SE5a CONSTRUCTION BEGINNING TO . . .

[Guest]

Grahame, just something you may find usefull one day.

Most camera's have a two stage shutter release and the vast majority set focus and exposure on the first stage and then actually open the shutter on the second stage.

In your picture above if you had placed an object next to the subject at the same distance away from the camera as the point you want to focus on, focused on that by pressing half way and then holding the shutter release button at the first stage point. Then simply swing the camera across to your actual subject and press the shutter release button all the way. Holding the button at the first stage holds the focus and exposure settings which can be usefull for just the type of shot you have tried there.

If your camera does not do this then I apologise but I think it was worth mentioning anyway.

[Greyhead]

Richard


Thanks for that tip; it’s still not perfect but a lot better and the technique obviously works!

[Guest]

Wow, thats an impressive model. Its amazing reading your construction commentry!

I want more.

Euan

[Guest]

RichardThanks for that tip; it’s still not perfect but a lot better and the technique obviously works!

Definately an improvement and at least the camera is not focused on the end of the tunnel now.

[Guest]

Hello Grahame,

now that some weeks passed since you last read a message from me I really have to post here in your SE5a development thread. It's great to see the plane get better from day to day. Most pleasure for me is that you don't lock your know-how away. It seems that you're doing your best to improve our modeling skills.

Seeing how you lay your interest on details and how you scale them down to an eyecatcher that is looking real is pure joy.

Thank you for that, Grahame.

:respect1:

Dirk.

p.s.: Please greet your brother from me and tell him, that even if he doesn't like to document his project here, I would be very happy about finding some photos in my mailbox or just some written lines about the kit and the differencies to the original.

[Greyhead]

I’m only to pleased to pass on any tips that I have, if it encourages more people to advance from ARTFs it’s an effort not wasted! One thing I have learnt in my years of aeromodelling is that you never stop learning; every new model presents new challenges.


I’m not sure whether this is the third or fourth version of the control pulleys but they are now at a stage of development that I feel warrants a trial. The problems that have arisen during tests have been the pulley wheel jamming and the cable jumping out of the groove in the wheel if there was any slack in the system.


Here is a photo of the new components and a finished assembly.





The jamming has been cured by using a larger diameter bush in the wheel and an extra length of tube slightly longer than the thickness of the wheel through which the pin goes; this ensures that the wheel doesn’t bind on the shackle when the pin is peened in position. The extra “arms” on the shackle are bent around the edge of the wheel to prevent the cable jumping from the groove.

[Guest]

Hello Grahame,

perhaps it wouls be possible to etch the unrolling of the guiding (you showed us on the photo of the pulley wheel in one of your first postings in this thread) out of copperplate. By soldering that part together you should get rounded edges on the inside of the guiding and a quite exact part which could easily be installed, wouldn't harm the wire (rounded edges on the inside) and which would really serve as an eyecatcher. Last but not least this solution should be exact enough to help you getting rid of the jumping out problem you have.

Greeting from the continent.

Dirk

[Greyhead]

Having made 2 pulley assemblies I decided to trial fit them in one half of the tail plane before making the rest. Fitted temporarily and using button thread for the cables has proved that the pulleys are OK but that my calculations for the height of the elevator horns were wrong; they need to be 2mm taller to prevent the cables catching on the covering support.





The final cable runs will all be through the ribs but at this stage it’s just easier to leave them on the outside.





I was talking to a friend about the elevator controls and he wondered why I wasn’t going to use the scale system for the elevators, but was for the ailerons, especially as I’d gone to all the trouble of making working pulleys; so here’s the explanation:


The pulleys have to be incorporated anyway because they are a very “visible” part of the model, but the problem is getting the control cables into the fuselage in such a way as to be useable. If I’d designed the tail plane as a one-piece unit it may have been practical but it just wouldn’t look right and making the tail incidence adjustable would then have been impossible without having gaping holes in the side of the fuselage. With the aileron linkage there’s a lot more room and only one cable per side, which can be attached directly to a servo, should be no problem (famous last words!!).

[Greyhead]

The elevator control pulleys work far better now that they have their solid attachments and the tubes for the cable runs. The tubes are free if you’re lucky; they are what lengths of piano wire are in when they are delivered to your local model shop and are usually thrown away.





