Weight & Balance

S

Steve Fisher

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

Thanks!
Steve
 
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
 
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
 
N180PB weighs 1178# with cg of 10.4" Superior XP-360, Sensenich prop, 8:00-6 tires, Bob's tailwheel, skylite, PC680, full electrics
 
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.
 
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?
 
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.
 
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
 
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. :)
 
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.
 
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.
 
Rollie said:
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.
Click to expand...

You mean like a 172 envelope and similar?

71eb3035e431659dc345e7f2bcb7f7a6.jpg


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.
 
Bergy, Thanks for the program! I am starting to believe that scales in a workshop will improve results of every aircraft. I also ought to plan my empty wt and CG, and know where I stand as I build rather than arrive at it by accident after everything is done.

Chris and Rollie, One factor that I am familiar with and may contribute to the slope is elevator effectiveness at slow speeds.

The quantitative element of the the slope on the forward end of the envelope may be the elevator's inability to provide pitch authority at a slow speed (the landing flare) while operating at a forward CG. Forward of the line, I am guessing that the aft stop on the elevator will be contacted during the landing flare.

I flew a Beech 56TC Baron once upon a time....the very large engine that Beech could put on this four place Baron fuselage moved the CG forward. (Lyc TSIO-541, 380 hp, 46" MAP on takeoff) With one 150 pound pilot and no freight, it required 50lb. ballast in the aft most baggage area to be in the CG envelope. If not, one would be forward of the CG limit, and hit the aft elevator stop during the landing flare resulting in a near three point landing.

The Flight Test Phase is the time to test this stuff. We can find out "How heavy and how far forward can the CG be and still have satisfactory elevator authority?" I suspect that the Patrol with a carefully targeted empty weight CG is so well designed that the elevator never looses effectiveness in the flare.
 
I asked a question about engines and CG issues a month or two ago. I was thinking that to make the airplane more "useful" , as in useful load, it might make sense to plan to build it so that flown solo, you needed ballast to either put it within the CG envelope, or in a better part of the CG envelope to make it fly better.

Apparently that is not a unique thought. I was perusing Van's forums and several RV-10 builders do the exact same thing. To increase their "useful" useful load, they carry ballast in the cargo are when flown solo. When they want to carry more people/stuff, they remove the ballast, which takes all of 30 seconds. I was also wondering if this was "legal" per FAR's. Someone mentioned that the US does permit an aircraft to be signed off with a CG forward of the limit and carry removable ballast, but Canada does not.

For my personal plane, it will be flying over rugged, remote terrain 98% of the time. Having some basic camping/survival stuff, and water, would probably be prudent. Throw in a bit of fishing gear and a case of beer, and an unexpected overnight camping trip could be downright enjoyable. My "ballast" gets heavier every time I think about it.
 
My first build was a Glasair II TD. Not a IIS, which was the 'stretched' version. It was a 'short one. Being young and foolish, through a series of strange events, I powered it with a Continental IO520D (300hp) and a 3 blade McCauley prop. Can you say "NOSE HEAVY". I put the battery as far to the rear as possible. I ended up molding a 12# lead weight, that I bolted above the tailwheel spring. AS i recall, minimum pilot weight was about 150#. Ideal? No. If I'd known then what I know now, I wouldn't have built it with that power plant. It flew great! If I'd known better, I wouldn't have had the pleasure and excitement of flying a 1180# (empty) plane with a 300 hp engine. Talk about a RUSH! Picture attached.
I guess my point is not to get too wrapped up in engineering the CG. If you don't stray too far from the designed parameters, you can adjust the CG by common means. My lead ballast was a bit extreme, but produced a plane with no adverse tendancies.

Bill
 

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I've enjoyed playing with my online W/B program, http://poplar.us/BWB.html

I am really beginning to appreciate Bob's Ribblet Patrol airfoil. As I've stated earlier, by starting with a basic fuselage without an engine and then positioning the engine with my mathematical model one can really configure the aircraft to haul some fantastic baggage loads and still feel relatively safe.

As a grade-school kid, my buddies and I would run around the countryside in our old '31 Model-A Ford sedan. The Ford had a gas tank up front not that different from a J-3. The gas-gauge always read "E". Before a jaunt we would jump on the running-board and if the gauge wiggled we assume we had enough gas for our trip. Well if we assume that no pilot is going to try run their aircraft on fumes in like manner, and we assume that if we return home with extremely low fuel only after a cross-country trip and therefore have some baggage we can really configure the Patrol to manage a huge usable load (Example: me at 200#, my wife, full fuel, and 200#+ of baggage). This is accomplished by pushing the engine a bit farther forward, especially if using smaller engines and lightweight props.
 
Thanks for the program Robin, it will surely be useful in my case too. Hopefully I'll sort out the numbers needed for my four place soon.
 
Yesterday was a big moment of truth for me: Weigh in day. I knew I was building heavy, especially compared to Bob. I came in at 1269 total, 91 at the tail, empty cg 12.9 That's 8 quarts of oil, unusable fuel, (I had to taxi it to the shop with the scales and drain the fuel) full IFR avionics, two garmin autopilot servos, electric fuel pump with filter, Hatrzell Trailblazer prop.

I figure the battery, alternator, starter and associated wiring added a significant chunk of the weight over Bob's then the avionics and the few other mods I did account for the rest. Mods like removable belly panels, big cowl flap, plus I insulated the inside of the boot cowl and the bottom of the floor boards and I'm running dual mufflers and dual heat.

Its a bit heavier than I was hoping for but it has everything I want in my plane and I built up the engine to cover for the expected weight gain. My IO-360 should be putting out around 205-210hp. Hopefully in a couple weeks I'll know how it flies.
 
I just did a few computations and found that there is no way I can exceed the CG envelope without doing something like loading the tail full of stuff. I even tried it with nobody in the front seat, like flying solo from the back, which I don't plane to do, and with full fuel, 150 lb in the baggage and 200lb in the back seat and the front seat empty, it just almost touches the aft cg limit. and with a light pilot, solo, no baggage and low fuel, its still aft of the empty cg, which is within the forward limit. It should fly fine, now I need to get back to work so I can get it inspected next week.
 
I just saw this, my number is 740-221-6490. My phone is off or in airplane mode a lot so if you don't get me, just leave a message and I'll get back to you when I can.
 
This really doesn't apply to this category but will post for those who may have a similar built or components in their project. First of all this was basically a scratch built Patrol. Weight and balance was done a few days ago with an index of 11.48" at 1192 lbs. This fuselage has left and right windows and doors, full light and medium fabric interior, leather seats, aluminum floor with carpet, baggage door, and no sky lights. The prop is a CS McCauley hub with 80" Whirl Wind blades. The engine is a heavy Lyc I0-360 with counterweights, angle valve cylinders, and was modified for a carburetor. The basic weight (no accessories) was 263 lbs and was estimated to be 290ish with light weight starter, alternator, S4 mags, prop gov, and carb. Bob B suggested the engine mount be shortened by 2" to accommodate the heavier install which would be 54" flange to datum. I built the mount at 54" but installed a 1" bushing at the firewall through bolts to give it 55" in case it may need to actually come back the other inch. I was afraid it might be tail heavy. Anyway the numbers worked to out to be acceptable.
Steve W P203
 
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