Take off distance in j4xx

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Re: Take off distance in j4xx

Unread post by BenSmit » Sat Feb 27, 2010 11:54 am

I will do some rework on the graphs

I used the POH on the P166S to compile the graphs and I know it goes over top a bit but the Piaggio is very sensitive to all these factors and I am sure it influences the JAb. On a normal runway you can discount many of these factors but when it is a critically short take off, with weight and high DA you will need this
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Take off distance in j4xx

Unread post by kbimu2 » Sun Mar 14, 2010 9:17 pm

Hi All, I'm new to the Jabiru scene. factory is busy building my J430 - ZU-FHR. Cant wait. I have 100's of hours on Cessna 400 twins, twin turbine time and even a little time in a Boeing 727 and I think the J430 is a wonderful aircraft.

Anyhow on the subject of TO distances (roll), yes we must have density altitude (altimeter press altitude or actual field elevation and temperature, wind and velocity and distance to reach 50 foot height), without this information we could really hurt someone. We also need the runway surface condition.

Also does anyone have a J4xx or J250 with glider towhook? I'm very keen to evaluate the Jabi for use as a glider towplane.

Cheers,

Keith
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Re: Take off distance in j4xx

Unread post by ZuluBen » Tue Mar 16, 2010 11:00 am

Welcome Keith

Inteesting how many of the Heavy Metal drivers like to fly Jabbies for fun!

The POH is written very "sterile" for certification purposes, we are collectively gathering more accurate details, and as expected found that the POH figures could by and large be bettered upon.

You are correct though, the max all up Jab is a very different animal from the 2 up Jab :wink:
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Re: Take off distance in j4xx

Unread post by BenSmit » Fri Mar 26, 2010 6:37 pm

Ok guys, I promised to do more work on the graphs, so I have a little play time and I am working the numbers.

Problems: If I take the POH numbers and plot a straight forward TO graph, not allowing for wind or slope. then I cannot reproduce a chart that corresponds to our tests. I have used Phillip and Francois's data at Brits, the FAVV data as well as Ben and Hennie's data.

The physical tests correspond well but the POH data is VERY conservative. For instance: If I take a random Test

EYJ, DA of 6500, AUW of 600kg gives us a distance of 550m measured.
Working the POH data it gives an estimated 984m IMPOSSIBLE!

The POH says : Sea level take off is 400m (assuming MAUW) Then they add a factor of 1.3 taking it to 520m. WHY? what is this factor?

They further say add 115m for every 1000ft of PA (I am assuming it would equate the same factor for 1000ft of DA as well as the relationship between DA and PA is constant), Surely it cant be a straight line increase ad infinitum?


Unfortunately all our tests were conducted at around 6500ft DA, we will need some guys to test at sea level
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Re: Take off distance in j4xx

Unread post by BenSmit » Fri Mar 26, 2010 7:27 pm

So much for POH

I have used all our test data and have worked the fomulae according that. I flattened the data out because there were discrepancies in the test data, - assuming technique has a lot to do with it.

I also added a 750kg band for the newer models.

The first graph is for take off weight and DA only with a flap setting of 15, and standard prop

So erring on the conservative side, this is what our test data says: Check you own data and comment please.

Can the coastal guys run some tests please to validate some of the data, if it does not correspond then I have to adjust the values
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Re: Take off distance in j4xx

Unread post by ZuluBen » Fri Mar 26, 2010 7:35 pm

Thanks Ben, good work between your studies! =D>

Can confirm your 750kg at sea level data, flew out of FAGG last Saterday at MAX, could not believe how quickly she popped up.

Outeniqua pass had a bit of fog in it, so 2 lazy orbits over Fancourt saw me at 4500ft to proceed over the mountains.

Compared to our tests at FAVV where the hill at the end of the runway grew into a mountain... :shock:
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Re: Take off distance in j4xx

Unread post by BigglesSA » Fri Mar 26, 2010 8:39 pm

Ben, this is brilliant =D>

Ben, refer to your first graph, it was exactly the same problem I ended up with. Hence my question around the "flat" increase rate! I must say that the second graph may just as well be as close as it can get to what we are looking for. I would suggest that we all print this, and before every takeoff look up the fore-casted value and compare with the actual distance achieved. My prediction is that your graph will be very close to the actual figures that will be achieved. If we can all do this for a couple of weeks and provide you with feedback on our findings against your graph you can fine tune if needed (I doubt).

There is one test that I would like us to do in the future to complete what I would think the process. I would like to see the same plane at the same weight at the same altitude at different temperatures (DA). Previously we tested the planes all at different weights. Now keep the weights the same, but vary the temperature!!!

