FX707S Albatross - 1.2m foam chuck glider RC conversions

[Simon Chaddock]

As I really don't like that big "V" slot (on my first not flapped FX707 I filled it in) I decided to go ahead and built a bigger, longer Depron flap using 2mm skin top and bottom.

At the same time I printed the tailing edge extensions for the aileron and the short bits that go on the rest of the  edge

A comparison of the original & extended wings.

 

It is the underside that shows the biggest difference.

Of course the aileron will have to have a "V" slot added but as the ailerons will have differential movement the slot will be less pronounced.

As I commented on the conversion of my first FX707 I doubt any of the changes will make a significant difference to the performance unless I do a conversion without any wing modifications and that I am not going to do.

[Simon Chaddock]

Not much progress but I have excavated out the inside of the cockpit canopy.

As supplied it weighed 5.2g. It now weighs 2.6g.

I am sure a 2.6g saving on what is likely to be a 360g plane will make no difference at all but its the principle of a 50% reduction that counts.

The extra space it creates inside the cockpit might come in handy too.   

[Simon Chaddock]

Still waiting for the servos so I decided to install the one that I have as a flap servo. Fortunately is the same as those I have ordered.

The installation is a bit unusual as what I am using as a flap was originally intended as an aileron so the servo cut outs are 'handed' which of course is no use for flaps and the cut outs were intend for top hinge/lower link. My flaps are bottom hinged with a top link so the cut out was going to need some modification anyway. Stared with the LH wing as this was likely to need less modification to get the linkage in the right place.

The underside with the servo in place.

 

Servo cut out is not quite deep enough for a 3.7g servo but I did not fancy trying to make it any deeper. The servo is glued in with POR all round so it adds a bit to the stiffness of the wing.

The top surface.

A video of the flap in operation.

https://www.youtube.com/watch?v=QKhpe6EniMo

It took a bit of trial and error to get both the flap horn geometry and the link to give the correct movement whilst retaining full servo travel.

At least I now know what is required to be done when the servos arrive. 

 

[Simon Chaddock]

After much dithering I have decided to keep the same type of motor on the flapped FX707. I have ordered a slightly larger prop as even the 5.3x3.3 was only drawing 7.5 amps on a 3s.

This decision means I could use the existing printed motor mount and cowling. However I never particularly liked the cowling side air exits so I will try bulkhead holes to exhaust the motor cooling air into the cockpit and thence to a low pressure region further down the fuselage.

The top inlet cowling with no side exits.

The motor mounting has two large holes in it.

These holes will be matched in the nose foam that supports the motor mount.

Well that's the plan.  🙂      

[Simon Chaddock]

At last the servos have arrived so I can proceed with the aileron servo installation on the LH wing.

A short video of both surfaces running on a servo tester.

https://www.youtube.com/watch?v=ptL8G_Vt2AY

Now I have to do the same to the other wing before they can be permanently joined together.

 

[Simon Chaddock]

Boy has this been slow going!

At last the  4 wing servos are in and connected up so the wing can be permanently joined.

This allows the wing to be test fitted on the fuselage.

 

The underside showing the servos and their wires buried into wing.

Even so there is quite a bit to do. In theory it is just a repeat of what I did on the first FX707 but it tends not to work out quite like that!

Next is the tricky job of cutting the nose off at the right place and angle to install the printed motor mount.

Given that the weight of the 4 wing servos act at about the same point as the previous 2 and everything in the fuselage should be the same the CoG of the flapped XF707 should end up about the same point.

We shall see.  

[Simon Chaddock]

The cowling and motor with the printed mount glued onto the cut off nose.

The ducts matching the holes in the motor mount exit into the cockpit.

This layout ensures the air from the nose inlet will travel across the motor, hopefully. Just as well it is only a 100W motor!

The "exits to air" will be added further down the fuselage.

ESC next, likely to bed semi recessed externally as in my first FX707. 

[Simon Chaddock]

The tiny 10A ESC added outside the cockpit.

 

[Simon Chaddock]

Now more or less complete and with such rotten weather I painted the control surfaces.

 

I am still waiting for its 5,3 x 3.3 prop. If necessary it could be flown with the 5x3 fitted. The current weather forecast suggests it could be some time before it can have its maiden.

A short video of a full control test.

https://www.youtube.com/watch?v=z7KZm0SCYVI

With an 850 mAh 3s LiPo it weighs 332g. Which is just 50g more than it did as a chuck glider out of the box. 

[Simon Chaddock]

And it does fly!

With the flaps up and with the same CoG position not surprisingly it flies just as well as the my unflapped FX707 so no problem at all.

However as soon as flap is applied it quickly runs out of down trim to compensate for the nose up pitch. In some respects I expected this as I normally set a bit more up elevator travel than down. I had the same problem with the Push/Pull which had rather more extreme flaps.

There the solution was to set the elevator position so it needed almost full up trim to fly level so increasing the down trim range. 

