Date: Thu, 30 Oct 1997 09:48:39 -0600 From: Chris Anderson Subject: Re: COZY: Home made AutoPilot and Nav. ( was How do you vote?) At 09:26 AM 10/30/97 -0600, you wrote: Cool, I'll check out opendos, and yea I REALLY prefer assembler, at least for controls work. Although for any kinda string manipulation I'd rather eat glass... >Now to bring the discussion back to Cozy, I have thought about putting >strain gauges in the landing gear, for doing weight and balance right >on the ramp. I am just barely into chapter4, so I have no idea where >would be best to put 'em, but I am thinking in the landing gear mount >points. Is there much movement there, or is the a place in the gear >legs where landing stresses wouldn't break the gauges? Hadn't thought of that. I got a ride in Kyle Howard's VariEZ. Because the gear is so flexible she would lift one wing after moving it on the ground to spread the gear a bit. I would think that how much the gear flexed would depend on how the plane had been moved, and weather or not the tires were exactly parallel. (I'm assuming at this point the gauges would be in the "knee" area of the gear, half way up from the wheel) Thats my guess. =-=-=-=-=-=-=-=- Chris Anderson andersoc@idcnet.com Less Thought More Work! - My ex-boss Sure if it's free I'll cram some more down. - Nate Woodruff From: Marc J. Zeitlin Subject: COZY: strain gages Date: Thu, 30 Oct 97 10:58:33 EST Tom Brusehaver writes; >Now to bring the discussion back to Cozy, ...... Thank you :-). >...... I have thought about putting >strain gauges in the landing gear, for doing weight and balance right >on the ramp. I am just barely into chapter4, so I have no idea where >would be best to put 'em, but I am thinking in the landing gear mount >points. Is there much movement there, or is the a place in the gear >legs where landing stresses wouldn't break the gauges? Hmmm. Interesting question. The moment would be highest up near the tabs that attach the lg strut to the fuselage, but since the strut is tapered, the stresses/strains might not be the highest there. I might suggest putting the gage right at the root of the axle, just before the mounting flange, if there's room between the flange and the bearing (I think there is). Since this is metal, you've got a nice, linear stress/strain curve with which to work, it should be easy to calibrate, and you don't have to worry about the geometry of indeterminate structures, since the axle is just a cantilever beam. I wonder whether you'd be able to get accurate measurements, though, since you'd be looking for differences of a few pounds out of 1500 - 2000 pounds. It would be even more critical to have a gage on the nose gear, since the weight on the nose gear is a much stronger indicator of the location of the C.G. The main gear weights would only give you an indication of loading, but not much in the way of C.G. information. As far as putting a gage on the nose gear, you'd probably want it just below the MKNG-3 mount, although just above the MMKNG-15A would probably give you reasonable strength readings as well. You won't break the gages in any case - if the strains were that high, you'd have collapsed the gear long before. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 30 Oct 1997 11:36:37 -0500 From: Bulent Subject: Re: COZY: strain gages I noticed that the narrow part of the landing gear between the mounting points moves up and down when the gear is loaded. How about installing the gage there? Bulent From: AlWick Date: Thu, 30 Oct 1997 14:54:04 EST Subject: Re: COZY: Home made AutoPilot and Nav. ( was How do you vote?) Organization: AOL (http://www.aol.com) In a message dated 97-10-30 10:41:22 EST, tomb@augusta.netperceptions.com writes: << Now to bring the discussion back to Cozy, I have thought about putting strain gauges in the landing gear, for doing weight and balance right on the ramp. I am just barely into chapter4, so I have no idea where would be best to put 'em, but I am thinking in the landing gear mount points. Is there much movement there, or is the a place in the gear legs where landing stresses wouldn't break the gauges? >> I would be quite suprised if strain gage failure was an issue. Great idea. I am doing similar with other sensors. Have to admit I didn't think about doing gear, but I have extra inputs available, so why not? -al ps Sorry I missed the original post. Sounds interesting. Date: Thu, 30 Oct 97 14:56:54 EST From: "KEN SARGENT" Subject: Re: COZY: strain gages You could use a company called SRTRAINSERT (215) 825-3310 that makes instrumented bolts, clevis, and spindles etc. These already have the gauges and signal conditioners built in. I think they do custom work to, so if you gave them an axle they would mount gauges to it. I have used them on