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Old 01-16-2020, 03:47 PM   #31
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Re: New To Me Cub!


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Originally Posted by NEW222 View Post
I guess after seeing so many Cub models with the engine in the middle of the cowl like the original, I had just assumed they would all be like that.
Yeah, we all have made assumptions that turn out to be incorrect. "Plan ahead, plan ahead, plan ahead....." is a good mantra.

I would use either the LA .25 or the Leo .28 (whichever has the shorter thrust washer to rear engine plate dimension), use an engine mount with the thinnest backplate and use a Dremel to remove material on a composite mount to make clearance room for the rear engine plate bolts/rear exhaust stack and follow Kurt's advice to slid the cowl forward...… the first two changes should reduce the thrust washer to firewall dimension by 1" to 1.25", reducing how much cowl slide forward is needed.

I would continue to mount the engine with the cylinder in the horizontal position.

The Sig 1/6 scale full and clipped wing models, I strongly suspect, were not re-engineered for four stroke engines with their rear hanging carbs, greatly increasing the overall length of the engine over a two stroke engine with their front mounted carbs. I don't have the plans for the model but I note that the free downable manual for both the full and clipped wing cub make no mention of how to accommodate this difference (or for electric power either).

A second and likely more controversial comment is that the OS .48Surpass is too much engine for this model, both in weight/overall length and power.

The original full 71" wing cub by Hollinger and Berkeley that Sig took over for their Cub was powered by two stroke .19 non-schneurle engine, when rc gear was a lot heavier than today.

Check out this thread where a DPlumpe discusses his successful use of a OS .26Surpass on a 1/6 scale Sig full wing cub....he acknowledges he built light, with an overall weight of 3.75lbs but says the same engine works when he converts the model to a float plane at 4.75lbs. (the OS .26Surpass, with muffler, weighs 9.7ounces and its front to back dimension is .75" shorter than the OS .48Surpass which, with muffler, weighs 14.8ounces.) Great picture of his model with the small four stroke muffler sticking out of cowl in "scale like" manner.
https://static.rcgroups.net/forums/a...0%26%20Cub.JPG

Apart from front to back engine dimension and over powering issues, consider any weight/center of gravity..... the OS .48Surpass is going weight 5 ounces more that either the OS .25LA or Leo .28 and those 5 ounces are going to sticking further out front.

I'd do a wing loading calculation.... at a overall weight of 4 lbs, and a wing area of 557sqin, the simple wing loading is a very comfortable 16.5oz/sqft and 8.4 cubic; at 5 lbs the wing loading is 20.7oz/sqft and 10.5 cubic..... I wouldn't want to be much beyond 5lbs on this model for tension free flying.

good luck
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Old 01-16-2020, 05:50 PM   #32
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Re: New To Me Cub!

I'm actually surprised that the 48 is that much too large on the nose. Sig actually recommends a 40-45 4 stroke. I would be more curious to some plans and a measurement comparison of the model. Something just seems really out of whack and I suspect that maybe something was modified to fit the electric motor. Unfortunately, if that's the case, the work involved in chopping things up to get the 4 stroke in probably isn't worth it when you have the 25/28 2 strokes available. It's a cub, it will fly fine with either of those.
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Old 01-16-2020, 06:24 PM   #33
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Re: New To Me Cub!

Wow. Thank you very much Michael for the information and recommendations. Something I had never done yet, till moments ago, was weigh the plane. Complete plane, minus the struts that I have yet to design and build, one servo for engine control, engine, mount, battery and fuel tank weighed in at 2 lbs 12 oz.

I also just weighed the following:

Futaba S3003 servo, 5 cell NiMh battery, 10 oz fuel tank, engine mount, propeller, and Leo .28. Weight is 1 lb 5 oz.

Futaba S3003 servo, 5 cell NiMh battery, 10 oz fuel tank, engine mount, propeller, and OS LA .25. Weight is 1 lb 4.2 oz.

Futaba S3003 servo, 5 cell NiMh battery, 10 oz fuel tank, engine mount, propeller, and OS FS-48. Weight is 1 lb 12 oz.

