Test Pilot time: Short field landings.

[flyingcheesehead]

We had a healthy discussion on the Mooney Pilots group on Facebook regarding landing technique that morphed a bit into short field landings, and there were plenty of unresolved assertions. Well, my engineer brain didn't like that, and my pilot brain decided that doing some testing sounded like fun.

I’m planning to do some research/flight testing to determine the theoretical and actual effectiveness of some different techniques, and I figured that crowdsourcing the design of the tests would help to make them as effective as possible. I will take another pilot with me to help collect and record the data safely. I’ll update the remainder of this post as we refine the plan:

First of all, to eliminate as many variables as possible, I’ll do all my approaches to the same runway, using the GTN 750 visual approach feature with autopilot and a consistent power setting so that the approaches are all the same. That means at least a 3-mile final, I’ll probably plan a base leg around 4 miles out and drop the gear at 3 miles as the glide slope is intercepted.

I’ll also rotate through the following scenarios rather than doing all reps of a single scenario and moving on to the next scenario. By rotating through them, the effect of the inevitable changes in wind, temperature, and aircraft weight should be minimized.

I’ll have a GoPro mounted underneath the plane to help with measuring where touchdown and the end of the roll occur.

I'm planning on doing the entire following list of scenarios 3 times. Here are the scenarios I’m thinking of doing:

1) Flap retraction time, engine off.
2) Flap retraction time, engine running, airplane stationary on the ground.
3) Flap retraction time, in slow flight.
(The above don’t need to be in the rotation, as they don’t involve a landing - I'll do them first)

4) Landing distance and flap retraction time during landing roll, no wheel braking. Will take airspeed at touchdown, beginning and end of retraction as well as the amount of time it takes for retraction.
(All of the above will give us the time it takes to retract flaps and determine the variation, if any, caused by differing bus voltages and aerodynamic loads.)

5) Landing distance, Flaps down throughout landing roll, no wheel braking.
6) Landing distance, Flaps down throughout Landing, speed brakes extended upon touchdown, no wheel braking.
7) Landing distance, Flaps down throughout landing, speed brakes extended at end of flare, no wheel braking
8.) Landing distance, Flaps down throughout landing, speed brakes extended at beginning of flare, no wheel braking.
9) Landing distance, flaps down throughout landing, speed brakes extended at end of flare, nose held off until control effectiveness is lost, then full aft elevator for remainder of landing roll, no wheel braking.

(“Max braking effort” as used below means as much pressure as possible without skidding, thus the pressure will necessarily vary throughout each individual landing roll and between tests.)

4a) Landing distance, Flaps retracted upon touchdown, max effort braking after retraction complete, elevator neutral
4b) Landing distance, flaps retracted upon touchdown, max effort braking right away, elevator neutral
5a) Landing distance, flaps down throughout landing roll, max effort braking
6a) Landing distance, flaps down throughout landing roll, speed brakes extended upon touchdown, max effort braking
7a) Landing distance, flaps down throughout landing roll, speed brakes extended at end of flare, max effort braking
8a) Landing distance, Flaps down throughout landing, speed brakes extended at beginning of flare, max effort braking.
10) Landing distance, Flaps down throughout landing, speed brakes extended at end of flare, elevator full aft, max effort braking.

I’ll do the tests in the following order to minimize the effects of brake temperature: 4a, 4,4b, 5, 5a, 6, 6a, 7, 7a, 8, 8a, 9, 10. I’ll also take a break after each series to help with my alertness and performance, replace the batteries in the GoPro, and give the brakes a chance to cool further.

Other data to record: Temp, Dewpoint, and winds for each test.

Any thoughts or suggestions are appreciated. I've got a thread on the Mooney Pilots group, but I'm posting the link here mainly because it's freaking impossible to find anything on Facebook after a couple of days have passed.

 

[eman1200]

hhhmm, what, exactly, are you trying to accomplish? (I didn't go to the facebook link)

 

[evapilotaz]

The first test is to understand what was posted lol

 

[flyingcheesehead]

hhhmm, what, exactly, are you trying to accomplish? (I didn't go to the facebook link)

First of all, to see how much of an effect the drag devices (flaps and speed brakes) have at landing speeds, how much of an effect raising flaps has on wheel braking ability, and hopefully arrive at the best short field landing technique, at least for a Mooney. Others are free to run the tests in their planes too, hopefully using good methodology which is what I'm trying to crowdsource the design of here.

FWIW, the POH just says to use full flaps, approach at 70 knots, and maximum braking. Nothing about speed brakes or raising flaps.

