Sky Pup News

    Newsletter No. 6                                                               January, 1985

North Carolina Sky Pup Almost There


Building Tips

Changes & Modifications

 Airspeed Indicators


SKY PUP NEWS is a quarterly newsletter for builders of the Sport Flight “Sky Pup”. The purpose of the newsletter is to make builders aware of revisions, suggestions and ideas which are brought to our attention.

We solicit your input in the form of photos, ideas, and time or money-saving tips. Please share your progress and comments by sending them to Sport Flight, c/o NEWSLETTER.

Subscriptions to SKY PUP NEWS are $12.00/year (foreign add $6.00, Canadian add $2.00). All subscription are based on a calendar year, i.e. not from date ordered. Please use your plans Serial Number in al correspondence with Sport Flight, and specify which calendar year your subscription fee is for.

North Carolina Sky Pup

The Pup featured in the photos below was built by Rick Autrey of Autreyville, NC in about 5-½ months of spare time effort. Total time invested was almost 500 hours, but Rick says he could “build another one in lot less”. This was Rick’s first airplane project and he appears to be hooked since he’s already talking about selling the first Pup to finance a second one.  

SN 2176’s first flight was on January 6, 1985 and went off without any problems. Rick reports a “very lively” acceleration and climb, but feels that things will be even better when he takes care of a minor engine tuning problem.

Power is a stock Cuyuna 215 with CPS reduction and a 59 inch Ultra-Prop. Colors are white overall with light blue trim and white wheels to match. This Pup appears to be pretty much per plans except for a unusual modification to the rudder control system. The rudder bar was replaced with pedals, and the cables were routed inside the fuselage—mostly for aesthetic purposes. Rick also added a steerable tailwheel and thinks it helps ground handling on the hard surface runways.

Rick has some previous flying experience in ultralights, and says that the Pup is very easy to fly. We enjoyed getting calls from him while he was under construction, since he was working in a radio station and communications were interrupted every three minutes while he went to “spin” a record or say something over the air. All in all, Rick liked the Pup project so well that he’s ready to start another one!

Almost There

In previous newsletters, we have featured only Pup’s which were completed and flying. The photo below, however, so captured the spirit of homebuilding that we felt we should include it. Dan Grunloh (SN 2028), of Potomac, IL, is about two-thirds done with his Pup and is shown engaged in one of those moments of daydreaming that all of us find time for. If the detail photos he sent are any indication, this looks like it could be one of the nicest Pup’s we’ve seen yet. All the workmanship appears to be neat and clean, and Dan hopes to be done in time for the summer flying season. Dan is also responsible for some of the building tips in this issue. Think ALTITUDE, Dan!


Several builders have suggested a general Sky Pup/Sport Flight update, so…here goes.

Since it was introduced in 1983, over 1600 sets of plans for the Pup have been sold. Approximately 85% of these are in the U.S., with about 10% in Canada and 5% in other foreign countries. We know of about three dozen Pups which are completed at this time. Undoubtedly, there are many flying that we haven’t heard about. Conservatively, 250-300 are under construction, and the start/finish ratio seems to be going very well. Builders comment that the Pup construction is relaxing and fun, and that it seems to be a very “do-able” project compared to most homebuilts.

We also get frequent inquiries about the “next model” or encore to the Pup. While we have no intentions of doing a Pup “re-hash”, we’re always doodling with new ideas. Up to the present, our engineering consulting business has kept us too busy working on other people’s designs to spend much time on new ones of our own. We have taken a couple of our ideas to advance design stages, but have not constructed any prototype because of a lack of clear input on the desires of sport flyer/builders. If you have ideas or design objective for an aircraft that you’ve been waiting to see, we encourage you to send them along. We can’t design your dream machine until we know what you want!

Building Tips

The following are some of the suggestions and tips which have been sent to us by Sky Pup builders. Pleas send us any others you have found to be helpful.

1. Several builders have reported good results with thinning the polyurethane varnish prior to applying th finishes to their fabric. The thinner varnish apparently “wets out” the fabric more readily and saves in weight build-up on the total finish.

2. For those who wish to avoid the lock washers normally used on the axle attach U-bolts, coarsed threa nylon locking nuts are available at many hardware stores. NOTE: The substitution of hardware store materials is not endorsed in any other place in the construction of the Sky Pup.

3. Two builders have recommended cellophane tape as a substitute for wax paper on nailing strips and other fixturing materials where it is necessary to avoid epoxy bonding. The obvious advantage is that the tape can be positioned and will remain in place for many jobs.

4. A suggestion for simple, inexpensive clamping (such as is required when bonding the spar caps to the foam cores of the empennage spars) is as follows. Clamp blocks are positioned at the desired station above and below the work. Rubber bands are used on each side to squeeze the blocks tightly an achieve the necessary clamping action.

