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What Are Negative Factors Of Stol Kits?

Sun Jun 21, 2009 3:08 am

A STOL kit on a Cessna 172 helps deter stalling and decreases takeoff and rollout runs. But does the kit hamper the plane's speed, climb rate, or ceiling?
 
njxc500
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RE: What Are Negative Factors Of Stol Kits?

Sun Jun 21, 2009 4:24 am

I have read claims of 3-4 knots lower stall speed.

http://forums.piperowner.org/read/5/80476/page=2

As for negative effects, I don't know of any and a quick search didn't turn any up. I would imagine since the aerodynamics could be 20 or more years old, there are some places to make up wing efficiency without compromising top speed.

Good Luck
 
lowrider
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RE: What Are Negative Factors Of Stol Kits?

Sun Jun 21, 2009 4:31 am

The biggest drawback I can think of is insurance. When you start talking STOL to insurance companies, they start to get nervous as to what you might be doing with it and will raise your rates accordingly.
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ThirtyEcho
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RE: What Are Negative Factors Of Stol Kits?

Sun Jun 21, 2009 5:43 am

I have some experience with a STOL kitted Cessna and I can't say that the performance was worth the money spent. Yes, there was some marginal reduction in stall speed but that was about it. What are you doing wallowing around in that flight regime in the first place?

The best short landing device was installed at the Cessna factory in the form of the old 40 degree flaps. You could drop in over trees right on the arrival end of the runway and stop very short, or land very slowly on a soft or rough strip.

Since I had a lot of back country airport experience early in my flying history, I learned how to use the 40 degree flap setting safely. On the other hand, I wouldn't want to use them except as mechanically driven with a flap lever, never as the electrically operated flaps.
 
KELPkid
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RE: What Are Negative Factors Of Stol Kits?

Sun Jun 21, 2009 6:35 am

The only negative thing I can think of that a STOL kit does for the aircraft performance is reduce crosswind component on landing...

Quoting ThirtyEcho (Reply 3):
I have some experience with a STOL kitted Cessna and I can't say that the performance was worth the money spent.

I beg to differ. I have had experience in the same 172L, before and after Horton STOL Craft installation. After installation, you could get this plane airborne in much less runway and land using much less runway (assuming, of course, you were using STOL techniques...). If you weren't flying in the STOL regime, it performed pretty much like it did before conversion...

I remember watching my instructor do a STOL takeoff, solo, one cold and calm winter night in this bird. He was off in about 300 feet (the bird also had the Air Plains 180 Horsepower conversion with climb prop), and I can still see the path that those navigation lights cut through the sky in mind to this day  Smile
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L-188
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 5:02 am

Don Sheldon had a wreck with a new 185 with a STOL kit. His book says he refused to fly one after that.

The problem with any stol kit is that you are trading off performance in one area for another. The one thing these kits don't see to really address is control authority. If you are going to fly slower you are going to need to have larger surfaces to stick out in the breeze.
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KELPkid
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 6:07 am



Quoting L-188 (Reply 5):
The one thing these kits don't see to really address is control authority. If you are going to fly slower you are going to need to have larger surfaces to stick out in the breeze.

Hence the reason that the STOL kit manufacturers lower the max crosswind component on STOL-kitted aircraft  Wink
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DiamondFlyer
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 6:20 am



Quoting KELPkid (Reply 6):
Hence the reason that the STOL kit manufacturers lower the max crosswind component on STOL-kitted aircraft

You mean the lower the maximum demonstrated crosswind? Most light aircraft have just a maximum demonstrated crosswind component, which is not a limitation. Just beyond that, and you're a test pilot

I flew a Horton STOL (I think it was Horton) Cessna 150M. Not sure that it really did anything, other than drop the stall speeds down a bit. Might take a couple knots off the top end as well, but on something like a 150, its really not worth the money, IMO.

-DiamondFlyer
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 1:52 pm

A STOL kit will lower top and cruising speeds slightly; my 182 was a 1962 which was before Cessna adapted the modified drooped leading edge (which came from a STOL kit). I also had a fair amount of time on a newer 182 (a CAP plane) that had the drooped leading edge. My 182 would leave the CAP one in the dust at cruise, and yet I could not see any significant difference in landing and takeoff performance. The other primary airframe difference between the two was that my horizontal stabilizer was 10" shorter, which would also mean less drag. During the time I operated the airport I had a chance to fly a couple of other (newer) 182's; mine would outrun all of them by a considerable margin.
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KELPkid
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 2:58 pm



Quoting DiamondFlyer (Reply 7):
I flew a Horton STOL (I think it was Horton) Cessna 150M. Not sure that it really did anything, other than drop the stall speeds down a bit. Might take a couple knots off the top end as well, but on something like a 150, its really not worth the money, IMO.

-DiamondFlyer

Read the STOL kit supplemental to the POH. To take advantage of the STOL kit, you have to follow the STOL kit manufacturer's recommended techniques on takeoff and landing. The Horton STOL craft kit is incredible, IMHO (well, in the 172 at least, that's where I have experienced it).
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DiamondFlyer
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 01, 2009 4:29 pm



Quoting KELPkid (Reply 9):

Read the STOL kit supplemental to the POH. To take advantage of the STOL kit, you have to follow the STOL kit manufacturer's recommended techniques on takeoff and landing. The Horton STOL craft kit is incredible, IMHO (well, in the 172 at least, that's where I have experienced it).

