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John Wagg08/07/2020 21:20:35
105 forum posts
19 photos

Hi' Jeff, that's good news.

Funnily enough just an hour ago I was thinking, with the spring system, there will always be some force on the servo. Even at centre there must be some force from the spring and what effect on current draw would this cause ?

P.S. Assembled the Gaucho plan but having a problem getting the wing ribs to the right length. I downloaded the PDF ribs from the site you suggested and printed them out. But first print came out too small and the second lot are too big. Just need Goldilocks to come along and sort out some just right. smile

Keep us informed on your progress.

Regards

John

Edited By John Wagg on 08/07/2020 21:21:21

Richard Clark 208/07/2020 22:16:57
422 forum posts
Posted by Barrie Lever on 08/07/2020 08:52:52:

Richard

How did the Sirotkin Spacehound fly as an RC model?

I have not heard of Sirotkin much in the last 20 years but at best he was a formidable character at worst he was something quite nasty.

B.

It's fine, very light too, which I don't usually achieve.. I enlarged it by about 10% and lengthened the tail moment slightly.

It flies exactly the same as the equally thick winged Wolfgang Matt Superstar RC pattern model - I've built three of them over the years.

Jeffrey Cottrell 208/07/2020 22:46:05
186 forum posts
31 photos

Hi Dave

Racking my brains trying to remember how I got mine to the right size.

Must have involved screenshots somewhere along the line. Can only imagine I downloaded the screenshot into paint, and then adjusted the image size from there.

Trouble is I found a page which allowed me to adjust the zoom percentage one point at a time. Darned if I can remember how I got to it.

You say you downloaded a pdf version. The original drawings are in jpeg, so how did you get to pdf?

Might jog my memory.

About the servo, had the same thought myself.

I am using one of the new Plush32 esc, which has a 4a sbec, so I don't think current draw is going to be an issue from that point.

I pinched a slim wing servo from a stalled project which would fit in the pylon. The one I used is this,showing as 1.4Kg @4,8v.

Knowing I would complete the stalled project sometime I cast about for a replacement, and came across these, seem to be the same servo.

Will do some experimenting to see how much pull I actually need.

Jeff

Further to the rib size issue.

I have a Canon iP1800 printer. If I go to print from the original page (not the screenshot) I get a page set up choice, which does include changing zoom percentages one point at a time.

Dug out the prints I did originally to find correct setting, On one I have a cryptic note saying 130%=136mm

The rib size you want is 138mm. I very seldom use page set up, so when I looked at it it had 133% as scale.

I'm guessing if 130% is a fraction short, maybe 133% is the magic number.

You may have noticed I'm not the most computer literate person in the world, but this might help.

Good luck

Jeff

Edited By Jeffrey Cottrell 2 on 08/07/2020 22:48:55

Jeffrey Cottrell 208/07/2020 23:10:50
186 forum posts
31 photos

Hi Again

Things I do in the cause of science.

So, clamped the rudder down to my bench, attached a length of Kevlar thread, over the edge of the bench and tied to a milk bottle.

Kept adding water until I got figures for rudder central, and full deflection against the spring, then weighed the bottle and contents.

Results I got were surprising, but in a good way.

To move the rudder to its central position only took 137g, and to full deflection was 328g.

Both well within the rating of the servo.

I would say good to go.

Any thoughts?

Jeff

John Wagg09/07/2020 11:05:30
105 forum posts
19 photos

Ribs - Finally got a print off matching the rib lengths to the plan. (13 tries) On the .jpg (not PDF as I thought) page there is a drop down box to resize. It gives the option to keep the "define custom size" and to "maintain aspect ratio". So with a bit of hit & miss I managed to print off a set of rib patterns.

Jeff - with such a small rudder I have no idea of the air pressure on it. As long as the "spring" will withstand it then all good. We will wait for the report to see what effect on turning control you will end up with. Same goes for elevator and what effect that has.