5. When cutting the trailing edge stock for the wings and control surfaces on a table saw, a blade angle o 10-12° is said to produce the desired taper correctly on the first try.

6. When using staples to attach gussets and D-skins during the bonding process, blunt staples are less likely to cause splitting of the material beneath the plywood than chisel point staples. This is especiall important when attaching the D-skins to the leading edge strips and the spar caps.

Changes & Modification

AIRSPEED INDICATORS—We view the airspeed indicator as a top priority item in the list of instrumentation possibilities for the Pup, since speed control can be so important to safety. Those builders, who for any reason have made changes to their Pups which could allow them to attain higher speeds should be especially vigilant to stay below the maximum structural cruising speed unless in smooth air. (Please note that the max. structural cruising speed is not the same as the redline speed…it’s lower!).

The best instrument is only as accurate as the installation of the sensing source. Two varieties are commonly used: the pitot/static type and the generator type. Many ultralight owner pilots honestly believe that their machines have stall speeds in the 12-15 mph range simply because that’s what their indicators say during the stall. Many installations are made with complete disregard of slipstream and angle of attack consideration and are not real airspeed measuring devices even though they may have some value as a reference guide. Th sensing source must be located in relatively undisturbed airflow in order to have accuracy. The logical location on a tractor aircraft (like the Pup) is ahead of the wing and well outside the propeller slipstream.

The most inboard wing location for avoiding the slipstream on the Pup would be just inboard of the wing attach joint. This location may still give some irregularities in high angle of attack or high angle of yaw conditions. It does, however, avoid the problems associated with disconnecting the sensing source whe removing the wings. The tubing or wires between the sensing source and the instrument may be routed insid the D-cell of the wing, but care must be taken to avoid creating weak spots by over-large holes through the skins.

The preferable locations would be on the outboard wing panel. Some builders have made removable “booms” for the pitot or generator unit so that the risk of damage while handling the wing panels is reduced. One builder solved the electrical connection problem by attaching the sending wires to the upper and lower win attach fittings so that the connection is automatic when the wings are attached to the center-section. After any installation is made, it should be calibrated by making timed passes between landmarks a known distance apart. Passes should be made in at least two different directions (into and with the wind) to compensate for wind effects on the aircraft’s ground speed. Obviously, the more calm the conditions, the less chance of error in the speed checks. Builders who live anywhere in the mid-west will find that section line are a very convenient reference as landmarks, but the distance between major ones can be obtained b measurement from any sectional chart.

Ultralights, in general, have gone overboard on un-needed instrumentation. Airspeed indicators are legitimate addition, though, and will help you stay inside the design envelope.


Newsletter No. 10                                                                                                                                                                                                      January, 1986

Howlings In the Litter

Parachute Attachment Ideas

Wing Gap Covers

Building Tips

Sky Pup Historical Trivia



SKY PUP NEWS is a quarterly newsletter for builders of the Sport Flight “Sky Pup”. The purpos of the newsletter is to provide for the open exchange of information and to encourage builders t share their experiences of building and flying the Sky Pup. Beginning with this issue, the newsletter will be written by Sky Pup builders and enthusiasts. Unless specifically stated, all ideas, suggestions and building tips are strictly the opinion of the contributor and have not bee approved by Sport Flight Engineering Inc. No warranty is made as to the airworthiness o suitability of modifications or building tips. When in doubt, you should follow the plans as clos as possible and contact Sport Flight Engineering if you have questions.

SKY PUP NEWS is compiled and distributed by Dan Grunloh…Rt 2, Box 82, Potomac, Illinois, 61865. Subscriptions are $7.00 per year ($10.00 overseas) and will include four issues. This issu is being sent to all 1985 subscribers so everyone will have a chance to be included. Please send your comments concerning the type of material you would like to see in future issues. I have collected enough material for this first issue, but I need to receive additional articles, ideas and photos from you the subscriber if the newsletter is to be a success.

Howlings In The Litter

This issue will begin with some of my own ideas, opinions and observations. Next time lets hav someone else take their turn at “howling in the litter”. For my own part, I realized when I started building my Pup in late ’83 that the design would become a classic. Most homebuilt ultralight before that time were modified hang gliders. Many other homebuilt designs are not actually ultralights and are much more expensive. I believe the success of the design will be difficult to challenge until someone comes up with building materials cheaper than wood and foam. The possibility of doing your own repairs (at low cost) will be invaluable as manufacturers of other kitbuilt planes go out of business and no longer supply replacement parts.

I first met the prototype Sky Pup and it’s designer at Oshkosh ’83 where I was working as a ultralight judge. We gave it an award for “Outstanding Engineering Innovation”. It was the first such award given and candidates in recent years have been harder to find. At Oshkosh ’85, I spent a lot of time with Jerry Coppock and other Sky Pup builders. I remember some long “bull ssessions” that went late into the night. Next time we will organize a group camping area and have our own Sky Pup “headquarters”.

