Q-talk 26 - COMPOSITE TIPS
- Category: Q-Talk Articles
- Published: Thursday, 28 February 1991 06:11
- Written by Jim Masal
- Hits: 1122
I received a phone call from QBAer Brian Martinez of Quartz Hill, CA. He had a fuel system question that I consider to be very good. He wanted to know if he lined his composite fuel system parts with a chemical resistant vinyl ester (two words, not one!) would it then be safe to use auto fuel without threat of dissolving the resin matrix. He is right on!
Particular types of vinyl ester have been developed to yield great chemical resistance properties favored by the petrochemical industry. Vinyl ester is made from reacting an epoxy resin with an acrylic or methylacrylic acid. It is then said to have an epoxy "backbone". The plastic airplane builders could take advantage of this and "line" the inside of their fuel systems while building (I don't know what to tell you boys that are already built, there is a rubberized coating out there that you can "slosh in" but it is hard to take a full grown plane and tumble it to coat everything).
I want to make it clear, that just "any ole" vinyl ester won't work. One needs to use something like Dow Chemical's Derakane 470. This resin is formulated to resist petrochemicals like alcohols. The only drawback is that it is a little more brittle than other vinyl ester resins, so one could use it as a liner to the epoxy. It's epoxy backbone permits great bonding to an epoxy resin matrix.
The thing that one doesn't do is apply wet vinyl ester over wet epoxy, or vice-versa. Depending on which resin you lay up first, you want to either advance the cure to the "green" stage or B-stage (not completely cured but tacky to the touch) then come back over the top with the other resin. A clever trick is to sprinkle liberal amounts of cotton flock over the wet surface of whichever resin you lay up first. Let this cure completely and brush or vacuum off the excess. Then come back over this fuzzy surface with your other resin system and this way you can achieve a great mechanical bond and don't have to baby-sit the cures waiting for that tacky state. In addition, make sure that it is two wet layers of vinyl ester and chopped strand glass mat you use as the liner. Brian, thank you for your inquiry.
A closing thought. Go back in the educational section of the plans and read where the author (Rutan's boys not Sheehan or Jewett!) tells us to keep the fibers in our layups as straight as possible. Fiber reinforced composites are poor in compression (relative to tension) and the fibers fail in a type of column buckling. Note the limiting loads in an airplane design are compressive (WINGS!). So you would consider each individual fiber as a little column. Now if these fiber columns are "bent" they'll take less load. This can be demonstrated by taking your index finger and loading it with the palm of your other hand when it is straight and then when it is bent. Which can withstand the most load?
Sooooo ... keep those fibers laid as straight as possible?
Thanks guys, until next time ...
Enclosed is my $20 for the '91 subscription. Regarding my bird, it still has not been off the ground. Although I take it out of the hangar and taxi it all over the airport every few weeks (much to the chagrin of the local controllers, I'm sure) I just don't intend to really fly it. It isn't that I don't have faith that it won't fly, it wants to and I'm sure it will. It is just that I now have a Cessna 182 that I can fly anywhere, anytime that I want to, and so why should I take a chance at my stage of life in an unproven plane?
By the way, I still have full-scale drawings available of my vertical opening canopy hinge with quick release pins for anyone who wants them. I'm only asking a donation of $2 and an SASE. I'll even throw in plans for my "open with a coin" cowl latch plus other ideas as appeared in earlier editions of "Q-TALK".
As my plane is for sale, I would appreciate it if you would run the following ad in the next appropriate edition.
Saylor S. Milton
1100 Cliff Ave., Fillmore, CA 93015
Sorry I missed the wine & cheese at Oshkosh. Some Florida friends arrived for a very brief visit. As always at Oshkosh one needs to be able to bi-locate if they are going to attend all of the good stuff. So far I don't know how to do that yet.
My project has taken a different turn. It is going to be a conventional design with wing and tail but use the Q200 fuselage. This has turned out to be a monumental task. I highly recommend Martin Hollmann's Modern Aircraft Design - Vol. 1. This book contains all the engineering info about aircraft materials you need. Also included there is a Composite Wing Design program which is very useful.
I have completed the aerodynamic design and am presently working on the structural design of my project. Landing gear is next and finally construction.
