Hang Test questions

[13brv3]

Greetings,

I'm looking for a hang test procedure for the Dominator, and I didn't see a section in the manual for it. Is there a "how to do a hang test" procedure posted somewhere?

From searching, I've found that Ernie recommends 9-12 degrees at the keel. I'll assume that's correct for now.

I also assume that this is like weight and balance on a plane, in that you want to be within that range for all conditions of pilot and fuel weight. Since there's no obvious way to calculate any of this, I guess you test with empty and full fuel?

On another thread (not about Dominators), there was talk of fixing the rotor head at a particular angle for the hang test. I would think you should let the rotor head seek it's own position, just as it would with the rotor blades attached. Which method is correct?

Thanks,
Rusty

[Mac]

http://www.rotaryforum.com/forum/showthread.php?t=12331

Hope this link helps for double hang test

[Doug Riley]

Put the rotorhead in the middle of its range (stick neutral). Try the hang with empty tank and with full tank.

A VCG test (double hang) is not necessary with a stock Dominator, since the configuration has already been tested. If you add, subtract or move masses, however, do the double hang. A stock Dominator's CG will come out a few inches above the thrust line (a so-called low thrustline, or LTL, arrangement).

[13brv3]

Thanks for the comments. Stick neutral. Roger.

I don't have any plans to do a double hang test, and even the single hang test is probably more of an excercise than anything else. I'll do it, but if it's not in spec, there are hundreds of other Dominators that aren't in spec either :p

Cheers,
Rusty

[Timchick]

Rusty,
Having someone else there to assist you would be a great help. That way you can sit in the seat and the other person can check the angle.

[Chris Burgess]

13brv3 - Once you establish where your limits are by the hang test, you can convert it all to a "calculation" method, (measure three points), and always have it fall within that CG range. I can do all mine by calculations. It is done just like any other CG calculations. The aircraft must be level and you should use quality scales. You can back calculate all added weights for the moment arms.

[Udi]

Chris - since your gyro hang angle is not vertical, your CG calculations should include the vertical location of the item you are adding or removing. For example, moving a weight up the hang line would move weight from the nose wheel to the main wheels, but the hang angle remains unchanged.

Udi

[13brv3]

Chris,

I'm still thinking about how you could calculate this. If you have any example calculations, I'd be interested to see how you're doing it.

Thanks,
Rusty

[helipaddy]

I don't have the Dominator manual to hand at the moment, and yes its a little vague with the hang check procedure, but I think it says somewhere near the front of the manual that the mast angle should be 0 to 3 degrees nose down from the vertical.
Paddy.

[13brv3]

Hi Paddy,

If the info was near the front of the manual, I probably wouldn't have seen it. I was looking near the end, around the engine break-in and test flying sections. If there was going to be a section on hang testing, I'd figure that's where it should be. I'll take another look though.

Thanks,
Rusty

[Mac]

Rusty
Here is a spreadsheet (CG5.1) which can be attributed to Chuck Beaty on mathematically computing the horizontal and vertical cg. I have lost Chuck's instructions so here is my rendition..??..??.


Needed: one scale and two blocks of wood the same height as the scale, level used in setting the prop pitch, tape measure, a cinder block for the front wheel and a friend.

Steps:
1. Locate gyro with rotor mounted on a level smooth surface and place level on keel, gyro should have front wheel on the ground, verify that keel is level and at zero degrees.
2. Measure the height from the center of the axle of one of the mains down to the floor. Record this height (Cell D44).
3. Measure distance between centerline of main axles to the center of front axle, then record the distance (Wheel Base Inches for Cell D40).
4. Place scale under front gear and two wood blocks under mains.
5. Climb aboard gyro and have a friend record the scale readings (Nose Wheel Weight Cell D43).
6. Repeat steps 4 and 5 by moving the scale to each of the main landing wheels with the wood blocks placed under the other wheels (Cell D41:42).

At this point, you have now taken scale readings at your front landing gear and the mains which resulting in three point weight readings of your gyro.

7. Chock the mains so that the gyro will not roll forward or backward.
8. Raise the front landing gear up and place underneath - a cinder block with the scale on top of the block.
9. Record the weight at the front landing gear with you aboard (Cell D50).
10. Place level on the keel and dial in the degrees the keel is while front gear is on the scale and cinder block. Record the angle of the keel (Cell D48).
11. Record what you feel your accuracy and the level accuracy (Cell D49)

You are now ready to enter weights and angle into Chucks excel spreadsheet. Cells in yellow is the output information.

[13brv3]

Hi Robert,

Thanks very much for the instructions and spreadsheet (thanks to Chuck too of course). I haven't run through the math, but I can easily see how this will locate the actual CG of the gyro. I like this MUCH better than trying to hang the thing :cool:

The only problem would be that balance is always given as hang angle, but once you locate the actual cg, you could draw a line from the teeter bolt, through the CG point, and past the keel. Once that line is established, the angle could be measured between the line and the keel. Yep, I like it :D

The question would be about the weight of the rotor. Since a normal hang test eliminates the rotor weight, then I supposed this W&B method should be done without the rotor as well.

