extended baggage?

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cmsusllc
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Re: extended baggage?

Post by cmsusllc »

All my info is at the hanger but I have found a situation where C/G moves back with fuel burnoff. My B-model with the Avcon conversion gains 20# with the constant speed prop way out front so I have a problem with foreward C/G with two adults in front. With fuel burn off it gets worse. For now I strap in a 60# sandbag in the back of the baggage area which keeps things within the envelope. I calculated a 10# lead weight at the end of the tail would put the C/G exactly where it was when it left the factory at empty weight. Run the numbers with full fuel and even load in the cabin and the C/G moves back with burnoff. My goal is to add an extended baggage, lightweight starter, battery relocation and whatever else I come up with and see where I end up. I'm going to reweigh before I do anything as all calcs. are from original 53 paperwork.
Scott
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GAHorn
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Re: extended baggage?

Post by GAHorn »

If you have a forward CG problem due to heavy engine conversion... and as fuel burns off you have a worse problem... then that would be due to a CG moving forward as fuel is burned, No? (Such airplanes are great candidates for Javelin fuel tanks.)

The CG in the 170 does move forward in terms of Index units as fuel is burned. <addt'l comment removed>

This is quite different than some other airplanes, such as model 35 and 33 Bonanzas, which have the majority of their fuel forward of the aircraft CG, and which suffer aft movement as fuel is consumed. Bonanza pilots can take off completely within CG limits...and yet, at the end of their flight, be out of aft CG limits, making for a very tricky stick-reversal during approach.

Unlike those Beech models, whose main fuel is in the formost areas of their wings, (forward of the forward spar, actually), our Cessnas have their fuel within the chord of the wing where the CG envelope is. Since their fuel is within the mean aerodynamic chord (MAC), fuel burn has little influence on most single-engined Cessna's.

Cessnas are such GREAT airplanes! We forget some of their finer points, sometimes.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Bruce Fenstermacher
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Re: extended baggage?

Post by Bruce Fenstermacher »

Well I finally looked at this W&b problem. George I think you are confusing the issue with your aft trim statement. I know I had to read it twice.

As George and others have said the CG moves forward as fuel is burned. Below is my W&B sheet with a graph that shows a typical 2 adult front seat loading in my plane. Full fuel is indicated by the green dot, no usable fuel by the red triangle. With the simple fuel loading information given us from Cessna, drawing a line between the dot and triangle would show the CG path from full to empty. (this is not the case with aircraft with more sophisticated fuel systems).
Picture 4.jpg
Just guessing at the arm of an extended baggage area I added 20" to the 95" arm of the normal baggage area to arrive at 115". This might not be the actual arm but close enough for this. The W&B sheet below places the 20lbs max at that arm. There is no other change between the first W&B sample and the second so you can see how far just this 20lbs would shift the W&B.
Picture 5.jpg
I've attached these sheets before for all and they are also available at our members page. If you find anything wrong with them let me know. They've been given out for nearly ten years with only one small fix so I believe they're accurate.
48-170_WB.xls
(26.5 KiB) Downloaded 1168 times
170_A_or_B_Model_WB.xls
(26.5 KiB) Downloaded 1206 times
170_A_or_B_Model_WB_with_Javelin_Tank.xls
(26.5 KiB) Downloaded 1148 times
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GAHorn
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Re: extended baggage?

Post by GAHorn »

N9149A wrote:...George I think you are confusing the issue with your aft trim statement. I know I had to read it twice. ...

Yes, I worried about that when I wrote it. In fact, I'd posted similar comments twice-before and removed them for fear they'd cause confusion. I've stricken them.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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jrenwick
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Re: extended baggage?

Post by jrenwick »

My extended baggage area has a documented arm of 123". I don't know where that lies in the baggage area, but I assume it's the center. I'm careful how I load it. I wouldn't want to put a small 20-pound package in it, because it would tend to sit aft and be at an even longer arm. I use extended baggage only for light, bulky things like pillows and sleeping bags.
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award, 2016 Best Continuously Maintained Swift
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GAHorn
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Re: extended baggage?