So now I have some more reading to do regarding my engine choice for the plane. I just may go the LEO or OS LA yet. Also, if I get a smaller servo for the throttle control, I will shed even a bit more weight. This may get interesting yet! Thanks also for the link. I will go read it right away.

Just did the math quickly, and depending on engine choice, the airplane will be somewhere between 4 and 4.5 lbs. All I have yet to make is the struts, but should not add too much weight.

Last edited by NEW222; 01-16-2020 at 06:48 PM.
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Old 01-16-2020, 06:30 PM   #34
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Re: New To Me Cub!

I too was very surprised that the OS FS-48 was that big as well. I do understand that it is just a hair bigger than the recommended engine size, but did not think it would not fit in the cowl. From what I have read and can gather online without having a set of plans for either 1/6 Cubs here, the length of mine may even be about a 1/4" longer than what they state, if my measurements are correct. I wish I had a set of plans here myself too, but am waiting on hearing back from someone on getting a set. Also, I was not too keen on the idea of chopping up my cowl just yet, especially if it would require that much chopping.
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Old 01-16-2020, 07:08 PM   #35
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Re: New To Me Cub!

Overall length may be correct, but it's possible somebody lengthened the nose and shortened the cowl. It just seems really out of whack to me. What's the distance from the firewall to the front of the cowl?
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Old 01-16-2020, 07:44 PM   #36
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Re: New To Me Cub!

The distance between the firewall and the front edge of the cowl is just under 2 5/8". With that said, I would guess that it should be 2 1/2", as I had just put a new 1/8" firewall on top of the existing one to cover up the holes from the electric motor holes.
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Old 01-16-2020, 08:15 PM   #37
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Re: New To Me Cub!

Ya, that seems REALLY short. I measured my OS32 heli engine which doesn't even have a prop hub and it's more than 2 1/2 inches.
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Old 01-18-2020, 02:14 PM   #38
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Re: New To Me Cub!

Good news. Plans are on their way. Sitting at a post office in New York, waiting to make their way here. The plans are the Sig 1/6 scale Cub w/71" wingspan, but apparently they show a clipped wing version, and all other dimensions are identical. Also, both use the same build manual, so I will now be able to finish her up, struts and all. Now sitting idle waiting patiently!
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Old 01-28-2020, 08:36 PM   #39
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Re: New To Me Cub!

Well, just another little update. I did not yet receive my plans, but I was fortunate enough to find a decent picture of them online. With that said, I was able to zoom in enough to read that the struts were made of 3/16 x 3/8 spruce/hardwood. So I grabbed 2 sticks quickly on my way home today and began to make my struts. I cut some tin to insert into the ends that screw to the wing, and bolt to the fuselage plate I also made from modelling tin plate. The fuselage mount was and is definately not stock by any means, but it will function, I hope.... Anyways, I took 2 pieces of music wire and layed them along side my strut pieces so I could get a straight cut into the spruce for the mounts. Once done, I drilled a 1/16" hole right through and put a tiny piece of music wire in as a pin. Then wrapped the ends with thread and CA'd. Then I made the rear piece that joins to the front one, installed, marked and cut. I then used wood glue to glue them together, and clamped to dry. This is where I am currently at. Waiting for them to dry. Tomorrow, I will drill and install a pin on the bottom part followed by wrapping with thread, then I will give them a little sanding, seal them, and paint them. Sorry I have no pictures currently, but will grab a couple tomorrow. Being short and close to the fuselage, I will be omitting the two upright support ones though me thinks.
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Old 01-28-2020, 11:00 PM   #40
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Re: New To Me Cub!

Ok. Struts almost done. I omitted the pin at the fuselage mount as I do not want to compromize them. So I used my thread again and wrapped them good, followed by a coat of CA to wick in. I do not know what kind of load they will have or be bearing, so hope they will be good enough. Tomorrow I may brush on a coat of Minwax to seal them, and sand them. Hopefully paint them Saturday. Weight so far as seen here is 1 oz.
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