> ...we just use the number the manufacturer publishes.
From the article it sounds like this plane was radically modified, to the point where the manufacturer's stall speed would be irrelevant.
Why wouldn't you want to confirm for yourself where the speed is after so many changes?
The aircraft was modified with a Robertson STOL kit. A common type of modification to make to a "bush aircraft". In the USA the modification is covered by an STC (Supplemental Type Certificate), the installation needs to be supervised and approved by an A&P technician with IA (Inspection Authority). The STC will modify the airspeed indicator markings, including the stall speed markings (bottom of green and white arcs), and modify the approved flight manual/pilot operating handbook and maintenance documentation for the aircraft. Since this is a major alteration (in a 14CFR regulatory sense) that modifies the flight characteristics of the aircraft it needs to be test flown after the work, and the STC will also separately requires this. I expect/hope the STC includes instructions for checking stall characteristics including airspeed. In European countries a similar level of regulation/documentation is followed based on the USA STC.
Give the description of the pilot's sad lack of understanding of basic operation of the aircraft I am doubting they even read the pilot operating handbook.
> A further issue was that his Cessna 185 had been extensively modified. The addition of floats, cargo pack, short take-off and landing kit and a three-blade propeller had never had their combined effect documented.
That’s a lot of things that modify the flight characteristics of a plane, all interacting together in what seems to be a previously untested configuration.
I can completely see how each individual modification might modify the planes flight characteristics in a well know manner. But I struggle to see how anyone could realistically predict the result of all the modifications without some basic empirical testing.
You are over inflating issues here. Are you a pilot? The issue here is straight up incompetent operation of an aircraft.
Operating a floatplane and separately operating with a STOL kits can increase complexity and risks especially when aircraft are mishandled/abused like here with an incompetent pilot who does not know what they are doing. You don’t need to dream up issues from combination of stuff here, the simple linear addition of issues was more than enough for an incompetent pilot to get into trouble, and seems they are lucky they did not get into more trouble before, and lucky they were not killed.
The C185 is a beautiful well behaved workhorse used extensively in bush and floatplane flying, often with multiple STCs to upgrade these aircraft.
But the article does say that investigators had to get another aircraft set up with the same modifications and fly it around with bits of wool all over it in order to understand the stall characteristics.
So I assume this plane setup isn't so widespread that its stall behaviour is common knowledge.
One Citabria I've flown had vortex generators installed on the leading edge of the wings, but the club sold it over a year ago and I don't remember if it listed a modified stall speed. I do remember it said "not airworthy if more than N of the VGs are broken off", I think it was three?
It’s nothing too radical.
Edit - Here’s a copy of the 1975 owners manual:
https://www.seaplanescenics.com/documents/1975-cessna-185f-p...
Weight, altitude, density altitude, angle of attack etc. are all going to have an effect.
In other words, sure, you might want to confirm it, but you should also give yourself some margin since you don’t ever really know what the stall speed is until you stall.
In a certified aircraft the manufacturer has already done the test flying
But most homebuilts will still have a stall speed for planes built to plan.
In any case, this is an article about a Cessna. Where the stall speed is in the POH and also marked on the ASI.
This is wrong.
The angle of attack is not a parameter of the stall speed, it is the cause of the stall (for a given configuration, assuming well below transonic speed). This is why for example, for precise handling you should use an angle-of-attack indicator (a large majority of fighter jets and more generally military aicraft have it).
> you should also give yourself some margin since you don’t ever really know what the stall speed is until you stall
The manufacter speed already take into account the afore-mentioned parameters into account, and the resulting speed is the worst case scenario, if not told otherwise (usually max weight, max forward CG).
One should not fly with an arbitrary speed margin, but instead use well-known speedq (1.3Vs, 1.45Vs, where Vs=stall speed in the given config) depending on the flight phase, and remember well the bank angle limit associated with them.
You're right of course, based on the real definition of angle of attack which is based on relative wind. When people say angle of attack is a parameter of stall speed, they're separating speed from pitch.
This isn't really useful but people seem to struggle with the concept of relative wind, so it's a kind of shorthand.
Also there’s planes that have slats and other devices that effectively change the angle of attack of the wing.
And then there’s planes that direct prop wash over the wing so that the power on stall speed is much lower than power off despite the angle of attack being different.