My dirty power off stall speed is about 40 mph light and up to 55 mph with two people, lots of camping gear, 104g fuel (around 3200-3300 lbs). I have Sportsman and Wing X but also flap gap seals.. yes I realize that’s a bit contradicting but airplane came with the seals. Is a 15 mph variance what you guys are seeing? I have a buddy with Robertson but he says he doesn’t see much variation in stall speed between different weights. Would love to hear what the community thinks and how your wagon changes with heavy loads. Thanks!

Let's start with the fact that "speed" is not the optimum parameter for defining the stall, however, since this is the parameter in question, lets run with it. Stall "speed" can be mathematically defined as the square root of (2 x weight) divided by (air density x wing surface area x Cl max for the airfoil employed), in the case of the 100 series Cessna's, the NACA 2412. Therefore, one can see that weight is the parameter with the greatest impact. One can, and should IMO, both calculate and validate these calculations when transitioning to a new aircraft. The "number" on the speed indicating device (typically the ASI) becomes only relative as what we are really searching for is a number that results in predictability of wing behavior at the given weight (including realized weight at load factors greater than one). My wagon spent most of its flight time taking off at gross and flying 7-hour (110-gal fuel) maneuvering missions (wildlife research). The maneuvering capability (as defined by available load factor) of the wing at hour one (near gross) is far less than hour 6. Said another way, the stall speed is higher at hour one than hour 6. Anyone that claims otherwise is mistaken as this is one of the physical "absolutes" validated by math. Yes, aerodynamic modifications (VG/Cuff etc.) alter the results compared to a non-modified airfoil, however, keep your eye on the prize, which is validated predictability. One truly in tune with their machine do not require a number as they know by experience and feel how much their wing can give at any parameter (operating weight and load factor), however, few operators reach this level of capability.

TR

Thanks for the in depth response. I am aware of the above and that stall “speed” isn’t optimum measurement. I’m not saying one needs to fly X speed, just being inquisitive since my partner had different results when he was playing around collecting data on his bird. For this exercise, I just thought it was interesting to see the variation of indicated stall speed on an airplane that can almost carry its own weight in load. That’s a large percentage increase. 1900 lb plane that can legally carry 1500-1650 lbs depending on wing x or not. Those data points from others in the community are just interesting to us.

Edit: Just realized you have a 185, so probably apples and oranges. Sorry.

55MPH is only 47kts

Here’s are the speeds for a 185 with a full Robertson (aileron droop + fences) kit







Not sure I’d want to approach at 47kts that’s like 1.07VSO

MAYBE if it was very cold and the plane was very light, but even then that might be the speed I’d get to at 50’, but I’d be much hotter than that on approach

Thanks for the info. 55mph sounds about right on approach if you’re light. What’s your plane weight Oregon?

I’d like to load mine up to 3500 lbs and see what my stall speed is just for data sake. The only problem is that I’m not about to haul all those sand bags and passengers aren’t ever thrilled when I tell them I’m going to go up high to stall the airplane so I can “test” something. Just curious how many people actually go stall their plane at max gross.

CG has a lot to do w stall speed. In the cert world, at max published weight and published forward CG provides the highest stall speed (the one published in your docs and airspeed ind), while full aft provides lowest. This has everything to do w critical AOA. Your forward envelope limit is generated by this critical AOA and elevator authority during landing rollout.

Aft CG limit is determined by stability, as in do you have enough?

So if you really want to lowest stall speed, look at your loading. Of course the downside of full aft CG can make stall recovery more difficult. Try something just ahead a few inches of your aft limit. You will also enjoy lower elevator drag and fuel burn.

See FAA AFH 13-14.

I've flown a number of C-185s, with stock early wing, with stock late wing (the late wing has a cambered leading edge). I've flown them with a number of different wing mods and combinations of mods.

As noted above, stall speed MUST vary with weight and with CG, though the CG effects are slightly less dramatic than the weight effects.

I'll throw in another variable: The fact that most airspeed measuring devices are relatively inaccurate at one or the other end of the airspeed range, due to the significant difference of the pitot angles. And, often, depending on the airplane, pitot systems at the low end may not be very accurate.

I too worked 185s, so few flights started out very light, even if I was going somewhere to pick up a load or move a crew, I generally left base with quite a bit of fuel aboard. And, light isn't really what that airplane was designed for. Landings were all over the scale, from relatively light to fairly heavy, but almost never right at gross weight.

And, frankly, I can't tell you my landing speeds, because I never look at the A/S indicator close to the ground during approach.

That said, the 185 that I've flown the most was equipped with a Robertson STOL kit on a late model wing (1985). That wing, with pretty much full fuel and two people aboard (checkrides) stalled right about 37 to 40 knots indicated, with full flaps and no power (don't forget that variable as well....). The RSTOL really does permit very low stall speeds, but the roll off at the stall can be (not always) a little "brisk".

We then installed a Sportsman leading edge and aileron gap seals on that plane. Stall speed was 35 to 37 kts, and no roll off at all, it'd just hang there, nose up and sink. Magic.

The modifications to these airplanes that are most common that may influence the stall speed (and of course stall AOA) of the wing are the RSTOL kit, the Sportsman kit, wing extensions, and vortex generators. They all exhibit SOME change in stall speed, but how much?? Good luck sorting the advertising hype from real world flight test data.

Of those, the only mod that actually completed a FULL flight test program to document the changes the kit induced is the Robertson STOL kit. That kit's Flight Manual Supplement provides the changed stall speeds, posted above. While the other mods went through a flight test program, they don't generally provide Flight Manual speed changes.

I love the RSTOL modified airplanes, but adding the Sportsman kit to the RSTOL makes a significant difference, by totally mellowing out the stalls, even at very slow speeds.

But, all these airplanes WILL stall at a higher speed when loaded than when empty.

MTV

It is a different airplane at 2100 lbs than 3600 lbs, as one would expect. I figure about 1 knot per 100 lbs for stall speeds and approach speeds.

So 15 difference is about right.

Having flown many 180/185 combinations under controlled test conditions from nearly empty to at gross the plane is a complete different animal when loaded.

As Mike stated they will all stall at a higher A/S when heavy. As Ross stated the 15 MPH is not out of the ordinary.

MW

Great info. Thanks

I don’t have near the experience as previous posters, but generally I add 10-15 mph when landing heavy. I will say that when I’m on final, I trust the feel of the airplane more than the airspeed indicator. I honestly couldn’t give you a direct number because the airspeed indicator is pretty well useless below 50 mph. Oddly enough, I tend to roll the plane ever so slightly left and right on short final, to get a sense of how it feels, depending on conditions obviously. I have the Wing X and Sportsman fitted to my nose heavy 185, you have to really work to get it to stall. Power off, level, yoke to the aft stop…….no way