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**Exciting new F5j model**


thermaldoctor
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thermaldoctor

This has been in development since last year with a huge amount of thought and design, and I have been lucky enough to have been part of this process. This is the new model from the makers of the Infinity - called the Eternity. I wanted to call it the Intensity simply because I can see if any orders are late people will comment their model took an Eternity to arrive ! 😄   But...Eternity is the better name so we went with that.

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With a very complex and highly efficient brand new aero package from Dirk Pflug, the new 3.97m 4 piece wing / 2 piece fuselage Eternity has gone to full solid core technology. The quailty of the parts I have seen so far are as good as anything currently available, and probably better. Finish looks basically like a top notch hollow moulded model due to the very high spec CNC alloys molds that have internal heating elements to heat up the curing system under very high pressure followed by a very high temperature post cure to give a shinier more ding resistant finish than anything currently available in solid core.

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We went for a triple dihedral wing as this is more efficient in a straight line and in circling. Having more, slightly smaller angle dihedral changes rather than one bigger change of dihedral looked a worthwhile gain in the calculations especially when combined with an optimised planform and aspect ratio all designed to work together as a package. The new wing features a whole set of new airfoils designed to allow the Eternity to travel well and handle stronger winds at lighter weights. One of the things both myself and Bohuslav (the manufacturer) wanted was also the widest speed range possible and this design goal has been achieved with some very clever airfoil design with extended laminar boundary layer flow across a wide range of angle of attacks meaning lower drag across a wider speed range. Coupled with an optimised 'big flap' hinge line (no need for turbulators on these control surfaces unlike some others) helps open up the speed range even more from slow minimum sink to fast low drag. All the computation and analysis kept showing that the best results were coming from a thinner set of airfoils that were more suited to solid core than hollow core and so the decision was made to go solid core to keep the wing stiff at lighter weights.

We thought long and hard about X tail or V tail. The V tail used on the Infinity works very well and is better than most other X-tails in terms of stability and handling so the only thing going for an X-tail was perhaps just commercial. In the end we went with the same long boom V-tail arrangement as on the Infinity Evo knowing it would provide the same super low drag arrangement but with arrow straight tracking and impeccable manners and handling.

Now we are glad we did it as the whole Eternity project has been about getting the lowest drag, widest speed range possible out of an F5j airframe but just as importantly to have perfectly balanced handling and a model that is safe and easy to fly so that the pilot can get the most performance from it. 

One thing that I really wanted and insisted on was lots of free control movement. One of the Infinities greatest strengths is to be able to circle effectively within its own wingspan. This helps it stay in tricky lift, gives great confidence lower down, and the extra control available makes for easier handling in windy turbulent conditions and also of course better landings. I didn't want the great potential of the new larger Eternity to be wasted by a model that is lethargic and lazy in roll. Pilots not liking a quick nimble model can easily tone down the control movements and tune it to how they want it to handle, but if you like larger control movements then the Eternity will not disappoint. 

The 2 piece fuselage will give a choice between longer front section or shorter front section to accomodate different motor and battery weights. I was up for a removeable nose cone that you can cut down like other models but Bohuslav really does not like this method. As i had no real opinion either way we went for the different length fuselage option. After all it wasn't me having to make another mold and i think it gives a slightly stronger more secure solution.

To get the most agility we could, even with lesser control movements, it was important to have both the main ailerons and the tip ailerons working together. But no way did we want a 6 servo wing as this is definitely not the way to go. So we decided to mechanically link the tip ailerons into the main ailerons. The manufacturer of the Infinity also makes some big moulded scale gliders and the same system used on the Eternity has been extensively tried and tested over several years on some very big and very expensive models and works perfectly.

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So there it is the new Eternity. The one above is the first production model to fly (which Bohuslav did at the weekend) and it can be confirmed it covers sky extremely well like a larger glider but remains highly agile with the feeling and ease of handling of a smaller model. The speed range is indeed wide and it is happy and efficient travelling quickly and efficiently between thermals and also very slowly at minimum sink on the edge of the stall.  

Mine is the second production model and will be with me soon. I am actually quite excited about this one..!

Not sure of prices yet. But like the Infinity it will be a complete package with factory fitted IDS and wing wiring as standard, and with ballast and a complete set of wing/tail/fuse bags.

The Eternity does not replace the Infinity Evo. They are very different models so the Evo remains in production.