Many builders still ask about changes and modifications. Even I’ve been tempted by the though of spoilers for glide path control. Any change must be carefully checked for it’s effect on structural strength and on aerodynamics or flying characteristics. Changes in the airfoil, landing gear arrangement, wing structure, and such cannot be made without a complete redesign of the aircraft. It is basic truth that the best aircraft are optimized for specific design goals. For the Pup, it was the combination of low cost and excellent performance. In contrast to flying machines buil by “rule of thumb”, a well designed aircraft includes only the materials needed to meet the design goals. All the extra “stuff” adds cost and weight and reduces performance.

If you are thinking about a minor change or modification, please check with Sport Fligh Engineering first and try to devise methods which can be used after the airframe is completed so others may benefit from your ingenuity. If you were to talk with builders who are already flying their Pups, you would find that most proposed improvements are simply not necessary.

And now a message for slow builders like myself. If you don’t have a heated workshop or only work irregularly on the project, it can take a couple of years to build. The prototype took 700 man-hours to construct. For first time builders like myself, the most difficult decisions relate to clamping, fixturing and alignment. Each builder must make these decisions based on his skill and available equipment. I was astounded by the ingenuity and variety of methods being used by Sky Pup builders. It’s obvious that each Pup is unique because each is built a little differently. I you are still building when you thought you would be flying, don’t be discouraged. Lots of Sk Pups are still under construction. A large number of Pups, including my own, are nearing completion and will join the litter this year.

I hope that as more Pups are completed and flying, we will have more articles on the flying and social aspects of pupdom. Eventually, we may try to organize some local or regional fly-in specifically for Sky Pups. Write and tell us about your flight experiences or the performance with your particular engine. For instance, the prototype has reportedly flown for 3 hours on 2.5 gal. o gas with the Rotax engine. Is there anyone out there flying who can match or exceed that record?

Parachute Attachment Ideas

As you may realize, the Sky Pup was not designed for a parachute attachment point. The shock loads on deployment are probably greater than any other load the Pup would be expected to endure. No one can guarantee that any method used would be totally satisfactory. However, if your wife insists that you have a parachute, then you must have something to hook into. At a Sky Pup builders forum at Oshkosh, someone suggested that the seatbelt bolt be used for the attachment. A hardwood block could be inlayed between the wing support members for reinforcement. I extended the antipeel fiberglass to include this area, though I haven’t yet decide how to attach the caribiner to the bolt. Another possibility is at the landing gear and seat crossmember area. A webbing loop, as used on hang gliders, might be able to pass under and around these two members. Some experts have stated that a Kevlar bridle will absorb some of the opening shock better than a steel cable. The decision to deploy a parachute should be based on whether or not the aircraft is controllable. Once the parachute is open you lose all control and may drift into powerlines or other obstacles. Please send your comments.

Wing Gap Covers

1. The prototype used an aluminum sheet metal strip joined under the trailing edge wit screws. The only reported problem is that the metal may tend to chafe the fabric. Steve Wood says that it is not critical if the covers tend to sag away from the fabric on the underside of the wing.

2. Jerry Coppock used white vinyl siding (smooth side out) held in place with snaps. His covers seem lighter than any other method I’ve considered. Vinyl siding, like aluminum sheet, cannot be rolled up for storage when not in use.

3. I’ve seen a Mitchell B-10 with a strip of naugehyde (seat cover fabric) wrapped around the wing with Velcro under the trailing edge to join the ends. This method would probably result in a greater weight increase but would eliminate the problem of chafing of the fabric.

Building Tips

1. Several builders reported they pre-laminated the forward fuselage upper longerons to the required curve using a simple jig. This ensures that both sides are identical and simplifies their installation.

2. I joined the aft ends of the fuselage sides with the upper ply gusset and skid block befoer the aft fin spar and side gussets were added. With this method, the joining strips can be sanded to achieve the best possible alignment of the aft fin spar and the front stabilizer spar mounting holes.

3. One builder stated that his plywood sheets for the leading edge were enough over-size that they were bonded in place as a continuous piece from upper spar cap to lower spar cap.

4. Leading edge plywood splice doublers were added to the outside of the plywood by one builder. This is easier than undercutting the splice noseribs and inlaying the doublers. The resulting bulges would probably not be a problem.

5. Hotwiring the underside of the intermediate centersection noseribs was a problem for me. The procedure worked fine but resulted in the ribs being undercut too much. It’s possibl to end up with a compound curve to which the plywood cannot conform. I suggest removing material gradually with frequent checking for the best fit.

