So now I'm even MORE interested, in your "experiment" I wish you total success of course. If this works out OK - and hopefully it will (if worst comes to worst you can mount the antenna outside the fuselage - there are a lot of CF sailplanes out there, so there must be a solution) - your design modification will open up a lot of kits and plans to rework with carbon fiber. I regularly break 3/32 x 3/32 balsa (klutz!) so there is no way I can build small models. But if you show it can be done with carbon fiber I will totally rethink my lower size limit
Good luck
Martin

Originally Posted by Iceman59

So now I'm even MORE interested, in your "experiment" I wish you total success of course. If this works out OK - and hopefully it will (if worst comes to worst you can mount the antenna outside the fuselage - there are a lot of CF sailplanes out there, so there must be a solution) - your design modification will open up a lot of kits and plans to rework with carbon fiber. I regularly break 3/32 x 3/32 balsa (klutz!) so there is no way I can build small models. But if you show it can be done with carbon fiber I will totally rethink my lower size limit
Good luck
Martin

Martin - that was one of my reasons for posting this. A pc of 1/8 CF tube weighs as much as a firm pc of 1/8 balsa sq stick.

I have a design for a 93" Storch - which was the reason I did the small one - was going to do stainless tube but thinking now I may use CF.

Very interesting build Rob.

I was also wondering when the Storch would surface - but I wasn't expecting it at 30" span. The frame is insane at that scale!

Alec

Originally Posted by balticS2

Very interesting build Rob.

I was also wondering when the Storch would surface - but I wasn't expecting it at 30" span. The frame is insane at that scale!

Alec

Alec - thanks for the comment. I have an evil plan to do this for the larger Storch model which was one of the reasons for doing both the little Storch and the Stosser.

As I noted, it wasn't really that hard to do, just tedious. And you have to be very careful with building variations - ie "errors" - since it's so small. But even that thing with 1mm tube is seriously strong. It's quite amazing. My Stosser seems to be getting a bit porky at this point but it has a lot of wing. The stringers are heavy since I have to use firm balsa along with the internal structure. I also realized that I made a mistake in interpreting the framework of the Stosser. It's more like the Storch with the aft fuse comprised of angled rectangles vs what I did. Could have saved some weight had I done it correctly....

I schmutzed in the tail section first with .75 glass and Minwax Satin polycrylic ("PC"), all of which goes on very nicely and stabilizes the skinning. I then painted on a mix of vinyl spackle, PC and water to fill in the weave and any imperfections. This stuff sands in very nicely and yields a great surface for priming and finishing.

I then began skinning the forward section of the fuselage which is pretty easy. I used true "contest balsa" on the port side, but it was so soft, the underlying stringers showed through, making the skin faceted.

Sometimes I should just go with my instinct and use firmer wood like I did on the starboard side which looks better. Sure, the contest balsa is lighter to start, but what's the point if you have later slather on tons of filler to get an even surface? The starboard side's skin is still on the soft side, but a bit firmer which made a big difference.

Since I wetted the skin slightly to conform it to the fuselage, I try not to use pins which would cause further flattening between the bulkheads and stringers underneath since the wood will shrink. This is another reason I like wood glue (Titebond III) for this as it takes time to dry and allows the skin to contract to its final form. The fuselage also lent itself to the use of rubber bands to keep it conformed with out preventing the wood from contracting.

Coming along nicely, Rob.

Tom K

Originally Posted by slow_flier

Coming along nicely, Rob.

Tom K

Hey Tom - not a particularly difficult model but wish that I had more time to work on it!

Plinking away on this thing, installing the port side stringers from fairly firm 1/16 balsa. Stringered fuselages are very pleasant structures to admire, but I have found that they tend to come out heavy due to the need for firm wood for the stringers, the multiple bulkheads needed to support them and the strong infrastructure under it all to keep the tail from doing funny things under load - mainly torsional loads. The stringers themselves add virtually no twist resistance whatsoever.

This is one of the reasons I did the CF tube thing and it is very twist resistant, but I don't think I have saved much weight. But, for sure, a balsa or harder wood or ply structure would be seriously heavy to get a comparable level of strength. I just have to refine my finite analysis calculations. That's all.

Getting a properly contoured structure is all about the accuracy of the bulkheads - first, they have to be positioned accurately (correct station) and properly (square in two axes) on the framework which, in itself, has to be true and they have to be properly shaped and sized so that the stringers bridge smoothly as they proceed aft. And then all the slots have to line up. I had a couple boogers here, but no show stoppers. Some of the bulkheads were a tiny bit shallow, so I shimmed a few stringers with some 1/32 in spots - it's actually better if they are too proud so that the stringers can be sanded down at the end if you left yourself enough meat.

Very nice work, I am also considering this build. Two questions: Where did you source the laser cut parts? Is the cowl on the Stosser the same as the cowl on the Storch?

Originally Posted by Mannock

Very nice work, I am also considering this build. Two questions: Where did you source the laser cut parts? Is the cowl on the Stosser the same as the cowl on the Storch?

Mannock - I have a laser to cut the parts and designed in 2D CAD

Good question on the cowl since both aircraft used the same engine. The short answer is "no" even though the overall shape is similar to house the inverted V-8 engine. The Stosser does not have the prominent exhaust shrouds found on the later model Storch's although the prototypes did not have them. The upper part of the Stosser's cowl towards the nose also has a bit of concavity just aft of the prop opening on each side which most models miss. The Storch's was convex all over.

The fuselage is mostly framed up, although I have to now glass the nose section as I did with the tail. Since the soft 1/16 balsa skinning that I used flat spotted over the open areas (between bulkheads and stringers), I first doped the area twice with 30% thinned nitrate and then block sanded it lightly to take off some high spots and the raised balsa grain. You don't want to sand too much here as the high spots are actually the true areas of the surface - just enough to round them down.

The by-product of doping is that the dope waterproofs the balsa and when you apply water based spackle, it goes on quite smoothly since the balsa is not sucking the water out of the filler. I slathered the entire area with a fairly heavy coat of spackle and blocked it all off to a round fuselage, taking off almost no balsa. You can see from the photo how uneven the bare balsa was by where the filler has remained since the fuselage is now perfectly egg-shaped - as it should be. Yes, this add weight but the surface finish is everything.

From here, I will apply the glass/Polycrylic process as I did with the tail to stabilize the balsa grain.

I had resigned myself to make a proper mold for this model rather than using a vacuum formed plastic forming as a mold. The latter is great for one offs, but they take a lot of additional work to fit up. I have done a lot of both proper molds and vac formed molds and this cowl is really too large for a vac-mold although I feel it could be done. Plus, I don't have a vac table big enough to handle this size comfortably and foam cannot be used for vac-mold plug.

While mold making is a protracted and expensive process, I nevertheless have gotten pretty fast with making the needed plug and mold over the years and this one has a simple shape and therefore can be a two-stage (half and half) mold.

Thanks for posting this build! I always learn something useful from watching your builds.
-Tom

Originally Posted by TomJacoby

Thanks for posting this build! I always learn something useful from watching your builds.
-Tom

Thanks Tom, glad you're getting something out of it which is why I post this stuff. This not a very difficult model, but I have not gotten to setting up the wings yet which are still being built - without plans! I do have to post some pics as I am pretty far along on the cowl plug.

Thanks for the comments

Interesting to see how much spackle is needed to get a perfect shape even over carefully planked balsa. I'm assuming that it doesnt matter that you have sanded through the sealer coat if you are going to glass with epoxy rather than a water based product?

Alec