Q-talk 159 - Waddelow Canard and Main Wing
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- Published: Sunday, 30 June 2013 10:04
- Written by Dan Yager
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by Leon McAtee
Quickie aircraft originally produced the Q-2 with what is referred to as the GU canard. It was soon discovered that if flown in rain, dirty, or with spanwise paint stripes that the aircraft experienced extreme nose down pitch problems. Vortex generators, dull sanded paint and Rain-X were all tried with various degrees of success to “solve” this problem.
Quickie aircraft eventually developed a new canard referred to generally as the LS-1. This canard used pre-made, tapered carbon fiber spars and the “non-critical” NASA laminar airfoil LS (1) 0417MOD. This airfoil is thinner than the GU and therefor would have required a more substantial spar cap to retain adequate strength. Quickie Aircraft decided that this would weigh too much and spent the time and money to develop the tubular carbon fiber spar in conjunction with their O-200 modification.
Things changed slightly when the Tri-Q conversion appeared on the scene. Since the canard on the Tri-Q didn’t have to support any ground or landing loads both the original GU and the new LS-1 canard designs were stronger, and therefore heavier than needed. In addition, a new set of carbon fiber spars from Quickie Aircraft Corporation were relatively expensive.
Mr. Waddelow being a mechanical engineer and Tri-Q kit owner decided to apply his talents to designing a new canard for his Tri-Q project. The following document is the result.
I am not recommending or advocating any particular method, technique, or practice. These documents are provided only for historical and/or academic purposes. The reader assumes all responsibility and liability for any use of the information herein. This includes my comments/Ed. Notes: which are in Italics.
Waddelow Tri-Q Canard And Main Wing
by Marc Waddelow
The enclosed information package contains the results of a computer design study for the Tri-Q main wing and sparless LS(1) 0417MOD canard, including stress analyses and lay-up schedules. This work does NOT apply the Q-200 canard although the main wing data does. Also enclosed is a detailed explanation of what these numbers mean. How they were derived, and the limitations on their use, along with several diagrams. I would like to take this opportunity to offer some of my own thoughts on aircraft design and provide some flavor for how all this came about.
I hold a BS (LSU, 1979) and MS (U.T. Austin, 1981) degrees in mechanical engineering. I presently make my living designing microprocessor software for an aerospace company. We stress analysis computer program, named ”Q2ANALYSIS” was written to aid in modifying my Tri-Q. My goal was to produce an aircraft with high altitude, 200 mph cruise capability. I selected a 150 hp dual rotor Mazda RX-7 engine that weighs about 70 lbs. more than an O-200, installed, wet. I designed 20” wingtip extensions to increase the aspect ratio and gross weight limit (1200 lbs.) and used the computer to design revised lay-up schedules.
First I ran the “design” program to determine the actual air loads. Then I came up with a trial lay-up schedule to determine the actual air loads. One or two iterations refined the final lay-up schedule pretty close. Early in the course of the analysis, I discovered that some relatively high stresses and stress concentrations in the QAC’s (Ed. Note: QAC = Quickie aircraft Corporation.) main wing lay-up schedule. I exchanged several letters with Gene Sheenan, president of QAC, on this subject; but more about that later. Several people have contacted me for lay-up schedules on the stock 200” span, 1100 lb. Tri-q. The package contains the lay-up schedules I would use to build a stock Tri-Q. I will also make available, upon request, the designs for my own 240” span 1200 lb. aircraft.
Let’s get this unpleasant subject out of the way right up front. It is sad that every new idea must be accompanied with a disclaimer paragraph, like this, in a vain attempt to protect against those few who refuse to think. Soon, when no one thinks, there won’t be any new ideas.
Here’s the bottom line: Anyone building a sparless canard is acting as his own designer as well as builder. Therefore, each designer/builder explicitly accept full responsibility for the application of any of my ideas and/or data, and must independently verify the applicability and validity of this work. This design was developed solely for my own aircraft and may not be correct for any other. No actual test data is yet available – it has not yet flown. (Ed. Note: I believe that that subsequent to this report that load and flight tests were conducted by Mr. Waddelow and/or other individuals. I am attempting to verify this and will attach an addendum on this subject). This work is intended for those aviation pioneers with the courage and expertise to evaluate a better, but as yet unproven, idea. If these conditions are unacceptable, stop here.