I will do the same for the flapped FX707 bur thinking about it I can do a bit better. By moving the servo arm one spline anti clockwise it will impart some mechanical elevator differential movement, more down than up, which will further increase the down trim range all be it at the expense of some up elevator travel.

Just as well I had not permanently fixed the push/pull lines. 

After all the object of the flapped FX707 is to demonstrate its flaps rather than do aerobatics.😉

Unfortunately the weather looks like it could be more than a few days before I can try it. 

[MattyB]

14 minutes ago, Simon Chaddock said:

...With the flaps up and with the same CoG position not surprisingly it flies just as well as the my unflapped FX707 so no problem at all.

However as soon as flap is applied it quickly runs out of down trim to compensate for the nose up pitch. In some respects I expected this as I normally set a bit more up elevator travel than down...

 

There the solution was to set the elevator position so it needed almost full up trim to fly level so increasing the down trim range. 

I will do the same for the flapped FX707 bur thinking about it I can do a bit better. By moving the servo arm one spline anti clockwise it will impart some mechanical elevator differential movement, more down than up, which will further increase the down trim range all be it at the expense of some up elevator travel.

 

Just as well I had not permanently fixed the push/pull lines. 

 

Good stuff, glad you've been able to test it. Did you try a dive test to check the CG? I know it isn't everyone's favourite technique, but I have found it's good at telling me if I'm in the ballpark, and generally I've found getting the CG further back tends to reduce the flap/elevator mixing requirement and improve the dead air glide performance (as long as you don't go to far and end up with it getting twitchy on pitch).

[MattyB]

PS - @Simon Chaddock, hoping to get at least one of mine done over the xmas period, family commitments permitting.

PPS - Do you have any tips on how to connect up the lightweight pull-pull, or a video that describes it? I've done a few of these way back in the day for larger models, but always avoided them for small stuff, but accept it's definitely the best option in this case. What do you use, kevlar thread?

[Simon Chaddock]

 

MattyB

On the pull/pull for the FX707 and some other lightweights I use 15lb (7kg) monofilament fishing line. Many think it is too "stretchy" but the amount of stretch a 3.7g servo can generate, even when it is stalled, is pretty small. It is also well below the force required to permanently stretch the line so within reason the line stays taught. As a side benefit the slight give in the line provides a degree of protection to the servo gears. I have yet to damage a servo connected by a monofilament line. The same could not be said for the rigid short links I also tend to use.

I use one long piece of line to connect the servo and horns. I tie off the line at one elevator horn end. 

Then pass it through the appropriate end of the servo arm, across to the hole at the other end of the arm and then back to the other elevator horn to be tied off.

I have painted the line as it is almost invisible to the camera.😉

With care when tying off you can use the monofilament's stretch to remove any slack but avoid too much tension as it will over load a small servo's bearings as well as the elevator hinges.

As the line is free(ish) to pass through the servo arm you can adjust the position of the elevator so it is neutral when the servo is centred. Once happy with the line position it can be permanently fixed with a blob of glue over each servo arm hole.

Note on the above installation the line has been "trapped" by the servo arm screw so it can be readjusted at will. Convenient but such clamping is not kind to the monofilament so it will revert to glue in the final setup. 

I would not recommend using monofilament for anything but lightweights. For serious pull/pull installations you have to use a braided line but with virtually zero "give" you do have to be aware of any geometry issues that might seriously tighten the line at some positions causing bearing overloads or in the worst case actually limiting servo travel.

As an aside nylon monofilament line is very "slippery" so it is possible to go round corners using tiny wire eye rings glued into the structure.

This Fokker V25 uses a single centre 3.7g servo in the fuselage with a closed loop monofilament pull/pull line to work both ailerons.

This requires the line to pass through four 90 degree bends.

   

It even works!

It is however a true lightweight. It has a wing span just under half that of the FX707.

I look forward to seeing your FX707 in due course.

        

[Simon Chaddock]

The 'flapped' FX707 is now finished.

It has its intended 5.3x 3.3 prop and spinner. I even found a bit of sun to take the picture. 😀

I was going to fly it this morning but when I got to the field it was 1/3 under water!  Heaven only knows how muddy the rest was and there was a pretty firm breeze. Not really the conditions for a test flight so it was a case of turn round and back into the warm.

The weather will get better a some point, won't it? 

[Simon Chaddock]

Between the very wet days I have managed to fly it twice in calm weather.

With the flaps up it flies exactly like the one without flaps. No real surprise there but although the effect of the flaps is impressive the pitch up when they are applied is even more so! 😲

In fact far more that the down trim available to overcome.

For the second flight I altered the servo arm position so it gave a mechanical differential favouring the down travel and I set the full up trim to give a neutral elevator position. This gave a full down trim effect that was not far from the previous full down elevator.

