This page documents my efforts to create a working flying Lego glider similar to ones made by Daron Williams and Milan Reindl . My design objectives are:
1) fly +30 feet in a straight line without stalling
(1a) fly indoors - no cross winds
(1b) fly outdoors - with cross winds
2) Modular design
(2a) can be dissembled and reassembled easily so I can carry it in my car
(2b) crashes by modules separating but modules staying intact for the most part
to absorb force of impact of a crash.
(2c) landing gear or shock absorber module.
3) be as close to 100% Lego, tape is allowed, no glue
(i.e. to be Brickfair-like Lego competition ready).
4) to be able to carry +30 grams of payload,
e.g a wireless First person video camera with battery pack is 60 grams.
5) to be inexpensive to make.
6) adaptable to a glider launcher or
by wire electric motor propeller(payload = +35 grams) assisted flight
version 4 (top photo - this is not the final version - still being rebuilt):
Flat wing airfoil(*) using Lego retail store bag plastic as wing cover/cowling..
Wing and the stabilizers with an Angle of Attack of 12 degrees.
Reinforced detachable 28 inch long Polyhedral wing.
Reinforced detachable rear vertical stablizer.
Nose cone shock absorber.
Total Weight = 161 grams.
Wingspan = 28 inches = 71 centimeters
Wing surface area = xxxx. square centimeters.
Fuselage length = xxx. centimeters.
Horizontal Stabilizer surface area = xxx sq centimeter.
Vertical Stabilizer surface area = xxx sq centermeter.
My initial efforts to reinforce the wing and airframe made it too heavy (+165 grams) when I added the plastic and tape for the wing cowling - so I had redo the wing and airframe to make it lighter. It looks like my current design using 28 inch wingspan limits me to a maximum of about 160 grams. Currently - the airframe is tail heavy and will have to be redone....
Early indoor flight tests of version 4 are promising. Early demo this prototype's indoor flight characteristics at the 2013 Sept Washington DC LUG meeting. An experimental 9 gram single wheel 2 shock absorber landing gear severely shorted the glider's flight path and indicated that at this time the glider does not generate enough lift to have a mechanical landing gear mechanism.
I am having trouble designing with the *discontinued* rectangular Lego wing cowling (from the Lego 7471 Mars Explorer Rover set ) which were used by the Drat Soarer (a lego glider by Daron Williams) which have arrived from Germany. I am still working making an optional wing using these these parts for Version 4. In addition, I have triangle and circular plastic forms on special order from Lego (Denmark) that uses the same stiff blue translucent plastic ( from lego education W779686 Simple and Motorized Mechanisms Base set) which I will also be experimenting with.
I displayed a still-work-in-progress Version 4 Lego glider at the Washington DC Metro Area Lego User Group (WaMaLUG) kiosk on Saturday, September 21, 2013 at the Smithsonian Air and Space Steven F Udvar-hazy Center (Chantilly VA) Family Day event = Hispanic Heritage Month: Innovators in Air and Space.
Version 3 (no photo /decommissioned) :
The main photo is of my third version of a Lego Glider - ParaGlider. It has a wingspan of 40 inches. Keeping the model 100% Lego is a bit problematic since Lego does not have any shrink wrap plastic that is normally used by hobbyist RC model airplanes to make the cowling that covers the wing and stablizers. The cowling on the wing surface must be stiff as possible to create lift. Reindl abandons the 100% Lego requirement and used trash bag plastic for his Lego Glider wing surface - but by doing so keeps his glider smaller and cheaper to make. Williams  increases the cost and size-weight of his glider inorder to keep his glider 100% Lego - His Drat glider uses multiple plastic sections from the Mars Exploration Rover Set to create a wing surface. In version 2, I used plastic from Lego Retail Store bags - in order to keep my glider 100% Lego - but abandon that when I altered my wing geometry in version 3 so I could use clear plastic sheets (from the plastic bags used to protect newspapers from the rain) to test/examine for flaws in the wing superstructure design. An added benefit is that the clear plastic sheets which I am using is also lighter than Lego store plastic bags.
While there are no Lego Glider Competitions there are Lego Boat Racing Competitions. In the 2013 VA BrickFair Lego Boat Racing Competition, glue is not allowed but tape is allowed. So in that same spirit - the wing cowling/cover is being taped on instead of being glued on.
