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Author Topic: CO2 Duration Anyone?  (Read 8657 times)
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DaddyO
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« on: March 27, 2010, 05:09:11 PM »

Having ventured into the realms of weedy power models last season with the E30 logically building upon that experience and trying open electric or F1Q would be sensible...

Inevitably therefore I've chosen to have a go at another of the 'rice pudding skin puller' classes instead Wink

Don't worry we're not embarking upon some F1K super model... I'm thinking of something similar to a P30 powered by CO2.

The comp. we fly is 5 flights to a 2 minute max and then a (usually) unlimited flyoff.

The only rule in the book is that the tank capacity cannot be greater than 3cc. Inevitably this lead to some (half joking) suggestion that I bolt a CO2 motor onto the back of an open rubber model (No rule that says it needs to be the only power source!) Shocked Wink

Then I started looking more seriously at what other folks have been successful with. Weight appears, or its lack at least, to be crucial. Most of the winners seem to be paired down to a minimum; usually spurning either a tracking bug or tomy in the bid to make 'em light. 45-55gms being typical. (12gm wings and 2-3gm tails)

Possible motors are the usual suspects - Telco's etc. or modern Gasparin's (sometimes the twin ballrace version). Freezer sprays to chill the tank so it will accept more 'fuel', pre-running, in fact lots of fun and games can be had. A few years ago high thrust line pushers were the way to go, latterly more conventional layouts seem acceptable. Props are usually fixed rather than folding (a bit like E30 the motor run can be loooooong)

I've singled out a couple that I like the look of -

First up is Ian Davitt's apparantly low tech approach. Looks can be deceptive however, this one has a run of National wins to it's credit and not all of those can be just down to Ian's careful choice of air. (Ian is also a highly competitive coupe flyer)
And in the Blue corner we have Chris Strachen's highish aspect ratio job complete with skinny tailboom looking like a mini wakefield.
I've also got a couple of idea's of my own to throw in the mix so we'll see what comes out the other end Cheesy

Ain't life a gas
Paul

ps
Hopefully the nitro users won't mind me hissing around on their board Wink
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« Reply #1 on: March 27, 2010, 05:59:38 PM »

Paul

Just a petite correction, namely that it's only three flights now. When I first started flying the class it was five, but like mini-vintage it was cut to three a few years ago.

A P30 wing on a rolled balsa fuselage (1/32") is an easy way to go and you could make use of the Teacher's Pet wing. The model I fly at the moment has a Fuit (vintage coupe) wing on a pod & boom fuselage. It's no lightweight at circa 65 grams, but still flies well. I wasn't worried about the weight as I wanted to use it in pukka F1K comps where there is a minimum weight of 75g.

I have two others, one is a Jedelsky winged job with a Modella, and t'other also with a Jedelsky wing of Depron/balsa with a GMW 73.

Get building, we want to see photos Grin

Peter
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« Reply #2 on: March 28, 2010, 03:12:42 AM »

Thanks Peter

That's a relief - it means that flying CO2 and F1H on the same day is 'on' (must admit 12+ comp flights in a day is a bit much for my aging limbs Grin

I'll get some pics up for you later

Paul
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DaddyO
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« Reply #3 on: March 28, 2010, 02:35:12 PM »

Okey Dokey folks

Here's the couple of designs I singled out as likely candidates. Not much to add to my earlier ramble. I like Ian's use of thin carbon capping on the main spar and the general layout of Chris', (apart from that high aspect ratio wing), so that's the sort of thing we're looking at.

I found a couple of templates for the ribs that I've used previously on a Coupe that looked like they'd do the job. Starting with Chris' design I decided to increase the chord to 4" on the wing and added a bit more tail area by increasing the chord on that too. This is all a bit TLAR and subject to change as the build progress' Roll Eyes

Some nice QG (1mm) wood from Flitehook, a new blade in the scalpel and a bit of old mount board to act as cutting mat soon saw a pile of ribs. Cheesy
(Because of the depth of these I just cut the notch for the top spars; I'll use a file to notch for the bottom ones once they are assembled. I've come a cropper in the past cutting both at this stage...) Top wing spar will be 3/32" balsa with a carbon cap. The tail will be all wood with 1/16" spars to keep the weight down.

