This site is filled with recommendations for the best bush mods. Leading edge cuffs, slats, long props, big HP, etc. We're pretty amazing at figuring out ways to spend other people's money. As a long time lurker (thanks for the constant reminder, Bigrenna), I can't recall a single post where someone has posted hard data showing the effect of these modifications. It’s always seat of the pants nonsense or vague references to a VSI reading of 1000+ ft per min. As an engineer this annoys me. WHERE IS THE DATA?!?

As I continue to get comfortable flying my 170, I have been recording pattern work in foreflight (getting fed via WAAS GPS data) and reviewing it in google earth. My 170B is stock, but the performance section of the POH is thin. I wanted to know if Sparky Imeson’s “Takeoff distance varies as the square of gross weight” rule worked.

60 Degree Day. Wind 5-10 down the pipe. Field elevation is 441’.

Solo + half tanks + covers/tools = 1750lbs or 80% of gross. Square that and the takeoff distance should be 64% of the book value.

Book gives 1625 at gross and 60 Degrees. Pull off 10% for the headwind. And 64% for Sparky’s Rule and we are at a whopping 936’.

Here is the track in Google Earth. At the beginning of the 1000’ mark we are 68’ AGL doing 58mph over ground.




Does anyone else do this? Have I totally lost my mind?
What other tools are available for similar/improved data collection?

Good use of technology Smokey

I just use a go pro and google earth to measure my takeoff and landing distance. I figure my method is good to +/- 10’

As for landing distance, I measure from the leading edge of the pavement as this is more real world in the backcountry. Luckily we have a grass strip too, and I utilize that as much as possible. I just measure from the cones to my stop point for landing distance on the grass

I've played around with Google earth trying to get a better sense of my flight profiles as shown in this pic.



What I really want is a graph that will help me estimate my aircraft's performance given the density altitude, aircraft operating W&B, and field conditions (rough turf, packed gravel or pavement) so I have a better feel for the takeoff distances my plane will use. Getting into a strip I'm interested in is never a problem - it's getting back out that makes me hesitate. I have a 180 Hp Maule with a tired engine and the Maule Pilot Operating Handbook (POH) doesn't have any performance data or graphs in it. I can either generate these Google Earth tracks for every condition I might encounter, or develop flight data for my plane using something like the Lowry's Bootstrap Approach to Predicting Airplane Flight Performance. AVWEB had two articles about this system a few years back. Here are the links:

Part 1 is here: https://www.avweb.com/features_old/the-bootstrap-approach-to-aircraft-performancepart-one-fixed-pitch-propeller-airplanes/

and Part 2 is here: https://www.avweb.com/features_old/the-bootstrap-approach-to-aircraft-performancepart-two-constant-speed-propeller-airplanes/

I found a full copy of Lowry's paper online and will give this a shot in the spring when the weather is better. One good thing about this method is that it uses data collected from flying your plane. That means the results will take into account any loss of ooomph in the engine from age, wear and tear. I like that more than ideal numbers published in the POH for some planes. I just need to find someone willing to fly with me and record data while I'm putting the plane through the required maneuvers.

https://backcountrypilot.org/forum/beta ... hilit=tlar

The guy that wrote this app is a great friend of mine. You two need to chat!

The below is what I use when calculations are needed:

Take-Off and Landing Calculations

Density Altitude
3% loss of performance per 1000’ DA

Headwind
A wind of 15mph will decrease Landing Distance by 10%

Tailwind - Add 10% landing roll for every 3mph tailwind ~10mph Maximum~

Gradient Effect on Landing
Each 1% of slope will effect about 3% of landing distance
Each 1% of gradient is about equal to 10% change in effective runway length

Unimproved Strips
Add 20-30% for Long Grass (longer than 4”)
Add 45% for Sand
Add 20-75% for Mud or Soft Surface depending upon severity

71% of Vr speed should be reached by the mid-point of the runway

Gross Weight
1% increase in Gross Weight will increase Take-Off about 2%


So in addition, you need to know your performance numbers at a certain DA and then you can use the above to calculate getting into and out of short unfamiliar strips.

I used the above when I was flying a Rans S-21 with a Rotax 915 to great effect. The S-21 took a lot more to takeoff in higher DA’s than it did to land. I have yet to fly my BH Companion, but ever single person who flies a BH (Bearhawk) says it takes off shorter than it lands, and that is based on a 180hp engine, I think with my 200hp I will be fine….. But I always keep the above in laminated form in the cockpit along with my checklists.

I think one of the most important in the above is the 71% of Vr by the mid-point of the available runway. Don’t be afraid to abort.

As a fellow engineer I appreciate and enjoy data. Looking at the methods and results is a lot of fun. However, I feel like the takeoff and landing performance realm has so many variables that it is incredibly difficult to capture a truly inclusive dataset.

I took the path of just flying a bunch, learning to feel the plane, and be able to eyeball what I was comfortable doing. I’ve had some close calls but I really don’t think that having a chart or graph would have changed that.

The hitch is that you have to learn each plane and that takes a lot of time. I could put my 85hp Luscombe in places I still can’t take my Bearhawk. But again, I don’t think a performance chart would help me much. There’s just too many variables.

