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Dec 22, 2015, 04:24 PM
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nerdnic's Avatar
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nnDLG


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Hi friends.

For a little more information on DLGs check this episode FT did.

The general consensus on DLGs is that if you want something that performs, you better be ready with the $$$. There are some more affordable foam options but they just don't perform as well compared to the CF competition gliders. Bringing DTFB into the equation would mean you're settling for a sub par DLG experience at best. Well.. that's the impression I get when reading about DLGs around the Internet, at least.

I've read similar things about performance planes being made of DTFB also. Now that I've set a new bar of what performance means in a DTFB plane with my speedwing design on my nnMiG 3 and nnP-39, I decided it was time to push the limits of what DTFB can do in a DLG.

My goal is to make a DLG that performs better than any store bought foam DLG, and for a fraction of the cost.

SPECS
WINGSPAN 51in
FUSE 34
CHANNELS 3-4
WEIGHT 300g

ELECTRONICS
BEC - Suppo 3a
BATTERY - Zippy 350mah 2s
SERVOS - 4 5g

BUILD DIFFICULTY
Beginner – You’ve never flown a plane before, let alone done a scratch build
Novice – You’ve flown a plane but have no experience with scratch building
Intermediate – You’ve flown and built a few FT style planes before
Advanced – You’ve mastered the standard FT build style and are looking for a new challenge
Expert – You’ve mastered all build techniques and aren't afraid to improvise or tackle tedious builds

The nnDLG is an intermediate build.

PILOT SKILL Beginner

MATERIALS
2 sheet DTFB
1 sheet poster board
1 27-29" carbon fiber arrow (cut to 24")
1 45" flat aluminum
1 BIC pen
1 2 liter bottle


PLANS
Beta plans are finished but has performance bugs. I'm opening the beta testing to the community! For plans please see www.nerdnic.com/beta


BUILD LOG
March 6th 2015 - BETA 1
First round of plans are done and I'll be doing my first build test shortly!


Cross section of airfoil


90g weight so far




I have some initial concerns about wing strength so far but I think the wing style I chose is to blame. The wing is sturdy as you move from the center toward the wing tip until you get to the slope in the leading edge where the top and bottom wing seperate in the plans. I will be changing the leading edge to be straight. Also, after removing nearly all the inside paper and beveling all surfaces the foam is left with no strength. What little stiffness DTFB has is lost once you remove paper and cut away massive amounts of the foam.

Something that I've never had to deal with on a plane before also came up - wing balance. Somehow I came out way off on the weight between the two wings.

From a weight perspective I have no idea if 90g is good or not but it feels like nothing in your hands. I have decided I will be adding ail. The nose I designed was too small to fit servos so I need to enlarge it a smidge.

With electronics it's 180 g. I am using 9 g servos and a 350 mah 2s. And I actually need that amount to get the right CG. I think to build it lighter I have to bring the tail section in a bit or extend the nose.

Beta 1 survived many full power throws but finally failed. This was expected and ultimately the entire plan with beta 1. I wanted to learn where the weak points were and then make design changes to address them.





Failure occurred on the nose and launch wing. The weight from the electronics causes a lot of strain on launch at the CG point of the wing. The wing was also just not strong enough with just the strapping so I need to rethink the wing. This is also needed because I just wasn't getting the glide I wanted in general. This is because the wing area is just too small for the weight so the goal is to reduce wing loading with a bigger wing area AND make it stronger WHILE keeping it lighter per sq inch. This will be quite a challenge. So here are the changes being made after beta 1 testing:

-add reinforcement to nose
-increase the wingspan. The weight will be increasing so this is needed.
-increase the wing cord. This should help lower wing loading.
-switch to a nnSpeed wing. The strapping worked well enough but by it's self it is not strong enough to prevent the wing from folding.
-increase surface area of tail feathers. The authority at slow speed was not good enough.
-increase length of plane to accommodate the larger wingspan.

May 9th 2015 - BETA 2


As I said before beta 1 was purely to test and stress. Not to my surprise, all the damage was due to the stress of launching.