6. At the insistence of several “wood experts”, I decided to use white ash instead of maple for the landing gear spring. Ash is lighter, not quite as strong, and more springy than maple. I’ll let you know how it works out. Because it can be difficult to find a really good piece of maple the required size, it would be nice to have an alternate method of lamination from smaller pieces. I’ve been told that epoxy is not used in propeller lamination because of excess rigidity.

7. I decided to steam and bend the wingtip cap strips to reduce stresses in the wood and make them easier to bond into place. If you try this, remember the secret is the heat. Once the wood reaches the necessary temperature, it will bend easily and it will stay bent when it cools.

8. Most fabrics, including sheath lining, tend to shrink more in the lengthwise direction tha perpendicular to the bolt of the cloth. For best results, this difference must be kept in min when applying the fabric to the airframe.

9. Jerry Coppock sends the following suggestion for windshield installation. The windshield should be hinged so the direction of the airflow from the prop will tend to hold it close while in flight. (Hinge on the right side for the gear-drive Rotax and on the left side for the belt-drive Cuyuna).

Sky Pup Historical Trivia

The first and only cartoon which I've seen about the Sky Pup is reproduced here for those who may have missed it. It was seen in Glider Rider magazine, July 1984.

Our thanks go to the artist Ken Johannessen and to the publisher Tracy Knauss.


The state of Michigan could claim the title “The Land of the Sky Pup”. In 1985 there were more subscribers to Sky Pup News from Michigan than from any other state. As many as 18 Sky Pup may be under construction in that state. California ran a close second.

For a description of a method for covering the wheels with fabric, see the following article; The Wheel Thing by Frank Beagle, EAA Ultralight magazine, March 1984.

News from Sport Flight Engineering is that a new design is in the works. I have no details abou the new design or even if a prototype is under construction. Possibly future issues of the newsletter could include a paragraph or two from Sport Flight.

I would like to include information in future issues about the different engines that might be use for the Sky Pup. If you are flying with an engine other than the Rotax or Cuyuna, please sen some details so we can share the information.

I want to extend my personal thanks to the following builders who sent letters of encouragemen and ideas for the newsletter; Raymond Maynard, Irving Gitten, Ken Hayward, Tom Anderson, Donald Diggs, Paul Pontis, August Reil, Ken Thompson, and Jerry Coppock.

Original Newsletters edited by Sport Flight Engineering (issues 6-9)  and Dan Grunloh (issue 10), electronic edition compiled by Edwin Lelieveld and Roger Ford.

Sky Pup News

Newsletter No. 9                                                                  October, 1985

Another Flying Pup

Konig Powered Pup

Changes and Modifications


Oshkosh ‘85


Since the introduction of the SKY PUP NEWS in October of 1983, this newsletter has served to make builder aware of building tips, revisions and suggestions. It appears that most of the major items have been addressed and that the Sky Pup has become established and accepted as the leading plans-built ultralight to date. We feel that the time has come for the newsletter to evolve from a building-oriented periodical to on covering the social aspects of Pup-dom through which builders can keep one another informed of thei progress. Due to the completeness of technical information contained in the previous newsletters Sport Flight has decided to make this October, 1985 issue of the SKY PUP NEWS the last one written entirely by us.

Dan Grunloh (SN2028), Rt.2 Box 82, Potomic, IL 61865, has volunteered to be one of the coordinators of builder-written Sky Pup newsletter if reasonable interest is shown. This newsletter will concern itself mainly with the social aspects of Pup builders and flier, i.e. howlings within the litter. We feel that this will give many builders an opportunity to write about their Pup projects. Also, the newsletter will keep builders abreast of th future fly-in and “bull” session schedules. If you are interested in a continued Sky Pup newsletter pleas contact Dan and help him get off to a great start.

Discontinuation of SKY PUP NEWS does not mean that Sport Flight is leaving the ultralight business or abandoning Sky Pup builders. In fact, we wish to emphasize that Sport Flight will continue to offer builder support along with plans sales and other technical services just as we have in the past. We have enjoyed putting together the SKY PUP NEWS over the last two years and would like to thank the many builders wh have sent letters and photos to us. We would like to encourage builders to continue to send photos of their partial or completed Pups to keep in our scrap book.

Those subscribers who have already paid for their 1986 SKY PUP NEWS subscription will find a refund check enclosed. Back issues of the 1984 and 1985 SKY PUP NEWS will still be available from Sport Flight for $6.50 per year while supplies last.

Another Flying Pup

Phil Hartzell of Aurora, Nebraska made the maiden flight in his recently completed Pup (seen in the photo a the top of the next page) near the end of July. SN 1746 was covered using the Ceconite 7600 process and finished in yellow with white trim using Ureglo urethane paint. An irrigation pipe equipped with a J-3 style gauge (cork float with wire) was used for a fuel tank. Phil opted to use T-88 adhesive throughout the structure of his Pup. Provisions for a radio were made since Phil is a HAM radio operator. He is also the owner of Hartzell Auto Interiors, so naturally his Pup is equipped with the “Hartzell Super-Duper Deluxe Tuck Seat”!

