The Triplane/s build thread

[Tim Mackey]

Should be fine...but pricey !

[Terence Lynock]

For such a small and cheaply constructed model I cant see the point of installing expensive motors, an Emax Cf2805 off Ebay for about £8 should give these all the power they need, if you want a Bipe version of an Exocet then stick a 2412 in it,

                            regards,        Terry

[Tim Mackey]

I agree. However, this may be just a little thirsty on the amps, and with a small battery compartment and very light weight, you need to maybe keep the amps down a bit, cos I can only really get a 450 m/a pack in mine! The one below is also dead cheap ( about 6 quid  ) and only weighs 20 grams.

hows this one ?

[Terence Lynock]

Looking at the plan if you subsitute hard balsa for some parts of the bulkheads around the cockpit area you can make a lot of space for just a few grams extra weight, this allows a more powerful battery/motor combo and with so much wing area anyway it would give a better performance.

I would try to keep any hard balsa close to the CoG though so as not to upset things too much,

                       regards,             Terry

                                  

[Tim Mackey]

Yes Terry I reckon your right....a quick rough test is looking like it will NOT be tail heavy anyway, and a bigger battery might well be possible. Still easy enough to change things around a bit after first trials if necessary.

[Terence Lynock]

Just checked up and you can get two Cf2805 brushless motors for £6 and £1.50 post and packing from https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5353

Nice little motor with bags of wumph for its size, I have one on a 21'' span Sea Fury with an 8x4 APC-clone prop (they sell them for about 40p and they work well), at present they have a stock of over 170 motors so no waiting for backorders, motor does about 2850Kv,

                 regards,       Terry

[Rafa L]

Hi Timbo, Hi Terry, Thanks for your help. I agree with you: these AXI aren’t cheap, but the mine is collecting dust in the drawer waiting for a plane.   AXI 2204/54 + APC SF 9x 4,7 + 2 lipo =  25 W out / 38 W in (%66 efic.)If the target-weight is 6,25 oz., power ratio will be  64 W/lb. Is it enough for a little floater like this (the SOPWITH)? AXI 2204/54 + APC SF 7x 3,5 + 3 lipo =  35 W out / 45 W in (%77 efic.)In this case power ratio will be 89W /lb, which sounds better, but…This second combination is more efficient, but I think I’d burn it. What do you think? Thanks Rafa

[Tim Mackey]

I'd go for the 3s version,  you can always throttle back and remember too that the prop will unload in the air, and amps will drop accordingly. Why do you think you will burn it ?

The motor is rated at around 7A , and you will be consuming around 4 -5 max on this setup.

45 watts in on a 3s ( 10.5V average under load ) is 45/10.5 = 4.3A. 

I expect 90Watts per lb will be plenty for this little bird. 

[Rafa L]

Hi Timbo,

 Most of the tests on 2204-54 in Modelmotors’ web are done under 2 Lipo, that’s why I was afraid of burning the motor. But you’re right and figures are clear. I’ll take your advice and go for 2204-54 + 3 Lipo + 7x3,5 prop.    

The nest point: the battery: I saw in your post you’ll use 460-3s. The smallest I’ve got are 800-3s. I’ll have to purchase smaller ones.

 Motors without this mounting tube the C&K’s got will allow a completely empty battery bay to put the ESC in (and maybe the RX too). That will help me in right balancing the model. (I usually use plenty of glue and often my models are tail heavy)! Thanks for your help. Rafa

[Tim Mackey]

I do have some 900s but they would not fit in the bay due to the motor tube being in the way - so as you say, without the tube, might be poss. I assume you will use a lite ply former to mount the motor, or maybe balsa, rather than just the foam F1 ?

[Kit Carson]

PLE HELP ME WHAT IS/DOES THE MOTOR TUBE DO?

ROY

[Tim Mackey]

If you look at the first of my pictures posted above, you will see a black rod at the front end. This is a carbon fibre tube into which this particular type of outrunner motor is fitted. It is glued into holes in the first three formers. The only bit of tube I had lying around was a bit short, so I simply inserted a little lite wood dowelling into the end to reach F3 - also look at the 3rd picture down ( click them to see full size, and all should be clear )

[Rafa L]

Hi Timbo,

 

You’re right, I’ll to make F1 with something stronger than depron.

 

I’ll also need a mounting box or something similar to get the motor 10mm or so forward.

 

[Tim Mackey]

This is what I did on a foamy fronted model a few years back - would work fine for you on the Sopwith.

