Continuing along the Firebird road 2

[Aussie_Paul]

As I said in another Firebird thread, last Saturdays certification inspection, double hang test, and drop testing was successful as well as exciting.

Here are the awaited CoG pics that were done by people other than myself last Saturday.

Aussie Paul. :)

Dual.....................................Solo

[dragonflyerthom]

PB

Those are some exciting pics. I do have a question. What is your dangle angle in the first pic?

[StanFoster]

Paul: Looks like just a slightly high thrustline...maybe 1.5 inches?


Looks good.

Stan

[Aussie_Paul]

Paul: Looks like just a slightly high thrustline...maybe 1.5 inches?


Looks good.

Stan

An engineer has drawn lines with a pencil on a hard copy of the pics and show Firebird to be approx 2" LTL solo and approx 2" HTL dual. That is what I was aiming at.

I was happy with the results Stan. A heck of a lot of work to get Firebird to this stage.

I now have 2 new partners. One is an aircraft maintenance engineer and the other a retired structural engineer with excellent business skills. We signed the documentation today.

Firebird can now proceed to the next level, production. :)

A great day for me.:rapture: :rapture:

Aussie Paul. :)

[dragonflyerthom]

As I said in another Firebird thread, last Saturdays certification inspection, double hang test, and drop testing was successful as well as exciting.

Here are the awaited CoG pics that were done by people other than myself last Saturday.

Aussie Paul. :)

Dual.....................................Solo

Paul

Do you have pics of both hangs dual and solo?

[Timchick]

Congratulations Paul. For those who may have been interested in purchasing an RAF, they now have a better option.

[PW_Plack]

Paul, pic 1 looks like the nosewheel is still on the ground. ???

[StanFoster]

Paul- The cg location has to have both hangs or one hang and one wheel balance with the same payload for the intersecting vertical lines to locate the cg. I am on my cellphone and cant see your pics, but was told that one pic shows 1 person and the other shows 2 people. Of course this wont show the true cg unless both are in the cabin or just the pilot. I missed this this morning and I will look again tonight. STAN

[Aussie_Paul]

Paul, pic 1 looks like the nosewheel is still on the ground. ???

Paul it was very close ..

Aussie Paul. :)

[Aussie_Paul]

Paul- The cg location has to have both hangs or one hang and one wheel balance with the same payload for the intersecting vertical lines to locate the cg. I am on my cellphone and cant see your pics, but was told that one pic shows 1 person and the other shows 2 people. Of course this wont show the true cg unless both are in the cabin or just the pilot. I missed this this morning and I will look again tonight. STAN

The 2 pics shown give the CoG for solo and dual occupancy.

All the neccessary pics were taken but only the ones with the final result were sent to me.

There are pics hanging solo and others balancing solo also hanging dual and balancing dual.

What did you think of the drop test? Quite exciting to be there :):)

This is the link for those who have not seen it was made by one of the guys in attendance.

http://www.youtube.com/watch?v=k8SEuNo9DTY

Aussie Paul. :)

[dragonflyerthom]

That was great Paul. Sure looks to bee beefy.

[Razzum]

Hello Paul. Great stuff and best of luck.

Am a little puzzled by the CofG/thrustline pics and interpretation.
I do understand they depict solo and dual cases.

Picture #2 : I may be wrong (not for the 1st or last time) but should the yellow vertical line not be generated from the fulcrum; ie axle ?
I fail to see the pourpose or significance of the blue U/C reference lines.

Picture# 2 :If the above is true, then the 'corrected' lines projected onto both pictures would tell quite a different story would they not? HTL in both cases to some degree maybe.

Certainly very clever to use the open doors to compensate for the missing spats and the blue reference plumbob to the left is rather high tech !

This is just an observation, NOT a criticism, as I think others & scg's might be thinking the same thing eh.


Keep plugging along . . . may be exciting times ahead.

[birdy]

Just one quiere PB, as ol mate asked, why isnt the bottom of the yellow [ mains balanced ] line in the second pic actualy on the axle center??
Am i missing sumthn here?
[or would it show the COM to be too low?] ;)

[Razzum]

Paul. On reveiwng pics , I see the testers have determined (somehow) where the theoretical axle centre should be, had the camera (& picture) been centred on the axle axis, not the thrust line as appears to be the case.
Three dimensional data for a two dimensional result, or vise versa ! !
Not sure how to overcome this parallax for an accurate result; perhaps an overlay of the two centered images . . . Stan?

