Cessna 175 gross weight increase

[ateamer]

Our 175A has a gross weight of 2350 pounds, with a useful load of 810. It has the Avcon (Williams/Doyne) O-360 STC with a constant speed prop. Two years later, Cessna raised the gross weight on the 175C to 2450. The only apparent physical changes that I could find are that they switched the fixed pitch prop to constant speed (with the same 175 HP Continental) and added cowl flaps.

The STC for my plane did not raise the weight, nor does it provide any performance data. (STCs prior to 1981 did not have to.) There is an STC to put a Lycoming in a 175 and incorporates a gross weight increase to 2500 along with a wider CG range, but that’s not an option for me since ours is already in place and freshly overhauled.

So, just as a firepit chat, what is the physical difference between the -C and previous models that it can handle a hundred more pounds, or a seemingly identically-equipped 175 but with a different source for the STC? If I had the bucks it’d be interesting and fun to so the engineering and testing to bring the GW increase to others, but as it is it’s just an idea.

Anyone know if there is a structural difference, or is it just a function of how far the STC developers wanted to go with it?

 

[flyingcheesehead]

What about flap travel, is that the same? Cessna increased gross weight on the 172 from 2350 to 2450 in about 1980 or so by limiting full flaps to 30 degrees (previously 40), which allowed it to go around with full flaps at the higher weight, which I understand is/was a certification requirement.

Of course, the 175 was produced much earlier than that change, but I figured it was worth mentioning as they may have done it earlier on the 175.

 

[Jim Carpenter]

In general I think both physical and certification factors play. STCs without new performance charts, etc. often say “performance meets or exceeds original” or such. I can only guess how much that simplifies certs and testing.

 

[Bell206]

Anyone know if there is a structural difference, or is it just a function of how far the STC developers wanted to go with it?

STC developers tend to only meet the limits they perceive as each OEM limit change adds cost and certification requirements. However, as I recall there was a "STOL" kit for early 175s that added different wing tips and strapped the spars which gave you the extra 100lbs for take-off only. But I don't remember any details.

 

[ateamer]

STC developers tend to only meet the limits they perceive as each OEM limit change adds cost and certification requirements. However, as I recall there was a "STOL" kit for early 175s that added different wing tips and strapped the spars which gave you the extra 100lbs for take-off only. But I don't remember any details.

There is an STC for wing extensions that bumps the gross weight. I just re-read the Del-Air engine STC and confirmed the gross weight and CG range, and that the conversion is for the engine and prop only.

Del-Air doesn’t appear to have a website, so no luck there for more info. I’ll give them a call and see what they say.

 

[Skylark23]

This thread is relevant to my interests. I'm also looking for a gross increase for a 1961 Skylark.