Paul
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DaddyO
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« Reply #4 on: March 29, 2010, 03:17:55 PM »

Not really a build thread, but I thought a few pics as I go along wouldn't go amiss Smiley

Fuz is a simple balsa box. Ian uses 32nd sheet for his, mines a bit longer so I've gone to light 16th for the sides and top and 3/32 for the bottom. I'll give it plenty of sanding to keep the weight reasonable (hopefully) and may cover it in mylar rather than tissue. My experience of balsa fuzes on vintage gliders has demonstrated that they like to bend in strong sunlight (inconveniently straightening again when in the cool of the workshop!) Undecided

The carbon I used on the spar is some unidirectional cloth (Free Flight Supplies) that I laid up using 24hr araldite and 2 pieces of thick polythene. Cut the polythene about an inch or so larger all round. Place on a smooth surface; lay on the cloth and smear on the Araldite (use gloves it gets a bit messy). When it's all well coated, lay on the top piece of polythene and squeeeeeeze as much resin out as you can. Add a sheet of glass and some weight and go to bed - in the morning you will have a nice sheet of fibres that can be superglued to balsa easily and cut with scissors Grin

Pics to follow
Paul
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DaddyO
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« Reply #5 on: March 29, 2010, 04:03:31 PM »

Interrupted for a few rounds of Wheels on the bus! Tongue

Anyway here are the pics.

I laid superglue onto the spar then inverted it onto the carbon. When dry it's easy to cut using a sharp scalpel, using the balsa as a guide.
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DaddyO
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« Reply #6 on: March 30, 2010, 04:47:41 PM »

Wing and tail being laid up

For the wing I used my cambered board (now looking rather dilapidated) Embarrassed A piece of kitchen worktop (@45mm thick) cut into a plank 7" x 36" by those nice chappies at B&Q a few years back. 'Negative' ribs (ie matching the undersurface camber) are glued every 4" or so and then the top sheeted with 3/32nd balsa - a light sanding and you will wonder how you ever managed without one. Wink

I waxed the drawing I did of the wing layout with a candle and spray mounted it in position ready to go.

At the point shown I'll remove the panels, put in the dihedral and add some ply braces to the back of the leading edge. Then the missing ribs are put in (I'll use thick ribs @ 1/8th to make covering that bit easier) and finally I'll add the spars...

Tail is all as expected. I'll harden the centre inch or so of the leading edge with cyano and leave it at that.

Thinking light thoughts
Paul
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« Reply #7 on: March 31, 2010, 03:20:53 AM »

In terms of building, I think that you should be renamed Speedy Gonzales Grin

Enquiring minds (well I think I just about have a mind!) want to know what motor you've acquired? Also, the type of DT you intend to use? Speaking from experience, lightweight CO2 models have a propensity for flying away in strong lift, even when DT'd. I've lost one at Rissington (got the model back a week later sans motor) and one in France. Both had GMW 73 motors, and those of you who have looked at prices on e-bay will know how much that hurt :'( :'(

Peter
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« Reply #8 on: March 31, 2010, 04:37:34 AM »

Ouch! :'(

Enquiring minds may have to wait a wee while, since I've not actually got a motor yet...

I've been promised a mixed bag of engines from another club member (nice to have friends) Smiley Included are Telco's, Modela's and a Gasparin (G63 I think) so I'll have a selection to choose from which is nice. At the moment I'm expecting to go down the Telco route because quite honestly Gasparin's are too nice to cast into the wilds of the Somerset countryside.