The sparless Tri-Q canard is constructed very much like the main wing. I’m building mine straight across on the top surface (i.e. just a tiny amount of dihedral) but anything near flat is OK. If you have not already cut your templates or cores, I suggest the canard cores be cut with the shear web at 60% of the cord (.60C); the carbon spar is at .55C, The Q2’s is at .63C. I wasn’t able to use the QAC templates for the sparless design so I carefully re-plotted the LS(1)-0417MOD airfoils from NASA’s original coordinates (NASA report TP-1919, Nov. 81). I also designed a slightly different planform to simplify cutting the cores and installing the elevators. If there is interest, I will provide the paper templates, foam layouts, etc. used for my own canard; these should work for the 200” wing as well. If you have already cut your own cores, it may still be possible to use them by filling the half-round slot with X-40 pour-in –place foam and shaping so the vertical shear web is at what was the carbon spar centerline (.55 C).
I used the following technique on my main wing with excellent results; it is more work but the airfoil is perfectly shaped and smooth so the finishing process should be a snap. After joining the cores, squeegee dry micro into the foam. Then sand the hardened cores with a 2’ spline board and 36 grit paper until the airfoil is smooth and straight. Since the core surface is hard, there’s no tendency to gouge like a bare foam core. All low spots are filled with micro BEFORE the lay-up instead of after. The glass is applied with epoxy only, no micro slurry should be used.
When the cores are perfect, lay-up 2 UNI at 45 degrees crossing then add the spar caps. In beams, structural material is more effective the further apart the top and bottom surfaces are from each other (that’s why the thick airfoils are stronger than the thin ones for the same amount of cloth) so keep the caps on the thickest part of the airfoil. Put the widest cap down first with the aft cloth edge near the shear web (say within ½’ +/-) and center the others on top of the first cap. Glass the bottom surface, then fill, sand, and lay-up the top. Don’t forget the glass “ribs” between the cores at BL 15 on the canard. Lay-up a 4 ply BID, 6’ wide strip chordwise on the top surface centered at each BL 16. These will help spread the local compression loads where the wing joins the fuselage.
The shear web MUST be reinforced. This is definitely needed for the sparless canard and, in my opinion, the QAC design is deficient in this area for the main wing too. For the main wing, I like BID strips applied over the four UNI plies on the vertical shear web; one from tip-to-tip, one from BL 60 left to BL 60 right, and similarly for BL 40 and BL 20. These BID strips should be cut on the bias and butted together (don’t overlap) to form the longer strips needed. Arrange it so that no joints lie over those in the other ply. Use this same treatment on the canard shear web at .60C, in addition to ANOTHER shear web at .30 C from BL 15 to BL 57 (see canard planform sketch). Slice the BL 15-57 core vertically with a hot wire, then lay-up 2 BID from BL 15-57 on the vertical surface; then add three more, starting each at BL 15 and stopping at BL’s 50, 35, and 25. Align and rejoin the core with micro. Tie the new shear web into the spar caps with flox corners.
I urge everyone to load test their wing and canard as a precaution against any hidden construction defects. Do this after a minimum 4 week curing time and before applying any fillers or paint or installing on the fuselage.(Ed. Note: Don’t forget to post cure your unit before this 4 week period).
Begin by building a stand such as the one shown on the enclosed sketch. It is vital that the "saddles" match the top airfoil contour. Use a different set of saddles for the main wing and canard. The saddle must be padded - some 1/2" Clark foam or a 2" thick, piece of seat cushion foam will do. Loading the wing directly on the hard wood is likely to cause local compression damage; then you'll get to build another wing.
Place the ring upside down in the padded saddles. Weight is loaded on the BOTTOM wing surface to simulate positive G loads. Weigh, and record, each sandbag placed on the wing. See enclosed weight schedule and sketches. (Ed. note: this was not included in the document I received. I am looking for it to include). Do not apply any weight between the saddles. And don't support the tips with a jack. The wing isn't designed to handle loads applied in that fashion – besides there won't be any “helping hand" in the air, just load the wing evenly, with layer by layer of sandbags, until the correct totals ore reached. (I'm referring here to the “Q-Tip” in the Sept/Oct '85 Quicktalk; it's generally good info except for the jacks idea). Measure the wingtip height above the floor before, fully loaded, and after the test. The before and after heights should be the same. Any permanent deformation indicates structural failure. After the test, carefully examine both sides of the wing for damage - particularly the top wing surface near the saddle.
