mjgundry

Yet another link: http://home.houston.rr.com/pieceofwork/

I'm a structural PE and partner in a small engineering firm. My job duties are all over the board. My work entails designing and constructing roads and bridges. I also handle some airport work and structural analysis of whatever people want me to check. I wear a second hat as a sys-admin/IT type where I manage our office network and write software for converting survey and design data. Mostly, though, I'm a happy dad and husband. Interesting to to see what others are about. Cheers, Matt

Try here: http://www.kgarden.com/cozy/chap27.htm A little better than halfway down the page, where he talks about the fly-in at Shady Bend. Is that it? I too would like to see more of this technique. Cheers

No evil spirits...just a move to a new server. You should be getting messages from the Cozy list again shortly. Matt

The issue with the gear struts is that they utilize a different type of glass. In order to fully realize the strength of this different glass, a quality of layup is required that is not easily accomplished by the normal builder. I also believe these parts are autoclaved to prevent material creep while sitting on a hot ramp. I do wish there was an alternate gear design that I could build myself with spar cap tape and cloth. Even if it resulted in a little less than optimal gear (weight or aerodynamically wise). I've also noticed the lack of some critical dimensions needed to create some of the metal parts. I'm not sure if I've overlooked the dimensions on a related drawing, or if they simply aren't in the plans - so I've withheld comment thusfar. Most builders just get their parts from brock, so it isn't an issue. Like you, though, I'd like to build whatever I can myself. Perhaps one of the crew working with Dust in MI (Clifford?) can comment here. I believe they are making their own metal parts. Cheers

Jon, don't start sucking down all those pages just yet Stuff that disappears from the web is typically still available here: http://web.archive.org/collections/web.html Granted, the link embedded in a forum post will be broken, but the URL can be used with the Wayback Machine to recover the old information. Matt

For those interested, I've fixed the above mentioned mathcad->html file. It wasn't the gifs, but all the extraneous (and incorrect) information put there by the tool I used to convert rtf to html (Word 2000). Time to upgrade to the latest version of MathCAD which supports html output directly, I suppose. http://www.faa-engineers.com/~mjgundry/ductedfan/design.html I've also cleaned up the sketch of the duct cross section. N joy, Matt

Whether or not a Lancair, or any other prop driven plane, has experienced mach stall at 300 mph is immaterial. The overall aerodynamic cleanliness doesn't really matter either. Those other aircraft are using airfoils designed for higher speeds - not a fat Roncz like the Cozy canard. You simply can't make a meaningful comparison between an airfoil with Mcr of .5 with ones on the order of .7 (or better) at this speed. I wouldn't count on the drag rise to save you. The canard is small, so the overall drag rise may not be as dramatic as the forward loss of lift. At low angles of attack that drag rise might be delayed just enough that you don't experience it until after it's too late. Once the nose is pitched down by as little as 10 degrees, gravity is providing more push than your engine was. By 15-20 degrees the gravity "thrust" has doubled. Are you sure you can recover before then? Also note that the pitching moment of your main wing may be starting to rise dramatically (another mach effect), further loading the canard. I'm not saying you are wrong about the ability of the Cozy to fly safely at 300 mph, but I sure wouldn't be using the Lancair or any other aircraft designed for high speed as evidence to that ability. Matt

What would be the problems involved with changing the heat source from the plans heat muff to a heater core as Velocity and Mr. Wilhelmson have done, but leave the heater core in the back instead of plumbing it up to the nose? Seems to me this would be lighter and safer. Matt

Agreed about Perry, I find no end to the enjoyment of pouring over the data at his site. At the same time, I don't think he has missed the critical flow thing either. His older logs spell it out that his blade tips are nearing 1000 ft/sec. Then in the latest log he discusses eventually trying a smaller diameter fan. There are tradeoffs, and accepting the higher blade tip velocity to get higher mass flow may result in better efficiency overall, but I think his move to a smaller fan is worth a try. Matt

There is definitely more drag with the duct. However, the fan desn't have tip losses that the prop does. If you try to expand the flow too fast in a duct exit, you get flow separation, and even more drag, but we'll try to avoid that. I expect that the PSRU is more efficient, at least when comparing as we are here. Perhaps other factors will enter in, and the fan will make par on efficiency. I don't know, and I'm a long way from feeling comfortable making a guess. Regardless, efficiency isn't my only goal. Mechanical simplicity and cost are also major factors. We have a saying here that goes "When cost becomes a factor, it becomes the only factor". I can fly a long way at a 10% disadvantage for the cost of a PSRU! You'll be way ahead of me if you finish in 2007, but I'm game. Matt

