BY TONY BINGELIS, 85O9 GREENFLINT LANE, AUSTIN, TEXAS 78759

CANOPY OPTIONS

J. HE BASIC ESSENTIALS for fitting and installingcanopies were detailed in three of my earlier articles ap-pearing in SPORT AVIATION. These were entitled TheInstallation of Sliding Canopies, Doors, Latches andStuff, and appeared in the December 1974, January 1975and February 1975 issues. Essentially the same informa-tion is contained in my book, The Sportplane Builder, inthe section entitled Canopies/Windshields. (This informa-tion will not be repeated here.)

Almost ten years has since passed but the referencedinformation is as applicable today as it was then. This isnot to infer that there have not been changes in canopiesand canopy installations. There have been some, of course.But actually, the methods described for fabricating andinstalling canopy frames, canopies, doors, hatches andwindshields were time proven even then and will probablyremain unchanged for many, many years to come. How-ever, as we all know, new canopy shapes, new materialsand construction methods have come along giving buildersgreater flexibility and more options for making cockpitenclosures. Among these are refined construction prac-tices that rely almost entirely on fiberglass and epoxy inthe fabrication of unitized enclosures.

For the first time, materials such as Kevlar and BoronFibers are becoming more readily available to home-builders who are constantly striving to find better waysto build quicker and stronger.

Take weatherstripping materials, for example. Allkinds and shapes are commonly available that permit sol-ving almost any type of canopy or windshield wind noiseproblem.

You may not have been aware of it, but acrylic plastic(Plexiglas) bubbles and vacuum formed canopy shapeswere not always readily available to builders. A few yearsback, many a builder didn't know where he could find orget Plexiglas formed to his needs. He often had to makehis own canopy forms and molds, build a makeshift ovenand then invest heavily in a number of expensive Plexi-glass sheets before he finally succeeded in "blowing" acanopy or stretching a canopy door for himself. Even so,many builders had to put up with poorly formed canopiesand windshields that were far from being optically perfect.Sometimes the distortion was so bad that it was hard totell if it was a 747 or a buzzard crossing your line of flight.

Fortunately, a few of the more successful canopy mak-ing builders in an attempt of necessity to recoup part oftheir huge expenditures, branched out and began to make

canopies and windshields for other homebuilders . . . alucky break for the rest of us indeed.

As you would expect, a Plexiglas canopy produced espe-cially for the design you are building will usually be thesimplest to install with predictable results. However, sincemost homebuilts have similar cockpit dimensions, findinga good alternative to the original prototype canopy shapeis generally no great problem. Even the builder who hasan original design of his own can find a stock canopy (beingcurrently produced) that will fit his expectations andneeds. It would, therefore, make just about as much sensefor a builder, today, to attempt to make his own wheels,tires, tubes and brakes as it would be for him to undertakethe fabrication of his own canopy. Some will, of course,certainly not to save money but just to see if they can.

Well, since so many canopy designs are available, howis a guy to decide what is the best installation for his ownproject?

There is one sure way. Arrange to visit other builderswho are building the airplane. Talk with them andexamine their installations.Look for the good features and

PROVIDES MAXIMUM HEADROOMHERE

HEADROOM SEVERELYRESTRICTED HERE BY

THESYMMETRICAL

BUBBLE--.,

SINGLE SEATER TWO SEATEH

"FREE BLOWN" BUBBLE CANOPIES

OPTICS GOOD TO EXCELLENTDEPENDING ON QUALITYOF THE MOLD IMPROVED HEADROOM

HERE

TWO SEATER

CANOPY VACUUM FORMED (IN A MOLD)

FIGURE I

CANOPY TYPE AFFECTS HEADROOM

SPORT AVIATION 15

don't overlook the shortcomings. Hereare a few things to think about and toresolve in your own way.

A lot will depend upon whetheryour airplane is a single seater or atwo seater, won't it? If it is a twoseater, is it a tandem or a side-by-sidearrangement? Single seaters are theeasiest to fit with enclosures(canopies) and offer the greatestnumber of installation options.

Your first concern, naturally, isheadroom ... not only vertical but lat-eral as well. If the canopy is too nar-row, you will not be able to tilt yourhead to peek at the landscape below.Bumpy air can cause bumps on thehead, too.

What else would you expect of acanopy? It must, of course, provideeasy access for entry into the aircraft.It must be airworthy and well securedin flight. It should also be easy toopen, shut and latch from both insideand outside the aircraft. And, cer-tainly, it should have good optics andyour vision, in all directions (except,perhaps, straight down), should beunobstructed.

