CUSTOMIZINGWHEEL PANTS

THESPORTPLANEBUILDER

By Antuni (Tony) BingelisEAA Designee Program Advisor

8509 Greenflint LaneAustin, Texas 78759

IN BUMMING AROUND airports I find most fixedlanding gear installations are dirty aerodynamically andwould benefit, both aesthetically and performance-wise,by the addition of customized fairings to the wheel pantsalready installed.

All wheel pants installations have some sort of astrut or axle sticking out of them. Usually out of theinboard side or the top of the pants. Most of us realizethat if a landing gear leg, strut or whatever doesn'tintersect the wheel pants at approximately a 90 degreeangle, that intersection will generate quite a bit ofturbulence and drag. If this is so, it is hard to under-stand why more homebuilders don't remedy the defi-ciency by constructing and installing a fairing to en-close or alter the drag producing area.

Some landing gears are difficult to fair. A good exam-ple is the type of gear installed on the Emeraude, Jodeland similar designs. Their cantilever gear legs, withattached scissors, must be the dirtiest of all conven-tional installations . . . and the most difficult to stream-line. The only way to effectively reduce the drag of sucha gear is to enclose everything in a customized housingor fairing. European designs have long used large bul-bous wheel pants to enclose all the drag producing ele-ments.

The Zenith design utilizes a similar installation andI understand wheel pants designed for it may be ob-tained from Canada. For the most part, however, youwill have to make your own customized version usingstock wheel pants and tailoring them to suit your air-craft.

The original wheel pants installed on my latestEmeraude were the long pointed type used on someCessnas. Their pointed noses complemented the largepointed propeller spinner installed on my aircraft andthe sweeping lines of the pants matched the lines of theEmeraude's fuselage. Initially they looked pretty goodto me but in time, with those ugly scissors sticking outin the open for everyone to see, I found the installa-tion crude and offensive. So, some cosmetic surgery wasin order. Although the treatment the wheel pants re-ceived is adequately detailed in the photos for experi-enced builders, some behind the scenes comments mightbe helpful to anyone who wants to try his hand in cus-tomizing his own wheel pants.

The Customizing ProcessAlmost any kind of foam is good enough for building-

up wheel pant fairings. I used a sheet foam manufac-tured for homebuilders (I mean house builders). It is asmooth textured material, pale blue in color and maybe purchased in 4' x 8' %" thick sheets. Thicker sheetsare available too. This material is stocked by almostall lumber yards. It is inexpensive and easily worked.

To enable me to get started with the foam build-up24 DECEMBER 1979

Reinforcement plates for the attach points of the wheel pants.They were epoxied inside the pants.

The foam slab is glued to the inboard side of the pants to pro-vide a reference base for all foam build-up.

and to provide a good reference surface to work from, Iglued a slab of roughly shaped foam to the inboard sideof the pants with a few dabs of 5 minute epoxy. I wouldcaution you that because this foam dissolves in the pre-sence of fumes or contact with volatile liquids (lacquerthinner and polyester resins, etc.), use an epoxy adhesive,white glue or any other adhesive which will not attackthe foam. How can you tell if a glue is O. K. to use? Trya small sample. If the foam doesn't dissolve or erodeaway before your eyes when in contact with the glue,it will work. However, another problem you'll have withmost glues (other than the 5 minute epoxy), should bepointed out. They set-up too slowly. Of course, theywould be all right for overnight gluing and when timeis not a factor.

With pants installed, glue additional pieces to thereference slab to fill out the profile needed. Use theglue sparingly and try not to apply the glue dabs to

Here the foam build-up is almost completed.

\In this photo the shaping of the foam fairing is under way.

areas where the foam is to be sanded or cut away as itwill leave hard spots. Those hard areas do not sand welland will make your contour finishing a bit more difficult.