I flew the plane once, and had no non-STOL 150 time to compare it to. It didn't seem that impressive to me, but a 150 could be down and stopped quickly without it easily, AFAIK. Putting STOL on a 150 is kind of a waste of money.

-DiamondFlyer
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geotrash
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RE: What Are Negative Factors Of Stol Kits?

Tue Jul 07, 2009 6:49 pm



Quoting L-188 (Reply 5):
The one thing these kits don't see to really address is control authority. If you are going to fly slower you are going to need to have larger surfaces to stick out in the breeze.

I have a Horton STOL equipped 182 and just returned from a trip to Alaska from Denver and back. I also spend a fair amount of time flying in the Rockies here locally so perhaps I can add some color.

The stall fence on the Horton STOL kit provides enhanced control authority in the stall regime because it prevents the stall from progressing outboard of the fence, ensuring better airflow over the ailerons. The rudder is a non issue in cosswinds as the 182 has plenty of rudder to work with- at least I've never run out of rudder with mine in a crosswind.

Some other observations:
-Will liftoff in short field takeoff at 42 mph indicated airspeed. In non-STOL 182s I've flown it's closer to 50 mph.
-In slow flight to a stall it will not break into the stall if I hold the wings level, it simply descends in a nose high attitude
-To get a true break in the stall, I have to push forward on the yoke and then pull back abruptly to induce the stall
-Little roll tendency in the stall and less chance of an incipient spin due to better aileron authority
-Doesn't help much on landing because the sink rate increases below 60 mph in landing config to a level that makes touchdowns firmer that I like. Likely why the rudder authority is a non issue.
-Best estimate is a 3 mph loss in cruise speed with the kit vs. without

Happy with the results overall.

Dave
 
L-188
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RE: What Are Negative Factors Of Stol Kits?

Wed Jul 08, 2009 3:54 am



Quoting Geotrash (Reply 11):
The stall fence on the Horton STOL kit provides enhanced control authority in the stall regime because it prevents the stall from progressing outboard of the fence, ensuring better airflow over the ailerons. The rudder is a non issue in

Agreed you can engineer "fixes" into the STOL kit that will work. But control authority is a design issue. If you have a kit that droops the ailerons with the flaps, it definately is an issue.

I think the most incredible example are the fences on the upper wing of the Wren conversion. They turn with the control inputs, interesting thing to see when it is running up on the ground.

But then you start to get into the question about mechanical complexity vs. costs.
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Illini_152
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RE: What Are Negative Factors Of Stol Kits?

Thu Jul 09, 2009 8:34 pm

Best STOL kitted Cessna I flew was a 402B with the Robertson STOL kit. It replaced the split flaps with slotted Fowler flaps and drooped the ailerons (5 degrees IIRC) with takeoff flaps selected.

The slotted Fowler flaps increased the wing area enough to reduce Vmc by 25 knots, and Vyse by 20. The numbers escape my memory, but we'd rotate and climb out at the new Vyse (which was slower than Vmc in the normal aircraft) then at 500 feet we'd accelerate to normal enroute climb speed before retracting the flaps.

The 20+ knot reduction in rotation speed really helped the takeoff distances in that pig, especially when it was hot out at heavy weights (which they almost always were, hauling freight...)

After flap retraction the plane was a normal 402 again, and cruise performance didn't suffer. think we took a 100lb hit on the empty weight, and flap speeds were adjusted; takeoff/approach flap speed was increased, while landing flap speed was decreased, oh, and you couldn't extend the flaps with the main door open, as the bottom half of the clamshell interfered with the extension sequence. Good way to trash a flap and flap-motor doing that...
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geotrash
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RE: What Are Negative Factors Of Stol Kits?

Fri Jul 10, 2009 4:57 am



Quoting L-188 (Reply 12):
Agreed you can engineer "fixes" into the STOL kit that will work. But control authority is a design issue. If you have a kit that droops the ailerons with the flaps, it definately is an issue.

I think the most incredible example are the fences on the upper wing of the Wren conversion. They turn with the control inputs, interesting thing to see when it is running up on the ground.

But then you start to get into the question about mechanical complexity vs. costs.

Agree on control authority. Less airspeed generally equals less authority, usually made worse in the stall regime by the progression of the stall toward the ailerons. The stall fence and also vortex generators I suppose are adequate mitigation in most cases.

Didn't know the wren had movable stall fences...sounds trouble-prone  Smile

Dave
 
geotrash
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RE: What Are Negative Factors Of Stol Kits?

Fri Jul 10, 2009 5:04 am



Quoting Illini_152 (Reply 13):
The slotted Fowler flaps increased the wing area enough to reduce Vmc by 25 knots, and Vyse by 20. The numbers escape my memory,

Wow! Impressive indeed. Makes for a much safer aircraft if an engine fails I should think.

Dave
 
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RE: What Are Negative Factors Of Stol Kits?

Sat Jul 11, 2009 4:52 am



Quoting Geotrash (Reply 14):
Didn't know the wren had movable stall fences...sounds trouble-prone

When I first saw one running up and checking controls it was the weirdest thing to see.

Just wasn't expecting to see them move. Later I got a closer look at one, and you will see that all of them are just mounted the middle, they aren't riveted down.
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