Other attributes are also impor-tant. The canopy should be easy toseal against wind noise and rain . . .and it should be aerodynamicallyclean. This means that when thecanopy is closed the airplane will pre-sent its sleekest image with smoothlyflowing lines that are pleasing to theeye.

Have you ever speculated overwhat aesthetic degradation or trans-formation would take place before acanopy was opened? Would it raise up,tilt over, slide back or what? Maybeit would be a flip-over canopy or onethat rises up and backward on spindlystruts. (That kind often presents aflimsy and fragile "you ought to dosomething about that" appearance tome.)

With so many of the canopiesbeing of the "high rise" variety whenopened, what would you do in a strongwind? Wait until it subsides? Havefood and water brought in? Maybe youcould take a chance that it won't blowaway and open it anyway. I'm onlykidding! Some of those installationsare well executed and stouter thanthey first appear.

The ones that can best cope withrather gusty wind conditions arethose that are fitted with stay struts.These nitrogen cylinder lift struts aresalvaged from a variety of foreign andU.S. manufactured used cars . . .hatchbacks mostly. Not only do thestruts help in raising the heavy twoseater canopies, they also stabilizethem considerably while in the openposition.16 FEBRUARY 1984

The side hinged flip over canopy is the most popular of all types. Particularly with singleseat builders as it is also the simplest to install and to secure. Windshield may beseparate or integral with the canopy.

A forward sliding canopy is most difficult to fit closely and to seal against wind noise.One good thing, a separate windshield and frame are not necessary.

Instead of a canopy, why not install "gull wing" doors. A flat wrapped windshield andrear windows can be used although stretch forming of the windows over a special moldwill be required. This type installation is easy to seal against wind noise . . . and affordsexcellent headroom.

I guess I have to conclude thatthere is no single best canopy installa-tion. Of all the airplanes you haveseen and liked, I'll wager that manyof them had cockpit enclosures thatwere "deficient" in one or more of thedesirable features mentioned earlier.

You will notice that I have madeno mention of the ease of fabricationand installation as being a desirablecanopy feature. We all know that thathas nothing to do with a canopy's ulti-mate appearance or with theaerodynamic qualities of the aircraft(sorry, Charlie, no sympathy here).

Although acrylic plastic weighsbut 43% as much as aluminum, aPlexiglas canopy installation isheavy because of its Vs" to '/T' thick-ness. You should, therefore, attemptto get the maximum vision in allquadrants with the minimum use ofthe material. This merits some think-ing and planning before you startcutting any material for installation.

Selecting a canopy that is wideenough for your aircraft is more im-portant than concerning yourself withits length. Fiberglass or aluminumfairing skirts allow you to alter thecanopy's shape remarkably.

A Plexiglas bubble that is muchmore than an inch or so too narrow(or too wide) could make the fittingmore difficult and the final appear-ance something less than you hadhoped for.

If you have to spread a too narrowcanopy to make it fit, you will be re-ducing (however slightly that maybe) the amount of shoulder room andheadroom you could have otherwisehad. Conversely, if you have tosqueeze in the sides too much, it willcause the canopy to bulge and takeon an odd waspish look when viewedfrom the front or rear of the airplane.

Let's confirm what you alreadymay have suspected. "Free-blown"canopies are great for single seatersbut they are lacking in headroom forside-by-side installations (see Figure1).

Better than blown canopies formost of those two seaters are thevacuum formed type. These can beformed in a mold that can departfrom the radial symmetry charac-eristic of a blown canopy. Thisvacuum forming permits designslike the somewhat flattened top ofthe typical T-18 canopy. This styleof canopy provides the maximum ofheadroom for a side-by-side two seat-er and a minimum frontal area. In-cidentally, the T-18 canopy has beenbeautifully adapted to a number ofother aircraft designs . . . the re-cently completed crop of MustangH's attest to this.

A side hinged canopy could be impractical in an amphibian. These double hingedhatches permit the occupants to dock easily or to do some serious padding. Usuallyin such installations the windshield frame and the rear frame are grooved and guidesin the bottoms of the hatches ride in them.

An up and over canopy is, at best, one that requires careful attention to the geometryof the hinging mechanism. In a two seater, the heavy canopy is difficult to stabilizeagainst lateral breezes (lateral breezes?).

For the sight-seeing sport flyer this door treatment can hardly be improved. Althoughentry and egress are awkward in the J-3 Cub, you can fly it with either or both doorsopen or closed.

