Date: Tue, 10 Oct 1995 22:50:47 -0400 From: pinnock@magicnet.net Subject: Main Spar shear web break Hello fellow builders and flyers. I thought I might pass on a incident that happened on my MK IV recently. On a recent trip from Orlando to Tallahassee I accidently let my plane enter into a 230mph dive, resulting in a shear web failure on my main spar. It looks as though the top outer attach point sheared through the 4 layers of uni about a 32th of an inch, resulting in the forward edge of the wing moving up about 3/8th inch. The right wing shear web failed, the left wing did not, although both wings moved up, left about 1/8th. __________________________________________ . / / / / / / . | / / / / / / . | __________________________________________| The failure looks something like the above, with the uni looking like waves in the above pattern. The spar caps did not move, it seems as if the outboard attach points twisted slightly, taking the shear web with it. You could see in the access hole under the spar where the foam had cracked. In Europe I believe it is required to have a 4th attach point on the leading edge of the wing and strake. This would remove the 16in moment on the twisting action on the attach points. Needless to say I'm adding this strong point on my rebuilt wing and spar, as well as beefing up the end attach point on the inside. We also added 2 additional bulkheads to the spar and a much larger metal hard point inside, making it require much more force to pull the upper bolt through. Something to think about. 2nd Item.. This was quite a trip, first I had this shear web problem on the way up. Which I did not even notice until after 3 hours of flight later. ( I know I'll catch hell for that, but these things happen). On the flight back, after landing in Pensacola, while at 10,000' over the Gulf at 10:00 at night, the number 4 exhaust stack sheared completely. After reducing power it was almost an hour before I was able to land Cross City. After inspection and a jerry rigging I was then able to fly the last hour home. Still did not notice the wings in their new angle of incidence. It gets worse. Finally the next day the wings became obvious, and the plane was completely disassembled. The heat of the exhaust make its way through a very small hole above the aileron torque tube, worked it's way down the rib, took a right at the wing shear web and preceded to shrink the blue foam back about 3 inches, all the way. It also started down the space between the spar shear web and wing shear web and got into the rib of the wing, and started to shrink it too. The fiber fax used did a good job of protecting the glass on the rib. But the hot gas was able to escape through the very small hole at the torque tube opening. Needless to say pay close attention to seal off any exit route for hot gas to the foam in those wings. The good news... Even with the above problems the plane flew perfectly, and the wings seemed to be very strong in their new positions, thank god. The repair work, going on for almost a month now is fairly easy, and I feel with the added bulkheads, additional layers andforwardd attach point the plane will be much stronger in the future. Nat was very helpful with repair suggestions, but not sure of why this happened at such a speed. He is continuing to look into the possible reasons, I'll keep you posted. In about 2 weeks we'll be doing some high speed test on these repairs, over the ocean and wearing a parachute, I'll let you know how it goes. I have also located a low pressure warning indicator that can be set in the 190 to 240mph range, which will sound off a buzzer when tripped. I'm going to set it at about 205, which should prevent this from happening again. Until Next Time..... Date: Wed, 11 Oct 1995 16:06:21 -0400 From: JIMWHI@aol.com Subject: Re: Main Spar shear web break Thanks for the information on the problems you experienced with your plane. It does raise a lot of questions though. 1. Is it possible that the exhaust failure caused the shear web failure? Based on the information you stated in your letter, you did not notice the spar damage until after the exhaust failure. If the shear web had been heated like you explained, it could have yielded under the heat. Heat deformation seems like a possible cause. 2. Could it be that the 230 mph dive did not cause the damage at all? Vne according to the POH is 220 mph. 10 mph extra could make a great deal of difference, and you probably have a good reason for thinking it did. What led you to think it was the 230 mph dive? 3. Did the additional 10 mph somehow create extraordinary stress or unusual vibration? 4. Did you pull a lot of g's when you pulled out of the dive? 5. Was the air turbulent? 6. How heavy was the plane when this occured? 7. Was your exhaust the same as the one shown in the plans? 