This actually made my day, since I've been dreading the hanging.

Thanks,
Rusty (got scales, no rope)

[Mac]

Rusty
Chuck's spreadsheet CG5.1 does require the rotor to be mounted.
I will edit my error in the post.

Thanks
Robert

[13brv3]

Rusty
Chuck's spreadsheet CG5.1 does require the rotor to be mounted.
I will edit my error in the post.

Thanks
Robert

Hi Robert,

If that's the case, then the results can't be compared to the standard hang test angles that are typically given. It's not that they wouldn't be valid, but you probably don't have factory specs for that condition.

Also, a question. The instructions ask you to measure the distance between the main gear. I don't see how that's important to the balance, but I do think you'd need the distance from the main gear to the nose gear, which isn't requested. Is that maybe what's supposed to go there instead?

Cheers,
Rusty

[Mac]

Rusty
You are correct!!
Wheel base is from mains to front gear.
I will edit the post.

Thanks for catching my error.


Also, gyros with shocks, lock the shocks to normal flying position (extended position - Butterfly) if possible. This will change the keel degrees but should then should take into account the wheels which extend during flight.

Hopefully, Chuck will comment.

[C. Beaty]

The sole purpose of a hang test is to center the controls; it has absolutely nothing to do with stability unlike the case of a FW. If a gyro has a horizontal stabilizer, then dangle angle produces a secondary effect on stability by affecting the angle of attack of the stab. But it’s quite minor.

If you get someone to do a test flight, he’ll be able to tell if the stick is properly centered, hang test or not. If built by the plans without major modifications such as substituting a Subaru engine for a Rotax, the hang test can be skipped.

[Dean_Dolph]

Rusty, I've been confused (easy to do!) starting with your intial post. You mention the keel angle but then the thread turns into a treatise on a hang test to determine the CoM. So, what are you trying to determine the CoM or the keel angle?

The Com is always going to be somewhere on the vertical hang line as we all know. But this has nothing to do with the keel angle which is set to provide the correct pitch control range.

Changing weight along the pitch axis will cause the keel to either drop or raise because the keel balance point has changed. You are saying that Ernie specifies a 9 to 12 degree keel angle; he specs this to assure that there is enough pitch control range. It has nothing to do with the CoM which is always going to be above the keel. If the keel angle doesn't lie within the spec range then some mods have to be done.

EDIT: I see that Chuck B. replied before I did so I hope I supplied the correct info!

[Mac]

Rusty
Your question may or may not have been answered.
Does your dominator kit include sacrificial cheek plates with which multiple holes have been or can be drilled into it? The cheek plates mount to the mast top. Placing a pin across the two cheek plates and hanging the gyro with you aboard, the gyro's keel (nose) should point down 9 - 12 degrees below the horizon per plan specifications. If the angle is less than 9 degrees, the pin should be moved rearward and consequently if the angle is greater than 12 degrees, the pin should be moved forward. This determines the location of the rotorhead mounting.

If a 150 lb pilot flies this gyro, the rotorhead might need to be mounted to cheek plates 4 inches behind the mast.

If a 250 lb pilot flies this same gyro, the rotorhead will probably need to be mounted to cheek plates 4 inches ahead of the mast.

[13brv3]

If built by the plans without major modifications such as substituting a Subaru engine for a Rotax, the hang test can be skipped.

Hi Chuck,

Thanks for the comments. The machine was a rolling chassis with pod, and the only change is a 12 gallon seat tank in place of the 7 gallon that was there originally. It's got a 582 with hyd pre-rotator, and I weigh 190 lbs. Best I can figure, it doesn't get much more stock than this.

My plan is to do the test with scales, rather than hanging, though I'm convinced I can determine the "hang angle" from that.

Cheers,
Rusty

[13brv3]

Rusty, I've been confused (easy to do!) starting with your intial post. You mention the keel angle but then the thread turns into a treatise on a hang test to determine the CoM. So, what are you trying to determine the CoM or the keel angle?

Hi Dean,

My only goal is to verify that the machine is within RFD specs, and that it's safe to fly. Doing a hang test would verify that, by directly measuring the keel angle. However, the same keel angle can be derived from the scale method given previously. When I'm done, I'll have CoM, and keel angle.

Cheers,
Rusty

[13brv3]

Does your dominator kit include sacrificial cheek plates with which multiple holes have been or can be drilled into it?

Hi Robert,

My pile of misc parts from RFD has only the real cheek plates. There are two extra holes, but I don't see how they could allow you to change the positon of the plates any. Best I can tell, there's only one choice, and that's how it was when I got it.

Rusty

[GyroRon]

Rusty, I admire you for asking questions rather than not, but geeze your over thinking this stuff and making a big deal out of small stuff really...

Although I agree with Chuck Beatys last post, I personally would want to do the test to insure the angle was in the correct range before I flew it.

