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Help with level flight attitude for Mark II

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cristalclear13

Joined: 19 Sep 2007
Posts: 363
Location: Southeast Georgia

Posted: Sat Oct 27, 2007 7:35 am Post subject: Help with level flight attitude for Mark II

Hi guys.  I am trying to do my weight and balance today for my Mark II.  I don't have any information on what the level flight is.  We leveled up the horizontal stabilizer.  I've attached a picture.  



Any information (very soon) would be appreciated.



Thanks,

Cristal

LevelFlightKolbMarkII.jpg

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_________________
Cristal Waters
Kolb Mark II Twinstar Rotax 503 DCSI Sept 2007 - sold Sept 2012
Private Pilot Aug 2008
ELSA Repairman for N193Y April 2008
Rotax 2 stroke maintenance April 2009

ElleryWeld(at)aol.com
Guest

Posted: Sat Oct 27, 2007 7:42 am Post subject: Help with level flight attitude for Mark II

In a message dated 10/27/2007 11:36:14 AM Eastern Standard Time, cristalclearwaters(at)juno.com writes:

  	  Quote: 	
		  http://forums.matronics.com//files/levelflightkolbmarkii_177.jpg 	


 it should be 9 degrees angle of wing cord on a kolb



See what's ne [quote][b]

possums(at)bellsouth.net
Guest

Posted: Sat Oct 27, 2007 9:08 am Post subject: Help with level flight attitude for Mark II

At 11:35 AM 10/27/2007, you wrote:

 	  Quote: 	
		  

<cristalclearwaters(at)juno.com>



Hi guys.  I am trying to do my weight and balance today for my Mark 

II.  I don't have any information on what the level flight is.  We 

leveled up the horizontal stabilizer.  I've attached a picture.



Any information (very soon) would be appreciated.



Thanks,


	




Here's an old drawing.

weight.jpg

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jb92563

Joined: 23 Mar 2007
Posts: 314
Location: Southern California

Posted: Fri Nov 02, 2007 2:53 pm Post subject: Re: Help with level flight attitude for Mark II

That small attitude difference will not make a difference big enough to measure on your scales I think, unless you are using a very precise scale.



Don't take my work for it though, simply measure it both ways and see if you can register a difference on your scales.

_________________
Ray

Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider

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jindoguy(at)gmail.com
Guest

Posted: Fri Nov 02, 2007 4:59 pm Post subject: Help with level flight attitude for Mark II

Ray, it's pretty a simple trig problem to see that measuring the W & B in the landed configuration will be inches off. Really bad advice on your part. Do it on your own plane if you like, but don't advise someone else to do it. 



Rick



On 11/2/07, jb92563 <jb92563(at)yahoo.com (jb92563(at)yahoo.com)> wrote:[quote] --> Kolb-List message posted by: "jb92563" <jb92563(at)yahoo.com (jb92563(at)yahoo.com)>



That small attitude difference will not make a difference big enough to measure on your scales I think, unless you are using a very precise scale. 



Don't take my work for it though, simply measure it both ways and see if you can register a difference on your scales.



--------

Ray

Riverside County, CA



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Read this topic online here: 



[b]

jb92563

Joined: 23 Mar 2007
Posts: 314
Location: Southern California

Posted: Mon Nov 05, 2007 9:08 am Post subject: Re: Help with level flight attitude for Mark II

Hey Rick,



I did advise them to do it both ways and satisfy themself(not take my word for it).



However, what is it you are telling me about the "CG being aft" in the ground position, (similar to a climb attitude)?



If what you say is true then it means that initiating a climb attitude makes your CG go aft and would be rather alarming if true.... right?



That implies that upon initiating a steep climb the CG goes way aft and SHOULD result in uncontrolable spin as the CG goes beyond the aft limit.



We all know that CG does NOT change from a simple pitch change...right?!



How many of us are spinning in on takeoff?



So there is something else going on here....and I am going to illustrate with an example as soon as I can so people can understand what I am telling them.



