Mt 03....

Dean_Dolph

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Zilch!
....... This demands accurate scales as well as an accurate clinometer since the angles are small. Ordinary bathroom scales aren’t good enough but commercial clinometers such as the “Smart Level” are fine.

I have a spreadsheet that performs the calculations if anyone would like a copy.
Chuck, I also would like a copy of your spreadsheet.

I think I had it at one time but this was before my computer was a little more organized. That means I can’t find it!

I’m curious as to how accurate you think the scales should be since you say ‘ordinary’ bath scales aren’t good enough. It seems to me that the bath digital scales that indicate to 0.2 (3+oz.) of a pound and probably measure considerably closer than that, can’t be any worse than the double hang test and picture method. Using a picture of a double hang test seems to be crude by comparison and provides several places for error. And the main one is human! Taking an accurate picture, judging the prop thrust line and then using a drawn line to determine where the Cg is what I’m questioning.

I’m not sure how much effort is required to determine this but I wonder just how much effect 3 ounces of error has on Cg calcs if the attempt is just to get within the 4 inch (+/-2”) Cg box. I recognize that in the worse case scenario, the errors could be cumulative and add up on the wrong side but hopefully the probability is that they would cancel out.

I’ve never performed either one of these tests but just looking at what is required for a double hang test makes me favor using scales and an inclinator. If digital scales, that have had a full scale calibration plot created, were used then an interpolation should provide better accuracy and precision. And I would think that the results would be satisfactory; especially since true CLT is impossible to attain for all flight conditions. The flight conditions meaning a changing fuel load and the fact that pilot and clothing weight and distribution may change from flight to flight. I mention this because I don’t recall the pilot being brought into the equation on stability. This has always seemed strange to me, especially when talking about ultralight machines, since the AUW and not just the flying machines weight is going to be the determining factor on stability and performance.
 

C. Beaty

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Send your E-mail, Dean, and I’ll get a spread sheet oozing down the wire in your direction (my rural telephone line doesn’t squirt, it oozes).

The main error from either weighing or photographing is the acute angle between the two positions. If the angles could be at 90º, there wouldn’t be much of a problem.

[email protected]
 

StanFoster

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I have always wanted to do a double hangtest this following way ....maybe its been mentioned before...but probably not with use of a laser level.


I would hang test from the teeter bolt....and set up my laser beam so as it shoots a vertical red line going right through the teeter bolt. The vertical line could be marked on some posterboard taped to the mast.


I would then place the real wheels on an elevated platform that is high enough to allow the gyro to be tipped to its balance point on the mains.

With the gyro just sitting very nose high right at this balance point...the laser level could then project a vertical red line right through the center of main wheel axle. This line would then intersect the first line right at the cg of the gyro.

This of course is another slightly different way of double hanging it,,,,but I bet would be dead on accurate as the laser beam wouldnt have the parallax problem that using a plumb bob would have or trying to take a picture and "sighting" it in.


When I finished my SparrowHawk....GBA had me send them the weights taken from a scale under each main wheel and the nosewheel. I borrowed a set of very accurate scales that stock car racers use. Digital readouts and guaranteed within a few ounces of accurate. This didnt give me the CG of course..but was to replace hanging the gyro and measuring the keel or mast angle.


Stan
 

C. Beaty

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I’ve seen laser levels that seem to go around corners advertised on TV, Stan. That might be the ticket but I have no idea how they work.
 
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StanFoster

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Chuck: First of all...your posts are super informative. I enjoy reading them until my eyes start glazing over. :der: Take that as a big compliment because it is.

Anyway....I use my rotary laser to project either a horizontal plane of red light or a vertical plane. This vertical plane of red light can effectively "visually cut the gyro right through the teeter bolt...on through the CG and on below.

Its just an electronic plumb bob.....except the light beam can easily go into all the nooks and crannies effectively splitting the gyro down its hang line. A physical item like a plumb bob has to be held outside of all obstructions and thats where the parallax error comes in.

I use my rotary laser in my stairshop mainly to project my 2d stair layout on the shop floor vertically so that I get a true 3d projection from it. It is the best investment I have ever made as far as controlling my stair build. It has to be dead on....or my stairs would never fit the cylinder on the jobsite they have to fit in.

Hey Chuck...I am going to look you up at Bensen Days and see if I cant soak up some sunrays and some IQ rays from you.:whoo:


Stan

Stan
 

steveb

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.... The MT as far as I know has never had the v c of G tested as this isn't a requirement for sec T, which relies more on flight testing and this it obviously passed.
Brian, the POH for the UK MT-03 comes with a chart which shows the poistion of the C of G at various pilot / passenger / fuel weight combinations.
 

C. Beaty

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How do those lasers that project a plane of light work, Stan? Is it a fan beam or is there a vibrating mirror that scans a single spot?

Whatever the case, that would be the ticket. Adjust the vertical beam to light up the suspension point of the hang rope and hang the gyro at two different angles.

That would eliminate errors from scales and landing gear extension. You wouldn’t need a clinometer. The greater the angle between the two suspensions, the smaller the error.
 

bpearson

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I stand corrected Steve. What does POH stand for ?

My point was that comparing the ELA and MT when refering to vertical c of g / thrustline by looking at photos is pretty meaningless because of different blade weights etc. Saying these are more likely to be clt compared to the Magni (the only other clone of the JT-5) cannot be judged by just looking and guessing.

I would rather the test of stabilty be in the air, although it seems the American tests have flaws that render them inadequate.
 

Walter

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Poh

Poh

POH stands for Pilots Operating Handbook.
It would be good to have a lookup table for all the abreviations you guys use, since it is difficult (e.g., CLT) for newcomers like me.

Walter
 

StanFoster

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Chuck: My rotary laser has a laser beam on a rotating head. You can either turn that head 360 degrees by hand...or make it rotate by itself and it then projects what appears to be a red plane of light.

My laser is about the sixe of a rubiks cube puzzle.

I have an idea Chuck. Why dont I bring it down to Bensen Days...and we could do some double hang tests with a few gyros.....maybe one NCLT and maybe a low rider Air Command with a HTL. This could be a very easy demo and all it would take is the hoist they had down there last year and some posterboard to tape to the mast to trace the laser beams line. Two hangs..and voala....the intersection is the CG. :)

Stan
 

steveb

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Poh

Poh

Brian

Someone beat me to it on POH!

I should have finished my post " .... and you can take a look next time we meet up - it's interesting stuff and supports your position that you can't tell what's going on by just looking."

Looks can be very deceptive. For example, the VPM / Magni has a heavy rotor, the MT-03 has a light one - but you can't tell that from a picture. The position of the VCG of the MT-03 varies according to the weights of the occupants and the fuel load, and I'd hazard a guess that the same is true for other aircraft with similar configurations.
 

StanFoster

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Chuck: This could turn into a mini event down there .....:first:


Stan
 

gyrogreg

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Glossary of Gyro terms

Glossary of Gyro terms

POH stands for Pilots Operating Handbook.
It would be good to have a lookup table for all the abreviations you guys use, since it is difficult (e.g., CLT) for newcomers like me. Walter
Check out the Glossary of Gyro Terms on the PRA website.
 
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