Weight & Balance

[Steve Fisher]

I would like to get the empty balance location on any completed Patrol. Anyone responding please list your engine and prop specifics.

Thanks!
Steve

[JimParker256]

Eric posted his here, and also on his web site. Search is your friend.

[bergy]

I am building a conical mount for my Patrol's 0-320 and I have two questions:
1: On plans page 17 it shows the thrust line down 1 degree below horizontal and located 18.5" above horizontal datum line, I am not sure where that 18.5" is measured ... at the firewall, prop-flange, or somewhere else. The 1 degree down-angle could give me a half-inch error if I measure in the wrong place.
2: The Bearhawk newsletter shows forward placement of engine at 56" to 58" in front of the datum line as measured to the prop-flange. I assume one would use the front surface of the flange. If I keep my O-320 light with no electrical and use a lightweight fixed-pitch prop, I would guess that I should use the 58" figure or even slightly more.
Your opinions are appreciated.
Bergy

[JimParker256]

For something like this, I would call Bob Barrows and ask his advice.

[Bdflies]

Mine is as follows;

1259# / 14.45"
Lycoming O-360 full oil
MT 2 blade 80.5" C/S prop
Bearhawk Tundra tailwheel. (Notably heavier than the smaller ones)
PC680 battery - full electrics - 2 A/P servos

Bill

[Collin Campbell]

N180PB weighs 1178# with cg of 10.4" Superior XP-360, Sensenich prop, 8:00-6 tires, Bob's tailwheel, skylite, PC680, full electrics

[Bcone1381]

Regarding #2.

The FAA has a weight and Balance manual.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-1.pdf

I recalled using formulas in the previous century when taking a commercial written test. I just scourged around the FAA manual and found one in that you might be interested in.

The change in CG =

Engine Weight x Distance it will be shifted
Total Aircraft Weight

So, if you have a 1000 pound Patrol, and shift a 250 pound engine ahead 2 inches, it will shift the CG .5 inches forward.

There are a lot of other formulas that apply for adding or subtracting weight that could be applied using some known airframe numbers to predict an optimal location for your engine in your lighter aircraft. Sometimes I think we just build and at the end we find out what CG we got, kind of like having a baby. Surprise!! But we can use these formula's in the FAA manual and predict and thus control the outcome.

[bergy]

I am working on a generic weight/balance computer program. Does anyone have the the forward/rear C.G. envelope limits for all models of Bearhawks that they could share with me?

[JimParker256]

There are excellent W&B programs already in the app stores, already built into ForeFlight, and several other EFBs... Why re-invent the wheel? My personal favorite for iPhone and iPad is WnB Pro.

[bergy]

I am NOT the least bit interested in available W/B programs (and I refuse to use an Apple or Google product and assist them in their quest take-over of the world).

Every book/posting/website/etc I know of assumes one knows where the engine is located on the airframe, and many assume one is working with a mostly complete basic aircraft where one has put the gear and tail-wheel on scales; I am trying to head off problems produced in the design-phase which do not show until it is too late to change basic structure.
I am writing a program (actually, I am now just in the testing phase) which I can use to experiment with different engine placements, props, seat-locations, etc.

At last week's EAA chapter meeting one of the members said he had to add a chunk of lead near the tailpost of his airframe to make his W/B work out. Other guys land up moving their batteries around just to make it all work out. That is what one gets when using off-the-shelf design tools.

So I am still looking for basic C.G. limits for the various Bearhawk/Ribblet airfoils. Anyone help me out here?

Bergy

[Chris In Milwaukee]

Basic Patrol limits: 10.5" (16%) - 21.5" (32.5%)

I've only got BH-A plans, so can't help out with the BH-B W/B.

Good luck with the world-takeover thing with whatever platform you're planning for.

[bergy]

Thanks Chris!

My program is written in very simple legacy HTML with some Java-scripts to crunch the numbers, so it should run on virtually any platform.

I had not written any Java-scripts in 12 years, found a bug in my Linux browser so the project took much longer than I had intended.

[Chris In Milwaukee]

Ah, Javascript. Good times I still write a lot of stuff with it. Calculators are a lot of fun to write in JS.

[bergy]

If anyone wants to know how/where to hang an M-14P radial on their BH, you can take a look at the latest version of my program and do some trial calculations at http://poplar.us/BWB.html

[Rollie]

I've been meaning to ask, is it really that simple - 10.5-21.5" at all weights? No taper at heavier weights? That makes it easy, I'm just not sure I've ever seen a CG limits chart that didn't get smaller at higher weights.

[Chris In Milwaukee]

I've been meaning to ask, is it really that simple - 10.5-21.5" at all weights? No taper at heavier weights? That makes it easy, I'm just not sure I've ever seen a CG limits chart that didn't get smaller at higher weights.

You mean like a 172 envelope and similar?



I’ve often wondered the same. Like if there's some sort of quantitative measure that the test pilot was looking for to get that slope, or if it's completely subjective.

[Rollie]

Yup, exactly like that.