As you can see the most torque is applied to the center of the plane, right where my arrow shaft and nose/fuse connects the the wing. I have added bbq reinforcement to the nose to see if that's enough to stop breakage for beta 2. The arrow shaft is embedded into the foam in the wing and was very solid after many many throws on beta 1. So for now I'm not changing that design but we'll see how it holds up at larger scale.

I plan to use a bic pen body as my finger peg and it will be held in place with some glue and anchored with a large plastic patch inside the wing.

May 11th 2015 - BETA 2
Beta 2 build update

New wing went together real nice. This thing is super solid.














The wing is incredibly strong. Right now I have no worries about it failing.

Beta 2 complete!


Size compared to the nnMiG 3


Testing
Quick sample
https://instagram.com/p/2uLfVXi-Lt/?taken-by=nerdnic
https://www.instagram.com/p/29nuxHC-A1/
https://www.instagram.com/p/3Cqv7OC-LM/

Oops
That moment when..








After about 10 full power throws the nose broke again. This time it didn't stress break like on beta 1, but rather the entire nose broke free from the wing. This was because my bbq spar was too high in the nose and left only a sliver of foam between it and the wing. This caused that sliver to break free, leaving the glued portion still stuck to the wing. Beta 3 will fix this issue and some other bugs I found with beta 2.

May 17th 2015 - BETA 3


Beta 3 plans are finished and ready to be tested. For the first time I'm opening the beta testing to the community!

December 22nd 2015 - BETA 4
I have been reworking the plans to fix performance issues and launch challenges. I will be posting these plans soon!

For plans please see www.nerdnic.com/beta

January 4th 2016 - BETA 4


Beta 4 is built. It still comes out to 300g with the design changes.

-Wingtips redesigned.
They now allow full movement while your hand is on the peg.
-Alum spar placement and length
Spar is longer and in a new position
-Bbq removed from wing tip
It's not needed anymore
-Patch size reduced
-Ail is designed around 5g servo now
-Ail bevel is on underside of wing
-hstab and vstab design tweak
Sizes changed and corners rounded
-hstab connection joint redesigned
-Nose redesigned
4inch cut of CF arrow sticks out of the wing and joins the nose. New shape of nose and built in hatch
-New airfoil

January 13th 2016 - BETA 4


Beta 4 plans are posted with a nearly complete redesign!
Last edited by nerdnic; Jan 15, 2016 at 07:52 PM.
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Dec 23, 2015, 01:11 AM
Allways the hard way!
georgy's Avatar
Watching with interest.. been drooling over the DLG's at my LHS but the $$$ can't be justified in my case!

Just a Q?: Will using a longer arrow shaft running into the nose not help? (Though it may make fitting lectrics a challenge)
Dec 23, 2015, 03:39 PM
Registered User
nerdnic's Avatar
Yes! Using the left over arrow is the next attempt in v4. Basically the alum spar sits embedded in the foam so the arrow has to be cut. Not a big deal at all, the way I've designed the arrow/foam/alum joint there is no strength issue. Doing the same technique out the nose will prevent the stress from getting to the foam joint.
Dec 26, 2015, 05:55 PM
Registered User
nerdnic's Avatar
Cutting the v4 kit with my plotter:
Dec 29, 2015, 08:26 PM
NewFlyer
KenChin's Avatar
Perhaps fiber glassing the pod would help than bare foam and sticks.
Dec 29, 2015, 10:33 PM
Registered User
nerdnic's Avatar
Great suggestion!

Initially the issue was that the nose would snap, I think you're right, glass would help with that. The skewers fixed the nose issue though, and only added 3g, but now the entire nose detaches from the wing. So the connection itself between the two pieces is the current challenge.

In v4 I'm using a 3inch section of carbon arrow that embeds into the wing and attaches to the nose. I think this might do the trick and again only add a few grams.

One of the main goals I have with this design is to make a DTF DLG that will hold up and not cost more than about $20. Using exotic materials is a last resort right now, but it's definitely been in the back of my mind. :-)
Dec 30, 2015, 12:22 AM
skumgummi dave
The $20.00 cost is a noble pursuit. Keep up the good work!

