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| Home > Articles & Tips Index > Mark Drela's Allegro-Lite 2m [Courtesy of Mark Drela, drela "at" mit.edu,
October 2000+
Wow!
Also see James Osborne's online Allegro Lite Construction Guide: The Allegro-Lite 2m
The Allegro-Lite 2m is a built-up version of the original composite Allegro RES 2m sailplane. The intent of the Allegro-Lite is to make the original Allegro's high performance accessible to builders preferring traditional wood construction. The usual spruce spars are replaced with off-the-shelf carbon fiber strips, but the construction method remains nearly the same. The resulting structure does not quite match the (admittedly excessive) strength of the original Allegro, but it still provides full-pedal zoom capability on the winch. Careful sizing of the spar and all other components has resulted in a very low flying weight of 18 oz.
The exceptionally low weight and low wing loading (5 oz/ft^2) gives the Allegro-Lite great versatility. It can be flown as an oversize HLG, or as a full-pedal winch glider, or anything in between. A mini hi-start will give a very high launch in small fields. It can be ballasted up to 32 oz or more for windy weather. The long tail moments and powerful spoiler provide good landing control for RES contest landing tasks.
The Allegro-E-Lite 2mThe Allegro-E-Lite is the electric version of the Allegro-Lite RES 2m glider. The same fuselage pod shell is used. The motor replaces the RX battery, and the motor battery is placed in the ballast compartment, so the overall CG location is largely unaffected. The intent is to use the wing and stab of the winch glider with the electric fuselage, with the wing's spoiler servo being disconnected when flying electric. A dedicated wing without the spoiler will save 1 oz for a 5% increase in climb rate. The power train is an ungeared 6V Speed-400 motor, a 6x3 folding prop, a 7-cell 600 mAh low rate battery, and a 10-Amp motor controller. This simple and inexpensive setup exploits the clean light airframe, which allows climbing at relatively high speed (about twice the best glide speed), much like with a Zagi-400. A high airspeed partly mitigates the losses of the small prop, and makes the un-geared drive more attractive. Total estimated climb altitude is about 1500 ft, based on the dead air flight times of 25 minutes have which been measured in very still foggy air at dawn. An optional modification to the prop to improve the blade airfoils gives a noticable (estimated 5-10%) improvement in the climb rate and total altitude gain. Drawings and Construction NotesThe Allegro is designed for 2m RES (rudder elevator spoiler) competition tasks. The Allegro uses a set of custom-designed airfoils, tuned for the airframe design parameters. Detailed construction notes and target weights are provided in the plans - please pay close attention to these if you wish your Allegro to have the strength it needs, and the performance it should have! Allegro-Lite PlansPlease note: Most of the construction notes are included on the drawings and plans listed below. It may help to read the plans in the order presented below for best clarity (you may want to print them out and compare them side by side for some details...). OVERALL PLAN WING PLANS Allegro-Lite 2m full-size wing plans (to build over!)
Full-size wing plan in PostScript format (36 kB postscript file)
SPAR AND JOINER DETAILS Allegro-Lite 2m wing joiner details (Adobe Acrobat PDF file)
WING RIBS Allegro-Lite 2m rib mid-tip outlines (Adobe Acrobat PDF file
CAD DXF file) DXF files of rib outlines - no kerf (61 kB PKZip archive) PDF files of rib templates (24 kB Adobe Acrobat PDF file) FUSELAGE Allegro-Lite 2m wood fuselage plans TAIL AND V-MOUNT Allegro-Lite 2m tail shaping data and diagram (also see "Accurate shaping of solid balsa surfaces without templates" below - 20 kB Adobe Acrobat PDF file) Allegro-Lite 2m stabilizer v-mount diagrams and construction details (21 kB Adobe Acrobat PDF file) Home-brew v-tail design ideas - plans for aluminum and carbon formed v-tail mounts (21 kB Adobe Acrobat PDF file)
Allegro-E-Lite PlansAllegro-E-Lite 2m plan (Adobe Acrobat PDF file CAD DXF file) Allegro-E-Lite 2m electric fuselage plan
(full size printouts) - Hatch
loading fuse plan 1 (Adobe
Acrobat PDF file
CAD DXF file) Graupner CAM 6x3 high performance prop modification (25 kB Adobe Acrobat PDF file) Allegro Construction NotesAllegro-Lite 2m panel building sequence (5 kB Adobe Acrobat PDF file) Allegro-Lite 2m wing building sequence and wing construction details (12 kB Adobe Acrobat PDF file) Allegro-Lite 2m Fuse Plug
Construction Accurate Shear Web Cutting (13 kB Acrobat PDF file) Allegro-Lite Boom Stiffness (to aid with selection of a tailboom - 1 kB text file)
Pushrod Selection (notes from Mark on lightweight pushrods - 3 kB text file)
Airfoil Coordinates and PolarsThe AG35..38 airfoils on the Allegro-Lite have been specially designed for built-up construction. All parts of the airfoil with open covering are flat by design. This completely eliminates the airfoil modifications due to covering sag and thus avoids the associated performance penalties. Wider than usual rib spacing can also be safely used. Each airfoil has one flat facet on the bottom, and three flat facets on top. Their % chordwise extents are:
The intent is to have the bottom sheeting back to at least 30% chord, and the top sheeting back to 45% chord. A top support strip is to be placed at 65% chord. The trailing edge strip forms the remaining facet back to 100% chord. The AG35..38 airfoils are similar in some respects to the Selig S3021 airfoil, which also has a flat bottom and was designed for built-up construction. The AG35..38 airfoils are thinner, and perform noticably better at lower Reynolds numbers. Hence they are especially attractive for smaller gliders, where the small thickness is less important from a structural viewpoint.
Polar Comparisons
Related Construction NotesHere is a view of the Allegro tail
Integrated cloth hinge design (8 kB Acrobat PDF file) Accurate shaping of solid balsa surfaces without templates (12 kB Acrobat PDF file) Allegro-Lite Materials ListsThe following may not be 100% complete, but should provide a great start on finding the materials to build your Allegro. Please let us know about anything we've missed... Allegro-Lite Materials - Composites Best of luck, and please let us know how you're doing with your Allegro-Lite 2m!
Document Version HistoryJanuary 27, 2004 - jaf June 10, 2001 - jaf April 29, 2001 - jaf April 17, 2001 - jaf March 1, 2001 - jaf January 30, 2001 - jaf November 28, 2000 - jaf October 30, 2000 - jaf October 22, 2000 - jaf October 17, 2000 - jaf October 14, 2000 - jaf October 11, 2000 - jaf
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Construction notes are included in the drawings, which you can download as
Acrobat v
