The Model (Phase 4)

Apologies for not updating this sooner but over the next few weeks we should get to it all finished up to the current state of the model.

With the beaching gear nearly completed we wanted to test fit it to the model to check it was fit for purpose before using it. A few small changes required but it works as designed and is stable even without the lateral supports connected to the rear ski mechanism. Buoyancy will be an issue but we will see how much of a problem it is in the first water test. If necessary we’ll add holes to allow the tubes to flood with the main wheeled section probably requiring a few kilos of weight to be bolted to it.

This is with the beaching gear in the extended position and no lateral support allowing the ski oleos to actuate and the skis retraction to be tested before it goes into the water.

by Alex Jones, on Flickr

by Alex Jones, on Flickr

A scale model wouldn’t be the same without at least some head scratching. :)

Photo 30-07-2020, 11 33 21 (1)
by Alex Jones, on Flickr

Please note these are not current pictures, the various COVID restriction we now face were not in force when these images were taken.
I managed to finish the last of the installation on the electrics and engines before doing the first few engine runs. I always get excited seeing a model come alive for the first time. I was working insane hours to get it ready for testing so I didn’t take many pictures, those I have of the final engine installation are below.

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr
With the model ready for the initial engine runs we took it BMFA Buckminster. Phil and Graham from FighterAces came down to help as it needs three people to safely handle the model. Phil has been with us from the start of this project so I was pleased he got to see it run for the first time, I know its not as interesting as seeing it on the water but it was a big deal for me. :)

The team at Buckminster were excellent, very friendly and accommodating, I’m looking forward to testing some of our other projects at the site once we’re allowed out again. It was great to finally get to this stage and have everything working, although there is still much to do before it gets wet but at least things are now starting to come alive. The engines ran well after some tweaking with the initial start voltages. I wanted to make sure that the expense of hiring a lake isn’t wasted because we can’t get the engines started so a dry test seemed sensible when running them for the first time in the fuselage.

The beaching gear is shown here in its scale configuration with Phil giving it some scale. The model with the pitot probe attached is nearing 5 meters long so its not the smallest of things. :)

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr

by Alex Jones, on Flickr


Staff member
Phil from Fighteraces sent me a short video he took on his phone, Phil you need to get a better phone! [:)]

Battery wise, we have two 5500 2S Lipos for the ECU's, two 6200 LiIons on the the CB400 and two 3200 LiIons for the animatronic pilot, hull lights and afterburner rings.

Thanks guys :)

After the engine runs it was just a few weeks to go before the first water based tests which was going to be a push. We had to book the lake and flights etc… for the team months in advance and with the lull in the pandemic it was probably going to be our only chance to get some tests in this year. Anything we learn from these could be addressed over the winter ready for further tests when circumstances allow. Unfortunately the tests had to be private as we couldn’t accommodate spectators with the COVID restriction in place at the time.

The model above the waterline isn’t designed to be water tight but it is important that it is splash proof. One of the areas I’ve put off doing for a long time is the cockpit seal as I couldn’t decide on the best way to approach this. In the end we created a 1mm recess around the inside of the canopy and use 1.5mm neoprene rubber with a compression of 40%. This allows the canopy to close then the locking mechanism pulls it down compressing the seal but still keeps the canopy flush to the fuselage. Due to time constraints I couldn’t detail the canopy myself so luckily FightAces managed find time to do the detail work and make the recess. Within a few weeks it was back with me and looking really good. Thanks Fighteraces. :)

by Alex Jones, on Flickr

by Alex Jones, on Flickr

The locking mechanism consists of two conical latches that actuate via a servo. These extend into a recess on the front of the canopy and gradually pull the canopy down.

by Alex Jones, on Flickr

by Alex Jones, on Flickr
The moment I’ve been most looking forward to for years is getting the model in the water for the first time. There are so many possible problems that we’ve had to overcome purely in a theoretically sense. Time to see if it works in practice. No pressure then….

There are so many unknowns that we have to take the testing slowly ticking off each item as we go while gently building up to the more exciting stuff.

We found a suitable lake close to Cambridge for the initial tests at Dams Watersports in St Neots. The team there were very friendly and supportive and provided everything we needed. It is not an easy thing to explain to a company outside of the industry and I had some interesting reactions in my search for a suitable site. Most of these reminded me of that scene in Top Gun where the guy in the back seat exclaims “you’re going to do what” accompanied with some eye popping then a polite “no”.