8. Do you think the exhaust pipe failure may have been related to the wing movement or vice-versa? 9. Are you making any modifications to the exhaust system? Thanks for sharing with us and we are all glad you made it down safely. Jim White From: Lee Devlin Subject: Re: Main Spar shear web break Date: Wed, 11 Oct 95 16:45:52 MDT pinnock@magicnet.net wrote: > I thought I might pass on a incident that happened on my MK IV recently. On > a recent trip from Orlando to Tallahassee I accidently let my plane enter > into a 230mph dive, resulting in a shear web failure on my main spar. There was a mention of a similar incident in the most recent issue of Central States Newsletter, except in that case, the pilot had dived into a hole in the clouds (I presume to get from VFR on top to VFR conditions under the clouds). Perhaps this is the same incident. Al Mooney was the 'inventor' of Vne. Up until he convinced the CAA to require manufacturers to publish the Vne figure on an aircraft, there really wasn't a Vne limit and many test pilots died as a result of this oversight. Vne is required primarily for one reason: To prevent structural failure while pulling out of a high-speed dive. There are several other reasons not to take a plane above limits to which it has been already tested, such as flutter, but wing attach points are not stressed nearly as much by the induced drag as they are by excessive lift when trying to pull out of a high-speed dive. I can't speculate on what happened here, but I'm hoping that the damage that occurred to Mike's plane can be attributed to the wings experiencing a load above the design limit. The only way I can imagine that happening would be if the hole led to VFR conditions with a rather low ceiling which required a hard pull up at the bottom of the maneuver to avoid getting too close to the ground. Perhaps Mike can elaborate a little more about the estimated G forces involved in the maneuver. Lee Devlin Date: Wed, 11 Oct 1995 20:40:20 -0400 From: pinnock@magicnet.net Subject: Main spar shear web failure, the real story Dear fellow builders and flyers Good News, it looks as though we have discovered the real culprit in my recent incident. After sending out my first story on the incident last night a copy was faxed to Nat. It seems as if in my phone conversations that Nat misunderstood the exact chain of events of the trip. The fax cleared it up, and Nat was able, with the help of some other sharp guys, find the real problem. After a lengthy conversation today it all begins to add up. Nat has always said, as well as many others that the plane should easily withstand 230mph, and the only known structural failure was a long e-z exceeding 400mph, going straight down. The other factor would be improper building, but Dennis Oleman built these, and his work is second to none. To reconstruct the flight a little, without being redundant, the dive occurred on the first leg of a two stop trip from Orlando to Tallahassee, then on to Pensacola and back. The dive happened while flying over the top at about 1800 feet 50 miles southeast of Tallahassee. Cruising at 185 mph I noticed a nice hole in overcast and rolled right and started descending on through. While focused on the ground I glanced up and saw the IAS at 230 mph. I eased up on the stick and slowed to 200 and came out at 800 feet, then continued to Tallahassee. Nothing other than knowing I exceeded the limit seemed wrong. I even complemented Nat on a design that flew so well at 230. I made a fairly through pre flight before takeoff at Tallahassee and was satisfied that nothing was amiss. Next leg was uneventful. After just leaving sight of the lights off St. Andrew island and out over the gulf the engine sound made an abrupt change. Performance was unaffected, but the noise level was obvious that something had happened. I've had exhaust stacks and mufflers fly off conventional aircraft before, and the noise difference is substantial. On the Cozy is was not that pronounced, but noticeable. After throttling back to 1800rpm I noticed #4 cylinder not cooling off at all. The other 3 had settled around 280 to 310 degrees, # 4 was around 400. By this time all my available airports were far off. I choose Cross City because I knew it, and it was just a couple of miles farther than turning back. Airspeed was now around 145 mph and it took about 50 minutes to land at Cross City. At Cross City the stack was patched and I then flew home. The wing problem showed up the next day. For some reason I was fixed on the dive being the problem. But after a reevaluation of the facts, and speaking with more experts, (thanks to the power of the internet) it became obvious that heat had done the damage. The glass tends to soften up when exposed to high temperatures for extended periods of time, this weakened the attach points and allowed the upper bolt