Perhaps they are not using one of the correct methods for determining CG, but I'll straighten that out with my example.



People can then choose to use which ever method they feel most comforatable with.



They should all continue to use the W&B method THEY have proven works for them and their particular aircraft.

_________________
Ray

Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider

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NeilsenRM(at)comcast.net
Guest

Posted: Mon Nov 05, 2007 1:15 pm Post subject: Help with level flight attitude for Mark II

Ray



The CG does shift aft when in a climb and with the tail on the ground, just 

denying that fact doesn't change anything. Anyone that has ever lifted the 

tail of their airplane knows that the tail is lighter when lifted to the 

specified W&B position. Lift it high enough and the tail will keep on going. 

Now maybe where ever your head is at it doesn't do that but it does here in 

the Midwest. The CG ranges are calculated based on a specific attitude. If 

they were calculated with the tail wheel on the ground they would be 

different. The CG ranges are given with the idea that the plane will be 

flown in allot of flight attitudes and not get us in trouble. You can do 

your weight and balance your way but please don't try to advise others this 

way. Also please if you do your W&B your way don't take anyone up in your 

plane or fly over populated areas.



It is obvious you think you know more than than everyone else and that is 

fine.  Just keep it to yourself and keep flying. Some day when the grim 

reaper comes calling your bad advise will stop once and for all.



As usual this is just my opinion and worth what was paid for it.



Do not archive



Rick Neilsen

Redrive VW powered MKIIIC



---

Possums

Joined: 03 Nov 2007
Posts: 247

Posted: Mon Nov 05, 2007 2:16 pm Post subject: Help with level flight attitude for Mark II

At 04:15 PM 11/5/2007, you wrote:

 	  Quote: 	
		  

<NeilsenRM(at)comcast.net>



Ray



The CG does shift aft when in a climb and with the tail on the 

ground, just denying that fact doesn't change anything. Anyone that 

has ever lifted the tail of their airplane knows that the tail is 

lighter when lifted to the specified W&B position. Lift it high 

enough and the tail will keep on going. Now maybe where ever your 

head is at it doesn't do that but it does here in the Midwest. The 

CG ranges are calculated based on a specific attitude. If they were 

calculated with the tail wheel on the ground they would be 

different. The CG ranges are given with the idea that the plane will 

be flown in allot of flight attitudes and not get us in trouble. You 

can do your weight and balance your way but please don't try to 

advise others this way. Also please if you do your W&B your way 

don't take anyone up in your plane or fly over populated areas.


	


Here are the "old" instructions, again.

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Possum

russ(at)rkiphoto.com
Guest

Posted: Mon Nov 05, 2007 2:38 pm Post subject: Help with level flight attitude for Mark II

Weeeeel, this is MY opinion and everyone is welcome to ignore it. CG does NOT change unless weights are shifted on or within the airplane. IMHO it is a constant, when  in  the air! --  unless you move baggage, lean way forward, shift weight around. In any  case the aircraft's ATTITUDE will  not move the CG, has nothing to do with it.

This is a serious and potentially dangerous area. if you're confused, forget the amateur experts and consult a knowledgable person. May take some work to find one but your life is worth it. Ignore any advice that sounds questionable.

IMHO; feel free to ignore if you wish.

Russ Kinne

On Nov 5, 2007, at 4:15 PM, Richard & Martha Neilsen wrote:

[quote]--> Kolb-List message posted by: "Richard & Martha Neilsen" <NeilsenRM(at)comcast.net (NeilsenRM(at)comcast.net)>

Ray

The CG does shift aft when in a climb and with the tail on the ground, just denying that fact doesn't change anything. Anyone that has ever lifted the tail of their airplane knows that the tail is lighter when lifted to the specified W&B position. Lift it high enough and the tail will keep on going. Now maybe where ever your head is at it doesn't do that but it does here in the Midwest. The CG ranges are calculated based on a specific attitude. If they were calculated with the tail wheel on the ground they would be different. The CG ranges are given with the idea that the plane will be flown in allot of flight attitudes and not get us in trouble. You can do your weight and balance your way but please don't try to advise others this way. Also please if you do your W&B your way don't take anyone up in your plane or fly over populated areas.