SPORT AVIATION 17

A door type canopy is the preference of aircraft manufacturers. However, a homebuildershould realize that a generous cut-out in the roof is necessary to make entry easier. . . most homebuilders have to use a smaller door opening as cutting away a longeronis risky unless properly engineered.

Something different here?You bet. The familiar sidehinged canopy has given wayto this two piece installation.The front end is hinged mili-tary style and the less fre-quently used back portion re-mains side hinged.

Fitting a canopy to the aircraft entails considerable planning, fitting and trying. Evenafter the frame has been constructed and the "glass" epoxied in, the installation andalignment of all the hinges and hardware can take much more time than most builderswould believe.18 FEBRUARY 1984

It has become quite apparent thatthe most popular of canopy installa-tions, particularly in single seaters,is the side-hinged flip-over type. Itmay be installed in one piece (includ-ing the windshield) or the windshieldmay be mounted separately. There isgood reason for this popularity; it isalso the easiest of all types to installbecause little or no framework isneeded to reinforce it.

Two seaters cannot indulge in theluxury of a frameless installationbecause a large unframed Plexiglasbubble is about as undisciplined as alarge mound of Jello . . . and aboutas manageable, too. For these instal-lations a canopy frame is essential.

Even though finding a suitablecanopy is no longer difficult, the prob-lem of canopy installation, unfortu-nately, still remains somewhat of ananxiety producing period in the life ofmany a homebuilder. Crack thecanopy while drilling that last instal-lation hole and there goes severalhundred dollars down the drain.Tighten the fasteners too tight andsometime later . . . CRACK! The samething might happen months later inan installation where the screw holeswere not large enough for the fasten-ers used.

Would you believe that the holesin acrylic plastic should be about %"in diameter if a 3/ie" screw (fastener)is used? You can expect Plexiglas tocreep (expand) up to Vie" per linealfoot with temperature changes.

It is no wonder that the buildersof composite aircraft are smiling morethan builders using aluminum andsteel tubular frames for theircanopies. The composite builders caneliminate the need for using steelscrews and fasteners and rely, in-stead, on epoxy bonding of the "glass"to the frame. Very obviously thissimplifies the installation and virtu-ally eliminates the dreaded drilling ofholes for fasteners. Naturally, thisepoxy bonding method is most effec-tive with wood and compositefiberglass frames.

All things considered, I wouldclassify a sliding canopy as being thefussiest to install. It has a number ofmoving parts, is difficult to match tothe windshield, is difficult to sealagainst wind noise and requires themost complex of latchingmechanisms. It is a painfully fussyprocess as you will have to install,drill and remove the canopy and itsfasteners numerous times during thefitting process, but all that shouldn'tdissuade you from installing a slidingcanopy. They are nice! We'll save thedetails for next month.

MOLDED FIBERGLASS SHELLTIME-CONSUMING MOLD MUST BE MADE FIRST

EASY STEP INENTRY

SIMPLE WRAP AROUND PLEXIGLASINSTALLATION ON A 200 MPHCASSUTT

FIBERGLASS CAP

NOTE- COMPOSITE CONSTRUCTION LENDSITSELF TO FLUSH FASTENER FREEPLEXIGLAS INSTALLATIONS HAVINGA GOOD SERVICE LIFE .

GULL WING HATCHES

ACCESS OFTEN AWKWARDLIMITED

ACCESS CAN BE AWKWARDIF DOORS ARE SMALL

EASIEST TO MAKE-(NO SEPARATEWINDSHIELD)

SIDE-HINGE-MADE FROM HALF,OF A FREE BLOWNBUBBLE

UP AND OVER - FLIMSY WHEN OPEN PASSENGER CANNOT ENTER OR EXIT UNTILPILOT CLOSES HIS HATCH

HATCHES - CENTERLINE HINGEC

HEAVY TO RAISE UNLESSNITROGEN CYLINDER LIFT STRUTSARE INSTALLED (SALVAGE FROMMOST ANY HATCHBACK AUTO)

.WINDSHIELD SLANTED FOR EASIER ENTRY

Mi 11 TAR r TYPE FRONT HINGED

NO REAR FRAME -THAT1 SA WEATHERSTRIP SEAL

SIDE /

EASY TO BUILDTO SEAL AND SECURE

SLIDING CANOPY

FIGURE 2.

CANOPY FEATURES . .. GOOD AND OTHERWISEMODIFIED GULL WING TYPE

SPORT AVIATION 19