Sailplane Preparation For Competition

by Paul F. Bikle

I would sure like to talk some about the things that George and A. J. were talking about but I've come to the conclusion, after some years of trying to compete with A. J. and George in competition, that I'd probably find it more appropriate to act in line with my demonstrated inadequacy and act as Crew Chief of this operation. I'm going to talk about preparing a sailplane for competition.

When Ed first asked me to talk about this subject I was a little bit dismayed because I didn't think I had any particularly earth shaking things to say about it, so I asked a lot of people what they considered to be most important in preparing a sailplane for competition. After I got to thinking things over I found there was a great deal to talk about, still none of it very earth shaking. Before I get around to that, I might address the thing that most of the people mentioned first when I asked them. That had to do with ways of improving performance and the most frequent thing mentioned was the matter of smoothing wings (sanding), and how much this might be expected to help them out.

I have observed that people spend a great deal of time sanding wings and many seem to find the best time to do this is during the contest practice days and even during the contest itself. I think we might consider whether this is the best way to spend time and effort, or maybe work on things that really don't take so much effort and might have a better chance of payoff. Most of us, in buying a sailplane or anything else have a limited amount of time so you should try to get the most chance of help from the time you spend. It might be of interest to take a look at just what people are achieving with their sanding efforts and surface smoothness.

We just finished a 57-flight evaluation of nine sailplanes over the holidays and have the plots of the surface waviness measurements that we made on the sailplanes.

Figures 1-2

Figure 1 is of Alex Aldott's LS-1C. As you can see, it is very highly polished and also has had a great deal of sanding done on it, This was the LS-1c that was flown by one of the French pilots at Marfa. As you may also see, the reflections in the wing would not indicate that the smoothness was of the degree that you would like to see.

Figure 2 is a picture showing Anne Enevoldson and Alan Bikle making surface waviness measurements on the wing tip of the same airplane.

Figures 3-7

In Figure 3 we have plotted the surface gage data obtained at six span stations along the upper surface. The scale along the bottom is in inches of wing chord with the vertical dash line drawn at 50 percent chord as a reference. On the vertical scale, each increment represents 0.001 inch curvature in a two inch arch for each increment of scale along the left side of the plot. The curved dash lines are mean surface lines while the heavy lines shows the actual surface and the difference between these two lines gives a fair picture of the amount of waviness in the surface. The left hand side is toward the leading edge. We can see that we have a fair number of waves and some of these are as great as 0.004 inch in two inches on the forward part of the wing.

In the plot of Figure 4, the same kind of data is shown for the Standard Cirrus that we flew. 'he wings on this ship had also been sanded. It is the ship that was flown in the U.S. Nationals last year and placed the highest of the Standard Class sailplanes. This one also has waves about 0.004 or 0.005 inch in two inches and these waves tend to occur just in front of the 50 percent chord line and are at a place where they could be expected to cause early transition.

Figure 5. The same type of curves for the Standard Libelle. The wings were just as they came from the factory--they were not sanded although they were clean and dry. On the whole, the waviness is about the same order as shown before, except for the one wave on the left inboard part of the wing which is a bit worse with a double amplitude to about 0.005 inch in two inches.

Figure 6 is of the wing of an ASW-15 as delivered from the factory and at first glance it looks like it has more waves; but the deviation is less--it is about 0.003 inch in two inches.

Figure 7 represents the measurements made of the 1-34; there are more waves and the amplitude is more than any of the other sailplanes-more than 0.015 inch in two inches.

Figures 8-12

Figure 8 is similar data obtained on the LP49. It is smoother than the 1-34 but still almost double the amplitude of the waves that were measured on the fiberglass sailplanes.

In Figure 9, the curves are for the wing of the Diamant 18 that Ross Briegleb flew to win the National Championship at El Mirage last year. He had done a great deal of sanding on the wing before the contest. It's the best of those we have seen so far in these figures but it still had a few waves--as much as 0.004 inch in two inches.

