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Bob Grimstead
Unregistered
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 Posted Monday, May 23, 2011 @ 11:01 AM
Hi Guys,
OK, so it's pretty much a contradiction in terms, but Donald brought up this subject on another thread, so let's open it up to general discussion..
That earlier thread was http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=ViCv8C5vBjvL42b65llIDqcXyA&forum=18&thread=794 and in it I gave my general advice for short take-offs.
Some more Fournier-specific stuff now...
NEVER try flying out of a short field in a standard, 1200cc Rectimo Fournier (R3 or RF4D).
Rectimo said their engine produced 39 horsepower, but it didn't.
35 to 36 hp is all you can expect, and then only on an ISA day (pressure 1013HPa and, much more important, temperature just 15°C)
So DO NOT BELIEVE THE TAKE-OFF AND LANDING DISTANCE FIGURES PUBLISHED IN THE HANDBOOK.
With 83mm cylinders & pistons (the 1400cc engine) you actually get 41 to 42 hp, and short field flying becomes a possibility.
Note, I only said POSSIBLITY.
Flying my 1400cc HDO off bitumen, and in still air, it gets airborne in little over 150 metres (say, 500 feet) and once the wheel is up and locked, it climbs at 600 feet per minute.
Flying any Fournier off grass about doubles its take-off run, and that goes in spades for a 1700cc RF5 with two aboard.
Our airstrip is a little less than 400 metres long (say, 1,200 feet) but we keep the centreline grass VERY short (about one inch if possible) so that we can safely take off.
Then we have to choose very carefully which direction we go, because there are 40-foot power lines across one end.
With all small airplanes (Cubs, Champs, Luscombes, Vagabonds - all those lovely little things with small Continental engines) and with most Volkswagen-powered airplanes, it is the obstructions that will get you.
It is often possible to lift off in 100 to 200 metres, but you don't accelerate to climbing speed until another 200 or 300 metres have gone past, which can make things extremely hairy when flying from a 400-metre strip.
And anything of a headwind will help enormously.
So, those are your four important considerations, the distance to the first obstacle and its height, the temperature, and the headwind component.
Anything much of a crosswind, especially from the right, can make you open the throttle more slowly, and cause you to make several rudder and aileron inputs, all of which cause both aerodynamic drag and a side-force (more drag) on your wheels.
So, there is a lot to think about.
To put this into perspective, Matt & I both have 1400cc motors.
Matt has hundreds, maybe thousands of Fournier hours, having been a professional Skyhawk display pilot for several years.
He has flown my Champ, Maule, Turbulents and several other aeroplanes in and out of my airstrip for 25 years.
He carefully and critically watched my operation from my strip in my Fournier.
We trimmed the hedge at one end, and chainsawed the small trees in the next field at the other end until they were below the runway's surface.
And yet he waited more than six months, until precisely the right conditions prevailed, before flying his RF4 into my strip for the first time.
Even now, having each made perhaps 100 departures from it together in the past 12 months, we very carefully assess the wind, check mow the strip's centreline if we are in any doubt of the grass length, thoroughly brief for emergencies, pull our airplanes to the VERY end of the strip (tails in the bushes, I kid you not).
Donald, you are quite right, it is vital to practice many take-offs from a strip of intermediate length before trying to fly in and out of your local farm strip.
First, pace it out (understanding that one pace is not a metre, but more like 80cm) counting the paces in both directions to allow for changes in pace length due to slopes etc.
Then pace out your target strip and compare those lengths.
Compare the lengths and densities of the grass crop on both strips.
When practising, vary your techniques and judge, not your lift-off distances, but your distances to clear fifty-foot trees.
Finally, when you do fly into this short strip, make sure the conditions are cooler and with a more favourable wind than when you practiced.
And get in a couple of practices on the way to your destination.
Having done that, you will be surprised at how very easy the actual operation is, and what huge and unexpected margins you have.
The corollary to that of course, is that if you don't do those things, you might well frighten yourself, or worse.
Go ahead, take your time, and you will be surprised at what a great sense of achievement you get when you finally do it.
Maybe you will save yourself some money by basing there in the future!
Yours, Bob
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Donald
Unregistered
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Posted Monday, May 23, 2011 @ 04:30 PM
Thanks Bob, thoughtful and informative as always.
I've flown in and out of a few tight places and I'm happy on grass but since my goal is to base at the local microlight strip I have to be confident that I can do it every time. I'm not sure I've ever done any repetitive thing in my life with a 100% perfect success rate so I have no intention of going at this rashly.
