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Old Jul 06, 2009, 04:01 AM
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mikegbogh's Avatar
Roodepoort, South Africa
Joined Aug 2007
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Build Log
group build Nimbus 4 "1/4 scaleish"

Hi There,
I convinced a group of interested guys to form a group and each build a 5mtr semi scale glider using fiberglass and epoxy ,with the little knowledge I have gained over the last 3 years of working with these materials on my own projects.
Anyway Howard, Adrian, Mike and myself have worked on the plug molds and the first fuselage , which was layed up this past weekend.
Today it's my birthday and the one present I really wanted to open was all clamped up at my office. I released the bolts /nuts and clamps and started twisting , the first one is always stubborn but eventually it was "extracted"
and it's great .
This time I have incorporated a canopy lip and it will certaily do the job, makes that area nice and rigid, only concern was the weight at 1.2kg it may be a tad heavy but is very strong. This fuselage is 1.8mtrs long.
regards
Mike
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Old Jul 06, 2009, 05:05 AM
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PeteSchug's Avatar
Elmhurst, NY (Queens in NYC)
Joined Apr 2004
7,044 Posts
Fantastic!

You make me feel so lazy, building with balsa and spruce.

Pete
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Old Jul 08, 2009, 02:08 AM
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mikegbogh's Avatar
Roodepoort, South Africa
Joined Aug 2007
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Another day , another fuselage

I had started a build thread on the composites page, but will now continue
on the scale page, as its a semi-scale project .
Well fuselage one was a good prototype but heavy at 1230grams.
The guys in the building group will probably want these gliders for aerotowing and flat field flying so getting a light wing loading is important.
I quickly polished up my molds and spayed up fuselage 2 during my lunch hour on monday. I did the lighter layup on monday night 7-11 (lousy TV on mondays anyway )Did the edge trimming early before work on tuesday morning and put the molds out in the sun to post cure the resin.
Lunch time tuesday did the join layer and last night joined the 2 halves with
a mix of resin and flox.
Early this morning I released the part and this one is excellent
I shaved 300 grams off and its still plenty strong , so it passes my QC.
Regards
Mike
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Old Jul 08, 2009, 06:34 PM
yyz
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USA, CA, Paso Robles
Joined Dec 2004
2,400 Posts
Very cool

Looks great, Mike. When you get a chance, can you provide some more details like airfoil, how you made the plug (by hand, cnc, etc) and molds (tooling resin, epoxy and cloth), etc?

Did you enlarge the drawings from the Schempp-Hirth site?

Like the way you ran the carbon tow around the boom and up the fin, by the way.

It'll be interesting to see if the 1/3 scale Discus will have the well-behaved flight characteristics of the full-scale version.

This is a TON of work! Thanks for sharing it,

Mike
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Old Jul 08, 2009, 07:05 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Mike, what is the length/scale of the fuse? 1.2kg, 2.7lbs is not that heavy if you are looking at a 1/4 scale size sailplane. If this is closer to a 1/3 scale, then I would say you have it too light. What will be the wingspan?
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Old Jul 08, 2009, 10:42 PM
aka Schleppmeister
PA
Joined Feb 2006
1,930 Posts
Great accomplishment! A flying buddy of mine and his friends built 1/3 scale Ventuses from scratch. His came out at 18lbs and I have towed him this April. It flew great! I am kindly forwarding their thread in case you might be interested:
http://www.rcgroups.com/forums/showthread.php?t=754360

http://iflytailies.jimdo.com/
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Old Jul 09, 2009, 12:42 AM
yyz
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USA, CA, Paso Robles
Joined Dec 2004
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Think the original post said 5 meter (1/3 scale for the Discus/smaller Ventus). Discus 2 would be cool but the multi-break, polyhedral wings might add a lot of work. I guess the V2 would have the same issue.

This has probably been answered a hundred times but why do the fuselages on these 1/4 & 1/3 scale gliders end up looking so wide through the shoulders?

Don't get me wrong, these ships look fantastic but they end up looking chubbier than their full-scale counterparts, at least to my eye.

1/3 scale? That's amazing!

Tony, was your eta 1/3 scale?

The Other Mike

ps: can't find a 1/4 scale LS-4/6/8. Can you build me a 1/4 scale ASW-20 fuselage from the Viking molds?



