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UL SAILPLANE - Footlaunchable, foldable

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ultralajt

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I will introduce here my design of ultralight sailplane.

It is result of my years long dreaming of concept that will suit my wishes.
It is result of my flight experiences with Hang Gliding, Sailplane soaring, and evaluating of other footlaunchables, that were caught in my eye by their particular features.

So far it is only virtual, preliminary design…nothing more.

I am hoping for some help from HBA members in checking or directing me to do proper stress analysis of some cruical composite parts (tail boom and D-box skin).
As it will be UL in my country it will be just OK to calculate it to +6 and -2,5 G (safety factor of 1,5 included), same as Hang Gliders.
As you will see from explanations and drawings, my sailplane is very different in some areas from what is common at this moment in field of footlaunchable 3 axis gliders.

First of all, my sailplane will be:
1. Ultralight
2. Footlaunchable
3. Foldable for a car rooftop transportation
4. Affordable price
5. Ease of construction and assembly
6. Use of common and available materials
7. Builder friendly manufacturing

I am willing to sacrify some of the sailplane (let say »Glider«) performances in order to achieve goals written above.
That means that I will reduce awerall size of the glider. Less size, less material, less weight…

Some of preliminary measurements:

Wing span: 11 m
Wing area: 12,1 m2
Total length: 5,2 m
Expected weight: 35kg max






Regarding the glider performances, my goals are pretty modest:

Max glide angle: ~15-20
Min sink speed: ~0,75m/s
Stall speed: < 30 km/h
Maneuvering speed ~70 km/h
VNE ~ 110 km/h

These performances are somwhere in range of modern Hang Gliders.

Why one want such »poor“ performances, equal ordinary hang Glider?
Would not be better to just fly one of these Hang Gliders?
I flew Hang Gliders for 15 years, and now as I am becaming older, wishes for true 3 axes control, comfortable hammock, wind in hair… became obvious.
And landing on the landing wheel of course.
With such »poor« performance one can still easily stay in the air for hours and even do some XC flights.

My glider will not be designed for competitions. It is hard to compete with these days best footlaunchable gliders such as SWIFT, Phantom Rigid, Atos Rigid, Archaeopteryx sailplane, Xxtherm sailplane…
They are way better in performances, but larger, heavier and also very expencive!
They are somehow »clumsy« for transporting, heavy, and vounerable at not perfect handling on the start or landing place and during transport.
At Swift one must take much care where to hold and where not to grab the wing at manipilating on the ground in order not to damage the skin.
(just read the Swift manual)


So, how it looks my glider structure?








Wing



Wing consist from torsion D box in front that include a spar. Torsion box skin is composite laminate.
Probably a carbon/glass laminate. It is only one skin, not sandwiched with foam. Sandwiched skin could be stronger, but not resistant to local »garbage loads« so it can be punctured easier, than equal heavy one layer skin.
These so called »garbage« loads are present at transporting, loading/unloading and manipulating at assembly/deassembly on the start/landing place. I want pretty resistant D box of the wing.
Forward of flaps and ailerons hinge line location, there is another spar in the wing. This spar has four colapsable compression struts. They are hinged on the main and rear spar. The sewn dacron covering is over the wing as and »sock«. When both wing spars are tensioned appart by compression struts, this dacron sock sail is tensioned in proper shape. As airfoil contour at upper and lower side aft from D torsion nose is straight, there is no need for any internal wing ribs.
On the outside of the aft spar, a plastic profile is attached. This profile create a short lip for the flap, and also for the aileron.
Flap will be with short lip to create as much as possible lift, and ailerons will be plain.

Wing will have same basic airfoil over entire wingspan, to simplify D box molds, and to simplify wing folding.
Only flaps will be tapered to bring some more chord to the root of the wing.