We plan to test the buoyancy and general handling at slow speeds before we start to stretch its legs and get the aircraft to plane on its skis. The smaller North lake was chosen for the initial tests as its size was good for the first round of slow speed tests. The longer stretches on the south lake can be used for the higher speed runs if all goes well.

by Alex Jones, on Flickr

There is no escaping the fact that this is a complicated model and it does need a checklist to ensure nothing gets missed. A lot of time has been spent in the background on this checklist and checklists for the various tests.

by Alex Jones, on Flickr

The weather looked kind for the the days we had arranged so an early start got us on site at 0700. We found the lake had large deposits of floating weed which had only appeared in the last few days. When I scouted the site out the condition of the three lakes was perfect and I hadn’t considered this might change. For the slow speed work it didn’t matter but some thought would be required to find a clear path for any high speed runs. Much of the first day would be spent by the slipway anyway...

by Alex Jones, on Flickr

by Alex Jones, on Flickr

The first job was to get the model in the water and do a basic leak test along with checking the buoyancy. It needs to sit at the correct waterline or it will just look odd when compared to the real aircraft. Thankfully it worked out well… We did have a leak in the rear bulkhead where the rudder servo wire comes into the dry section of the hull. Unfortuantley this did cost us 3 hours as we had to get the aircraft out of the water dry the area, remove some internals before sealing the leak and putting it back together again. It was a bodge job but allowed us to carry on for the day… subsequently the model stayed in the water for over 5 hours without issue but it will be properly addressed before the next set of tests.

Sitting ready to go into the water for a second time.

by Alex Jones, on Flickr

No leaks and sitting how it should, time for some fuel...

by Alex Jones, on Flickr

by Alex Jones, on Flickr
A few pictures from the first test…

The model coasting out for the first time on one engine as the other starts to spool up.

by Alex Jones, on Flickr

by Alex Jones, on Flickr

And another with the model disappearing a haze of spray.

by Alex Jones, on Flickr

I am biased but it was much more impressive in person than the photos perhaps show. The rooster tail is over 30ft long and about 9ft tall coupled with the noise of the two 300’s did make it a real spectacle. It did really blow my mind as it was much more realistic than I ever imagined or hoped it would be. This is only one small step along the path to flight and ultimately in will only be a success if it flies as well as I hope but for the time being I’m happy with its progress.

The engine runs did cause a few issues, disappointedly but not surprisingly when the exhaust shroud is installed the engines make a great paint stripper! The good news is that it is purely aesthetic as we used a specific resin system that can cope with the temperatures caused by the efflux. The composite wasn’t damaged or even soft to touch after extended running on the water at slow speeds and high power settings so it would appear to cope with the worst case scenario in regard to cooling i.e very little bypassed ram air that you would have if in flight.

We should have used high temp paint from the start so we’ll see how a coat of heat resistant stuff does on the next test or maybe use aluminium tape and try and make it look scale that way… It does need some thought and any suggestions are gratefully received. It is a problem the full size had so at least we are having the full scale model experience. :)

The other issue is that the backend is running hot and this only occurs with the exhaust shroud in place (large silver section at the rear) and I also believe only when the aircraft is in the water. When the model is running in the water at slow speed and high power settings we’re vaporising the water and producing super heated steam which is being drawn back into the thrust pipes, this can even be seen in some of our images and only occurs when the turbines are running above 80%. You can see a sort of fog form inside the shroud at these power settings which is really interesting, for me anyway. :) We did have some static 3D printed Nylon engine petals that looked great but were completely destroyed and the after burning light rings were also damaged. These have now been removed and two new thrust pipes ordered as a precaution. The molten Nylon also blocked what little cold bypassed air they might have been contributing to the heat in the rear. We operated the model for 25 minutes with both engines running in two separate tests so this does represent the worst case configuration for cooling. Our next set of tests will explore this area further with some infrared cameras and tufting of the exhaust to see what’s happening with the heat and airflow.

by Alex Jones, on Flickr

There isn’t anything we can do to stop this as we want to keep the model scale and changing the entire backend isn’t an option. What we can do is be aware of the problem so when positioning to the takeoff area we use a low power setting and accept that for around 10 seconds we will be getting the back end very hot until the tail lifts from the water and the aircraft starts to plane on its skis, at this point it should start to cool again and once airborne will be getting a good amount of ram air through both intakes.
Thanks for all the kind words and suggestions [:)]

I've not yet decided between tape or some high temp engine block paint... I might try the paint to begin with and if that fails go to the tape?

With the knowledge that it’s now no longer taking on water at the rear, sitting at the correct water line and we can easily manage the aircraft in the shallows using waders we can move onto the RC boat bit of the test. With Dave in the follow boat along with three others either driving filming or taking photos we set off for 25 minutes of testing the model at slow speeds. Dave will be able to talk in more detail but the handling seemed ok although it was hampered by weed collecting on the ski struts as you can see below.

by Alex Jones, on Flickr

The water rudders at the back which are actuated by two big Savox waterproof servos worked well and continued to work even when submerged for over 5 hours. The wind was around 8 knots and the huge vertical stabiliser did hinder things but it was still possible to turn in either direction without assymetric thrust. The full size aircraft used a combination of asymmetric thrust and rudder to turn and in the second test the water rudders were not used but it was still possible to control direction using only asymmetric thrust.

We've learnt a huge amount on the first outing and I'll try and go through some of this while we wait for the second test.