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US NAVY SeaDart F2Y (Flying boat) Build

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US NAVY SeaDart F2Y (Flying boat) Build

Old 08-06-2020, 12:10 AM
  #301  
Alex48
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Onto assembling the oleos... This was a relatively simple affair. I cleaned up the machined components and polished all the surfaces to the specified finish which should help the stanchion move freely in the oleo. The seals were installed and the entire assembly greased. They were tested overnight with no pressure loss seen.

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Old 08-06-2020, 12:12 AM
  #302  
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With the oleos assembled and installed we could move on with getting a better understanding of how our ski retraction system works. The first task was to add pressure to the rear actuation while moving the front of the ski by hand. We’re using relatively high pressures (for a model) with large pneumatic rams some capable of large linear forces that would happily crush your hand. With this in mind we started off just adding a little pressure with a hand pump to the extension stroke of the ram.

We designed the gear to retract on ram extension as you get the most force from the ram on this stroke and we knew that we needed all we could get due the short moment involved. Initially I had chosen a set of large Bimba actuators for the rear retraction but on reflection this was the wrong choice as they were very industrial and on the heavy side. I had squeezed the largest actuators possible into the space available and really it was too tight for these. I changed the design to accommodate two Festo DNSU-25-60-PPV-A actuators. These have a bore of 25mm and a force of 29kg on the extension stroke at 6 bar (87psi). These actuators are light, well made and being off the shelf readily avialable.

Our first attempt captured on my phone.


The main pivot block is only dry fitted but as you can see in the above video the ski retracts but not in the correct position. It seats too high in the ski well hitting the top edge of the well aperture. This isn’t entirely unexpected… Ourselves and the engineers we worked with on the ski mechanisms could never get it to function in CAD as we would have liked. We built in ways of moving the geometry to try and achieve a scale retraction. The twist in the ski you saw was one of these variables moving to help the retraction. This is not scale but does help us get closer to the desired actuation.

We are able to move the geometry of the two most crucial elements in the system. The first is the position of the main slider bar as seen in the below picture. Once the ideal position is found I’ll have a carbon part made which will plug all the gaps and make this section watertight.

IMG_0305<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

The other variable geometry change we can make is the rear ski attachment point. This is a crucial angle which effects how the ski retracts and how it sits in the ski well.


IMG_0303<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>


Old 08-06-2020, 12:13 AM
  #303  
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With the ski in the correct position when retracted it binds on extension and just won't move if we have it extended and try to retract it. There is a balance somewhere in the geometry that will make it work but we now have to make small steps from the extended to retracted position to try and hone in on the correct balance of geometry's.

Incidentally through our research we don't believe the original worked that well to begin with. The two video clips we have show a rather staggered affair. Also the two clips show different sequence of retraction. Reading between the lines in some of the test pilot notes indicates that perhaps this was the case.

You can see the skis retract on this footage from critical past.

Old 08-06-2020, 12:14 AM
  #304  
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After much fettling with angles and changing the offset claw on the main oleo to be central we got a ski that retracts into the ski well. I’d say we were about halfway there as it is still a very modular retraction. The sequence works slightly better with a different actuation order of the front and rear rams but I didn’t film this.

I’m happy so far in that it all seems to be going in the right direction but I do have some redesign work as there are clearly a few issues which I’ll detail in the next posts. Nothing insurmountable but I’m confident I can get a really smooth scale retraction with a little more work.

Old 08-06-2020, 01:02 AM
  #305  
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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.

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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.


IMG_0314<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

This hopefully solves the issues internally, we now need to address the problems in the external mechanism and main pivots.
Old 08-06-2020, 01:05 AM
  #306  
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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 the post production CMM reports on the 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.

PB102 Bushings<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

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

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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

IMG_0356<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>


Old 08-06-2020, 01:08 AM
  #307  
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Wow!!
Old 08-06-2020, 01:22 AM
  #308  
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Alex

You have a calculation on the ‘shock’ pressure on the Oleo Festo fitting? I have seen those plastic ones burst when used on landing gear suspension.

Dave
Old 08-06-2020, 01:25 AM
  #309  
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Thanks

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.

_DSC8171<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

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After the third design iteration we are getting close to what we started out to achieve.


Old 08-06-2020, 01:42 AM
  #310  
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After a few more tweaks and some subtle design changes we have arrived at the final design of the mechanism. I've posted a lot of info today to quickly get to the state that the model is actually in with regard to the skis. If you've missed any of todays posts and want to see the ski mechanism development this section starts at post #300. These last 10 posts represent a huge amount of work spread out over a few years and a near mental breakdown

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 now.


I have a lake booked for the initial water based testing in early September so fingers crossed things work out to get everyone there. It won't fly during that test as we have a lot of work to do before committing to the air. It should be fun though...
Old 08-06-2020, 02:00 AM
  #311  
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Originally Posted by Dave Wilshere View Post
Alex

You have a calculation on the ‘shock’ pressure on the Oleo Festo fitting? I have seen those plastic ones burst when used on landing gear suspension.