Construction of flaps and ailerons is like a small wing. Main spar is a tube. Flap will get a styrofoam nose shape at face end of that tubular spar. Trailing edge is a triangular cross section balsa wood encaptured in carbon fabric sock. Ribs are diagonal to enhance torsion rigidity of the flap and are made from sandwich plates. Extruded styrofoam with laminated skins.
Surface will be covered with heat shrinkable Oratex UL.
Structure of the aileron is pretty the same as for flap, except nose styrofoam insert.

Wing will have strut, for lowering the stress in the spar and for less weight and more simplicity of hardware and rigging.

There is an diagonal strut inside wing at wing root, which goes diagonally from front spar near wing strut attachment, down to the rear root attachment of the rear spar. This spar will introduce horizontal forces from the wing to the fuselage pylon and of course also the torsion loads.

Tail surfaces.

Tail surfaces are of full flying type. To prevent flutter, they are partialy aerodynamic and static balanced such way, that a surface and some mass is located in front of their hinge lines. Well the speed of this glider is not high, but as it is light build, flutter shall be prevented anyway.

As all surfaces (wing and tail) are foldable, also a tail feathers are covered with dacron fabric.


Basic structure.


Dacron covering added. Note some similarity with Hang Gliders structure.

Main spar is tube (aluminum or composite..yet to be defined). In front of the spar, there is an extruded styrofoam insert, that create an airfoiled nose. It is covered with thin glass laminate or even simplier, just self adhesive tape. To achieve foldable surface, there are some ribs and struts hidden under the skin. Ribs or better »battens« are the same design as at Hang Gliders. They make tension between rear od the main spar and edhge of the sail at the trailing edge. Sail is sewn from dacron and attached to the spar at end points. At the root, there is an colapsable diagonal strut that is mainly responsible to accept torsion loads and asure tension in the sail. Tail tips can be left bare or covered with teardrop shaped plastic caps.

Fuselage.







Fuselage is so called »pod and boom« design. At this moment I am thinking at »lost foam« composite sonstruction. It is made from foam parts carved out from extruded styrofoam and covered with carbon composite cloth. At points of hardware attachments, some hardpoint inserts will be placed into laminate or inside the part. Pilot compartment consist with only two side beams. In the front end these two beams are connected together. There is also a cross spar and a front landing skid.
Rudder pedals are hanged from that cross beam.
Pilot is equipped with a harness, similar to early paraglider harness, that allow inclined and also sitting position. Left and right side of harness is equipped with attaching brackets to connect it to the hang points inside each cockpit beams. Hanging front or aft, pilot can set proper C.G.
Rearward from pilot, at the underside of the beams, there is an lightweight retractable landing gear.
Here, two cockpit side beams goes together to the area, where a tail boom and wing pylon are joined. At this moment I am not sure to make tail boom deatachable for the transport or no.
Pilot controlls are situated at top of each cockpit side beams. At left hand there is a control stick with two functions. Left/right it controlls rudder when pilot has legs outsire of the cockpit (starting). Forward and back sliding it controlls flap deflection. For flap operation, also electric drive should be considered . At the right hand, another control stick is situated and it operate usual way with elevator and ailerons. Ailerons acting also like flaperons, as they travel slightly down proportional with flap deployment.
This bare structure of the fuselage is further refined with some aerodynamic fairings to lower the drag. Cockpit is covered with dacron fabric, streched over light carbon tube longerons. Aft of the wing pylon is tapered with elastic fabric.

For pilots that dont want to do footlaunch, an optional composite shell is possible, that represent a bottom side of the cockpit, with integrated pilot seat. This shell is bolted to the side cockpit beams.
It allow to make start by aerotowing, or just rolling down the slope.

Glider will be folded in 5 main components, of each will be placed in tfabric transporting bag:
- left wing with wing struts, flas and aileron
- right wing with wing struts, flas and aileron
- fuselage
- elevator
- rudder
Making so, it will be easy for the user to load relatively light components on the cartop for the transport.
Also cariying of the components from the parking lot to the assembly field will be much easier handling light components rather than carying whole glider at once.

