Experimental Cowling Repair Pics

Post Reply
akholland
100+ Posts
Posts: 435
Joined: Wed Sep 12, 2012 12:25 pm
Contact:

Experimental Cowling Repair Pics

Post by akholland »

Experimental Cowl Repair

https://www.dropbox.com/sh/jpf36jtj5lb8qeg/6yRK0072yP

Took some pics of a cowling that i'm playing with. After all this work, the $3500 for a cowling doesn't sound too unreasonable lol..

Common Problem being the original dzus style fasters ripping out and wallering out of the fiberglass. Also, when you pull the upper cowl off, the dzus's aren't self ejecting, and they tend to catch in the holes. I decided to do a layup of aluminum on the inside of the cowling which would be held on by Epoxy Resin, and the new style Self Ejecting Dzus Fastners themselves.

The previous repair from the old owner consisted of putting an aluminum doubler along the inside AND outside of the cowl. It had two rows of rivets spaced every 2 inches. This was very ugly and the butt's of the rivets were facing outward which isn't smooth. You can't sand that down and paint over it very well either in the future. It had also failed by the nose and cracked out by the two #10 machine screws.

It had 9 coats of paint on it! I have spent 3 weekends so far with 40 grit sandpaper and a Palm Sander with a bad case of the glass itch ... Also these little 3M Roloc sanding discs came in very handy for grinding down fiberglass and tight spots. Their kinda spendy though. like $3 each

I used West Systems Epoxy Resin with 205 Hardener, and some of the Glass Powder for a filler. This stuff is super expensive (250/gal) but it's worth every penny. It doesn't stink (unlike polyester resin), One pump from each container for a mix ratio, and it's much stronger than the original polyester. To do my layup's I just took a piece of 6 mil plastic clear sheeting cut into a 2'x4' square, folded it in half, placed the fiberglass and resin between the fold, and pushed it around with a scraper untill it had a nice even wet coating. This method keeps you from Gobbing it onto your piece. It also wastes way less epoxy and is stronger. Lots of you tube video's on this method.

I decided against a carbon fiber repair because it's so darn expensive and won't gain much. Just used the regular cross hatch grain mesh stuff. If I were to build a cowl from scratch, maybe I would go carbon. One day..

So after sanding down the area to repair, took measurements and cut the aluminum to length and width for a perfect fit. Laying it up inside the cowl, clamping it down, and tracing out the exact shape it needed to be. Made the strip about 2" wide, although now I wish I went wider. I sanded down the piece of .020, (Would go .025 next time) aluminum with 40 grit so that It would stick good to the Resin. Then mixed up some powder/resin and smeared it down the area where I wanted to stick on the aluminum. (Making sure all oil and grease was removed and area on cowl was sanded, It WILL NOT STICK TO OILY SURFACE) Clamped the aluminum on, filled in all the holes I could with epoxy powder mixture, and let it dry. It helped to use some Mould Release Agent on the clamps, helps keep from breaking them to get them off. Epoxy is tough stuff.

After it dried, I removed the clamps, sanded down the outside of the cowl, and then did another two or three layup of fiberglass on the outside to strengthen it even further and continue filling in all the damaged holes that were torn out. After sanding everything down, I ended up with about 1/8" of fiberglass on top the aluminum.

The self ejecting dzus fastners will be installed with a countersunk rivet, head being inside. I might put a few extra regular rivets on to further secure the aluminum. I worry about the aluminum expanding and contracting at different rates than the fiberglass, therefore separating the bond. These would go just above the Upper/Lower Cowl overlap in a line from front to back, but the round head would be outside so that it was sandable. More rivets at the front because that seem's to be where most of the stress/failure point is.

Decided to go ahead and do the same thing for both the upper and lower cowl where it touches the firewall. I'll just have to put anti Chafe fabric strip around the entire boot cowl before I re-fit the cowl and drill all new holes for everything. I'm a little worried about losing the original alignment of the cowl and re-fitting all the new holes, but with some patience and a hole doubler, it should all work out.

I'll post more pics after getting it primed with EP420.

I hope I never have to look at another cowl again.... Have 48 hours invested so far....

User avatar
crbnunit
100+ Posts
Posts: 1890
Joined: Tue Mar 18, 2008 12:42 pm
Location: Alaska
Contact:

Post by crbnunit »

I had to replace all of my fasteners and reinforce the top cowl. It was in pretty bad shape after 34 years of use. We used carbon fiber for the Dzus and screw lines. The cowl ended up being much more ridgid and now flexes less which will hopefully prevent the stress cracks in the fiberglass from removal/installation over time. We'll see. The holes show no signs of wallowing out again... So far.

Fitting was a pain. Fit, remove a bit of material, refit. Rinse and repeat. Over and over and over. It was worth it in the end but is very time consuming. I'd hate to do the top and bottom at the same time. I wish I had gone to a different fastener system. The self ejecting Dzus would be much nicer.

We had to use ratchet straps to pull it together for the first time. It has loosened up and relaxed now after several years of use and is pretty easy to get together.

I like the metal reinforcement. That should work well!

I wonder how much weight a full carbon cowl would weigh. I don't even want to think about how much it would cost!
You have to make up your mind about growing up and becoming a pilot. You can't do both!

akholland
100+ Posts
Posts: 435
Joined: Wed Sep 12, 2012 12:25 pm
Contact:

Post by akholland »

If you buy the material in bulk it think it would be around 1000 bucks...I found epoxy in larger quantities for like 60 or 80/gal instead of 150 or whatever west marine charged. . Just wish I had a mould. You would think enough maule guys were around to put heads and funds together to build a mold. I think a mould could be made from fiberglass fairly easy if someone had a clean cowl to go off.

