Sigma

They stay up by magic!
User avatar
Carl
Posts: 267
Joined: 16 Feb 2018, 13:26
Location: Way down in the South West
Contact:

Re: Sigma

Post by Carl »

A little while ago I got hold of a ready built Sigma that needed a little work that I have now done. Different to Wayne's approach I would like to make an electric power pod for mine. I've worked out how to mount one, but would like a little advice on what motor/prop combo would you think will do the job. Or just a starting point would be good as prop size basically will determine the height of the pod.

The wingspan is 45" with AUW of 410g (14.5oz). It's quite a short model - I'm so far used to seeing the fuse having a similar length to the wingspan.

Another point of guidance would be the positioning of the motor in relation to cg. Best over cg, a little ahead or behind?

Thanks for any help and I will take a few pictures in the next couple of days.
Carl

------------------------------------
STILL LEARNING
------------------------------------
User avatar
Sundancer
Posts: 122
Joined: 07 Jun 2018, 09:28
Location: Limousin, France

Re: Sigma

Post by Sundancer »

Any motor that will give you 60 - 80 watts should fly this very nicely. One with a Kv of around 2500-3000 will suit the use of a 6 inch prop (6 x 4 or 6 x 5.5 APC would be good) so that the pod can be quite compact. See https://www.brchobbies.co.uk/brc_en/ema ... motor.html for one inexpensive example. I have a few of these and they fly 16 - 24 ounce vintage models very well.

I would personally mount it with the motor on or around the CG, but further forward would also work well especially if you have nose ballast which can be reduced to compensate. The ideal thrust line for pod mounted motors varies from model to model, but a couple of degrees upthrust relative to the wing incidence is a good place to start.
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Sigma

Post by Wayne_H »

Hi Carl,

For inspiration & insight, I recommend you check out DB's "Apprentice"
(https://outerzone.co.uk/plan_details.asp?ID=1621)
& "Kestrel"(https://outerzone.co.uk/plan_details.asp?ID=7923).
The Kestrel is more akin to the Sigma having a tapered wing & a flat sheet tailplane.

Both have similar power pod arrangements you could easily modify for a 2212/1300-2000 kv on 2s or an 1810/12 ditto. There are heaps of 5"-6" 2 & 3 blade drone props you can use. The 750-1100 mah 2s pack could go in the fuse or in an extended power pod, mounted on the CofG in either case. If you intend to make the pod removable, mount the battery behind the CofG to offset the motor weight, so there is no CofG change with or without the pod.

Have fun ;)
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
User avatar
Carl
Posts: 267
Joined: 16 Feb 2018, 13:26
Location: Way down in the South West
Contact:

Re: Sigma

Post by Carl »

Thanks George and Wayne for your sharing you experience and helpful information - that's given me something to go with.

Amazing to get help from France and far flung places like Australia :D
Carl

------------------------------------
STILL LEARNING
------------------------------------
User avatar
Sundancer
Posts: 122
Joined: 07 Jun 2018, 09:28
Location: Limousin, France

Re: Sigma

Post by Sundancer »

Good point that Wayne makes about three blade props Carl, a way to be able to use a shorter pod. And one other thing to mention (forgive me if you already know this),if needing to extend the wiring, lengthen the three motor-ESC wires, not the two ESC-battery ones. The wires for the little 1811 on my Tarquin (below) run in a hollow pod strut with 1 mm ply sides around a balsa core.
Attachments
T3.jpg
T3.jpg (19.47 KiB) Viewed 7075 times
User avatar
Carl
Posts: 267
Joined: 16 Feb 2018, 13:26
Location: Way down in the South West
Contact:

Re: Sigma

Post by Carl »

Sundancer wrote: 16 Nov 2018, 13:24 (forgive me if you already know this)
As my sign off says "STILL LEARNING" so any advice welcome. Thanks for the picture - that helps.
Carl

------------------------------------
STILL LEARNING
------------------------------------
User avatar
Shaun
Posts: 1049
Joined: 15 Feb 2018, 21:49
Location: West Yorkshire

Re: Sigma

Post by Shaun »

Hi Carl,
Why not use one of the 2205-2300kv motors you have spare and a 5x4.5x3 prop.. that should deliver the beans on 2 S even better on 3s.
Shaun.
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Sigma

Post by Wayne_H »

Hi Carl,

I've just posted details (including all parts) for the 1980's(??) Graupner power pod in the Documents & Files section --->> here viewtopic.php?f=8&t=507

While originally intended for 1.00 to 1.5cc glow or diesel motors to launch the Graupner Cirrus or Cumulus 2800 semi-scale sailplanes, it will hopefully provide further inspiration/insight. ;) :P
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
User avatar
Carl
Posts: 267
Joined: 16 Feb 2018, 13:26
Location: Way down in the South West
Contact:

Re: Sigma

Post by Carl »

Thanks to those for their input.
Wagga_Wayne wrote: 19 Nov 2018, 06:00 I've just posted details (including all parts) for the 1980's(??) Graupner power pod in the Documents & Files section --->> here viewtopic.php?f=8&t=507
I've come across the Graupner power pod and thought it a neat setup for models with plug-in wings. It's good to have more detail.

So what I've done is come up with something that is basically combination of what has be suggested.

The Sigma has plug together wings using a joining piece, so I'm going to make a new joining piece that incorporates a pylon power pod. I've produce a version in card:

You can see the original ply joiner to which I've attached a card template of the power pod to see how it works out
You can see the original ply joiner to which I've attached a card template of the power pod to see how it works out
The motor isn't the one I'll use. It'll be what Shaun suggested (2205-2300kv) but just waiting for them to arrive. The prop is a 5x4.5 - I do have a 5x4 4-bladed prop too
The motor isn't the one I'll use. It'll be what Shaun suggested (2205-2300kv) but just waiting for them to arrive. The prop is a 5x4.5 - I do have a 5x4 4-bladed prop too
I'll use balsa block behind the circular ply plate to which the motor is screwed and shape it
I'll use balsa block behind the circular ply plate to which the motor is screwed and shape it

There is a shaped piece that goes over the wing joiner over which you band the wing into position. So I'll need to in-fill some block to get the same result. Because I've installed a 2 channel 27 mhz system I plan to use my motor timer on the Sigma. But will add another new feature. At present if you set a zero motor run time, the timer counts down and does nothing. So I plan to add a feature whereby you can activate a switch operated by full up elevator to turn the motor on and off when the timer is set to zero (I will eliminate the countdown blips in this situation). If the timer is set for a motor run, then I will still allow the switch to override the timer and cancel the timed motor run, and from that point the motor controlled by the on/off switch.

I have a few pictures of the model. So I'll do that next...
Carl

------------------------------------
STILL LEARNING
------------------------------------
User avatar
Carl
Posts: 267
Joined: 16 Feb 2018, 13:26
Location: Way down in the South West
Contact:

Re: Sigma

Post by Carl »

Here's a few pictures of my Sigma that I picked up for virtually nothing :)

It came even with the case as per original plan!
It came even with the case as per original plan!
And inside the model fits nicely, including my Horizon transmitter
And inside the model fits nicely, including my Horizon transmitter
Out of the case
Out of the case
All togther
All togther
I installed my Horizon 2 channel set
I installed my Horizon 2 channel set
Had to do some remedial work on the rudder and elevator
Had to do some remedial work on the rudder and elevator
Carl

------------------------------------
STILL LEARNING
------------------------------------
Post Reply