To do a hang test is NOT A BIG DEAL!!!! Really.... The hardest thing is to find a place high enough to lift it up. I use a chain hoist secured to a 12 foot tall beam in my hangar.

Find a beam or truss in your hangar, or a tree limb outside in your yard etc... and what you do is slide in your teeter bolt through the rotorhead, and hook the chain hoist to the teeter bolt and then lift the darn thing off the ground about 3 foot between the bottom of the main wheels and the ground.

Do this with no gas in the tank.

Get a helper there on a step ladder next to the gyro and you climb into the seat and have the helper go up the ladder and watch the rotorhead as you pull the stick back and when your torque tube is about even between the stops have him tell you to hold the stick still, then he places a angle finder on the front of the mast and check the angle. It should read between 0 degrees to up to 5 degrees nose down.

After doing this test, you can turn around in the seat and help your friend on the ladder to pour 6 gallons of gas in the tank and then turn around and get the rotorhead centered again with the stick and have your pal take another reading with the angle finder, again looking for 0 to 5 degrees nose down. And one more time, help him fill your tank up with 6 more gallons and see what you get.

Don't assume yours will be okay just because it is like everyone elses. It is likely it will be okay, but it might not be and checking it is very simple. We checked Ken Ashelys new Dominator 2 or 3 weeks ago in my hangar and I bet the whole process didn't take more than 20 minutes tops. His gyro also came out a hair nose heavy and it too was as standard of a dominator as they come, so so much for assumptions....

The rotorblades stay in the box. No need for them for this test. for some reason a few people must have thought you want to do a vertical CG check or something and all their advise seems to have been confusing. A hang test you do to check control centering and should be done before it is flown....

[13brv3]

Rusty, I admire you for asking questions rather than not, but geeze your over thinking this stuff and making a big deal out of small stuff really...

Yep, that's just how I am, and how I'll always be :lol:

We checked Ken Ashelys new Dominator 2 or 3 weeks ago in my hangar and I bet the whole process didn't take more than 20 minutes tops. His gyro also came out a hair nose heavy and it too was as standard of a dominator as they come, so so much for assumptions....

So what did you do to correct the nose heavy condition?

The result is all that's important, and I believe I can get the same result by using scales. Since I have 3 nice digital scales, I bet I can do the whole procedure in the same time you can hang one. I can do it much quicker and easer than I can hang it, because I have no ladder to reach the roof of the hanger, and no hoist to hang it from.

If I'm not satisfied that I get an accurate result, then I'll find a way to hang it. Also, since it's likely that Dofin will do the test flight, we can hang from his hoist before putting the blades on.

Thanks for the comments.

Rusty

[RobO]

Hi Rusty,

Aside from the logistics, hanging isn’t too hard. I called a tow truck to do my hang test. They can come right to you at a moment’s notice and their rear boom hoist easily handles it (but make sure theirs goes high enough). It cost $50, but it was easy and I had nowhere else to hang mine. The driver/operator works well as a helper and it is easy to do multiple tests.

I created two square dummy cheek plates with rotor head mounting holes at 1-inch spacings. This allows adjusting the rotor head location to get the right hang angle.

I wedged the rotor head in neutral position and secured the wedges with…duct tape of course. If the rotor head is secured neutrally, then you don’t need the stick position or pushrods at all as long as you (later) make the pushrods to length as Ernie says.

Once you know where the head should be, you can make the final cheek plates and the push rods. As other say, do the tests with empty and full fuel.

[GyroRon]

Yep, that's just how I am, and how I'll always be :lol:



So what did you do to correct the nose heavy condition?

The result is all that's important, and I believe I can get the same result by using scales. Since I have 3 nice digital scales, I bet I can do the whole procedure in the same time you can hang one. I can do it much quicker and easer than I can hang it, because I have no ladder to reach the roof of the hanger, and no hoist to hang it from.

If I'm not satisfied that I get an accurate result, then I'll find a way to hang it. Also, since it's likely that Dofin will do the test flight, we can hang from his hoist before putting the blades on.

Thanks for the comments.

Rusty

Your just not listening.... You need to HANG the dam thing rusty!!!! This is not a weight and balance like on a airplane......... Take the thing with you to Wauchula and have Davey Seace help you hang it, they got all the stuff right there in their hangar.

I have hung mine before using a large winch type tiedown strap to lift it. You surely have the room in your hangar to lift it, you only need to raise it up a few feet high.


the fix for Kens gyro was to shift some items around to help balance the weight on the machine. He ended up in the range but on the nose heavy end of it. The proper fix is to create new cheekplates to locate the rotorhead forward or back to get the hang angle right. You move the rotorhead one inch for each degree your looking for, so if your hanging nose low at 7 degrees then you would need to locate your rotorhead forward about 5-6 inches to get you in the middle of the acceptable range. On a Dominator with a nose pod, I prefer to see a hang angle of zero degrees as on some longer flights you will be tempted to throw things in the front of the pod, things like extra oil and jackets and drinks and so on and all that weight is out on a pretty long lever up in the front of the pod making the hang angle change quite a bit.

