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May 23, 2009, 01:14 PM
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Franny B's Avatar
Build Log

Shereshaw Cumulus build

Hi All,

Our club has an Old-Timers event each year in August and I thought it would be fun to enter this year. After a bunch of searching on the web and looking at different designs, I stumbled on Allan's beautiful Cumulus. I just fell in love with that classic style and decided that the Cumulus would be it. I looked through Klarich's catalog and sure enough they have a couple versions. I decided on the original 96" span version and ordered their short kit of cut wood. After carefully looking over the plans, I spent an hour at the LHS picking out all the flat and string wood. I plan to power it with an AXI 2826-12 motor on a smaller 2000mA 3S lipo. At Allan's suggestion I'll be adding ailerons as well.

So, here we go.

I'm starting with the wing halves first. This is my first model with an under-camber airfoil which means the spars don't lay on the board. No biggie, just new (well old I guess). I set up the ribs and then tucked the spars into the notches in the ribs and locked everything down with thin CA. The ribs in the kit are pretty good except that the spar cut outs are wrong for the smaller ribs out at the tips. I had to move the slot somewhat.

Last edited by Franny B; May 28, 2009 at 02:33 PM.
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May 23, 2009, 01:21 PM
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More on the wing

More on the wing:

Once the main ribs were placed and locked to the fore and aft spar, I added the sq leading edge. For the trailing edge, the rib lengths didn't line up with the plans so I notched the trailing edge so that the thickness of the rib would line up with the thickness of the TE triangular piece. This pushed the TE slightly behind it's place on the plans, but not a significant difference. I am noticing that these cut pieces are not entirely accurate. It was more of an issue at the tip and I'll show you that when we get there. With the LE and TE in place, I started on some of the tip pieces.
May 23, 2009, 01:48 PM
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More on the Tips

The tips were a little difficult to figure out. The kit has solid balsa tips to attack and sand, but the need to be mated in such a way that they flow well from the sheeting. One thought was to sand then down and then sheet the entire tip, but I think it would have been more difficult to get the final shap just so. And, remember, the under side is under-cambered so that makes things interesting. The photos I'm posting are actually from the right wing half after I stumbled a bit through the left half. I determined that I needed a small additional rib to go flush against the block top st really set the shape and to have something for the sheeting to sit on. That way it wasn't just butted up against the block. I used the last rib as a template and just scaled it down a bit. Another problem is that the block tips are a little small and so I had to add a little filler strips to be shaped later. I guess my biggest concern is that, looking at the front view of the tip didn't reveal much except that the bottom side flairs up a bit. The rear spar is flat on the board at this point so it needed to be shaped to match the taper. Not to mention, I'm thinkin' the two tips need to be pretty similar
May 23, 2009, 01:56 PM
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May 23, 2009, 02:01 PM
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Sheeting and cross bracing

I made a little dihedral angle template for placing and setting the inside most rib that will join with the other wing half. There is a front view of the center section on the plans so I was able to get the angles from there. One important little step is to web the fore and aft spars out three rib bays. This needs to be done before the sheeting. I might think about going on a bit further towards the tip. I want to see just how it all feels when they are finished. Once the last rib is set and the webbing is in place, the wing's LE and tips are sheeted top and bottom. After that, cross bracing members are cut into the top and bottom of the ribs to control "gating" of the wing fore-aft. Finally there is a bunch of sanding and shaping especially at the tips.

Next up will be figuring out the ailerons and their linkages. I have these nifty little side actuators I might use or I also have some very stiff carbon fiber tubes I could use at torsion rods. The loading will be quite light and absolute precision in control isn't really necessary so they may be kind of trick. I'll have to see where I am after the ailerons are cut out and boxed in.

Until next time...

May 23, 2009, 02:02 PM
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Franny B's Avatar
Thanks Thermic! Just getting started. I'm sure the fuselage is going to be a little crazy.

May 24, 2009, 05:25 AM
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Tim Trick's Avatar

Looking really great - nothing beats a large vintage design for shear building pleasure! I have a Ben Buckle Falcon that was based on the Cloud cruiser that flies on an Axi 2826/10 on 8 NIHM cells with an APCE 14 x 7 prop. Your setup will work just fine if you keep the weight under 6 lbs.

