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About athomp58

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    Aubrey Thompson
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    Wilmington, NC

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  1. athomp58

    SQ2000 project

    Hi Tom. Welcome to the rarified community of SQ2000 fans! I have a fairly long history with the SQ2000 and rotary powerplants. I'll be at Sun N Fun the entire week this year (my daughter is helping Dave with the radio station). Shoot me a text msg at my number on file. Maybe we can get together there. I usually use the Alternative Engines tent as "home base" when I'm there.
  2. Aside from the landing gear made by Infinity, what were some of the problems with the SQ2000 kits? Aubrey
  3. It's best to keep your $$ in your own pockets on this one guys. Innodyn has taken many deposits and delivered zero engines after many years of advertising and exhibiting that CNC machined chunk of aluminum at shows. You will notice that the website promises future information in January of 2005. They have yet to publish dynomometer information for this engine. With a single stage turbine and a single stage compressor, one would need to discover some new principles of physics to achieve the results they have advertised. Aubrey
  4. Folks, let's be very careful about the generalizatiions here. As I stated, the dynafocal type mount with a ring structure that ties the engine mount points together is NOT "similar" to this mount. It is a frame type structure. My comments are directed toward this particular configuration. It was as incorrect in 1983 as it is now. It could probably be made correct by the addition of a dynafocal type ring structure. But, then it would be a different mount and not "similar" to this one. Chrissi, EAA publications are not peer reviewed. The fact that this design was published does not necessarily make it correct. Jack, I did not consider tubing diameters and wall thickness. So, there was no need to mention engine weight, torque, hp, "g" loads, safety factors, etc. That is a separate set of issues. I have read of numerous firewall hardpoint repairs. I did not say "failure". I agree with you that a failure is a remote possibility. Your mount is probably some variation of a dynafocal type. Do you have a photo you could post? You will not find this particular mount configuration on a certified aircraft.....for good reasons. Be safe, Aubrey
  5. Jerry, I appreciate your skepticism. My background includes BS and MS degrees in Physics. Before retiring last year, I taught physics, hydraulics, engineering mechanics, and electronics at the college level for many years. During the 8 years preceding my retirement I was the Chair of the Science and Math Department at Cape Fear Community College in Wilmington, NC. My department employed about 50 faculty and served typically around 4000 students per semester. I am an applications oriented physicist and have taught the Statics and Strength of Materials courses that cover the design of these structures many times. These courses were actually not offered by my department, but, by our Engineering Department. Cape Fear Community College engineering students have participated in several competitive international engineering events (human powered submarines, remote controlled underwater vehicles) we have always placed first, second, or third and we usually win the secondary "best design" award. Not a bad performance, especially considering that MIT and CalTech are usually in the competition. So,...we know how to build mechanical "stuff". What does the engine mount need? This mount should be designed as a truss type structure. In a truss structure the tubes or truss members should experience forces that are only either tension or compression. No bending forces are allowed. The four engine mount points must each be independently fixed in 3-dimensional space by tubes that transmit only tension or compression back to the firewall mount points. Fundamentally, this means that each of the engine mount points must be contacted by at least three tubes. In this instance the engine case cannot be part of the structure because the rubber bushings allow motion. The dynafocal type mount you mentioned is an entirely different type of structure because the engine mount points are connected together by the (fairly heavy) ring system. I've attached a marked-up version of your photo. We need tubes where I've marked lines. The yellow and red tubes will fix points "a" and "b". The lower X structure should consist of straight tubes that lie in a plane. I would replace the existing tubes with the green tubes. Finally, on composite aircraft, I worry about how "hard" the hard points on the firewall actually are. So, although this is probably optional, I would tie the four firewall mount points together with the blue tubes. These would be tension members and could be made of 3/8" tubing. They would represent very little weight penalty and may save a major airframe repair at, say, 1000 hours or so. (guessing here) Of course, what I've penciled in may interfere with existing components on the firewall or with engine components, etc. In that case, some other tube configuration may be needed. I don't know about Chrissi's engineering qualifications. I meant no offense. All I can say is that everybody makes mistakes occasionally. I am reminded of a machinist who worked on the 2nd shift at a textile mill who, when I was a kid, would help me with my "build it" projects. "Red" Thompson was his name; his favorite saying was: "Don't worry about making mistakes, I've never made one I couldn't fix". Aubrey