Post by GAHorn »

Can you imagine what would happen when you take off and your anvil-collection slides aft when you rotate? 8O
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Bruce Fenstermacher
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Re: extended baggage?

Post by Bruce Fenstermacher »

John,

Using the '62 and prior maintenance manual as a reference looking at the 172 which is the same as the 170, the bulkhead the rear top back attaches to is 90". The rear baggage area bulkhead is 108". If the extension is truly a 20" extension then the very rear of it would be 128". This would place 123" just aft of center. You should reference the maintenance manual and measure the extension for real numbers.

Anyway using my aircraft with 360lbs combined in the front seats, 180 lbs in the rear seat area, the max 120 lbs in the baggage area and the max 20lbs at 128" (what I believe might be the very back of your extension), you can see by the sheet below that you are still well within the rear CG range. You could move more stuff from the front seat to the rear seat area, still be under max weight and not out of CG.
Picture 1.jpg
CAUTION - My forum posts may be worth what you paid for them!

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jrenwick
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Re: extended baggage?

Post by jrenwick »

gahorn wrote:Can you imagine what would happen when you take off and your anvil-collection slides aft when you rotate? 8O
And simultaneously the pin slips out of the seat track and you realize you forgot to take he gust lock off your elevators.... :twisted:
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award, 2016 Best Continuously Maintained Swift
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jrenwick
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Re: extended baggage?

Post by jrenwick »

Hi Bruce,

Yes, you're right, with a 20# limit in the rear baggage area you have to work pretty hard to get the C.G. beyond the aft limits. I'm sure the reason for the 20# limit is to make it almost idiot-proof (as long as the idiot follows the rules! :wink: ).

By the way, I use CoPilot on my Palm PDA to plan flights and do W&B for all my aircraft. I'ts a perfect little gem of a software app, and it's always in my pocket (because my PDA is my phone too). It also runs on iPhone and iPod Touch devices. I highly recommed it to anyone who has the hardware to run it on.
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award, 2016 Best Continuously Maintained Swift
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flyguy
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Re: extended baggage?

Post by flyguy »

gahorn wrote:Yeah, I was afraid that comment would start a CG-Wars thread. :lol: (But I couldn't resist giving Ol' Gar a blown brain-fuse. :lol:
YEW DINT BLEW MY FUZE I GOTS PINNIES BEHINE THEM LIL SCREWED IN BUGGERS AND UNLESS THEY THEM CHEEP LOONIUM PINNIES THAT OLE LECTRIK JES KEEPS ON ZIPPIN ROUN ! :!: PEE ESS : I DOANT WANNA GIT IN NO WARZ WITCHU CAUSE I NO U GOTS LOTS OF GUNS AN AMO BUTCHA WUNT SHOOT A BUDY WOODJA? 8O

Thanks joneeb I guess that is what my "ASSUMPTION" was although I didn't really check out the little graph for that dif - It certainly showed me, graphically, that I probably flew "out of the envelope" too many times :oops: But here is the question - you load the plane with 850#(Or 975# in our case flying to Kitty Hawk George). The front seat pax are 36" - 46" (depending on seat location) aft and the full fuel tanks at 48" aft and both are in flux. But the rear seat pax @ 70" and the baggage @ 95" (or 100+) are static, Has the configuration of the load dynamics changed as the fuel burns off? It would seem logical. We know that the further aft the load is the more arm it exerts on the dynamics.

My seat of the pants, flying "solo" . and with 500 # + in the rear of the cabin and on back into the baggage compartment , I found out that sliding my seat back to stretch my long legs, best be done while the tanks were closer to full than empty! I could tell, the further I slid back the more trim I would have to roll in and nearing reserve limits on fuel I'd need a little more trim than usual. In order to feel at ease when fuel got down to nubbins. I felt better with the seat slid almost fully forward. My flights from Atchison KS to Toledo Bend usually took 4 hours or so. I was close to reserve when I got here and that was when my load was heaviest aft, Don't know for sure what the CG had to do with old Delta's response but it certainly let me know there was some different dynamics in play.
OLE GAR SEZ - 4 Boats, 4 Planes, 4 houses. I've got to quit collecting!
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GAHorn
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Re: extended baggage?