“The Pup is fun to fly” reports Phil, having logged several hours the last we heard. He tried a steerable tai wheel but converted back to the tailskid because “…it’s more romantic”. Like many homebuilders, Phil like building as much as flying and can’t wait to get started on a new project.

Konig Powered Pup

A nice installation of a Konig 3 cylinder engine on a Sky Pup has been completed by Newton Borden (SN 2625) of South Weymouth, Massachusetts. The engine is equipped with an electric starter and a direct drive groun adjustable propeller, yet, reportedly weighs less than either the Cuyuna or Rotax powerplants. The bottom fins on the lower two cylinders were trimmed and the exhaust pipe was modified for this installation.

The neatly designed cowling, shown in this photo, incorporates a hatch which allows access to the battery, fue tank and instruments. Newton plans to attach a windshield as soon as some hinge details are addressed. This should prove to be quite an interesting and unique Pup variant when completed.

Changes and Modification

Due to the number of builders who have asked about the addition of windshields to their Pups, a brief discussion of this modification is in order.  The addition of a windshield to any Rotax powered Pup will render it too fast to meet the F.A.R. Part 103.7 paper test. Since the presence of the windshield awards the aircraft a lower net drag factor (regardless of it true aerodynamic value), a tail wheel or other device can be added to meet the paper test if desired. Cuyuna powered Pups will meet the speed limit requirements with a windshield installed and no additional modifications.

Since entry and egress from the cockpit is through the opening ahead of the wing, any windscreen will need to be removable to accommodate easy access. As a rule of thumb, the top of the windshield should meet the wing centersection at a point below the leading edge to avoid possible turbulation problems. 1/16” plexiglas is entirely adequate, but watch the weight of this and any other additions.

In our estimation, the only two factors which warrant serious consideration of a windshield installation ar bugs and bitter cold. The first problem can be easily solved by wearing a helmet with a face mask, while the second probably cannot be solved entirely by any method. Consider the extra weight, cost and building time carefully before deciding to add a windshield.

Oshkosh ‘85

We would like to close this newsletter with a unique photo of “Gerry’s Dog House”, as seen at Oshkosh ’85 (compliments of Dan Grunloh). This Pup (SN 1173) is owned by Gerry Coppock of Escanaba, MI and wa featured in the April 1985 SKY PUP NEWS. Gerry reported that a large crowd of Pup builders and would-b builders kept him company throughout the week long event. The photo shown below reflects the quantum step that aviation has taken in the years since the developmen of beasts like the Concord. Maybe next year more builders will be able to bring their Pups to Oshkosh enabling the public to experience a real LITTER!

As we sign off in this the final issue of SKY PUP NEWS, we want to express our thanks to all the enthusiasti builders that have made the Sky Pup a very enjoyable project for us. It is our hope that the fraternity of Pu fans will remain active and united for many years to come. We encourage any builders who are passin through our area to drop in and visit if possible—we really enjoy meeting you. Let’s all do what we can t keep the concept of simple and low-cost flying alive for future generations to enjoy.

Sky Pup News

Newsletter No. 8                                                                        July, 1985

Long Time Coming

EAA Chapter 560 Pup

Building Tips

Spar Delamination Inspection

Engine Side Thrust

Control Surface Deflection


SKY PUP NEWS is a quarterly newsletter for builders of the Sport Flight “Sky Pup”. The purpose of th newsletter is to make builders aware of revisions, suggestions and ideas which are brought to our attention. We solicit your input in the form of photos, ideas, and time or money-saving tips. Please share your progres and comments by sending them to Sport Flight, c/o NEWSLETTER.

Subscriptions to SKY PUP NEWS are $12.00/year (foreign add $6.00, Canadian add $2.00). All subscription are based on a calendar year, i.e. not from date ordered. Please use your plans Serial Number in al correspondence with Sport Flight, and specify which calendar year your subscription fee is for.

Long Time Coming

One of the most interesting stories behind a Sky Pup project came to us from Jesse Buckle of Lockhaven, PA. Jesse is 70 years young and spent 40 of those years with Piper Aircraft in Lockhaven where he was a inspection supervisor. Through the years, he had accumulated a fair amount of stick time in Cubs but neve felt he had the resources to finance an aircraft for himself. After retirement and some other interesting projects (violins, steam engines, and an X-ray machine!) Jesse ordered his set of Pup plans and went to work in the basement. SN 1591 was completed and test flown on May 25 of this year. Jesse says the initial flights went very well with no trim adjustments needed. This Pup is yellow overall with navy blue leading edge on the wings and a black lightning stripe on the fuselage—not unlike the venerable Cubs which Jesse knows so well.

