With all the issues of accurate W&B, real world vs book performance I thought it might be a good idea to lay down a performance baseline for my C-180. It has a few mods, but the only relevant ones are the Sportsman STOL... O-470R/ 2 Blade McC Prop... computed 1826lb. It had full main tanks, me and about 10 lb of gear. The filmed events in the video were done with about 6 knots headwind, we redid the T/O and Landing portions the next day with no wind (at least the 10 Degree flap Takeoff, 30 Degree flap takeoff and 40 Degree flap landing). Not a purely scientific test... distances are within 10', temps (~45F degrees) and weights and such just don't matter much. The way I figure it it is an approximation so close 'ballpark' is good enough for me. I'll redo the tests with Big Tires and then when it gets hot to allow for some density altitude issues. I dream of doing the Wing-X kit and a Pponk.... if that happens we'll redo the tests for those.

Is this about what everyone else is seeing?
http://youtu.be/l9JxrXa8XQI

gunny

Field elevation?

Thanks for posting this, it gives me something to compare my very stock 180A too.

MM

KMWL is 974'.

Of course, the only relevant factor in a short field roll out is how fast the airplane is going at touch down, which is why nailing approach speeds at 1.3 Vso is so critical. Any over that will materially increase the roll out. But since Vso is dependent on weight, if you're running light, you can safely approach at a much slower airspeed than if you're running at gross. Higher density altitudes will result in higher TAS for the same IAS, which obviously means a faster ground speed and longer roll out, as well.

Both density altitude and weight will materially affect take off performance as well--often much more than we realize.

Fundamentally, to know how your airplane will perform at a given weight and at a given density altitude, you have to fly it under those conditions. It's nearly impossible to accurately extrapolate how it will perform, from running light tests at a low density altitude.

But the testing is fun, right?

Cary

Cary-

It was fun. But I think you may have missed the point. I am trying to do just as you suggest. I wanted to establish a baseline.... not use a book number. I'll redo the tests at high density altitudes and weights (at least for here) and that will give me a better idea of what it will actually do rather than pulling it out of a chart from 1958. But from a scientific standpoint I could actually pull out the conversion factors and apply them to my numbers to achieve an extrapolation as you suggest... this is done all the time. Not every test program hits every test point.

As for approach speeds, I mentioned in the video that they were all done at 60 mph to the flare. We'll see how the airplane handles at higher weights and that has the potential of materially affecting the roll out. The difference in roll out distance can plainly be seen in the landings at various flap settings.

cheers,
gunny

Cary wrote:Of course, the only relevant factor in a short field roll out is how fast the airplane is going at touch down, which is why nailing approach speeds at 1.3 Vso is so critical. Any over that will materially increase the roll out. But since Vso is dependent on weight, if you're running light, you can safely approach at a much slower airspeed than if you're running at gross. Higher density altitudes will result in higher TAS for the same IAS, which obviously means a faster ground speed and longer roll out, as well.

Both density altitude and weight will materially affect take off performance as well--often much more than we realize.

Fundamentally, to know how your airplane will perform at a given weight and at a given density altitude, you have to fly it under those conditions. It's nearly impossible to accurately extrapolate how it will perform, from running light tests at a low density altitude.

But the testing is fun, right?

Cary

Actually, 1.3 Vso is REALLY fast on a landing approach, at least for a speed over the threshold, assuming you are actually trying to land short.

There are several factors that complicate this:

Airspeed instrument error at high AOA is typically pretty high. Varies with A/C type and installation, but the only way you can find out for sure is to go fly the airplane...THAT airplane. Find out what indicated airspeed YOUR airplane checks out at. And, I'm sure the fans of the speed indexers are going to chime in here, and same applies to those devices....find out where your airplane stalls.

Second, power ON stall speed is always slower than power off stall speed. Vso is power OFF stall speed. A really short field approach is going to generally be done with at least a little power. So, now you also need to find out what your power ON stall speed is. Not only that, but what does the airplane tell you when you approach that speed/configuration?