In fact they work so well with the cables connected, at the moment only using button thread, that I’m wondering if it may be possible to actually use them for the elevator control. I’ll get them covered and leave the decision till later; it’ll involve some quite major “surgery” to the rear of the fuselage but if at all possible it will be worth the extra effort.





Here’s a photo of the tail plane in position; the elevators have already been covered.





I have usually covered my models with white Solatex as I find that any colour paint produces a good solid cover over it, but for the SE5a I’m using natural as the underside is plain, doped linen. When I covered the fin and rudder I used scraps of white Solatex for the rib tapes, but for the elevators I used the same Solatex that I’m using for the main covering and this was when I discovered that it is so much easier the fray the natural Solatex.


If you are building a WW1 model and you’re going to fit rib tapes I strongly suggest that you use natural Solatex even if it’s not the best match for your paint, it really is that much easier!

[Guest]

Wow, thats amazing, down to last little detail!!!

Euan

[Greyhead]

My original thoughts on the elevator control were that the 4 cables would have to run forward to a servo, or more probably a “slave” bell crank, just behind the cockpit. This would involve 4 extra pulleys mounted behind the tail plane fixing block, therefore the cables would have to exit the tail plane at least the diameter of the pulleys plus half the thickness of the fixing block behind the pivot point. This in turn means that if the tail plane incidence needed to be changed, almost a certainty, the cables would move through a considerable distance so the pulley fixings would have to be able to accommodate this; all very complicated and therefore most likely unreliable. Not the sort of thing you want in such a vital system so I decided against!


As I took the photos, for the previous post, of the pulleys with the cables in place I held them tight with my finger and thumb; this is when I had a “eureka” moment, if I twisted my finger the elevators moved!





My idea now is to use a horizontal drum mounted close behind the fixing block with one cable going from the top horn of one elevator, a complete turn around the drum to the bottom horn of the other elevator; a “slave” cable will join the other horns together to transfer the pull.


That’s the theory anyway; I’ll build a test rig and do some experimenting but I’m not going to cut off the “working” control horns just yet! This is still at the early “thinking” stage so any suggestions will be gratefully received.

[Guest]

coming along nicely greyhead

[Greyhead]

Well having spent a couple of days with the tail plane on a jig experimenting with various pulleys, drums and bell cranks it’s back to plan A!! The problem in the end was not the pulleys etc. but being unable to get the correct and equal tension in all the cables. The aileron controls will have an adjustable “quick link” where each wing joins the centre sections but with the tail plane there just isn’t the space.


The elevators will actually be moved via a snake and ball link, which will be pretty much hidden inside the rear of the fuselage.


The cables go straight from one side of the tail plane to the other and are for “effect” only but look quite convincing; these photos show the final trial set up on the jig.

[Glider Guider]

I’m not surprised that you had such problems trying to use the pulley system in what was essentially a closed loop system, unless I’ve misunderstood you. Closed loop systems seem simple on the face of it but to get just a straight forward servo to rudder system working where one wire doesn’t go slack can be a challenge and there is a lot of geometry involved not to mention the Ackerman effect.

Anyone wishing to read further on the subject of designing closed loop systems could do worse than to read this excellent on-line article by Brian D. Felice at http://members.cox.net/bdfelice/Ackerman/ackerman.htm, he has a lot of other useful articles on his website as well.

The SE5 is coming along fine Grahame and I'm hoping to try a instrument panel along the lines of yours in my Auster J1.

[wonwinglo]

There is a lot of scale effects coming into play here,take a study of a Tiger Moth control system next time you see one,cables flapping around and twanging against the fuselage fabric,it is all about tension and adjustment,sadly when working to such a small scale things get exagerated and slop becomes a real issue,and dont forget that most full sized machines have balance cables,these ensure that there is adequate tension on the control system,and there is another important difference between full sized and model,whereby our models rely on a fixed servo to operate the controls via cables there is no balanced aerodynamic effect to take the load away from the power source ie servo,full sized controls literally 'fly' and are assisted with mass balances to make the aircraft more pleasant to handle.

So this is one area that is heavily dictated by the sheer small scale down effect,it cannot be emulated exactly the same as its real counterpart,so we have to compromise.