In any event, an explanation would be helpfull for any others doing the same.

[birdy]

I see the testers have determined (somehow) where the theoretical axle centre should be,
Why would they go to all the trouble of workn out where the axle is theoreticaly, wen its there in reality?

[Aussie_Paul]

Paul. On reveiwng pics , I see the testers have determined (somehow) where the theoretical axle centre should be, had the camera (& picture) been centred on the axle axis, not the thrust line as appears to be the case.
Three dimensional data for a two dimensional result, or vise versa ! !
Not sure how to overcome this parallax for an accurate result . . . Stan?
In any event, an explanation would be helpfull for any others doing the same.

Apparently this is the correct way to adjust for parallax error as confirmed by a number of people within our ASRA hierarchy.

Aussie Paul. :)

[StanFoster]

Razzum: I believe in keeping it simple. Hang test the gyro with a vertical laser beam trace down from the hang point....and perpendicular to the frame. Record that line on some posterboard taped to the machine.

Then either do another hangtest from a different attachment point and do another laser trace. The intersection is the cg.

If you decide to do the axle balance test instead of the 2nd attachment point hang.....then keep it simple. Align the vertical laser beam through the axle.....and have this plane of light perpendicular to the frame by simply having the axle parallel to this laser trace. Its so simple...that my simple mind is convinced that this is correct. If you start shooting angles up through the axle that arent perpendicular to the frame...then a lot of high tech mathmatical explanations have to follow.

Its so easy to just shoot the vertical plane of light square to the frame and letting this intersection of its vertical trace with the first hang tests trace show the exact CG. No parallax, no high end cyphering....just a plain ol intersection on the CG.


Stan

[birdy]

Wot the hell is 'parallax' ???

Where is the TL if you do the common 2 pic thing then PB?
Is it the same place or not?

[StanFoster]

Birdy: If you have a hood ornament on your vehicle...dead center... and are driving down the road right over the white centerline.....the driver will see the hood ornament projection to the right of the centerline...and the passenger will see the hood ornament projection left of the centerline...


Of course you down unders drive opposite, so just reverse the passenger and drivers perspective on that hood ornament. That difference is an example of parallax. If you were sitting dead center in the vehicle...ok...to be exact....one eye closed and the open eye centered in the vehicle...and looking down the hood ornament...it will be exactly projected over that white centerline. That is 0 parallax error.

Now...the laser beam projecting a vertical trace up from the axle centerline...if not perpendicular to the frame....will envoke some parallax error. The greater the misalignment from being square...the greater the parallax error. My point is to keep it simple and keep the laser trace perpendicular to the frame....thus having 0 parallax error...just like the one eyed driver looking down the middle of his car over the hood ornament.

Stan

[birdy]

Gotya Stan, thanx.
But yeh, cant see why he'd be complicatn things, unless its to make it look like its only 2"HTL. ;)
BTW, its you blokes who drive from the rong side of y motorcars. :)

[StanFoster]

Birdy-I was very careful saying downunders drive "opposite" and not saying you drive on the wrong side. There is no wrong way-as long as we follow the laws where we are driving. Stan

[quadrirotor]

As a matter of fact, Birdy is flying his gyro UPSIDE DOWN!!! ;) so we can't take what he's saying for granted!!!

[StanFoster]

Parallax error-how much? If we are projecting a vertical plane of light at the center of an axle stub that lets say is 36 inches from our vertical trace from the first hang test, this plane of light should be perpendicular to the keel so that there is 0 parallax error. If this is so-then the intersecting lines will be on the CG. If the plane of light is cutting the axle tip that is 36 inches away at any angle other than perpendicular, there will be parallax error. This error will cause the projected vertical line to be moved laterally by the tangent of the number of degrees off perpendicular times 36 inches. EXAMPLE- Say the plane of light is off just 2 degrees, The tangent of 2 degrees is 0.0349. Multiply this times 36 and you get a parallax error of 1.257 inches ,thus making this plane of lights intersection with the hangtests line offset 1.257 incher. UNACCEPTABLE! It is easy to project this plane of light perpendicularly and thus have no parallax error. The reward? An accurate CG! Stan