Its just a 3 sided liteply box affair which the motor screws to.

[wess]

hi everyone. ive just about finished the sopwith and i am quite pleased with the result. has anyone flown one except cyril of course. lets hear how it goes. i have fitted a pot30 and will start with a 8by 4 folder with a 2 cell lipo. weight with 800 ma pack is 8 ounces. i laminated the wings from 3mm by pva glue on curved biscuit tin that had the right curvature. looking forward to replies

[Terence Lynock]

How do you get PVA to stick to Depron? every time I tried it just peeled off like a skin, I use Evo-Stick Impact but it can be used as a contact too and doesnt contain solvent so is Depron safe, make sure you get the can with the green bar label on the front saying it is solvent free,

                        regards,           Terry

[StarLoc FiveStar Adhesives]

You get a better bond with all adhesives on depron by sanding the surface to remove the shiny skin, this is with all adhesives, some of the `non depron` depron brands are very hard to bond due to the polymer makeup of the material (such as copolymerising with ethylene or similar ) for these you are better with an epoxy or odourless cyanoacrylate for high stress areas

A decent waterproof PVA should bond to depron , but being waterbased and non contact type they take some time to dry after you assemble the parts, a lot of the cheaper PVA`s do not have suitable chemistry to bond to depron due to being diluted to make them cheaper, then filled with talk, clay etc to thicken them, they have no additives to promote adhesion on plastics, good for paper and wood but not much else. High quality PVA`s adhesion is taylored during polymerisation of the PVA to enhance adhesion to specific types of materials as well as porous ones

Contact adhesives such as the Depbond dry before assembly ,  solvent or waterbased they dont have the drying problems as they dry to between 7 and 10% solvent/water before the surfaces are joined gaining final strenth after assembly 

The reason contact types are better bond on the shiny surface of foam (even though its better again if sanded) they have a naturaly high tack (unlike pva) so bond to low energy surfaces such as shiny plastics

The tack in a contact adhesive such as depbond is boosted by additives to promote adhesion on synthetic materials , so they stick to the surface sanded or not whereas most PVA only bonds by soaking into the surface of the foam, the contact glue is better if it soaks in, but stronger if it cant soak in than a non contact adhesive

sand the surface skin off,  to open the surface of the cells in the foam, the glue cant soak in much but it soaks in enough to improve the bond

[Rafa L]

I started making a firewall template with my CAD program and… what a surprise, there is a little trouble with the plan: whilst in front view the fuselage’s 46 mm. wide, on the top view it is 57 mm:

 How did you sort it out? Thanks.

[wess]

hi all. ref to my sopwith and the laminated wings from 2 pieces of 3 mm depron. seeing terrys remarks about pva i remembered that it was not pva but rc modellers glue with a drop of water to thin it down.     i did intend to use pva but have mislaid the tin somewhere so it seems i may have excaped delamination at 50 metres!   i am new to forums so please excuse any silly mistakes i make.

[Terence Lynock]

Thanks William,

                           I have quite a bit of PVA left over from my model ship construction past which I have retired from now and gone back to aircraft after something like 30 years so have a lot of catcching up to do,

                              regards,          Terry

[Tim Mackey]

I too decided to run the rudder control "cables" inside the fuselage. Some more pictures here, just before I fit the lower and top decking. Wings next and lastly, which I can't say I am particularly looking forward to, given the rather sketchy info on their construction and fitting.

As normal, click image for a larger view

[Ced]

Looking really good Timbo. I am painting and adding final details to the DR1. Looks like the weight will be 5.5 oz. ( depending on the battery). I found that just gently rolling the 6mm depron wings over a curved surface (edge of a table or worktop ) will produce a curve that stays. The sheet has a natural tendency to curve in one direction, so that is the way to go. Found a very interesting site for Depron, small brushless outrunners and associated bits. It is:- greenairdesigns.com which also has Replikit Vintage Kits and Accessories as part of the site.

[Tim Mackey]

Thanks Ced....I have tried the " rolling over the edge " method, with poor results so may try the slit and glue system mentioned by another post. Thanks for the link...good one.

[Rafa L]

SOPWITH - Enough place for the batt?

I adopted Timbo’s solution for the battery bay: I made a “ceiling” and opened a gate at F3 low part. I added a ply frame to reinforce F3.

[Rafa L]

SOPWITH- A template will help to place the struts in the exact place