In Figure 10, this was one of the three ASW-12 wings that we have measured and, in this case the wing was just as it came from the factory except for cleaning it. It is not bad--there are some waves that are 0.004 or 0.005 inch in two inches--but it is in factory delivered condition. The waves that are of some amplitude seem to be quite far forward on the leading edge where it might be anticipated they wouldn't cause too much trouble-at least waves of this magnitude-although we don't really know.

Shown in Figure 11 is the second ASW-12 that we tested. This is the one that Rudy Mozer flew for a number of years and which he had completely redone. As you can see, it is by far the best of those that we have seen so far. Generally, you could say that all waves are less than 0.002 inch in two inches.

Figure 12 is the surface data shown in Soaring magazine awhile back for Ben Greene's ship as measured last summer right after the Nationals and shortly after the time he flew the ship to a new World's distance record. We have something less than 0.002 inch in two inches.

The most that we can hope to get from this kind of data is some idea of what the waviness in the wings may be. What does all of this mean? Obviously, the LP-49 and 1-34 are not competition sailplanes although the wings were filled, painted and sanded to some extent. The resulting waviness is too much for consideration in this discussion although the wing on the LP-49 has about the same degree of waviness as my T-6 and is actually pretty good for conventional American metal construction. It's not very good but it's about the best the most of us are able to do.

All four of the fiberglass sailplanes had waviness of 0.004 or 0.005 inch in two inches and it would appear, just from looking at the curves, that the differences between the two that were sanded and the two that were not sanded were minimal; there was probably some slight improvement. The LSIC was also polished and although we had no way of really determining what this did, we couldn't see that it helped nor did we see any detrimental effect. The Diamant 18 wing was somewhat smoother--about 0.004 as we saw it. I might mention that on the four Standard Class sailplanes we couldn't see any correlation between differences in performance and differences in wing smoothness. However, this is a rather gross evaluation and I don't think we could see those changes unless they were fairly large.

In the case of the Diamant, I thought it was interesting that this ship was quite a bit smoother than the Diamant 16-1/2 that we tested last year. When we corrected the performance of the two airplanes for the difference in the aspect ratio, the polars fell right on top of each other indicating that, within the accuracy of our measurements, the extra smoothness did not help the Diamant although that again is a rather gross type of thing since they were two different sailplanes.

In the case of the three ASW-12's, the data may be a bit more interesting. Here the "as delivered" wing was better than those of the Standard Class sailplanes. The second one was very smooth and about 0.002 inch in two inches, and the third one was about the same although I felt overall maybe a little bit better. Here there was also a difference in measured performance with the better performance consistent with the degree of smoothness that we observed in the wing.

One could conclude that wings with less than 0.002 inch waviness in two inches did have an appreciable effect an performance. On the other hand, I really think you should be careful about such conclusions because, as is often the case, the wings that had the most work done on them and were the smoothest were on the sailplanes where the people that owned them probably had the greatest motivation; had sealed all the air leaks and had done all of the other many little things that you can do to help yourself out on the sailplane. I think it may be just as likely that the added performance came from those other sources as it did from the smoothness but I really don't know.

The main point is that some people spend one tremendous amount of time on sanding wings. I would say, that except for very few cases, they haven't really achieved any great degree of increased smoothness. I'm not even sure that when you do you get smoother wings, that you achieve any great degree of performance improvement.

Of course, all of this work is not going to do any harm and if you have the time to do it, fine, go ahead and do it, but it shouldn't be done at the expense of some other items which maybe were important and are a lot easier to do.

Before I talk about some of these other things, I would like to make it clear that success in competition is going to depend primarily upon the pilot and it's going to depend upon the kind of things A. J. and George have been talking about and all the preparation in the world won't make up for any deficiencies in the piloting department. On the other hand, even the test pilot may be all but eliminated from contention by problems, usually pretty mundane problems, which could have been prevented by more careful preparation of the sailplane. In a sense, this type of preparation is an extension of George's remarks of two years ago and of the type of things that both George and A. J. said this morning when they were talking about winning by not losing. All of these things are associated with being very careful and making a detailed inspection of the sailplane, cleaning everything up, correcting any deficiencies and providing tools and spare parts for quick repairs or replacements during the contest. There are so many items to be considered that there is not time to do much more than list them. On the other hand, these are pretty simple things and there is really no need to discuss them.

