Convair YF2Y-1 Sea Dart

[Dave Kellett]

The mind boggles, and the imagination runs riot with the thought of Phil Clark without any socks on, and trousers rolled up and paddling with pointed end in his hands !! ohhhh no pleasssssse. :-)

[John Greenfield]

On the servo side of things we decided to try the large Seiko servos, loads of torque but a little slow. They have a tie bar with a slot, this allows any disparity between the servo matching without loading the servo because they are fighting each other. It also allows movement of the elevon with one servo failed. This at least gives you a fighting chance depending on where in its travel it fails… a difficult situation but better than no control at all!

2ADBDE86-5AC5-438A-AF80-9F42D0618494-2 by Alex Jones, on Flickr

C8E443E8-328F-4C2B-80D9-B2B7CC3C8BFA-2 by Alex Jones, on Flickr

I have also designed a bolt on tray so we can try some other servos and decide what is best.

936BC4C8-6F9D-4952-AD55-F011F3E55A02-3 by Alex Jones, on Flickr

Redundancy with 2 servos but only one pushrod so not really meeting the requirements. On Over 20kg models where servos are ganged up like this (such as all flying tailplanes on big jets or gliders) we suggest 2 pushrods, one above the other, to meet the redundancy requirements.

John

[Phil Clark]

The mind boggles, and the imagination runs riot with the thought of Phil Clark without any socks on, and trousers rolled up and paddling with pointed end in his hands !! ohhhh no pleasssssse. :-)

I can assure you Dave, it'll not be happening....I'm allergic to cold wet feet!!!!

Phil

[Timothy Huff]

Ah, but it was an arresting image to conjur!

[Alex Jones]

Where does the time go? With the kids now off for the summer I can spend my mornings working rather than home schooling, I hope the circumstances will allow for a return in September.

So, onwards with the build…

Regarding the elevon mechanism I’ve been in close contact with Dave Wilshere and Phil Clark throughout the build and will of coarse do whatever the LMA require.

Our first thought with the elevon servos was 'torque' so we decided to try the Tonegawa Seiko PS-050 servos which do provide plenty of torque although they lack speed.

A video of the servos operating.

https://youtu.be/bn55FsDoiLo

They are slow as expected but also give feedback when the elevon is moved down and unexpectedly they appear rather notchy. They don't work well with the gyro due to all of the above. They also require a separate battery and BEC increasing the weight of the model by 2 kgs. We decided not to use these and go with another solution. Dave Wilshere did warn that we might encounter problems but sometimes you just need to see for yourself. They won’t be wasted as we have a few projects in the works where these will be appropriate.

A video showing the Tonegawa servos operating the left elevon.

https://youtu.be/nnceOhS8Do8

The next set of servos to try are the MKS HBL 388.

BE0A0D9B-E87A-4B9C-A371-6AB1CC1486D7-3 by Alex Jones, on Flickr

[Alex Jones]

Is there a way of embedding videos in the thread or is the only option a URL link? I couldn't see a way but thought I'd ask just in case.

[maurice northcott]

Hi Alex
Sorry I cannot help with how to embed a video, I hope others can. Just wanted to say I have watched your videos and thoroughly enjoying the whole of this thread from day 1. Please keep the videos and reports coming...... looking forward to seeing it take to the sky.This whole thing, the design, construction, finishing etc is absolutely stunning. Thanks everybody involved....

[Dave Kellett]

Hi Maurice
I for one could not agree more with you. It really is a wonderful piece of scale engineering and like yourself I am looking forward to seeing this take to the skies.
Congratulations Alex and your team, please keep us posted with the latest photo's

Dave

[Alex Jones]

Thanks guys,

I decided to try MKS because it's a brand I have experience with and the specification was within what we had calculated so thought I'd give them a go. I designed the servo trays to be removable so its very easy to try differing brands and specifications if these prove to be problematic.

Flight loads aren't really the problem... I'm interested to see how they react to the elevon hitting the water during our water based testing. Testing is booked for early September as long as nothing changes with the current travel restrictions... fingers crossed! Notice also that I have added internal lights within the hull. It's such a big area that for maintenance this seemed like a good idea, we also need to check for any water ingress using a borescope between runs and the lighting should help.