Aircraft weight does in fact affect stall speed, but the actual difference in weight of most of these small airplanes between GW and "normal" operating weight really isn't all that huge, and thus stall speed differences aren't THAT huge. We can get into a discussion of semantics here, but the point is, as in discussions of the indexers, these are not F/A 18s where the max weight to landing weight varies MASSIVELY. Our stall speeds change a little between normal landing weights and max weight, but....not huge differences. Fly and test at the weights you are most likely landing in, as he notes he's doing.

In fact, a true short field approach and landing should be flown (from fairly close in on final) at 1.0 to 1.1 Vso, NOT at 1.3 Vso, which will cause that airplane to float forever.

If you are really, actually landing in short spots, 1.3 is REALLY fast on short final.

And, it's great to see someone out there doing some actual testing to see what their airplane can do. These old airplanes often don't offer a lot of information in the POH.

FWIW

MTV

MTV-

Well said sir! Anecdotes only go so far. Some 'ballpark' facts take you a bit further! Short field landings aren't pretty and smooth...roller touchdowns are not the goal here. A real world idea of what the capabilities of the airplane and its pilot are...

I can't wait to see what, if any, impact the Big Tires have on performance. I have to wait... don't have jacks that can put the airplane that high:) (Actually I do, but its a time issue).

gunny

Nice gunny! I could get my 56 w sportsman an r motor off pretty consistently within less than 200 at sea level. Sometimes in less than 100. Not sure If it coincides w your testing but if u dump your flaps soon as u touch down you can stop shorter. Gets the weight on wheels faster. I'm sure you knew that. Probably not part o the test. Cool man. Curious to see change in 29's. I'm going that route on my 55 soon. Thanks for posting.

I like video's like this. Fun and informative. Would be cool if more ppl posted videos like this and explained all mods and performance changes. Thanks for posting.

Actually, 1.3 Vso is REALLY fast on a landing approach, at least for a speed over the threshold, assuming you are actually trying to land short.

[emphasis mine]Agreed--I'm talking about the final approach leg, not the over-the-fence speed, which I agree should be just above Vso.

I'm a little curious why 60 mph with each flap setting. I would think if 60 mph is a good stable IAS with no flaps, you should be able to reduce the approach speed markedly with flaps. Granted that the last 30/40 are more drag than lift, nonetheless I'd expect a slower speed would work.

Can't speak for a 180, but on my P172D, using my AOA gauge, I note about 5 mph difference at the same AOA reading between running at gross and running relatively light (just me and half tanks). Not huge, but notable. Again FWIW.

Cary

Gunny wrote:With all the issues of accurate W&B, real world vs book performance I thought it might be a good idea to lay down a performance baseline for my C-180. It has a few mods, but the only relevant ones are the Sportsman STOL... O-470R/ 2 Blade McC Prop... computed 1826lb. It had full main tanks, me and about 10 lb of gear. The filmed events in the video were done with about 6 knots headwind, we redid the T/O and Landing portions the next day with no wind (at least the 10 Degree flap Takeoff, 30 Degree flap takeoff and 40 Degree flap landing). Not a purely scientific test... distances are within 10', temps (~45F degrees) and weights and such just don't matter much. The way I figure it it is an approximation so close 'ballpark' is good enough for me. I'll redo the tests with Big Tires and then when it gets hot to allow for some density altitude issues. I dream of doing the Wing-X kit and a Pponk.... if that happens we'll redo the tests for those.

Is this about what everyone else is seeing?
http://youtu.be/l9JxrXa8XQI

gunny

Looks fine. Where you going you need better performance than that? Save the $$$

G'Day...Rob

Gunny:

Thanks for the video and info.

As to comparisons, hard to compare. I have a 59 180, but I am at 5,000 feet and it has a P-Ponk 520 and it does not have the Sportsman. I have only flown a few times at very low altitudes (couple of trips to Oshkosh) but it sure is a different bird at that altitude.

A while back I wrote down some numbers, but they were all at gross. I wanted worst case numbers.

Takeoff with 20 degrees flaps, no wind and gross weight is about 675ft.

