Mark Drela's Allegro-Lite 2m
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Home > Articles & Tips Index > Mark Drela's Allegro-Lite 2m

[Courtesy of Mark Drela, drela "at" mit.edu, October 2000+ 
- web presentation by Joel Foner, joel.foner "at" fonerassoc.com]

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.

Wow!  Also see James Osborne's online Allegro Lite Construction Guide: 
http://www.charlesriverrc.org/articles/allegro-lite-construction/introduction

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.

allegrolite_winchlaunch.jpg (162281 bytes)

Mark demonstrates winch launching technique for the Allegro-Lite. Once you look at the fuselage plan and think about holding the Allegro-Lite, you'll quickly realize that the low "wetted area" of the fuse leaves very little to hold on to during launch! (click on the small thumbnail image to the left for a large how-to picture - 158 kB image)

The Allegro-E-Lite 2m

The 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 Notes

The 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 Plans

Please 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
Allegro-Lite 2m plan (Adobe Acrobat PDF file    CAD DXF file)

WING PLANS
Allegro-Lite 2m wing plan details (Adobe Acrobat PDF file    CAD DXF file)

Allegro-Lite 2m full-size wing plans (to build over!)

Left Panel (single file***) Sheet 1 (8.5x11") Sheet 2 (8.5x11") Sheet 3 (8.5x11") Sheet 4 (8.5x11")
Right Panel (single file***) Sheet 1 (8.5x11") Sheet 2 (8.5x11") Sheet 3 (8.5x11") Sheet 4 (8.5x11")

Full-size wing plan in PostScript format (36 kB postscript file)

Please note - to create the full size wing plan, cut along the dotted lines of "Sheet 1" through "Sheet 4" with a sharp knife, align the edges and tape with clear tape. 
*** It seems that only certain printer setups can handle the single-file version, so if that doesn't work, use the 8x11" cut and paste approach

SPAR AND JOINER DETAILS
Allegro-Lite 2m spar details (Adobe Acrobat PDF file    CAD DXF file)

Allegro-Lite 2m wing joiner details (Adobe Acrobat PDF file)

50% de-rated joiners - for light duty use only! (10 kB Adobe Acrobat PDF file)

IMPORTANT: Wing joiner building instructions (3 kB text file)

WING RIBS
Allegro-Lite 2m rib center outlines  (Adobe Acrobat PDF file    CAD DXF file)
*** Please note - this file contains measured rules in both the vertical and horizontal direction.  Before using the printout to cut your ribs, please be sure that your printer has printed the page at the correct dimensions (some printers are not as accurate at this as others...)

Allegro-Lite 2m rib mid-tip outlines (Adobe Acrobat PDF file    CAD DXF file)
*** Please note - this file contains measured rules in both the vertical and horizontal direction.  Before using the printout to cut your ribs, please be sure that your printer has printed the page at the correct dimensions (some printers are not as accurate at this as others...)

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 standard fuselage plan (full size printouts)
- standard fuselage plan page 1 (Adobe Acrobat PDF file    CAD DXF file)
- standard fuselage plan page 2 (Adobe Acrobat PDF file    CAD DXF file)
- one-sheet fuselage plan (Adobe Acrobat PDF file    CAD DXF file)

Allegro-Lite 2m wood fuselage plans
- Wood Fuselage Plan 1 (Adobe Acrobat PDF file    CAD DXF file)
- Wood Fuselage Plan 2 (Adobe Acrobat PDF file    CAD DXF file)

TAIL AND V-MOUNT
Allegro-Lite 2m tail plan (Adobe Acrobat PDF file    CAD DXF file)

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)

allegrolite_tail.jpg (128470 bytes) Picture of yet another home-brew Allegro-Lite v-tail mount, not quite per the design, but may be useful for ideas none the less (click for larger image)

Allegro-E-Lite Plans

Allegro-E-Lite 2m plan (Adobe Acrobat PDF file    CAD DXF file)

Allegro-E-Lite 2m electric fuselage plan (full size printouts)
- standard fuselage plan page 1 (Adobe Acrobat PDF file    CAD DXF file)
- standard fuselage plan page 2 (Adobe Acrobat PDF file    CAD DXF file)

- Hatch loading fuse plan 1 (Adobe Acrobat PDF file    CAD DXF file)
- Hatch loading fuse plan 2 (Adobe Acrobat PDF file    CAD DXF file)

