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Flying Mk 3 Xtra tail heavy

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Dan Breitigam

Joined: 06 Apr 2011
Posts: 16

Posted: Wed Nov 15, 2017 7:56 am Post subject: Flying Mk 3 Xtra tail heavy

Hello all,



I am getting ready to test fly my Mark III Xtra after restoration and new engine (1.3 liter Geo Metro 100 HP). Weight and balance shows it is barely in the envelope on the tail heavy side. 



Question 1:  Is it safe to fly?



Question 2:  What arm do folks use for the distance to datum for pilot/passenger and 19 gal fuel tank?



Question 3: Does anyone carry extra nose weight when flying solo?



Thanx!



Dan in Chattanooga

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Nov 15, 2017 2:39 pm Post subject: Re: Flying Mk 3 Xtra tail heavy

As long as it is within the envelope, it is safe to fly, however, some of the questions you ask make me wonder how you calculated your weight and balance. (no offense, this is not an easy topic, and it is like using MS Windows: there are many ways to do one task)

Check out this link: http://oh2fly.net/oldpoops/Lexan%20rear%20enclosure.html

Scroll down until you get to the Gen-U-Wine Kolb MKIII W&B pages.

The CG of people is determined at the belly button. (seriously) So your moment arm from that point to what you think is the center of weight of your gas tank is what you would use for the difference between full fuel/empty fuel, solo or 2 up,  and all permutations of that particular equation.

I do not carry nose weight, but if I lose another 30 pounds I will need it if I fly solo. (LOL)

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

zeprep251(at)aol.com
Guest

Posted: Wed Nov 15, 2017 3:48 pm Post subject: Flying Mk 3 Xtra tail heavy

At 175# solo my mk3 is at the aft limit       Fine in smooth air but when bumpy it wallows like passing over the wake of a boat then back to stable. I have about 40 # of shot in a plastic and denim bag and the Claw tie downs secured to rings on pass side floor which cures the handling. Fuel affects CG almost none



Sent from my iPhone



 	  Quote: 	
		   On Nov 15, 2017, at 10:56 AM, Dan Breitigam <dbrtgm(at)me.com> wrote:

 

 all,

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Dan Breitigam

Joined: 06 Apr 2011
Posts: 16

Posted: Wed Nov 15, 2017 3:51 pm Post subject: Re: Flying Mk 3 Xtra tail heavy

I checked out the link you recommended Richard but the shape of the tank I got from Bryan is not square like in the plans. It is triangular or more accurately a trapezoid shape. So the center of mass is not intuitive. Therefore I don’t know how to determine the arm length to use in the formula which I have laid out in Excell. 



Of course I could weigh it with full fuel but I just wanted to calculate W&B with my Excell file. 



Thanx,

Dan

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Radegast

Joined: 06 Aug 2016
Posts: 15

Posted: Wed Nov 15, 2017 6:36 pm Post subject: Flying Mk 3 Xtra tail heavy

You can calculate the arm of the fuel by weighing the plane twice.

     Once with it empty and again with full fuel.

     Below is a made up example.  The result is that the fuel is at an     arm of 13.36.

     I can send you an Excel spreadsheet to do this if you email me off     line.

     

     

     

                                                

                      Left Main           Right Main           Tail wheel           

                      

                      

                                        Datum distance           9           9           195           

                      

                      

                                        Empty Weights           222.42           224.92           60.4           

                      507.74           Total Empty Weight                             Empty Moment           2001.78           2024.28           11778           

                      15804.06           Total Empty Moment                             

                      

                      

                      

                      

                      31.13           Empty Weight C.G.                             

                      

                      

                      

                      

                      

                      

                                        Full Fuel Weights           256           258           62           

                      576           Total Weight Full Fuel                             Full Fuel Moment           2304           2322           12090           

                      16716           Total Full Fuel Moment                             

                      

                      

                      

                      

                      29.02           Full Fuel C.G.                             

                      

                      

                      

                      

                      

                      

                                        Fuel Weight           68.2600000000001           

                      

                      

                      

                      

                                        Fuel Moment           911.940000000001           

                      

                      

                      

                      

                                        Fuel Arm           13.36

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baberdk

Joined: 23 Jan 2014
Posts: 53
Location: East Moline, Il

Posted: Thu Nov 16, 2017 2:39 pm Post subject: Re: Flying Mk 3 Xtra tail heavy

I would move the engine forward.

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zeprep251(at)aol.com
Guest

Posted: Sun Nov 19, 2017 8:30 am Post subject: Flying Mk 3 Xtra tail heavy

Thanks, what model are you presently flying?

 	  Quote: 	
		   On Nov 16, 2017, at 5:39 PM, baberdk <baberdk(at)gmail.com> wrote:

 

 

 

 I would move the engine forward.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=475095#475095

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