We've replaced the Tonegawa Seiko PS-050 servos with four MKS HBL 388. These give 68kg/cm (944 oz/in) at 8.4 volts and a speed of 0.14s/60degrees.

A short video showing the elevon, and mechanism.

https://youtu.be/KenOvBR26Ao

These worked well so we will see how they perform during the water based testing.

[Alex Jones]

If you remember way back I did a series of posts on the ski mechanism. This final video is where we are at with the model as of today with only a few scale additions to add, the velcro is just temporary! before anyone mentions it... Also the tubing will be black once it arrives from Festo.

It could do with being a little faster, I'm able to change the speed using manual meter valves within the fuselage so it's just a matter of tuning the setup.

I've used high flow festo valves for the actuation as the standard model valves couldn't handle the flow rates required. With these new valves installed and working from the transmitter it was all tested before the final electrical and pneumatic installation begins.

https://www.youtube.com/watch?v=DBIgF6bKAHU

[Alex Jones]

To round off the ski installation I thought I’d add this picture taken by one of the documentary guys to add scale to the model.

The skis are close to 5ft long and it occurred to me that there aren’t many models that you could stick your head in the wheel well… in this case ski well. There are other models approaching 4.5 meters (14’ 9⅛”) and larger but the sheer bulk of this always surprises me when assembled. It makes my 1/4 scale F104 look small even though they have similar fuselage lengths.

If anyone is ever near the Sun ’N’ Fun Museum in Lakeland Florida, take a look at the SeaDart near the entrance as it’s worth a visit.

A663EF20-9848-448C-92E3-3FB148EC78EE by Alex Jones, on Flickr

[John Greenfield]

Alex

"Documentary guys" Are you making a film about the build of the model?

John

[Alex Jones]

The development has been filmed over the last few years for a short documentary, I don't know where it will appear other than the usual streaming services I presume, but I'll make sure to provide a link on here when it's complete.

With the skis and elevons complete I can get on with the rest of the model.

I’m not a huge fan of after burner rings as they don’t look that great in photos and for my taste aren’t very realistic when operating, they just add weight for not a lot of benefit but its all personal preference. I did try and convince the clients to go without but their argument was that they are hoping for film and photos during those golden hours the rings may illuminate the spray during takeoff so wanted to give them a go. I can always remove the rings and wiring at a later date if they don’t work out.

4910B3BA-26FB-410B-B9F2-DE05AB8B5460 by Alex Jones, on Flickr

The first job was to try and make the ring splash proof, and disguise its presence which was just a matter of masking each light and spraying black.

The A/B lights are installed on a carbon ring that sits inside the main duct which allows a through flow of water. I’ve then designed a static part mimicking the look of the petals on the real engine that slots over this, you cant quite see the lights but should get the reflections off the exhaust shroud at least that’s the plan.

E88C3727-8172-4912-B9F4-76BA7EE24FF7 by Alex Jones, on Flickr

The carbon ring is also used to support the thrust pipe which is mounted inside the main duct using the bell mouth. This duct has a seal which compresses onto the aft turbine bulkhead when bolted allowing water to flow through the intake system. We expect sudden deceleration of the model when the skis submerge from the planed state so expect the following wave to enter aft the aft sections of the intakes. The full-size added considerable amounts of power during this phase to blast the water back out.

CB384615-E2ED-4F0B-820E-9598CE7AD960 by Alex Jones, on Flickr

669E03D7-0185-4349-A1B1-88EE0D620E1F by Alex Jones, on Flickr

[Alex Jones]

The main duct extends exactly 2mm aft of the last fuselage bulkhead to allow the addition of an o-ring which compresses into a recess in the exhaust shroud when this is bolted up, hopefully providing an effective seal.

3207BD95-4C0F-4168-8E45-0BA96A3EBDBB by Alex Jones, on Flickr

The problem with a hand built pattern which is then digitised and an internal structure designed in CAD is that you end up with a few compromises. Ideally I would have liked the diameter of the main duct to exactly match the diameter of the shroud but this wasn’t the case due to the large radius applied to the duct for moulding and its not exactly circular. The benefit is that it does create a small ridge to block water moving into the intake ducts caused by general surface conditions when the model is just floating waiting for use. It does however catch the light and draw the eye away from the scale parts of the rear end.