[Razzum]

Jeepers Stan, I just knew you had the simple answer . . Thanks

Birdy. Maybe spin one of the laser sights of your arsenal and check your 'HANG' Hands of the trigger tho

[SamL]

Gotya Stan, thanx.
But yeh, cant see why he'd be complicatn things, unless its to make it look like its only 2"HTL. ;)
BTW, its you blokes who drive from the rong side of y motorcars. :)

Birdy, if you look at the picture you will see one wheel (main) seems very high, and the other wheel seems to sit low. This is sort of a 2D optical illusion and is because of the angle and distance (too close) at which the photo was taken. This is what is called the parrallax error. The only way to minimise this is to have taken the photo from a greater distance and used the camera's zoom to get in close.
Ref Pauls pictures, what was done in order to cancel out the picture parrallax error was to find the centre on both extremes. Henze the 2 blue dots showing the axle centres and the central blue dot between the 2, being the centre of those extremes.
I you look back into some of the old picture showing machines CofG you will see most have parrallax error and so are actually wrong.
Stans method using the laser works and takes the error away.
Just need to buy a laser now. :help:
Regards SamL

[Fl90]

Hi Paul, thanks for posting.

I am curious about the hang angle. It seems to be the same for dual and solo, yet the line is behind the seat. Do you have an adjustable mast? Also, the angle I get is 6*, the blades you have must be the most efficient made. Obviously the blades would be laminar, but at what percentage is the major thickness, how much reflex, and are they twisted? Have you figured your blade loading, disk loading and optimum rotor RPM?

Amazing results.

Phil

[Aussie_Paul]

Hi Paul, thanks for posting.

I am curious about the hang angle. It seems to be the same for dual and solo, yet the line is behind the seat. Do you have an adjustable mast? Also, the angle I get is 6*, the blades you have must be the most efficient made. Obviously the blades would be laminar, but at what percentage is the major thickness, how much reflex, and are they twisted? Have you figured your blade loading, disk loading and optimum rotor RPM?

Amazing results.

Phil

Info that goes with the pics

The hang test solo was 3 degrees.

The balance test solo was at 1155 lbs.

The dual hang test was 6 degrees.

The balance test dual was at 1375 lbs.

The drop test was at 1342 lbs from a height of 14". The requirements are 1320 lbs from a height of 13".

Phil, I can't see how you get the rotor flying at 6 degrees from the above info.

Yesterday I measured the stick position from the dash while flying with the keel level. When I checked it on the ground the torque tube was at roughly 7.5 degrees to the relative airflow.

I am using 30' rotors that are tapered from 9" at the blade root to 8" at the tip, twisted, and are thinner at the tip than at the blade root. They are reving a bit high at the moment at 350 rrpm with a weight of 1276 lbs.

Maybe some of the number crunchers will work out a few things from the figures.

Aussie Paul. :)

[Fl90]

Paul, tanks for more info.

The six degrees I came up with is the difference between the blue horizontal line and the line drawn from the teeter. Both photos have the same line. Dual disk load is 1.95, solo is 1.63 (roughly). 20sqft of blade and 1276lbs should give 335-340 rrpm, so 350 isn't a big deal. I'm assuming cruise is in the 55-60kt range, the 7.5 disk angle shows a very efficient rotor. However, this info clashes with your cg pics. You may want to do the test with the camera properly aligned, reguardless of posting the results, for your peace of mind.

Phil.

[SamL]

Paul, tanks for more info.
Both photos have the same line.
Phil.

Phil, if you look at the amount of red pod surface area behind the yellow teeter line you will see it has changed.

[Aussie_Paul]

It is only a 3 degree change.

Sam I have had a guy who has done quite a bit of geometry work contact me and he belives that the blue line accross the axle and the vertical line from that blue line should intersect at the center of the aircraft ie. the keel. He believes that the vertical yellow line needs to be moved back a small amount.