 

[Bill Watson]

So it seems that you are just measuring ground roll and not distance over an obstacle. That would seem to eliminate the effects of approach speed and descent rate.

If so, is that the best measure of short field landing performance?


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[ja_user]

Obviously if your goal is to minimize ground roll, you should approach right before stall break, about 1" over the threshold. Minimum Energy.

But what will you do with this information?

 

[Hank S]

So it seems that you are just measuring ground roll and not distance over an obstacle. That would seem to eliminate the effects of approach speed and descent rate.

If so, is that the best measure of short field landing performance?

True. For short fields, I fly slower on short final by 5 mph or a little bit slower, just to reduce float (which can be considerable in a Mooney).

One trip into a nearby 2000' grass strip, I floated almost half its length at idle, half flaps and 2' agl. Raised flaps and she sat right down, barely braked at all to stop before the end (big gravel pile for the cement factory next door). Never needed that trick at my tree-obstructed 3000' paved home field, nor the other nearby 3150' paved strip with a mountain on final requiring the downwind-to-base turn to be all the way around toward the numbers (and the runway NA at night).

Cheese, while you're at it, see if you can prove Bob Kromer's statement that every extra knot of airspeed in the flare results in an extra 100' of float. Just be aware that 1.2Vx on short final is weight dependant; I reduce short final speed by 5mph for every 300lb the plane is below gross for that landing (per Don Kaye, another thing to prove that will directly affect short field landings).

Question: why 3 mile finals? Mine are generally 1/2-3/4 mile long.

I don't expect speedbrakes to do much, their effect is proportional to airspeed and the plane was tested and aproved to takeoff with speedbrakes deployed.

But have fun! And please, do report back with results.

 

[Tarheelpilot]

First of all, to see how much of an effect the drag devices (flaps and speed brakes) have at landing speeds, how much of an effect raising flaps has on wheel braking ability, and hopefully arrive at the best short field landing technique, at least for a Mooney. Others are free to run the tests in their planes too, hopefully using good methodology which is what I'm trying to crowdsource the design of here.

FWIW, the POH just says to use full flaps, approach at 70 knots, and maximum braking. Nothing about speed brakes or raising flaps.

Then don’t **** with the speed brakes or flaps. The procedure in the POH is what was used to generate the performance data. I don’t get what the debate is all about. This vaguely reminds me of the “watch me increase performance by flying uncoordinated” thread. Just do what the manufacturer recommended and when someone tells you they can do it better than Mooney you should congratulate them, give them a cookie for a job well done and go somewhere for waffles. Then don’t worry about what they said. That’s my vote. Good luck.

At least the stupidity of it all gives you an excuse to fly. That’s a good thing.

 

[Hacker]

Time probably better spent better understanding STOL approach and landing techniques rather than ground roll reduction techniques.

 

[wilkersk]

Obviously if your goal is to minimize ground roll, you should approach right before stall break, about 1" over the threshold. Minimum Energy.

But what will you do with this information?

Maybe figure out how to arrive at the threshold, 1" off the ground right before the "stall break". --- But, I'm no expert here, just guessing.

 

[tspear]

The only variable I see you do not account for is weight. Not sure how you can.

Also, not as fun but a more precise test since this is about ground roll. Is to go to a large runway, accelerate to a specific speed (e.g. 70mph) and then stabalize at that speed for a few seconds and the cut power and do the tests.
This eliminates a lot of the speed variation on final which is bound to occur, eliminates most of the flare technique variations...

Tim

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[Bill Watson]

Time probably better spent better understanding STOL approach and landing techniques rather than ground roll reduction techniques.

...with the understanding that ground roll reduction is only a part of the exercise.

I’m thinking that short field landings over the standard obstacle is the exercise to be studied. It requires optimizing descent angle, approach landing speeds, eliminating float, etc.

I only have a few hours in a Johnson bar equipped Mooney. It was fun learning how getting the approach speed under 85mph was the key to establishing a steeper approach angle. I assumed it was a function of the wing design but it was quite noticeable.

Using book procedures at book weights and book conditions to achieve book numbers is one exercise. Using alternate techniques and with aftermarket accessories to possibly better book numbers is another one.

In the end, a bit of practice will have the biggest impact on performance.



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[Matthew Rogers]

The OP is trying to answer a question posed in the forum earlier - does retracting flaps result in more available braking force as stated in several POH. It was argued that the flaps have little effect and that retracting them can cause a pilot to overload during the roll out and do stupid stuff like retract the gear instead or ground loop a tail wheel. I know the electric flaps in my 150 take several seconds to go from 40 to 0 and I have to hold the switch the entire time. It would be a different situation if I could just flip the switch and not have to hold it up or if I had a Johnson bar and could dump them all at once.