In the meantime I've managed to purchase a refilled SodaStream cylinder and an adapter for it too (both secondhand of course)

Once the bits of the airframe are finished there will be a pause in proceedings till the next area meeting, at which I should collect said goody bag.

DT wise I was going down the pop up tail route - maybe pop up wing is a better option given what you are saying Undecided

Popping off completely
Paul
aka SG
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« Reply #9 on: March 31, 2010, 01:49:22 PM »

Did a bit of mylaring whilst the little 'un was sleeping

(Covered the tailplane too) Wink

Using an old dope jar I thinned Evostick down with its own thinner (cellulose don't work no more!) to a creamy consistency and gave the framework 3 coats (a bit of time to dry between coats)

Here are the finished items. Sorry no weights since I dropped the nifty scales I normally use and they don't seem to work properly anymore - something else to buy Tongue

Butterfingers
Paul
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« Reply #10 on: March 31, 2010, 06:06:13 PM »

Paul,

Following this thread with interest - I have thought about making a model in this class too. I already have a GM63 that I would use.

Have you ever used balsaloc to apply mylar? If so, how does this compare to the thinned Evostik?

I also have a smaller CO2 motor that runs correspondingly longer on a 3cc tank - do you know if smaller than 'telco types' have been used to good effect?

Enough questions for now I think!

Russ
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« Reply #11 on: April 01, 2010, 02:29:07 AM »

Mornin' Russ

Yep I've tried Balsaloc, but didn't find it worked as well when it came to getting out those little creases - didn't seem to 'hold' the mylar quite as well. Others have found it okay of course. I've also tried RC56 canopy glue which seemed similar. Neither had the 'smell problem' of Evostick though Tongue
Whilst on the subject I do find that I use more coats of glue than most folks; The glued area is a very slightly tacky and will hold the mylar with very little heat.

The Gm63 is supposed to be a goody - have a go Smiley

I think the main drawback of the smaller motor route would be airframe size. You'll need a smaller model which is going to be harder to keep in sight...

Another option to extend the run is the larger, possibly single bladed, prop approach. Mark Croombe had a lot of success with his indoor duration models going this way. Needs a calm day though and long term it may cause damage to the motor swinging a big blade. Undecided

Paul
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« Reply #12 on: April 01, 2010, 03:43:28 AM »

Russ

I too have used Balsaloc and have found it inferior to re-activated contact adhesives. Rather than use the new Evostick, I recommend that you mosey on down to Wickes where they still sell the solvent based stuff. They do small tubes (which lasted me a couple of years) or 1/2 liter cans for not a lot more money, and that's what I have now. It thins down nicely with cellulose thinners, and I only need one coat (but I do paint the airframe with 50/50 or thinner dope beforehand).

Onto motors & models; there are some small CO2 designs around (principally from Austria) in the 90s issues of Aeromodeller. Personally I'd be disinclined to build one in view of "our" normal flying conditions i.e breezy & turbulent, plus the visibility point that Paul made. My view is that 30" span and about 120-140 squinches wing area is about the smallest practical size.

There are two 63 sized Gasparins, a plain bearing one for sport & the ballraced one for F1K (CO2 duration), and it's the latter that Chris Strachan uses and is the best for our purposes. The 120 FAI also provides a useful performance, but in my limited experience they need a good bit of running in. The Modella is much larger - from memory four times the capacity of the 63, and most of those available aren't fitted with a 3cc tank (FliteHook used to have a few in stock). The Modella runs lustily but not for very long on 3cc. The problem with Telcos & Modella is that the seal is a lip moulded into the piston, and as that wears the performance drops.

Good luck with whatever you build...... and don't forget a DT Cheesy

Peter
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« Reply #13 on: April 01, 2010, 03:35:34 PM »

Busy, busy, busy...

