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Convair F2Y Sea Dart | American Seaplane Fighter Aircraft

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Convair F2Y Sea Dart | American Seaplane Fighter Aircraft

Old 08-04-2021, 02:14 AM
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DominicM
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Default Convair F2Y Sea Dart | American Seaplane Fighter Aircraft

Sharing video of the first water trials of this amazing 1:4 scale twin turbine powered Convair Sea Dart created by The Little Jet Company.

The Convair F2Y Sea Dart was an American seaplane fighter aircraft that rode on twin hydro-skis during takeoff and landing. It flew only as a prototype, and never entered mass production. It is the only seaplane to have exceeded the speed of sound.

It was created in the 1950s, to overcome the problems with supersonic planes taking off and landing on aircraft carriers. The program was canceled after a series of unsatisfactory results and a tragic accident on 4 November 1954, in which test pilot Charles E. Richbourg was killed when the Sea Dart he was piloting disintegrated in midair. The four surviving planes were retired in 1957, but some were kept in reserve until 1962.

In this first video you will see the Sea Dart on the water and accelerate to a fast taxi for the first time. Video of the second test is coming very soon!

SPECIFICATION:
Length (including pitot tube): 5 meters
Power: Twin JetCat P300s
Guidance: Jeti Radio
Electronics: MKS servos on Flight controls. Savox waterproof servos on Water Rudder.
Weight: 100 kgs with fuel

Dave Wilshere was in the chase boat with his fingers on the sticks controlling this amazing aircraft so I hope he will chip in with his experiences.


Last edited by DominicM; 08-04-2021 at 02:17 AM.
Old 08-05-2021, 11:51 PM
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Day 2 of water trials of this amazing project with commentary from Alex Jones of The Little Jet Company.

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David J Ruskin (08-06-2021)
Old 08-06-2021, 10:23 AM
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LGM Graphix
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So maybe there is an obvious answer I'm not seeing but if there is such a range of speed between the water rudder and main rudder both being ineffective and having no directional control, but one of your problems being that the ski's if not extended exactly the same amount causes a turn, then why not allow the ski's to be controlled independently mixed to the rudder so that they can give some directional stability? I understand that they need to extend fully to reach the angle of attack needed but while doing that why couldn't they be allowed to move to turn the model and avoid situations like heading towards the reeds?
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Old 08-06-2021, 10:51 AM
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Alternatively, mix rudder with throttle, so that with (say) left rudder, the left engine throttle is commanded to some % less than nominal, to give some amount of differential thrust.

As this is needed during take off with full throttle commanded, the engine on the side of the direction of the rudder command would need to have a thrust reduction, as obviously no additional thrust on the opposite side is available.

While the engines are close to the center line, the effect isn't likely to be large, it may be enough to overcome the asymmetric drag of the skis.


Paul
Old 08-06-2021, 12:20 PM
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The testing does not really reflect where we hope to fly it. The narrow lake, speed boat close by creating wake, wind around the high trees all influence the tracking. When both ski come out equally it tracks straight and you can steer it on air rudder-what Alex meant was there is not enough power to overcome unequal ski heights.
We have asymmetric thrust available, it’s used on just about every run to help turn it in the narrow ski lake.
I’m convinced in open water with the wind on the nose it would be fine as it is, Alex was concerned that at full power it was not overcoming the drag fast enough, I feel that with air under the wing it will break that much quicker…we just have not found a lake that will allow us to run tests.

The time and investment in this project is huge, so we have been super cautious, also you can see I’m holding down in on some of the early runs, we don’t yet have flight permission, so we did not want it to unexpectedly leave the water!
It’s easy to reflect after, but watching the full scale film I can see it’s going to need a good pull to ‘unstick’ so I don’t think it would have ever unstuck on that lake…but it was not worth the risk at the time.
We expect a little more thrust with a revised tailpipe set up, that and some wing lift I expect it to accelerate quickly.

I think we will all be more relaxed without so many obstacles nearby 😉
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Viper1GJ (08-06-2021)
Old 08-06-2021, 06:13 PM
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Ron S
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I was going to ask if this was where you were going to fly it, but I think you answered my question "The testing does not really reflect where we hope to fly it." Cuz it looks like you're gonna need a bigger lake.

When you speak of unsticking the model, is it the skis that need to unstick? If so, would adding steps on the bottom of the skis help? I thought it could also be the aft lower wing too, but on the last portion of the video, it appeared the lower aft wing was clear of the surface of the water, which I'm sure you're happy to see...