After the gear assembly in the area to be faired hasbeen enclosed with foam pieces fitted and glued in place,determine where to cut out and temporarily remove thefoam build-up so that the entire assembly, wheel pantsfoam and all, may be removed from the aircraft for addi-tional work.

When you get the wheel pants with all that foambuild-up to your workbench, replace the cut-out hunkof foam by gluing it back in place. You should now havetwo wheel pants with a large foam mass affixed to eachof them ready for shaping.

The foam may be shaped with a Surfoam file, a hack-saw blade, large butcher knife, coarse sandpaper or al-most any other abrasive or cutting tool that you liketo work with.

Developing the Fairing ContoursWhile viewing the foam build-up from the front, shape

it into a smoothly curved contour that blends into thebasic wheel pants. Keep in mind that a minimum frontalarea is most desirable. Because the foam pieces werefitted around the gear legs with the wheel pants in-stalled on the aircraft you are assured of adequate clear-ances for the scissors and other linkages. You can, there-fore, cut the foam down to as thin as !4" wherever needed.When you have that side shaped to your satisfaction,turn the wheel pants sideways and shape the foam toblend into the profile view of the pants. The final shap-ing is that of rounding the foam and working it into astreamline shape. It could be that when you finish therounding and fairing process the completed contoursmay not be what you consider to be an ideal shape forobtaining a smooth flow of air around the pants. In this

case you could add a piece of foam to extend the con-tours or to modify them into the streamline shape youvisualize as being appropriate. Instinct can stand youin good stead here. Naturally, you should avoid abruptchanges in shape and keep the contour lines flowingsmoothly from front to rear. Later you can tuft the wheelpants and have someone take photos of them in flightto see how successful you were and whether you willneed to alter their shape to improve their efficiency. . . that is, if obtaining minimum drag is importantto you. For most of us with moderate performance air-craft, I think a striking ground appearance is satisfy-ing enough.

Fiber Glassing MethodsNow that the foam fairings are shaped to your satis-

faction you are ready to overlay them with fiber glass.You have two basic alternatives. One, you may lay fiberglass directly over the foam covered areas using epoxyresin making sure that the cloth extends at least twoinches beyond the foam line. After the fiber glass iscured you can pour lacquer thinner or just about anyother volatile l iquid into the fairings to dissolve thefoam. This will leave only the fiber glass shell perma-nently attached to the wheel pants. This method is thequickest and although it leaves you with a rough innersurface, this is of no consequence. All that is needednow is just a bit of outside sanding and fairing of thefiber glass edges.

The second method requires more extensive prepara-tion and work. Because polyester resin will be used(it's cheaper and sets up faster), this type of foam hasto be protected from its fumes and from direct contactwith the resin. A light coating of patching plaster overthe entire foam covered area will provide the necessaryprotection for the foam against the resin.

After the plaster layer is sanded smooth, lay a stripof masking tape around the border of the foam to delin-eate a smoothly curved outline for the fiber glass lay-up. This edging will aid in your trimming the glass shelllater.

Proceed from here as you would with any fiber glasswork, waxing everything heavily to insure easy removalof the fiber glass fairing after the lay-up has cured. Usewhatever methods you are familiar with.

Do not make the mistake of using too many layers

The foam shaping is completed and a layer of patching plasteris being applied as a protective shield against polyester resins.

of cloth. Remember when you are permanently attach-ing the fairings later, an additional layer or two willbe added around their periphery.

A maximum of three layers of cloth should sufficefor all areas of the fairing except those that must bereinforced. Actually, two layers of cloth is plenty whereverthe curvature is pronounced.

Before removing the fiber glass shells from the form,SPORT AVIATION 25

The wheel pants are now ready to receive the fiber glasstreatment.

In this view the fiber glass fairing is completed and ready forfinal sanding and finishing.

Here the wheel pants with its new fairing are tried on for fit-ting before the final dean-up is undertaken.

drill small holes around the outer boundary of the fair-ing so that they may be used to obtain exact realign-ment during gluing.