My own feeling is to load test to the 4.4 G's the wing was designed to carry. If it shows ANY sign of failure at this loading it's not safe to fly. Overloading to 125%(6.6 G) is probably OK, maybe even a good idea, but in no case would I go over 150%.
Concerning, negative G loads, the ring is designed to withstand 75% of the positive G limit, or -3.3 G. Since this is almost double the FAA required -1.76 G, load testing is not really necessary. If you do test for negative G loads, it will require new saddles and a new load schedule.
I have strong misgivings about repairing damage to primary structure. I recently learned of a fatal Q2 accident where the main wing failed in compression near the fuselage. The builder had previously repaired major structural damage in that area resulting from a landing accident. It is far better to discard the damaged ring end build a new one as fiberglass loses much of its strength when damaged (even dropping a wrench on it can cause local failure of the glass). It is critical that each strand of UNI in the spar caps be continuous without separations or splices, especially on the bottom surfaces. The foam/glass bond is important too, especially on the top surfaces.
The “controversy” began in August, 1985 when I first “reverse engineered” QAC’s main wing lay-up schedule. What I learned concerned me enough to write Sheehan and alert him (and then hopefully other builders) of what I considered a serious, and easily correctable, weakness in the area of BL 40. His rather rude response refused to acknowledge any such weakness. After two other attempts, I finally gave up trying to convince him. It you’re really into gore, for a $0.39 self-addressed stamped legal envelope I will return copies of our correspondence. They provide some interesting first hand insights inter the personality behind QAC.
The numerical printouts included here are listed every 5” to conserve mailing weight (computers are great for overwhelming you with paper). If you really want greater detail, send your request and the postage, The graphs, however, were calculated every 0.5” and so provide, qualitatively at least, greater resolution. Referring to those graphs, I invite you to compare the actual stresses in my tapered cap main wing design against the per QAC plans design.
Please note that the input parameters are identical; only the lay-up schedule is different. While the exact magnitude of the numbers may be open to discussion (see general Notes in the Explanations section), they do provide s valid RELATIVE comparison. Note the almost 2:1 stress concentration (a sharp jump in stress) in the QAC wing at BL 4O. I’m sure by now we’ve all seen pictures of, or worse, experienced a broken GU canard after a hard landing.
Have you ever wondered why they always break in the same place, right at BL 49 where the trough stiffener ends? Stress concentration. I need to comment on the “FAIL” indication of the QAC wing at BL 70. This is another area of stress concentration but the actual cap stresses are not as great as calculated near the wingtips.
The anomaly is caused by my not giving any structural credit to the two 45 degree UNI plies. Since UNI has only about 15% of its strength at this orientation, it was not considered in my design, effectively building in an extra safety factor (about 7%). It does, however, introduce some error (on the conservative side) in the sparcap analysis ranging from small near the root to moderate near the tips. If there was no sparcap, i.e. only the two 45 degree UNI, a 1” width was assumed to prevent divide by zero in the calculations.
In other words, the sparcap analysis is fairly accurate in the critical first half of the wing where the loads are large but does cause the sparcaps near the tips to appear more heavily stressed than they actually are; take that into consideration when comparing. Note that the QAC design does depend exclusively on the crossed UNI plies to carry the outboard 30” of wing stresses. Note the relatively snail stress variations, from root to tip, in the tapered sparcap design. Note the 12 ounce difference in estimated sparcap weights (that’s for the ENTIRE wing).
I have not performed a detailed analysis of the Q2 or Q-200 canard, and really don’t plan to since I’m not building one. Remember, these lay-ups schedules are not intended, and must not be used, for “wheel on the wingtip” designs.
At this writing, (August 1986) I have completed construction of my main wing incorporating 20” tip extensions, tapered sparcaps, and reinforced shear web. My Tri-q canard, using the LS-(1) 0417MOD airfoil, 20” tip extensions, tapered sparcaps, and an additional shear web, is under construction. I intend to load test both wings together sometime late this summer.
