I have a new to me 185F that has Robertson STOL and VG’s.

I am pretty let down by the stall speed compared to my previous 185.

Yesterday with just me and fuel, approximately 2500 lbs total, it would stall at 50 kts or 57 mph with full flaps, power off, gently approaching the stall wings level with ball centered.

I know my airspeed indicators are correct because they are brand new and were just tested Monday. Groundspeed also checks.

This thing is stalling at about the same speed a Cirrus does with a light load.

My previous 185 with Horton and Flint tips would still be flying with the ASI reading 27 mph with a light load (it was probably more like 40mph but the AOA was so high the pitot tube was inaccurate)

Robertson publishes 37 knots at 3,350 pounds.

What the hell is wrong with my plane?

Probably a silly question, what were you using to determine the stall?

If it was just the horn that could have some error




Id also ask how you were trimmed and CG

Probably not the case but could the VGs be installed incorrectly?

The horn came on 5 knots before the stall like it should.

By stall I mean buffet and nose drop.

"Yesterday with just me and fuel, approximately 2500 lbs total, it would stall at 50 kts or 57 mph with full flaps, power off, gently approaching the stall wings level with ball centered."

--With just you and fuel, the airplane would almost certainly be at or forward of forward CG limit....which will significantly increase stall speed. Unless, of course, you loaded a bunch of stuff in the aft baggage. CG position can significantly affect stall speed.

"I know my airspeed indicators are correct because they are brand new and were just tested Monday. Groundspeed also checks."

--Airspeed instrument is just one component of the Pitot/Static system. Was the entire system checked - and certified? Ground speed may or may not count, unless you know what the wind aloft is of course.

"My previous 185 with Horton and Flint tips would still be flying with the ASI reading 27 mph with a light load (it was probably more like 40mph but the AOA was so high the pitot tube was inaccurate)"

--When you say "Flint Tips", are you talking about the Flint Wing Extensions? Wing extensions will significantly change stall speed, but I'm betting you're dead on regarding the inaccuracy of your pitot system in that case. I haven't flown a 185 with wing extensions, but adding wing SHOULD decrease stall speed. That said, the RSTOL kits don't induce a dramatic angle of INCIDENCE as they approach the stall. They tend to stall at a relatively flat attitude. And, AOA isn't something you measure with your eyes.....

"Robertson publishes 37 knots at 3,350 pounds."

-- Correct, at Gross Weight and specified CG. Every RSTOL 185 I've flown (a bunch of them) has stalled down around 37 kts in those conditions. And, the A/S indicators SHOULD be marked with the white arc down to 37 kts. I've flown one with a Sportsman cuff and RSTOL, and the A/S in that plane went to near zero at the stall....totally useless,

--There are a few possibilities: Pitot/Static system error, for any of a number of reasons. Improper wing rigging (eccentrics). Improper installation of the RSTOL kit.

I have met two Cessnas on which the RSTOL kit was improperly installed.

Here's a quick check you can run to verify proper actuation:

Sit in the pilot's seat, and observe the AILERONS as you deploy and retract the flaps. At 10 degrees flap, aileron deflection will increase to a couple degrees, a bit more deflection at 20 flaps, and more yet at 30 flaps. But, when you deploy flaps to 40 degrees, the ailerons should RETRACT some from the 30 degree flap deflection.

Have you checked the FLAP deflections, to verify they are properly set, and accurate? Are they in fact deflecting to Cessna specs?

It is possible that the aileron "droop" isn't set properly. You can measure the droop at various flap settings. The precise amount of aileron deflection at each flap setting should be in the install manual and the maintenance paperwork.

I have also met at least one Cessna with RSTOL installed which had NO aileron deflection with flaps.....the RSTOL system was either improperly installed or had been disabled. No logbook entry. I didn't fly it......not airworthy and who knows what was done???

Finally, did the airplane roll off aggressively at the stall? Could indicate an installation problem as well.

Thanks Mike.

It had the entire 24 month IFR pitot static transponder check on Monday. The instruments are all new, I will make a separate post about that project at some point.

On short final the ground speed was showing about 7 less than airspeed with the wind sock and AWOS stating 7 knots right down the runway.

The flaps and ailerons are acting like they should by eyeball, but the next step is going to be to put a smart level on them.

Interesting about CG. Yes as you suspected I was at a very forward CG with just me and about 65 gallons of fuel and only about 30 pounds in the baggage. I was full nose up trim.

I will put a bunch of weight in the back and see how it reacts.

I normally don’t fly empty, but I do recall flying my old one (had the flint wing extension tips that upped gross to 3600) empty to see how slow it would fly, and it was completely different than what I am seeing with this one.

Ross4289 wrote:Thanks Mike.

I normally don’t fly empty, but I do recall flying my old one (had the flint wing extension tips that upped gross to 3600) empty to see how slow it would fly, and it was completely different than what I am seeing with this one.

The "old" Flint tip tanks installed by sliding into the outboard bay of the wing.

The wing EXTENSION made by Flint that increased the gross weight was approved later, and involves a LOT of labor to install. I've never flown one, but more wing is generally good in the kinds of flying I do.....

MTV

It didn’t drop a wing at all in the stall. Just buffeted and mushed along.

Get the CG more centered

Check the deflection of the RSTOL, I’d also look at the install of the VGs

My guess would be you were very nose forward CG, which would check with the degraded performance

If you think it’s pitot system error, record temp, altimeter setting and altitude and then record GPS groundspeed at stall on reciprocal headings and average the GPS result using both values, which will give you TAS at stall. Use any number of online calculators to give you CAS, which is IAS corrected for position and instrument error.

Ron

Ok so I put 140 lbs in the back, (40 in aft baggage and 100 in normal baggage) and it still stalls at 50 knots indicated.

Next step I will measure flap and aileron travels.

Checked flap an aileron travels and they are correct.

I went and stalled north south east and west and the average groundspeed was in the mid 40’s at the stalls. This was at about 5,000 ft so probably closer to 40 indicated.

So I guess it isn’t too far off. I was hopeful it would fly in the low 30’s when light.

Different airspeed indicators will read differently.
I put a loaner ASI in my 180 for a while--
cruise speed indicated about the same, but the indicated airspeed at stall was quite different.

this may be obvious but I find the inner arc knots is hard to read down low are you looking at mph? I think in knots but have to use mph to land mine because of the indicator.

Not too difficult to see your knots on this plane lol