to move back 1/32nd of an inch. The left wing moved even less. The shrinkage in the foam is evidence that heat got all round the hard points. The small hole above the torque tube bearing allowed heat into the wing, and the large hole between the wing and spar allowed heat to move all the way to the wing rib, past the 2 bolt attach area. Needless to say when installing the wing next time I will close the large hole with high temp silicone. The small hole will be glassed over and covered with fiber fax. All my fuel lines going to the bendix fuel injector were covered with a fire resistant material, thank god. The only visible damage in the engine compartment was a small blister on the cowling. The exhaust stack had cracked at about 100 hours, and was rewelded. I had the heater muff removed because this is where the crack started. The stack lasted another 500 hours before giving completely. I do inspect it and don't think there were any cracks in the stack before this trip. Upon reordering I requested that it be made without the heat muff, hoping that this will make it stronger. All other stacks seem fine. I will do more through inspections on these stacks from now on. The fiber fax did an excellent job of protecting the inside of the wing, absolutely no damage to the rib. I used 1/8" fiber fax with high temp glue on all the glass on the inside of engine compartment. Needless to say I am greatly relieved to find out there was no structural failure at 230 mph. Had I been able to land as soon as the stack broke there probably would have been no damage at all. All the reinforcement that has been added to the center spar and the 4th attach point are probably unwarranted, but I'm not gonna take em out now. I just want to get my bird flying again. You don't know how much you love it till it's gone! In closing I'd just like to thank all you guys who responded to the first letter last night, it sure speeded up the "finding the real cause" problem. I'll keep you all posted on our progress, and of course some serious testing results. Until Next Time... Date: Thu, 12 Oct 1995 08:13:25 -0500 From: timothy j busch Subject: Re: Main spar shear web failure, the real story > Nat has always said, as well as many others that the plane should > easily withstand 230mph, and the only known structural failure was a long > e-z exceeding 400mph, going straight down. The other factor would be > improper building, but Dennis Oleman built these, and his work is second to > none. Maybe this has been asked before, but why is it that vne on the Cozy IV is 230mph while the advertised max cruise speed is 220mph? I'm no aerospace engineer, but that seems like a slim margin. Date: Thu, 12 Oct 95 14:19:18 EST From: "Wilhelmson, Jack" Encoding: 3 Text Subject: Re[2]: Main spar shear web failure, the real story I believe the difference is IAS versus TAS. Only at sea level the slim margin would be 10 mph. So don't make low passes in death valley. Date: Wed, 25 Oct 1995 12:07:00 -0400 From: Dick.Finn@FNB.sprint.com Subject: Re: Crash survivability of composite aircraft I've often wondered about the gas tanks. I've heard so many stories about leaky fuel tanks that I can't help but wonder if there are alternatives. Joe Jackson, our EAA Chapter president, died a month or so ago in a Vari-eze crash. He smelled gas in the cockpit, landed to check it out and couldn't get airborn on the short runway (he was over gross). He burned to death in the crash. It was definitely pilot error. Even so, I guess the tanks were partially to blame in that he never would have landed had he not smelled gas and the tanks did rupture and caught fire. Did anyone ever consider using bladders? Does working with Kevlar require special epoxy/tools/etc.? Is there anything safer that would protect us should we do something stupid? I knew Joe and he was a responsible fellow who just made a bad mistake. If we had been sitting around having coffee Joe would have been the first to say that you shouldn't attempt to fly over gross. However, he did make the attempt. Dick Finn ______________________________ Reply Separator _________________________________ Subject: Crash survivability of composite aircraft Author: parkyn@citr.uq.oz.au at INTERNET Date: 10/24/95 11:12 PM The one area that composite aircraft designers have not addressed is that of fuel tank rupturing. Certain composite materials in particular KEVLAR is virtually indestructible and remains intact even after failure of the fibres. Although KEVLAR, due to its poor compressive performance, is not well suited for use in primary structures it would be ideal to use small amounts around the fuel tanks to improve crash survivability. Nick #0011 Date: Thu, 26 Oct 1995 09:33:41 -0400 From: jrosson@symetrics.IExpress.Com (Symetrics Industries Inc.) Subject: Sefety of Cozy Thanks to all who participated