Mark Drela's Aegea 2m Glider

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Home > Articles & Tips Index > Mark Drela's Aegea 2m Glider

[Courtesy of Mark Drela, drela "at" mit.edu, Nov 2003 - web presentation by Tomer Jackman, Jackman_Tomer "at" EMC.com] Photos courtesy of Jeff Newcum

About the Aegea 2m Glider

• To join the Allegro-Lite community, join the Allegro-Lite discussion group at http://groups.yahoo.com/group/allegro-lite.

Construction notes are included in the drawings, which you can download as Acrobat v6 PDF documents in the links below. If you need a copy of the Adobe Acrobat Reader, you can download it free from http://www.adobe.com/products/acrobat/readstep.html.

Introduction

Aegea is a fairly unique aileron 2m glider. It has the following distinguishing features:

* Very low weight (21 oz)
* High aspect ratio (12.6)
* Moderately low wing loading (6.2 oz/ft^2)
* AG4x DLG airfoils
* Relatively generous EDA (6.0 deg)

The main design goal is to achieve good thermalling performance via the low span loading. The AG4x DLG airfoil series with
full-span camber control are used to give good speed performance despite the low weight. The large flaps and ailerons, when set
at about +20 degrees, give acceptable winching performance despite the unusually small wing area of 490 in^2. The generous EDA makes
the Aegea very easy to thermal, especially at large distances which is a major problem with 2m gliders. The Aegea can be viewed as
a natural 2-meter implementation of the latest DLG technology.


The Aegea has proven to be a formidable structural challenge, mainly due to the very thin wing and the large pitching moment
of the cambered flaps and ailerons on tow. Everything is sized for stiffness. The aileron servos don't quite fit, so a careful
fairing job is necessary. The flap servo had to be put in the fuselage. This helps with CG, but gives a lot of mechanical
complexity due to the pushrod hookup and the flap torque rods and linked horns.

The Aegea II is a redesign consisting of a simple ~10% wing chord
increase. This greatly improves the practicality of the design, in that the structural constraints become much easier to meet.
The sparcaps can be thinner, and one layer of Kevlar becomes sufficient for the center section. The 4-servo wing is vastly
simpler than the 3-servo wing with the fuselage-mounted flap servo. The Aegea's tail has proven to be quite generous, so the same
tail is being used for the Aegea II. If you are considering building this glider, the Aegea II is strongly recommended.

- Mark Drela

 

Fuselage pod

Fuselage pod (Left) showing servo installation and radio gear. Wing saddle (right) showing wing connector, switch and wiring.

Pod to Wing filet showing removed from pod (left) and hatch open (right)

Wing

A view from the tip of the right wing (Left) and a view of the wing connector (right)

Aileron servo recessed into the wing pannel (left) and top view of the mounting bolts (right)

Tow hook options (left) as seen from bottom of pod and wing saddle (right)

Spar and Joiners

Joiner tube, control horn and servo arm detail (left) and top view of the joiners (right)

Pushrod detail and servo connector plug (left) and panels ready to be joined (right)

Tail

Horizontal stab V-mount (left) and bottom view of stab (right)

Rudder control horn and pushrod fillet (left) and a view of the pushrod tubing (right)

Building The Spar

The bend in the center panel was a bit more work than I expected, but there were no major problems and it was manageable.
It sure gets lots of "howd'yadothat?" questions? :-)

The first thing to make is a 5.8 deg (or 6 deg) wedge out of foam: 2.00" high, 19.0" long, and at least 9" wide. This will be used to:

* jig up the bent center spar
* jig up the center wing beds during core cutting
* jig up the center wing beds during core/spar assembly
* support the core during sanding and general preparation
* jig up the center wing beds during bagging

Use high-density foam for the wedge if possible. It will get lots of use. You can alternatively make two 1.00" high (3 deg) wedges if 2" dense foam is not available.

The center spar is glued up with the bend in it using the single 6 deg wedge, or the two 3 deg wedges. You gave to press down
extra hard right at the center bend so the kink is "sharp". Use plenty of epoxy at the center kink, so it doesn't pop apart
prior to application of the glass wrap. The cap/web bond away from the kink is not critical.

Put metal or glass plates on the foam wedge and table to make sure things stay dead flat. My spar got a slight wave on the side that
was on the foam wedge, because the foam dented slightly under the clamping load. It still fit within the wing contour, but barely.

The caps have significant built-in stresses at the kink, but this doesn't matter. The spar is sized entirely for stiffness and doesn't
come close to its failure stress.

