Good target weight for a 1m balsa DLG

[CthulhuJon]

I'm trying to do a scratch build of a balsa dlg. 106 cm wing span. ~200 in^2 area (~13dm^2)
not a super thin airfoil... just discus..launch-able is good enough for me. using modified (20% thinner) e205 airfoil.
might use on slope also.
~3.6oz/sq ft wing loading
~3.5 WCL
I've weighed all the parts before starting to glue it all up...
4 servos, 1S and RX come to about ~35g
and AUW I am estimating would be about ~150g... (~5oz) give or take a bit.
would 150g be, high, low or about average weight for a 4Ch, 1meter dlg?

 

[danskis]

I don't think there is a lot of data or experience out there on 1 meter balsa DLG so you might be part of the leading edge. Here are the specs of the Elf - a built up carbon fibre DLG with rudder/elevator only - about 95 grams. I think you're target weight sounds good if you can do it. Take a look at flyboa's threads for foam wing DLGs, I believe he has some plane weights in there along with his preferred weights. Look at RCGroups.com too.

flying weight of elf dlg - Google Search

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[CthulhuJon]

Thanks yeah I have seen that some of those carbon ones are very light ~100g which I probably can't match with my current design skills, 4 servos. but just curious...

 

[CthulhuJon]

discovered Wing Cube Loading..... this and this....
https://www.ef-uk.net/data/wcl.htm
https://www.sefsd.org/general-interest/wing-cube-loading-wcl/#:~:text=oz./sq.-,ft.,to 5 oz./sq.
So according to that... I'd have a WL of 3.6, and WCL of about 3.1 for the DLG,
which seems reasonable for gliders.

That Elf only has 2.6 WL, WCL =2.1 !! super light.

 

[Thermalbirb]

I'm trying to do a scratch build of a balsa dlg. 106 cm wing span. ~200 in^2 area (~13dm^2)
~3.6oz/sq ft wing loading
~3.5 WCL
I've weighed all the parts before starting to glue it all up...
4 servos, 1S and RX come to about ~35g
and AUW I am estimating would be about ~150g... (~5oz) give or take a bit.
would 150g be, high, low or about average weight for a 4Ch, 1meter dlg?

Looking to do the same, keep us posted with pics and progress report... Scratch built is where it's at.!

 

[RoosFlyer]

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https://www.facebook.com/groups/235097445497948

 

[CthulhuJon]

Thanks much for all the replies and info. Just started gluing together my pile of sticks this week… it’s coming along. This is what I have so far…
The basic plan is/was... scratch design/build DLG that I can easily transport, and throw about in any park I happen to be at, and a bit of slope if opportunity arose. Decent lift, doesn't need to launch to the moon. Light-ish and slow would be ok. I'm still learning ( crashing )
modified ( thinner ) E205 airfoil profile, similar to MH32... seemed to fit the bill. Should be ok for slope or a discus launch. 5mm spar, 2mm front edge to protect against dings. 4 servos, all crammed into that nose, to minimize needing much added nose weight.
I built a similar size and design sloper and it survived many crashes very well so far. haha. ( light weight combined with a bit of strategically placed carbon seems to be good crash insurance )

 

[CthulhuJon]

Thanks Roos, applied to the group.

 

[RoosFlyer]

This one answers loads of your questions
AUW - 175g But 150g would be better.
Spinnin' Birdy RE 1m

https://www.hyperflight.co.uk/products.asp?code=SPINNIN-BIRDY&name=spinnin-birdy-re-1m
or go crazy
Strike 3 DLG 1m

https://www.hyperflight.co.uk/products.asp?code=STRIKE3&name=strike-3-dlg-1m

 

[CthulhuJon]

Thanks Roos, I like designing and building my own rather than buying at the mo. I learn a lot quickly, and the whole process is satisfying. I can't justify those expensive carbon ones yet... I'm definitely on a budget though some of the gliders out there are definitely tempting to buy. That Spinnin birdy looks real nice.

 

[CthulhuJon]

AUW - 175g But 150g would be better.

We'll see if it finishes at 150 or not.... It could have been 10g or so lighter if I did not make the wings in two parts.

 

[Thermalbirb]

Thanks Roos, I like designing and building my own rather than buying at the mo. I learn a lot quickly, and the whole process is satisfying. I can't justify those expensive carbon ones yet... I'm definitely on a budget though some of the gliders out there are definitely tempting to buy. That Spinnin birdy looks real nice.

More ratification making your own bird too..

 

[CthulhuJon]

Progress… looks to be roughly on target. plane so far 98g and 121g with 4 servos. 132g with RX and battery. Then however much more for covering, peg, nylon bolts, some sheet balsa at wing root and any balancing weight.