roller coaster wheels, and they do a good job. I have thought of the same exact thing for WT and balance. Ken Sargent ken_sargent@wda.disney.com From: cdenk@ix.netcom.com Date: Thu, 30 Oct 1997 20:34:02 -0600 (CST) Subject: Re: COZY: strain gages Whats all this going to weigh? Burt: "Up in the air not to come down..." I think you'll find that the criteria becomes very simple, a front seat weight max & min, and a total weight. The fuel and rear seat and luggage do not effect the cg hardly at all. From: cdenk@ix.netcom.com Date: Thu, 30 Oct 1997 20:44:59 -0600 (CST) Subject: COZY: Strain gages - gear spread when moving. Good point, yes the gear does spread, and good practice is to put shoulders under wing end and lift a wheel off the ground to help the gear from taking a set. The wheel moves in around 1.5" That is considerable strain (deflection parallel to the load in (micro) inches / inch. Forget any strain gages that will be useable for weight and balance. The gages would have some to determine the nature of deformation of the strut. Then knowing the deformation, load test a strut, by duplicating the static loading (make a frame, use pulleys and weights) then proportion upward the loading to failure to find the factor of safety. Even then, this is only one test, subject to many variables that would make the results only an rough indicator. Combinations of braking, hard landings, dragging brakes, tire/pavement friction are just a few of the variables. From: Greg and Jill Hilliard Subject: COZY: strain guages Date: Thu, 30 Oct 1997 21:40:58 -0600 Tom Brusehaver writes; >...... I have thought about putting >strain gauges in the landing gear, for doing weight and balance right >on the ramp. I am just barely into chapter4, so I have no idea where >would be best to put 'em, but I am thinking in the landing gear mount >points. Is there much movement there, or is the a place in the gear >legs where landing stresses wouldn't break the gauges? I also gave some thought to mounting strain guages in the gear to to = calculate weight & balance. Something to consider: the forces acting on = a Cozy parked on a ramp are not those of gravity alone. Any slight = breeze is going to create lift on the wing and depending on elevator = position, lift or downforce on the nose. Put this together with an = idling prop (near zero thrust, but not zero)or being parked on a sloped = grade and they would introduce what could be a signifigant error in your = calculations. Not a problem if they err on the out of balance side and = force you to investigate further before flying, but dangerous if they = lead you down the runway with an out of balance Cozy. Do the airlines do this? If I'm not mistaken (& I may be) they perform = their W&B they same way we do. Greg Hilliard Cozy mk4 #456 finishing ch 4 Date: Fri, 31 Oct 1997 08:06:05 -0500 From: David Domeier Subject: Re: COZY: strain guages Greg, The 767 has onboard weighing but it is not used to compute CG. It's a gross error weight check against data supplied by a weight and balance land based computer which does the various load weight and location calculations. That info comes across a small onboard printer after the flight leaves the gate and is compared to the weight numbers in the cockpit...at least that's how it's done at the company I work for. I doubt that we could afford such a system in the MKIV, nice as it would be. Not to change the subject to drastically, I've been thinking about a brake temperature system for our airplanes. Brookstone has a digital temp device with 2 temps and a clock for about $29. I've been wondering if one each probe could be installed in a wheel pant....I will try it when I get my airplane flying, which I would like to be tomorrow but probably won't be until late spring. dd MKIV#155 Date: Fri, 31 Oct 1997 11:50:15 -0600 From: Paul Comte Subject: Re: COZY: strain guages Has anyone seen tire pressure sensors yet. I saw a spot on their use in Indy cars a few years ago. Wouldn't it make more sense to monitor the tire pressure? Have the system sample the pressure when you open the canopy, then again when you start the engine. Compare the values. The first set of numbers should be at least within tolerance of your preferred pressure setting. The second set of numbers should be higher by at least the weight of the pilot. Of course there is no way this will replace the REQUIRED weight and balance check. It would be a nice double check for what is a serious issue. As a side benefit you are going to have another chance at catching one of those slow leak or flat developed in-flight problems. The standard development hurtles are still with us. How to retrofit to an AC wheel? How to transfer data to monitor? How to process and present data to pilot? Of course there must