work that one out? Lots of taxi-trials starting at the harder end of the spectrum? I'm starting to see what an amazing achievement this aircraft was.

Dave Kellett
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Re: Convair YF2Y-1 Sea Dart

Postby Dave Kellett » April 2nd, 2019, 7:36 am

PM Sent


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