Dave-
Dec 30, 2015, 08:29 AM
Registered User
got me hooked 3 x 30" Carbon Arrow 7.8mm shafts ordered $9.99 on ebay
Dec 30, 2015, 01:16 PM
Registered User
nerdnic's Avatar
Awesome! Please share a link for others benefit.
Dec 30, 2015, 02:06 PM
Registered User
Change Head)30" Carbon Arrow 7.8mm Shaft Plastics Fletching W/Aluminum Seat 3pc

http://www.ebay.ca/itm/171627761355
Dec 30, 2015, 07:32 PM
Registered User
nerdnic's Avatar
Thank you
Dec 31, 2015, 03:06 PM
Registered User
I was going to buy the Alula but its never in stock so I ordered the $25 YG bird dlg off ebay last week . I plan on building NNdlg V4 as well
Dec 31, 2015, 06:30 PM
Registered User
nerdnic's Avatar
Awesome! I'm hoping to have the v4 plans available in the next few days.
Jan 02, 2016, 05:21 AM
Rusty
Rusty Nail's Avatar
Just had a quick look over your project and make the following points from my stream of consciousness on a boring rainy Saturday night:

* 'My goal is to make a DLG that performs better than any store bought foam DLG, and for a fraction of the cost.'

There are only two commercially available foam DLGs I am aware of at the moment. Both come from long term studies and high tech manufacturing efforts by large respected manufacturers, aimed at the mass market.
The little 620mm UMX Whipet based on an extrapolation of the very successful Champ has been successful as an entry level experience of a tip thowable glider.
The larger 1.2m 300gm Libelle from Dream-flight.com has been found to be mis-labelled as a DLG but a good sloper.
There was an EPP attempt by a local company, Canterbury Sailplanes called the Eagle DLG that was a floppy and heavy disappointment.
So after all that effort and expense, the bar is actually pretty low, so you may beat it!

* The point is though that the flying experience is not good, and may not be worthy of the effort, at any price.

* Making a flyable scratch built DLG for around $20 is possible - Drela foiled Apogee, Mimi, QFII, Gambler, Icarus and Traian's definitive recent Evolution are all good examples of balsa DLG's, and the DL50 of a simple foam based wing. There are many more examples in Europe.

* None of these is a beginner model however. The Whipet is as close to that as it gets. DLGs are not considered entry level models. A tow line, bungee or winched glider is a workable choice for DTF.

* There is nothing magic or particularly compelling in using DTF as a medium. A far, far better foam wing can be simply, quickly and cheaply made with the simplest, pivot hot wire cutter. Drela has a sanding bar technique that will put a good airfoil on his Apogee if you want to go real simple and messy. A bias layer of 3/4 to 1 ounce fibreglass applied with Minwax Polyurethane and a top and bottom strip spar will give a one metre wing enough strength in span and torsion. Ironed on 30 micron Polyester laminating film will do similar quickly.

* But you need a foil and a calculated foil as a departure point before anything else for a glider! It does not have to be complex - the HM51 is a thicker single foil that is suitable for a beginner. Keep the aspect ratio more than 8:1 to maximize wing area.

* Weight is the enemy - and so is weak construction. That is why these are top end design problems. There have been many attempts at scratch built foam DLGs and cheap commercial DLGs that have not proved successful. Including the awful Fling that is still being made after many years of panning, the Apache, ArtHobby, R2Hobbies... all heavy and floppy and not worth the low prices.

