The airframe certainly has the strength … anecdotally there’s a 150% design factor. The horsepower is the issue…. surprisingly long takeoff runs and frustratingly shallow climb-performance will be evident…. even frighteningly-so if you do this without consideration of Density Altitude….Flying a 170 overweight is certainly not unheard-of. I’ve unthinkingly done it myself…
….. in front of knowledgeable 170 owners.
as I did in the event I’m recalling.
Can you spell “stoopid”…??
(I’m reminiscing about the time I agreed to “lead” a flight of 4 fellow Members on the migration from ILM to FFA at the ‘02 convention… and myself, Ol’ Gar, Jamie and Deanna hopped into 146YS …which had been refueled on arrival a few days earlier for the convenience of the FBO… and me simply not thinking…not giving Any Thought to the matter when I responded to Ol’Gar.
Subsequently, when the FLy-Out on Airport Day was presented….Ol’Gar asked if he and Deanna could ride-along with Jamie and Me…and brain-dead Me only wanted to accommodate him…. never giving a thought to what the airplane would weigh. We were about 2500 lbs I believe….it was a warm Summer Day…(high DA)…. and were still on the main wheels when all our gaggle were airborne behind us…awaiting me to lift-off and “lead” them to FFA.
Departure instructions from ATC were “Make an immediate Right Turn to HDG 090 (?) … climb to X-thousand feet… “
Since the entire convention-flight was camped-out nearby….we were assigned and we used the intersection for take-off…which had plenty of spare rwy….For THEM… 146YS and it’s Cruise-propeller used considerably More…and we departed the end of the rwy only a few feet above elevation. IAS was so low…that I dared-not make an “immediate Right Turn”…. so the 3 guys following their “leader”…. the ATP-rated “Pro” they’d signed-up-for to be on His Gaggle….. were undoubtedly wondering why I was deliberately ignoring ATC’s calls to us fussing about our disregard of Departure Instructions.
(we made that right turn about a mile later than ATC had wanted)
We eventually reached cruise altitude and had a smooth and enjoyable off-shore flight up the coast,…all the stress quickly passed..…we descended and landed at destination…and taxied in, parked.
To make matters Worse…
Unbelievably… I accepted the arrival-FBO’s offer of a DIScount on Fuel if I “topped off”…..for the return trip!
I’m telling on myself to illustrate that it doesn’t matter who you are,… what your “qualifications” are,… your responsibilities are to your pax,… it takes an Active Mind and Conscious Pre-Flight Planning …and
Integrity… to be a true Aviator. One Lapse…only One… can make you Embarrassed, Disrespected, Foolish, …or Worse.) BTDT.
There’s more than just poor and undocumented takoff/climb performance to consider as well. There’s unknown stall speed. …and unknown gust-load-factor margins…. The belief that a 170/172 is structurally sufficiently the same as an (underpowered) 180/182 …is common…but not justifiable. The fact a 182 wing can be transplanted to a 170B does not account for gauge of skins, or rivet-spacing, or reinforced attachments between and of varying SNs ..which may not interfere with fitment…but nevertheless exist for strength to support higher operating/gross wts of the later models. (I am not intimately familiar with specific examples…I am only regurgitating what knowledgeable airframe repairmen have noted to me.)
As Instructors want to say: “Do as I say….Not as I do.”