DB Sport and Scale Auster J1 Autocrat

[Danny Fenton]

Thanks Cymaz, the exit pipe on the standard Saito pipe is only 7.2mm I.D. I hope four tubes totalling at least that much shouldn't be more restrictive.

 

I am now thinking about cooling baffles, do I need them? Electric is soooo much easier.

 

Cheers

Danny

[David Davis]

3 hours ago, Danny Fenton said:

...  Electric is soooo much easier.

 

Cheers

Danny

 

... but nothing like as much fun!

 

[cymaz]

3 hours ago, Danny Fenton said:

Thanks Cymaz, the exit pipe on the standard Saito pipe is only 7.2mm I.D. I hope four tubes totalling at least that much shouldn't be more restrictive.

 

I am now thinking about cooling baffles, do I need them? Electric is soooo much easier.

 

Cheers

Danny

Yes !

[Danny Fenton]

1 hour ago, cymaz said:

Yes !

Yes too electric is sooo much easier, or yes to needing baffles?

I have drawn an outline of the engine, how the hell do I fit that as a baffle in the cowl? Is there an easy way??

 

Cheers

Danny

[cymaz]

Danny 

 

Some  reading for you to do. It’s good that it shows examples.

 

This is the baffle work I’ve done for the T240. The exit is a large lip between the bottom of the cowl and the firewall.

 

 

 

[Danny Fenton]

Thanks Cymaz, I have tried to get the baffle tight, but I am struggling to get the baffle outer to match the cowl inner. This is just a balsa template.

 

So far trial and error but there must be a better way?

 

 

Cheers

Danny

[cymaz]

I think that’s good ?

[Danny Fenton]

Thanks, but you miss my problem. I can make a baffle to go around the engine. I can make a bulkhead to go inside the cowl, but I am struggling to align them in a single item. The baffle you see in the above picture is too high to fit in the cowl, if I shave some off the top then the bottom doesn't fit. Has nobody sorted an easy way to do this? I could saw the cowl in half, fit the baffle, then re-join the the cowl, but that seems a touch excessive?

I have seen this done on a radial engine in a round cowl, however this cowl is not round ?

 

I will sleep on it.....

 

[alan p]

Danny

Have a look on the DH 86 refurbishment thread . John Ricketts has a possible solution in his latest post.

Same cowling shape as the Auster . Dh 86 had same/similler engines.

[cymaz]

 

PAGE 26

Bottom of Page 3

Various ideas on this and subsequent pages. I did my Stampe using a mixture of ply and litho plate( or tin can). I’m just able to slip the cowl on and off, it means some slight poking to ease the baffles around the carb needles- a problem you haven’t got on the Saito. 

Getting the hot air drawn out from the cowl is very important. This doesn’t mean the hot air dams up in the cowl with nowhere to go. 

 

Edited November 17, 2021 by cymaz

[Nick Somerville]

Danny, as you mentioned things are easier with a round radial cowl so I had little difficulty with my Fury baffle plate. Yours looks nicely made to fit your Saito so I would trim it a little small around the outside and use some plasticine or a pack of Bluetack to hold it in place around the engine so it can’t move, but can be pulled off later with the cowl. Measure from the firewall to plate and then fit some hardwood lugs around the inside of the cowl exactly behind the plate  (3-5 should do). Put glue on the lugs gently place the cowl and when the glue has hardened pull the cowl and baffle away from the  engine. Obviously this leaves some gaps around the baffle plate where it was difficult to achieve an accurate fit, so this can now be filled with a little glass cloth and a micro ballon epoxy mix. An alternative to the lugs you could fashion 4 ply pieces shaped with the aid of a profile gauge on the outside of the cowl (top, bottom and sides) for the plate to be glued against. 
 

This is my Fury cowl with litho simply glued and screwed  to keep the air close to the cylinder heads. As mentioned, being circular made it  easier but it still needed fettling and a generous fillet of micro balloons and resin around the edge. 

[Danny Fenton]

Thanks Cymaz and Alan, those two solutions have good access to the area by enlarging the front f the cowl I don't want to do that. I also believe (but dont know) that the crank needs cooling too.

Thanks Nick, that's a good solution. I think that I am trying to make the part fit both the engine and the cowl and that will never happen unless you have access and I don't. The one above looks good but does not fit the cowl so is scrap.

I will do more or less as you say, remove the outer from my baffle so the cowl has room to move. The fit blocks or a narrow ring inside cowl at the right distance and glue one to the other with a slight overlap, once dry pull the cowl off and make good any gaps between the baffle and the cowl.