I suggest using Kevlar joiner tubes. Very light, and they won't nick the CF rods. If the permanent rod cracks, your wing is junked,
so Kevlar tubes are much safer than metal. The BD folder as the AL group has a PDF sheet on wrapping Kevlar tubes.

Before applying the glass wrap, I applied anti-burst CF tow wrap for 3/16" at the center-panel's spar ends, saturating while wrapping.
The caps are first sanded down at that spot to prevent a bump. About five 3K tow wraps are sufficient.

The spar wrap is 2.0 oz bias glass in the center spar, overlapped about 10" in the center (two layers there). The tip spars got 0.75 oz glass.
One extra 2.0 oz glass wrap was put over all four joiner blocks.

All glass was applied with 3M-77, then saturated, blotted, and bagged. No breather is necessary since compaction isn't critical.
Make the bags come off roughly in the middle of the balsa face. Be very careful not to nick the glass when cleaning up.
Glass failure in spar sample tests always occurs at the edge of the carbon caps, so round off these edges generously.

The bolt tab was cut from 3/16" thick PC board. Aluminum should also work OK. Plywood will wear too much with the small bolt I think.
To install the bolt tab, cut a small "window" in the glass skin which matches the tab. Using a bent piece of sharpened piano wire,
hog out the soft balsa top to bottom and slightly wider than the tab. Make sure the spar caps are exposed on the inside. Fill the void
with epoxy and push the tab into position letting the displaced epoxy ooze out.

Once I had the bent spar, the rest was nothing really special. I sliced the cores apart using the spars themselves as slicing jigs.
Some sanding was required to minimize the gaps. The center-panel core pieces also require fitting together at a bevel on the centerline.
Any voids can be later filled with Micro-Fill.

The foam core pieces were glued onto the spar with a minimal amount of 15-minute epoxy. This joint takes no load, and spotty coverage
of epoxy in the joint is OK. The bottom beds are used for vertical alignment. Masking tape on the bottom spar ensures that the spar
will be slightly within the foam contour. The gap is filled with micro balloons /epoxy and sanded flush. The top of the spar is also
below the contour, and that's also filled. The filler is not easy to sand. Micro-Fill would be a lot easier, but it's weak, and it's
important to solidly connect the spar to the skin. Hard balsa may be an easier alternative. A-grain balsa is better for this, since
it's stronger through the thickness than C-grain.

Any remaining voids between the core and spar can be filled with Micro-Fill. This is also effective on the inevitable dings put
into the foam during the assembly and preparation. Before filling, a ding should be first mostly sprung back with steam, by covering
with a wet paper towel and applying an iron set at about 230-250F.

For bagging the center panel, the bottom Mylar is one piece, and the top Mylars are two pieces, all hinged together at the
back edge. Fit the Mylar butt joint in the center as well as possible to minimize the epoxy ridge.

-Mark
 

Aegea Airfoils

Drawings and Construction Notes

Tail plan (Acrobat PDF file    CAD DXF file)

Aegea I

Original plans include a single flap servo in the fuselage

Aegea I Plan (Acrobat PDF file    CAD DXF file)  

Fuselage plan I w/3 servos (Acrobat PDF file    CAD DXF file)

Spar Layup (Acrobat PDF file)

Joiner (Acrobat PDF file)

Aegea II

4 servo wings with recessed flap servos, and two servo fuselage, revised skin and spar layups.

Aegea II Plan (Acrobat PDF file    CAD DXF file)

Fuselage plan w/2 servos (Acrobat PDF file    CAD DXF file)

Spar Layup II (Acrobat PDF file)

Radio Gear Recommendations

The Aegea I requires 5 channels, so a Hitec 555 receiver was used. JR241 servos for the tail and ailerons deliver high torque and are very light, and the HS85MG servo for the flaps is a strong durable servo that will keep from stripping on hard/inaccurate landings.

On the Aegea II, the flap servo was replaced with a pair of HS81MG's for the same reasons, and the 6 channel FMA Quantum receiver covers the required six functions.

Your transmitter should be able to handle the programming capabilities for the version you are building.

A: Wing incidence is largely a non-issue with the Aegea's all-moving stab. Setting the wing bottom surface parallel to the fuselage axis is about right, but a few degrees either way shouldn't matter.

For the first toss, set the stab parallel to the nearly-flat wing bottom surface.

Document Version History

Jan 27, 2004 - JAF
Added CAD DXF files from Tomer

November 27, 2003 - TJ
Initial

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