If you are building the model with the original dihedral, you will definitely not need ailerons -in fact the dihedral will greatly redice the effect of ailerons anyway. My Falcon turns very spritely indeed if I give it full rudder throw. Ailerons will just complicate things and add unwanted weight.

For your info, my build thread can be found here if it is of any help in your build:


May 24, 2009, 08:44 AM
Thermals, Tom
RyanNX211's Avatar
Best of luck. Your experiences are not unique among those who have built Klarich Kits. And, this is to be expected considering how many he cuts and the plans he has to work from.

I think you'll be please with the performance. The late great Dick Huang had them in all sizes with various powerplants.
Latest blog entry: Steak and Old Timers
May 24, 2009, 12:24 PM
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Hi Tim,

Thanks for the thoughts on the dihedral. That would have been my first thought as well. Allan, who has build a Cumulus said that they behave better with a bit of aileron input. I guess I'm still debating it in my head. I have a smaller Satin Doll which is a 1937 bi-plane with rudder only and it turns quite well.

I looked at your Falcon and that is really amazing work! Just gorgeous! I love the colors. That is close to what I've been envisioning for the Cumulus. How was that Solartex to use? That is what I have been looking at but I was concerned about the weight. I would like to stay under 5lbs and with a smaller battery and motor I bet I can. I really should have set up for spar caps, but I wanted to *try* and remain as close to original as possible. The plans that Klarich sent must have been photocopied about a hundred times and have quite a bit on noise. Also, several places there are 1/16" "issues" where things come together or sheeting ends that have to be addressed.

One more issue I need to iron out is whether I should make the wing two pieces or not. That is an 8' span and I don't have a very large car, but I can walk to the field. I always worry about dihedral braces and also the weight from a removable setup. I saw your removable tips. How is that working out? My Bird of Time has removable tips and they work well, but you can see the seams and I have to use tape to be certain they do not depart prematurely in flight. I don't know... still trying to figure it out... I'll spend more time going through your build.


May 24, 2009, 08:42 PM
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Great start Franny

It's lovely to see you have made such a good start Franny, you will love the finished model, Cumulus has a real presence helped by the shear size of the thing.
I don't want to get into the aileron debate again in this forum. For me, on this model, they improve the flyability. Yes, you must mix in a heap of rudder as well to provide positive yaw in the roll direction or the ailerons will be rendered ineffective. Do that though and you have good positive roll response even on the glide.

Franny if you are thinking of competition, you need to leave the ailerons out. While not banned by the SAM regs, I have heard that Contest Directors could ban you on the day, unfair though that sounds. If it is just sport vintage then go for it. You will love the aerobatic ability.

You will need to do a sub spare on the aileron hinge line. I'll do some photos of mine and post them.

Keep up the great work!

May 24, 2009, 08:56 PM
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Franny B's Avatar
Thanks Allan!

I did talk to the contest director and he wasn't too keen on ailerons but did say he would allow them. On the other hand, I don't want to seem like I'm pushing things unfairly either... At any rate, the wings are finished for now and I can add the ailerons later. I am now working on the horizontal stabilizer. I'm trying to come up with a good solution for the elevator that will work. Do you have any photos of yours? The thickness is tapered so I'll have to be a little careful and think this through before I start.

I am really looking forward to this build and eventual flying. I clamped the two wing halves together and that is one big wing! It should be quite the presence in the air.

May 25, 2009, 12:10 AM
Registered User
I'll get you some photos tonight. I put the servo in the tailplane driving one side but with both sides connected by a torque link through the fin. Although they are big, I've used the natural line for the hinge. I've added some sheet in the center section area to accomodate the servo. The pictures will explain.
Back to the ailerons, if a CD objected you could unplug them and lock them with clear tape and fly the event on rudder. Better still just program them out on your TX. That would really show you the differenct to.
The important thing is preserve all the moments, areas and angles same as the original.

May 25, 2009, 01:18 AM
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Chris Jenkins's Avatar
deleted - sorry
Last edited by Chris Jenkins; May 25, 2009 at 01:34 AM.

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