As seen from glider 3 view drawings it is pretty small. To achieve decent low starting speed at such sparse wing area, I opted for large flaps and force ailerons to also get some flaperons movements. This is only way to achieve large enough lift coeeficient.



What now?

I need to evaluate glider weight and calculate loads.
Then I must calculate main structural elements… wing spar, D box skin, tail boom, cockpit beams.. to set size and thicknes of elements.
I would like to get hints and suggestions in order to do proper thing…not to drift away to danger zone, neather be much conservative to fail make thing lighter enough.

I think, my goals are not too unachiveable as some of present designs are proof of some things such as:

- Wing of Rigid Wings hang Gliders are of similar construction (D-box and dacron skin) and they are foldable. Also the wing of sailplane AL-12 Alatus is proof of the concept.
- Archaeopteryx and XXTherm are proof that conventional glider layout (with tail) can be footlaunched.
- Rolling start from the slope is also possible option.

So much for now!


Mitja
 
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ultralajt

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Picasa Web Albums - Krzysztof Dudzi

axel bieszczady1 avi - YouTube

=polish AXEL=much heavier\55 kg\...

-Yours project is very exciting!
I know Axel sailplane as I follow it on the Internet from very begining.
But as you said it is way over my target weight, performence and "foldability".

Regarding foldability, the closest to my wishes is Alatus Al-12 from Aeros.

Look that for ease of transporting, to see what I am aiming for.
(photos in links above, property of Aeros company)

Mitja
 

autoreply

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My compliments Mitja, for a very nice design.

There's one big red flag I can see coming though. Transporting on a car rooftop. Do you plan to leave the wings in a single part (well, one per wing)? If so, the aerodynamic loads alone at moderate car speeds can be tremendous, especially since much of the airflow on the highway is turbulent. Even the wooden/fabric gliders (Ka4,6,7,8) are known to tear apart in minutes if you're driving above 80 km/h without a sturdy cover around the wings. Especially with this length (5.5 m per wing) they will see very high loads, possibly higher than ultimate flight loads.

I guess it's unavoidable to have some kind of hard cover around them (not just cloth like in your pictures), either on the roof, or on a trailer. A sailplane trailer might be overkill, but a light, simple and affordable one is probably the easiest way too proceed, from a few hundred euro's on you can have one:
http://www.segelflug.de/cgi-bin/classifieds/classifieds.cgi?search_and_display_db_button=on&query=category&category=Biete+Anhaenger&results_format=

You might also run into problems, not that many cars here can legally be loaded with 5.5 meters length. Don't know about your country though...
 

ultralajt

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My compliments Mitja, for a very nice design.

There's one big red flag I can see coming though. Transporting on a car rooftop. Do you plan to leave the wings in a single part (well, one per wing)? If so, the aerodynamic loads alone at moderate car speeds can be tremendous, especially since much of the airflow on the highway is turbulent. Even the wooden/fabric gliders (Ka4,6,7,8) are known to tear apart in minutes if you're driving above 80 km/h without a sturdy cover around the wings. Especially with this length (5.5 m per wing) they will see very high loads, possibly higher than ultimate flight loads.

I guess it's unavoidable to have some kind of hard cover around them (not just cloth like in your pictures), either on the roof, or on a trailer. A sailplane trailer might be overkill, but a light, simple and affordable one is probably the easiest way too proceed, from a few hundred euro's on you can have one:
http://www.segelflug.de/cgi-bin/classifieds/classifieds.cgi?search_and_display_db_button=on&query=category&category=Biete+Anhaenger&results_format=

You might also run into problems, not that many cars here can legally be loaded with 5.5 meters length. Don't know about your country though...
Hi Autoreply!

I want to transport my glider on the car top like I did with my Hang Gliders when I was active HG pilot.
My glider is just slightly heavier than ordinary HG, but HG is packed in just one fabric bag, while my glider will be packed in, as I told earlier, 5 separate bags.
Each bag will be very light and one can handle it with ease. (probably weights: each wing half 9,5kg, fuselage 10kg, elevator 4 kg, rudder 2 kg)

Regarding regulations here, there is no problem to load HG on the car rooftop. So also my glider will not be problematic regarding street regulations.
If load exceed rear of the car more than 1 m there must be a signal table hanged onto.