Tightest airfield I've been into is North Ronaldsay in the Orkney Isles. I went in on 21 which is published as 330m (314m TORA) and I reckon I almost left a tyre mark on top of the perimeter wall on the way in so keen was I to get maximum landing roll, but we made it both in and out OK. If you know Orkney you will know there are no tree height obstacles to worry about and I just had to make it over the wall.
I not infrequently use a farm strip not too far away which is 660m and I can get in and out on about half of that, even when going off in the uphill direction, but I've never measured and marked the strip for accurate figures.
The tightest field I've ever gone into was a farmer's field near Whitby for a WX related precautionary landing. I stepped the field diagonal at 300 paces and like you I reckoned that to be considerably less than 300m and knew it would be a challenge. On that day factors against me were:
(1) I was returning from France and the plane was heavy with camping gear, charts and flight guides etc;
(2) the field was uphill, quite steeply at the lower end but rounding out to the crest just before a slight drop to the boundary hedge.
Factors in my favour were:
(1) the grass was short;
(2) the ground was dry and firm;
(3) the boundary hedge was the only take off obstacle;
(4) there would be a decent into wind component as I came up over the top of the hill.
Living where I do I have Sparky Imeson's book 'Mountain Flying' which gives a method of evaluating whether or not you have a chance of getting out of some patch you've gone into and it is that you pace the strip and mark the half way point or note a feature you will be able see from the cockpit. On the take off run if you have 70% or more of required flying speed by that midway point then you will get off, but if you don't you won't but you have half the field to abort and stop before the fence. This calculator is purely for ground run and says nothing about obstacles on the climb out which have to be figured separately. Well I just had a low hedge to clear so I reckoned that would be OK but I upped the margin to 75% flying speed for the halfway point. (I factored a flying speed of 48kts, not my stall speed of 38kts.) Like you, I went down to the very bottom corner, got out and pulled the tail right in as far as it would go. My first attempt was not to fly but to see what I got at the halfway. A smidgeon over 75% so I went back down to the corner, got out and pulled the tail right in, strapped in and went for it. She came out, we cleared the hedge but not by a whole heck of a lot and I wouldn't want to be doing that as a routine.
The local microlighters tell me their strip is 340m. They say they've used a survey wheel on it to get that figure but I don't believe it and nor do my non-microlight friends. 340 yards maybe. I've paced it both ways and I reckon its about 300m useable. I've stepped out the same distance at a nearby grass strip and I can get in and out by my mark but as I said before there's almost no margin for error. Mitigating factors are that the strip and surroundings are flat, it's not much above sea level, the surface is pretty firm and there are no climb out obstacles other than the waist height post and wire fence around the perimeter.
My RF3 has a 1400cc engine but I would be lying to you and to myself if I claimed she was producing all the power a book figure would suggest but she does seem to go quite well. Going back to my last flight test in 2009 my initial rate of climb from 1000ft was 750 ft/min and after having had the magneto serviced last year which gave be a higher static RPM it might now be slightly better than that. Furthermore, I live above 57N, that's Alaska to the hosts of this board, and while we do have nice weather, sometimes we even think it's hot, really we don't have to worry too much about high ambient temps sapping our engines, props and wings.
So I'm going to experiment with this and see if I can work up to going local. I'm not sure it would save me too much money other than in fuel costs to and from the airport but the saving in travelling time would be wonderful opening up the possibility of 'on-a-whim' after dinner evening excursions and the freedom from the UK's airport security checks and annoyances would be priceless. Watch this space.
[Edit by Donald on Monday, May 23, 2011 @ 04:32 PM]
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Jorgen
Unregistered
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Posted Monday, May 23, 2011 @ 05:23 PM
Thanks to you both for a systematic and thoughtful write-up of an important subject. You've got a very good point with the half-way mark, Donald. Many claim that's the only safe way to operate out of grass strips with not-so-beefed up engines. A possible sugggestion based on Bob's and your reasonings; if you up the margin from 75% airspeed to beeing airborne at the half-way mark you should have sufficient distance left to accelerate to safe climbing speeds before the hedge/powerlines/treeline etc. Using a halfway (or similar) mark has the additional advantage of factoring in other important adverse influences that might not always be obvious, such as moisture.
A friend has a 550 m strip that is normally a breeze to fly in and out of with the 4, he cuts it often and there are no significant obstacles. One day I sensed I didn't accelerate as fast as I was used to and I chopped power early enough to abort safely. The strip were shadowed by trees and the dew + some of the nights rain persisted in the shadows, which made the ground roll much slower. I was very much helped by the plexi window in the snail, a very good "gear-in-or-out" indicator but also a sensitive "moisture indicator", I did notice the spray which helped me realize what was happening. Next attempt I did where the strip was sunlit and had no problems.