* Addressing your design specifically:
* Loose all the heavy building elements that are not good strength to weight choices: aluminium spar, arrow boom, plastics, wood strengtheners, paper, pen launch peg...
* Carbon fibre tow is very cheap and easy to apply using superglue or Minwax. Makes excellent spars and fuse longerons as well as a launching blade (pegs are uncomfortable and high drag)
* Kite spars and fishing rod tip blanks (or used broken rods) are far stronger and lighter booms. Carry the boom all the way to the nose as the main structural component. Make it long - there is no nose weight option and receiver and LiPo 1S battery is light. Use a light blown PET nose cone arla the Elf for the most efficient structure (Elf is 100gms for a one metre cheapish DLG).
Hang the gear off the boom and put the wing on top with pegs or a pylon.
The boom needs to be long for good launching so size the stabilizers and choose the construction carefully to get the lightest possible rear end. Use pull spring controls and light servos well forward. Dense meat tray foam feathers with laminating film strip reinforcement is sufficient. DLGs are supposed to be caught rather than landed.
* Choose the span and wing area to suit the materials. 50 inches is a bold size for your construction materials. 40 inches is more achievable. The launch forces involved go up very quickly with span.
* Keep it simple in the interest of performance and weight. Loose the ailerons. A smaller wing with 24 degrees dihedral will turn nicely without the weight of ailerons and servos. Ailerons are most useful as flaperons where the airfoil can be changed for different flight phases. A uncalculated foil is not likely to suit this, and small gliders stop well enough without drive brakes.
* Have the rudder half way up the horizontal stab with equal area above and below. Reinforce the lower rudder.

You have taken up a really, really difficult challenge. Best of Luck!
Jan 04, 2016, 08:37 PM
Registered User
nerdnic's Avatar
Quote:
Originally Posted by Rusty Nail
Just had a quick look over your project and make the following points from my stream of consciousness on a boring rainy Saturday night:

* 'My goal is to make a DLG that performs better than any store bought foam DLG, and for a fraction of the cost.'

There are only two commercially available foam DLGs I am aware of at the moment. Both come from long term studies and high tech manufacturing efforts by large respected manufacturers, aimed at the mass market.
The little 620mm UMX Whipet based on an extrapolation of the very successful Champ has been successful as an entry level experience of a tip thowable glider.
The larger 1.2m 300gm Libelle from Dream-flight.com has been found to be mis-labelled as a DLG but a good sloper.
There was an EPP attempt by a local company, Canterbury Sailplanes called the Eagle DLG that was a floppy and heavy disappointment.
So after all that effort and expense, the bar is actually pretty low, so you may beat it!

* The point is though that the flying experience is not good, and may not be worthy of the effort, at any price.

* Making a flyable scratch built DLG for around $20 is possible - Drela foiled Apogee, Mimi, QFII, Gambler, Icarus and Traian's definitive recent Evolution are all good examples of balsa DLG's, and the DL50 of a simple foam based wing. There are many more examples in Europe.

* None of these is a beginner model however. The Whipet is as close to that as it gets. DLGs are not considered entry level models. A tow line, bungee or winched glider is a workable choice for DTF.

* There is nothing magic or particularly compelling in using DTF as a medium. A far, far better foam wing can be simply, quickly and cheaply made with the simplest, pivot hot wire cutter. Drela has a sanding bar technique that will put a good airfoil on his Apogee if you want to go real simple and messy. A bias layer of 3/4 to 1 ounce fibreglass applied with Minwax Polyurethane and a top and bottom strip spar will give a one metre wing enough strength in span and torsion. Ironed on 30 micron Polyester laminating film will do similar quickly.

* But you need a foil and a calculated foil as a departure point before anything else for a glider! It does not have to be complex - the HM51 is a thicker single foil that is suitable for a beginner. Keep the aspect ratio more than 8:1 to maximize wing area.

* Weight is the enemy - and so is weak construction. That is why these are top end design problems. There have been many attempts at scratch built foam DLGs and cheap commercial DLGs that have not proved successful. Including the awful Fling that is still being made after many years of panning, the Apache, ArtHobby, R2Hobbies... all heavy and floppy and not worth the low prices.