I understand the issue of throttling down the model, and as it settles in, your trailing wake moves and swamps the back end - that stinks... Perhaps a longer lake could provide more planing time on the skis without having to do that...

Nice video production, Dominic! Good luck guys - keep pressing on!
Old 08-06-2021, 10:23 PM
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No, there are high trees surrounding this lake….I’ve driven right past it for 35 years and had no idea it was there! We need much more space for flight. The video only shows a couple of runs, Alex was not always filming, but we did multiple runs and each one taught us something, we did have a couple of runs where just as I was running out of lake it seemed to ‘skip’ like it was starting to unstick. The ski angle acts like a step, once it’s on the back of the ski the rest is clear of the water. Alex felt the flexing on the back of the ski was increasing the drag, I still think in open air it will lift clear of that much quicker, but we don’t know for sure and when we finally commit to flight, which is a huge logistical Job we want to have options.

Dave
Old 08-07-2021, 07:08 AM
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The changes we talk about in the video are all data driven. We have huge amounts of data from each run that took a good week to sift through but the direction was clear. With the skis at an angle of 5 degrees (oleo retracted) the maximum speed possible is 32kts but to reach this speed it takes 300 meters. This distance is unacceptable as we could end up needing 4 - 500 meters just to get airborne! The key to the whole takeoff is getting the rear fuselage out of the water. With the skis at 5 degrees it's just not possible to get the tail far enough out of the water to reduce the drag, in fact the speed stagnates once the thrust matches the drag and this can be seen on the telemetry. We could run in that configuration indefinitely and it would just sit at 32kts with full power. I agree with Dave that given the space we could get up to 30kts then extend the oleos cope with the slight asymmetry which results in a turn, this will eventually even out and I'm sure then the rear fuselage would rise out of the water... this however, requires a lot of space and isn't practical as we would need to be in a large expanse of water on a RIB at high speed, there is an unacceptable amount of jeopardy in that scenario which I'm unwilling to accept.

There is an optimum ski angle that will allow us to accelerate a lot quicker. An example of this was when we did extend the oleos the data shows a 3kt speed increase in under 1 second before they fully extended and the model started to slow. The reason it slowed was the extension was only at 20kts which is well below the speed required to support the aircraft on the aft ski footprint. It did show that when the skis started to extend they transitioned through a ski angle where acceleration greatly increased. By changing the oleos to hydraulic actuation we can experiment with differing angles and I believe greatly reduce the distance of the takeoff run which will allow the pilot to be stationary either on the bank or in a boat while flying. Currently it takes 18 meters to reach 16kts then a further 282 meters just to accelerate another 16kts! We can do much better than that and these changes should help reduce that distance significantly.

Using asymmetric thrust during the takeoff would be interesting and probably help but comes with its own issues especially during the early flight phase. Using a massive expanse of water and piloting the model from a Rib at speed while living with the heading change on oleo extension would also work but none of these solutions are actually addressing the core problem. I hope our chosen direction does... Fingers crossed!!

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Old 08-07-2021, 07:31 AM
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Originally Posted by LGM Graphix View Post
So maybe there is an obvious answer I'm not seeing but if there is such a range of speed between the water rudder and main rudder both being ineffective and having no directional control, but one of your problems being that the ski's if not extended exactly the same amount causes a turn, then why not allow the ski's to be controlled independently mixed to the rudder so that they can give some directional stability? I understand that they need to extend fully to reach the angle of attack needed but while doing that why couldn't they be allowed to move to turn the model and avoid situations like heading towards the reeds?
We're using pneumatics to control the oleos with a large volume at high pressure, they are either retracted or extended, there is no proportional control. It has crossed my mind to have them independently controlled but with pneumatics it won't help as the control couldn't be finessed quickly enough to help or even proportionally. Hydraulics will allow a degree of finesse and they won't be affected by unequal loads if the model has any roll when we deploy the oleos.
Old 08-07-2021, 12:41 PM
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Electric actuators,? Been using then on a lot of large UAV stuff for years. They are drop in drop out with a simple electrical control.

Very high force are available and you can get feedback and IP rated and also fully waterproof. Pricey yet you get what you pay for.