The way I suggest achieving this would be to get 4/5 planes together mid summer at say FAVV again or maybe this will be a good excuse to go visit Buzz-Jan in the Karroo.(In fact his place lends itself perfectly for test like this!!!! Sleep over, tests from first-light till finished, no rush to get home) Hi komma nogga deng!!!!!!!!!!!!

1. Load to 550KG
2. Load to 600 KG
3. Load to 650 KG
4. Load to 700 KG
5. Load to 750 KG (Only A2-UFO that really regularly flies at these weight, but maybe worth including) ZB sien jy kans?

First two (two for control purposes) runs at 6h30 with each plane. Then 9h30 another two runs each. 12h30 two, and again at 14h30 and 16h30. This should get a nice even spread increasing and decreasing effects of temperature (DA). Now filling the planes after each run, leaves the only variable in each plane to be the temperature.

The results would then show the increase/decrease of distance for each plane (Same models, closely the same performance) with the increase/decrease in temperature. If QNH would stay the same then giving a good DA result. If not maybe convert the results to a standard.

What thee say??????????
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Re: Take off distance in j4xx

Unread post by BenSmit » Fri Mar 26, 2010 8:54 pm

I would suggest we log 1 a/c and 1 pilot so we can get consistent figures in terms of specific a/c and pilot technique

The small errors we will flatten out by adding a safety margin.

We can then refine the figures by running the same test (at the same times and temps and weights) with a different a/c (Control figs)
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Re: Take off distance in j4xx

Unread post by BigglesSA » Fri Mar 26, 2010 9:09 pm

BenSmit wrote:I would suggest we log 1 a/c and 1 pilot so we can get consistent figures in terms of specific a/c and pilot technique

The small errors we will flatten out by adding a safety margin.

We can then refine the figures by running the same test (at the same times and temps and weights) with a different a/c (Control figs)
One plane one pilot make sense, but would that not take forever?

Using more planes at the same time (same condition) doing two runs each would that not give more "even" data when one consider both (or even three) runs into a single average for the runs in that time bracket for the specific plane???

Some pilot briefing and technique synchronizing exercises the day before can also help. I tell you loading/unloading those planes between runs is one heck of a job, as Phillip!

If it was posiable, I would even suggest rotating the pilots, but unfortunately my insurance would not like that :shock:
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Re: Take off distance in j4xx

Unread post by BenSmit » Fri Mar 26, 2010 9:46 pm

Sure, what I meant was that we need to log each a/c separately so we can get consistent figs, later we can combine the data but the tests can be run at the same time in different aeries
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Re: Take off distance in j4xx

Unread post by ZuluBen » Fri Mar 26, 2010 10:08 pm

5. Load to 750 KG (Only A2-UFO that really regularly flies at these weight, but maybe worth including) ZB sien jy kans?
long enough runway and we will be OK :wink:

Was not very far from there, around 700 kgs out of Gerrits place the other weekend...
Luckily he had that huge cliff to the left to drop into :lol:
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Re: Take off distance in j4xx

Unread post by BenSmit » Sat Mar 27, 2010 9:03 am

Well the test figures show an exponential increase as you get to 700kgs and up (for the newer models), this means at between 700 and 750, on a hot day you will need 800m, so best you have 900 avail.

I am still working the figs an I am expecting, in real life to see the take offs do on avg 10-15% better than the graph. It used worst case scenario and a margin for safety. I have not been trying to get to minimum distances, rather safe distances. Figs based on tar surface

I don't want someone wiping out because he used minimums and then something happens requiring more distance.

I am now working on wind component, but this is tricky cos we dont have test data. I will need an excelleration test zero to 60kts, windless. Anyone flying this weekend, please time your excelleration to 60.

Once we have that, we can start working on runway surface and slope
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Re: Take off distance in j4xx

Unread post by BenSmit » Sat Mar 27, 2010 10:53 am

Guys, remember the figures are adjusted to 50ft, not rotate point.

Oh yes, Keith, thanks for the input and welcome, keep it coming
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Re: Take off distance in j4xx

Unread post by BenSmit » Sun Mar 28, 2010 9:32 pm

Guys

I have reworked the graph, it has the same numbers but is more user friendly, so I will soon post a new one to check. When you guys fly, please try to get some acceleration times for 0 to 60 with no wind
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Re: Take off distance in j4xx

Unread post by BenSmit » Sat Apr 03, 2010 9:30 am

Hi Guys

Ok here is my latest attempt. I have added wind but have to stress we need to test as these figures are only calculated and not tested (the wind part)

I still need some accelleration data to accurately calculate this. Please remember the stop watch next time you take off to give me accelleration 0 to 50 or 60 with zero wind
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