The lay-up schedules presented here are overly conservative - they were designed with my neck in mind. I have tried improving the computer model by taking more factors into account (like the two 45 UNI, wing weight, washout, etc.). As it turned out, it didn’t make much difference in the lay-up schedule and the small reduction in sparcap weight (about 1 lb) did not, in my opinion, offset the added safety margins of the more conservative approach presented here. I hasten to add, however, that there is a balance between strength and weight, and that it’s easy to go too far in adding cloth. I also caution against exceeding the 1100 lb gross weight with the 200” span tapered caps based primarily on wing AREA considerations, rather than wing strength.
I concede that a main wing using the QAC lay-ups will not break at 4.4 G’s when new. However, fiberglass is notoriously weak in fatigue strength - that’s why glass designs use a safety factor of 2.0, or more, while most aluminum aircraft are designed with a safety factor of about 1.5. (Ed. Note: some that “know” would say that this statement is not accurate as to the fatigue life of composite structures or the reason for the higher safety factor used in composite design. However, the 2.0 number is a generally accepted number at this time). In QAC design, flex and fatigue are concentrated at the end of each cap layer instead of being spread evenly throughout the span as with the tapered sparcaps. I urge anyone with a high time Q2 to frequently and carefully inspect their main wing at BL 40, and especially the canard at BL 49, for signs of fatigue.
Some other things to consider: A Q, sitting on its wingtips in the hanger, has as much bending moment at the fuselage junction as the Tri-Q does in a 3 G pullout. Using the sparless canard will SAVE about 9 lbs over the carbon tube design (this includes the extra shear web reinforcement). Subtract the 10 lb. increase in the main wing (again including the reinforced shear web) for a total wing weight savings of 7.1 lbs. I don’t know exactly how much extra (if any) the Tri-Q gear weighs but let’s say for argument it’s 7.1 lbs. The net result is an airplane with the SAME empty weight as the stock Q2, but you’ve gained on even stress distribution in both wings, lower stresses in the shear webs, $720 in your pocket (for not having to buy QAC’s carbon spar), and of course the safer ground handling of the tricycle gear.
Redesigning aircraft primary structure is not something to be taken lightly. There are many critical and interrelated factors to consider - some can be approximated, even neglected, but all must be considered. I have slept with this work for many months, and I would not be building my own wings this way, or be writing this paper, if I did not believe these designs were truly superior. But I insist that each builder carefully examine this work and draw their own conclusions about its integrity. By providing the engineering data, my intent is to allow other builders to sleep as well as I do. I believe it’s important to explain how and why these designs evolved; I want your understanding, not your faith.
I wish to avoid the impression that I am “recommending” how to build your aircraft; I’m simply sharing information on how I’m building mine. Even though the tips presented here are written using active voice (to keep it interesting) they must not be construed as “instructions” - they are suggestions only. If you have any doubts at all, do not modify your primary structure; stay with QAC’s “safe”, “proven”, and “approved” per plans Q2. By the way, if you do make any modifications, don’t call your airplane a quickie – we don’t want to give credit. where it’s not due.
This work is being provided without charge to advance the free exchange of ideas relating to experimental aircraft. To this end I will gladly share anything I have learned with other individuals. If you find this work of value, your support is appreciated. I would also appreciate you taking a moment to write with your ideas, questions, and feedback on these designs and the issues I’ve raised here. Let me know what you decide to do and how it turns out.
See you at Oshkosh!
New Braunfels, TX
Cleaned up versions of Marc Waddelow's original drawings can be downloaded below in PDF format:
Many TriQ's are now flying with Marc Waddelow's sparless canard and main wing designs, resulting in several thousand hours of combined flight experience.
Paul Buckley is a builder in the U.K. who provided the following suggestion and drawing to make things even a bit easier.
". . .the Waddelow foam block layout for the Canard can be simplified considerably, but a new template for BL58 will have to be made, rather than using BL57, but it is only a fraction shorter.For the purists, the actual chord of BL58 can be calculated as 50% the difference between the chord of BL15 (root) and BL100 (tip), since it is halfway between the two.
Suggested simplified layout adopting a straight shearweb (much easier to jig, and stronger) inserting the rib at BL58 (instead of BL57) making the two outer blocks 43" each and the total span just 2" more at 202"