Dave
Hi Dave, that hadn't occurred to me to be honest, the fitting used is rated to 14bar. The testing in September will punish the whole mechanism although the only way of really knowing is to actually land it. Can you remember what burst? was it the pipe popping out of the fixing? I can look at other fittings that are not push fit. Thanks for sowing the seed of doubt I'll see what is available and do some quick maths.

Last edited by Alex48; 08-06-2020 at 02:04 AM.
Old 08-06-2020, 05:43 AM
  #312  
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It was the black plastic! I think the landing shock obviously over pressured it, tube will expand, but the hard plastic fitting either holds or bursts! I’m presuming there is no mechanical lock. The weight and beating water is going to give the skids will be tremendous 🙂
Old 08-06-2020, 12:29 PM
  #313  
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https://www.ultramotion.com/

These guys make electric actuators in a league of there own. IP ratings and huge outputs in small footprints.

Regards,

Old 08-07-2020, 02:01 AM
  #314  
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I like the look of those actuators! I'll bear that in mind for the next SeaDart build...

To round off the ski installation I thought Id 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 arent 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 its worth a visit.

A663EF20-9848-448C-92E3-3FB148EC78EE<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>
Old 08-07-2020, 02:04 AM
  #315  
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Originally Posted by Dave Wilshere View Post
It was the black plastic! I think the landing shock obviously over pressured it, tube will expand, but the hard plastic fitting either holds or bursts! Im presuming there is no mechanical lock. The weight and beating water is going to give the skids will be tremendous 🙂
I think they do metal versions... I'll take a look and see if I can replace them.
Old 08-07-2020, 01:29 PM
  #316  
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They do 🙂
Old 08-07-2020, 01:56 PM
  #317  
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They are great even work for aircraft surfaces and rotor heads, around 1500 a unit give or take yet risk reward ratio comes into play.

Just my 2 cents yet something that big, probably that heavy and guarantee that expensive, I not sure why an air system would be variable.

Regards,


Old 08-08-2020, 02:26 AM
  #318  
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We had to use air for the large oleos so they can retract fully for ski retraction with all the associated peripherals so this was onboard anyway. Using large bore air cylinders means we can use low air pressure and we have space for large volume lightweight tanks. I cycled the skis on a test stand over 100 hundred times and it works reliably. Although this model looks expensive we have had considerable sponsorship throughout and like everything there is a limit to the budget. Festo cylinders and fixings are cost effective, reliable, and I know their capabilities well so the client doesn’t have to pay for any learning or development time on our end with regard to systems use. Although for the next one...

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 and 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.

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The first job was to try and make the ring splash proof with sealant 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<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

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 a sudden deceleration of the model when the skis submerge from the planed state so expect the following wave to enter 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<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

669E03D7-0185-4349-A1B1-88EE0D620E1F<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

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.

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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<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

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

D443A24B-1290-4590-866A-EC96ED1BD284<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>\

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.

Last edited by Alex48; 08-08-2020 at 02:39 AM.
Old 09-07-2020, 01:42 PM
  #319  
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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.

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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 your 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<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

The geometry is set in such a way that with the rudder fully extended its 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 if required.
Old 09-07-2020, 02:47 PM
  #320  
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A short video on the water rudder setup. The squeaky right rudder was binding a little with the exhaust shroud... it's no longer

Old 09-08-2020, 02:18 AM
  #321  
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I like the systems side of things and always enjoy this part of any installation but before I start on the electronics I had to accept that no matter how hard I try water will find it’s way in. This maybe from wet hands while servicing, seals below the waterline or spray getting inside the hatch seals, either way it’s worth protecting the electronics. If I accept that it could get wet inside then all the electronics have to be splash proof so I designed splash proof boxes to protect the electronics. These are 3D printed SLS items with an O-ring seal and perspex lid. Below are some images from the CAD work I did…

43696B13-B225-4C32-9D19-752CB334EB62<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

A3DECA13-799D-40AF-A224-F8C3F2E24892<script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

I have provided cooling for the CB400 and pneumatic boxes which will maintain these areas at ambient. Tests with the equipment in the centre fuselage show an increase above ambient of 10 degrees which is well within the operating range of the electronics so I decided not to include cooling in these areas. We’re well within a decent safety margin if operating the aircraft in temperatures that don’t exceed 40C/104F.
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Old 09-08-2020, 09:01 AM
  #322  
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40 degrees ????
An ambient temp of 30 degrees when model sits in the sun will quickly surpass the inner temp of 40 degrees ..

temps are getting higher and higher every summer all over the globe , Id suggest to reconsider a cooling solution
Old 09-08-2020, 09:21 AM
  #323  
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Not in the UK...on water
Old 09-08-2020, 10:25 AM
  #324  
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We have telemetry data indicating the temperature in these areas and can add cooling to the other electronic bays as necessary. It will have hours of testing just on the water so we can gather data to support any changes if required.

The first set of tests will concentrate on making sure its a good RC boat the second set will make sure its a good RC hydro ski and the third set of days.... I don't think I'll be watching!


Old 09-08-2020, 01:28 PM
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Hope all turns in your favor

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