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Weight and Balance?
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grantr

Joined: 12 Sep 2007
Posts: 217

Posted: Tue Jul 22, 2008 12:36 pm Post subject: Weight and Balance?

John Hauck Wrote

 	  Quote: 	
		  Weight and balance of a Kolb is one of those unique areas. There are folks 

out there still flying Kolbs with lead in the nose to make the paperwork 

work. I put a 11+ lb tailwheel on mine for a couple reasons. Primarily, 

the Maule Tundra Tailwheel, 8" pneumatic with tapered roller bearings in the 

pivot, is the only tailwheel I could afford that will stand up to the weight 

of the tail on my MKIII. The other reason was to demonstrate Kolbs don't 

particularly have an aft cg problem, if built, more or less, according to 

the plans. In addition to the heavy tailwheel and prop on a 4" extension, 

I fly with 150 lbs of fuel and 100+ lbs of cargo aft of the cg. I do get 

some offset from my modified main gear being moved 8" forward, but not much, 

since they are very close to the cg. 



	




My Mark III manual says the airplane should balance between 25% and 35% wing chord which is 16.5 to 23.1 inches behind the leading edge of the wing.



I am a light pilot at 155 ready to fly so my weight and balance calculation says I need I  10 lbs in the nose to make the aft limit at 23.1 inches. Or a minimum weight of 177 for the pilot with no ballast.



So if I am reading this right you are saying to forget about the Weight and balance and do not add the weight?



With no ballast my cg would be at 23.95 or about and inch aft of the aft limit.



How do you know the difference between a trim issue and a CG issue?

Arty Trost

Joined: 25 May 2006
Posts: 203
Location: Sandy, Oregon

Posted: Wed Jul 23, 2008 6:03 am Post subject: Weight and Balance?

John -



Your comment on W & B was a real eye-opener...it reflects my own experience, but is something I've never heard anyone talk about.  When I did the original W & B on my Drifter, the A & P (also an experienced ultralight builder and pilot) guided me to putting 60 lbs. of lead in the nose, since I am a true ultra-light pilot at 105 lbs.  I flew with that weight for years - then had to re-do my W & B when I added an electric starter aft.  Showed I should put MORE lead in the nose. I was uncomfortable with that (most of the other pilots are trying to shave off ounces and here I'm adding pounds!) and took it all out, putting some tools up front for easier access.  It didn't fly discernably different! Even when I'm fully loaded with my camping gear, which also is aft of cg.  



Since weight and balance is a matter of physics - how come we've got such different results than would be expected?  Is this akin to the "a bumblebee can't fly"?



Arty Trost

Maxair Drifter

Sandy, Oregon

 	  Quote: 	
		   

 John Hauck Wrote

 

 > Weight and balance of a Kolb is one of those unique

 areas. There are folks 

 > out there still flying Kolbs with lead in the nose to

 make the paperwork 

 > work. I put a 11+ lb tailwheel on mine for a couple

 reasons. Primarily, 

 > the Maule Tundra Tailwheel, 8" pneumatic with

 tapered roller bearings in the 

 > pivot, is the only tailwheel I could afford that will

 stand up to the weight 

 > of the tail on my MKIII. The other reason was to

 demonstrate Kolbs don't 

 > particularly have an aft cg problem, if built, more or

 less, according to 

 > the plans. In addition to the heavy tailwheel and prop

 on a 4" extension, 

 > I fly with 150 lbs of fuel and 100+ lbs of cargo aft

 of the cg. I do get 

 > some offset from my modified main gear being moved

 8" forward, but not much, 

 > since they are very close to the cg. 

 > 

 > 

 

 

 My Mark III manual says the airplane should balance between

 25% and 35% wing chord which is 16.5 to 23.1 inches behind

 the leading edge of the wing.

 

 I am a light pilot at 155 ready to fly so my weight and

 balance calculation says I need I  10 lbs in the nose to

 make the aft limit at 23.1 inches. Or a minimum weight of

 177 for the pilot with no ballast.

 

 So if I am reading this right you are saying to forget

 about the Weight and balance and do not add the weight?

 

 With no ballast my cg would be at 23.95 or about and inch

 aft of the aft limit.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=194430#194430

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Wed Jul 23, 2008 9:03 am Post subject: Weight and Balance?

At 09:58 AM 7/23/2008, TheWanderingWench wrote:



 	  Quote: 	
		  Since weight and balance is a matter of physics - how come we've got such 

different results than would be expected?  Is this akin to the "a 

bumblebee can't fly"?