It is obvious you think you know more than than everyone else and that is fine.  Just keep it to yourself and keep flying. Some day when the grim reaper comes calling your bad advise will stop once and for all.

As usual this is just my opinion and worth what was paid for it.

Do not archive

Rick Neilsen

Redrive VW powered MKIIIC

---

ropermike

Joined: 28 Aug 2006
Posts: 40
Location: West Texas, South Mississippi

Posted: Mon Nov 05, 2007 6:31 pm Post subject: Re: Help with level flight attitude for Mark II

For what its worth, i weighed my MKll tailwheel on the ground and elevated 2'. It weighed 5lbs less elevated and the mains weighed 2.5 lbs more. I used the elevated weight for my weight and balance....Mike

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R. Hankins

Joined: 18 Jan 2006
Posts: 185
Location: Grants Pass, Oregon

Posted: Mon Nov 05, 2007 6:48 pm Post subject: Re: Help with level flight attitude for Mark II

"CG does NOT change unless weights are shifted on or within the airplane. IMHO it is a constant, whenï¿½ inï¿½ the air!"



Absolutely correct Rick!  Not just your opinion, but solid irrefutable physics.  Unless mass is moved, added, or subtracted, the CG of the plane does not change.  This is true on the ground and in the air.



The distribution of weight on the scales and therefore the calculation of C.G. with respect to a datum does change with attitude on the ground.  One can choose any attitude one wants with a new design to measure this position and verify limits with flight testing.  The important thing is that (once the testing is done and limits set) all those thereafter make their measurements in the exact same manner.  



Builders use different tire & wheel sizes, custom landing gear, short tail springs etc to costomize their craft.  Because of this. using the wing bottom at a set angle to level makes for a much more repeatable process than taxi attitude.  This lets us all benefit from the flight testing done by the initial designers.  Doing it any other way puts the EXPERIMENT back into EXPERIMENTAL.



Fly safe!

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1992 KXP 503 - N1782C

johnjoyes

Joined: 06 Nov 2007
Posts: 3
Location: Reading, UK

Posted: Tue Nov 06, 2007 2:16 am Post subject: Re: Help with level flight attitude for Mark II

Of course those who have replied that the CG does not change with attitude are right ! Those who have (correctly) observed that the tail weight changes as you lift the tail are getting confused -it does not mean that the CG is moving! 

The weight and balance check should be done with the lower wing surface set at 9 degrees to the horizontal. On my machine, the tailwheel is 9 inches off the ground to achieve this. 

What would be MUCH MORE INTERESTING is what other MkII owners use for the position of the Pilot/passenger CG,, as it makes a big difference in the calculation. Previous owners of my plane have used a figure of 4 inches forward if datum (the front wing edge), but I reckon it is more like 2 inches.  Are there any other opinions?

Interestingly, in the UK, the CG range allowed by the powers-that-be is much lower than in the Kolb manual, 16.8 to 24 inches aft of datum. When flying solo, it is necessary for even a heavyweight pilot like me to add ballast weight of 6kg in the nose ahead of the pedals.

1planeguy(at)kilocharlie.
Guest

Posted: Tue Nov 06, 2007 6:14 am Post subject: Help with level flight attitude for Mark II

<snip>

What would be MUCH MORE INTERESTING is what other MkII owners use for

the position of the Pilot/passenger CG,, as it makes a big difference in

the calculation. Previous owners of my plane have used a figure of 4

inches forward if datum (the front wing edge), but I reckon it is more

like 2 inches.  Are there any other opinions?

<snip>



One option is to use the exact position of the pilot CG for the calcs.

The easiest way is to do a weight with the pilot sitting in the plane.

