FX707S Albatross - 1.2m foam chuck glider RC conversions

[MattyB]

This thread will be for those interested in converting the cheap (~£20 inc p&p) FX707 / FX707S Albatross chuck gliders, which can be sourced from eBay, AliExpress or Banggood. My personal goal is to make a lightweight, cheap "Mini Radian" for the park - let's see how it goes!

 

 

More details to follow - @Simon Chaddock, feel free to post details of your conversion in this thread too.

 

Useful links:

• How I originally found out about this model
• RCGroups conversion thread (pitcheron version)
• YouTube build and fly conversion series

 

 

• Another useful Youtube vid:

 

 

[MattyB]

Kit details…

 

Nice box art, but the packaging inside is non-existent - they have relied on the intrinsic resilience of EPO to get it to you in the right number of pieces!

 

It definitely reminds me of a shrunken Radian 2m, though obviously without the pronounced curved dihedral. It a has a significantly thinner (but still flat bottomed) wing section than the Radian though; this should offer decent soaring performance with a lightweight powertrain, though it won't be a windy weather model in the form I build it.

 

Wing detail - will need some additional outboard carbon reinforcement, but the main spar seems up to the job. The second spar is inserted from the rear of the fuselage to reinforce that longitudinally. Both fit very well.

Tail and wing fairing detail. The rudder will definitely need enlarging if I go for R/E/F setup, but the wing is flat enough you could choose just ailerons and elevator (and at these sizes and a/r rations the absence of a rudder might not make a huge difference to soaring ability).

 

Them's some big balls of steel...! 😉😄 Plenty of room for a small 2S pack and ESC, especially if the ample walls are hollowed out a bit and reinforced with carbon strip and CA as req'd.

 

Fuselage from the nose. The plastic inserts seem well formed and glued in, and the servo pockets look suitable for some 4g Aliexpress specials or similar.

 

 

Plastic inserts for wing and tail attachment

 

Other than one very minor fault in the rear fuselage which I suspect was done in transit, the quality is just super high for the price -  the foam is cleanly moulded, dense and strong without being excessively heavy. It’s a smidgeon behind class leaders Multiplex, but better IMO than EPO gliders from the likes of Horizon Hobby such as the Radian. It’s an absolute steal for <£19 inc p&p!

Edited August 19, 2023 by MattyB

[MattyB]

If you want to get one yourself, eBay is the place - there are plenty of UK sellers with them at good prices, though the prices do seem to vary quite a bit...

 

 

This is the seller I used. It's so good I have ordered another one too experiment with - I may decide to extend the wings slightly using the second set, or lam film the other wing and turn it into a speedy(ish) pitcheron sloper. Certainly bargainous for <£20, though £69 on Amazon is a bit steep!!!

 

[John Lee]

Thanks for all that @MattyB It was not a thing I was aware of until you started this thread. I ordered one yesterday from the same supplier as yourself, there seems to be a number of sellers located in Cannock which I presume is the same chap mascarading under different names to expand his reach on searches. Like you I chose the cheapest!

 

I have a draw full of what should be suitable servos & motors from my indoor flying days (we lost our hall during Covid & activities were never resumed). 

 

Should be a giggle.

[Ron Gray]

I blame you Matty, I’ve just bought one too!

[Jake Bullit]

Thinking of getting one maybe for a twin conversion. Do you know of any 3d motor mount files?

[Simon Chaddock]

Jake

The FX707 wing mouldings do appear to have markings and attachment points for wing motors as well as a cut out for the motor wires.

The fittings are not included in the glider kit.

 

I have not yet decided on the details of my conversion. The objective is to get it to below 250g - ready to go.

This will be quite a challenge as the basic glider comes in at 280g bare! There is 83.2g of ballast but it is well forward so not easy to get all the 'electrics' that far forward.

The saving grace is the 'bare' wings, fuselage, tail feathers, canopy and wing fairing only weigh 173.3g.

Will need some thought.

To be continued.   

 

 

[MattyB]

Yes, I’m not sure sun 250g is possible with the “S” version of this model. Apparently according the RCGroups threads the original FX707 (which I’ve not found is available any more) was lighter, but didn’t have all the prep done for an RC conversion.
 