We shall start with inspection and cleaning. This may sound pretty mundane too, but actually open everything up where it is easy to get at. Take a look at things and at least you understand what is in there so if you have to do something during the contest you won't spend half of your time trying to figure out how to get in there and fix it. Look at all the fittings, brackets, rod ends and bolts and be sure that the safety devices are in place.

When I got my new SHK and I took the time to do this, a castellated nut on the little elevator control stud--the one that drives the ruddervators-didn't have a safety. If this had worked loose it could sure have spoiled the whole day. How many people ever check the rigging on their ship before a contest? I never realized the problem was so great until we started running these performance tests. We found flaps that were rigged as much as 50 off from the cockpit control readings used to match the flap setting to the airspeed for best performance. Aileron droop has been as much as 50 different from that specified and that's just like carrying 5 degrees of flap around in the wrong place over some 30 percent of your wing span. It can also affect thermaling and stalls in the thermal. Things like this can really hurt in some cases. The aileron travel has been as much as 10' less than called for and this is a loss in aileron power which can degrade thermaling and roll response in general. Improperly rigged elevators and rudder controls can influence spin recovery and again could spoil your whole day.

Speed brakes, which are not rigged and sealed properly can cause all kinds of problems. It would sure pay to check these while your ship is rigged and check it by loading your wings on the ground and make sure the speed brake controls go over center and will stay latched. A. J. told me yesterday he had the speed brakes come open twice on him while he was flying the LS-1 at Marfa this year. Regardless of the amount of checking we do on the ground the real way to check them is in the air. While you are checking the speed brakes, check the fit. Be sure that all the seals are tight and there are no air leaks around the brakes, and again under load as well as statically. This isn't always too easy to do. Looking at the 20 ships that we tested in the last year, at least one-half of them had pretty bad air leaks around the speed brakes before they were sealed.

The general problem of air leaks is probably the area where, for any given amount of effort expended, you could make the greatest gain in preparing for contests. Every air leak isn't necessarily going to really ruin your performance but we have had enough cases where it does so that it sure looks like the best thing is to be sure you have no air leaks. Wheel doors obviously should be sealed and, to make doubly sure, you should have a wheel well which is airtight around the gear. Air leaks in this area show at least as much drag as carrying a fixed gear did, not an extended retractable gear, but a good fixed gear.

Klaus mentioned yesterday about the necessity for sealing flaps and ailerons. This usually is riot too difficult and is probably high up on the list of pieces of work you can do with a good chance of a worthwhile payoff. Not only payoff in the sense of drag but also payoff in the sense of effectiveness which might even be more important than the drag.

Probably the worst leaks we have seen have been on the canopies. These are not too easy to check but they can be extremely costly. We've had one case with a ship with an L/D of around 40 where the aft canopy seal was lost. The performance dropped to an L/D of 33 and was brought back up to 39 fast by resealing the canopy. On the other hand, a number of people fly their ships around with canopies cracked. I am sure there are some cases, just depending upon how the flow comes out of the canopy, where it probably doesn't cause very much trouble but you don't have any good way to know this. Once again, I would suggest that a good place to spend some time is sealing these things up.

Air leaks around the wing roots can hurt your slow speed performance and increase your stall speed. Most ships have some provisions for sealing around the roots but if there is any question at all I certainly recommend taping in this area.

Just common sense things. Certainly check the tires for wear and cuts and replace them if they are not in first-class condition. Remove and inspect the wheels and grease the bearings; check the brakes and adjustments.

Carry a spare wheel assembly with tire and axle, spare wheel well doors, and a spare tail wheel and axle. On more occasions than I would like to think of I have seen pilots lose the best part of a day trying to repair or find spare parts for wheels or tires. If I remember correctly, George, you lost a good part of a day at El Mirage in the 1962 Nationals (two days). I think that this is probably more common than we realize (maybe only two or three times in a contest) but if it happens to you, all of the other things you do are liable to be of no avail.