[13brv3]

Rob,

I remember your tow truck pics, but mostly I remember all the snow in the background :eek:

Mine came with most everything fabricated, though I took it all apart to polish the edges, and clean up the holes. In theory, it will all be fine as is, but that's what we're trying to prove I suppose.


Ron,

I'm not sure why you're so focussed on the method, rather than the result. As long as I get an accurate angle, why does it matter how I get it?

Cheers,
Rusty (never been accused of being normal)

[Timchick]

Rob,

Ron,

I'm not sure why you're so focussed on the method, rather than the result. As long as I get an accurate angle, why does it matter how I get it?

Cheers,
Rusty (never been accused of being normal)

Because the hang test method is the normal method used by 99.9% of gyro builders.

[13brv3]

Because the hang test method is the normal method used by 99.9% of gyro builders.

Good thing I don't mind being that .1% that's different :)

Cheers,
Rusty

[GyroRon]

Ron,

I'm not sure why you're so focussed on the method, rather than the result. As long as I get an accurate angle, why does it matter how I get it?

Cheers,
Rusty (never been accused of being normal)

Rusty... I don't think it is even possible to get the results a hang test provides without HANGING IT!!!! I can not for the life of me see how putting the gyro on scales will help you with making sure the rotorhead is in the right position and that the controls will be centered in flight.

You should try to get in touch with Ken Ashely, the two of you guys are alot alike.... Got to do stuff YOUR way, even if it is the hard way. :lalala:

[13brv3]

You should try to get in touch with Ken Ashely, the two of you guys are alot alike.... Got to do stuff YOUR way, even if it is the hard way. :lalala:

Hi Ron,

Well this Ken Ashely must be a heck of a guy :p

I'm still convinced that I could get a valid number with the scale method, but of course I'd have to hang it to prove that, and if I'm going to hang it anyway, then why bother.

And the verdict is...
1.3 degrees nose down at the mast with me (190 lbs) and no fuel.
2.4 degrees nose down at the mast with me and full fuel (11.5 gallons).

Sounds like it's OK.

Thanks for the persistent advice ;)

Rusty

[GyroRon]

Rusty, just imagine.... pretty much all RV-8's look the same, and most have pretty much the same stuff as far as engines, props, avionics, etc... So would you just hop into a freshly built RV-8 and go flying without a proper weight and balance? I don't think anyone is that stupid.

Gyros are the same way, even though yours may look just like mine.... yours may not be in the " Range ", and the only way to know it is to do the hang test.

I am sure that a person with a masters degree in math and engineering could come up with a formula that would show hang test results from weighting the machine on the ground at the three wheels, but I would have far more trust in the ole fashioned hang test, and it isn't hard to do if you think about creative ways to lift it.

Sounds like your machine was right on the money, which I suspected it would be, but you just never know till you confirm it!

Ernies Kits are not all alike. They may look alike, but when you start measuring pieces you may find alot of stuff that is not the same as the next machine. So it isn't wise to just assume...

So how did you hang test it? Forklift??? Tow Truck???

[13brv3]

So how did you hang test it? Forklift??? Tow Truck???

Ron,

I never said there wasn't a place I "could" hang it. There just isn't a place I'm "allowed" to hang it. Let's just say there wasn't anyone around, the doors were closed, and I needed a reason to test my new ladder and come-along ;)

BTW, I finished my SP gyro add-on, and will be flying with Dave Friday and Saturday. The airworthiness inspection and first flight should occur before the end of the month.

Rusty (off to break-in the engine, mount the rotors, and weigh it all)

[Fl90]

Cool, I might see you this weekend. Depending on the wind in the afternoon, I'll go the opposite way in the morning.

Phil.

[OuterMarker]

can anyone help me with this program? It seems that I can only "read" it and not input data. thanks......albert

[OuterMarker]

what happens if you get neg numbers for cg locations?

[JEFF TIPTON]

A center of gravity (CG) is a point along a reference line. Along this line will be a point that all measurements are taken from called a datum point. Normally all points to the right are considered positive and all points to the left are considered negative in relation to the datum point. If the CG result is negative then the balance point is to the left of the datum point.

[OuterMarker]

Therefore, if the center of the axle is 0 degrees, then any number moving up the mast will be a neg. number. Is that correct?

I weighed my AC and here are the numbers I input to the spreadsheet.
Level on ground as measured from the front keel...0 degrees
Wheelbase.......56
LM...238 lb
RM...246.2 lb
NW...48.6 lb
Axle from ground...6"

Inclined Measurements
Angle measured from keel...5 degrees
NW...78.3 lbs

AUW...532.8 lb
H CG...5.11" in front of MW axle
V CG... -29.68" above floor

[JEFF TIPTON]

Running the program from here I get the following.