This will be a 60 sq. ft. wing of 23 feet span using the NLF(1)-0414 airfoil. This is a very low drag airfoil at high Reynolds numbers. At 200 mph my computer says the drag is .0032 while the LS(1)-0417MOD is about .0064. What this will mean on real airplanes is yet to be determined. Tricycle gear, 40 gallons of fuel and about 200 mph cruise with the 0-200 is calculated. I wonder if it really will do what the computer says? Most of my work to date has been studying aerodynamics and structures. As well as writing and using different computer programs to analyze performance and structures.
My structures program says that the shear stresses are the highest on the Q200 main wing at the leading edge and just in front of the rear shear web. That is where there are only two layers of BID. I would inspect these areas carefully at annual. Of course, the accuracy of my computer program is totally unproven at this point.
If Larry Koutz puts his sparrow strainers above the elevators they will be in lower velocity air and less effective. It sounds like he needs larger strainers or more angle of attack (pulling downward) on his present strainers. The downward pull of the strainers is used to counteract the upward pressure on the elevator. If the elevators float up at high speed, the nose pitches down and you need more effective sparrow strainers.
Jim, I am quite sure that you are now in charge. In fact all of these new people should just naturally refer to you as "Mother". After all Quickie Aircraft probably used that term often in reference to you.
See you at SUN & FUN '91.
Steve Whiteside, Ringwood, NJ
When my dad would write me in college, he would always include some pearls of wisdom and a little money. Later he would ask me what I thought about whatever he happen to write about. I once told him to "Forget the trash. Just send the cash." Well, I am sure it won't take a rocket scientist to figure out what happened next, suffice to say, I learned a good lesson ..... that was until I met you. I now find that sending the cash is not good enough, it must include some trash.
I have been working on my Avid Flier for about the last nine months and will be complete about Feb. or March. I have learned a lot and was able to use a lot of what I had picked up from building the Q to make improvements on the Flier.
When I do get back to the Q, I would like to look at the possibility of a new canard, mine has the old GU. I was able to find a new canard plan in the Q-TALK (As I write this I can't remember who to thank for this without looking for the drawing, but I do thank him). I would like to try something new, retractable gear. I know there are some bright fellows out there that have already completed their Q's and can't go back to that point, but have some ideas on the retracts. I even remember, at one of the tent forums Mr. Swing and Scott stating they had worked on this but didn't see enough demand to make it profitable. Why don't some of you send in your thoughts and maybe drawings and let us dumber workers try to build them. I feel that I can build anything, it's the thinking that confuses and humbles me.
Dale Warnix, Camden, AR
As a Johnny-come-lately member of Q.B.A., I offer my suggestions on the non-joining newcomers: First, there are some positive aspects. They have helped to make a market for unfinished projects that some of us had to give up. I once had to sell a Teenie Two project because of neighbor and landlord pressure. They may also be a source of new members for QBA once they learn the score. Since they seem to perceive you as a highly paid substitute for Gene Sheehan with nothing to do but further their new project, tell them you'll send them a letter which will clear up their misperceptions and convert some of them into good members. You might want to motivate them with a brief one or two sentence summary of the accident/incident history of these airplanes and name some of the fixes to be found (by them) in back issues. Let them know in a straightforward way that you cannot do individual research for material, which is available to all in the newsletters. Surely they don't want to build an airplane without all the information contained therein. You could even throw in a sheet of QAC plans changes. In this way, you might convert some good guys into QBA members, and save some lives and airplanes, and continue to be a hero.
With piles of white stuff all over the ground and the thermometer in a graveyard spiral it seems like a good moment to see if the typewriter needs a change to winter oil.
You may recall that I purchased Q-2 #2313 from Wes Foss after he decided to exercise the status of a senior citizen and watch from the sidelines. I had observed the construction of this plane from day one and was impressed with his amazing attention to detail and the quality of workmanship. Accordingly, when presented with the opportunity to purchase it, just after flying his time off, I sold my AA-1B Grumman and enrolled in the world of Plastic Pilots.
After much thought, reading, visiting and review decided to start out at once with the Tri-Q conversion and solicited the skills of Scott Swing. In due time the required components arrived and Wes pitched in to "manage" the project. We were able to rent a very excellent heated workspace so moved the plane from the RST FBO where it was hangared and started surgery. Being senior citizens and enjoying a nice warm project to keep us out of our houses, we have set a blistering work day from 09:00 to 15:00 with an option for coffee whenever a qualified tire-kicker stops by for a quality control inspection.