Bummer about the html sheet not apearing correctly. I checked, and I imagine it is because they are all little gif images. Unisys would have a field day. I'll convert them. The math really isn't very deep. If you remember Bernoulli, it's actually quite simple. Yes, I was thinking of a fixed pitch prop. A csu will do better than a fixed pitch prop, but I don't think it will match up to the duct. August Raspet at U. of Miss. was getting 560 lbs of static thrust with 90 hp, and 1800 lbs with 250 hp. Pretty impressive. Granted, this was an acedemic excercize. I wouldn't expect to get near that performance on the back of a Cozy. Thrust/horsepower falls off as disk loading increases, and I am working with a higher disk loading than Raspet's experiments. The duct accomplishes the high static thrust by vastly reducing tip losses, and by dropping the pressure on the front face of the duct, and increasing the pressure on the exit. Because of this pressure diffential, the duct itself can be providing over half the total thrust. As speed increases, duct drag starts to overwhelm this effect. True. Perry has upgraded his thrust bearings and I imagine I would do the same. Also, a direct drive fan wouldn't be as bad as a direct drive prop in this situation. Smaller diameter - less gyroscopic loads. Lower total disk force - less shaft thrust (remember, the pressure is recovered aft of the fan and the duct actually does some of the pushing). There is a point where you can't accelerate (low speed duct) the air any more because you are already so fast as to cause problems with compressibility. Nor are you fast enough to get gains by having an inlet diffuser (high speed duct) in front of the turbine. So you just have a duct that does nothing but add drag. That point is right about where the turbo props operate. IIRC, Marc de Piolenc, the author of the book I cite on my page, has said that speeds above 300 Kts are purely the realm of the turboprop and turbofan. Thanks. Obviously it's still very early in my Cozy quest. It's as likely as anything that I will drive to nearby Wentworth Aircraft and pick out a Lycoming, just as the plans say. Cheers, Matt

I am looking into a ducted fan for the Cozy Mark IV, powered by a 13b engine. If you are interested, I have a site with some *very* preliminary design data up at: http://www.faa-engineers.com/~mjgundry/ductedfan/ This very same topic was recently discussed on the Cozy mailing list... To recap: A perfectly point designed prop will probably just beat out the perfectly point designed fan at the cruise speed of a Cozy. I'd like to see if the difference can be made as small as <10% in real life (not my playing with numbers). Perry Mick's shrouded prop weighs 30 lbs, 5 lbs less than a PSRU. He says it is overbuilt, and the next one could probably weigh in at 20-25 lbs. The fan also weighs less than a prop. Venturing a guess, I would say that Perry's design is running into a problem with compressibility at the fan. Doing the math, his blades are moving near Mach 1, and the limit of the airfoils is probably closer to Mach 0.7. The loud fan noise that he speaks of seems to bear this out. He is currently planning to try a smaller diameter fan which would help alleviate that problem. I am anxious to hear/see his results. True enough, the inlet diffusers on high bypass turbofans are not efficient at low speeds. However, anyone trying that sort of geometry for an IC engine powered fan probably hasn't worked out the math. A properly designed ducted fan can actually outperform a prop at low speeds because it is capable of producing far more static thrust. There is no reason that you can't have high mass flows with a ducted fan. In fact, one of the first stages in my preliminary design was maximizing the mass flow by adjusting various duct dimensions. As opposed to an inlet diffuser, low speed ducted fans accelerate the air into the fan, then diffuse the flow afterwards for pressure recovery. Using this technique, mass flow and efficiency of the fan can approach that of a larger prop. If you want to compare diameters, you should probably be comparing the diameter of the "capture area" of the duct with the diameter of the prop, and that is a tenuous comparison at best. Yes, you can have variable exit geometries. I'm not sure than variable fan pitch has much utility. Variable exit geometry could help optimize cruise speed efficiency without adversly affecting low speed thrust, but I'm not sure that it is worth the complexity, given the speed range of a Cozy. I am currently at the point where I have a duct geometry I'd like to try, and so I am modeling it for CFD analysis using NASA's ADPAC. I expect a some refinement as I adjust the design to accomodate off-design performance. I'd really appreciate informed feedback on my site, if anyone is so inclined. Matt

For what it's worth, making the site MSE 5.5+ only, will make it almost inaccessable to me, and I suspect many others. Of course, with the access logs, you already have a better idea than me who would be alienated. If it is the main site, I guess it wouldn't matter to me, but if the change affects the forum, I would be pretty diassappointed. Matt

Skid pan training? Isn't that what church parking lots are for. Though I suppose they don't get quite as icy down in Florida as they do up here.

Is that in response to my post about not engineering a front hinged canopy? Sorry, I didn't mean to imply you shouldn't try to put one on your own Cozy. I just meant that you should take a look at those plans before starting over from scratch, as I intend to.

As far as engineering a forward hinged canopy, don't. The forward opening canopy for the Cozy has been done before. The Cozy Classic has it, and plans were available from Uli Wolter at one time. Check the description in the Wicks Aircraft catalog for the Classic. It describes the canopy, as well as gives contact inormation for Uli. HTH

I seem to remember Dick Rutan having a routine in a VariEZ/LongEZ at Oshkosh many years ago. I was quite young then, so the details may be way off, but I think he did loops and rolls, and ended the routine by cutting the engine at a rather low altitude, then did a couple 360s before putting it back on the pavement. Matt

The guys flying rotary engines are noting BSFC of .47 to .51. Maybe as low as .45 when leaned way past peak like Tracy Crook does. That's about on par with the Lycs and Conts. Maybe a little worse, certainly not way better. They are very compact for for their power output, so that may lead to other efficiencies. All indications are that the rotary is a very reliable engine. Just three moving parts that are not stressed very hard at all. Race guys run these engines multiple races while getting 200+ horsepower per rotor. Typical aircraft applications only demand 100 hp or so per rotor, so the stresses are even less. Cheers,

Does anyone have CAD files of the 13B? A model of the exterior form is sufficient. I'd like to place it on a virtual airframe and fool with the cowling shape a bit. Thanks, Matt

If it makes you feel any better, John, it appears you've got "redrive final install" on your list twice. Assuming you only plan to do it once, your list just got a little shorter Best of luck finishing your Cozy, Matt