	


The allowable c.g. range is set between two limits.  Go too far past the 

forward limit (nose heavy) and you may not have enough elevator authority 

to raise the nose at low speeds, which makes for hard landings.   Go past 

the aft limit (tail heavy) and the airplane gets less stable... go too far 

and it becomes dangerously unstable.  Within extreme limits, how much 

stability is required depends somewhat on the aircraft's mission (you want 

a Cessna to be more stable than a fighter or an acro ship) and also on the 

pilot's preferences.  Even a neutrally stable plane can be OK, if the pilot 

can handle it and is expecting it.  Like everything else on an airplane, 

the limits are set to insure some safety factor.  Depending on the target 

pilot audience, the designer may be more or less conservative when setting 

the limits.



That's the primary thing governing the limit.  But there are other things 

as well.  Gary mentioned a sudden pitch up when slipping hard; that's one 

example.  Or, very likely, a plane might fly just fine in most cases with 

an aft limit, but then be unable to recover from a spin, or some other odd 

flight condition.  It's one of the reasons that test pilots are well 

paid.  Fly your plane past the aft limit and YOU are the test pilot.



-Dana

--

  Everyone who lives dies; yet not everyone who dies, has lived.

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Jul 23, 2008 9:54 am Post subject: Weight and Balance?

At 06:58 AM 7/23/08 -0700, you wrote:

 	  Quote: 	
		  




	


Arty & John,



If you wish to deviate from the per scribed CG range for your aircraft, it 

would be best that you follow the testing procedure as set up by the FAA and 

report back the results.



Check: www.faa.gov/library/manuals/aircraft/media/ac90-89a.pdf



Especially important is page 57 that lists "Maximum Gross Weight Tests"



If you don't want to do this and prove that your new aft CG limit is ok, 

then I suggest that you climb to an altitude or 10,000 agl, and perform 

a departure stall.  Then report back to the List as to how it went.



Fly safe and know your CG limits.



Jack B. Hart FF004

Winchester, IN

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Jul 23, 2008 11:27 am Post subject: Re: Weight and Balance?

 	  Dana wrote: 	
		  At 09:58 AM 7/23/2008, TheWanderingWench wrote:

That's the primary thing governing the limit.  But there are other things 

as well.  Gary mentioned a sudden pitch up when slipping hard; that's one 

example.  

	




For what it's worth, my titan exhibits a pitch-up tendency in a max-effort slip when near the aft limit as well. When solo with full gas, I'm right near the aft limit listed for the plane and the nose comes quite a ways up in a max-effort no-power slip (doesn't hit stall AOA tho).



I notice this reduces as the flight goes on and some gas gets burnt (or with a copilot in the back seat max-effort slips are no problem).



Other flight characteristics are kind of nice with an aft CG tho - stalls are very gentle and it just mushes forward (still nice with a copilot but with a more abrupt stall break and a bit more pitch-over) and very high AOA, slow flares are possible with very light elevator pressure.



I am working on a ballast system to conveniently add ballast when solo tho since the pitch-up with slips would be nice to fix....



My FS II flew slightly nose-heavy and it accordingly didn't exhbit any pitch-up at all in a slip....



LS

_________________
LS
Titan II SS

kuffel(at)cyberport.net
Guest

Posted: Wed Jul 23, 2008 11:37 am Post subject: Weight and Balance?

One point which should be reiterated.  In the US it is the 

*builder* of an experimental who sets the CG limits, not the 

plans designer or kit supplier.



What we should do is set the CG near the middle of the suggested 

range for early flights.  Once familiar with the aircraft, the 

builder should use some of the 40 hour test period to determine 

the CG limits for *his/her* airplane.



Ballast forward (in small increments) until slow speed elevator 

authority starts to go away.  Set the forward limit back a 

little.  Ballast rear (in small increments) until stability 

starts to go away (particularly in turbulence).  Set the aft 

limit forward of this point a little.  Also check stall 

characteristics at each step.



Different pilot perceptions of approaching unsatisfactory 

handling will result in different limits.  So will differences in 

building techniques.  My understanding is it is difficult to get 

a plans conforming Kolb to be loaded in an unstable aft 

condition.  But no-one knows for sure with any given homebuilt 

until the limits are determined by test.



Tom Kuffel, CFI

EAA Flight Advisor

Whitefish, MT

Building Original FireStar

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Jul 24, 2008 8:51 am Post subject: Weight and Balance?

So if I am reading this right you are  saying to forget about the Weight and balance and do not add the  weight?



With no ballast my cg would be at 23.95 or about and inch aft of  the aft limit.



 Grant R

  

 Hi Grant/Gang:

  

 Nope, you are not reading it right.

  

 I try not to tell others how to fly or what to do  to their Kolbs.  I do share with folks what I do to and with my Kolb and  how I fly.

  

 I reinterate, I am not telling anyone to forget  about the Weight and Balance, and not to add weight in the nose.

  

 That is strictly up to the individual's decision on  what to do.

  

 However, it has worked for me and my Kolbs for many  successful years and hours.

