Jul 26, 2013, 12:13 PM Registered User Joined May 2009 584 Posts Build Log Shereshaw Cumulus (50%) - BIPLANE Plus Build Off July-Dec 2103 Well, the Klarich short kit items are still being gathered and an email from them tells me it will be ready to ship next week. I (being me ), have gotten a case of the itch and printed tiles of the plan downloaded from the Outerzone site. These were magazine pages and printed at some weird scale like 3/16" = 1". So, applying some of my math skills, I printed the fuse and wing plan at 270.5%. Formers and rib pages were full size on two separate pages. Those I printed out at 50%. Resolution is still excellent, so no problems there, The only thing is that I've always preferred a fine line drawing. With the scale-up I've done, it's anything but that. A quick check of the rib measurement to the fuse showed things were practically dead on, but that's as far as I've gone. When time allows, I'll get down to checking formers and wingspan. This is what I'll be working with... Last edited by cd_webb; Sep 04, 2014 at 06:47 AM.
 Jul 26, 2013, 01:51 PM I like real wooden aeroplanes! South-west France Joined Sep 2007 4,651 Posts Watching with interest! Latest blog entry: Frog Tomtit x2 Photo Build Sequence
 Jul 26, 2013, 11:55 PM Registered User United States, CA, Santa Ana Joined Jul 2010 445 Posts 50%, going to be electric ? Full size model is a real floater. Ross
 Jul 27, 2013, 07:33 AM Registered User Joined May 2009 584 Posts Ross, I think that electric will be my only option at 50% - if I want a semi-floater. As of last night, I realized that I have managed to get myself into the same mess that I just dealt with on the Midget. This is something that, as a surveyor, I should have known. When you multiply the dimensions of a plan by .5, every measurement decreases by 1/2 - except the area, and in particular the wing area. That quantity decreases by 3/4! Well now, that's convenient, isn't it? I don't know how smart it would be to build a structure as light as this one will need to be and then put a nitro engine on it. No, IF I push ahead with this project at all, it will have to be electric. At this point, I'm not at all sure that the subject matter or subject size won't change. Last edited by cd_webb; Jul 27, 2013 at 08:02 AM.
 Jul 27, 2013, 02:13 PM Registered User Southampton, UK Joined May 2007 802 Posts 1 to 1.5cc diesel would be just right for RC 48" span or a glo 10 but I would stay with electric and build ,ight - no fuel proofing etc. john am at page 8 of franni's cumulus build - getting there slowly - my wife complains I spend too much time on the net or in the workshop
 Jul 27, 2013, 03:31 PM I like real wooden aeroplanes! South-west France Joined Sep 2007 4,651 Posts I think the Cumulus will make a delightful and thoroughly practical model at 48" cd, especially for electric power. Agreed that due to the square law the loading may be higher than a full size one, but not to the extent where it would affect the flying ability. Bear in mind that you won't be expecting the half size model to be half the weight of the big one, more like a third or even a quarter I would think, so the loading will not be all that different. I hope you do go ahead with it. Latest blog entry: Frog Tomtit x2 Photo Build Sequence
Jul 28, 2013, 03:56 AM
Registered User
Southampton, UK
Joined May 2007
802 Posts
Quote:
 Originally Posted by Sundancer I think the Cumulus will make a delightful and thoroughly practical model at 48" cd, especially for electric power. Agreed that due to the square law the loading may be higher than a full size one, but not to the extent where it would affect the flying ability. Bear in mind that you won't be expecting the half size model to be half the weight of the big one, more like a third or even a quarter I would think, so the loading will not be all that different. I hope you do go ahead with it.
IF the materials were to be scaled exactly, then the weight would alter by the cube of the scale factor and keeping the power weight ratio the same, then the power requirements would also alter by the cube facor.

However, materials are not always same nor can they be scaled accurately ( eg using nearest size wood ) and some weight saving can be achieved scaling up or down with consequent savings on power. some redesign for the change in size can also achieve weight saving.