I would really like to see an aluminum cowl layout with a cub style nose like was in the last post. I think that would be comparable with the carbon fiber for weight and be easier to repair or build from a pattern.

My upper weighs about 11lb and lower 16lb... Pretty heavy m5 cowl, but many repairs

User avatar
crbnunit
100+ Posts
Posts: 1890
Joined: Tue Mar 18, 2008 12:42 pm
Location: Alaska
Contact:

Post by crbnunit »

Agreed on the aluminum. Access is my complaint. I would really like a hinged, side opening cowl. The cowl on the orange experimental looks like a big enough opening you should be able to do almost all maintenance without removing anything. That would be nice! Short of that solution, it would be nice to have a lighter setup.

The factory has a mold for the cowling... If they got a big enough order for carbon, might they consider laying a few up?

How much of a difference in dimentions are there between the different models, other than the scoop for the carb equiped?
You have to make up your mind about growing up and becoming a pilot. You can't do both!

akholland
100+ Posts
Posts: 435
Joined: Wed Sep 12, 2012 12:25 pm
Contact:

Post by akholland »

The length is different between 220 c210 and 235 Hp engines. Intake is different between carb and injected obviously. And the m5 has a round piece added to the upper cowl to match the airflow coming off the spinner. Their all same basic disign but look like minor variations.

Maybe they would loan us their mould for some experimentation! Time for a trip to Florida I think

Flybrian1950
100+ Posts
Posts: 149
Joined: Fri Apr 06, 2007 6:46 pm
Location: Monmouth, Oregon
Contact:

Aluminum Cowling

Post by Flybrian1950 »

It will be interesting to find out if Bill's nose bowl and cowling approach has all the cooling he needs for extended steep climb outs over in the Snake River Gorge in the heat of summer.
SN 8020C, The first M6-180 land plane.

akholland
100+ Posts
Posts: 435
Joined: Wed Sep 12, 2012 12:25 pm
Contact:

Post by akholland »

I had an original aluminum cowling which I really liked on my m4-210 and it overheated. they originally used the aluminum cowl with the 0-300. It didn't have big enough openings for the larger engine. Adding flare to the outlet of the cowl on the bottom helped a little. I suspect the same thing would occur putting a small cub nose cone designed for a 320 or 360 engine? Next time I'm around a cub i'll measure the cross sectional area of the inlets and we can compare them to the M5 235 cowl.

User avatar
cooker
100+ Posts
Posts: 133
Joined: Mon Mar 29, 2010 9:02 pm
Contact:

Post by cooker »

It will be interesting to find out if Bill's nose bowl and cowling approach has all the cooling he needs for extended steep climb outs over in the Snake River Gorge in the heat of summer.
My guess is yes ... as long as the baffles and seals are kept in real good shape ... Bill's inlets look pretty big compared to our original M4 220 inlets which are providing enough air to cool 250hp during a full power amphib climb out in what we call warm (~80F) (this was not the case prior to a complete baffle and seal overhaul)

We are still robbing air off the top cowl for the oil cooler also ... next mod is to re-locate the oil cooler and use other air so that all air ontop is used only for cylinder cooling

If someone has the different cross sectional area's for different maule cowls that would be interesting information though!

akholland
100+ Posts
Posts: 435
Joined: Wed Sep 12, 2012 12:25 pm
Contact:

more m5 cowl repair pics

Post by akholland »

Back to work on the cowl. Took some more pics. For the top and bottom surfaces to become form fitted, I rubbed mold release agent on some thin painters plastic and laid it over the wet glass. Then put the upper cowl on with cleckos. Should help keep the mating surfaces from wearing.

Also put another aluminum strip on the inside of the lower cowl to act as the backer plate for the dzus spring. This time I put down cloth, pop riveted a piece of aluminum to it, then more cloth over the back. I think it's goona be stronger encapsulated like this than just rivets and one side glued. The rivets were countersunk into the existing fiberglass so the heads wouldnt stick up.

https://www.dropbox.com/sh/jpf36jtj5lb8 ... mXxtBWxG3a

MauleMechanic
100+ Posts
Posts: 736
Joined: Fri Nov 08, 2013 8:13 pm
Contact:

Re: more m5 cowl repair pics

Post by MauleMechanic »

akholland wrote:Back to work on the cowl. Took some more pics. For the top and bottom surfaces to become form fitted, I rubbed mold release agent on some thin painters plastic and laid it over the wet glass. Then put the upper cowl on with cleckos. Should help keep the mating surfaces from wearing.

Also put another aluminum strip on the inside of the lower cowl to act as the backer plate for the dzus spring. This time I put down cloth, pop riveted a piece of aluminum to it, then more cloth over the back. I think it's goona be stronger encapsulated like this than just rivets and one side glued. The rivets were countersunk into the existing fiberglass so the heads wouldnt stick up.

https://www.dropbox.com/sh/jpf36jtj5lb8 ... mXxtBWxG3a
You are better off with your work than from a $3,500 new one that may still need that much work.

RT
100+ Posts
Posts: 163
Joined: Sun Sep 10, 2006 7:14 pm
Contact:

Post by RT »

Maule Mods was building carbon fiber cowls I think. I wonder what happened to there molds ect.
RT

User avatar
freedom
100+ Posts
Posts: 239
Joined: Fri Jul 17, 2015 6:34 am
Contact:

Post by freedom »

I'm looking into this mod since I'm redoing my cowling.
Could anyone who did it share some pics on the fastener receptacle on the aluminum side cowlings.

Post Reply

Who is online

Users browsing this forum: No registered users and 6 guests