Post by GAHorn »

Guess why our 170's have to be in the Utility category before spinning them? It's because the CG must be kept forward of 40.3 (170) and 40.6 (A/B models). This is to avoid a rearward CG from turning that thing into a falling leaf (flat spin) that cannot be recovered. This will likely require LESS than full fuel for most airplanes.

So.... the point is that as fuel is reduced, the CG move FORWARD in a Cessna 170 of any model. (The extreme-adverse example however, is one with a Javelin tank which does not move the fuel to the wings in a timely fashion.) :wink:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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cfzxo
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Re: extended baggage?

Post by cfzxo »

George. I have the 180 hp and javelin tank. On the long flights when I need that reserve I always get that aux. fuel pumped up to the wing so that I know that it used up first, it is only available to you as long as you have power to the lift pump. :D In the last 15 years that I have been flying my 170-B , I have had two electrical failures, in both cases they where on long cross country trips and it took about 1.75 hrs to drain the battery down to dead, but by then the fuel was up to the wing tank, and the rest is gravity. :D Master switch and broken field wire in the altenator, stuff happens.But it is nice on short local flights to have fuel in the aux tank for weight and balance management,somewhat easier than the anvil thing :lol: The short version is that I never count on my aux fuel until it is used.
Bill CFZXO
buzzlatka
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Re: extended baggage?

Post by buzzlatka »

My personal experience and my look at the graphs contradict one another. I agree on the graphs that the cg moves forward with fuel burn off, but I agree with flyguy that the airplane seems nose heavy with full fuel and tail heavy with empty fuel. I did a lot of short field testing at different loads/fuels in order to feel comfortable in my short strip. My non-scientific results were based on the flying characteristics of the 170 very slow in takeoff and landing. If I had more fuel in the airplane I always balanced it with a weight in the back to offset.

By the way George you seem to use Falling leaf and Flat spin interchangabley. They are 2 different types of departure from controlled flight.
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GAHorn
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Re: extended baggage?

Post by GAHorn »

buzzlatka wrote:..By the way George you seem to use Falling leaf and Flat spin interchangabley. They are 2 different types of departure from controlled flight.
They are related manuevers. I will agree that the term "falling leaf" has become associated as a separate aerobatic maneuver related to a spin. An unfortuanate choice of words on my part, perhaps.... but one that is germane...


From a short series of discussions for beginning ultralight flyers:
The falling leaf term is also used to describe a series of alternating sideslips and again to describe the technique of 'walking or pedalling down' a stalled aircraft by picking up a dropping wing with opposite rudder and then leaving the rudder ...
Full article >>> http://www.auf.asn.au/groundschool/umodule8.html

My primary reason for opposition to spinning these airplanes is a concern that while properly executed spins are relatively harmless, improperly performed spins (very commonly witnessed by myself and other CFI's) can rapidly morph into deadly events. I was horrified to hear one rather experienced pilot remark that if ever caught in a spin, he'd simply apply power and fly right out of it. (This would most likely have the effect of insuring a stablized flat spin. One of the critical parts of performing deliberate spins is that the power be off, and kept there. Application of power has the effect of flattening a spin.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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jrenwick
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Re: extended baggage?

Post by jrenwick »

Just a couple of observations about C.G. and fuel quantity:

1. In the TCDS for 170A and 170B models, the full fuel arm is at +48, but the unuseable fuel arm (see Note 1) is at +46. Maybe if you wanted a more accurate C.G. calculation for varying amounts of fuel, you'd have to vary the arm along with the fuel quantity. This would still give a more forward C.G. with smaller fuel quantities, however.

2. With some air in the tanks, it seems to me that fuel would tend toward the rear of each tank in the 3-point landing and climb attitudes. This might give the fuel a longer effective arm in those attitudes, and make the airplane feel tail-heavy.

I'm just sort of thinking out loud here -- I wouldn't be surprised to find out I'm all wet! :D
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award, 2016 Best Continuously Maintained Swift
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