Wing finished now ready for covering. I put in a couple of 16th balsa spars on the bottom using a needle file and a ruler to make the notches. You can just see the plywood braces on the wing leading edge. Slide a piece of 32nd ply into position, mark with a pencil, cut with scissors and sand a taper on the ends then superglue into position - easy Wink

I tried something different for the joins in the carbon spars. A 'sized' piece of 36gm kevlar is superglued over the joint.
(To 'size' it dope through the cloth on a piece of glass and let it dry. When dry peel it up and you can cut it with a pair of scissors) Smiley

The tailplane has had the tissue applied and this is to show how it looks initially after application Shocked
Fear not it all will look fine after the next application of dope/banana oil Grin

NB
I apply the tissue over mylar by drawing the tissue over the surface of a dish of water to wet it then laying it in position on the mylar and wiping excess water off with a piece of paper towel (kitchen roll). A lick of dope (which I'll often apply using a pad of kitchen towel rather than a brush) and leave to dry out

Happy covering campers

Paul
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« Reply #14 on: April 01, 2010, 11:11:53 PM »

Russ

Onto motors & models; there are some small CO2 designs around (principally from Austria) in the 90s issues of Aeromodeller. Personally I'd be disinclined to build one in view of "our" normal flying conditions i.e breezy & turbulent, plus the visibility point that Paul made. My view is that 30" span and about 120-140 sq inches wing area is about the smallest practical size.

There are two 63 sized Gasparins, a plain bearing one for sport & the ballraced one for F1K (CO2 duration), and it's the latter that Chris Strachan uses and is the best for our purposes. The 120 FAI also provides a useful performance, but in my limited experience they need a good bit of running in. The Modella is much larger - from memory four times the capacity of the 63, and most of those available aren't fitted with a 3cc tank (FliteHook used to have a few in stock). The Modella runs lustily but not for very long on 3cc. The problem with Telcos & Modella is that the seal is a lip moulded into the piston, and as that wears the performance drops.

Peter

Peter,

So a GM63 will fly something this large? I've picked up a couple of CO2 motors to fool with, GM63, GM120 FAI and got a Telco as a gift from a friend. I know less than nothing about CO2 at this point but I thought the 63 was pretty much restricted to models in the 22-23" range and the 120 maybe 28" or so.

bill
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« Reply #15 on: April 02, 2010, 11:15:36 AM »

Bill

Certainly the GM 63BB will. One of the plans in an early message from Paul is of Chris Strachan's 63BB powered model, which from memory is 30" or thereabouts. As much as anything, the weight is a factor, however most CO2 models fall into the "won't pull the skin off a rice pudding" category. If the windspeed is under 10 mph, the model will climb away slowly but surely (but quicker if you've picked a bit of good air). If it's windier, they fly a bit like a paper bag Cheesy.

I took a photo of my latest model this morning (the fus anyway), which is attached. Sorry about the poor quality, but it was raining & my indoor shots are worse.

This model uses a vintage coupe wing of circa 38" span and about 140 squinches. The fuselage is pod & boom with the pod made from two laminations of 6mm Depron, glued together, covered in 1/32" balsa and then tissue. I use a 1" tube to bore a couple of holes to lighten it, and the Tomy timer is inside. I'm sure that a stick & tissue fus would be lighter, but being an expert in making banana fuselages, I stick to something that is quick, robust and normally straight.

The motor is a Tornado 69, made by Aerographics a decade or so ago. It's basically a Humbrol Shark moulded plastic crankcase, plus crankshaft together with a Gasparin cylinder and piston (from the GM63 as I understand it). It runs nicely and is getting better with more running.

To put things into perspective, as I understand it, the Gasparin numbers (63, 120, 300 etc) refer to the motor capacity in cubic mm (unlike glow motors where it is cubic centimeters). However, I don't seem to get twice the power from a 120 than from a 63 (or the 69 to be precise).

Well there you have it - finished building yet Paul?

Peter
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« Reply #16 on: April 02, 2010, 03:13:11 PM »

Nice one Peter Smiley

Nope not quite there yet...