  6. Jerry, This engine mount is unsafe as it is designed. There will be bending forces where the four tubes are joined at the bottom. Fatigue cracks will develop there very quickly. Likewise, the top tubes are not properly supported. Bending loads will be present at the top firewall plates. The design of this mount is fundamentally flawed and it will probably fail with potentially disasterous results shortly after being placed in service. I regret having to convey such a bleak assessment. Perhaps CG Products can solicit the services of a mechanical engineer and re-work the mount with a more robust design. Aubrey
  7. Jack, What brand paint do you plan to use? Is it an acrylic urethane? Do you think clear coating it would reduce drag? Aubrey
  8. Tony, Your drawings are great! You are prolific! I haven't had time to get even one conceptual sketch done. Chill out a little bit. I don't want you to burn yourself out on this too quickly. Here are some thoughts I've had: 1) A pneumatic strut from a motorcycle front fork may be better. (I'm thinking of your first drawing here.) The spring rate could then be adjusted with air pressure. These are light weight, made of stainless steel and aluminum, and can handle substantial bending (side) loads. Your outer tube could then be non-structural and only transmit the steering torque. One advantage to a pneumatic strut is that under extreme loading the restoring force would be non-linear and the strut would be less likely to hit the end of its travel. We would need to choose a strut with the right amount of travel or limit the travel someway. How much travel do we need? During takeoff the strut will be contributing lift to the nose. Some of you who have experimented with nose strut height need to comment. 2) The axle of the wheel needs to be trailing the strut (or steering) axis to achieve the castering. Your later drawings have this feature. The early Lancair nose gear had trouble with shimmy. Is anyone knowledgeable about how this was fixed? 3) I can't let go of the image of the trailing link gear I saw on the jet. I like the trailing link concept for a couple of reasons. It would be easy to fabricate from off-the-shelf 4130 tubing with the energy absorption and support force done with light weight, off-the-shelf pneumatic components. And, we may be able to make it fold into a small space. Imagine a truss structure with a hinge at the top and a hinge about half way to the wheel. It would "coil up" into the wheel well and be actuated with a steel cable or small roller chain. 4) A question for the group: For a CozyIV, what is a reasonable range for the pre-departure nose wheel weight? 5) Finally, we need to open the floor for nominations for a wheel size. One of our design objectives was to have better operation on turf. It should be a readily available size with symmetric hub bearings. The feasibility of some of the above may depend on the wheel size. Aubrey
  9. Tony, Having the steering forces loosely coupled via springs is a good idea. The concept should be that the steering is for small directional corrections during taxi and landing/takeoff operations where it would be easier and more precise than differential braking. The worst case scenario for side loading the gear would be when differential braking is used to attempt turn the aircraft through a smaller turn radius than the nose wheel caster can accomodate. If we can make the wheel caster to + or - about 70 degrees and still be steerable, then the side load issue will not be very troublesome. The nose gear support box structure would be fairly easy to reinforce to take some additional side loading of the gear strut. I'm thinking about a cable around a wheel kind of mechanism to get more steering rotation than a bellcrank mechanism would give. The wheel will need to centralize when there is no weight on it. It's getting late, I need to dream on it until tomorrow. Aubrey
  10. This issue has been debated before (probably several times!) and I mostly agree with Marc on the issue of adding steering capacity. The airframe is not designed for side loads and designing a foolproof linkage to the canard type rudder system may be trickier than it seems. However, I think the Cozy type airframes need an energy absorbing nose gear with a larger wheel. This is partly motivated, for me, because it is looking like I may have to do my initial testing from a 5000' grass field. But, I have also heard several stories about slightly hard landings that could have been disastrous because of the bounce from the springy fiberglass nose wheel support. A couple of weeks ago, while I was at the gym, a show was on TV (without sound) that showed a small jet military trainer with a beautiful, small, maybe easy to copy, trailing link, nose gear. I've been mulling over this issue for several months and seeing the trailing link gear stimulated me to get active on it again. Aubrey
  11. Tony, I would like to take a look at the steerable nose gear adaptation of the motorcycle fork. Please send me a copy of the files. I'm using DesignCAD which can open most any CAD file. BTW can anyone steer me toward the old post that appeared either here or on the Canard Aviation Forum within the past two weeks that had the picture of the canard with the trailing link main gear struts. The original post was a question about identifying the aircraft. It appeared briefly when someone posted a reply. Now, I can't find it. I wrote the contributor to ask if he could post more pictures of the trailing link gear. But, his e-mail link failed. Thanks, Aubrey

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