I'm still perusing the plan and thinking about the practicalities of electrifying it.

Thanks for all the info' so far.

John

Edited By John Wagg on 09/07/2020 11:06:58

Jeffrey Cottrell 209/07/2020 13:03:19
186 forum posts
31 photos

Hi John

So, 13 tries. You score 10/10 for persistence. At least it only needs doing once.

As regards the rudder, remains to be seen. On my original thread here, John T did think the rudder could be a bit bigger. I moved the hinge line about 10mm further forward. No scientific reason, just looked about right.

One thing I did notice.

When you look at Andrew Newton's video, he inserts the torsion bar while the rudder and the fin are back to back. Even with the rudder central, the bar has already twisted some 180 deg. Can't imagine the airflow would be an issue, with that amount of twist already in place.

What it does mean, though is that even with the rudder fully deflected in the direction of the spring the servo will still be working to limit the amount of deflection. Back to the question of the servo under load all the time.

The system works well for dlg's so who am I to argue?

The model has a really long tail moment, which means the rudder has a lot of leverage to work through. I think that'll be fine on the glide, after all this is 'radio assist' rather that 'radio control' but I wonder what it will be like under power, when I might need more rudder response.

Won't know for sure till it's up in the air.

Cheers

Jeff

Jeffrey Cottrell 217/07/2020 16:58:28
186 forum posts
31 photos

I'm still perusing the plan and thinking about the practicalities of electrifying it.

Hi John

Word of warning.

Just completed my Gaucho, see new model thread, but despite fitting everything as far forward as possible I still needed some lead in the front to get the c/g right.

Granted I probably used a lighter motor than most, but if you're still thinking about one, could I suggest lengthening the nose. About 2" should do it.

If it comes out a little nose heavy, far less weight needed in the tail to balance.

Will give a flight report when I have maidened it. Next calm day and availability of my launcher should do it.

Wish me luck

Jeff

John Wagg17/07/2020 23:13:50
105 forum posts
19 photos

Hi Jeff - still perusing. I was considering a 2s Li-ion cylindrical battery in tandem to keep the fuselage slim. A bit slow in deciding what to do as other priorities this week. Decisions on where to put the receiver and servos etc. Seen your other post and looks very nice. Thanks for the heads up about possible longer nose. That's what has put me off other designs with their very short noses.

Cheers, John.

Jeffrey Cottrell 218/07/2020 08:18:54
186 forum posts
31 photos

Hi John
Thanks for your kind words. Have to admit it wasn't my finest covering job. In my defence it's been a while since I covered a 'stick and string' model.
Anyway, when it's 100' up in the air, who can see the flaws.
The purple is Hobbyking film, Modena if I recall, and the white is a roll I got from Bangood. Both have proved easy to use and worked well.
I have uploaded some more photos to my album. Feel free to take a look.
As regards battery choice, Li-Ion would work well, but I can see a couple of issues.
Wonder if these might be a better option.
I had a spare set of the earlier ones, 900Ma. The ones shown are the same diameter but about 10mm longer.
Best thing is they are only 12mm dia, that's slightly less than an AA dry cell.
As regards the longer nose, it would be better from the balance point of view, but don't go too far or, in my view, you will change the character of the model.
As you say, most models of this era and purpose had very short noses.
Distinctive part of the overall look.
On principle I hate adding lead to a model, but in the real world is it so much of a problem?
Even with the added weight my model only comes out to 376g or 13.4oz, which gives a wing loading of less that 7oz/sq ft.
Should give a good, if slow, glide performance.
That's all I've got so far. Waiting on the arrival of a couple of bits, then a test flight will tell us more
The instructions say 'test glide over long grass'. Boy, does that bring back memories!
Any questions, please ask
Jeff

Jeffrey Cottrell 218/07/2020 12:20:39
186 forum posts
31 photos

Hi John

PM sent

Jeff

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