After two weeks of this frantic pace we have finished laying up the ten layers inside the cockpit and attaching the support brackets to accommodate the main gear when ready. We mounted a suitable piece of plywood on the engine mounts, after removing the Revmaster and now the plane rests comfortably on its nose. We performed the surgery needed on the belly with a six-inch wide cut full span, where with luck the main gear will repose. While on its nose it seemed like an appropriate time to cut off the wheels and contour the resulting surfaces to match the canard.
I was relieved to note that this was not a difficult task. We will now enter the cavity created by the belly incision and layup the required glass to bond in the aft attach brackets and complete building in the required reinforcements behind the seat back. We have also finished the layups on the main gear and will be able to start construction of its two mounting brackets this week. I am pleased to state that as yet I have had no reaction to the epoxy. I am very careful, use gloves and wash both hands and gloves often. We had an excellent epoxy pump, which made the mixing task a piece of cake. I still don't like cutting glass, it's a pain.
While on its nose we will complete the installation of the brake system including toe brakes and lines because it is so easy to work with the canopy off and the panel removed. Both are in my basement out of any harms way. Wes designed and fabricated a beautiful trim mechanism, which we have installed to manipulate the elevator. I am most anxious to see how it functions in flight. I have removed the pilot's throttle and replaced it with a quadrant fitted in the slot previously occupied by the left hand brake. I'm sure that this will be more comfortable and provide a stable platform for my forearm not unlike the armrest we find the control stick located. Plus after thirty years of driving all manner and form of military equipment, you tax payers provided me, I am sure it will feel natural. We have made measurements for the nose gear and see no problem with that after we return the bird to its level position. By the way, the quality of the gear, wheels, brakes, etc. Scott caused to be sent appear to be of excellent quality.
While the panel is off I relocated a few instruments and reduced the size of one to make space for a Loran. Space required a round one so I have an Apollo II Morrow 618C loaded with 20,000 waypoints. Something every Q driver needs and I added Mode C to his King KT76A, which should make me legal. I have spoken to Greg Zimmerman in Iowa City and Ed Schweitzer in Minnesota and received good advice. I'll keep you up dated and pix will follow when finished.
Here are some negative comments on a couple letters from newsletter #20. No spitting contest intended, just that some things don't ring right so here goes. First - Maury Cosman's comment and sketch showing pop rivets being used to pass the torsional loads from skin to the elevator torque tube. It's doubtful this can be done in conjunction with the Q-2 plans. Plans call for the lamination to be done with two layers of UNI at 45 degrees to each other. Anyone who has worked with UNI finds that it does not lay up well on compound or small radii surfaces. I would not try this technique on my elevators when going finale -- this technique requires a full size practice section to include use of the slot form core. Second -- M. Moreau, R. Dimond and J. Parnigoni from Canada who are enlarging rudder by 18% and installing compression springs between the rudder and the tailwheel "like most other tailwheel aircraft". Any change from the Q-2 plans concerning lash up of cables from tailwheel to rudder must be done only after careful evaluation of the rudder's lower hinge and bellcrank. For example: the CS23, lower rudder phenolic bearing, may have to be increased in dimensions and the Q2CSA10 (rudder bellcrank) may have to be "beefed up" to support the additional forces that would be transmitted due to these proposed changes. If your plan is to route the rudder cables direct to the rudder, etc., etc., "like other tailwheel aircraft" then my recommendation is DON'T do it. Stay with the plans. If your plane is hard to keep on a straight line during a landing roll then you have problems that are not related to rudder size or the control cable hook up.
Fred Wemmering, Fayetteville, NC
I am performing the first serious update of the Q-2/Q-200/Tri-Q flying roster since July of '88 (mainly because I had to re-type the entire thing -- transferring from Atari to IBM computer systems). Much of the data on existing entries contained on the roster is obsolete. I would appreciate it if those of you flying your craft would take the time to drop me a postcard or note containing the following:
Your Name, State, No., Aircraft Weight, Engine Installed, Top Speed Realized, Date of First Flight, Months to Build, Total Time on Airframe, Current Status (Flying or Non-Flying), Any Damage Sustained, and Brief Comments.
Many of you have first flown since the roster came out and are not on the roster at all. PLEASE SEND THE ABOVE INFO TO: Ted Fox, P O Box 23, Mansfield, OH 44901-0023. Roster copies will be available when finished for a self-addressed, stamped envelope.
Ted Fox, Mansfield, OH
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