But I do still want to know if a Test Pilot on a 3 mile final has the right of way over my slow 150 on a tight base. (Had to do it, don’t debate this point, PLEASE)

 

[N659HB]

But can you slip with flaps?

 

[Matthew Rogers]

Ooo, good point! My POH doesn’t even have the word “slip” in it. So I can’t.

I am interested in these test results. They may even help me out when I try to go to Alton Bay and land on the ice this winter. Any bit of extra help would be nice on the ice.

Where is Flyingcheesehead located. We could setup some Lawn chairs and spectate.

 

[jsstevens]

But can you slip with flaps?

On an icy runway? Yes.

 

[tawood]

Although nowhere near the level of testing that you plan, I once did something similar (but much less complicated) with my Cherokee 140...I noticed people often argued over the effectiveness of wheel pants on the Cherokee, so I took it upon myself to run a series of tests on my Cherokee with and without pants. Now that I've run the tests, all I can say is, be prepared after doing all the work, for people to not believe your results, and tell you you're wrong. If you are doing it for your own knowledge, like I was, then fine.

 

[MauleSkinner]

So...21 landings with max effort braking. I say three ruined tires.

Price is Right rules...closest without going over.

 

[Mtns2Skies]

I will take another pilot with me to help collect and record the data safely.

I volunteer as tribute!

 

[Mooney Fan]

We had a healthy discussion on the Mooney Pilots group on Facebook regarding landing technique that morphed a bit into short field landings, and there were plenty of unresolved assertions. Well, my engineer brain didn't like that, and my pilot brain decided that doing some testing sounded like fun.

I’m planning to do some research/flight testing to determine the theoretical and actual effectiveness of some different techniques, and I figured that crowdsourcing the design of the tests would help to make them as effective as possible. I will take another pilot with me to help collect and record the data safely. I’ll update the remainder of this post as we refine the plan:

First of all, to eliminate as many variables as possible, I’ll do all my approaches to the same runway, using the GTN 750 visual approach feature with autopilot and a consistent power setting so that the approaches are all the same. That means at least a 3-mile final, I’ll probably plan a base leg around 4 miles out and drop the gear at 3 miles as the glide slope is intercepted.

I’ll also rotate through the following scenarios rather than doing all reps of a single scenario and moving on to the next scenario. By rotating through them, the effect of the inevitable changes in wind, temperature, and aircraft weight should be minimized.

I’ll have a GoPro mounted underneath the plane to help with measuring where touchdown and the end of the roll occur.

I'm planning on doing the entire following list of scenarios 3 times. Here are the scenarios I’m thinking of doing:

1) Flap retraction time, engine off.
2) Flap retraction time, engine running, airplane stationary on the ground.
3) Flap retraction time, in slow flight.
(The above don’t need to be in the rotation, as they don’t involve a landing - I'll do them first)

4) Landing distance and flap retraction time during landing roll, no wheel braking. Will take airspeed at touchdown, beginning and end of retraction as well as the amount of time it takes for retraction.
(All of the above will give us the time it takes to retract flaps and determine the variation, if any, caused by differing bus voltages and aerodynamic loads.)

5) Landing distance, Flaps down throughout landing roll, no wheel braking.
6) Landing distance, Flaps down throughout Landing, speed brakes extended upon touchdown, no wheel braking.
7) Landing distance, Flaps down throughout landing, speed brakes extended at end of flare, no wheel braking
8.) Landing distance, Flaps down throughout landing, speed brakes extended at beginning of flare, no wheel braking.
9) Landing distance, flaps down throughout landing, speed brakes extended at end of flare, nose held off until control effectiveness is lost, then full aft elevator for remainder of landing roll, no wheel braking.

(“Max braking effort” as used below means as much pressure as possible without skidding, thus the pressure will necessarily vary throughout each individual landing roll and between tests.)

4a) Landing distance, Flaps retracted upon touchdown, max effort braking after retraction complete, elevator neutral
4b) Landing distance, flaps retracted upon touchdown, max effort braking right away, elevator neutral
5a) Landing distance, flaps down throughout landing roll, max effort braking
6a) Landing distance, flaps down throughout landing roll, speed brakes extended upon touchdown, max effort braking
7a) Landing distance, flaps down throughout landing roll, speed brakes extended at end of flare, max effort braking
8a) Landing distance, Flaps down throughout landing, speed brakes extended at beginning of flare, max effort braking.
10) Landing distance, Flaps down throughout landing, speed brakes extended at end of flare, elevator full aft, max effort braking.