Good company is https://www.ultramotion.com/linear-actuators/#u-series

Who ever is backing this project obviously has deep pockets, it would be wise to look at CFD analysis to give you baselines for a lot of the questions you have. Water is a very tricky medium, as the waters surface is disturbed the normal effect of compression is reduced and is no longer uniform.

Green Marine was a good company in the UK for high end superyacht work they also did CFD work on high end racing yachts. They closed some time ago yet a company like that could help.

At 3 minutes into the video what was the throttle at?

Regards,

Last edited by Halcyon66; 08-07-2021 at 01:13 PM.
Old 08-07-2021, 01:14 PM
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I've used Ultramotion actuators before, in wind tunnel models. Used them with programmable controllers - pretty neat. Heavy in our case, but we were not limited in that regard. Using CFD to describe the interaction between the ski, and an air/water mediums could go down a rabbithole $$$ - unless someone picked it up as a "pet project".

But I think Alex's team will eventually get there.
Old 08-07-2021, 01:32 PM
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CFD $$$ have come down dramatically, yet as above the best guys for this would be yachties. I think you could get someone on this for not a huge outlay, as it looks like the model is actually all done is CAD that is haft the battel, the rest is constraints and the like.

You could approach a Uni to try and get them to do it as a group course or the like. $500 dollar price for the team that gets it sorted would certainly help. Or you could find the boffin that is really interested and just wants the kudos.

Canfield University would be a good start as well.

Regards,


Old 08-08-2021, 01:02 AM
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Hi Guys,

Thanks for the comments, I really enjoy the theoretical side of this project and it's good fun overcoming the inevitable challenges we face.

I do like those actuators but it would require a complete re-design of the oleo, we also need something that can withstand high shock loads. With this in mind the diameter of the actuator would be too large compared to the scale diameter of the oleo. With fluid all I have to do is fill the oleo we currently have with oil, add a pump and ESC and away we go.

We do run post grad courses but the scope of what I'd be asking is rather large for a Masters student given the time allotted for their projects. They need to be sorted in the Spring for tutoring in the months leading up to Christmas so the earliest we would get any results would be January 2023 as we have missed the window for this years students.

The work required for meaningful CFD is immense and not practical at this point due to time constraints with other projects. It would only tell us (assuming no correlation difficulties) what we have learnt so far in our real world testing. Of course it would help narrow down the ski length and optimum ski angle for the second phase acceleration but we would have to test that regardless which is what we are going to do anyway so its easier just to skip it all together. 🤞

We hope to get it back on the water in the next few months, with luck it will work as intended and we can move onto flight.

Cheers, Alex

Last edited by Alex48; 08-08-2021 at 03:46 AM.
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Old 08-08-2021, 01:56 PM
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Alex when you say you’re running post grad courses can you elaborate?

The project is definitely impressive yet again with the $$$ going into the hole, CFD cuts corners efficiently without the potential loss of what is I am sure is a very expensive airframe.

Your project is far outside the realms of model aircraft and into the UAV side with weight and complexity.

Regards,
Old 08-09-2021, 03:06 AM
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I do agree regarding the CFD... but with the hydrodynamics already tested in the real world and our data from these tests giving a clear direction I just don't see the benefit. I will of course keep everyone up to date (warts and all) and if I'm wrong I'll be the first to admit it! I've sent you a message regarding our University work.

Cheers, Alex

Last edited by Alex48; 08-09-2021 at 03:43 AM.
Old 08-09-2021, 08:40 AM
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Maybe a improvement? Seems simpler wich is always better, and it is scale too, as the Convair guys faced similar problems developing the full scale prototype.





Last edited by erbroens; 08-09-2021 at 09:10 AM.
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Old 08-09-2021, 02:50 PM
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From my experience with testing and developing racing boat hulls for RC I have to ask are the skis or the fuselage/hull aerated?
There are discreet ways to help mix in air to free up the hull and skis and keep the scale fidelity.
Old 08-12-2021, 04:23 AM
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Hi guys, thanks for all the comments, we'll get there eventually and hopefully have some fun along the way

The single ski was developed due to the huge vibrations evident in the twin ski design. They tried but failed to get rid of these vibrations which is where the single ski comes into development. We have no such vibration issues on our model and nor did Convair on their 1/4 scale test platform.

The key is the ski angle so developing a variable geometry oleo which can be controlled and stopped at any angle is our priority, we're currently looking at hydraulic and electric options. Currently the ski angle is either at 5 degrees or 15 degrees so we need to finesse the system. 🤞


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