A good brake. There is nothing I appreciate more than knowing my brakes are going to work when I am going into a small field and obviously it can be the difference between just a retrieve from a small field and working on a ship all night to repair a bashed-in nose or a wingtip.

When I talked to people, they hardly ever mentioned cockpit comfort. For most of us, this is an item of top importance and I do not think you want to wait until you get ready to take off before you worry about this. In the first place you have to try it in flight and I think you should be able to fly for six or seven hours without any feeling of discomfort. While you're doing this, make sure everything is secured in the cockpit and you are not losing things behind you and you are not having any-thing come loose and jamming things up at the wrong time.

I can remember watching one of our pilots sand on his wings. It might sound that I'm real hep on sanding wings but he did and practically up to an hour before takeoff. At the last minute, right on the takeoff line, he decided his cockpit was not very comfortable so he pulled out the seat back to give him a little more room to stretch out. He took off and as soon as he released he dove back to the field because he found he couldn't get his gear up because his chute jammed the landing gear. After a quick ground adjustment he was off again and got his gear up O.K.; he flew like gang busters until he crossed the finish line at 50 feet, did a low 180 for a landing; this time the chute was jamming the gear in the up position. He didn't lose very much except a night's sleep while he repaired the gear doors and the bottom of the sailplane.

While we're in the cockpit area, there is the simple matter of a clear canopy; get rid of scratches; make sure you can see through it well. A. J. talked about the importance of looking out and seeing what is going on and I couldn't agree more, but if you are going to do this to your maximum you have to have a clear canopy. It is not just a matter of being able to see through a bad canopy but you find that these things are distracting and it takes away your ability to see what is important.

I'd certainly recommend, and this isn't a lot of work, that you remove your instruments and have them calibrated and bench checked. At least make sure that they are working properly. You should have some spare instruments, a spare airspeed and a spare variometer, certainly, and these should be in good shape and checked each year also. As in the case of a spare wheel, there are always two or three cases during the contest where somebody is madly dashing around looking for an airspeed indicator because the needle fell off of his or because it's got a bad case leak or something. This happened to me at Adrian in 1965 and Ben Greene lent me an instrument. Sometime somebody is not going to be around to lend you one and then you are going to be in deep trouble.

I am always surprised at the number of sailplanes with leaks in the airspeed systems; about 30 percent of those we have tested have had bad leaks. You can't always say this is going to cause you trouble. In many cases it doesn't, but it can cause you a lot of trouble and it isn't that hard to correct and make your system leaktight. Last winter one of the test sailplanes we had leaked so fast when we put the leak checker on it we couldn't even raise the pressure in the line. A brief check showed that the trouble was primarily where the tygon tubing slipped onto the back of the airspeed indicator and, in this instance, it was just slipped onto the shipping plugs in the instrument. I talked to the pilot and he said he questioned that when to got the sailplane but the dealer told him that was a standard way of doing it so that's the way it was. It also happened that on that ship we also found leaks in the variometer and I don't think these are too uncommon; it's just that if you don't look for them you're never going to find them and they can cause you real problems.

It is probably a pretty good idea not to hook the altimeter up to any of your static lines; just vent it to the cockpit and at least it is not a possible source of leaks and you are not adding any lag where you don't want it. There has been a lot said about variometers recently. When you pull the instruments for a bench check, the variometer should be checked for both its calibration and the total energy compensation. Of course, anything you do on the bench here you have to do over again in the air anyway but it is well worth doing. Total energy compensation has been treated in detail by a lot of other people and I will not try to go into that here.