I think it makes sense to include a "when do I abort"- point in your take-off checklist to be mentally prepared for chopping power if you need to.
May the 4's be with you/ Jörgen
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Bob Grimstead
Unregistered
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Posted Monday, May 23, 2011 @ 05:39 PM
Hi again Donald,
You are obviously going about this in exactly the right way.
But first, to everybody, I must apoogise for being an idiot.
I should have started this post under 'Flying' and not under 'Miscellaneous' where the Fournier vid clips post just happened to be.
My sincere aplogies, and if you're new to the Forum, I hope you found this using the search fuction, 'cos you sure ain't going to find it any other logical way.
Anyhow...
Donald, even in your usual temperatures and winds, 300 metres is very short, even for a 1400cc RF4D.
Is there any way you can perhaps make the centre of the upwind fence frangible? (ie, if you hit it, it breaks and not your lovely aeroplane).
Even cutting a couple of strands and adding fuse-wire or string or something else breakable might save your Fournier.
When our strip was 360 metres I was very, very reluctant to fly the RF4 from there. That's why we had it lengthened.
As you suggest, we always pile a heap of grass cuttings at our halfway point as a rejected take-off marker.
I have not yet had to stop from there, and I'm not sure that I could come to a complete halt, but I should hit the fence at low speed, rather than falling down the bank and into the river at near take-off speed, which would severely damage both WGN and me (my fragile back particularly!)
The trouble is that, if all your take-offs are always marginal, you will defineitely have an accident one day when not absolutely everything is perfect.
I know what my good buddy Matt would say, 'If there's any doubt, there's no doubt.'
Please do be careful Donald.
For floating around on a lovely evening, there's nothing like a high-wing microlight.
Why don't you just buy a share in one of those already based there, and accept the drive to your Fournier on those days when you want to make longer flights?
I'm just trying to come at this from all angles (thinking laterally as Edward de Bono would call it).
Take care out there.
And we haven't even started to talk about minimum airstrip width and the pitfalls of catching a crop with your wing-tip.
Yours, Bob
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Donald
Unregistered
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Posted Tuesday, May 24, 2011 @ 02:55 AM
Hi Bob, and thanks again for the considered response
I agree that 300m is very short. I don't think it's impossibly short or I wouldn't even be thinking about this, but yes, it's short and really I'd like another 100m for comfort. If it were even 360m as your's was originally I'd probably have been in by now for I believe my RF3 is capable but the part I'm not so sure about is the nut on the stick.
I doubt it's practicable to make the far fence frangible. The surrounding pasture is grazing for cattle, not crops. The better course of action would be to see if the landowner would let us extend the length. One of my friends with a 90hp Cub has already been in and out without drama. For me, another 50 or 60 m would probably start to make it workable. Another of my friends who also would like to go there wants another 140 - 150m before he'll entertain the idea but that may be too much to hope for.
But to return to my original question about whether you always take off with the tailwheel down and your reply, I backtracked through this board to find something I'd seen and wanted to look at afresh, the clip in the opening post of this thread: http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=M84bgEaAj65FHF140YHRgk1wUG&forum=12&thread=705
Steve appears to use your technique of holding the tail low but with the wheel not touching while Joe keeps the tailwheel down for longer yet they both get off the ground in 24 seconds or so ( I timed Joe's run from when his tail wheel left the rough). You don't quite see Joe's actual lift off and it might be at 25 seconds rather than 24 but close enough for there to be little difference. By comparison, in your own takeoff clip which started this whole topic your time to lift off was around 14 seconds. I have two takeoff clips of my own shot from a digital camera mounted on the baggage compartment frame where the bouncing stops after about 13 seconds.
[edit] In light of this topic I've just been watching your YouTube RedHawks Sussex Stream Takeoff and while it's not really possible to determine when Matt lifts off, possibly after about 14 seconds, your own ground run lasts about 13 seconds. Interestingly it takes you 26 seconds to overfly the end of your strip and since you are travelling much faster over the second half than the first you're actually using a lot less than half the 400m strip length for ground roll.
In the seed thread to this topic I wrote "I have always raised the tail within a couple of seconds of opening the throttle and my impression is that the fuselage goes almost horizontal…" Speaking about this yesterday with one of my friends he confirmed that impression, that my tail lifts positively and the fuselage goes pretty much level, so that's my baseline. But I think I'm going to have to buy or borrow a video camera so that I can properly analyse what I do and what benefits, or otherwise, different techniques give.