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thermaldoctor

More pics of the new Eternity. These show the high aspect ratio (22:1) and long tail boom nicely. And just what a nice looking well proportioned glider this is. It will come with one central joiner (2 degrees) but with a choice of tip joiners (4 degrees and 6 degrees). The tip panel dihedral break is obviously fixed and is at 4 degrees. Testing has shown the 4 degree tip joiners to provide a very nimble agile model with a very flat, stable and penetrating glide. With the 6 degree joiners it becomes even more stable, almost like a free flight model (Bohuslavs description) but is a bit slower. Sounds ideal for very light conditions.

Although the solid core finish is already likely to be the hardest and best quality currently available, next week the factory is experimenting with very high temperature epoxy used in full size commercial airplane production. If successful, which I hope it will be, this will redefine the quality of solid core models. 

The model will pack down into a box 120cm long x 28cm x 10cm so very compact.

As per the Infinity, the front of the nose is aerodynamically designed by Giorgi Mirov (GM props) to make sure the blades fit as close to the fuselage as possible.

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slopelope

Congrats Neil.... looks really good and if it's anything like my Infinity Evo this is will be a fantastic glider... watching closely!

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thermaldoctor

Eternity wins first time out...!

Bohuslav just won a Slovak F5j National contest with the brand new Eternity fresh from the moulds and with only 2 testing days before the contest.

And this is against some very good pilots in the fly offs (Janny Litva 2014 F3j world champion and Juraj Adamec regular Eurotour fly off pilot). 

I spoke to Bohuslav about it and he said the Eternity proved the very best lift/drag as per design goal and was getting to lift faster and with less height loss. Also on coming home from 1km downwind thermals Eternity was coming back higher and faster than other pilots when all at same altitude in the thermal and taking the same path home.

It is all subjective and anecdotal at the moment until i try mine, but if Eternity promises even half the design goal we set out to achieve it will still be a top contender..

2nd by the way was Infinity Evo. Again proving this model has real legs and superior L/D than most other models. 

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  • 4 weeks later...

Interested to hear more about the wing construction. Are there any diagrams showing the core and layup?

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John Minchell

Could this be the new go to model for GPS Light class?

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thermaldoctor
On 23/07/2021 at 18:03, knewt said:

Interested to hear more about the wing construction. Are there any diagrams showing the core and layup?

Hi Kev wing production and spar / skin lay ups charts are a pretty closely guarded secret sorry. I could tell you but then I would have to kill you 😆

But basic construction follows along similar lines to others....CNC Rohacell core with carbon skins. And generally processed at very high temperatures (80 degrees +) to improve surface finish and hardness.

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thermaldoctor
On 24/07/2021 at 08:53, John Minchell said:

Could this be the new go to model for GPS Light class?

We will see John......there are already 2 GPS models booked for the 1st production run. It will be interesting to see how it goes

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  • 4 weeks later...
David Moore

Please confirm the nose diameter and max. battery size of the Eternity.

Are the two noses the same diameters ?

I found the Infinity Evo nose to be a tight fit to use 4S and a high power motor.

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thermaldoctor

Hi David thanks for your message.

I am putting my pre- production Eternity together as we speak and will be using exactly the same power train as my Infinity as it the same sort of fit.

On my Infinity Evo i used tenshock 1515 15t on 4s. And get just under 800W at 120kph pitch speed on a 14x10 prop. So i am happy with that speed and power.

But the key is to find a good 4s that fits. Many of them are meant for drones so they are short and fat.

You need longer thinner high 70C +  rating ones like Thunder power rampage or overlander FPV pro. Also I know people using the GNB range and these are getting good reviews too.

Another good option is the new Tenshock Viper 1030 long case on a 12 x 8 and then you can use the excellent Turnigy 4S 650mah on a 12 x 8 prop. This combination will fit in very easily and can give approx 500W.

Best regards

Neil

 

 

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thermaldoctor

Nose diameter is again 30mm and max battery that will fit is 1300mah 4s thunder power rampage 70C.

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David Moore

My Infinity Evo (Storm) built for high winds at 1920g unballasted has a Powerline 1025/9 4S (6120kv) with a 11x7 Vlad thin F5J prop and 650 Graphine 75c batteries.

Draws 43amps/573w at full power with a high flight speed to go upwind.

Can make 280-300m in 30sec at full climb (9-10m/s) and 2m/s at 35% power (flight idle).

The Eternity light will replace my Pulsar 3.6 as my light air model.