I’m not too worried though, as I suspect 200g might be a bit too light on most days for this windy isle given the relatively draggy non-DLG aerofoil. For comparison the AUW on the original Radian 2m was just under 900g, I’ve thermalled those in gnat farts… !

 

@Simon Chaddock , what sort of motor/prop combo are you going for? I think I will target 40-50W on a 12-15g motor and 2S pack, but what prop and kV I’ll need to achieve that I’m yet to work out…

[MattyB]

Am currently think this motor on a 7x3  or 7x4 on 2S…

 

https://www.4-max.co.uk/ppom-2321.htm

[Simon Chaddock]

7x3 should be ok if you keep the weight down. It is what I will use if I really can keep to within 250g ready to go.

 

A bit of progress/nonsense on my FX707s.

The servo cut outs and the rest do the wing no favours. In fact you can see the empty cut out distort as the wing flexes. The carbon tube insert works certainly stiffens things up but it does mean the inherent strength of the EPO is not being used!

I do not intend to use the prepared ailerons, I believe ailerons should be as far out as possible, so as much of the cut outs will be filled with Depron.

I doubt it will make the wing any stiffer but it should improve the aerodynamics a touch.

My intention is place the ailerons in the outer polyhedral section.

 

The servo wire will run in the long narrow pre moulded slot.

I also intend to make the wing as a single piece but removable. This will make the wing fairing redundant and should allow some of the wing mount  plastic moulding in the fuselage to be removed. 

Edited August 20, 2023 by Simon Chaddock

[Stephen Jones]

Following.

I was considering converting one of these some years back.

 

Steve.

 

[MattyB]

10 hours ago, Simon Chaddock said:

7x3 should be ok if you keep the weight down. It is what I will use if I really can keep to within 250g ready to go.

Even if it ended up 300g, on a 2S and 7x3.5 that gives 53W, which doesn’t sound much but equates to 80W/lb - should be fine for a motor glider I think.

[MattyB]

 

14 hours ago, Simon Chaddock said:

My intention is place the ailerons in the outer polyhedral section.

 

 

The servo wire will run in the long narrow pre moulded slot.

I also intend to make the wing as a single piece but removable. This will make the wing fairing redundant and should allow some of the wing mount  plastic moulding in the fuselage to be removed. 

 

I like the sound of your depron infills and removeable wing (I have been thinking how to achieve the latter), but I am not sure about those ailerons. They are very small and right on the tip, which might increase the chance of tip stalls and (with the polyhedral) exaggerated dutch roll characteristics. It also puts quite a lot of weight right out at the tip, well beyond a point that the carbon stiffeners are effective (could cause some structural issues), and means it will damp how the model indicates in thermals (probably not an issue worth worrying about). This is why I am thinking of keeping it in a R/E or R/E/F config, which for a model liek this should keep weight down and male it simpler to convert.

 

 

[Simon Chaddock]

MattyB

Just a point but weight out towards the wing tip does not add to wing bending under aerodynamic g loads. It is why many full have fuel tanks all along the wing or drop tanks out towards the tip, but of course it does create wing 'droop' when static. The inertia of weight at the tip will reduce the rate of roll application but not the ultimate effect of the control input.

 

The power of ailerons for a given deflection is a function of their area and distance from the roll axis. Smaller further out can be as effective a bigger further in and as a by product outboard create less drag whilst operating.

 

Of course with all small slow flying planes it brings into question whether the time and effort of such changes is worth it. Probably not.   

[Simon Chaddock]

The first aileron in the wing.

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

Note the servo wires makes use of the long pre printed slot in the wing.

 

Next to bring the other wing up to the same standard before permanently joining them together.

 

 

[MattyB]

15 hours ago, Simon Chaddock said:

MattyB

Just a point but weight out towards the wing tip does not add to wing bending under aerodynamic g loads. It is why many full have fuel tanks all along the wing or drop tanks out towards the tip, but of course it does create wing 'droop' when static. The inertia of weight at the tip will reduce the rate of roll application but not the ultimate effect of the control input.

 

My point was that because that additional tip weight is well beyond where the carbon spar ends, it is essentially unsupported by anything other than the foam. For that reason if I were going for ailerons out at the very tip I'd be putting in a few cocktail sticks or carbon strip across the polyhedral breaks to stop it sagging and becoming a flat wing. This will also help prevent any flutter at higher speeds (whilst having additional mass out at the tip doesn't make that any more likely, the twisting forces from the ailerons will, especially at speed).

