West Wings Skylark build thread

[rogallo]

I have the 4 ch spectrum rx for 30 euro. New. Can bring to mount l sat week.

[Happy Days]

I have to say that I don’t really understand the trend of using Li-Po’s to power radio receivers’ and servos in gliders. :?:

The cost of a 2 cell Li-Po of around 1000mAh capacity is about the same as  a 4 cell Ni-MH of the same capacity. The Ni-MH battery puts out exactly the correct voltage for rx and servos to operate with and doesn’t require the addition of a voltage regulator, (call it a Ubec / Sbec or whatever). Therefore the Ni-Mh works out cheaper.  


Whilst a 4 cell Ni-Mh is heavier than a 2 cell Li-Po of the same capacity that doesn’t really matter because, as Jumbo says, we all have to add weight to the nose of our gliders to balance them anyway.

And finally,…….. Although very unlikely in this day and age, but has been mentioned on this forum before, the risk that the more connecters and electrical gadgets you use in a model, (voltage regulator in this case), the greater the risk of something going wrong.

So although the Nickel Metal-Hydride battery is very much “old technology” in comparison with Lithium Polymers, when it comes to non-powered flight, I would say this is one of those rare situations where older is better.

I suggest that the only benefit that a Li-Po can offer over a Ni-MH (in this situation) is that it can be completely recharged in just one hour.

 Question: Is that one up side worth the downsides? Depends on your point of view!

Finally, while on the subject of batteries for model flight. I read an article today about a new type of re-chargeable battery that is close to production. Based on Aluminium and Graphite is has the advantage of being able to be re-charged in a matter of minutes, and even better from our point of view, it’s flexible and can be moulded into almost any shape. Should be no problem to mould it right into the nose of a glider then!
Even further down the road is the promise of Graphene batteries. This stuff could revolutionise the whole electronics industry,…..but it’s a good few years away yet.

The Keithy will now step down from his soap box, take a gracious bow, and retire to bed.  Good Night all.

Little Keith

[andrew wallace]

:lol:  :lol:  :lol:  Keith I use lipo's  cause they hold their charge and if I wanted to go flying now I can and wouldn't have to wait about for the nimh batteries to charge plus when using spectrum receivers you don't want the voltage to drop and end up browning out
 

[Happy Days]

Hey Andy,

You’re right, Li-Po’s don’t self discharge as much as Ni-MH and, as mentioned, they can be fully charged in a hour.
I guess I was looking at it from a personal perspective in that I always re-charge models the night before I fly them, or I “top them up”  as I’m driving to the slope. (To be sure, to be sure :lol: )

As for Spectrum Rx’s ‘browning out.’ I’m sure this problem is not unique to Spectrum. Surely any Rx can brown out, either through loss of signal or loss of voltage. In this regard it matters not if the model is being powered by Li-Po’s or Ni-MH batteries. Once the battery voltage drops below the rx’s operating voltage, the rx stops working. Then, when the rx (and all the servos) are no longer drawing any current, the battery voltage will recover slightly allowing the rx to re-boot,….. and the whole process repeats itself.

You know yourself Andy, the knack is to be sure the battery has sufficient charge before you launch, whatever type of battery is in it.

Oh, and the other thing you need to remember is……. to switch the model on before you launch it.   Ask me how I know! :oops:  :cry:

[andrew wallace]

    I remember putting a thermal model up on a winch without turning it on  :oops:  :oops: lol
A small down side to the lipo is its a good bit lighter than NiMH and it means more lead
As you say its personal choice I lost faith in the NiMH battaries as I was always worried of them not holding there charge especially when flying large models

[angry_muppet]

Rogallo, what receiver is it? You being it and I'll bring the money! Pardon my ignorance, but you can programme a DX8 to use two channels for ailerons and one each for elevator and rudder?

Keith, for me the merit of the LiPo option is the fact that I only need one charger.  I know it does mean an additional point of failure, but that's the trade off.

[selleri]

You should be able to program the DX8 to operate that way.

You could use lipos without regulators, most rx's can handle that but you'd need high voltage servos and they tend to cost quite a lot of Guinness tokens!