be commercial versions of this available... I can visualize a self contained sensor/transmitter that you could stick on the inside of a rim. I think you would want this kit to also have a counterweight to stick on the opposite side of the rim. Maybe the thing could self charge a lithium cell through some mechanism associated with the centrifugal force exerted on it while rolling. To report the data the sensor would just need to listen for a request (RF??) and then reply with a value and unit id. If someone likes the idea I'd love to share the liability!! ;-) -- Best Regards, Paul Comte A Plus Computer Service, LLC. 5100 West Blue Mound Road Milwaukee, WI 53208-3654 (414) 456-9700 Voice (414) 456-9701 Fax From: cdenk@ix.netcom.com Date: Fri, 31 Oct 1997 16:49:12 -0600 (CST) Subject: Re: COZY: strain guages Pcomte writes Theoretically it should work, but my experience with automobiles (Ford Escorts and Broncos) has been the weight on the tire doesn't effect pressure that much. Try checking with weight on tire, and then jack up. The difference might be a psi or so. But let the temperature drop 40F and the change can be 5 psi. What happens with landing at an airport, warm (hot) brakes (tires), take on passengers, luggage, and fuel, the pressure will be off considerably. Note that Every tire pressure checking procedure I have see, said check "Cold". From: AlWick@aol.com Date: Mon, 3 Nov 1997 13:54:20 -0500 (EST) Subject: Re: COZY: Boomerang data system, etc. In a message dated 97-10-31 14:02:17 EST, morro@inreach.com (Martin Orro) writes: << re: Strain gauges - Burt placed them on the spars to determine loads (almost a G-meter). Also, my previous experience with strain gauges and composite structures gave fits with thermal expansion (man do they expand and contract!), and visco-elasticity. >> I'm suprised about the thermal expansion problem. Most strain gages I've dealt with are only about 1/4" diam. Are you saying the expansion affected the accuracy of the gage? If that were the case, guess you would need to add thermocouple in vicinity to adjust value. I'd like to hear more about this problem. I saw photo's of Burt's approach. I assume he wasn't aware of off the shelf components that could do all that they did with custom software. Good stuff out there and you don't need to be much of a programmer to use it. fwiw -al Date: Mon, 03 Nov 1997 16:05:00 -0500 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: strain guages David Domeier wrote: > > I doubt that we could afford such a system in the MKIV, > nice as it would be. rutan certainly wouldn't stand for this kind of talk! ;) last winter i did a couple "library lunches" and found two decent papers on the subject of onboard weight and balance systems: aiaa paper 88-3919 "design of a certifiable primary on-board aircraft weight and balance system" by vetsch and burgener, 1988 sawe paper 1695 "weight and center of gravity determination on ground and airborne" by drachenberg, 1987 according to these two papers, attempts to accomplish accurate w&b [1] started in the 1940's by measuring oleo strut pressures. the second generation appeared in the 1960's and employed strain gauges to measure beam bending loads and then shear force. in the late 1970's, a magnetic reluctance sensor was developed that allowed such a system to be reliable enough [2] for certification. according to the first paper, honeywell produced a system based on this new type of sensor which was designed to be the sole means for determining the departure weight and cg. the system is supposed to be available for the 747-400, the A300, the A310, the A320, and the MD-11. the sensor is basically a magnetic plate attached to one part of the structure with two electromagnetic coils suspended above and below mounted to another part of the structure. the change in air gap between the plate and the coils effects the coil voltages. the design is such that only the vertical shear is measured, automatically eliminating side force errors. if only a couple people ask me, i could make copies of these papers for "personal or research use only" as far as i understand the us copyright laws... -- bil [1] accurate according to FAA advisory circular ac 120-27a and ARINC characteristic 737 [2] for a class i system: the system shall be capable of measuring the aircraft gross weight within an accuracy of 1%, and the aircraft cg within 1% mac (absolute), both with an interval of confidence of 3 sigma or better. the system must also be able to self detect any fault which would significantly degrade accuracy, so that the probability of an undetected catastrophic fault is less than 1 in 10^9. aiaa = american institute of aeronautics and astronautics sawe = society of allied weight engineers mac = mean aerodynamic chord