 

Having said that if you can maintain the polyhedral angles effectively my gut feel is this model will need very minimal aileron movement anyway, so it may not be a major issue.

 

15 hours ago, Simon Chaddock said:

The power of ailerons for a given deflection is a function of their area and distance from the roll axis. Smaller further out can be as effective a bigger further in and as a by product outboard create less drag whilst operating.

 

Agree on the drag and moment arms, but you don't see many ailerons on the very outboard sections of wings with appreciable polyhedral because that is known to make them susceptible to dutch roll. It may not be too problematic, but the handling might be a bit funky, especially if you use a lot of aileron in the turn. The good news is on a model as cheap as this it's not much of a risk to find out!

 

11 hours ago, Simon Chaddock said:

The first aileron in the wing. Note the servo wires makes use of the long pre printed slot in the wing.

 

Next to bring the other wing up to the same standard before permanently joining them together.

 

 

 

I suspect you will only need 1/3 of the down-going movement you have there. You could optimise that linkage by moving the connection inboard at the servo end, moving the servo centre in sub-trim so the arm is pointing well forward, and lengthening the linkage to keep the same neutral point. This will give some mechanical diff and improved resolution and holding power.

Edited August 22, 2023 by MattyB

[Simon Chaddock]

The video was the the first trial. The linkage is not in its final state.

My FX707 does not have significant polyhedral.

Really only dihedral tips.

I have several planes with such a layout with ailerons only in the outer wing section and in some cases flown with no rudder either.

 

the last bit of 'improvement' is the trailing edge. The FX707 TE at 3mm is far better than the 6mm edge of the Lidl chuck glider.

  

It can however still be improved to 1mm with LW-PLA printed "extensions".

The extensions add 3g in total. It also increases the size of the aileron by 40%.

Like most of the aerodynamic improvements I doubt it will be noticeable except it might allow my FX707 to fly on slightly less power.

 

 

 

Edited August 22, 2023 by Simon Chaddock

[MattyB]

That is a nice mod; it should help with torsional rigidity too!

 

Edited August 22, 2023 by MattyB

[Simon Chaddock]

The wing is now un one piece abd bolts onto the fuselage using the 3 bolts supplied.

All the plastic fitting for the tail & fin have been removed. It wil be simpy glued on.

Like this with only one aileron .servo it weighs 180g.

8g for the two other servos.

Motor. prop, ESC, Rx & battery for 60g? It is going to be a sruggle.  

[MattyB]

Having looked at it a few times now I’m of the opinion the horizontal tail could be cut down a bit span wise, as it seems very generous. That in itself won’t save much, but if it means less m/no nose weight it may be worth doing. 

[Simon Chaddock]

If you reduce the tailplane span it might be possible to remove/reduce its carbon tube. It would save a bit of weight in a critical location.

I have reduced the length of the wing reinforcement in mine as being light it does not need so much.  

[Simon Chaddock]

Porgress to date

The cockpit 'opened out' to give space to install the ESC, Rx and battery all well forward to achieve the required CofG.

The canopy will have the same hollowing out treatment.

The underwing area showing the 'reduced' wing mounting plates.

The remainer is also 'opened out' but it has all been done to save weight as there will be nothing in here.

The elevator servo will be 'let in' to the fuselage here.

Only the servo arm will protrude with nylon pull/pull wires to the elevator horn.

The enlarged fixed fin. It be flown AET with no rudder.

A 24g motor and 6x3 folsing prop are still to be ordered.

[Simon Chaddock]

The canopy hollowed out with the 'excavated' material along side.

Done more to create space than to save weight.

The original canopy weighed 5g. It now weighs 3.1g.

It will be secured by a peg at the front and a pair of magnets at the rear. 

[Simon Chaddock]

Just to make sure there is suffient depth in the cockpit the floor has been excavated to the depth of the 'indents' that located the ball nose weights.

 

In conjunction with the "excavated" canopy there is now enough room to fit a 2200mAh 3s in the cockpit.😲

Still waiting for the motor and prop.

[MattyB]

On 30/08/2023 at 15:19, Simon Chaddock said:

Still waiting for the motor and prop.

What did you go for?