Marty d's CH-701 build log

[eightyknots]

No Hank...they are super thin and if they were hard alu lines them maybe ok but you have a lot of vibrations in and around the engine....I dont know Hank it just doesnt sit right with my brain about using that...give me the correct rubber style lined reinforced hose any day..also for ICP its a way or further reducing build weight too

 

ICP still quotes the empty weight of a Savannah S to be 286 kg plus or minus 10%. In other words, a range of 257.4 kg to 314.6 kg. See the picture of the official plaque for my plane.

 

The 286 kg mass is close to the Zenith CH701 planes the earlier Savannahs were derived from.

 

I have never heard of anyone completing a Savannah S at 257.4 kg: not even the unpainted, fixed seat, two-tank, non-extended baggage variant fitted with an 80 hp Rotax as they have in Europe. I have heard of quite a number of people completing their Savannah S around the upper end of the range of 314.6 kg.

 

Perhaps these fuel lines are on of ICP's measures to reduce weight closer to the more realistic officially quoted weight?

[Marty_d]

So try #2... got the jig made up today and strapped the muffler to it. (Upside down, obviously, in the photo below). Screwed the outlet stubs to their equivalent positions.

Also made up a protractor to help with cutting the angles in the donuts.

 

[Marty_d]

Hey folks,

 

I need some advice... again...

 

The muffler pipes are all cut out and assembled on the jig ready for welding (dropped it off to the welder yesterday).

 

BUT I told him to hold off on welding the exhaust pipe to the muffler until I got some advice.

 

Firstly - it IS welded, isn't it? I've seen some installations with a longer stub coming out of the muffler that the exhaust pushes over and is clamped with hose clamp and held on with springs. But my muffler has the short stub, no spring holders, and the exhaust pipe is the same diameter as the stub so no way it's going over it.

 

Secondly - the angle. I've tried to look at as many 701 pics as possible but they're good at hiding the exhaust. I've seen a couple which seem to show the exhaust coming back under the firewall at a fairly shallow angle, I reckon about 30 degrees or less from horizontal.

 

I think where mine is mounted I may even be able to get 20 degrees or less, as shown below. Question is - is it better to have it angled that far?

 

Thanks!

 

[kgwilson]

Well your muffler has lugs on it that appear to take springs. My Jab 3.3 muffler is just a push in fit for all 6 pipes and 2 springs per side. That makes it easy to remove when required and it has never leaked, moved or vibrated when assembled

[Marty_d]

Well your muffler has lugs on it that appear to take springs. My Jab 3.3 muffler is just a push in fit for all 6 pipes and 2 springs per side. That makes it easy to remove when required and it has never leaked, moved or vibrated when assembled

 

It has lugs for the pipes from the exhaust ports in the engine, but it doesn't have lugs for the actual exhaust pipe.

 

[kgwilson]

I see. My exhaust pipe is welded on to the muffler. It is straight so that makes it easier and also the cabin heat jacket fits around that pipe so if the exhaust was clamped there is the possibility of carbon monoxide leaking in to the cabin via the cabin heater.

[Marty_d]

I decided to box up the engine until the plane's painted - almost finished whipping up the box this morning. I've also ordered a couple of electric pet blankets (about 20w, 12v with transformer) - one for under the engine and the other one for under our new puppy which will be coming home in 3 weeks!

 

[IBob]

I'm surprised you didn't get more informed thoughts on your tailpipe attachment.

The only comment I would make is that in a hard climb or a steep approach, the airflow round the cowl is quite different than when in cruise. (In the Sav what I see is rising airbox temperature, which indicates that the the airbox is taking significant air from under the cowl, instead of via the naca scoop on the top.) I would expect that exhaust fumes would also take a quite different route in those modes, and to be aware of that when positioning the tailpipe.

[Marty_d]

It's been a while...

 

Fortunately @wideblueyonder just lent me some cowl moulds, so this is inspiring me to get back into it.

 

I bolted the engine back on temporarily to test fit the mould.  I got some advice from the Fibreglass Shop in Hobart that the moulds are too thin and need beefing up, so the first job (while on the plane to maintain shape) will be to add wooden strips and fibreglass them on to the outsides of the moulds.  After that will be some more smoothing to the insides (surfboard filler epoxy was suggested, with sanding down to 1500 grit), then on to making the cowls.

I've never fibreglassed anything before, so hopefully beefing up the moulds will be good practise, and as always - if you have any advice gained from experience, please tell me!