in the safey issue of the Cozy vs. other aircraft in attempting to help me decide which airplane to build. Let me state that I have never considered the Cozy Mk IV to be unsafe by any means. I just want to be certain that, in the unlikely event I were to ever experience an engine out situation in my Cozy that I wouldn't be kicking myself for not building that Bearhawk, or some other slow airplane, in which I was assured (more assured??) of a safe outcome due to its 35 mph stall speed. One of the comments that really hit home was that if you are at 10,000 feet AGL when the engine dies, you have about a 25 mile radius to find, if not an airport, at least a flat place to put her down and be able to walk away from it. Also, you all have convinced me that the foam and fiberglass is very protective of its occupants. I even called up Nat himself to discuss the issue and he pointed out essentially the same things that you all said. He also quoted that 25% of all accidents are due to stall/spins so that automatically increases the safety and, provided you put in a good aircraft engine and keep it properly maintained, the odds of a complete loss of power are quite slim indeed. Probably a lot less that being broadsided in a car by a drunk driver. So, on my preferred list of airplanes, the Cozy IV has moved up a few notches above the rest. I can't say I like the long ground rolls and hot landing spped, but then I can't point out to any short fields I want to operate out of anyway, so I guess the few disadvantages are outweighed by the advantages. Hey, if later on I decide I want to go low and slow into cow pastures, I can always build that wood airplane I have dreamed about for 30 years, right. :-) Everyone needs two airplanes and I do have the plans already for the Falconar F-12 that sure would be joy to build (I'll take saw dust over fiberglass dust anyday!). On another issue, after wondering about my fixation on losing an engine and crashing, he indicated he is well on his way with the Franklyn engine. We didn't talk much about it, but he seems to think it will make a good match with the Cozy, though it will require some balancing weight up front. I am probably 5 years away from needing an engine, so hopefully there will something safe and economical out. Again, thanks for all of your helpful comments. The existance of this forum makes a decision to proceed with the Cozy more comforting, and I thank all of your, in particular Marc, for your participation. Jeff _______________________________________________ Jeffrey K. Rosson, P.E., KE4KZ Ph. 407-254-1500 Director of Engineering Fax: 407-259-4122 Symetrics Industries, Inc. E-Mail: jrosson@symetrics.IExpress.Com "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position that we are now in.'" Mr. Spock in "Tomorrow Is Yesterday" ______________________________________________ Fri, 27 Oct 1995 11:02:39 +1000 Date: Fri, 27 Oct 1995 10:54:09 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Crash survivability Dick Finn wrote: >Does working with Kevlar require special epoxy/tools/etc.? You can use the same epoxy resin. You should use special scissors (shears) to cut it. It is difficult to finish - but this would not be an issue in this application as it would be under / between glass laminates and internal. I will be designing suitable laminate for my tanks and will make details available when I do. The only other option is race car fuel cells, but they probably will not fit into the fuel bays, or if they did they would severely reduce fuel capacity. Nick #0014 Date: Fri, 27 Oct 1995 13:18:55 -0400 From: KSPREUER@aol.com Subject: Re: Cozy Safety There was an extremely good safetypoint made in Tims note. The glide ratio of the Cozy is excellent. A few years ago I had a low oil pressure indication and elected to land to check it out. I pulled power and glided 17 miles to Kingman airport from and altitude of 8500 ft. and landed on the numbers with no power application. That's a damm good feature! Date: Sat, 28 Oct 1995 21:22:42 -0400 From: pinnock@magicnet.net Subject: Hello everybody, 615PM is flying again, all the spar work is done, and finish is to primer. First flight was 10/26 and was uneventful. All the repair work added about 35 lbs to empty gross, requiring some added weight to the ballast. After about 3 hours testing to make sure all was ok, I made 3 dives at 200, 210 and 220 mph. All three were uneventful. More test will be coming, I'll keep you posted. Until next time... ---------------------------------------------------------------------------- ----------- Mike Pinnock E-Mail pinnock@orl.com 1124 Highland Acres FAX (407)297-9197 Apopka, FL 32703 Voice (407)880-8564 HM (407) 297-8884 WK Cozy MK IV 615PM Sanford, Florida (SFB) 585 hrs TT ---------------------------------------------------------------------------- -----------