Assuming you have already done the EMPTY weighing and calculated the CG

you can work the whole "weight x arm = moment" thing in reverse, since

you have the empty CG and then you get the CG with the pilot in the

plane (from weighing) that can be extrapolated out since you know the

change in CG position and the weight of the pilot...just solve for the

ARM.



I hope that is clear as mud...would have to dig up an example to explain

further...



Jeremy

by0ung(at)brigham.net
Guest

Posted: Tue Nov 06, 2007 6:33 am Post subject: Help with level flight attitude for Mark II

Let me add my 2 cents worth....   before you start you know it is worth what

it cost.

Basically in an aircraft we are concerned with the cg in the for and aft

position....  you could also figure it in a top to bottom,, and a left to

right moment......   that would give you the center of mass for the plane as

a whole.....



Now unless there is movement on fuel in the tank,,,,  or people or objects

move while in flight,,,, the Center of Mass will not move....   

Now lifting the tail plot...

 Lifting the tail will change the weight of the tail, only because the

center of mass has changed reference in relation to the wheels...  and if

you lift the tail high enough that the center of mass moves in front of the

wheel axels....  the tail will show a negative weight,,,  the center of mass

of the plane has not moved,  only the relationship with other members , the

wheels for example, has moved....



Ok  the question comes up...  why do we have to have the plane at the

correct attitude when measuring the cg....    let me over emphasize with the

following examples....



1:  plane in the proper attitude and the cg is at 21 inches from the leading

edge....   the center of mass cg would line up with say the top center of

the fuel cap.... draw a vertical line from the fuel cap to the bottom of the

wing and will intersect  at 31 % of the wing cord.....   all ok!!!!



2 same plane,,,,  rotate the nose down till the  nose cone touches the

ground:

 The center of mass has not moved,,,,  but if you draw a vertical line from

the center of the fuel cap  to the bottom of the wing it may be at 85% of

the wing cord   ok or not ok!!!!



3:    pitch the nose up....  again the center of mass has not moved....  and

draw a vertical line from the fuel cap to the wing.....   it may be exactly

at the leading edge...  or 0% of wing cord.....   again  ok or not ok!!!!   

  Or are the examples 2 and 3  ok or not!!!!   The center of mass has not

moved.... the plane would be safe....   but if the manufacture instructs

that the wing cord % cg limits should be from    x to y    if measured at z

angle....  then follow the instructions and you will know that it is within

limits...   it is a paperwork issue....   



Now if the manufacture changed the angle... he would also have to change the

limits of the % of wing cord at that angle.  Rotate it too far... say 90

Deg..   and you could not get results that are helpful.    



If you do the cg work according to the plans the results are predictable...

if you come up with your own angles  say tail wheel on the ground,,,   or

the bottom of the wing level... you will have to come up with your own

limits that are acceptable in % wing cord...  and do the testing to make

sure your results are acceptable.... and it can be done...  but why reinvent

the wheel.  



Ok   maybe that has been 3 cents worth....  



Boyd

jindoguy(at)gmail.com
Guest

Posted: Tue Nov 06, 2007 7:36 am Post subject: Help with level flight attitude for Mark II

Ray, It is said a picture is worth a thousand words. Perhaps this will help you understand why your idea that it makes no difference the position in which the airplane is weighed is mistaken. 

Rather than doing trig problems as I suggested earlier, just look at what happens to the relative position of the datum between setting on the ground and level flight position.  

Notice the tailwheel position changes very little. 

Look at how the cg of the major components, wing, empenage, pilot, and engine, move.

Now, compare the arm from the datum to the tailwheel contact SHORTENS when you measure it. while setting on the ground. This mismeasurement of the arm is why you will get a total CG that appears to be forward of where it is actually when the airplane is in flight. 

Hope this helps.



Rick



On 11/5/07, Russ Kinne <  russ(at)rkiphoto.com (russ(at)rkiphoto.com)> wrote:[quote]Weeeeel, this is MY opinion and everyone is welcome to ignore it.  CG does NOT change unless weights are shifted on or within the airplane. IMHO it is a constant, when  in  the air! --  unless you move baggage, lean way forward, shift weight around. In any  case the aircraft's ATTITUDE will  not move the CG, has nothing to do with it. 