One last observation on this is that my RF3 is not heavy. It's not loaded with mods and additions, no long range or auxiliary tanks, no alternators or transponders or panel mount avionics or gyro horizons or nav and strobe lights. Can't quite say the same about the pilot, though.
[Edit by Donald on Tuesday, May 24, 2011 @ 05:39 AM]
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SteveBeaver
Unregistered
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Posted Tuesday, May 24, 2011 @ 06:47 AM
Some comments on that video:
1) The grass was longer than it looks, and very wet, hence the soft field technique of keeping the tail very low. It was a very draggy surface
2 ) Yellow a/c has 1400CC, white/red one 1200, but they both had the same prop at that time.
Steve
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Donald
Unregistered
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Posted Tuesday, May 24, 2011 @ 10:55 AM
Thanks Steve, it does look heavy going. In fact the tailwheels almost look as if they're running under water. Looks like you have plenty runway length, though.
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SteveBeaver
Unregistered
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Posted Tuesday, May 24, 2011 @ 12:02 PM
The field is in the flood plane of a river, and is underwater for some part of most years, including right now to the tune of close to two feet 
http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=butler+ohio&aq=&sll=40.163219,-83.133476&sspn=0.009035,0.020471&ie=UTF8&hq=&hnear=Butler,+Richland,+Ohio&ll=40.597108,-82.430098&spn=0.008977,0.020471&t=h&z=16
The runway is more than 3,500 feet long with just a low barbed wire fence at the far end.
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milnerd
Unregistered
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Posted Thursday, May 26, 2011 @ 08:13 AM
It may be a dumb suggestion...but how about putting a strategically located dirt berm close to the end of the runway that would at least get you over the fence if you do duff it and end up too slow and too late to abort? (Think Sea Harrier ski jump). There is a grass airfield near me in New Jersey that has three gentle humps in the middle that are only a foot or so above the level of the runway. On take off you definitely feel the first one making you light on the gear and the second one heaves you into the air a good 10mph slower than you would normally expect to lift off. It is then quite easy to hold it in ground effect and accelerate. It worked especially well with the big, heavy,somewhat underpowered Max Holste Broussard. The nice springy gear gave you an extra boost on the bump too. I once had a frightening experience in the Broussard on a short uphill 2200' runway where part way through the take off the wind switched to a tailwind (due to a thermal I think) and I no longer had distance to stop but the airspeed wasn't increasing either. It was a long few seconds with the R985 firewalled and the trees looming in the windshield!
As a worst case insurance policy you only need to clear the 4 foot fence. By the time you got there you would be so close to having enough speed that a 2 foot high ramp would easily catapault you over the fence. You would then have the option to can set it down in the next field on the other side and get it stopped, or if you can keep it in the air, just keep going. The dirt pile would be close enough to the fence that there is no chance you could clip it on landing without taking the fence out first.
Dave
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SteveBeaver
Unregistered
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Posted Thursday, May 26, 2011 @ 11:34 AM
Here is another idea:
See http://www.jpl.nasa.gov/jplhistory/captions/jato-t.php
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Bob Grimstead
Unregistered
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Posted Saturday, May 28, 2011 @ 10:49 AM
Hi Guys,
Great photo Steve, and you don't often see Porterfields, even in old photos.
Some folk have thought our smoke pods were some kind of take-off assistance. I guess they never stopped to think what might happen if one didn't fire!
You know Dave, that's a very good idea about that ramp.
As well as boosting Donald over the fence if he doesn't quite have flying speed (or if there's a sudden drop in the wind, a plug misfires, the magneto starts to act up, there's moisture in the fuel or carburetor icing, unexpectd drag from grass clippings, or any of the other myriad unexpected things that only ever occur when you're making a marginal take-off) it will prevent him getting his head sliced off by the wire fence (cheese-cutter) on the upwind boundary.
At our strip we have a drop of four feet down to the next field, and the fence is on the lower field, so that's no issue for us (going down hill).
Going uphill, we will either duck under the power lines (there is just enough space -- double the Fournier's height and double its wingspan) and yes, I have done that in my responsive little Turbulent, but never in a Fournier. Otherwise the hedge will stop us abruptly. Unfortunately that would write off the RF4, but its pilot should live.