  

 john h

 mkIII

   [quote][b]

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Jul 24, 2008 10:07 am Post subject: Weight and Balance?

Hi Arty:

 

Could bee!  

 

Good thing I am not an engineer or I would be hauling 60 lbs of lead in the nose of my mkIII.

 

NOTE:  I am lost in the mountains of Tennessee, dragging around my 5th wheel and ATV.  There is joy in riding the wonderful green mountains of this fine State.

 

However, email does not work so well.  Right now I am parked at the Comfort Inn north of Knoxville, TN, on my way to Brimstone ORV, near Huntsville, TN.  If I do not respond to an email, it is because I do not have the capability to do so, not because I am being a grumpy old fart.

 

john h

mkIII

 Since weight and balance is a matter of physics - how come we've got such different results than would be expected?  Is this akin to the "a bumblebee can't fly"?



Arty Trost

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Dave Bigelow

Joined: 29 Jan 2006
Posts: 103
Location: Kamuela, Hawaii

Posted: Fri Jul 25, 2008 9:56 am Post subject: Re: Weight and Balance?

The 25% to 35% range for CG is pretty standard for conventional aircraft with tailfeathers rather than a flying wing or canard.  If your CG falls within that range and you have a pitch trim problem, the solution is not to to change CG.  You should add a trim tab to the elevator, a bungee or spring to the stick, or a more radical solution - change the angle of incidence of the tail.



A CG aft of the recommended rear llimit is dangerous.  The aircraft may feel and handle just great, but in certain situations like a deep stall or spin, may not be recoverable.  There's nothing wrong with flying at or near the rear limit.  Sailplane pilots do it all the time to optimize handling and reduce drag.



If you do a good weight and balance with the aircraft in the proper pitch attitude with good accurate scales, and the CG is aft of the limit, you should add ballast to keep it within the llimit.  This stuff is basic and is applicable to all conventional aircraft.  



Homer didn't design aircraft that beat the rules.  If his planes don't exhibit dangerous flight charactoristics with the CG slightly behind the limit, that means he probably was being conservative when he published the limits.  Somewhere back of his published limit is "never never" land, and you don't want to be the person who finds out exactly where that is unless you are conducting a flight test program with a drag chute, etc to be able to recover from a deep stall or flat spin.



If Dennis Souder (did most of the flight testing at Old Kolb) is reading this thread, it would be good to get his input.

_________________
Dave Bigelow
Kamuela, Hawaii
FS2, HKS 700E

pj.ladd(at)btinternet.com
Guest

Posted: Sat Jul 26, 2008 1:27 pm Post subject: Weight and Balance?

Gary mentioned a sudden pitch up when slipping hard; >>



Hi,

in the UK the tendency for the nose to lift when sideslipping is 

incorporated in the test write up for the Extra. Probably different for the 

single seaters.. It is attributed to , not the weight being aft but the 

airflow sideways across the nose cone producing lift.

The information in the test results merely said `Not dangerous if the pilot 

is aware of the effect.



Is there any point in sideslipping a Kolb?. There is so little side area and 

the flaps can produce a pretty good descent angle antway. Anyone done any 

comparative tests?



Off line for the next week as I am off to Summer School at a local 

university.



Cheers



Pat

pj.ladd(at)btinternet.com
Guest

Posted: Sat Jul 26, 2008 1:30 pm Post subject: Weight and Balance?

plane might fly just fine in most cases with an aft limit, but then be 

unable to recover from a spin,>>



Hi,

I understand that the Thud could not be got out of a flat spin. Standard 

drill was to take your hands and feet off, and wait. That took guts.



Cheers



Pat

lcottrell

Joined: 29 May 2006
Posts: 1490
Location: Jordan Valley, Or

Posted: Sat Jul 26, 2008 2:20 pm Post subject: Weight and Balance?

---

_________________
do not archive

jbhart(at)onlyinternet.ne
Guest

Posted: Sat Jul 26, 2008 3:59 pm Post subject: Weight and Balance?

At 10:24 PM 7/26/08 +0100, you wrote:

 	  Quote: 	
		  

Is there any point in sideslipping a Kolb?. There is so little side area and 

the flaps can produce a pretty good descent angle antway. Anyone done any 

comparative tests?



Pat,
	




Side slipping is nice for cross wind landings.  I prefer it as apposed to 

crabbing and straightening the FireFly out just before touch down.  With 

side slipping, I can stabilize the FireFly relative to the runway center 

line.  I am not good at multi tasking as I am just about touch down.



I am curious.  What course are taking in summer school?



Jack B. Hart FF004

Winchester, IN

russ(at)rkiphoto.com
Guest

Posted: Sat Jul 26, 2008 6:26 pm Post subject: Weight and Balance?

