Bistormer 60" (A Barnstormer with more ribs)

[Tim Hooper]

Posted by Danny Fenton on 15/04/2014 21:19:44:

Thanks chaps, still a bit plain, but I kinda like it that way

Not plain. 'Understated' is the correct term, and it suits this model admirably!

tim

[Lindsay Todd]

Nice one Danny, I particularly liked the red trainers, very stylish Linds

[Nigel Day]

Hi Danny.

I've just got to the ailerons and was wondering how the differential was achieved just by connecting the pushrods up to different arms of the same servo whilst the horns/connections to the ailerons are identical?

As I understand it, each aileron goes down less than it goes up so how does this arrangement make the left aileron go up more than the right aileron goes down - and vice versa?

Thanks in advance,

Nigel

[Phil Winks]

Posted by Nigel Day on 26/08/2014 18:26:21:

Hi Danny.

I've just got to the ailerons and was wondering how the differential was achieved just by connecting the pushrods up to different arms of the same servo whilst the horns/connections to the ailerons are identical?

As I understand it, each aileron goes down less than it goes up so how does this arrangement make the left aileron go up more than the right aileron goes down - and vice versa?

Thanks in advance,

Nigel

 

Its not usually possible to have aileron differential with only one servo Nigel, one of the reasons I used 2, mechanically this is done by setting the servo arm of centre away from the aileron by a couple of degrees the only way this can be done with one servo is if the servo horns aren't diametrically opposed IE: they form a shallow V, this can be done by making a servo horn from typically 1.5mm glass fibre sheet and attaching it to the original horn as shown in this rough sketch

the red dotted line is the original servo arm the black line the new arm fitted on top

the offsett of the holes will determine the amount of differential the further you shift them away from the aileron the greater the resulting differential

Edited By Phil Winks on 26/08/2014 19:00:56

Edited By Phil Winks on 26/08/2014 19:01:54

[Danny Fenton]

Hi Nigel, great question and you are quite right the down going aileron travels much less than the upgoing.

On my Bistormer I achieved this by mounting the two aileron pushrods on the servo output disk at two points about 60 degrees apart. I used one of those 6 sided star output disks that nobody uses

As the servo pulls the wires it brings the ailerons up, so you can see the wire being pulled travels further as the arc passes under the servo. The wire being pushed, almost immediately starts to curve and rise with the rotation of the disk, and doesn't travel as far.

Hope this rubbish explanantion helps?

Cheers

Danny

[Phil Winks]

Totally forgot about those star arms/;discs Danny been a while since I got one with a servo such is the down side of the popularity of computer TX's where mechanical mixing isn't required so much

[Danny Fenton]

Lol I know what you mean Phil, we forget the old school stuff now and then. There are a few other ways of doing it, the angle of the aileron horns to the hinge line, and also the angle that you set the bellcranks in the wings. But this was the easiest, with hind sight it needed more so could have done with the bellcranks turning also. But hey ho it flys well enough.

I managed to pick up some more cream Solarspan 2000 at the Nats and will repair my silly tear in the fuselage film that I caused removing the camera

Cheers

Danny

[Phil Winks]

To be fair Danny I'd also forgot the ailerons on yours were on bell cranks and kinda assumed we were talking torque rods which would more or less leaves you with alterations to the servo arm, especially if you want any way to adjust the differential in the future

[Colin Leighfield]

I got enough differential on my Depron Barnstormer this way. Knowing the adverse yaw tendency of parasol wings I've dialled in 40% coupled aileron/rudder as well and it turns very nicely. perfectly.

[Nigel Day]

Thanks Obi Won.

I figured it must be something to do with the geometry involved with the connection and spacing on the servo 'wheel' but couldn't visualise it.

It's the same with the differential travel resulting at the aileron end. I'll need to connect it all up to see how the rod being pushed (not so far) causes the aileron to go down (and not up). I suspect that this is dependent on the servo being fitted the same orientation that you've used. I'll be copying anyway so I know it'll work - it's just that I need to work out why so that I can apply it (or not) in future builds.