Quote:
Originally Posted by SoarScale2
Mike, what is the length/scale of the fuse? 1.2kg, 2.7lbs is not that heavy if you are looking at a 1/4 scale size sailplane. If this is closer to a 1/3 scale, then I would say you have it too light. What will be the wingspan?
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Old Jul 09, 2009, 02:21 AM
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Roodepoort, South Africa
Joined Aug 2007
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Ventus/Discus semi-scale project

Wow ,
A few interested parties , thats great, the idea here was to build a glider for aerotowing and slope work. The fuselage is pretty much a generic shape and losely copied on the Schempp Hirth webpage 3 views.
It will look the part at the end with the correct decals, numbers etc.
The range of models we can make would include the various Ventus Ax bx cx cz etc and Discus , one guy wants to strecth his wings and make a Nimbus.
The building group all want ,wings with polyhedral tips and winglets.....of course they would , because its sexy and a hell of a lot more work.
The airfoil which I used very successfully on my last big bird (6.6mtr Lak) is the HQ3-13,3-12, 2.5-11 series and the SD 8020 for the tailplane, the fin is fattened using the outside edge of my HQ3-13 template and will fit a standard size servo in the tail to direct drive the elevator.

I have included some photo's of the beginning, because at my club recently there was a debate that I could not possibly shape fuselages by hand and eyeball alone, well thats exactly how.

I will also add the layup specs as we go, oh yeah the scale is closer to 1/3 than 1/4 , the plane seemed to evolve into something bigger than intended.
Two of the builders in the group flew full size, Howard a Beechcraft Bonanza and Adrian an ASW20 so they are cool with a 5mtr glider, Mike used to fly F3b a few years back just before hollow molded gliders appeared.
Its their first attempt at a full composites glider build.

Regards
Mike
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Old Jul 09, 2009, 07:52 AM
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Roodepoort, South Africa
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Quote:
Originally Posted by SoarScale2
Mike, what is the length/scale of the fuse? 1.2kg, 2.7lbs is not that heavy if you are looking at a 1/4 scale size sailplane. If this is closer to a 1/3 scale, then I would say you have it too light. What will be the wingspan?
Hi Tony
I am now "dazed and confussed" as usual, the fuselage is 1.8mtr from nose to
rudder post. I can see it's deffinately not as big as the 1/3rd scale model
So my new questimate is between1/4 and 1/3.5 scale with stretched wing tips to 5mtr.
I will keep calling it "semi-scale" to be safe .
The weights I commonly see on kits are generally higher than what my models come out at , we aim for about 1kg per mtr of span, but that is a basic model, no retract or cockpit/pilot detail. I know these big birds can carry some weight but in Johannesburg at 1800mtrs above sea level the lighter gliders thermal better. IMHO.
Cheers
Mike
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Old Jul 09, 2009, 10:05 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
mikegbogh - my comments were based on my personal preferences and the fact that I add detailed cockpits, retracts and pilots etc. It would be difficult for me to make a scale 5mtr sailplane weigh 5kg (11lb) with all those "scale" accessories. However, if you are making a hollow molded plane and do not intend to add the bells and whistles like retracts, tow releases, seats, pilots, instrument panels etc, then I suspect you could make a sailplane that light - just look at the RnR SB-XC - 9.5lbs at 6.7m!

You obviously need to build what works for you and since I don't fly at 1800 mtrs in Johannesburg, I really should keep my mouth shut It's just that experience tells me that at 5+ mtrs, building the plane heavier than 2.2lbs/mtr yields good flying, wide ranging models with good penetration for distance work.

Mike Deleo, call me. My telephone number is on my website - www.laserflight.com
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Old Jul 09, 2009, 10:34 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
mikegbogh, I did take a little time to weigh some of the fuselages I already have in inventory and they are generally 1:4 scale (or very close to that). I use gelcoat as my outer layer to add stiffness to the fuselage structure. At 1:4 scale, they are about 0.9 to 1.2kg depending on the model type. I would say that at 1230 grams - you are right in the ball park at 1:3.5 scale and should not be worried about the weight of the fuse. If you get much lighter you risk increasing fragility and having fuses crack under hard impact.

As a specific example, I have a 1:4 scale ASW-17 fuse that is 1.2kg also, 73" (1.85m) long and I consider it about the right weight for a 1:4 scale, 5mtr ship.

If this was a 1:3 scale Ventus type sailplane, your fuse would be around 2.2m and at that length I would say 1.23kg was a little light.

Given the size of 1.8mtrs, I'd say you were right on target!
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