Gonna try to hit two birds with one stone on this one.

I've got a CG Chipmunk that I plan to build and am considering putting an OS 91 Surpass II in it. I see that Slimline makes an inverted pitts muffler for this engine (ref. 4012).

What are your thoughts on this combo considering looks, cooling, etc. - the thing costs around 90 bucks.

Also - I'd like to cover the plane with something like solartex so I can paint on the paint scheme.

Your thoughts on this? I'm tired of having iron-on coverings come off after a while. If I went the monokote route, can I spay the whole thing down with a polyurethane varnish to seal in all the stickers and stuff??

Thanks in advance for any input!

Zipperneck

Just an additional thought...
I ordered a set of fiberglass wheel pants and cowling from AeroFiberTech - hope it was the right choice.

Zipperneck

Zipperneck,

If you mount the engine inverted, the stock muffler may work since the cowl is somewhat narrow. If not, see if you can get a flexible pipe to go between the motor and the muffler. I know they make them for Saito four strokes, but I'm not sure about OS. If they do, you can mount the muffler anywhere inside the cowl and connect it to the engine with the flexible pipe.

I'm sure you know this, but if you decide to paint your plane, use thin coats to minimize the weight penalty of the paint versus Monocote. If you go the Monocote route, you will only need to seal the edges between the colors and around the decals. I've had my best results using Balsarite for covering to seal the edges on my planes. If you're not familiar with Balsarite, its a clear liquid you paint on with a small model paint brush. I've also heard that clear fingernail polish does the same thing, but I haven't tried it.

Good luck with your build and keep us posted with your progress.

Hrrcflyer,
Thanks for the flex tip. I'll check that it -may be a more cost-effective way to get an in-cowl muffler setup.

I'll check into the balsaright method also.

Tnx!
Zipperneck

The Goldberg Chipmunk and an OS 91 are made for each other. Great Combo!

On mine, I mounted the engine sideways and just let the stock muffler stick out, but you can also swing the muffler inside the cowl and let it vent out an opening in the bottom

The pitts creates a bit of a problem in a tight cowl, and even in an open one. These photos are of one mounted on a Magnum 91 that is in my Super Aeromaster. I don't know how it's going to run, I'm not quite finsihed with the model yet. I think that I would use either a flex pipe or one of the optional headers for the engine the next time. It seems that Slimline could have routed a header into the end of the muffler and cut down the bulk a bit.

Don

And here is an OS 91 Surpass with the muffler turned inside the cowl

Mike that cowl would be turned into a conopy with the pitts. I'm not sure what the metal is in their mufflers, but a little hacking could turn it into a usuable muffler. I've already butchered my cowl so I'll stick with it as it now stands. Next time though

Don

Minnflyer,
Great idea! I hadn't even considered a side mounted arrangement... that's a good idea. I'll have to consider that possibility....

Thanks!
Zipperneck

Hrrcflyer,

I checked into the Balsarite product on the Tower Hobbies website. Apparently this product is painted onto the wood before the Monokote is applied. What I'm looking for is something to put on top of the covering to keep it in place so no fuel gets under the edges and eventually lead to it coming off.

Also, apparently Balsarite cannot be shipped by air... Since I'm in France and will be taking a load of RC stuff back with me after visiting the States, I may have a hard time transporting the stuff. I have no idea of this stuff can be shipped surface (by boat)....

There may be an equivalent to this product in the "old country" - I'll have to look into that. Thing is, things are so damn difficult to get here - in a respectable time frame and at reasonable cost.

Zipperneck

Zipperneck, If you use MonoKote brand covering, once the covering is finished, dip a Q-Tip in acetone and run it around all of the seams.

That will hold them down forever, but it doesn't work on Ultracote/Oracover

Ouch - acetone around my planes gives me shivers...

I suppose the word "sparingly" should be applied here.

Funnily enough, most of the hobby outlets here in France sell Oracover or Solartex (kinda cheapo and doesn't adhere well).

I'll have to order some monokote for the Chippy and give it a try. They also have the matching pain spray can, but I wouldn't be able to take that on the plane with me (along with my shampoo and aftershave!). Ground shipment might work, though.

Thanks for the idea!

Zipperneck

You can safely use Acetone on covering. It is very agressive on MonoKote's adhesive, but it doesn't hurt the covering at all.

In fact, it's a great way to remove CA glue from covering.

You need to be careful with bubles arond the edges. When I trimmed out my 4*60, I had a couple places where the trim wasn't really stuck down like I thought. As I applied the acetone. I could see it wick under the trim. I pushed it down with my finger and discovered that the adheasive is also the color. I ende up with a couple ugly spots along the edge. Make sure you seal the edges well with an iron before doing the final seal with the acetone.

I was using one of the pipettes for applying CA. THe acetone was flowing to freely from and that caused part of the problem I later discovered the tip to use a cotton swab to apply it. It would be nice to have a felt point to like a marking pen to apply the acetone.

Don

PS, one more tip to keep in mind. Cleaning the model at the end of the flight day with Windex with Amonia will cause the edges of the monokote to lift. The Amonia is what desolves it to begen with.

OK, thanks for the tip. I use denatured alcohol to clean the plane down at the end of the day. Do you think that could cause the trim to come up?
Zipper

I'm building the goldberg chipmunk right now and have installed my os 91 four stroke sideways. I've cut the cowl so that the cylinder can stick out into the breeze, but am having trouble finding a way to get the cowl to fit over the propeller shaft. I know the cowl fits over the cylinder nicely and the cut-outs match the shape nicely, because I've put the engine in there while both were off of the airframe. Once the engine is bolted to the airframe, I cannot seem to get the cowl to fit over the shaft. Perhaps somebody could post some pictures to show how they've done it?

MinnFlyer...
Got pics?

Sounds strange enough. This question is very interesting to me as I will be starting my Chipmunk soon and I have exact same engine!

Thanks
Zip

You may need to make the hole for the head larger.

You don't want that hole to be just large enough for the head to stick out, you want some room for air from inside the cowl to flow around it too.

I usually leave about a 3/8" opening around the head - and even then you sometimes need to make the rear a little wider in order to get the cowl on.

Another thing you can do with the CGP Chippy, is a neat little trick my dad showed me, but it may be too late if you've already glued the two halves together (Unless you can easily get them apart) - and of course, this only applies to the stock ABS cowl.

Instead of gluing the two halves together, glue a strip of the ABS scrap to one side only and attach the other side with sheet metal screws.

Now you can remove just one side of the cowl so you don't have to remove the prop to get it off.

A side benefit of his is that one of the screws can go through the top of the cowl and right into the side of the engine mount to give it stability

Got pics of what?

Waagbuck,

You may have to move the motor mount to the right (if you are looking at it from the front of the plane) because of the motor location on the mount and the right thrust that should be built into your firewall.

Zipperneck,
If you are still concerned about using acetone to seal the edges of your trim, clear fingernail polish does a good job of sealing the edges as well.

This may be a really stupid question... but what about just giving the whole plane a coat of polyurethane varnish... or is that just reserved for painted planes ?

Zip

Naw, Poly doesn't stick well to any of the plastic coverings without scuffing it up first - and if you try to scuff it up, guess where you can't get with the steel wool?

Right next to a seam - which is exactly where you want it.

Thanks for the replies. I will start with expanding the cut-out for the cylinder head. If that doesn't work sufficiently, I might try the split-cowl method suggested by minnflyer. I'm still curious to see if anybody has photographs showing close-ups of their cowl installation.