Graupner CAM 6x3 high performance prop modification (25 kB Adobe Acrobat PDF file)

Allegro Construction Notes

Allegro-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
- Mark's notes on creating a fuselage plug (6 kB text file)
- Rick Hallett's alternative approach (3 kB text file)

Accurate Shear Web Cutting (13 kB Acrobat PDF file)

Allegro-Lite Boom Stiffness (to aid with selection of a tailboom - 1 kB text file)

D-Tube Sheet Forming instructions (how to pre-form the D-Tube sheeting before installation)

Pushrod Selection (notes from Mark on lightweight pushrods - 3 kB text file)

Tail Construction Notes

Tail Sanding Sequence (diagrams and notes on sanding the tail feathers)

Other Construction Tips #1

Other Construction Tips #2

Airfoil Coordinates and Polars

The 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:

Airfoil Bottom Top Facet 1 Top Facet 2 Top Facet 3
ag35 30%-100% 45%-65% 65%-83% 83%-100%
ag36 30%-100% 45%-65% 65%-86% 86%-100%
ag37 30%-100% 45%-65% 65%-88% 88%-100%
ag38 30%-100% 45%-65% 65%-89% 89%-100%

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.

Airfoil Coordinates CompuFoil COR files Polars
ag35 ag35.dat ag35.cor ag35_polars.pdf
ag36 ag36.dat ag36.cor ag36_polars.pdf
ag37 ag37.dat ag37.cor ag37_polars.pdf
ag38 ag38.dat ag38.cor ag38_polars.pdf
ht08 ht08.dat ht08.cor tail section 1
ht12 ht12.dat ht12.cor tail section 2

Polar Comparisons

Related Construction Notes

Here is a view of the Allegro tail

allegro2m_tail_closeup.jpg (66787 bytes)

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 Lists

The 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 - Wood

Allegro-Lite Materials - Composites


Best of luck, and please let us know how you're doing with your Allegro-Lite  2m!


Document Version History

January 27, 2004 - jaf
- Added CAD DXF file

June 10, 2001 - jaf
- Added alt_fuseE1.pdf and alt_fuseE2.pdf (hatch loading e-fuse diagrams)
- Added joiners2.pdf (50% de-rated joiners for lightweight use)
- Added sheet_forming.txt (how to pre-form D-tube sheeting)
- Added tail_sand.pdf (tail sanding sequence diagrams and notes)
- Added templates.pdf (PDF diagram of rib templates
- Updated tips_1.txt

April 29, 2001 - jaf
- Added "Tail Construction Notes" (Allegro Construction Notes section)

April 17, 2001 - jaf
- Added a postscript file of the Allegro plans (Wing Plans section)

March 1, 2001 - jaf
- added "Wing joiner building instructions" (Spar and Joiner Details section)

January 30, 2001 - jaf
- added "wood fuselage plans"
- added "home-brew v-tail design ideas" drawing
- added a picture of the v-tail mount

November 28, 2000 - jaf
- added "one-sheet fuselage plan"
- updated fuse1.pdf, fuse2.pdf, tail.pdf, vmount.pdf, wing_plan.pdf from Mark
- added non-kerf dxf rib templates

October 30, 2000 - jaf
- added "Allegro-Lite 2m information site as a 1 MB Adobe Acrobat v4 PDF file" to Drawings and Construction notes
- added wing joiner detail drawings
- added tail shaping tangents drawing
- added "boom stiffness" a document with some test results to assist with choosing the right tailboom
- added "Fuse Plug Construction" to Construction Notes - notes by Mark and Rick Hallett on how to build a plug for molding the fuse pod
- added "Pushrod Selection" to Construction Notes
- added "DXF Files of rib outlines"
- added "Other construction tips #1" and "Other construction tips #2" with various tidbits from Mark
- added materials lists for wood and composites

October 22, 2000 - jaf
- added picture demonstrating winch launch technique for the Allegro-Lite
- added two page full-size fuselage plans with more details, both for the standard and electric fuselage options
- added full-size tail plan
- added stabilizer v-mount diagram with construction notes and details
- updated intro description of Allegro-E-Lite with climb altitude information

October 17, 2000 - jaf
- added link to the new Allegro-Lite discussion group

October 14, 2000 - jaf
- added individual PDF sheets for printing full-size wing plan

October 11, 2000 - jaf
- "all new"

   


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