[Bob Gregory]

Outermarker,
Here is a version I found that agrees pretty well with your data.
The vertical does not agree with Ralph Taggart's DOS version.

Verify with balancing and a plumb bob.

[Udi]

The nose wheel is supposed to weigh less, not more, when the gyro is tilted back - you were suppose to tilt the gyro back! I don't know if the trig works for a forward tilt.

See attached spreadsheet with complete instructions.

Udi

[Timchick]

Or, just hang it.

[Udi]

Doing a double hang test is not easier, or more accurate, than placing the gyro on some blocks and scales, Tim. All you need for this method is three bathroom scales, a Smart Level, and some concrete blocks - all of which I have right here in my garage. This method is in fact more accurate than the double hang test - using a standard Smart Level (0.1 deg accuracy) you find the location of the CG within 0.5" or so.

Udi

[All_In]

The nose wheel is supposed to weigh less, not more, when the gyro is tilted back - you were suppose to tilt the gyro back! I don't know if the trig works for a forward tilt.

See attached spreadsheet with complete instructions.

UdiOh man you are the best Udi!
Thanks for the spreadsheet!!!

[Jazzenjohn]

What would happen if a gyro that was supposed to have a hang angle of say 10 degrees only had an angle of 5 degrees, but the control stick was centered at that angle? Wouldn't it be fine, just fly normally with a slightly higher front end?

[All_In]

What would happen if a gyro that was supposed to have a hang angle of say 10 degrees only had an angle of 5 degrees, but the control stick was centered at that angle? Wouldn't it be fine, just fly normally with a slightly higher front end?Yes but what would it be like at the edges of the flight envelope?

[Udi]

What would happen if a gyro that was supposed to have a hang angle of say 10 degrees only had an angle of 5 degrees, but the control stick was centered at that angle? Wouldn't it be fine, just fly normally with a slightly higher front end?
Yes, John, the gyro would want to fly nose high 5 deg. But think about the big picture. Your stab will be flying with a positive AOA, lifting the tail and trying to keep the keel level. So... your centered stick is now held back, not centered any longer. This might restrict your back stick range for maneuvers and landing.

Other than that - on takeoff - your gyro would come off the ground with a higher nose attitude than other gyros.

Udi

[OuterMarker]

When I raised the main gear on blocks, more weight is tranfered to the nose, hense the higher nose weight. The spreadsheet then sees the weight on from a level surface then a raised surface which is the double hang. What I have learned, with my weight, on a AC low rider style gyro, with an inverted engine, the engine thrust line is about 12" above the 30" vertical CG location with respect from the floor. I guess I now understand why the AC CLT seat location is so high. Now, the bigger question is do I fly under the current situation as many have done before me for so many years? That would mean flying in only winds less than 10kts and no aggressive flying, or build or buy the AC CLT upgrade and have peace of mind knowing the machine is closer to harmony?

[Doug Riley]

In a PPO-prone gyro, the PPO sequence is self-energizing once it begins. The engine provides the motive power to flip the gyro.

The PPO chain reaction can be triggered by events other than winds and aggressive flying.

Sunny-day thermals can produce substantial variations in G load that can start things off. These thermals appear on gorgeous, calm blue summer days with puffy cumulus clouds that look perfect for flying.

Rolling back to level from a climbing pattern turn can do it, too. During the turn your rotor will pick up RPM. In fact, it needs to in order accomplish the turn. When you roll out, though, the leftover RRPM will cause you to balloon. This will feel like an updraft, even in perfectly calm air. It will tempt you to push the stick forward. Such a control input at high power can trigger a low-G nose drop and even a PPO.

The Air Command CLT conversion is neither very expensive nor very complicated. There's no excuse for tolerating the deadly and unnecessary risk of a HTL design.

[Ron E]

.............. There's no excuse for tolerating the deadly and unnecessary risk of a HTL design.

Human nature is a very strange thing. They do it because they can, not because they should or because it is "good" for them, to take that risk.

It could be that the added danger of certain death due to a just a moment of inattention enhances the thrill of flight.

I personally don't like anything I operate to be squirrelly in any way. I like flying in a relaxed state---Not in Red Alert mode constantly.

[Udi]

...What I have learned, with my weight, on a AC low rider style gyro, with an inverted engine, the engine thrust line is about 12" above the 30" vertical CG location with respect from the floor.
You have made a mistake in your calculations, Albert. Based on the numbers you posted above - your vertical CG is 41.7 inches above the floor. I calculated this number based on your measured 5 deg nose-down angle. To verify that my calculation is correct - I will tell you the height of the blocks that you have used. You have raised the mains by 4.88" above the ground to achieve a 5 deg nose down angle (assuming your wheel base is really 56").

Udi

[OuterMarker]

This is interesting. I did not measure from main wheel to nose wheel. I think? I measured back from the axle of the nose wheel to where the center of the axle would be on the main wheel. Perhaps that is why the wheelbase is only 56"? If the vert. CG is at 41.7", that is where the engine thrust line is when measured from the floor with me sitting in it.