Using a felt pen and a flexible straight edge, markthe area of the fairing to be cut out to provide accessto the gear legs for easy installation, maintenance andinspection. Use straight lines as much as possible al-though this is not mandatory . . . simply easier thanworking with curved joints. Refer to the photos for ideas.

A hand held hacksaw blade may be used to make thecut-out. An electric jigsaw with a metal cutting bladeis also effective, but be careful!

After the opening has been cut out you might wantto cut away some areas of the original wheel pants. Oryou can cut a few lightening holes with a large diameter26 DECEMBER 1979

(2") hole saw. Be sure not to weaken the wheel pantsattachment points. This lightening process is feasiblebecause after the new fairing sections have been gluedto the wheel pants the entire unit will become extremelystrong and rigid and parts of the original wheel pantswill be redundant to the new customized shape.

Attach l'/4" wide aluminum strips to the undersidearound the cut-out in the fairing to form an edge forfasteners. These strips may be pop-riveted in place. Ifpop-rivets are used, their heads may be covered with apiece of glass cloth to hide them and provide a smoothersurface.

Place the fairing cover piece in position and drillthe attachment holes for it. Drill through the fiberglass shell and the metal edging under it. Install a few

The fiber glass fairing shell is now ready to be epoxied to theoriginal wheel pants. A strip of fiber glass around the peripheryof the joint will turn this into a single smooth unit.

Note the spring loaded access door for airing the tires.

This rear view shows how wide the wheel pants have becomein order to enclose all the drag producing mechanism.

Here is the final result. Note the drag reducing plates in frontof the tires. They are necessary because the opening for thewheels was much too large.

Note the large access plate on the inboard side of these pants.Important for inspection, maintenance and removal of thepants.

Here is a fine example of drag reduction. This is another way to customize your wheel pants to improveappearance and to reduce drag.

Another good example of what can be done to dean up land-ing gear installations.

cleco fasteners or screws in each hole as soon as it isdrilled. Next, install nut plates in the metal strip topermit easy installation and removal of the access panel.

Now all you have to do is finish sand the newly fairedpants to the degree of perfection you want.

This is the time also to correct a deficiency commonto many stock wheel pants designed for production air-craft . . . that tremendous opening they have in themfor the wheels. This cavernous opening.is a high dragproducer and may be the reason why many buildersrealize little or no increase in airspeed after wheelpants have been added. If your wheel openings are ex-cessive — greater than V6" in front or in back of the tires— you should fabricate small metal or fiber glass platesto reduce the opening around the tires. These platesor covers may be installed with nut plates or perma-nently glued in place.

Tire Valve AccessA totally enclosed wheel pants installation must have

access to the valve stems so that the tires might be airedwhenever necessary. A small spring-loaded door canbe installed to provide this access. Take care in locatingthis opening properly otherwise the tire's valve stemmay still be inaccessible to an air hose.

A Cosmetic TreatmentEven the best fiber glass work seems to have tiny

indentations or pits in its finished surface. These showup even after you have carefully prepared the surfaceand have given it a surface primer treatment. Thesecan be hidden by taking a bit of wet primer on your fin-ger and rubbing it across these offensive areas. Afterthis cosmetic treatment dries, resand the area. Keeprepeating the process until you think you have gottenrid of all of them.

And . . .Large fairings such as these will naturally weigh

more than the basic wheel pants originally installed.You can expect the 3 pound wheel pants to double inweight. Mine weighed 6 pounds each. I think I couldhave reduced them to 5 pounds with a bit of extra lighten-ing effort. Of course, some landing gears require onlysmall fairings and the resultant increase in weight willbe much smaller.

My own modified wheel pants turned out to looksomething like a couple of dolphins. I like the effectfrom any angle although at least one or two of my friendsdon't seem overwhelmed. Still, I like them and I'm sureyou'll like yours too.

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