C-145 Starter

[cessna170bdriver]

The B&C starter spins the engine much faster than the Delco starter, but not fast enough to defeat the impulse couplings. After pre-oiling my engine with a small pressure pot, I spun it with the starter with the top spark plugs out and almost messed my pants at the noise the engine made . I recovered when I realized it was the impulse couplings snapping away. My new tach has a low end stop at 300 RPM and doesn't register RPM generated by the starter, but the prop is flying by almost too fast to follow visually. I estimate engine RPM at about 200.

I don't know how most C-170 weight and balances work out, but mine leans toward the nose heavy side. There is no reasonable configuration that puts the CG outside the aft limit (full fuel, a 180lb pilot, no co-pilot, 319 lb in the back seat, and 120 lbs in the baggage area comes close), but when I was an FAA-standard 170 lbs, solo with low fuel put me well forward of the limit without ballast in the baggage area. I like not having that 8 lbs at 43+ inches forward of the forward CG limit.

Miles

[GAHorn]

Miles, unless you sit in the baggage compartment, YOU are at 31 inches forward of the forward CG limit.
The 8 lbs is only at the point-two (.2) index forward of the datum....not a location that makes much difference in CG at all. (About the same as a few quarts of oil in the sump.)

[johneeb]

George,

The 8 lbs is only at the point-two (.2) index forward of the datum....not a location that makes much difference in CG at all.

Won't that 8 lbs at (.2) index forward of datum add up to a lot more than 8 lbs of Cheese Burgers and Fries that Miles can comsume with his chair at 35.88" aft of datum, assuming more than 8 lbs does not put him over gross.

[wa4jr]

I have been wobbling back and for on the modify or not modify starter issue. Yes the old DR starter is more economical in terms of cost, but is more tempermental and requires more routine service than the B&C unit. The B&C is indeed a big hassle to install, but then it is done and all the advantages of a current technology starter are enjoyed. The B&C has been in service since the early 90's and is standard equipment on the IO-240 engine becuase no other starter would reliably work, especially in cold temps. I'm told they stopped testing the starter at 5000 starts because they could not get it to fail I'm getting bitten here on the front end with the B&C starter, but I think that as the hours and years pass I'll be glad I made the change to present-day starter technology I did a similar conversion with my MGB a couple of years ago after messing around with the heavy old OM starter. The new starter was much smaller and had its own sealed gear case, was much lighter, and consistently spins the engine so fast that I can almost take out the spark plugs and drive on the starter motor alone

[cessna170bdriver]

Miles, unless you sit in the baggage compartment, YOU are at 31 inches forward of the forward CG limit.

Check again George. The forward limit of A and B models is 37 inches behind the firewall. The front seats are at 36 inches behind the firewall.

The 8 lbs is only at the point-two (.2) index forward of the datum....not a location that makes much difference in CG at all. (About the same as a few quarts of oil in the sump.)

You're mixing apples and oranges here. You talk about me being forward of the CG limit, then you talk about the starter being forward of the datum. The location of the datum is arbitrary, and chosen for convenience of measurement. Whether the datum is located at the tip of the spinner, the firewall, or rudder hinge line, it doesn't affect the location of the CG relative to the wing at all. What does make a difference is adding/subtracting weight at relatively large distances from ACTUAL CG LOCATION. That's the reason small airplane designers put seats near the CG range.

The TCDS says the B-model CG limit is 37 inches behind the firewall (the datum on C-170's). According to my original equipment list dated October 26, 19, the starter CG is 6 inches forward of the firewall, putting it at least 43 inches forward of forward CG limit. Lowering it's weight by 8 lbs changes the moment around the CG by 344 inch-lbs. At light weights that's about .2 inches aft shift in the CG, not insignificant if you're running close.

Miles

[c170b53]

So, I can now join Miles in enjoying that Cheeseburger deluxe and fries ?.

[GAHorn]

Actually, Miles, I was deliberately mixing apples and oranges (inches/index units/datum/CG) in an effort to minimize the 43 inches comment. Index units was what I was using... and in the comparison I was making, the starter is actually farther aft than the oil in the sump (which everyone reduces by a couple of quarts anyway.)
( I didn't consider .2" change in CG to be significant.)
The pilot's seats are shown to be at 36" as an average location. You and I probably sit a bit farther aft than that.

In a more serious light, a forward CG does not frighten me at all. When fuel is put on the airplane the CG always moves aft, as it does with any other payload. (So I view a heavy starter almost as a blessing.) The rearward CG's are the ones that won't allow a spin recovery.

Anyway...it's just a piddling, silly argument in support of my penchant for original starters. It's "owners choice", of course.