 

[CthulhuJon]

I found another good 1m balsa DLG comparison, ALT dlg. ( 2 CH ) at about 200g AUW. I think mine will be lighter... ( hopefully strong enough ), I might need some added nose weight, but I think from initial tests... none or not much if I can get all the electronics to fit in the nose as planned... working on hinges for control surfaces at the moment... ALT dlg ->
https://www.hyperflight.co.uk/products.asp?code=ALT-DLG&name=alt-1m-dlg

4 CH..
Spinnin Birdy with Ailerons. AUW 200g
https://www.hyperflight.co.uk/produ...BIRDY-AIL&name=spinnin-birdy-with-ailerons-1m

So the weight range for a balsa 1M DLG seems to be up to roughly 200g. ( looking for more examples of lower weight ones )
mine will be 4CH with 106cm span. so I think I'll be doing ok if I can keep it around 150-160g

 

[CthulhuJon]

Update.... almost finished... total weight = 153g, I'm only only missing the weight for the covering, some CA to harden the nose, and any nose weight for CG balancing. CG is currently about 1cm behind estimated CG point.
I can shave a bit of weight off all the servo cables, which are all too long at the moment... but that won't save much.
I had to rebuild the nose... lengthen it by 1cm... needed more room in there...

So its only a little over my initial estimate of 150g and in line with other models . Tail end seems to be a critical factor... I could have built it lighter, which would probably have meant no extra weight needed on nose... for overall weight saving... But I feel the tail is the fragile point on the design already.

I would estimate that if the wings were glued together instead of 2-parts, and my bottom-front part of rudder was not balsa ply (or a smaller tail), then it could easily be 10g lighter. Without ailerons would be another 10-15g lighter (2 servos gone, and lighter wings) but would need to add weight to the front to compensate for CG balance. So I think 130g (plus covering weight ) is pretty do-able with 2 channel setup, probably less if careful or use competition balsa and a more expensive/lighter boom.

any progress on your plans @Thermalbirb ?

 

[cdfigueredo]

A few days ago I started my DLG. I am building the Falke according to the plans I drew myself, guided by several pictures from the manual.
Here is the Falke DLG

The balsa I can get is extremely heavy and the electronics I have are not the most suitable, so I have had to modify the original plan.
The tail rudder still needs to be cut and a lot of sanding, but it's already getting a bit heavy.
I assume that the final weight should be around 200g.

 

[cdfigueredo]

Since the balsa I can get here is extremely heavy, I want to build the wing using fiberglass rods to reduce weight. The spars will be in balsa because it is not easy to get carbon tubing here.

 

[Piotrsko]

If you are making it out of fiberglass, why not make laminated spars the size and thickness you desire. You could even use paper or plastic drinking straws as an internal form, skewers with waxed or oiled paper as a mold release.

 

[CthulhuJon]

A few days ago I started my DLG. I am building the Falke according to the plans I drew myself, guided by several pictures from the manual.
Here is the Falke DLG


The balsa I can get is extremely heavy and the electronics I have are not the most suitable, so I have had to modify the original plan.
The tail rudder still needs to be cut and a lot of sanding, but it's already getting a bit heavy.
I assume that the final weight should be around 200g.

Thats a pretty looking DLG, I hope the build turns out well.
You can maybe find light weight balsa online, search for "competition balsa" for example... https://www.nationalbalsa.com/Aero_Light_Balsa_p/116348ct.htm, but depends where you live I suppose...
but in some strength critical areas you might still want to use heavier balsa or balsa ply anyway...
I've found balsa ply to be a very strong compromise between weight and strength.. just go really easy on the glue, 3 ply balsa, alternate the grains, and clamp it well. I used that for the bottom half of my rudder and the wing-tips).
Is that tail boom 100% balsa, or are you going to glass the outside?

I have 5mm carbon tube which I am not sure is stiff enough... but the Pug's spar seems less than 5mm diameter tube and seems ok.
Can you buy arrow shafts where you are? you might be able to get some nice glass-fiber, aluminum or carbon tubes that way.

My last glider is a sloper with 3mm spar plus a coupe of balsa stringers for extra strength... it seems pretty stiff wing and is also about 1m span, I'll dig up some pics.

one thing can make a big difference in weight is to get the servos and electronics as far forward in the nose as possible, that minimizes how much extra nose weight you'll need to add later to balance it for the CG.
Also you can get away with small lipo battery but still a long flight time... my 220mah 1s lipo battery is only 6g but good for about 40 minutes or so.

 

[cdfigueredo]

If you are making it out of fiberglass, why not make laminated spars the size and thickness you desire. You could even use paper or plastic drinking straws as an internal form, skewers with waxed or oiled paper as a mold release.

No, I whish I could have that fiberglass. What I h

If you are making it out of fiberglass, why not make laminated spars the size and thickness you desire. You could even use paper or plastic drinking straws as an internal form, skewers with waxed or oiled paper as a mold release.

it is not fiberglass, i mean this: https://es.aliexpress.com/item/4001214588311.html