Jesse’s Pup appears to be very faithful to the plans with Cuyuna 215 and Manta reduction for the powerplant. A 2” steerable tailwheel was added as shown above with a “yoke” in the rudder cable (it appears that the line between the rudder cable and the tailwheel may be bungee or something with some give). Heavy-spoked steel rim wheels were used in place of the molded nylon variety. Jesse also made an airspeed indicator which involves a washer moving up or down a wire (sorry, no details available). Total cost of the project was between $2200 and $2250. Jesse had fun building the Pup and hopes to enjoy it for a long time to come. Our thanks to him for sending the photos and a fine article on the project from THE EXPRESS, a local newspaper.

EAA Chapter 560 Pup

In the last issue of the newsletter, we gave a progress report on the Pup being built by EAA Chapter 560 of Allegan, MI. Chapter president Lawrence Bloss was kind enough to send the photos below of the recently finished project. Power is the Lloyd two-cylinder—details of reduction and propeller are unknown.

Lawrence says they are enjoying the Pup and hope to have all the members fly it. Note highly visible sunburst paint scheme—a very nice touch!

Building Tips

The following are some of the suggestions and tips which have been sent to us by Sky Pup builders. Please send us any others you have found to be helpful.

1. Some builders have reported using an old-time building trick in the application of the wing D-skins. I order to obtain very tight skins (no wrinkles), the plywood is dampened a very small amount just prior to laying it into position. This can be accomplished with a moist sponge which is wiped over the outer surface only. The plywood will thus expand or “relax” on installation, shrinking back as the bond cures. The result is drum-tight skins.

 2. Two builders have reported the appearance of bulges between the nose ribs in the leading edge D-ski after the aircraft is completed. This phenomenon is caused by difference in pressure between th inside of the D-cell and the atmosphere (brought about by changes in temperature and ambient pressure). On aircraft which are already complete, venting of the nose bays can be accomplished b drilling 1/8 – 3/16” holes in each bay just ahead of the lower spar cap, and just outboard of each nose rib. I.E. the lowest point in each bay. If construction is still in progress, these holes may be added before fabric and finish are applied. After covering, holes can be made in the fabric with a solder tip a discussed for general drain hole installation.

3. Since our recommendation that epoxy be used throughout the construction process (see Newsletter No.5, October ’84), several builders have pointed out that the materials list should reflect the increase amount of epoxy needed. Most builders report a total epoxy usage of around 1-½ gallons, which shoul allow for a substantial amount of waste.

Spar Delamination Inspection

We were recently contacted by a builder who experienced a spar cap delamination on the centersection of his wing during the construction stage. The centersection was fabricated during the fall and winter and the stored in his basement until summer when he resumed work. Inspection revealed that the lower spar cap was delaminated from the foam core along its entire length with exception of the areas where gussets were bonded to it.

Several factors may have been involved, and the exact cause of the delamination is subject to some conjecture. The spar assembly was subjected to a rather dramatic change in humidity without the benefit of any protective finish—thus the moisture content of the wood went from one extreme to another. A moisture content rise would cause the wood to expand in each dimension, the most noticeable being length. A increase in length of the cap could cause it to bow away from the foam core (which is extremely stable wit regard to moisture content) thus causing a peel load along the bondline. This type of problem could also be aggravated by making the spar cap thicker than specified in the plans or using a too-small radius in th transition area at the fuselage sides.

No other caps on the centersection or the outboard wing spars suffered any delamination in this case. Al builders should inspect spars, especially those which may have been stored for any length of time withou protective finish on the wood and where a significant change in humidity may have been encountered. We have not heard of any other cases of this occurrence, but solicit input from anyone who has had s similar problem. The important point in this instance is that the builder caught the problem by visual inspection before construction continued, thus avoiding a dangerous situation with the finished structure.

Engine Side Thrust

All builders using the Rotax 277 gear-drive engine on their Pups should be aware that side- thrust setting is opposite the direction indicated for the Cuyuna installation in the plans.

This applies to any installation with a left-hand turning propeller, since the torque of the engine ants in the opposite direction of a right-hand turning propeller- To determine the rotation direction of any propeller, stand behind the engine so that the slipstream will be blowing in your face--the direction of movement of the prop at the top of the prop arc is the direction of rotation. E.g., if the propeller is rotating clockwise as viewed from behind, the propeller is right-hand.

* c optional Rotax installation drawing details the changes necessary and should be on hand for anyone using this engine. An engine installed with sidethrust opposite the correct direction will cause an increase in rudder deflection required for trimmed flight, a potentially dangerous situation. Builders using engines other than the Rotax 277 or Cuyuna 215 who are not sure of the proper sidethrust should contact Sport Flight before making the installation.