Brownout can, and does, happen to any electric appliance what ever the name of said gadget, the next phase is a bit worse and called blackout, that one can surpass the appliance level and happen to humans too!  :roll:
Spektrum got the ill rep for brownouts from the early days of DSM when it took quite a few seconds to re-establish connections after a brownout.
That was fixed with DSM2 and modern incarnations take fraction of a second to start up again.

[angry_muppet]

Talking of servos; they're the next thing to be fitted...

I'm thinking of placing two small bits of balsa to screw them into rather than glue them in place.

The clearance for the servo arm through the underside of the wing through the ply mount is minimal, I would consider connecting everything up to make sure they move right. But if I want to try and have it ready for the 18th, what is suggested for keeping the fitment square?

I'll put up a picture later, after work.

[rogallo]

wrap in masking tape and epoxy. Simple and easy to field repair.

Just a thought

R

[angry_muppet]

After a little work tonight, here's how she looks...




One question, should I have put the curved part of the control horn flush with what the curve should be at the hinge? :oops:


As you can see, the outline of the tail assembly is there; over the weekend I hope to get more done on, and hopefully finish, the main wings.

Do I cover and then glue on the tailplane, or glue and then cover, or is it just a matter of preference? And, crucially, how do I make sure it's straight?  I think the afternoon end fuselage is slightly favouring the right and the nose, the left...  :x

[Happy Days]

Checking that the fuse, wings and any other part of the build is straight is something that is a constant part of any ongoing build. Whenever you’re about to glue parts together check first to ensure that the build is straight. Check it again immediately after glueing, and in my case, I check it again when the glue is set,…not that there is normally much I can do about the matter if it isn’t! :roll:

Your fuse is of a ‘built up’ design. If there is a slight bend or twist you might be able to straighten it out when you come to fit the covering.
By applying a little more heat to the covering on one side of the fuse you might be able to shrink that side a fraction more, so the covering pulls the airframe straight. Of course, this can only happen  if the covering on the opposite side has enough slack to allow the fuse to  straighten.

Talking of covering,……fit the tail to the fuse and then cover the airframe. Start covering on the bottom, and work forwards and upwards. What I mean is, start at the underside of the tail. Then do the underside of the fuse working forward, overlapping the joins of the covering by aprox 5mm. Try to ensure there are as few joins as possible.

Next cover the sides of the fuse, again starting at the back and working forward. Then of course finish the model by covering the top, starting at the back and working forward. The idea of starting at the back and working forwards is so all the joins in the covering face backwards so if any of them start to come unstuck they wont catch in the airflow and open up all the more.

Small twists and distortions of the airframe wont stop the model from flying so don’t worry too much if the finished produce isn’t perfectly straight. Some of my models that have been repaired umpteen times are quite bent, ( the fuse of my P6 looks like a banana) but they still fly. I just have to trim out the tendency for the models to fly in circles! :lol:


Oh, and finally………turn your blood predictive text off will you. :evil:  Then may be we can understand what you’re talking about…….”I think the afternoon end fuselage is slightly favouring the right “ WHAT??? :!:  :!:

[angry_muppet]

Well, in the afternoon I do tend to drift right and become a grammar fascist...

In the length of the fuselage, the warp is about 5mm.  I was hoping that you would say that the covering will pull it in as it doesn't take much pressure to take the warp out.

[angry_muppet]

As of last night, both wings have most of the balsa sheeting on.  In some fashion... I've found it exceedingly difficult to keep the sheeting in place to allow the glue to set.  Using clips and tongue depressors seemed to work ok when you finally got the clip to stay on.

The leading edge requires shaping and I need to fit the extension wires for the aileron servos and leave a hole to pass them into the fuse.  I think a little epoxy to hold them in place?

Just the sheeting to be done on the nose and base of the fuselage as well.

After that, out comes the iron!

[johnfireball]

Hi angry,
           Try using cellotape to hold sheeting down.
John.

[angry_muppet]

Latest update:

Wings completely assembled; now require the leading edge to be shaped.
Fuselage has the snakes in place, but not glued to allow alignment with the final position of the servos.
Some sheeting to be done - talk about springy, it just doesn't want to stay down to get stuck!

Pics to follow.