Jerry,

I don't mean to call into question your mechanic's weighing skills, but I'd find a few other 175's with similar mods and check out their W/B. The 175 was born with a GEARED, six cylinder engine. I'm trying to understand how your CG could move that much forward from a stock airplane???

For perspective, I have flown two of the eleven or so C 175's which had Continental O-470's installed. THOSE airplanes were definitely a forward CG airplane, but with some load in the back they didn't run out of elevator. One of those airplanes was a stripped out load hauler, and I hauled several big loads of lumber in it to a beach, and returned empty.

My airplane, a 170, was well within forward CG limits, even before I went to a lighter propeller. And, my battery is on the firewall, and no back seat.....

In short, something sounds funny here. But, I been wrong before, and every airplane is different.

MTV

My empty CG figure is a little different than the factory's since my plane was weighed completely empty on fuel and the factory figures had 10 Gallons of unusable fuel. That won't matter on a loaded CG Figure position but it would change the empty CG a little. The Bush Conversion is basically the same as the Avcon without a CS Prop. I have never heard anyone with the Bush Conversion have these problems.

The engines weight should be pretty close since the 0-300 alone is 20 lbs less than the O-360, http://www.bearhawkin.com/FAQ-Engines.html

I guess it is possible my Mechanic made a mistake but I doubt it. There are several guys that have posted on this thread and other forums that have the same plane as I have. They all have the same forward CG problems I have. Plus the yoke seems to confirm what the CG Chart says. I did put 180 lbs in the back the other day and it was the first time I was able to hold the nosewheel off while I was rolling out on landing.

Here is a copy of a form I made to keep in the plane to figure the W&B:
http://s720.photobucket.com/albums/ww20 ... 125TWB.jpg

Looking at the chart again, the plane is actually within the envelope while empty. If you guys can figure how I can get it balanced and stay light while loaded, I am all ears.

Jerry,

That airplane was never equipped with an O-300. The C-175 came with a GO-300. Is the weight you stated for a GO, or for an O-300?

Also, weighing the plane completely empty of fuel may be okay, but you need to have unuseable fuel included in empty weight. I also prefer to have oil included in the empty weight so I don't have to do any more math than necessary.

Whatever. I can tell you that the 175's with the O-470 (which is a MUCH heavier engine than the Lycoming 4) I've flown were forward CG airplanes, but they flew fine.

One final question, then I'll leave it alone: Has your mechanic checked the elevator control limits? If your elevator stops aren't set right, you won't get the appropriate nose up elevator authority.

Good luck.

MTV

Jaerl wrote: My 175B is 1416 lbs and the CG is 35.7. When it came out of the factory the CG was almost 3" back farther. At 1416 lbs my forward moment limit is 52" so I'm not even close to the envelope. At gross (2350 lbs) the forward limit is 97". . ............

Those figures (52" & esp the 97") don't make sense to me for the forward CG limit. I would guess somewhere close to what my 170 was: from 36" to 41". Guess I'm confused.

Well guys, I think we have just beat this thread to death. I'm pretty sure I know what I need to do.

MTV, I can have my Mech look at the elevators but the symptom I am trying to cure is the nose dropping and having to use so much back pressure in the first place. I know that's not normal because the two other planes I have owned didn't require that. If you get out this way you can take it up and see for yourself how it is on landings. I also know the 175's had the GO-300 but my point was that there really shouldn't be much difference in weight since the O-300 (which is what the GO-300 is based on) is a lighter engine with reduction gear added.

Hotrod, My last post has a form I made to caluclate W&B. The graph on it came right out of my POH. I have been stating it wrong. At gross weight I need a moment of 97.5 (X 1000) to be on the forward limit. That puts my CG at 36.72 empty and 41.45 at gross. Sorry about that.

Jerry,

The elevator authority is what GIVES you nose up control. If the elevators aren't rigged right, OR if the cables are stretched or stretching, you won't be able to GET full up elevator, which would provide you with pretty much what you're describing.

The GO 300 is a heavier engine than the O300. In fact, I'd bet it's close to the weight of a O-360 Lycoming. So my point there was Don't compare your new engine to an O-300, compare it to what the airplane was originally equipped with.

MTV

Jr. CubBuilder, everything you said makes a lot of sense. I think someone else suggested going to a fixed prop too. That might be worth looking into and would get me out of the 100 hr Inspections too.