[Udi]

Yes, the wheelbase is measured from the nose wheel axle to the center between the main wheels axles. Can you confirm the 4.88" height of the mains above ground in the second part of the test?

Looks like you might have a CLT gyro there...

Udi

[OuterMarker]

I was using 6"x6" wood blocks. I used 3 scales which were only 1" thick so I did not add the scale thickness. I checked the floor first to make sure it was level where I took the weights.

[Udi]

ok. With 6" blocks and 56" wheelbase, the angle you measured should have been 6.1 deg.

Using these numbers, your vertical CG is about 35.2" from the floor.

Udi

[OuterMarker]

Not knowing what spreadsheet you used, your numbers get me 7" below the engine thrust line. Can you send me the link you used? I will weigh everything again once I extend the rear keel and rotate the engine upright. thanks.....

[All_In]

Great Thread!
Think we are all learning a lot!
Thank you

[Udi]

See spreadsheet with your numbers below.

To calculate your keel angle:

Angle = inv-tan (block"/56") = inv-tan (6/56) = 6.1 deg

[OuterMarker]

Hi Udi.....thanks for hanging (no pun intended) with me through this. My mistake I found!!!

I put in a positive number for the keel angle instead of a neg. number!!! Using a neg number because the angle is neg when raised on the blocks the valid vert CG does move up from the floor to 35.21". Much closer to the engine thrust line. again, thanks for taking the time to check my work....such a newbie mistake!!!

[Bob Gregory]

Udi, please send the CG5.1.xls formulas as a CG5.2.xlr or C5.2.wks extension.
I collect formulas and the last two are missing on your version. Only gives the answer.

Also the word text instruction is missing when I copy and paste,
Could you send it as text.
Thank you.

[Udi]

Bob,

Your computer may be having problems with the double-dot file name. Here is the file attached with another name.

Udi

[Bob Gregory]

Udi, same problem, all formulas there except last two.

I have multiple copies of this file and they are all the same from years past.

Thought I could get a workable copy this time.

[Udi]

Last 2 formulas:

Vertical CG---------------------------- =(D43-D50)/(D54*TAN(RADIANS(D48)))*D40+D44
Vertical CG Accuracy-------------- =((D43-D50)/(D54*TAN(RADIANS(D48-D49)))*D40-(D43-D50)/(D54*TAN(RADIANS(D48+D49)))*D40)/2

[Bob Gregory]

Thanks, Man.

[Dean_Dolph]

Udi, I know just enough about Excel to be dangerous! But it doesn't look like this file is protected so that the formulas can't be messed with. I say this because I can delete the formulas.

Anyone want to guide me through locking the formulas in particular and the spreadsheet in general so it can't be messed with while still allowing the required input?

[JEFF TIPTON]

Dean open the Excell document.

Look at the top of the window. You see format tools etc. Click on tools.

In the tools link click "protection".

Click on "protect sheet"

That should do it.

[OuterMarker]

Hi Udi,
Another question. When I first began this, I rasied the main wheels up 6". I didn't have the directions with me, and I didn't think from a level floor I could raise the nose wheel up 6" without having the rear keel wheel on the ground. The formula should still work reguardless of which wheel(s) are raised?

I am going to extend the rear keel and rotate the engine (Rotax 503) and repeat the test to see how much movement takes place. I'll post the results when concluded.

I am expecting to then complete the CLT upgrade after that. Again, I will weigh again and post the results. This way, everyone can see what changes CG-wise from a stock AC 503 inverted, extended keel and rotated engine mod, to a AC CLT upgrade.

[Aussie_Paul]

Now, the bigger question is do I fly under the current situation as many have done before me for so many years? That would mean flying in only winds less than 10kts and no aggressive flying, or build or buy the AC CLT upgrade and have peace of mind knowing the machine is closer to harmony?

Bob, why take the risk? More HTL gyros have PPOed than CLT gyros!!!!!!!! For the CoG to thrust line offset I use +or- 2" as CLT.

Good luck with your project.:wave:

Aussie Paul :)

[Udi]

Yes, Albert, the calculation works both nose high and tail high - as long as you enter a positive angle for nose high and a negative angle for tail high. I think I will add another option to this spreadsheet to calculate CG based on block height instead of angles for people who don't have a Smart Level.

Dean - see attached copy of this spreadsheet for non-excel-savvy end-users. ;)

Hi Paul! Good to have you back mate :wave:

Udi

[gyromike]

Udi,

Let me know when you think you have the wrinkles out of this program.
This might be a good topic to start a new thread and make a 'sticky' out of it.

Shoot me a PM if you want to do this.

[Dean_Dolph]

Jeff, Udi, thanks for the help!

Having a protected sheet may have value for others if Mike makes it a sticky. You know how gyroheads always want to mess with something!

[Bob Gregory]

Udi, I am getting some erroneous vertical cg's the longer or shorter the wheelbase is from 57.3 inches in comparison to Ralph Taggart's DOS CGcalc.exe from a Sep 99 PRA magazine.