Control Surface Defections

It has come to our attention that some Sky Pups may have inadequate control surface travel caused by improper shaping of the foam along the hinge-lines. The radius of the corner at the hinge-line should be 1/16 to 1/8'' in order to prevent the hinge from binding before full travel of the control surface is obtained. Care must also be taken when attaching the control surfaces so that the hinge material itself is flat against the foam and ''crowding'' the movement.

The necessary control surface deflections are as follows:

Elevator -- 27 degrees of up of and 15 degrees of down travel

Rudder -- 30 degrees of travel in each direction (left and right)

These values are minimums, and are referenced from the chordline (centerline) of the fixed stabilizer portion of the tail-plane. Additionally, the rudder should not be able to contact the elevator when deflected fully. All Pups should be checked to insure that the above control deflections are attainable before flight. Inadequate control travel could cause serious control deficiencies. Again, when in doubt, please give us a call.

Sky Pup News

Newsletter No. 7                                                                                                                                                                 April, 1985

Michigan Sky Pup

Survey Results

Building Tips

Important Points


SKY PUP NEWS is a quarterly newsletter for builders of the Sport Flight “Sky Pup”. The purpose of th newsletter is to make builders aware of revisions, suggestions and ideas which are brought to our attention. We solicit your input in the form of photos, ideas, and time or money-saving tips. Please share your progres and comments by sending them to Sport Flight, c/o NEWSLETTER.

Subscriptions to SKY PUP NEWS are $12.00/year (foreign add $6.00, Canadian add $2.00). All subscription are based on a calendar year, i.e. not from date ordered. Please use your plans Serial Number in al correspondence with Sport Flight, and specify which calendar year your subscription fee is for.

Michigan Sky Pups 

Gerry Coppock of Escanaba, MI has recently completed and flown his Sky Pup (SN 1173). Gerry is a low-time pilot with about 12 hours in “real airplanes”, but reported no difficulties in test-flying his Pup after careful taxi testing and a few low-level hops at the local airfield. Gerry’s Pup is built pretty much per plans with the exception of a steerable tailwheel for hard surface operation and use of Ceconite “7600” fabric covering process rather than the sheath lining specified in th Sky Pup plans. Fir was used throughout the airframe instead of just in areas where it is required. SN 1173 is white overall with a “Red Baron” Snoopy on the vertical tail for accent (see photos below).

A couple of interesting innovations which Gerry added were Lexan “see-thru” bombay doors over the floor opening, and the use of vinyl house siding material with snaps for wing gap fairings. Engine is the Cuyuna 215 with Manta reduction drive and Ultra-Prop. No trim problems were encountered and performance is very good. Gerry told us that the Pup “exceeds all my expectations and sure is FUN to fly”. Given the relatively close proximity to Oshkosh, maybe we can talk Gerry into bringing it to the big Fly-In this summer.

Another interesting Michigan Pup project was reported to us by Lawrence Bloss of Allegan, MI through newspaper clipping he sent. It seems that EAA Chapter 564 is building a Sky Pup which at last report (late January) appeared nearly ready for fabric cover. By using the “divide and conquer” approach to the construction, the airframe was built by various individuals in the Chapter over a period of about two months. Quoting from an article in the “Twin Cities News”…Ed Crandall and Pete Bloss bought the plans for the Sky Pup in May, but…it was November before enough materials could be rounded up to really get under way…in January actual assembly of the major components is taking place…Certainly the project has helped to fuse the members of Chapter 564 into a single force capable of great accomplishments.”

The members plan to use a Lloyd engine with a 54” propeller and think that they will meet their original goal of building an ultralight for under $1000. We hope to hear an update on this project soon—it should be a inspiration to other Chapters in need of a low-cost project which can generate plenty of interest among the membership.

Survey Result

Those of you who received the January newsletter found inserted a questionnaire regarding what type of aircraft Sport Flight should develop next. We’re happy to report that the response was very good (over 35% return of questionnaires) and we can present you with the results. In a nutshell, your preference is for a one- or two-seat, high-wing, tractor-engined, taildragger homebuilt available in plans or possibly partial kit format. LOW COST is the most important design consideration, with portability, short building time, one-man setup, and beginner suitability ranking high. Wood and operations associated with working it seem to be the most popular and expected. We interpret this to mean that most of you must like your Pups pretty well, but may have in mind an aircraft with a little more cross-country capability. We’ll keep you posted on new developments.

Building Tips

The following are some of the suggestions and tips which have been sent to us by Sky Pup builders. Pleas send us any others you have found to be helpful.