Unfortunately you're gonna give up some performance at either the low end or the high end or maybe both ends by going to a fixed pitch prop. I'm all in favor of the light and simple aspect of it though.
I couldn't get the link to your W&B form to work. It sounds like you're using the Cessna POH chart, which utilizes "moment/1000" and/or a graph to figure out if you're in the envelope. I never did like that way of doing it-- when I do a W&B, I strictly use weights in pounds & arm in inches at the various stations (fuel, front seats, baggage, etc), then do the math: weight times arm equals moment, total moment divided by total weight equals CG. No offense, but it almost sounds like you're mixing up the "moment/1000" with the CG in inches.

Eric

Eric,

Thank you!! I've always hated those dang Cessna W/B charts as well. I prefer to just add weights, divide by arm, and get on with life.....LOTS less opportunity to screw up. I'm still not convinced that weight and balance is as ugly as is being suggested, and I sure wouldn't start swapping props till I was absolutely sure I had a handle on it.

And, if you've got the Avcon conversion, there is no provision for a fixed pitch prop....so field approvals again. Good luck.

MTV

Hi Eric, I was mistating the moment for the CG. I said that a couple of posts ago and put the corrected CG for the forward limits both empty and at gross. I don't like the charts either but that is all I have to work with in my POH. To get the CG range in inches I still have to go to the chart and figure minimums and maximums from the weight on the envelope chart, so I just started using the chart.

If you cut and pasted the link it probably didn't work because it had the (img) on both ends. I took them off so try the link again.

Jerry,

From the C-175 TCDS:

I. Model 175, Skylark, 4 PCL-SM (Normal Category) (cont'd)
C.G. range Landplane:
(+41.5) to (+46.4) at 2350 lbs.
(+36.5) to (+46.4) at 1850 lbs. or les

Model 175 A/B (Normal Category)
C.G. Range Landplane
(+41.5) to (+46.4) at 2350 lbs.
(+36.0) to (+46.4) at 1850 lbs. or less

Model 175C:
(+39.5) to +46.4) at 2450 lbs.
(+36.0) to (+46.4) at 2050 lbs. or less

You can find out the LOCATIONS of stuff in the cockpit from the diagrams in the Airplane Flight Manual, then use the distance aft of datum as your arm for that item, then just do a simple multiply each weight by its arm to get moment, add all weights, and divide into total moments for your loaded CG.

Those CG Ranges don't seem too out of line to me. Compare those to the C-170 B:

Landplane:
Normal Category (+40. to (+46.4) at 2200 lb.
(+36.4) to (+46.4) at 1733 lb. or less

But, whatever winds yer watch.

MTV

Thanks MTV, I didn't realize that was on the Type Certificate. I understand I use 36" for the forward limit under 1850lbs, but do I use from 41.5" for the Forward CG from 1850lbs to 2350lbs? What you posted says "at 2350 lbs". I already have the locations and their respective ARM's from the POH.

If I am using 41.5 as the forward limit, it doesn't matter if I use the chart of figure it mathematically. With two people up front (420lbs @ 36"), Full Fuel (312 @ 48") and my plane (1,416 @ 35.70) That puts the weight at 2148 lbs, the Moment at 80.65 and the CG at 37.55. I am still outside the forward limits.

Guess I need a drastic diet.

I probably wouldn't miss it at all to tell you the truth. With the vibration, I have been running it at 2500 RPM to keep it smooth anyway. What do you think the prop would be worth if I sold it? If I had the money I would be putting on the MT composite one. I hear it gives 60 lbs more thrust than the one I am running too.

Jerry,

No, you plot straight line variation between points. Plot those weights and limits on a piece of graph paper. I liked the C-170 TCDS better, cause it gives you the diagrams.

Just plot a straight line between the lightest weight forward limits and the highest weight forward limits, and that's the forward limit line.

Your Hartzell is not worth much, frankly. If the blades are near virgin, as in really good shape and not filed much at all, they might be worth $500 to $700 each. Maybe. The hub is junk. So, don't expect to get much out of it.

MTV

Jaerl wrote: Thanks MTV, I didn't realize that was on the Type Certificate. ..........

The TCDS is available online- the web address is pretty long & I'm not up to copying it, and I ran out of paste for any cut-n-paste work. Just google TCDS # 3A17.
Interestingly this type certificate not only includes the C175 Skylark, but also the T41 & the Hawk XP.

mtv wrote:....
I liked the C-170 TCDS better, cause it gives you the diagrams.....

The older TCDS's like the 170, are more useful. The 170 TCDS listed all the stuff approved on the type certificate, different engines props, etc usually including the weight & arm to use when calculating W&B revisions. Lotsa good stuff there.
The TCDS for the C150 gives some useful info, but almost nothing as far as approved equipment. It does go on ** extensively** with the complete texts of required placards & stuff like that though.
Also repeats itself with the same info over & over for each the different model (A,B, etc).