SmokeytheBear and Flyhound...can you guys mathematically compare total energy available between a low ground effect down the runway until cruise airspeed compared with a Vy pitch attitude climb once reaching Vy airspeed? In other words on SmokeytheBear's Google Earth track, what would his airspeed be at 1,000' down the runway at 1' AGL?

I expect the airspeed at 1,000' down the runway at 1' AGL would not look as good as the 68'AGL given an airplane operated fairly light. Compare any crop duster max load takeoff and the A36 crash video in my Total energy management on takeoff post. Weight, DA, and conditions can make the level in low ground effect look better. The A36 was going for Vy pitch attitude. He was going for the 68' AGL. That is why his nose was up at least to Vy pitch attitude even though he did not have Vy airspeed. Would he have made it if he had lowered the nose to stay in low ground effect when the mains came off at 700' down the runway? He never got out of ground effect because his nose was too high anyway, but the airplane was struggling with the nose up that high.

Those who crop dust live by the level in low ground effect pitch attitude all the way down the runway at full power total energy takeoff. It would be nice to have the numbers to support what we know, by staying alive, works. No, we don't do the math and yes we overload based on what it carried last time with the same conditions.

The FAA must have recognized the greater energy of ground effect because they changed the ACS to accelerate in ground effect to Vx or Vy as appropriate. Why not go the distance and find out the energy advantage of staying in low ground effect until cruise on runways of sufficient length?

I'm in Whee's camp, so many variables that I basically have resorted to using my worst case scenario, add in for not being on my game at times, and use that for most of my flying. Guys tell me that I am too conservative. Guess that comes from being busted up and knowing how quickly things can turn to sh!t! But I sure can appreciate the engineer guys wanting to put it all into numbers and graphs. Makes it much easier for us that abhor computers! LOL

FYI...I'm being quite broad in my response, and am actually more precise. In fact, the other day I flew a couple hours (on bushwheels in 3-4" snow) I walked my strip before taking off and felt the snow wasn't deep enough to be much of a factor. BOY! What a mistake! Crosswind forced me slightly to the side where the snow was deeper. Scared the begeezus out of me! Needless to say, my takeoff run was at least 30-40% longer from the additional drag from the snow. After landing, I walked down and stepped off my T/O and landings. This was just another variable I need to account for.

Last summer, we tried something that’s been used in Alaska for a while: A “Practice Runway”.

What this consists of is putting “non standard” markings on a grass or preferably, gravel runway to create a simulated confined runway within the bounds of a much larger runway.

The practice runway we created at Canyon Ferry airport in Montana consisted of runway markings of 2 x 4 feet, painted on the gravel surface, to create a 25 foot wide by 900 feet long “practice runway”. 2 x 4 markings were painted every 100 feet.

Now, you can accomplish a couple things:

1. You can SAFELY work on touching down exactly at the end of your “runway”, with no risk if you touch short.

2. These markings are easy to see with peripheral vision, so on takeoff and landing it’s easy to evaluate your performance. Got a Go Pro? Even better…..review your performance on “film”.

Use those markings in a variety of conditions, and you’ll have a much better idea of your and your airplane’s performance.

Just make sure you get permission from whoever owns the runway. If it’s a public runway, I was told by the FAA runway safety guys that non standard markings are okay on a runway that has NO instrument approach procedures.

MTV

My personal minimums are landing distance/takeoff distance (which ever is longer) times two plus 100’

So if I am using 350’ to land and taking off in 375’ I will limit where I will go to a 850’ strip

I add the 100’ in case I float or get an updraft on short final.

800’ is the shortest strip I landed in the S-21 and only used 1/2 of it. But in that plane I used about 550’ for the takeoff, the strip is at 4,685’ elevation and the temp was about 75°.

My Father, as well as flying his 180 for 45 years, was a particularly good golfer. He used golf as analogy. When he stepped up to the Tee he hadn’t measured the size of the club head, its weight, the length of the shaft, the flex of the shaft, the weight of the ball, the strength of the wind, the distance to the green before hand in order to use charts to calculate the speed he needed in the club head to deliver the energy required to hit the ball the distanced needed. His brain did all that automatically. The same with flying. Your brain does that all the time, automatically. What it needs thought is LOTS of practice. And following on from MTV’s post, on his farm strip where he kept the 180 he mowed a 10’ wide X 800’ long strip inside the bigger grassed area. Every landing required accuracy to stay inside that strip, loaded and light. The margins loaded were skinny but you soon learnt what those margins were, and as MTV says, without the risk. it was also a one way strip when loaded, so that meant quickly learning what a tailwind will do. As well as collecting the physical data you are talking about your brain is also collecting that same data. The variables can be huge but with enough practice your brain will actually do it all automatically and with a very high degree of accuracy. But it only comes by doing lots of it.

Your Dad knew the difference between repetition and iteration.

