Thread: Discussion Hobbyzone Champ Mods
View Single Post
Old Jul 11, 2012, 12:09 AM
jbarchuk is offline
Find More Posts by jbarchuk
Registered User
DeBary, FL
Joined Nov 2010
2,052 Posts
Quote:
Originally Posted by North_of_49 View Post
I'm also working on 2 sets of Champ floats... one from scratch using the plans available here at RCG and one from modified Carbon Cub floats (size reduced and hollowed out).
(BTW I still remember your asking about the CF rod 'wing flattener' I just haven't gotten to a pic yet. I want to also find the same angle of a stock wing to show the difference.)

The scaled down CC floats, please please I'm beggin ya please don't do it. If I hadn't already spent a lot of time already thinking about it many times I wouldn't be -repeating- saying this. In a time/reward sense it is simply not worth the effort AS COMPARED to a scratchbuilt set.

If you weren't going to do a scratchbuilt set then I'd say yes it -might- be worth the effort, but there are still caveats.

The scale factor is 15%, comparing 20.5" to 24" wingspan. (Whether 'Champ' vs 'Cub' is exactly 15 doesn't matter all that much, maybe it's closer to 10 or 20, but let's use 15 just to pick a number.)

CRITICAL: To scale this accurately you must reference everything from the step. More correctly, from where that 'inside corner' of the step, where the back half of the float meets the flat surface at the rear of the front half.

From that inside corner, you must scale the upper half down by 7.5%, the lower half 'upwards' by 7.5%, the front half shorter by 7.5%, and the back half shorter by 7.5%.

I don't have a CC float right here but the fuse is 15" and floats are around 2/3 the length of the fuse so let's say the floats are 10".

To scale the 10" length down by 15% that leaves the final Champ float length at 8.5".

OK I'm off by a little, because the jingjingjing floats are 9.25". But those are flight tested not necessarily pure scale. For discussion purposes and ease of arithmetic let's semi-split the difference and call it 9".

EDIT: Rats I'm off again. The *fuse* length on the Champ is 12", 2/3 of which is 8" not 9". But the numbers that follow are based on 9" and I really don't feel like writing it so screw it let's go with the 9. Whether you want the scale it down to 9 or 8 you do the math.

Scaling the 10" down to 9" needs 0.5" trimmed by both the front and back halves. No big problem, just cut it the ends off.

Now here's where the accuracy of scaling it by eyeball-sanding comes in, and how fabulously difficult it is. That 0.5" is to scale the front and back halves of the full 9" down by down. IF you trim off an extra 0.05" (appx. 1/16") you have scaled it down by an additional several %. (At the moment I don't particularly care to do the arithmetic to figure it accurately what the error is.) The point is that do you really think you can lay that foam against a sander, or even use a block sander, and sand it down with 1/16" accuracy? Well, yes, I'll bet maybe you can. But...

But... that' LENGTH dimension is the LARGEST dimension that needs to be scaled down. The width and height must be scaled TO A FINER ACCURACY TO MAINTAIN THAT 7.5% SCALE!! And if the length to height ratio is appx 10-1 the *accuracy* must be 10x higher.

It gets worse... This is all talking about straight lines and flat surfaces. Consider the -curves- of the bottom of the floats, that must be have accuracies held down to the 0.00x" tolerances. Now we're beyond the realm of hand/eye/sanding block capability -within- a reasonable amount of time. Sand off too much and you can't put it back on.

OK now the weight thing. I weighed one CC float, it was 1oz. That's 2oz plus let's say another 0.2oz for the wire. Let's say it's scaled down by 10%, that's 0.2oz leaving 2oz. That's 2oz hung off a 1.5oz AUW airplane. Folks have hung 2 keychain cams of Champs, that's 1oz, they they fly pretty well. But consider hanging 4 cams, 2oz, PLUS the effort of getting off the WATER. It'll get off the water like the Spruce Goose, and handle about as well. (Meaning 'just barely' for each aspect.)

To get rid of the weight let's say you go through the further effort of splitting the floats open and hollowing them out. I'd guess you can save 1/2 the weight easily and 2/3-3/4 with a lot more time/effort. From the 2oz now it's down to 1oz or possibly 3/4oz. Cool. That would help tons, that's reasonable.

I weighed the cut foam for a set of scratchbuilt floats, 0.4oz.. Add another 0.1oz for CA, stiffener, and mounts, total 0.5oz.. The scaled/hollowed floats are definitely heavier than the scratch, but even 50% isn't too extravagant considering they came out pretty light.

Cost: The two 8.5x11" sheets of 2mm Depron cost $0.75, but that's because as I said I'm lucky to have a monster LHS. The spruce and wire add another $0.25, that's $1 total.

So, to sum up, that's a $20.00 set of floats and the time-time-time-time-TIME to do all that fine hand rework to get the kind of accuracy needed, vs $1 plus scratchbuilding time.

Deimos, Phobos, Bottomos, please please don't do it.

I've got a lot of experience in production manufacturing. The time it took me to write this, I could have cut out several sets of depron, spruce, and wire. Drill holes, bend wire and assemble is another 90 mins per set. Time/effort/reward, just do the math.
jbarchuk is offline Find More Posts by jbarchuk
Reply With Quote