Landing with 40 degrees flaps, no wind and gross weight is about 475ft.

Also need to take into account skill set of pilot. Quite a few pilots on this website that I expect could beat those numbers especially on the landing side. The book for a 59 says I should be able to land in 375ft at gross at 5,000 feet, but there is no way I could consistently do that. My takeoff is better than book, but I have the bigger engine.

Did you have the airplane before the Sportsman was installed? If so, any report on the changes from the conversion?

Thanks!! Larry

Those calm wind numbers are in the ballpark with what I have seen, the only anomoly being that it seems like the difference in performance I see between the 6-8 kt headwind and calm conditions are more significant than you noted. Full fuel, just me I am off in 425' calm, 325-350' with 6-8 kt headwind. The displaced threshhold is exactly 500' at the airport I fly out of so it is pretty easy to judge the distance that the tires break the ground. MIne is a 53 with MASA STOL kit, a tired O470L and an 82" MacCauley prop. I am at about 60' Elevation. Temperature makes a little difference too. One thing I noticed improves takeoff distance considerably is to keep the tailwheel as close to, or on the runway as possible. Seems like larger tires would really help performance and keep the tailwheel from taking too much of a beating.

I have a bigger issue getting it on as short as it can get off. Getting the speed just right so you hit your spot with no bounce so you can get right on the brakes has been a challenge for me. Without any cross or headwind I am usually down and stopped past the reference line in about 450', to 500' on a bad day, but seems like unless I hang her a bit on the prop and just drop her in 3 point I either bounce it or float 50-100 feet past my touchdown point more often than not. Sometimes everything works just right and I can get it stopped in 330' past the threshold, but not consistently. I'd really like to get to the point of being able to consistently land it in 300' or less. Just takes practice, I guess.

Flynengr

This is good stuff, fun to compare and learn what other similar planes are doing.
I would just add (with all the VSO talk) build your own speed card. If your wing has been modified, toss the POH speeds. Find the MCA for your wing and go from there.

Thanks guys for the comments, questions and comparisons. All good stuff!

-I do want to get some numbers for the present config, dumping flaps on landing, but this first test was a baseline. And the airplane came with the Sportsman cuff, so I don't have 'before' number. Having your 'own' performance card gives you peace of mind you just can't get otherwise... at least it does for me;)
-Interesting difference with flynengr's numbers... MWL is just about 1000' MSL. I'll try the tail low takeoff and see if that makes a difference.
-88H, I was wondering what the performance might be at higher elevations.... someday I want to head to the mountains and with my baseline/mod numbers I can get a warm fuzzy about operating at higher elevations/density altitudes.
-Rob, are you kiddin.... whats the point if you can't tinker;) I didn't buy a 185 so I could do this and buy gas too.... or maybe it was the Beaver I didn't buy so I could do this!
-Cary, I used 60 mph as the over the fence speed because the wing feels good at that speed with zero flap, with the Sportsman it doesn't really stall, but develops a serious mush/descent rate around 45 mph or so. The technique I think is important includes enough energy on the airplane to maintain elevator control throughout the landing... you can see that I landed short on the 0 flap landing.... I held it off until it started to mush at each flap setting... you can see that impact on the location of each touchdown spot. I wanted to compare aircraft feel at those speeds with an outside the window look at performance.... flap 40 was by far the best (this is not the case in other airplanes I've flown... I wanted to know if a lower flap setting gives a better feel). Does that answer your question? BTW, I love AOA.... swear by it.... but am not totally convinced that you can get an accurate AOA without a vane... and I have yet to see a vane type AOA system for light GA.
-The weird thing was the fact that 30 degree flap for takeoff was a little bit better for ground roll... I did not expect that at all. I've done a lot of teaching in a big ol round motor twin and going through the flap settings, 10,20 lower the stall speed, 30,40 actually increase stall speed (demonstrating the lift to drag effect). This result was counter-intuitive to me.

I'll keep you posted on the numbers I get as this goes on! Thanks for participating!

gunny