My original 38" mamselle is powered by a 0.5ccs diesel dart engine

a clapped out irvine 20 ( 3.3ccs 7 times the dart) - built very light as guided
free flighter trainer for air cadets adequate power and would loop indefinitely

an early saito 30 4 stroke ( 5 ccs 6/7 times equivalent ? ) heavier built for
myself power about right - not a lot in reserve

a saito 40 4 stroke ( 6.6ccs about 8/9 times equivalent ? ) much heavier
-built as a test model for doped polyester dress lining. - slightly overpowered

And finally my 108" version which is on its second 90 4 stroke ( 15 ccs which is 30 times the size of the dart ( scale factor cubed is 27 ) but how do you equate a 0.5ccs diesel with a 15ccs 4 stroke glo ??

Another factor to take into account is that the larger props are more efficient than smaller props - or so I have been led to believe

to sum up the giudelines I use to estimate final weight and powere required is to take the scaling factor and cube it and use that factor as a gudeline to where my model is likely to end up for weight and power

john
 Jul 28, 2013, 07:56 AM Registered User Joined May 2009 584 Posts George, John, thanks for the responses. Up until about a year or so ago (about the time I began frequenting this forum), my modelling experience was limited to buying a kit and following the written instructions - EXPLICITLY! Things like we're talking about here were never an issue, so never a need to think them out. The Trenton Terror was the first in a short string of 5 models built with no instruction. The Deacon, Skyline Kitten and Titch were my first 'cut out your own parts' plan builds. Nothing I've built has ever been scaled up or down, so I'm learning, and there's still more learning to be done. I'm getting used to construction techniques that sometimes are a first for me. Then throw in the fact that these things often incorporate undercamber, lifting tailplanes and other things alien to me and I'm really in "Never Land". This one will be very similar in size to the Midget, which turned into a bit of a porker. The dimensional similarities set off the alarm bells, but without the 4-stroke up front, trimming down the wood sizes, maybe the wire sizes and a little bit of redesign where possible, I'm thinking a 30oz model might be realistic? That would be like shaving 8 oz off of the Midget. Of course, I'll do my best to get under that figure, but as I've said before, building light seems to be beyond me. There's my goal. Now, I guess I'll work on getting some rib templates cut.
 Jul 28, 2013, 10:14 AM I like real wooden aeroplanes! South-west France Joined Sep 2007 4,651 Posts I don't see any reason at all why you shouldn't hit 30 ounces cd.I have two 36" biplanes which are around the 16 ounce mark and a 60 inch cabin model (the Halfax Spartan) which is VERY substantially built that weighs in at 40 ounces (all electric models), so 30 ounces would seem to be a very realistic target for a 48 inch monoplane. Just bear in mind that, when scaled down the structure will be quite "dense" (some Shereshaw designs do tend to have a lot of wood in the airframe, although the Cumulus is not so bad in this as, say, the Cloud Cruiser)), so you need to err on the side of going with smaller cross sections for the components if in doubt, especially for the subsiduary structures like stringers etc. And also try and use a light grade of wood throughout (not so easy these days I know, as choice is often limited). As an example, it might be tempting to use 3/16" square for the basic sides, but I would opt for firm 1/8" sq with 1/8" x 1/16" for diagonals and 1/8" x 1/16" (on edge) for stringers. Last edited by Sundancer; Jul 28, 2013 at 10:21 AM.
Jul 30, 2013, 04:30 PM
Registered User
Joined May 2009
584 Posts
Quote:
 Originally Posted by Sundancer ...As an example, it might be tempting to use 3/16" square for the basic sides, but I would opt for firm 1/8" sq with 1/8" x 1/16" for diagonals and 1/8" x 1/16" (on edge) for stringers.
Which is exactly what the scaled down plan from Klarich calls for (did I just end that phrase in a preposition?? ). I do believe there's knowledge tucked away in your head, George!

Still puttering around with ribs, half done.
 Aug 06, 2013, 03:18 PM Registered User United Kingdom, England, Gt Man Joined Jul 2012 272 Posts HI guys. My 50 inch span high wing1949 Frankenstien weighs 21 oz and my 48 in span STOMPER weighs 16 oz , so no worries, CD...KBO