Cheers

Danny

[Geoff Copping]

I used to work on Gypsy Major engines and the baffles are attached to the crank case, not the cowling, and they are not a tight fit against the fins of the cylinders but form a channel to direct the air around the fins because you want a good quantity of air moving quickly past the cylinders to provide sufficient cooling.

I would suggest two straight plates attached to the engine bearers which drop straight down either side of the engine. the front of these can be fashioned to mate with the opening in the front of the cowling and the air exits through the gap between the rear bottom of the cowl and the fuselage.

Depending how scale you want it to be, the side panels of the cowling swing upwards for access to the engine, leaving the front cowl in place, attached to the engine bearers, or the cowling can be fashioned in one piece to slide on and off independent of the baffles.

[Danny Fenton]

Thanks for the insight Geoff I have got at least a 1mm gap all around the engine. Its not practical to mount the cooling to the engine, at least not on this model.

I am following Phil Clarks guidelines and he leaves a 1mm all around the entire engine as you say forcing the air over the fins.

 

When I was in my teens and last messed with IC we didn't do any of this and simply buried the engine in the cowl. We never had any problems, but I bow to more recent knowledge, no doubt these engines run hotter and are more powerful than the engines we ran in the 70's and 80's.

 

Anyway I have made a baffle from .3mm fibreglass board, the outer circumference is deliberately smaller than the inside of the cowl.

 

Blocks will be fitted in the cowl to temporarily align the baffle centrally in the cowl.  Hopefully the cowl will still come off the model!!

 

I can then add some resin and coloidal silica to seal and attach it to the cowl permanently.

 

 

Thanks for all your help and suggestions, it really is good to talk through all these great ideas, helps me anyway ?

 

Cheers

Danny

 

 

 

[Jon H]

I tend to fit the baffle plate in the cowl and then nibble it away later to clear the engine. 

 

An alternative would be to glue a 1/4 wide former in the cowl at the point you want the baffle to sit, and then mod your nicely fitting baffle to let the cowl slide on with your 1/4 former overlapping the baffle plate. The advantage of this method is you can be pretty crude with your adjustments as the overlap will hide and gaps and once all glued, painted, sealed etc it will look all nice and smooth

[Danny Fenton]

Thanks Jon, your second option is similar to my plan ?

Cheers

Danny

[Danny Fenton]

Well, fingers crossed I can get the cowl off when the silicon sets, complete with an attached baffle plate! Peering through the front cowl openings the blocks are in contact with the baffle, so far so good.

 

 

Need to find some slightly more flush cowl screws, but these socket head will do for now

 

Cheers

Danny

 

[Danny Fenton]

meant to wait until tomorrow but the tension got the better of me. 

Amazingly the cowl (complete with baffle) slid right off. Result!

 

 

A bit of coloidal silica and resin tomorrow and the job should be complete

 

Cheers

Danny

Edited November 17, 2021 by Danny Fenton

[cymaz]

I would also toy with the idea of adding some baffle from the cowl face opening directed to the cylinder.....this would also direct the air more to the engine. Hopes this helps

Edited November 18, 2021 by cymaz

[Danny Fenton]

Thanks Cymaz, but this solution should not need anything else the whole inside front of the cowl is pressurised, and the air can only exit via the small gaps.

I can always do more later if its an issue, but this is all Phil Clark does.

 

Cheers

Danny

[cymaz]

No worries ?

[Danny Fenton]

51 minutes ago, cymaz said:

No worries ?

And you can always say I told you ?

[cymaz]

4 hours ago, Danny Fenton said:

And you can always say I told you ?

 

I wouldn’t have the temerity !

Edited November 18, 2021 by cymaz

[Danny Fenton]

Added a couple of layers of 160 GSM glass cloth around the gap, to make it more solid. Once dry (not long with Polyester) I was able to slide the cowl on and off fairly easily. Will add a little more tomorrow Then I will tidy the cowl in general, as it has some nasty cracks.

I am using polyester resin, of which I am not a fan, however that's what the original was made of, and as you all know you cannot mix epoxy and polyester, not reliably anyway ?

 

 

Cheers

Danny

[Danny Fenton]

so the exhaust extension arrived from Just Engines, seems great But I am not sure I can use it, sigh.

 

Can you IC guys look at the way I have use these two 90 degree knuckles? If I feed it to a long cylindrical chamber with four stubs using a silicon tube joiner will that work?

 

 

Cheers

Danny