 

Even so this was still not quite enough to fully compensate for the full flap pitch up but the landing speed with 3/4 flap. about 45 degrees, was suitably slow.

The fight was terminated when the motor started playing up. Later traced to a poor soldered connection than was relying on the shrink wrap for contact!. Not that surprising as space to run the motor wire is very limited.

The next solution is to move over to 2.4 so I can use a flap/elevator mix and still have a normal trim range. Flying a plane with no up trim at all is not very comfortable.

If a mix proves inadequate, the elevator is really quite small, then the obvious solution will be to enlarge it to the full tail plane span.    

 

[Simon Chaddock]

With the 2.4 installed an flap/elevator mix could be used. In fact the Hobby King TX6i has such a mix preinstalled in the menu so you only have to add the elevator and flap positions for each position of the selected 3 way switch.

https://www.youtube.com/watch?v=Ae4A2i_EROA

These settings are just an educated guess. It will take some flight testing to determine the appropriate flap/elevator deflections.

 

With such a large flap deflection available (0 to 75 degrees) it would be useful to have say a 5 position switch.

Better still would be a flap slider and an the ability to create an elevator deflection  "profile" to go with it. 😉

 

All I need now is a period of calm dry weather. Maybe next year some time!   

Edited December 17, 2023 by Simon Chaddock

[Arthur Harris]

On 19/08/2023 at 15:41, Simon Chaddock said:

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.   

 

 

Although it might not quite meet the 250gm threshold, it might still be a fine small park flier for experienced pilots.

[Arthur Harris]

2 hours ago, Simon Chaddock said:

All I need now is a period of calm dry weather. Maybe next year some time!   

No, don't say that! We'll have many calm days in December, we have a couple of weeks yet!

[Simon Chaddock]

I did try to fly the Flapped FX707 with the 2.4 gig radio but for some reason it did not like working with the Hobby King TX6i transmitter. The very short flight ended with no control or power but only slight damage as the field is really soft and muddy.

The replacement Lemon 6ch has been installed but this time in the cockpit.

 

It does make it rather congested but the Lemon has a long shielded part of the aerial which is led back to under the wings so the important bit is as far away as possible from everything.

 

Almost impossible to see against the white EPO but the true aerial is between the red marks.

I managed a reasonable flight yesterday but the wind was rather too strong for it so I had no opportunity to try the flap/elevator mix.

As I expected the Lemon Rx had no range issues with the HK TX6i.

Roll on some better and dryer weather! 

[Edgeflyer]

Is this foam able to withstand the temperature for covering with laminating film? Also does anyone have a link to the 2204 motor?

[Simon Chaddock]

Edgeflyer

The EPO that the FX707 is moulded from is pretty flexible but it does have a particularly smooth and almost shiny skin.

I have not tried a laminating film but this shows the effect on the EPD using the sort of heat level required for shrink wrap.

 

The LE 2204 motor I used is not that easy to come by in the UK as AliExpress won't deliver it to the UK. I got mine through Amazon but is now showing "out of stock".

It is available though Ebay but in the £25+ range. In other words more than the FX707 itself!

 

Most motors of this size are intended for multi copters that use a large diameter threaded prop mount rather than a 3 mm shaft needed for a folding prop.to be 

 

Flew the flapped FX707 again today in not ideal conditions but managed to use the flaps. The stage 1 flap (20% flap down, 20% elevator down) seems just about right with no trim change it just flies a bit slower. The stage 2 setting (40% flap down and elevator 40% down) also has little trim change. it flies even slower.

It will need better conditions (and a much dryer field!) to experiment with different flap/elevator settings up to 100% flap (75 degrees).

[Shaun Walsh]

https://www.aliexpress.com/item/32983518203.html?src=google&aff_fcid=c3e1c681505f4da796b6b4a8c527f1fe-1704183421153-03829-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=c3e1c681505f4da796b6b4a8c527f1fe-1704183421153-03829-UneMJZVf&terminal_id=07991e08b74e4974b7a594159376896c&afSmartRedirect=y

£7.76 including UK shipping

Edited January 2 by Shaun Walsh

[Simon Chaddock]

The recent high pressure apart from stopping the rain also means light winds.

This morning was very grey overcast but absolutely no wind so the Flapped FX707 flew again and this time I took a video. Actually there were 3 flights but this was the best demonstration of the effect of the flaps. Although I kept low for the camera the very poor light quality did nothing for the video quality.

https://www.youtube.com/watch?v=TOD5ESqYwDY   

Edited January 13 by Simon Chaddock

[Linds.W]

I'm enjoying the build on the FX707 so much that I've ordered on from E-bay so keep the "mods" coming!

 

[Fraggs]

What measurement from the leading edge of the wing are you guys setting the C.G ? (Fx707s)

I think I remember it being somewhere around 56mm but have lost the measurement that I had made a note of before I started converting it.

If someone could please let me know I would be very greatful

Thanks in advance