It looks like we need to get a laser Sam. :)

Aussie Paul. :)

[dragonflyerthom]

Paul B

I don't know if you have a Wal mart there in Alice springs but a simple laser lever will work for you. Black and Decker make some inexpensive ones here.

[Fl90]

As I said, for your peace of mind.

I am using a protractor on the pics shown. If it hung with the keel 3deg. down, solo, it would fly uncomfortably nose high (4deg or 3/4 stick forward) as the rotor disk flies at 7.5deg. That is why I inquired about the adjustable mast. Definately wise to redo the cg test with another method, though the size of the machine makes it more of a challenge.

Phil.

[Aussie_Paul]

As I said, for your peace of mind.

I am using a protractor on the pics shown. If it hung with the keel 3deg. down, solo, it would fly uncomfortably nose high (4deg or 3/4 stick forward) as the rotor disk flies at 7.5deg. That is why I inquired about the adjustable mast. Definately wise to redo the cg test with another method, though the size of the machine makes it more of a challenge.

Phil.

Phil, the hang test numbers are the result of adjusting the head until the keel flys level at cruise speed with a neutral setting on the h/stab.

You can't just use the old Bensen figures, although they are a good place for someone not experienced in this sort of adjustment, to start with.

Aussie Paul. :)

[Aussie_Paul]

Paul B

I don't know if you have a Wal mart there in Alice springs but a simple laser lever will work for you. Black and Decker make some inexpensive ones here.

Thanks for that info Thom.

Birdy lives near Alice Springs, I live down south 70 miles west of Melbourne.

Aussie Paul. :)

[dragonflyerthom]

Sorry PB.

I was watching some wierd stuff on the Discovery Channel here and it mentioned Alice Springs and mistakenly thought you were there. You are right it is Birdie that lives there.

[birdy]

Geez PB, your maken me look pretty high tec ere.
Iv bin usen a lazer level for buildn stock yards for years mate. Recon its bout time you caught up. ;)

[Fl90]

Paul, YOUR number is 7.5 degrees. Bensen's number is close to 10.

If your keel is flying level with a 3deg hang and your disk flies at 7.5 deg (your number), then your machine has a HUGE thrustline offset. Think about it. It has been a topic on this forum many times. The cg lines up with the rotor thrust line (vector). You have given a number of 7.5. It has been stated in other areas that an efficient disk can fly at 7deg and a draggy one can fly at 11deg, so the 7.5 is believable. It has also been stated that a HTL machine(no names) uses a lesser hang number to compensate for the frame roll from the thrust line. I'm not arguing, I'm just saying the numbers don't add up. YOUR NUMBERS, YOUR PICS, YOUR LINES, no one else.

Phil.

[Aussie_Paul]

Geez PB, your maken me look pretty high tec ere.
Iv bin usen a lazer level for buildn stock yards for years mate. Recon its bout time you caught up. ;)

Geez, Birdy I just use my eye. :lol: ;)

Aussie Paul. :)

[Aussie_Paul]

Paul, YOUR number is 7.5 degrees. Bensen's number is close to 10.

If your keel is flying level with a 3deg hang and your disk flies at 7.5 deg (your number), then your machine has a HUGE thrustline offset. Think about it. It has been a topic on this forum many times. The cg lines up with the rotor thrust line (vector). You have given a number of 7.5. It has been stated in other areas that an efficient disk can fly at 7deg and a draggy one can fly at 11deg, so the 7.5 is believable. It has also been stated that a HTL machine(no names) uses a lesser hang number to compensate for the frame roll from the thrust line. I'm not arguing, I'm just saying the numbers don't add up. YOUR NUMBERS, YOUR PICS, YOUR LINES, no one else.

Phil.

Ok Phil, I must be misunderstanding Something. My appologies if I have things confused.

The measurements of the torque tube were approx.

I have conducted tests at each change of the mast height and head position.

What I do know is that flying Firebird at the moment, at 1270 lbs with neutral stabs, she is slightly LTL, the stick is slightly more forward than center, and the keel (the Firebird datum) is flying level at cruise.

I will also conduct the CoG calculation using the weighing the n/wheel etc. at 2 angles usiong the XL program. I have the gear availible to do this.

Aussie Paul. :)

Some things we have tried. The pics are from m y phone and not that good.