If you read my wing description, my wing will "colapse" berween main and rear spar, so it will be folded very much and only D-box (torsion nose) remains, some folded dacron and rear spar.
Cross section of the bag for this folded wing is approx 15 x 30 cm.
Bag will contain unpolsthered slots for flapy and ailerons. Bag will have zipper and carying straps-handles.
Bags for tail feathers will be even smaller.. about 15 x 6 cm x 250 cm (elevator), 140 (rudder)

Did you look at the Alatus AL-12 prepared for the transport?
My will be pretty same, but less mass and lower weight.



Mitja
 

ultralajt

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There is a pdf file, where my earlier drawings and descriptions for my glides is explained.
Well, my current Glider design is slightly different than Kanja FL in this file (I simplify many parts), but the basic philosophy is the same.
Look at the attached file below. If you read blue text on page 1, it shortly explain what was in my mind.. what I like, and what I dont.

Mitja
 

Attachments

autoreply

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If you read my wing description, my wing will "colapse" berween main and rear spar, so it will be folded very much and only D-box (torsion nose) remains, some folded dacron and rear spar.
Cross section of the bag for this folded wing is approx 15 x 30 cm.
Yeah, I read that. Despite the much smaller area, you'll be driving at speeds around or above your "flying VNE" and I wouldn't be surprised if you would see loads of the same order as maximum flight loads on the highway. It not so much the force at itself, but it's the forces that (can) occur if it starts to vibrate, basically a form of flutter. Maybe I'm over-cautious, but I've seen some gliders being hurt on the highway pretty badly and they are designed for much higher aero-loadings as your design.


Another point I would change personally is the separate parts. Assembling separate airframe parts can be a bit of a mess. Not only does it involve placing them on the ground, they're also easily blown around, especially if so light. If possible, I'd hinge both wings to the pylon, such that it's one single part. If you use the attachment of the 801 STOL and the like, that doesn't involve any extra weight, you can simply rotate the wings and fold them backwards for a fairly compact package. Not sure whether that fulfills your mission though..
 

ultralajt

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Assembly will be pretty simple.
Each wing half still in its bags, just unzipped at their roots, will be connected by quickpin to main bracket on the pylon at main wing spar. (this bracket with its design provide some free angular movement at joint)
Then a diagonal spar is connected to the rear pylon bracket. Now the wing spar is halted perpendicular to the fuselage centerline.
Then a zipper is opened further to free the wing strut. Wing strut attached to the fuselafe side bracket.
At this point lowering the wingtip end of the wing bag to the ground, assembly stays firm.
Now same to connect the other wing half. Renmember, wings are still wrapped with bags. No aerodynamic lift can occur in wind..only drag.
Now bags are unzipped all the way and rear wing spar is spreaded appart from main spar with compression struts. That will tighten the wing skin. Now the wing tip is added and wings are assembled.
Short steel wires from wing strut joint towards cockpit nose and root of the rail boom are connected now, to add aweral rigidity between wing and fuselage in yaw.
Now elevator and rudder are fre from transport bags. Diagonal struts art their roots are spreaded and tensioned, battens inserted on their places and tightened with rope (usual manner as at Hang Glider battens and sails).
Flight controlls connected and preflight check to do.

In order not to make mistake at controls connections, there is a colored code (links that must be connected together are in same color) and elevator uses different joints than rudder, so no way to make mistake.

Flaps push pull rods are connected to flaps at their roots. Ailerons are acutated by steel wires in the wing and at their ends connected to brackets.