1. When using staples to obtain gluing pressure under plywood gussets, one of the problems often encountered is removing the staples after the bond is cured without gouging or damaging the gusset material. Where nailing strips (as discussed in the plans) are not necessary for even distribution of pressure, twine, cord or plastic strapping material can be used underneath the staples. When the bond is cured, the cord can be used to pull the staples loose. Even the ones which do not come completely out can be easily removed with pliers without touching the plywood.

2. Among the many alternate methods (to hot-wiring) of cutting wing ribs and other foam parts to shape is the use of an electric knife. This is the same type used for cutting meat in the kitchen, and is reported to yield a very smooth cut surface without the hassles associated with hot-wiring and bandsawing.

3. Several builders have added fairings around the intersection of the vertical and horizontal tail surfaces. These were omitted from the prototype simply to save construction time, but can be very effective in increasing rudder power (by sealing the gap at the base of the vertical tail), and improving th appearance of the aircraft. Additionally, they prevent rain and insects from entering the aft fuselage bay. Fairings are fabricated of shaped foam blocks with fabric covering, but should not be added until after the aircraft has been test flown. This allows adjustments in stabilizer incidence to be made for correcting any pitch trim problems.

4. Several builders have encountered difficulty in obtaining taut fabric covering on their Pups while using the materials and fabric outlined in the construction text. The problem stems from intentionally leaving the fabric somewhat loose on attachment and anticipating some shrinking effect (as is common with aircraft dopes) when the polyurethane finish is applied. Polyurethanes are very non-shrinking, and wil actually loosen the fabric somewhat when applied by either brushing or spraying. For that reason, care should be taken to attach the fabric as tightly as is reasonably possible to begin with. Additional shrinking with the heat iron should take care of any minor wrinkles which remain. Excessive tightening of the fabric could result in distortion or damage to the structure, but we haven’t had any reports of this problem.

Important Points

In talking with builders daily, we have become aware of some items in the plans which are frequently misunderstood or need to be emphasized. It seems that those who most need the additional explanation are those who probably do not subscribe to the newsletter, so forgive us if we are “preaching to the choir” so to speak. We all need to listen carefully when talking to other builders so that if we detect some confusion or lack of concern over critical areas we can help resolve a potentially dangerous situation.

Many builders neglect to taper or shape various components as shown in the plans, thinking that the taper i only for weight reduction and not worth the effort. In almost all cases, weight savings is a secondary consideration in the shape of the part. A good example, and an item which has been mentioned to us several times is the taper on the ends of the wing attach bearing blocks (at the joint). The taper is essential fo reducing stress concentrations at the termination of the block and providing a smooth transfer of load from the block into the spar cap. Gradual transitions in cross-section are a structural engineer’s method of avoiding stress concentrations in a structure. Often, the stress at an abrupt change in cross-section is amplified by a factor of two or three over the stress predicted by simple analysis. When the plans specify fish-mouth gusset or taper transition on a part, the integrity of the structure would be jeopardized by neglecting to follow the plans.

Other items which are very shape-critical are the fish-mouthed gussets at the attach points on the wing an empennage spars. Do not be tempted to cut them with square ends to save time since this could cause “notch” effect in the spar structure. Wing attach fittings should be tapered as shown also.

One point which was possibly not made clear enough in the plans and has caused considerable confusion is planform of the outboard wing spars. These spars are constant width for the first 15 inches from the joint and taper after that to the tip. The taper is on the rear face of the spar—the front face of the spar is a straight line from wing tip to wing tip. Some have attempted to taper the spars evenly on both the front and rear faces. Technically, this should cause no loss of strength since the net load carrying member is unchanged, but it wil certainly complicate the fabrication and attachment of the nose ribs. The leading edge attachment won’t b very easy to fit either!

Although the plans allow locating the wing 1-½ inches above the nominal dimension, tall builders should be aware that making this change can provide somewhat limited extra head room. When the wing is moved up, the angle of the seatback becomes more upright (since the seatback still has to meet the wing trailing edge),

thus reducing the benefit sought. Tall builders should leave the lower surface of the wing uncovered betwee the two fuselage side ribs to gain the maximum amount of head room.

Pitch trim adjustments should be made by changing the incidence of the horizontal stabilizer. Raising th leading edge of the stabilizer will effect a nose down trim change, while lowering the leading edge of the stabilizer will effect a nose up change. Either type of change is accomplished by varying the length of th spacer between the front spar of the stabilizer and the fuselage longeron attach hole. Stacking washers up t three deep is acceptable, but the attach bolt should always be snug after the change is made. Some builder have attempted to solve minor trim problems by adding springs or bungees which bias the elevators one way or the other. These should be avoided since they generally detract from control “feel” at the stick and ar unnecessary weight items.

Please remember to send us questions, comments and suggestions as your projects take shape. Whe sending photos, black and white glossies are preferable since they can be used in the newsletter more readily. Color shots with good contrast are fine if they’re more convenient. Keep those photos coming!