* Addressing your design specifically:
* Loose all the heavy building elements that are not good strength to weight choices: aluminium spar, arrow boom, plastics, wood strengtheners, paper, pen launch peg...
* Carbon fibre tow is very cheap and easy to apply using superglue or Minwax. Makes excellent spars and fuse longerons as well as a launching blade (pegs are uncomfortable and high drag)
* Kite spars and fishing rod tip blanks (or used broken rods) are far stronger and lighter booms. Carry the boom all the way to the nose as the main structural component. Make it long - there is no nose weight option and receiver and LiPo 1S battery is light. Use a light blown PET nose cone arla the Elf for the most efficient structure (Elf is 100gms for a one metre cheapish DLG).
Hang the gear off the boom and put the wing on top with pegs or a pylon.
The boom needs to be long for good launching so size the stabilizers and choose the construction carefully to get the lightest possible rear end. Use pull spring controls and light servos well forward. Dense meat tray foam feathers with laminating film strip reinforcement is sufficient. DLGs are supposed to be caught rather than landed.
* Choose the span and wing area to suit the materials. 50 inches is a bold size for your construction materials. 40 inches is more achievable. The launch forces involved go up very quickly with span.
* Keep it simple in the interest of performance and weight. Loose the ailerons. A smaller wing with 24 degrees dihedral will turn nicely without the weight of ailerons and servos. Ailerons are most useful as flaperons where the airfoil can be changed for different flight phases. A uncalculated foil is not likely to suit this, and small gliders stop well enough without drive brakes.
* Have the rudder half way up the horizontal stab with equal area above and below. Reinforce the lower rudder.

You have taken up a really, really difficult challenge. Best of Luck!
Wow! Thanks for taking the time to type up all this. When I decided to design a DLG I really had no idea what I was getting myself info. I've loved learning every step of the way through this design. I'm gonna reply directly to some of your comments for the sake of discussion

* There is nothing magic or particularly compelling in using DTF as a medium. A far, far better foam wing can be simply, quickly and cheaply made with the simplest, pivot hot wire cutter. Drela has a sanding bar technique that will put a good airfoil on his Apogee if you want to go real simple and messy. A bias layer of 3/4 to 1 ounce fibreglass applied with Minwax Polyurethane and a top and bottom strip spar will give a one metre wing enough strength in span and torsion. Ironed on 30 micron Polyester laminating film will do similar quickly.
----
I think the compelling aspect to DTF is the cost and ease of use. Doing something like a hot wire cut isn't the most complicated thing, but it's immediately harder than any building technique with DTF and requires additional equipment. With DTF it's really easy to create a repeatable design also. Someone with little experience and limited tools can reproduce a complex, well performing design, with little overall effort and investment. In the end very few people hot wire cut compared to general building so going this route (for me) would limit the number of people who could build one.

* Loose all the heavy building elements that are not good strength to weight choices: aluminium spar, arrow boom, plastics, wood strengtheners, paper, pen launch peg...
----
The materials selected were all chosen with cost in mind, initially. They are also common materials that most builders will have access to. Think of the first attempts here to be a poor mans DLG. I think I will branch out to other materials once the design is proven ineffective.

* Choose the span and wing area to suit the materials. 50 inches is a bold size for your construction materials. 40 inches is more achievable. The launch forces involved go up very quickly with span.
----
Right now the wing design with the alum spar is a winner. For its weight, cost, and reproducible design, I've not found a cheaper or better option. I am using my speedwing design, though slightly modified, which is used on my performance plane designs. If anything, the wing is the only part of the design that is holding up to full power launches so far.

nnSpeedWing Stress Test (1 min 42 sec)


* Kite spars and fishing rod tip blanks (or used broken rods) are far stronger and lighter booms. Carry the boom all the way to the nose as the main structural component. Make it long - there is no nose weight option and receiver and LiPo 1S battery is light. Use a light blown PET nose cone arla the Elf for the most efficient structure (Elf is 100gms for a one metre cheapish DLG).
----
I'm not familiar with these materials , can you link an example? The CF arrow I'm using weighs only 8g for 30". AUW on the 54" span right now is 300g with 4 5g servos and 300 mah 2s. I'm looking to switch to a 1s and drop the BEC.

* Have the rudder half way up the horizontal stab with equal area above and below. Reinforce the lower rudder.
----
This is a good call. My first designs twisted a bit on launch due to having less stab bellow the boom. I've made it more equal now but still have more up top.

Use pull spring controls and light servos well forward.
----
Can you share what materials you've found work well here? I really like this idea but am not sure what to get.

I have finished v4 of the design and will start testing it shortly. I made a handful of changes to the design but no switches in build materials yet.



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