Total energy compensation and the altitude effects on the compensation have been covered very well and its importance depends pretty much on the individual and what reliance he tends to place on the speed ring. If he uses it for any-thing, then obviously the relationship between the speed and rate of sink should be meaningful. I have been sort of curious about this on many ships with relationships that were as much as 20 knots off. You could conclude that it might be better not to have one under those occasions. These errors may come from not taking into consideration a gross instrument error in either the rate of climb or the airspeed indicator. On ships where there are large errors in the airspeed static system, I have never seen anyone take these into account. There is one other thing that can be done very easily although I seldom see anyone do it and that is to take into account the effect of the fact that you are flying at some altitude above sea level. You get the speed and rate of sink relationships from looking at a sea level polar and here of course indicated airspeed and rate of sink can be used directly because indicated airspeed and true airspeed are the same. If you are flying at 10,000 feet average density altitude as you do in the vest quite frequently this could cause an error in the relationship of as much as 20 percent. If you are flying in the east where you might consider your density altitude as 5,000 feet, the error would be closer to 10 percent. You might think 5,000 feet is a little high for back here but normally you are flying on days that are warmer than standard and your density altitude tends to be 1,000 or 2,000 higher than what you are showing an your altimeter on the average. I'm not sure that this is real important because this whole idea of the speed ring is really dependent on what you think is going to happen in the next thermal. Whether you need to be any more accurate than a guess, which on many occasions may have a 40 percent uncertainty in it, I don't know. It does seem that if you do fly by airspeed a lot, you might as well have the best information you can.

Of course, if you carry oxygen, check the system; you shouldn't accept any leaks otherwise half the time you will find your bottles are down and you don't have what you thought you were going to have. I've seen many ships that do not have a fill valve where you can get to it real quick without taking any covers and things like that off.

I wanted to talk a little bit about radios and I might first say I certainly enjoyed Gren Seibel's book where he managed to wedge in about four, five or six choice remarks about electronic marvels and cans of worms. I couldn't help but think of this as I watched TV last week and listened to Al Shepherd and Ed Mitchell tinkering with Al's suit radio for an hour before they could go out for their first walk on the moon. These things are probably the greatest source of frustration I can think of. Obviously, you want to have your radios checked and have them checked by somebody who knows what they are doing and tuned up before a contest. It is probably a good idea to carry a spare but I think the really best words of advice would be to be fully prepared to carry on without radios. Once you start having your troubles, the frustration probably affects your flying a lot more than any real problem the lack of a radio causes. The only thing that is going to interfere with that type of advice is the general dependence on the radio for getting information at the starting line.

A whole talk could be given on ballast tanks. We have seen pilots flying around the contest sitting in a half a foot of water in the cockpit because the ballast tanks leaked into the cockpit. That might be just an inconvenience and maybe not too important. Of greater concern, there were at least three cases last year where there was structural damage with ballast tanks because of plugged or sealed vent lines. I do mean sealed; in one instance the pilot had taped off the vent line and as he went up in altitude the pressure change across every square inch of wing where these bags were laying in it caused the surfaces to be noticeably bulged out. There was damage in the epoxy joints; a very risky operation. Of course, there is no sense in tying off the vent lines but I have seen cases of plugged vent lines.

Preparation of the sailplane should include the turnpoint cameras. If you think about it the camera, under the present rule, is a pretty fundamental part of' the sailplane. Again, you do the obvious thing. You have them cleaned; check them over and be sure you have at least one spare with you (I always carry two); and make sure your mounts are rigid and properly aligned and checked out in flight. It pays to make some of those turns you make in taking practice turnpoint photos and practice turn photos are well worthwhile just from the pilot's proficiency standpoint. Go over the photos afterward and make sure that you can aim the cameras easily with the wing tip and that you know what you are going to take when you press the button. Also, check to see if the marks on the canopy show up like they should because the first contest day is pretty late to find out that you have troubles here and that you have to do something about it.

In spite of what I said about surface finish, you should check over the surface finish on your wings and while you are doing it look at the fuselage nose and the portions of the tail where there might be a chance for laminar flow. You want to repair any of the obvious cracks and other defects.

