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Flying Mk 3 Xtra tail heavy

 
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Dan Breitigam



Joined: 06 Apr 2011
Posts: 16

PostPosted: Wed Nov 15, 2017 7:56 am    Post subject: Flying Mk 3 Xtra tail heavy Reply with quote

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: 1519
Location: Blountville, Tennessee

PostPosted: Wed Nov 15, 2017 2:39 pm    Post subject: Re: Flying Mk 3 Xtra tail heavy Reply with quote

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)
Kolb Firefly Part 103 legal (Repairing the fiberglass nose bowl. Ugh.)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.
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zeprep251(at)aol.com
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PostPosted: Wed Nov 15, 2017 3:48 pm    Post subject: Flying Mk 3 Xtra tail heavy Reply with quote

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

PostPosted: Wed Nov 15, 2017 3:51 pm    Post subject: Re: Flying Mk 3 Xtra tail heavy Reply with quote

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

PostPosted: Wed Nov 15, 2017 6:36 pm    Post subject: Flying Mk 3 Xtra tail heavy Reply with quote

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: 50
Location: East Moline, Il

PostPosted: Thu Nov 16, 2017 2:39 pm    Post subject: Re: Flying Mk 3 Xtra tail heavy Reply with quote

I would move the engine forward.

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PostPosted: Sun Nov 19, 2017 8:30 am    Post subject: Flying Mk 3 Xtra tail heavy Reply with quote

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.




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