A radian is 57.3? inches and is what is used in all the calculations for vertical cg.

Outermarker's wheelbase was 56 and led to a reasonable answer.

When wheelbase is shorter or longer the discrepancy is greater.

Ralph Taggart uses these data points.
Nose wheel radius
Main wheel radius
Wheelbase
Weight nose level
Weight left level
Weight right level
Block height of mains
Weight nose angled
Prop height

[Udi]

Bob - When I find a little time I will try to go over the other CG spreadsheet and see if I can find a reason for the discrepancy you have found. It is not always easy to check somebody else's spreadsheet because you have to back-engineer the equations (I have already done that with Chuck's CG51.xls).

Mike - The latest version posted (CG52.xls) is good enough for a sticky post - I am a little busy right now and it will take me some time to come up with an improved version.

Udi

[Russ Hobbs]

Questions/Hang test

I have 9 degrees nose down with a centered rotor. Question, should I move the cheek plates back one inch (pre-drilled holes) or change over to a larger T-tail with a longer moment arm or both? I currently have a Watson tail with a centered horizontal T that measures 40" across and 17" front to back. The airfoil is about 1" tapering back, and sits below the prop wash by 10 inches
Suggestions/direction appreciated.
Thanks, Russ

[Doug Riley]

The HS, if set up properly with some down-load, will actually DEcrease your effective hang angle in flight (i.e. it'll crank the nose up). Therefore, you need to increase your keel's nose-down angle by 1-2 degrees.

You can accomplish this either by moving weights forward or moving the rotor head back.

[Russ Hobbs]

Thanks Doug, I can easily move the rotorhead back. Now I can try to double hang and see how high my thrust line is.
Thanks again, Russ

[OuterMarker]

ok....I did another double hang test with the scales this week. I rotated the engine up, moved the engine back 4", lowered the engine 4" and rotated the reduction box down. I also moved the keel back 2 feet. Remember I only have a 503 and 60" prop.

When I did my first hang test I was 5 degrees nose down, I'm a dough-boy. Now, with the extended keel, and engine moved back 4" I did another hang test and I am now 1 degree nose down. that is with 5 gals of fuel.

My engine thrust line I assume is the center of the prop. If so, it is 39" to the floor. After weighing the data now shows my VCG at 35.6" from the floor.

So, now what to do? Do I raise the seat another 2" and weigh again to see if I can bring the two numbers within 2" of each other? That would lock me into a 503 engine. Or, just put the engine mount back, do the upgrade and if I want to get a larger engine it is a simple conversion. I suppose it might make the gyro easier to sell at some point if the upgrade is done....but remember, the upgrade is for the larger engine, larger prop and taller mast.....

[OuterMarker]

I have a question because the answer sorta bothers me...
I measured another gyro last weekend.....with the gyro sitting on the floor I checked the angle of the front keel which was going to be the reference point. It measured +4.2 degrees. When I raised the main wheels 5 1/2" and measured the keel again it read -7.9. I see this as -12.1 degree movement. Am I correct? Because if so, then this gyro has almost a 13" difference between the engine thrust line and VCG......that is why I questioned myself.....

[Udi]

I think you have made a mistake, Albert. If raising the mains 5.5" is tilting the keel by 12.1 degrees, the wheel base must be 2'-2" (5.5/sin(12.1)). Does this gyro really has a wheel base of 2'-2"? If the wheel base is longer than 2'-2" than your numbers don't add up.

Udi

[OuterMarker]

This is a friends Benson. I checked the angle of the keel with him sitting in it and the gyro was sitting +4.2 degrees...large nose wheel. So, when I raised the mains and checked the angle of the keel it was now-7.9 degrees, which is what I expect, short wheel base will give a higher - number. However, the "total" spread is 12.1. But, do you subtract the neg number from the positive? Or, like I did, just add the total swing between the two numbers? Because if the level had the ability to zero itself at any angle, then the +4.2 would be zero, my reference point. The when the mains were raised you would only have the -7.9. I don't know how to resolve this issue.

[Doug Riley]

Albert, for a Bensen a typical keel slope with the wheels on the ground is 2-3 deg. nose-up. If the nosewheel is larger than the standard 4" wheel, the slope may be a little more. As long as the blades don't smack the ground in back, the extra keel slope is actually helpful in getting the blades going. No biggie.

None of this has anything to do with hang testing. As long as the angle between the keel and the mast is 9 deg. and the rotorhead is mounted correctly on the mast, then the standard hang numbers for keel-based measurements will work.

If OTOH, you have a non-Bensen-ish frame, with possibly weird angles of mast, head and/or keel, then your hang numbers are best measured right at the rotorhead.

This makes sense when you recall that the purpose of a hang test is the centering of the control stops on either side of the spindle when the spindle is in its "cruise" position. The angles of the keel and mast are indirect evidence of the angle of the rotorhead itself. We sometimes measure mast or keel angles in hang tests for convenience -- but, again, it's the head the really matters.