Pat

IMHO sideslipping is a valuable maneuvre (note correct spelling) in  

any kind of aircraft, but I admit to  no experience  in  a Kolb.

Little side area should make her slip and descend even better than most.

BTW in your 'Summer School' -- are you instructor or student ?

Fair winds,

Russ

do not archive

On Jul 26, 2008, at 5:24 PM, pj.ladd wrote:



 	  Quote: 	
		   



 Gary mentioned a sudden pitch up when slipping hard; >>



 Hi,

 in the UK the tendency for the nose to lift when sideslipping is  

 incorporated in the test write up for the Extra. Probably different  

 for the single seaters.. It is attributed to , not the weight being  

 aft but the airflow sideways across the nose cone producing lift.

 The information in the test results merely said `Not dangerous if  

 the pilot is aware of the effect.



 Is there any point in sideslipping a Kolb?. There is so little side  

 area and the flaps can produce a pretty good descent angle antway.  

 Anyone done any comparative tests?



 Off line for the next week as I am off to Summer School at a local  

 university.



 Cheers



 Pat

pj.ladd(at)btinternet.com
Guest

Posted: Sun Jul 27, 2008 1:59 am Post subject: Weight and Balance?

BTW in your 'Summer School' -- are you instructor or student ?>>



Hi Russ,

very funny. Definitely a student studying `Noel Coward` and  `Musical 

Composition` (unrelated courses). In previous years I have `done` Water 

Colour Painting` `The History of the Third Reich`(the whole class decided 

that if we were German in 1935 we would have voted for Hitler) `Musical 

Improvisation`

Wendy is `doing` Photograph Manipulation by Computer` amnd learning to play 

Croquet.

Grandchildren are canoeing, abseiling, horse riding, shooting, raft 

building. Its a great holiday as we just feed the kids breakfast and they 

disappear with their instructors until the next mealtime. Then we feed `em 

and throw `em back.



I bet you are glad you asked. Leaving this afternoon.



Cheers



Pat

pj.ladd(at)btinternet.com
Guest

Posted: Sun Jul 27, 2008 2:41 am Post subject: Weight and Balance?

Side slipping is nice for cross wind landings.>>



Hi Jack,

aven`t really got into very strong cross wing landings in the Kolb yet so I 

have that to come. In the Challenger I almost always side slipped into a 

landing. I just liked the precision of landing on a pre chosen spot.

<<I am curious.  What course are taking in summer school?>>



Oh dear, I hadn`t realised my throwaway remark would generate such interest. 

See the detail in my reply to Russ.



Its a bit of a b****r in fact as the weather has come good for almost the 

first time this summer and I should be flying, not `larnin`. Still, I flew 

twice yesterday and took Wendy up for the first time the day before. I think 

that is the first time I have flown two days in succesion this summer.

Return from school next Saturday and there is a very big fly- in about 60 

miles away on Sunday so I hope to make that. The fly-in is a re-run of a 

previous date which had to be cancelled, for the first time in 29 years, 

because the field was flooded. Fingers crossed.



Cheers



Pat

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Jul 27, 2008 8:11 am Post subject: Weight and Balance?

I just liked the precision of landing on a pre chosen spot.

 	  Quote: 	
		   

 
	


 	  Quote: 	
		   

 Pat

 
	




Patrick:



Aren't there also other methods of landing at a prechosen spot?



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Mon Jul 28, 2008 4:59 pm Post subject: Weight and Balance?

At 05:24 PM 7/26/2008, pj.ladd wrote:



 	  Quote: 	
		  Is there any point in sideslipping a Kolb?. There is so little side area 

and the flaps can produce a pretty good descent angle antway.


	




Unless, of course, you fly an Ultrastar which has no flaps... 



-Dana

--

  The difference between a hero and a fool is the outcome.

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Mon Jul 28, 2008 5:04 pm Post subject: Weight and Balance?

At 10:23 PM 7/26/2008, Russ RKIPhoto wrote:



 	  Quote: 	
		  IMHO sideslipping is a valuable maneuvre (note correct spelling) in

any kind of aircraft, but I admit to  no experience  in  a Kolb.

Little side area should make her slip and descend even better than most.


	


Russ, a slip makes an aircraft descend faster due to the increase in drag 

due to the relative wind impinging on the fuselage side.  Little side area 

means little added drag means little effect on descent.



-Dana

--

  The difference between a hero and a fool is the outcome.

russ(at)rkiphoto.com
Guest

Posted: Mon Jul 28, 2008 5:57 pm Post subject: Weight and Balance?

DanaIMHO the reduced vertical area of the wing when it's tilted also has a  considerable effect. Less lateral area (covered fuselage) would make her travel sideways faster, and down faster. As they say, just my 2c worth

Do not archive



On Jul 28, 2008, at 9:00 PM, Dana Hague wrote:

[quote] [quote][b]

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