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Weight and Balance-KF4 with 912 was Model 4 engine swap

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Lyle Persels

Joined: 10 Jan 2006
Posts: 34
Location: Osceola, IA

Posted: Tue Jan 09, 2007 2:09 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

Thanks for all your tips regarding the need to work with the local  

FSDO after my engine swap. I'm preparing a letter now.



According to the specs, the Rotax 912 ULS with which I've replaced my  

912 UL weighs 12.5 lbs more than the old engine.  Does anyone know  

the moment arm of the standard installation of the Rotax 912 on a  

model 4? I'm trying to determine a new W & B without going through a  

complete new weighing process.



Lyle Persels

kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Tue Jan 09, 2007 3:02 pm Post subject: Re: Weight and Balance-KF4 with 912 was Model 4 engine swap

Not to be dissapointing.  But it really isn't that hard to reweigh the plane after the swap.  Usually after a few years of flying we put things in our planes and we take a guess at what it weighs.  Just take a bathroom scale and lift up on a wing (at the tips) and have someone slip a scale under the wheel and then do it to the other side.  Of course to be more accurate build up the other side with boards to equal the scale.   Then level the plane and put the scale on the rear.  You just might be supprised at what you get.  Oh, one more thing the sportpilot site, I think, has a neat weight and balance program.

rjdaugh

Joined: 30 Aug 2006
Posts: 195

Posted: Tue Jan 09, 2007 3:11 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

Lyle,

I believe in your owner's manual there is a drawing with that info.  I

remember digging it out to compare a 912S to a Jab 3300 before I finally

decided to go with the 912S.



Randy



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Randy
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dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Tue Jan 09, 2007 3:24 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

I have to agree with you that  you are changing the weight and should do a w 

& B .

It is not complicated and you should know that you are within the C of G 

range for your aircraft .

W & B is only way to do it really.  You should do it for every change in 

weight and moment of anything in your plane.

A engine change , especially with a weight difference should be no exception 

.   AS would  a prop change.



Would really suck if you did not do it and an insurance policy became null 

and void in the unfortunate event of having to make a claim.



Dave

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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 09, 2007 5:08 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

The plane should be level for all weighings (tail up).  Getting the tail the

right height to level the plane can be the biggest problem.  Best way is get

three identical scales... They're not expensive and they can be calibrated

with water jugs... 1 Imp. Gal. = 10 lb.



Remember to weigh with no usable fuel ( about 1/2 Gal or so in tank) Oil in

engine (4 stroke) and Fluid in radiator ( Liquid cooled)...  A good time to

clean out the glove box and any cargo slings etc.



Readings will be close enough for government work 



Noel



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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 09, 2007 5:15 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

I think the Regs (Canada) require that if the weight of the plane changes

more than 10% the plane should be re-weighed.  On any major weight change

it's probably a good idea to re-weigh and make sure the math is in your

aircraft log.  As has been stated we all add little things to our planes

which can in combination cause the W&B to be out.  



Noel



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kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Wed Jan 10, 2007 7:01 am Post subject: Re: Weight and Balance-KF4 with 912 was Model 4 engine swap

I forgot to put in that yes I had my plane leveled for all reading, I used two scales that went to 300.  On the rear I used two saw horses with a door over the top and then put the tail wheel on that.  The saw horses were the plastic ones.  After I was done with the front weight I put one of the scales to the rear and weighed the tail.

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jan 10, 2007 2:13 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

I  checked the local Walco (you know who) store to day and they had analogue

scales $9.95 ea. for that price 2 sets won't break the bank....  If the

weight goes over the 300 mark you have to get out of the plane to weigh it





Noel



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kirkhull(at)kc.rr.com
Guest

Posted: Wed Jan 10, 2007 4:40 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

If you are close to Kansas City MO. You can rent the EAA chapter scales for

$10.00 ( up to 2500 lb)



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Lyle Persels

Joined: 10 Jan 2006
Posts: 34
Location: Osceola, IA

Posted: Wed Jan 10, 2007 6:57 pm Post subject: Weight and Balance-KF4 with 912 was Model 4 engine swap

Again, thanks to all for the suggestions. I have access to certified  

aircraft scales, so weighing is no problem. I've used them before and  

have an excellent previous weight and balance. I just wanted to avoid  

reweighing since I have a relatively small weight change not far from  

the cg. Of course I understand and agree that the best, most accurate  

course is to do it all again with the new engine. Maybe I'll be  

surprised. I'll let you know the results of the new weighing as well  

as what my FSDO says.



And I'll also post a price on my used 912 UL before long.



Lyle



On 01 10, 07, at 6:40 PM, kirk hull wrote:



[quote] 



 If you are close to Kansas City MO. You can rent the EAA chapter  

 scales for

 $10.00 ( up to 2500 lb)



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