Earlier Test flights with earlier version of this glider indicated aerodynamic drag was contributing to stalling and generally poor flight performance so this version incorporates a swept wing design by using Technic Axle connector #3 (23 degree angle of attack) to reduce aerodynamic drag. A swept wing design also moves back the wing's center of gravity a bit too. The wing location is fixed. The wing tips are tapered to lessen air turbulence/drag at the wing tips.
I've also used the Technic Axle connector #3 to create a polyhedral wing design (aka gull wing design) to resist rolling momentum. Version 2 had a Polyhedral design but the dihedral wing section was longer than the regular flat wing section. While a dihedral wing section does resist rolling momentum it has poorer lift performance compared to a flat (parallel to flight vector) wing section so in version 3 the flat wing surface was increased and the dihedral section of the wing was decreased.
Early test flight showed that rigid wing surfaces provided superior lift and flight performance over less rigid wing surfaces. The version 3 wing air frame was switched over to Technic Axle 12L instead of the longer Technic Axle 32L (used in Version 1 and 2) because the 12L was stronger, more rigid, and could support the weight of the wing.
The tail section also uses the same connector to create a swept tail-stabilizer design. To get the front base/bottom swept angle for the rear vertical stabilizer I used a universal joint.
To fly true-straight the rear horizontal stab(ilizers) must be parallel to the main wing and the rear vertical stab(ilizer) must be at 90 degrees from the main wing. To maintain this wing-to-stablizer geometry relationship the fuselage must be very rigid/stiff. This has led to favoring heavier rigid fuselage designs used by Williams over lighter weight less rigid fuselage design that Reindl appeared to be using. I'm still trying to figure out how Reindl airframe design stays rigid enough during flight.
A Technic competition missile-arrow was use to create a shock absorbing bumper in the front of the glider. This glider weights 165 grams! The Center of gravity (CG) approximate in the center of the plane. This glider has a estimated max payload capacity of 25 grams.
Version 3 has been scrapped. I'm now working on version 4.
Version 2 (decommissioned/scrapped) :
Flat airfoil cross section. Polyhedral wing design ( the outer dihedral wing section uses a 32L axle, the inner flat wing section uses a 12L axle). Plastic Lego store bag used for cowling. In the front there is an adjustable payload (dead weight=20 to 30 grams) section on a shock absorbing rail system. Adjustable wing location. Version 2 has been scrapped.
Version 1 (decomissioned/scrapped):
curved airfoil cross section. Flat wing section. Food cling wrap used for cowling. adjustable Cord/wing location. Version 1 has been scrapped.
(*) How does a flat airfoil wing fly? Don't you need a curved airfoil wing?
That is a common question. The answer is yes a flat airfoil wing can fly and
it generate lift the same way a kite creates lift. As air moves across the wing,
gravity pushes the wing down naturally creating less air pressure on the top and
more air pressure on the bottom as air move horizontally across the glider -
thus the larger the wing surface the more lift is created. Essentially - this glider is "falling with style" as Bud Lightyear might say. :-)
If the wing is not stiff but wobbly then there is unequal pressure between the wings and the flight become unstable and the glider will crash - hence for fix wing designs it is very important to use a very stiff lightweight material to make an air frame for the wings.
Milan *Grohl* Reindl, his bio is on the Lego Technic Designer website
Reindl is a Junior Technic Designer for The Lego Group.
Remember seeing you demonstrate this a few years ago at a WAMALUG meeting, didn't know you had a MOCpages. Pretty cool man!
I like it
August 28, 2013
Very cool glider! Personally I'm still a purist, but I can totally understand why you used outside materials for this. And just because I'm a purist doesn't mean I want everyone to be just like me. I like to see what people can do when given greater license, and your glider is an excellent example of the possibilities. Finally, the write up is fantastic. SCIENCE!!!
A brilliant idea and it's great to know that it really flies too. The idea of using bags from a Lego store for the orignal wing surfaces is a fun way to keep it all Lego. On an techincal note, I think that sweeping the wings back won't have reduced the drag much on a slow glider. It will have shifted the centre of lift further behind the centre of gravity, which will have helped to stop the glider from pitching nose up and stalling.