Horton STOL and the C172

[DeflectionShot]

Ok folks. Here's a question for the experts here. Our club has a C172N with a Horton STOL kit. The boys tell me it floats a lot on the flare. They're right. I had it out last weekend and sure enough it does. My landing config? 20 degrees of flap...I came over the threshold at 60 knots. Headwind about 7 knots. A touch of crosswind.

But the question is why is it floating so much? Our other C172 - non-STOL equipped - doesn't do that. It's gotta be bad technique on my part. I should be able to get on without a lot of floating. How is the STOL kit impacting performance on the flare??? I'm going to guess I should try 55 knots over the threshold next time and maybe 30 degrees of flap (depending on winds of course). Thoughts?????

[John Swallow]

I have not flown a '172 with the Horton kit, but from reading the testimonials about the Horton kit (if you can believe them) and what you've posted, I'd hazard a guess that you're too fast.  Take it up and find out the stall speed at various flap settings and go from there...

John

[Colonel]

John is right.  Stock 172 speeds aren't going to work
for you, because of the change in Vs.

You won't believe how slow you can approach with
those Horton and Robertson kits, especially if the
aircraft is light.

I wouldn't fuss about the flap setting right now -
I would mostly set it to control the pitch attitude
in the flare (don't laugh).

15 degrees of flap will generally give you most of
the stall speed reduction, which is probably good
thing most of the time. 

Beyond 15, what you're adding is drag, which is nice
if you have to approach steeply over an obstacle and
keep the speed down, but if you're landing at certified
airport, that probably isn't what you are doing.

Learn to land the aircraft well under normal conditions,
then go for the weird approaches and strips later.

[Colonel]

If you're approaching at 60 knots, try 55 and see
what that does.  If you still float, try 50.

You know how I set approach speed in any light
aircraft for any short field landing, where I want
to minimize kinetic energy and thus rollout distance?

Set up a nice long final and get the aircraft in
it's landing configuration.  Then decrease the
airspeed 5 knots/mph at a time, perfectly on
the glide path, until you feel it settle, and you
have to add power.  Maintain that airspeed - [b]NO SLOWER[/b].

You are now perfectly just on the back side of
the power curve.  You might need a squirt of
power in the flare to cushion the landing.

Fun Fact:  both lift and kinetic energy are
functions of velocity SQUARED.  It's terribly
important to get it right.  But first, you need
to figure out what "right" is  :D

[John Swallow]

DeflectionShot:

Let us know how you make out. 

J

[cgzro]

I assume the STOL kit is an STC in which case a lot of flight testing and as a result updated POH etc would have been generated. I would have thought it would be helpful with revised stall etc speeds? Also as an aside wont your Va be reduced with a STOl kit?

[John Swallow]

I found this on a thread about the Horton STOL kit for the SkyMaster from 2004:

"The Horton STC does state what the limitations are: Simply stated, it will meet or exceed the Cessna numbers and that you should go out and experiment with it to determine the actual numbers"

I think that will be the same for all such kits. 

John

[cgzro]

Wow, I find it hard to believe that TC, the FAA would consider that acceptable. Horton must have had to do a full series of flight tests and as I said your Va must be reduced with the lowered stall speed so that would have to be documented.


The STC should have proper POH ammendments unless its a 337 mod or something.

[Colonel]

Deplorables and other [b]Bad People[/b] know that paperwork
is bullshit anyways - airplanes can't read - and that engineering
and physics is what matters.

Hell, I've seen an ASI with +20 and -20 mph errors, through
it's range.  Placards and POH's and AFM's and STC's and all
that crap go out the window anyways.

Any pilot that trusts his life to paperwork needs to get a
life insurance policy and make me the beneficiary.  I will
happily pay the premiums.

[DeflectionShot]

Thanks for the input guys. I haven't had a chance to test this out thoroughly yet but I will. I can confirm there are no revised V speeds posted and we are a full-blown FTU. The only thing they warn you about is that it floats - a lot - so be prepared.


I tried 55 knots today with 20 flaps, couldn't quite get the 15 degrees as CS suggested, the flaps are notched and I was too busy keeping my eyes peeled for traffic to frig around - so there it is. With no headwind it floated like a SOB. Fortunately we have giant runways so it doesn't matter a lot but it's the principle of the thing. On the flare I tried to round out three times to get the mains down and the nose wheel in the air, and I ballooned slightly every time until it finally settled. Again could be shit technique on my part but I will follow the advice here and report back.


Cheers