I have seen surfaces on two fiberglass sailplanes now where there was evidence of continuing curing after the wings left the molds and this has become evident after the sailplanes have been in this country for awhile. These almost look like the old plywood ships when we bought them up in the desert and they dried out; not nearly that bad but they had that appearance. These look worse than they really are; most of these defects have been only a matter of a few thousandths of an inch but since you can see it running along the spar all the way it looks terrible. Where you have a discontinuity it is obvious that you will want to do some filling and smoothing and it is not that hard because you can see where it is and you can work it out easily. Unless there are obvious deficiencies like this, just give the wings a light sanding to clean off all the small defects and wash them and wipe them dry before each contest day. If you plan to do more than that, it should be looked upon as a major modification type effort which does not come in the context of doing it in a month or so before the contest. If you try to do it at the last moment, you are going to end up doing that and probably not doing the other things. It is the kind of thing you do in mid-winter.

I mentioned spare parts and you also want to be ready to make repairs. You should lay out the tools that you need for this and pack them carefully along with the spares. Don't just throw them into a big box out in front of every-thing but when you do need them you want to get at them right away so store them pretty carefully. They ought to be in the car or trailer someplace where you can get at them. While you are at it you ought to go over your car and trailer in the same way and use the same care as the sailplane. I'd make up spare kits for these too and I would certainly suggest providing for carrying spare gasoline and water because the failure of the car or trailer can have a shattering effect if you land 15 miles out on a good contest day if you don't get back again. As mentioned earlier, the problem is not one of what are all of the things you would do if you did all of the conceivable things you could think of. It gets down to the matter of what can be done best in the time available--where should you spend your efforts--what is the most likely to pay off.

I have talked about sanding wings and suggested that there may be better ways to spend your time. Maybe you should forget about this because I think there are some people that get some sort of a philosophical or a mystic recharge out of going out and sanding and polishing wings at the last minute. If this helps the pilot's frame of mind, I would say go to it; make sure the lucky penny is stuck under the instrument panel; and make sure you have your lucky hat. If any of these improve the pilot's state of mind, they are more important than all of the other things put together.

Questions And Answers

Question: (Tom Smith) Regarding this statement you made on apparent continual curing, I have a Phoebus whose rear spar appears to be encountering this condition. When you get in the light just right you can see this condition. It appears to be a drawdown somewhere back around the 70 percent chord point. What comment would you have on the effect that this condition might be giving me?

Answer: (Bikle) My guess would be that it would not hurt too much, but this is only a guess. We have not made any measurements on this particular phenomena.

Question: (John Slack) This question refers to the speed ring. Do you, Paul, utilize this ring? Would you care to comment on this?

Answer: (Bikle) I use it enough so that I feel that I want to know what it's telling me, so I, therefore, take the trouble to get the right numbers on the ring. I am very much concerned about the problem of what's going to happen next and because of this we shouldn't place too much reliance on the ring. There is certainly never any point in going any slower than what the zero thermal speeds on the speed ring call for. In fact, it can really hurt you if you do. So, if things are weak I tend to use it more so that I can make sure I am not going too slow; and I tend to use it at high speeds to make sure that I am going fast enough.

Question: (Steve DuPont) This concerns sealing of the tail fuselage junction. I find that this has significance on the HP series in both handling and performance. Would you care to comment?

Answer: (Bikle) Yes, I think I forgot to mention that in my regular lecture when I was talking about sealing. I had it in my notes. I think there is just as much reason to pay attention to the gaps on the tail. A. J. tells me that he has even devised a way to seal the air leaks around the gap of the moving tail stab on the new fiberglass ships. This certainly sounds like a good idea.

Question: (Gren Seibels) Paul, in your various tests and on the data that you have been collecting on performance, have you had any opportunity to compare performance on a given ship with an eggshell or matte finish on the wing and then compared with a same type ship with a glossy type finish on the wings. In other words, is there any data to indicate that this different finish has any significance.

Answer: (Bikle) I did touch on that, Gren, but I haven't done that recently. But I did it a number of times many years ago on the ships I had. About all I can say is that any effects are small enough so that I cannot measure them. I really don't think you can do that type of measurement in flight unless the effects are very large. This is the kind of stuff that should be done in the wind tunnel. There is a fair amount of data in the wind tunnel on this subject. I think the people have their own little tricks but the best data that you can draw from the tunnel test is that the 400 sandpaper finish is certainly adequate. And you are not going to gain anything by going any smoother. Certainly you don't want the polish or wax, or anything like that because you tend to pick up bugs more. I guess that might be a more general statement of what the general opinion is. If you are asking specifically about facts measured in flight then I just don't think there are any.