E73CAE32-D2FD-4F84-BE8B-785F6745156C by Alex Jones, on Flickr

Weathering applied to the shroud and inside edges of the thrust pipe help pull the eye to the static petals. Hopefully this creates a more realistic looking exhaust section.

D443A24B-1290-4590-866A-EC96ED1BD284 by Alex Jones, on Flickr

The lighting is courtesy of my sons Philips Hue gaming lights… I was just playing around with effects wondering if a better way A/B lighting would be to get light up the inside of the thrust pipe somehow… anyway, that’s as far as my thoughts went for the time being, perhaps on another model.

[Dave Kellett]

Hi Alex, hope you are well and managed to have avoided this covid-19 problem.
We haven't heard anything for a while now, and have been wondering how the Sea Dart is progressing? have you managed to carry out any water trials?

This may seem a daft question and I'm sure someone on here will give me a daft answer, but is the Sea Dart capable of flying off snow and ice because all in all it does have some pretty robust ski's?.

Take care and regards to you all,

Dave

[Alex Jones]

Alex,

How will this be manoeuvred from trailer or vehicle to the water normally? I imagine during testing it'll be a case of all concerned playing "rock-paper-scissors" until one poor sod takes their shoes and socks off to go paddling with the front end!

With the skis, I imagine it's not the easiest thing to get from dry-land to the water and vice versa? P'raps we could have a competition for a means to avoid Phil taking his socks off?

Sorry I missed this post and have just noticed it while getting up to speed with what I've done so far...

In answer to your question, the model will have a dolly that can be wheeled down a slipway. We need a few guys in the water but nothing some chest waders won't be able to handle.

[Alex Jones]

Hi Alex, hope you are well and managed to have avoided this covid-19 problem.
We haven't heard anything for a while now, and have been wondering how the Sea Dart is progressing? have you managed to carry out any water trials?

This may seem a daft question and I'm sure someone on here will give me a daft answer, but is the Sea Dart capable of flying off snow and ice because all in all it does have some pretty robust ski's?.

Take care and regards to you all,

Dave

Hi Dave,

I've been slow to update the thread I know... I plan on getting it up to date over the next few weeks so keep an eye out. I should be doing a few posts a day starting on Monday.

It's purely a water bound craft as the skis lift the aircraft out of the water to become a hydroski although if the snow was 3ft deep powder it might I suppose. I can say with confidence that we are not going to try

[Dave Kellett]

Hi Alex
Thanks for the reply.
So it seems it wasn't such a daft question after all.
So that leaves just one thing....Phil Clark (Fighter aces) is just going to have to roll up his trousers, and paddle out with the pointy end in his hands.
Take care, and I will be certain to be looking at the new posts when posted.

Dave

[Alex Jones]

While we’re on the backend I should probably mention the water rudders…

These use a 3D printed hinge box that is tied into a carbon structure. This is then covered with a carbon molding and all bonded together with Hysol.

E14BA8DD-C618-4056-9F28-0B6A1E420DF1-2 by Alex Jones, on Flickr

654E923F-7C47-4E14-82C6-ECA7B4F1FFC8-2 by Alex Jones, on Flickr

E0E15785-275D-4059-80A3-745F6E7F22C9-2 by Alex Jones, on Flickr

We decided to use waterproof (IP67) 50kg Savox servos for the rudders. These were tested for several hours submerged and kept working so we shall see how they cope being used in the real world.

If you don't know and are interested in what IP67 means… Water and dust proof connectivity products are defined by their Ingress Protection (IP) numbers. ... IP67 equipment is the most commonly found in the connectivity market. It is 100% protected against solid objects like dust and sand, and it has been tested to work for at least 30 minutes while under 15cm to 1m of water.

0C7C33E2-529C-43D9-8CA9-04DD7E0B9D5B-2 by Alex Jones, on Flickr

The geometry is set in such a way that with the rudder fully extended it's mechanically locked in that position reducing the load on the servo in the fully extended position. It will be interesting testing the turning radius with the rudders and without, we also have the ability to add asymmetric thrust.

[Alex Jones]

A short video on the water rudder setup.  The squeaky right rudder was binding a little with the exhaust shroud... it's no longer  

https://youtu.be/AIFpapopdxE