Flyhound - Glad i'm not the only one dorking out with google earth! Thanks for the avweb article link. I've never heard of that technique before. Will be fun to load up the 170 to gross and see how close it comes to the book numbers...

slowmover - I didn't realized that TLAR - "Pro" has a datalogger feature. Definitely going to give it a try. Thanks for the heads up!

Utah-Jay - Great info!

Whee - No doubt I just need to fly more. But its nice to have some data to calibrate the seat of the pants estimate.

WWhunter - Yikes! My issue is that I'm currently so conservative I'm scared to have fun. Have to convince myself I can squeeze out of some shorter strips. Got to leave the bunny slope eventually...

MTV - Killer idea. Now I just need a friend with a grass runway...

I use Cloudahoy, mainly as a training tool for teaching my son. I get excellent TO and Landing data and can note my weight, wind and so forth.

I load up my Husky with sand bags and fuel to be at gross or slightly over, then fly warm days north of Denver (DAs 9-10K) and use marked off grass adjacent to RW at home airport. Use my consistent landings/take offs and add 100'. If I fly under gross and/or lower DAs, my max numbers are safe. The extra 100' is for the unknown strips.
Have fun.

flyingjack wrote:I load up my Husky with sand bags and fuel to be at gross or slightly over, then fly warm days north of Denver (DAs 9-10K) and use marked off grass adjacent to RW at home airport. Use my consistent landings/take offs and add 100'. If I fly under gross and/or lower DAs, my max numbers are safe. The extra 100' is for the unknown strips.
Have fun.

If I did this with my 170 there wouldn't be any airports that would meet my minimum numbers!! HAHA

Flyhound wrote:I've played around with Google earth trying to get a better sense of my flight profiles as shown in this pic.

Where is that, Gary?

You haven't lost your mind, and guys like me that don't do heavy analysis actually really appreciate your hard work because at a bare minimum , it gives us 'something to shoot for' or a 'starting point' in our own red neck approach to evaluation.

But I think I Solidly agree with Whee.

I *think* the reason you don't see more hard data from posters on various forum with respects to what a mod did etc. is because there is 'aircraft performance' and then there is what an aircraft can do with a given pilot on board. If we were in the same room, or around a campfire, your demeanor would at this point give a tell as to wether I am wasting good finger tips on keys or?

I am not suggesting that some guys have the Jedi flight touch and others have ham, but when you want more than 'book' values, there are certain motor skills and art (the minds motor skills) that go in to this thing, and those require as much effort to build as 'knowledge'. You can read about how to shoot hoops like a pro, or how to smoke a guitar similarly, but doing it to uber levels, requires more than data. I think most posters modding aircraft are looking for something different than the numbers. This is not to suggest that you can't create data of what Micheal Jordan or Stevie Van Zandt did, I'm just suggesting that there comes a point where that data is inapplicable to the next guys use.

As a general rule, when a new visitor wants a tour of our neck of the woods, I ask them what they're comfortable going in and out of. I really enjoy running around with the guys that say something like 'oh about half your strip'. When someone say's something like " 300' " I usually offer them up the lead, and soon find out that yep, they can get it shut down in 300', they just can't pick which 300... Fun, but not as fun. By the way, my minimums are almost exactly calculated as Utah - Jay's. The fact that I have landed a cub in double digit' does not mean that this is a very useable data point for actual bush wacking,

Most guys aren't knowledgeable, trained or frankly experienced enough to produce actual aircraft flight testing. To suggest otherwise is demeaning to the guys who spent years at school and in aircraft to craft that. On the other hand, most all of us are interested in what we can make a specific aircraft do.

My experience, having flown with many folks over the years who want to expand on their flying envelope, or even those who want to just go have fun, has been that some of the most intelligent book smart types have been the most challenging to get to fly well. And some of the most bass akwards, illiterates could actually fly (basic grass roots barnstorming) really, really well.

All opinion of course!

Take care, Rob

Having said all that, all the seat of the pants hyperbole and conjecture drive me nuts as well if the user can't connect the dots of what they're actions vs what the outcome will be.

As an example, I have said before that many are the folks that wander in to Idaho , take a course in the 'canyon turn' and now are convinced that they can now 'turn an airplane about itself' 'bring the tail right around' etc.... I don't intend to delve in to how to best escape that situation, I've been on record to say that if you find yourself there, turning an airplane was not your weak point. My point is, none of those people ever really know how much real estate they are burning (typically around 600' ) and almost always, they have no idea what the space looks like while in flight. Misjudging a turn in a confined space by 600' is the difference between what could have been a controlled crash, and a spectacular smoking hole....

So yeah... I guess we've both lost our minds.

Take care, Rob

I very much agree that turning is not the weak point for those who intentionally fly in canyons, Rob. Our weakness was/is getting paid to do some interesting flying. Back to back and getting a fully loaded airplane turned onto a target 50' from where we left the target field (35' back in the Pawnee days) is a pretty efficient canyon like turn back. Just not as dangerous because if we are going to miss we can level the wings and bail out. And GPS technology has made the race track pattern workable without a lot of logistical support for flagmen or the drama of finding a toilet paper flag that went down into the crop. And putting a bigger engine on the front makes no real difference. They will just give you a bigger load.