[Friendly]

ok....I did another double hang test with the scales this week. I rotated the engine up, moved the engine back 4", lowered the engine 4" and rotated the reduction box down. I also moved the keel back 2 feet. Remember I only have a 503 and 60" prop.

When I did my first hang test I was 5 degrees nose down, I'm a dough-boy. Now, with the extended keel, and engine moved back 4" I did another hang test and I am now 1 degree nose down. that is with 5 gals of fuel.

My engine thrust line I assume is the center of the prop. If so, it is 39" to the floor. After weighing the data now shows my VCG at 35.6" from the floor.

So, now what to do? Do I raise the seat another 2" and weigh again to see if I can bring the two numbers within 2" of each other? That would lock me into a 503 engine. Or, just put the engine mount back, do the upgrade and if I want to get a larger engine it is a simple conversion. I suppose it might make the gyro easier to sell at some point if the upgrade is done....but remember, the upgrade is for the larger engine, larger prop and taller mast.....

usually rotating the gearbox down raises the engine.

[OuterMarker]

Hi All...well, it has been a very long process doing the CLT conversion. Here are the latest numbers for my A/C with 503 and 60" prop and 3 gals of fuel.

Pilot weight with all gear...220lbs
Wheel Base...69.5"
Axle height above surface...6"

LEVEL WEIGHTS
L main...257.4 lbs
R main...249.4 lbs
Nose wheel...68.2 lbs

Raised main wheels up 5.5"
nose down angle...-4.6 degrees
Nose wheel weight...95.4 lbs

Engine thrust line from floor...43.5"

I might be wrong and will have to check my notes, however, it seems that my VCG did not move from when the prop clearance was set for a 60" prop or a 68" prop. Therefore, what effect in VCG should I have seen by moving the engine up or down by 4"???

Will post photos after DAR sign off.......
albert

[Bob Gregory]

6 nose radii
6 main radii
69.5 wheelbase
68.2 level nose
257,4 left
249.4 right
5.5 block height
95.4 nose block
43.5 prop height
8.243 horzon cg
47.414 vertical cg
-3.91 Low Thrust Line is near perfect according to Glasgow University

Glasgow University equates 100 mm below as perfect for all aircraft according to EAA Sport Aviation about 1987. Inches of 3.91 is 99.3 mm.

[OuterMarker]

I would like to copy CG program to CD so I can take it to the hanger with me...is this possible? Are the macros locked?
thanks....albert

[JEFF TIPTON]

I copied the file to a memory stick and it does OK.

The cd should work just as well.

[OuterMarker]

In the never ending saga of the CG spreadsheet, I need some help in understanding. I have weighed some two-place gyros and the VCG results I don't understand. I am going to post the weights with one pilot and then two. The VCG mark with one pilot is confusing to me. My hope is to weigh a half dozen or so gyros and write an article with the results. I need to make sure the formula works for 2-place as well as single place.....so, here goes...

Oh, yeah...another very important point. With the gyro sitting un-elevated I take a reading of 1 degree negitive angle. When the nose is then elevated the reading is positive 3.6 degrees. For the formula to work should I look at the spread between the two numbers (4.6 degrees) or just ignor the first number and only use the second? One degree makes a huge difference in VCG location.

SINGLE PLACE
Pilot=200 lbs
Fuel=8 gals
Prop hub center to ground= 41.25"
Wheel base=59.5"
Main axle height to ground=6"
LM=464 lbs
RM=411 lbs
NW=52 lbs
elevated Angle= +5.6 degrees
elevated NW weight=12 lbs

TWO PLACE
Pilots 200 & 210 lbs
Fuel=8 gals
Prop hub center to ground= 41.25"
Wheel base=59.5"
Main axle height to ground=6"
LM=488 lbs
RM=498 lbs
NW=149 lbs
elevated Angle= +5.6 degrees
elevated NW weight=86 lbs

Notice the VCG moves lower with only one pilot than with two???
thanks....albert

[OuterMarker]

Doug and Udi,
I was reading the CG52.xls instructions again because I want to weigh some gyros again. Since the program is locked, perhaps either of you can consider a few suggestions which will help others understand.

1. for some, it might be easier to raise the main gear instead of the nose gear to get a higher angle. Therefore, a mention of inserting a positive number for nose high and a negative number for tail high at line #4.

2. This will really change the number on the difference between Vertical CG and Prop Thrust Line. The statement with Vertical CG should say, "Distance from Main Axle Height at flying weight, not on scales." Since this is a reference point asked for earlier in the program. Should it not be used again as a reference point in determining Vertical CG? It seems that since tire sizes vary, that is why the axle height is used as a reference point. In my case, the 6" difference between the reference on the ground and axle height really change where the Vertical CG point is with respect to the engine thrust line.
Your thoughts?
thanks...albert

[Doug Riley]

I don't use the spreadsheet and wouldn't know how.