CG change

[colospace]

Just a curiosity about CG movement. Anyone know how much the CG moves when converting a Series 7 between trigear and tailwheel configurations?

[jiott]

I'll bet the CG is in a sweeter spot with the tri-gear. As a tail dragger my SS7 CG is always very much toward the rear no matter how I load it. It stays within the limits, but always toward the rear limit.

[jrevens]

I'll bet the CG is in a sweeter spot with the tri-gear. As a tail dragger my SS7 CG is always very much toward the rear no matter how I load it. It stays within the limits, but always toward the rear limit.

That's why I'm not worrying about weight in my engine compartment, Jim. No lightweight, expensive batteries for me! (No real heavy tailwheels either). ;)
I'm hoping the Oratex will help in that regard too.

[jiott]

You're absolutely right John, however I still really like my lithium battery. It doesn't do anything to help CG, but it saves 10 lbs, which is a lot of baggage and helps make up for my heavy tailwheel. It is also nice to not have to always hook up a trickle charger because it doesn't lose 1/10th of a volt in months of sitting.

[rv9ralph]

Paul Z might be able to comment on this. He had his SS7 converted from a tri-gear to a tail wheel.

Where are you Paul Z?

Ralph

[HighWing]

For five years I worked on the ramp at KSFO,s United Airlines ramp area. This was a few years after the Arab Oil Embargo. I found it curious that they would load every departing flight to nearly the aft CG limit. I learned that during the embargo anything and everything that would improve fuel economy was employed. Aft CG is very efficient. Improving airspeed and or economy depending on one's preference.

[Dave S]

An aft CG, within operational limits at the same loaded weight, also allows a slower touchdown speed and slightly shorter rollout in many aircraft:)...with a forward CG bias a person may run out of elevator to keep the nose up before they run out of airspeed.

[jrevens]

Yep, many aircraft display that characteristic. I know my Thorp is faster with baggage & a passenger than without.

[RobS]

A good illustrated read on the benefits of an aft CG (within limits):

http://www.boldmethod.com/learn-to-fly/performance/how-does-cg-affect-aircraft-performance/

[Paul Z]

I'll have to got to the airport tomorrow to get the tail dragger weight & balance. Once I get both I'll post them.

Paul Zimmermann

[Paul Z]

Here are the weight & Balance sheets for 703KA

Not very legible, I'll try again!

[Paul Z]

Here is the Tri-Gear
12879
Here is the Tail Dragger.
12880
I hope you can read them!

[jrevens]

It is pretty hard to read many of the numbers, Paul. If you could post it as an attachment, perhaps a .pdf or .jpg, it would be able to be read easily.

[Paul Z]

John, That is what I thought I did. I used the Paper Clip, I attached the Files, both .png files. That is how they come in! That is the only way I know how to attach files.

If Gary want's the files directly I'll attach them to an e-Mail and send them directly to him.

[colospace]

Thanks, Paul. The CG numbers were clear. So, bottom line is that the CG for the tailwheel configuration moved forward ~3 inches from your initial tricycle configuration.

[jrevens]

Thanks, Paul. The CG numbers were clear. So, bottom line is that the CG for the tailwheel configuration moved forward ~3 inches from your initial tricycle configuration.

I think that's backward. :confused:

[Paul Z]

Both CG Calculatins were done at the Kitfox Factory. I do have the 21" smoothies. The plane gained weight from the first Weight & Balance I would suspect from not getting all the fuel out of the tanks, when they did the conversion.

[jrevens]

I guess that moving the heavy main gear (along with the bigger tires) forward more than offset the weight of the nose gear, moving the CG forward. So... it would seem that tricycle gear Kitfoxes MIGHT benefit even more from a little extra weight in the engine area as far as being able to load more baggage and remain within CG limits. Conversely, taildraggers should be able to carry more weight in the baggage compartment & remain within CG limits, all else being equal. Does that make sense? This is all predicated on comments made that the newer Kitfoxes tend to reach aft CG limits well before the published structural weight capacity of the baggage compartment is reached.

[Paul Z]

Yes you loose the weight of the nose gear. However, you are moving the massive spring gear forward probably 2 feet, and the weight of 2 Desser Smooth Tires 10 lbs each. It only makes sense the CG will move forward.