This is a serious and potentially dangerous area. if you're confused, forget the amateur experts and consult a knowledgable person. May take some work to find one but your life is worth it. Ignore any advice that sounds questionable. 

IMHO; feel free to ignore if you wish.

Russ Kinne



On Nov 5, 2007, at 4:15 PM, Richard & Martha Neilsen wrote:

 



[quote]--> Kolb-List message posted by: "Richard & Martha Neilsen" <  NeilsenRM(at)comcast.net (NeilsenRM(at)comcast.net)>

Ray

The CG does shift aft when in a climb and with the tail on the ground, just denying that fact doesn't change anything. Anyone that has ever lifted the tail of their airplane knows that the tail is lighter when lifted to the specified W&B position. Lift it high enough and the tail will keep on going. Now maybe where ever your head is at it doesn't do that but it does here in the Midwest. The CG ranges are calculated based on a specific attitude. If they were calculated with the tail wheel on the ground they would be different. The CG ranges are given with the idea that the plane will be flown in allot of flight attitudes and not get us in trouble. You can do your weight and balance your way but please don't try to advise others this way. Also please if you do your W&B your way don't take anyone up in your plane or fly over populated areas. 



It is obvious you think you know more than than everyone else and that is fine.   Just keep it to yourself and keep flying. Some day when the grim reaper comes calling your bad advise will stop once and for all.

  As usual this is just my opinion and worth what was paid for it.

Do not archive

  Rick Neilsen

Redrive VW powered MKIIIC

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henry.voris

Joined: 02 Mar 2007
Posts: 116
Location: Pueo Field, Kula, Maui

Posted: Tue Nov 06, 2007 8:15 am Post subject: Re: Help with level flight attitude for Mark II

Cristal,



If I were in you position I believe I would:



First... I would assume that most of the Kolb flying have had their W&B done according to the manual... So, I'd do my W&B according to the photos that were kindly sent by Brother Possum. Those are photos of the pages of the construction manual, and they show how the Factory expects the W&B to be performed (9 degrees deviation of the bottom of the wing from horizontal, is the expected attitude of the plane...). 



Second... To do a W&B balance by the book requires that that you have scales and other measuring devices in position... So... it wouldn't be a big deal to run a second set of measurements with the tailwheel on the ground. 



Then you could inform us (your buddies on the list) if there is a significant deviation between the two methods of measurement.



Again... I would expect the factory method and expected CG numbers to be correct. I would do the W&B by the book firstâ€¦ use that data as a baseline, then experiment with other methods...



Good Luck...

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Firefly Five-Charlie-Bravo

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jb92563

Joined: 23 Mar 2007
Posts: 314
Location: Southern California

Posted: Tue Nov 06, 2007 8:21 am Post subject: Re: Help with level flight attitude for Mark II

Folks, I'm going to have to concede on this whole point about the attitude not mattering.



I did the calculations and found that it is true that you CAN derive the same CG point no matter what the attitude is, BUT you have to figure out the difference in attitude between the level flight attitude and the angle you are measuring and do a bunch of extra calculations to get the answer.



Its just not worth all that extra math(and potential errors) when you can just block the plane up for level flight attitude and measure it that way and do the plain simple method of weights, arms and moments.



I do agree that simple is the BEST method of doing a weight and balance.



However, the CG does NOT change in flight unless weight is moved, say from fuel burn, a passenger leaving the aircraft, or your bowling ball rolling to the front of the plane.



You Voodoo guys can also lift the hexes and grim reaper curses as I have given in to practical conventional practice in this case.....(even though I was theoretically right    )



I do want to thank the contructive comments made by a bunch of you in helping me understand THE POINT of the question!



Now if only I could figure out what the "Level Flight Attitude" of my Ultrastar is....anyone???

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Ray

Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider

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