Tail's all done. Covering with tissue on the top only gives a nice bit of cowhorn dihedral - which I have obviously allowed for in the careful area calculations Wink

I've added a band hook and ply protection plate on the trailing edge, although I'm unconvinced about a popup tail DT An amusing email from a well known power flyer suggested that the only sure fire way of getting them down out of lift is to allow the DT fuse to set the model aflame which also helps the timekeeper keep them in sight longer Shocked

He also mentioned that there were drawbacks with this method... no kidding, eh! Cheesy

So we are left with either pop up wing or flyoff wing (or tail).
The problem with these is the angle of descent bringing them down onto the rather thin propshaft if landing on concrete. (Which means anywhere on Merryfield that doesn't have trees) Tongue

John T also mentioned that hairspray can be used as an effective 'sizer' for lightweight cloths which is something I'm looking for an excuse to try...

I've also covered the main part of the fuz with silver mylar which looks nice. The front part will have some of the aformentioned light glass cloth and tissue to finish it once the motor appears on the scene.

Right back to the Easter eggs

Paul Cool
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« Reply #17 on: April 02, 2010, 04:52:17 PM »

Some lightweight P-30's (and Coupes too) use a pop-up wing AND pop-up stab. The claim is that the sink rate is much faster with both popped (then just the stab or wing) and the orientation is with the fuselage horizontal on decent.

Something to consider.

Tony
-nice work by the way!
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« Reply #18 on: April 02, 2010, 05:05:49 PM »

Some lightweight P-30's (and Coupes too) use a pop-up wing AND pop-up stab. The claim is that the sink rate is much faster with both popped (then just the stab or wing) and the orientation is with the fuselage horizontal on decent.

Something to consider.

Tony
-nice work by the way!


My latest coupe DT's that way and it is quite effective. The leading edge of the wing pops up at the same time as the stab. It looks wild when it happens. It is surprisingly stable as it comes down. I haven't had it boom away in a big thermal yet but the rate of descent is noticeably faster than my stab only coupe. It think it would work very well on your plane.
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« Reply #19 on: April 03, 2010, 03:35:35 AM »

Paul

Both of my fly-aways were with pop-up wing DTs which are normally very positive. However if you get into a brick lifter, nothing is going to work particularly well, except perhaps John T's suggestion. I suggest that the best of the bunch for a lightweight model would be a fly-off wing or tail. The tail is easier to do, and this is the method I've used on another CO2 model.

As for bending the prop shaft, to put it into perspective, I've bent two in well over a 100 flights, and one of those can be discounted - some kids on Beaulieu beat me to the model down wind, removed the wing and were using the fuselage as a javelin Angry. However, the prop shafts are just machine screws with standard threads (Telco 10BA if I recall), and are easily replaced with no damage to the crank.

Another couple of bijou snippettes of information - very few shops do Sodastream refills now, by the Dyas hardware stores still do, as I checked last week. Numero deux, you'll need to lubricate the motor every few runs (3 -4), some people use gun oil (but I'm told that it can embrittle plastic props) and an alternative is genuine Singer Sewing machine oil (but no cheapo substitutes though Wink)

Peter (off to walk the dog)
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« Reply #20 on: April 03, 2010, 03:21:03 PM »

Thanks for the input guys Smiley

I think I've got some fine clock oil Peter which I may dig out to try. I didn't realise that they needed lubricating as often as that so it's good to know

I'm hedging my bets till the airframes complete about the DT. I like the simplicity of a fly off tail. I just keep picturing it happening 10 feet off the ground Shocked The advantage of the combined wing /tail set up is that it's very trimmable and using one or the other for trimming flights may be a help. I'll need to think out the easiest way of doing it...

Thanks for the reasurance about the prop shafts old fruit, I'll lay in a few 10ba bolts to be on the safe side.