I’ll do the tests in the following order to minimize the effects of brake temperature: 4a, 4,4b, 5, 5a, 6, 6a, 7, 7a, 8, 8a, 9, 10. I’ll also take a break after each series to help with my alertness and performance, replace the batteries in the GoPro, and give the brakes a chance to cool further.

Other data to record: Temp, Dewpoint, and winds for each test.

Any thoughts or suggestions are appreciated. I've got a thread on the Mooney Pilots group, but I'm posting the link here mainly because it's freaking impossible to find anything on Facebook after a couple of days have passed.

What virtual RWY length are these parameters meant to document? I flew a M20C Ranger that was based out of 2700' field that was more than adequate for landing purposes, but you needed to be on the mains first 1/3. IOW, what constitutes a short field one would want to land a Mooney at?

 

[eman1200]

I volunteer as tribute!

you do realize mooneys are low wings, yes?

 

[Mtns2Skies]

you do realize mooneys are low wings, yes?

The things I will do in the interests of STOL...

 

[Salty]

I predict your measurements will show differences well below the margin of error for your tests.

 

[flyingron]

Retracting the gear greatly decreases the landing roll.

 

[dtuuri]

The only variable I see you do not account for is weight. Not sure how you can.

Not needed. For a given speed and within brake energy limits, the stopping distance will be the same.

 

[Half Fast]

Retracting the gear greatly decreases the landing roll.

But increases the landing skid.....

 

[Mtns2Skies]

I volunteer as tribute!

Alternatively I'll use my plane and we can see who will land shorter

 

[texasclouds]

OP is getting loved tinderly...

 

[Lachlan]

3 mile final? Isn’t tha5 usually referred to as “straight in?”

 

[Mooney Fan]

3 mile final? Isn’t tha5 usually referred to as “straight in?”

Meh, the FAA wants us to 'drag it in' these days in favor of the 'stabilized' approach. Bad idea

 

[FastEddieB]

Meh, the FAA wants us to 'drag it in' these days in favor of the 'stabilized' approach. Bad idea

Source?

 

[Salty]

Source?

I think he means "instead of" rather than "in favor of".

Maybe.

 

[Flyhound]

If you are sticking with a standard localizer glideslope approach, then you're only assessing the contribution that breaking technique has on stopping distance. That's a very small subset of factors that affect short field landing performance. A steeper approach at lower than standard landing speeds will result in a shorter overall ground roll for a given level of braking. Brian Painter is one of the few pilots I know of that has used a Mooney for backcountry flying and he perfected techniques for getting his M20 down and stopped quickly. Ultimately he decided the Mooney wasn't the best plane for the job with his growing family, but here's a video of him in action when he was flying the M20:

 

[Flyhound]

Here's another clip of Brian in action with his Mooney on a short grass strip in Western Washington: https://backcountrypilot.org/forum/mooney-short-field-landing-and-180-go-around-19755

 

[tspear]

Not needed. For a given speed and within brake energy limits, the stopping distance will be the same.

More weight is more mass. More mass is a greater inertia. More inertia is more potential energy that the brakes must absorb.
So there will be differences in distance. If just 2 gallons of gas, it likely is within the margin of error. Otherwise, to complete 21 approaches I would guess the OP will consume 30 or so gallons. A 180 lbs likely will have a significant adjustment to stopping distance.

Tim

 

[dtuuri]

More weight is more mass. More mass is a greater inertia. More inertia is more potential energy that the brakes must absorb.
So there will be differences in distance.

Nope, there will be more brake heat. Max braking occurs just before the tires skid. The more weight on the tires, the harder they can brake before they skid.

 

[eman1200]

If you are sticking with a standard localizer glideslope approach, then you're only assessing the contribution that breaking technique has on stopping distance. That's a very small subset of factors that affect short field landing performance. A steeper approach at lower than standard landing speeds will result in a shorter overall ground roll for a given level of braking. Brian Painter is one of the few pilots I know of that has used a Mooney for backcountry flying and he perfected techniques for getting his M20 down and stopped quickly. Ultimately he decided the Mooney wasn't the best plane for the job with his growing family, but here's a video of him in action when he was flying the M20:

that looked more like 'rough field' than 'short field'.

 

[flyingcheesehead]

So it seems that you are just measuring ground roll and not distance over an obstacle. That would seem to eliminate the effects of approach speed and descent rate.