Eric

Here's the URL for Type Certificates: http://rgl.faa.gov/Regulatory_and_Guida ... enFrameSet

Eric,

Well, you're sorta right, but....

The TCDS does, by definition, spell out what engine, propeller, etc. was approved on a specific airplane. Here is that information as given for the 150:

I - Model 150, 2 PCLM (Utility Category), Approved July 10, 1958
Model 150A, 2 PCLM (Utility Category), Approved June 14, 1960
Model 150B, 2 PCLM (Utility Category), Approved June 20, 1961
Model 150C, 2 PCLM (Utility Category), Approved June 15, 1962
Engine Continental O-200-A
*Fuel 80/87 min. grade aviation gasoline
*Engine limits For all operations, 2750 r.p.m. (100 hp.)
Propeller and 1. Sensenich 69CK 24 lb. (-32)
propeller limits Diameter: not over 69 in., not under 67.5 in.
Static r.p.m. at maximum permissible throttle setting:
not over 2470, not under 2320
No additional tolerance permitted
2. McCauley 1A100/MCM 21 lb. (-32)
Diameter: not over 69 in., not under 67.5 in.
Static r.p.m. at maximum permissible throttle setting:
not over 2475, not under 2375
No additional tolerance permitted
3. McCauley 1A101/DCM 21 lb. (-32)
Diameter: not over 69 in., not under 67.5 in.
Static r.p.m. at maximum permissible throttle setting:
not over 2600, not under 2500
No additional tolerance permitted

Any other propeller, engine model, etc, has to be installed via a SUPPLEMENTAL Type Certificate. Or, on rare occasion in past, via a field approval.

But, the basics are there in the TC for each airplane model.

It's important to note here that the manufacturers generally don't change engines much during a production run of an airplane type. Too much $$$ and testing, for limited payback unless the first one (think Cardinal) was a real dog.

MTV

Punch up the TCDS #A799for the 170 & scroll down to spec's-pertinant to all models & check out the extensive listing of approved engines, props, accesories, landing gear,electrical equipment, interior equipment, and "misc", including weight & arm for W&B purposes.
Now check out the TCDS #3A19 for the 150, under data pertinant to all models-- what follows is pretty much just approved maneuvers & required placards. Nothing to speak of in the way of approved equipment, other than basic engine & props as MTV pointed out, and so not as useful as the 170 TCDS. For example- what brakes are approved? What size wheels & tires? What's the approved model starter & generator/alternator, and their weight & arm? Are the RH flight controls required or optional? (optional, BTW) Etc, etc. This information might be available elsewhere but having it all on the TCDS like the 170 does sure makes it a lot easier.

Eric

Actually, the requirements for what goes on the TCDS haven't changed at all. What changed between the 170 and the other airplanes is Cessna policy. When the C-170 was certificated, Cessna incorporated a number of options and modifications into the airplane's Type Certificate. An example is that I have a Fairbanks Aero Service sling rear seat for my airplane. That seat design was STC'd by FAS, then was sold to Cessna. Cessna then incorporated that data into the TC. You'll note also that a lot of the things on the C170 TC are pretty much standard on the 150 and 185, for example Vacuum system and gyro instruments. The 170 was not equipped with a vacuum system, so IF it was going to be IFR approved, it needed to have venturis and a "blind flying kit", all of which had to be specified as options on the TC. Those items were'nt optional on the later airplanes, they were part of the basic airplane.

And, in any case, try to find a "blind flying kit" for a Cessna 170, or some of the skis provided for on that TC. Much of the stuff listed there is irrelevant, unless the airplane left the factory with it. And, there are dozens of STCs for the 170 out there, none of which appear on the TC.

The 150 and 185 TC give you all the information that is required to operate the airplane, except that which is provided in the Airplane Flight Manual and supplements. They specify (in the case of the 185) floats, amphibious floats, etc. There's a lot of good information there.

I'm always surprised by pilots who have never even looked at the TC for their airplane. It's free, after all.... Maybe that's the problem, eh?

MTV

I know the TC for the 175's aren't very detailed but the equipment list has everything you could put on the plane from winterization kits to skis. If you don't have one for your plane you can buy them from Cessna. I need to go and find mine because I think I just solved my forward CG problem. I just won a Cessna 19 Gallon Auxiliary Fuel Tank on Ebay for my plane!!

Of course that will only help when full but I would rather carry around extra fuel than lead. Now I need an extended baggage for sure since I will be loosing 6" of space back there.