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thermaldoctor
20 hours ago, David Moore said:

My Infinity Evo (Storm) built for high winds at 1920g unballasted has a Powerline 1025/9 4S (6120kv) with a 11x7 Vlad thin F5J prop and 650 Graphine 75c batteries.

Draws 43amps/573w at full power with a high flight speed to go upwind.

Can make 280-300m in 30sec at full climb (9-10m/s) and 2m/s at 35% power (flight idle).

The Eternity light will replace my Pulsar 3.6 as my light air model.

It will be very different to a Pulsar David. Light versions will be approx 1050g (FAI Light) and 1300g (standard Light) but it will still have legs. I will be flight testing my Eternity shortly and will post my findings

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  • 2 weeks later...

Goodness I find myself lusting after an Eternity! Is there much point in ordering one this late in the season? I've no idea how long it's possible to thermal in the UK.

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I find that there's lift available all year round.  I have thermalled over snow-covered ground.  There have been long DLG flights throughout the year, looking back through past duration challenges.

 It will be more difficult to get longer flights on cold cloudy days than it is on warm sunny days but It will make you a better pilot if you are having to look for the more subtle signs.  Good luck with your decision.

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thermaldoctor
On 04/09/2021 at 10:22, MikevE said:

Goodness I find myself lusting after an Eternity! Is there much point in ordering one this late in the season? I've no idea how long it's possible to thermal in the UK.

Mike is right there is lift all year round so it's never a bad time to order an Eternity! 

The first batch of 4 have all been sold and are starting production this week. But a second batch of 4 is already starting to sell with 1 order so there are 3 places left

Best regards

Neil

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50 minutes ago, thermaldoctor said:

Mike is right there is lift all year round so it's never a bad time to order an Eternity! 

The first batch of 4 have all been sold and are starting production this week. But a second batch of 4 is already starting to sell with 1 order so there are 3 places left

Best regards

Neil

Cheers, in which case I'd like to chat to you and probably order one. Have left you a whatsapp.

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thermaldoctor

Okay...!  Now about 2 dozen flights under my belt with the Eternity.

First set of flights were done in <10mph warm sunny conditions with smooth cycling air and the second set of flights done in 15mph in very choppy very turbulent conditions but again warm and sunny with cycling air. CG range is 98mm-102mm and I am flying at 99mm simply because that is where it balanced out and I have not started to experiment yet.

I copied my Infinity Evo settings straight over onto it as it seemed a good place to start. Immediate impression in the <10mph conditions was of how manouverable it was for a 4m plane. Just like the Infinity there is a lot of roll control available and you can easily change direction in a thermal very quickly and easily. It can turn very tight and slow and overall the handling is extremely well balanced. It feels more like a much smaller plane and with such control authority available it gives the confidence to make a turn at every inkling of lift. It definitely likes to move forward and responds well to reflex and camber. In good air camber between 1mm and 4mm works well but lots more testing needed. When encountering sink 1mm of reflex works well just like the Infinity and it noticeably steps up a gear slightly and accelerates forward.

In the horrible choppy 15mph air it was good to have the control authority available to keep it on the straight and level. This time also pitch response was also being tested as the strong wind coming over the town and trees was causing huge eddys such that you could suddenly find yourself banked over at 45 degrees with the tail right down and falling out of the sky. Thankfully pitch response was excellent but not twitchy. When lift came through, the Eternity would clearly show it well and turns confidently and accurately made despite being shaken around in the turbulence. At times the lift was quite strong and several times it ended up very high and a long way downwind. This time the 1mm reflex didn't help much. So as on the Infinity I also have 2mm of reflex and a bit of down elevator in and this did noticeably help but I needed to balance it out on the elevator stick a bit (ie sometimes coming forward with too much down in and other times not enough) which isn't the case with the Infinity but for the time being I will put this down to the conditions as even at altitude it was smoother but still quite rough.

So early conclusions are very favourable. I am pleased it is so easy to fly and so responsive. It definitely handles beautifully and is very well balanced. Performance wise yes it certainly seems a step forward but performance is very subjective until compared over a reasonable period of time and across a wide range of conditions against similar models. But I know enough already to commit to only flying Eternity's next season....

Any negatives..well yes some small niggles. But bearing in mind this is a pre-production prototype!!  And some of the details this particular Eternity were never meant to be on production models in the first place and were done just to get it to me as quick as possible and to get it in the air asap. All niggles fed back to Bohuslav were all well documented and not ever intended for production models. 

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