Please be patient, as I will prepare more detailed drawings, where all these features will be clearly presented.
It is easier to make drawings, than explain in text, as English language is not my "favorite" ;)

So much for now. Stay tuned!
:ban:
 

harrisonaero

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Very nice Mitja. I think there's a strong market for a commercially available airchair like the Goat but perhaps a bit more streamlined. There's a saying in the US about offroad racers, "With age comes a cage." In other words many of the ex motocross racers are transitioning to buggies and trucks with roll cages.

Many of the 70s and 80s vintage hang glider pilots would like to fly but aren't feeling up to landing on their feet. Something that can be roll launched is the ticket to allow these guys to fly with their buddies. Even better if the glider performance is similar to modern topless hang gliders.

At many of the HG launches a trailer isn't feasible so making the design car toppable is key. And it really should fit on a standard HG rack without anything else needed besides what can you can fly with. Bags in other words. When you land out and need to be brought home by a HG buddy you don't want to miss an opportunity because you didn't have a storage box.

So all that to say... looking good and on the right track as far as I see it :)
 

ultralajt

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Thanks Henryk for the video!
Many years ago we practice such start in our Hang Gliding club. We use about 1700m of rope.
The main "drawback" was that we often damage the rope as it rubs against all sorts of things.
Also the car clutch was "smelly".

My glider will start footlaunch or rolling down the starting ramp. That is the mission.

Mitja
 

Monty

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Neat design!! I would love to have something like this. Recently on a trip back from Dallas TX, my wife and I took the scenic route. The weather was awful, which is why we didn't fly. While passing through a little town in the middle of nowhere, I saw a car pulling a glider trailer turning onto the highway. What the.......????

When I got home I used Google to find out what was going on. There is a ridge with very good soaring conditions, including a wave that goes to at least 16Kft only an hour and a half drive from here!!!!!! This has only recently been discovered by the local glider crowd after a couple of guys who used to fly hang gliders in that area became glider pilots and decided to give it a try. I have been aware of ridge lift in my area, but unfortunately there are virtually no outlanding possibilities, it is just too dangerous to attempt. The Ouachita mountains to the South have wider valleys and run predominantly E-W, but this area is very remote and therefore not many people are familiar with it. Previously you had to go 500 miles east or west to find anything like this....I'm VERY excited about it.

Needless to say I'm thinking of flying gliders again. There are the usual logistics issues of getting a tow pilot and plane in the area. I'm also not willing to spend $30K on something I might get to use 2 or 3 times a year. Something like what you have designed would be perfect. There are a lot of areas used by the hang glider pilots I could launch from.

Keep us posted!

Monty
 

bifft

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It looks great, but I have a question. With the tail so low, can you get the nose up enough to flare to land without hitting tail first? Or do the flaps prevent that?

The target weight is very ambitious.
 

ultralajt

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It looks great, but I have a question. With the tail so low, can you get the nose up enough to flare to land without hitting tail first? Or do the flaps prevent that?

The target weight is very ambitious.
Yes, flaps will help glider to have "tail high" attitide on start and landing. Furthermore, landing will be done on the landing gear.

Regarding small aweral size of the glider and strut braced wing, I dont see target weight too ambitious.
Remember, all other UL gliders (named in my first post) have cantilever wing. Such wing is heavier than wing with a strut for same strength.
Also lower wing spar helps a lot in reducing weight.

Mitja
 
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ultralajt

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ultralajt

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I made a small table regarding empty weight per wing area unit for some gliders:

table 1.jpg

The most effective structure is at flex Hang Gliders. Large area of the sail spreaded over some aluminum tube spars. Quite effective
Next is classic Rigid Wing. Remember, this wing has cantilever wing. D box is stressed with both bending and torsion loads.
Next is VJ-23. Impressive as it was build from wood...but not firget it is designed weak! Only +2G!
Next is Archaeopteryx. Build from carbon sandwich mostly... impresive weight/area ratio!

My Kanja is placed somwhere between Rigid Wings and Archaeopteryx, what is by my opinion possible.. a little heavier than Rigid Wing as it has tail, and a little lighter than Arch. because of strut supported wing.

Mitja
 

henryk

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