 

 

[Kyle Communications]

Marty Glassing is easy..just messy. Must get all the air out of the weave thats all so use the ribbed rollers. You probably need to cut some 10mm ply and cut out to match the curves on the outside then glass those onto the outside of the cowls to make them hold their shape..then your good to go. A tip though is to make those supports all level so you can lay the mold on them and they are solid on the ground as you layup the glass. The only other thingis good canuba way first and many coats then spar on your release agaent then go to town glassing and make sure you squeeze as much loose resin out of the weave. Have a look at Mike Patey's Youtube channel...carbon fibre and normal glass there is really no difference in the way he does his layup..although he prepregs everything because he can but the old way is fine with a brush

 

 

[Marty_d]

Got the welded up exhaust tubes back from the welder a couple of weeks ago, only just got an hour to test fit.  I also bought a threaded stud and 8 new lock nuts from Bert Flood, but for this fit just used the original nuts.

 

It's gone on mostly ok but the ball of one of the long pipes is not quite seating.  Not sure whether to get the welder to cut and insert a very short length to make it a bit longer - any advice??

 

Sorry about the darkness of the photo - need some more light in the shed!

 

 

[Blueadventures]

Having a stab at a fix, and depending on how short it is, say 6mm.  You could consider cutting the pipe. Then fit the pipe back on with the ends located, into head and muffler. With a gap presented you could steel epoxy some steel rod ( serious, No laughing) to just under 180 degrees around the pipes, like a splint and also tie wire around them to hold in place.  Then you can remove and have your welder slide in an insert and weld it half way round.  Then remove the steel epoxy and rods, clean and prep and weld that bit.  It is like being held in a jig.  I say this because it seems your taking the job to the welder not doing it in sitsu.

 

other wise you may need to have the one pipe sliding adjustable and clamp at it’s correct length.

 

the pipes need to be perfect length for a solid firm fit.

 

disregard if you get a better suggestion.

[Marty_d]

I can't edit the previous post now, but @red750 kindly brightened up the photo.

 

[planedriver]

That's what mates are for.

Thanks Red, well done!

[Marty_d]

No photos this time, but have taken the plunge into fibreglassing and strengthened the outside of the mould with another layer - after reinforcing with some timber strips glued on with construction adhesive.

 

I'm now eyeing off the inside and will do some gap filling with Bondo or equivalent, before sanding back with increasingly finer paper. 

Then will be the ultimate challenge of producing a relatively good cowling from inside the mould.  Having seen how quick the resin goes off, I'll need to have my ducks in a row with all the sections of glass fibre cut to shape first.

 

Questions for those who have done this:

1. Do you lay up your second layer while the first is still wet, or wait until it's gone off?

2. Do you paint a layer of resin onto the release agent first and then press the glass fibre onto it (before painting more resin onto that), or put the fibre down first?

 

Any advice welcome, as always.

 

Cheers, Marty

 

Edited December 31, 2020 by Marty_d

[Blueadventures]

I have used tissue mat at times for first layer then the lays of mat ( lessens the small bubbles that you have to fill for painting). Hey talk to a local laminator for some tips for your area.  If using polyester resin and it’s raining and humidity high you need a little extra catalyst. Some I know paint the primer on like gel coat for the first inside coat. Also what resin are you using. Epoxy?

Edited December 31, 2020 by Blueadventures

[nomadpete]

Step one is to cut your mat to fit the inside of the mould - lay the pieces out so you know whit bits fit which curves. Don't try to do the whole cowl with one big piece of mat.

After applying hard Cornubia wax to the mould, followed by a thin spray of mould release, apply a layer of gel coat - brush it on. After it goes off, brush on a layer of resin (well mixed 50:1 with hardener). Just brush on a area for one piece of mat at a time. Whilst wet, press the mat onto it, stipple with brush and roll bubbles out until the mat looks translucent. Repeat with next piece of mat, overlap the joins. By the time you've got to the other side of the cowl, the first layup will be going off and you can either retire for a wash up and cold beer, our go back and continue with a second layer. Try not to use too much resin. Just enough to wet out the mat without visible air amongst the fibres.

 

Watch a couple of YouTube's.

[Blueadventures]

1 hour ago, nomadpete said:

Step one is to cut your mat to fit the inside of the mould - lay the pieces out so you know whit bits fit which curves. Don't try to do the whole cowl with one big piece of mat.