I see on the plan that the Chippie has separate servos for ailerons and flaps. I know that the (aileron) differential) will be programmed in then. That's a topic for a different thread a little way into the future.

Thanks once again (and to you Phil).

Nigel

Edited By Nigel Day on 26/08/2014 19:55:24

[Nigel Day]

Thanks Colin.

It's more a case of 'why does it work your way (that I'm copying) Danny?' than 'how do I make it work?' Danny's explained it well enough and I'll hope to understand the rest with a close eyeballing when I've put it together.

[cymaz]

It's to do the the arc of travel that the arm makes.

[Nigel Day]

Thanks Cymaz. Yes, I can visualize it now. It'll become clear from servo to aileron when I put it all together (I hope!)

[cymaz]

Try this Nigel.

[Danny Fenton]

Nice link CYMAZ That shows it better than my rubbish explanation, hope the young Padawan understands

Cheers

Danny

[Phil Winks]

Posted by Nigel Day on 26/08/2014 19:58:23:

Thanks Colin.

It's more a case of 'why does it work your way (that I'm copying) Danny?' than 'how do I make it work?' Danny's explained it well enough and I'll hope to understand the rest with a close eyeballing when I've put it together.

Just in case you didn't find the picture on there Nigel this shows the geometry perfectly

the red arrow shows clearly the differing amounts of linear travel for the same amount of turn in each direction of the disc/arm

[cymaz]

Umm...that does , he surely must ..the young apprentice.

Edited By cymaz on 26/08/2014 20:36:47

[Nigel Day]

Understand it now I do. Thanks to all I must give.....

[Colin Leighfield]

The other easy (easiest)? thing that you can do is to set the horns into the ailerons at an angle forward, which does exactly the same thing as angling the arms on the servo as shown on my earlier pictures. That way you maximise the final upward movement of the aileron and minimise the downward movement. You can do that with your single servo set-up and don't need to change anything else. You can easily test it to see if you can get enough that way. Definitely consider the coupled aileron/rudder as well, this is basically a design that was intended to turn on rudder originally as I recall it and CAR gives you the best of both worlds, I think.

[Phil Winks]

Colin is indeed correct this was a 3 channel design originally, whether you mix rudder to aileron at the Tx or fly fully on the sticks is personal choice, to be fair I tend to do the later but it really is a horses for courses thing. my only comment on achieving differential at the control horn is most times this is a once only adjustment and once done its done for good, without surgery (unless some one knows where to get adjustable horns for this purpose), which in my humble opinion is best avoided if possible

[Colin Leighfield]

As Phil says, you can do it on the sticks, but if ever there was a lazy waffly kind of a model, this is it, so I'm for the easy life and just mix it in. If you make the horns yourself, it's not difficult to engineer them to have different fore and aft hole positions, but this isn't exactly arerodynamically critical and if it looks about right, it's generally ok. Something like twice as much up as down won't be far off, or even eliminate the down completely, it will all work.

Phil's a craftsman who rightly takes pride in his workmanship, I tend to be satisfied with the lazier option. Something of a (not so) artful codger, which others might have noticed!

[Robert Parker]

Bookmarked for later reading

[Robert Parker]

Here's my 72" version

Followed some of the tips and made a canopy, steerable tail wheel and 4 ailerons

Regards

Robert

[Dodger]

GPosted by Robert Parker on 09/02/2019 16:51:43:

Here's my 72" version

Followed some of the tips and made a canopy, steerable tail wheel and 4 ailerons

Regards

Robert

Gwhizz indeed. I'm impressed.

[Danny Fenton]

Hi Chaps, that looks ace Robert

Seeing this post has made me realize I missed several replies, sorry chaps.

I gave my Bistormer away to a clubmate at Lower Drayton, haven't seen it since, though he did fold the back seat on it as he loaded it to take it away

Cheers

Danny