I notice that there is another SodaStream adapter on that well known auction site at the moment for anyone who is after one. Pauline (Flitehook) mentioned that the newer Sodastream bottles have a different thread arrangement (fewer threads?) which makes using the adapters difficult - something to be aware of when it comes to getting them refilled/exchanged.

Couple of questions

Props - what's suitable or recommended?
Filling using one of these Sodastream bottles - what's the best technique?

I also came across a drawing of me old club mates CO2 model (Steve Philpott) which is a high thrustline tractor design - I'll scan it if folks are interested. I was interested to see a large amount of upthrust being employed - anyone else find this necessary? (Okay that was more than 2 questions, put it down to a chocolate rush) Wink

Toodle pip
Paul
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« Reply #21 on: April 03, 2010, 10:46:36 PM »

Hi DaddyO

I have been following this thread on CO2 motors with interest as a have a few of them in my collection. I might be able to help with a couple of points you queried. I have a good article on how to fill the tanks on the on the CO2 motors and their running generally that I found on the net. Let me know if you want it. It is in a DOCX file format.

I also found out the latest information last week on the K.P. CO2 Sodastream adapters themselves and if they were still available by contacting the makers K.P. Aeromodels Limited by email. (I have one-great little unit)

Spoke to Derek himself the helpful guy who owns and runs the business. He told me that they no longer make the adapter but still hold stocks of spares. So if you already have one, or can get hold of an adapter you will still be able to refurbish it if needed. Very good information to find out.

Hope that little bit helps


Cheers

Algy
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« Reply #22 on: April 04, 2010, 03:45:27 AM »

Paul

The "every 3-4 flights" is recommended by Gasparin if I recall/

On the prop front, it depends on the motor size. The Tornado 69 on my model goes quite well on a standard Modella prop (50p from Pauline). Others to try are the 8" Gunther rubber job, and Chris Strachan swears by the GWS 7x6. I did some tests on half a doz different props a few years ago & will try and find the results. It was a mix of testing rpm vs motor run and then flight tests - a thrust rig would have been easier Cheesy

Filling - you need to hold the sodastream bottle inverted in order to get a liquid charge (& longer run). Cooling the motor gas bottle increases the charge. The continental experts employ "pin outs" - charge the bottle & then unscrew the cap to release the charge, which supercools the bottle. I worry about damaging the O ring seal and cool mine with a spray of electronics freezer (available from Maplins). This is legal by the way!

Steve is a mean competitor and I too have his model 3 view somewhere. I don't know why upthrust is needed, but Gerd Wobbeking's CO2 pusher also has it in spades (see FF Forum 2004).

I thank Algy for the info on the K&P spares and will lay in a stock for the future (the little plastic inserts are easily lost Wink)

Peter
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« Reply #23 on: April 04, 2010, 09:02:03 AM »

Regarding The proper oil to use. I have a load of "air-tool" oil, every light grade high quality stuff that we used at work, as almost all our power tools were air driven. CO2 motors are, in effect, air tools so I was wondering if this would be a suitable substitute - Singer oil is difficult to find here as dedicated sewing stores are few and far between.

I have a MODELA and a TELCO - both never run, but only the charger for the TELCO. The filler probes appear to be the same size (haven't measured, just used calibrated Mk. I eyeball). Does anyone know if they're compatible?
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« Reply #24 on: April 04, 2010, 10:22:49 AM »

Pete

I don't see why not, and the best way is to try it and see - I don't believe that it will harm the motor.

I understand that the reason why gun oil is used is because it remains thin at low temperatures. Given that the CO2 is likely entering the motor at well below freezing point, oils that thicken at low temperature will slow the motor and reduce performance. Under some circumstances CO2 motors can ice up and stop, and you can see frost forming on the tank as the motor runs. I assume that in order to expand (and run the motor) the CO2 needs to take warmth from its surroundings, and on a cold day it's often necessary to warm the tank with your hands to get adequate rpm. Not a problem in Algyland Cheesy or the summer I suggest........ England's another matter!!

Peter
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