After applying hard Cornubia wax to the mould, followed by a thin spray of mould release, apply a layer of gel coat - brush it on. After it goes off, brush on a layer of resin (well mixed 50:1 with hardener). Just brush on a area for one piece of mat at a time. Whilst wet, press the mat onto it, stipple with brush and roll bubbles out until the mat looks translucent. Repeat with next piece of mat, overlap the joins. By the time you've got to the other side of the cowl, the first layup will be going off and you can either retire for a wash up and cold beer, our go back and continue with a second layer. Try not to use too much resin. Just enough to wet out the mat without visible air amongst the fibres.

 

Watch a couple of YouTube's.

Peel ply is worth the effort to also remove excess resin.

[nomadpete]

Peel ply sounds great but I've no experience using it. Two questions pop into my head:

 

Does it work with polyester resin?

How do you get it wrinkle free on the inside of a compound curve such as the female mould of a cowling?

[Marty_d]

13 hours ago, nomadpete said:

Step one is to cut your mat to fit the inside of the mould - lay the pieces out so you know whit bits fit which curves. Don't try to do the whole cowl with one big piece of mat.

After applying hard Cornubia wax to the mould, followed by a thin spray of mould release, apply a layer of gel coat - brush it on. After it goes off, brush on a layer of resin (well mixed 50:1 with hardener). Just brush on a area for one piece of mat at a time. Whilst wet, press the mat onto it, stipple with brush and roll bubbles out until the mat looks translucent. Repeat with next piece of mat, overlap the joins. By the time you've got to the other side of the cowl, the first layup will be going off and you can either retire for a wash up and cold beer, our go back and continue with a second layer. Try not to use too much resin. Just enough to wet out the mat without visible air amongst the fibres.

 

Watch a couple of YouTube's.

I hadn't heard of Gel Coat before.  So you put that on first and let it go off fully before the first layer of resin?

Now for the mat.  From a few videos I've seen, chopped strand mat seems to be the choice for car panels.  Would you use that or woven mat for a cowling?

From what you're saying, it seems that it doesn't much matter if the first layer has gone off or not when the second layer is started?

Thanks Peter!

[Blueadventures]

5 hours ago, nomadpete said:

Peel ply sounds great but I've no experience using it. Two questions pop into my head:

 

Does it work with polyester resin?

How do you get it wrinkle free on the inside of a compound curve such as the female mould of a cowling?

Yes, it’s a nylon so very plyable. 

[Blueadventures]

1 hour ago, Marty_d said:

I hadn't heard of Gel Coat before.  So you put that on first and let it go off fully before the first layer of resin?

Now for the mat.  From a few videos I've seen, chopped strand mat seems to be the choice for car panels.  Would you use that or woven mat for a cowling?

From what you're saying, it seems that it doesn't much matter if the first layer has gone off or not when the second layer is started?

Thanks Peter!

Marty I’ll pm you with my contact as too many variables depending on what you are doing, I personally would use epoxy resin and get mat from an aircraft supplier / repairer, worth the extra cost.

[planedriver]

If working in a confined area, a powerful fan to assist with airflow through your working area will help a bit to save you breathing in more fumes than necessary and let your neighbours know what you are up to. Also wear a respirator so you don't breathe in the fine airborne fibreglass dust strands. Cover your arms with a long sleeved shirt, or you'll be scratching like an alley-cat in the middle of the night. As you'd realise by now, the stuff stinks and get right down in your gut's. 

Nomadpete is right about the order of applying Carnuba wax followed by release agent before a gel coat, and I also have normally started off with a tissue layer following the gel coat which is pretty smooth and wets out easily, and then go straight out with the chopped mat previously cut to approximate shape. This should give you a smoother finish with minimum pin holes to fill later, and my view is that one layer bonds better to the previous layer if still a bit wet. As also mentioned, try to get a bit of and overlap on each layer which adds to the overall strength.

Good luck mate, it's not really very hard to get good results, and if anyone can do it, you can.

Rgds planey

[Marty_d]

Thanks Planey, good advice!

 

The trouble with my shed is that I'm building a plane in the back half of it, and my wife uses the front half for her business.  Paint and fibreglass fumes tend to migrate to the other half.

 

So for the last bit of glassing I did, I moved to under the carport where I have no walls at all to keep in the fumes.  Also wore a full face 3M mask which cuts down the fumes as well as stray fibres.

 

Hoping to go back to the fibreglass shop tomorrow and stock up for the first attempt at a cowl.

 

Luckily our nearest neighbours are about 200m away, so it's only the kid's yelling that disturbs them.

[IBob]

Hi Marty, I have no practical experience of fibreglassing, but this: do use a gelcoat first if you can, otherwise you will a have a myriad of tiny pinholes in the finished product, which require repeated filling and sanding, and are surprisingly difficult to get rid of.