If so, is that the best measure of short field landing performance?

Well, nobody was arguing about techniques used in the air.

Obviously if your goal is to minimize ground roll, you should approach right before stall break, about 1" over the threshold. Minimum Energy.

But what will you do with this information?

Tell the people who retract flaps after landing that they're wrong.

One trip into a nearby 2000' grass strip, I floated almost half its length at idle, half flaps and 2' agl. Raised flaps and she sat right down, barely braked at all to stop before the end

Interesting. Nobody said they raised flaps before touchdown, but my technique is to pop the speed brakes at the end of the round-out, basically 1' AGL, because that sets the wheels right on the ground immediately. I think that the sooner you can get the wheels on the ground, the better, and once the nosewheel is down you can start to brake. Once you do that, there's some pitch-down moment so you can then pull the yoke fully aft which gives you some aerodynamic braking (not a ton due to the speed) and helps put more downward force ("weight") on the wheels to help increase friction.

Cheese, while you're at it, see if you can prove Bob Kromer's statement that every extra knot of airspeed in the flare results in an extra 100' of float. Just be aware that 1.2Vx on short final is weight dependant; I reduce short final speed by 5mph for every 300lb the plane is below gross for that landing (per Don Kaye, another thing to prove that will directly affect short field landings).

Sounds plausible... But I'm going to try to have everything perfectly stabilized to minimize differences in approach speed causing erroneous results.

Question: why 3 mile finals? Mine are generally 1/2-3/4 mile long.

To ensure that the approaches are all consistent, I'm going to use the visual approach feature on the GTN coupled with my autopilot and a consistent power setting to get the approaches as identical as I can. It should take just about a 3 mile final to get down from pattern altitude that way, and that will give me plenty of time to get things stabilized.

I don't expect speedbrakes to do much, their effect is proportional to airspeed and the plane was tested and aproved to takeoff with speedbrakes deployed.

I think their main advantage is getting weight on wheels as soon as possible, but they also help to blank out part of the wing so that there's more weight on the wheels than there would be otherwise. But, testing out the magnitude of these effects is part of the reason for doing all this.

But have fun! And please, do report back with results.

Wilco!

Then don’t **** with the speed brakes or flaps. The procedure in the POH is what was used to generate the performance data. I don’t get what the debate is all about. This vaguely reminds me of the “watch me increase performance by flying uncoordinated” thread. Just do what the manufacturer recommended and when someone tells you they can do it better than Mooney you should congratulate them, give them a cookie for a job well done and go somewhere for waffles. Then don’t worry about what they said. That’s my vote. Good luck.

At least the stupidity of it all gives you an excuse to fly. That’s a good thing.

I would guess that, speed brakes being optional, the factory decided to do their tests without them rather than have to go through the testing twice (which would increase costs).

The only variable I see you do not account for is weight. Not sure how you can.

Well, there won't be a huge difference in weight. Obviously I'll be burning fuel and thus getting lighter, but one trip around the pattern will barely affect it. This is also part of the reason for doing the full rotation and starting over rather than doing all 3-5 of the same test before moving on, so that weight won't change significantly between the different tests.

Where is Flyingcheesehead located. We could setup some Lawn chairs and spectate.

Wisconsin. My lawn chairs have about three inches of snow on 'em right now.

I volunteer as tribute!

I was going to take Ron, but it looks like he went off to Utah again. PM me your cell #, somehow I didn't get it last month...

What virtual RWY length are these parameters meant to document? I flew a M20C Ranger that was based out of 2700' field that was more than adequate for landing purposes, but you needed to be on the mains first 1/3. IOW, what constitutes a short field one would want to land a Mooney at?

In my Mooney (M20R), I think of anything less than 2500' paved as short... As in, "I need to look at the performance charts before I do this" not "I need extreme techniques on a 2400 foot runway".

But, I'll probably be looking to do the testing on a 5000-footer so that the no-brake tests don't, well, require brakes.

I predict your measurements will show differences well below the margin of error for your tests.

Quite possibly... And that will still tell us something.

 

[scorpio]

The idea of reaching a certain speed on the runway and measure the braking under different configurations sounds like the best option. It takes out so many variables.

 

[Salty]

Quite possibly... And that will still tell us something.

My comment was just a prediction, not an attempt to talk you out of doing it. This is something I might do even if pointless to others, it amuses me.

Another prediction. You won’t learn anything of use to anyone else, but you’ll learn a lot about how to land your airplane yourself.