Question: (Bill Felbaumer) You emphasize the importance of sealing up the canopy. Would you comment on what effect these little air vent windows have on the performance?


Question: (Rob Buck) A lot of us Libelle owners have been curious about the canopy and the way it can be opened up in flight. I thought I would do some tufting around the canopy area. Have you tufted the Libelle? Is it critical as to size of yarn and placing relative to adjacent tufts?

Answer: (Bikle) No, I don't think so. All tufts are going to tell you is what the airflow is and whether you have separation in flow or nonseparation in flow, and it will show you what the direction is. It isn't going to tell you anything about laminar flow or nonlaminar flow. I think you have an excellent idea and I say, "Go to it and let's see what it does." I had in mind the canopy on the Libelle and also Ed made remarks on the canopy of the Kestrel when I said that canopy leaks per se are not necessarily bad. I think Ed has said that he can fly in thermals with the Kestrel canopy cracked open and doesn't seem to have any great effect.

Comment: (Ed Byars) It doesn't seem to have any effect that I can discern, Paul, however, perhaps I don't discern too well.

Comment: Bikle) I have the same problem, Ed.

Question: ( ? ) Paul, would you care to comment on how important trim drag is?

Answer; (Bikle) Again, I don't have the answer but I have been working on it. There was a paper given at the OSTIV last year in Marfa. The author asked me afterwards if we could do some flight testing to verify the paper. We checked the paper and it certainly seemed to be technically sound. We have been running test points as we get a chance but it's an extremely difficult thing to measure. It seems like it's a little more important than minor differences in surface finish, anyway. I haven't come across anything yet that would make me indicate that it would show anything different from the theory. For example, on my own ship I have been checking this by moving in flight the CG by 30 percent. This means that I have been taking 75 pounds of lead and shifting it from the nose to back behind the trailing edge of the wing. I use another sailplane as a reference plane while we are doing this. It is a very time consuming and expensive thing but I think by the summer we will have enough points so that we can publish generally for that type of ship. By theory it shows that you would have increases in rates of sink in the order of ten fpm, more or less, throughout the speed range. It was surprising to me that when I first thought about it showed more increase in rate of sink at the high speeds than at the low speeds although not more percent increase. Now remember, that's over 30 or 35 percent shift in CG. I hardly think anybody is flying that far off in CG. I think as a general practice it pays to run your CG back as far as you feel you can satisfactorily fly the sailplane. This is pretty much an individual pilot judgment. For those of you that have the certified sailplanes I would say that you should balance the airplane so that you would be at the aft limit because they are supposed to fly all right in that position. Then if you don't like it, you can always move it forward A five percent difference in CG is probably going to make a difference in sink of maybe one or two fpm in sink. Once again, let me say that I have difficulty in measuring these types of things, but you certainly cannot afford to give it away either.

Question: (Gleb Derujinsky) You nave mentioned sanding the wings but have you thought of any way to keep bugs off the wing such as teflon coatings or such things?

Answer: (Bikle) There is no question about it. This is one of the reasons I am not too carried away with sanding wings. No matter how good the finish is it's probably not going to last any longer than it takes to get bugs on it. I don't know of any practical way to keep the bugs off. I guess it's not impossible but it depends on whether you want to do it. When we were running tests on airplanes in studying laminar flow, we used to cover the wings with a cover during takeoff and when we got up to altitude and the test conditions we would pull a rip cord and the covers would fly off. If someone was that concerned about it I guess they could do it.

Question: (Doug Gaines) Paul, how about fairing in projections that you can't get rid of, for example, aileron horns, and that sort of thing?

Answer: (Bikle) I tend to say, sure, go ahead and do it. You are certainly not likely to lose anything. Again though, I would urge that it not be done at the expense of not doing other things like bringing a spare tire.

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