Some other clips you should look at and time Donald are the ones I took when our strip was 'only' 360 metres long (or 60 metres longer than your proposed destination). http://www.youtube.com/watch?v=L9oL-oZ7k20 and http://www.youtube.com/watch?v=AEOmqOvSg-Q and http://www.youtube.com/watch?v=kXoUpaoQ57o
You will see there is much less margin on these take-offs, not so much because the strip is now significantly longer, but much more because the new, extended length is on ground twenty feet or more higher than the upwind threshold. So we now start our take-off run ABOVE the height of the far trees
Other factors I've forgotten to mention...
Since we are almost always going on aerobatic sorties, we only ever carry fifteen litres of fuel out of our airstrip (that's three gallons for our transAtlantic cousins) and there is never, ever anything else on board... no dipstick, no chart, no rags, no dirt, and certainly no tools.
That is also true of those older film clips.
And I haven't even mentioned the strip's mown width.
We used to have five feet clear off each wing-tip .
Then I saw Jorgen's RF5B and increased the clearance to two metres (seven feet) on each side.
I would regard that as an absolute minimum.
Do you know what happens if you catch a wing-tip in the crop beside the strip?
I always presumed you would be dragged gently into the crop, perhaps at an angle of thirty degrees, and maybe get a bit of propeller erosion or the odd scrape on your cowlings.
I now know that hitting a crop with your Fournier's wing-tip will rip open its belly as the tailwheel is torn off its mounting.
That's kinda long and difficult (not to mention expensive) to fix, so we've paid our farmer more money to have a wider strip.
That's just one other consideration for Donald and anybody else considering a short field take-off in their Fournier.
Did I mention the surface condition?
It needs to be pretty smooth for that small mainwheel.
You also want a high typre pressure (for minimum rolling resistance).
And before you do it, you might be wise to raise up your aeroplane (using an engine hoist) and check your brake is not dragging.
Also that it is properly adjusted, so that it will stop you promptly if needed.
There's alot to consier.
Happy flying.
Yours, Bob
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Donald
Unregistered
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Posted Sunday, May 29, 2011 @ 07:23 AM
Thanks all. RATO bottles might work on a metal Ercoupe but I don't fancy the idea under my wood and fabric RF3.
Ski jumps? Hmmm, that sounds a good idea as a last chance, save-my-neck option but it's not something I want to be relying on to get out the field. The excitement of every take off, assuming there was more than one…or even one, would be just too much to bear.
But Dave also writes about gentle humps that helped the Broussard out of his New Jersey strip. Most grass strips seem to have a few of these, often barely visible, and I've frequently gotten airborne by massaging a 'loft' from one, courtesy of nice elastic bungee suspension, into a takeoff. So, say experimentation suggests my RF3 ought to be ready to fly after 250m, perhaps a strategic hump there might work wonders. That's not to say there couldn't be the 'last chance' ramp at the fence too in the event that everything went to hell at once.
This is all food for thought, well, not the RATO bottles, but I have no intention of being reckless with this. If I roll my RF3 up in the fence and assuming I walk away from the wreck, where do I get another? I probably can't, so if after proper evaluation I reckon I would need this kind of assistance to get out of the local microlight field then I'm not going in in the first place. It's as simple as that and it's what has kept me out so far.
If our crappy weather would clear up and settle down I could start to look at this. The joys of a maritime climate.
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Jorgen
Unregistered
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Posted Sunday, May 29, 2011 @ 05:40 PM
| Quote: |  | | If our crappy weather would clear up and settle down I could start to look at this. The joys of a maritime climate. |
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Amen- we got just the same here. Donald, I think it might turn out not to be such a grand idea to piss the Icelanders off with all that financial collapsing business, now they've fired up another volcano!
In the old days, they used bungees to launch gliders on to dynamic soaring sites. Fourniers are gliders, aren't they?
http://www.youtube.com/watch?v=gZucjDMIJ9A
May the 4's be with you/ Jörgen
[Edit by Jorgen on Sunday, May 29, 2011 @ 06:47 PM]
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Donald
Unregistered
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Posted Saturday, June 4, 2011 @ 01:58 PM
I'm a convert.
Despite the poor weather forecast today was really quite a good flying day so I went off to begin my evaluation of short field technique. I reckon my pace is equivalent to about 80cm or 0.8m so after flying in to my practice field I paced out the lovely field of buttercups and daisies and noted markers at various locations up to my target take off run of 300m, 375 paces.
Using my first attempts at Bob's tail-off-the-ground-but-held-low method I was astonished to find myself airborne at the 175 pace marker! That equates to 140m! I've never flown off in anything as short as that.
Tomorrow I'm going to go along to the local microlight field, by bike, and walk it again to review its condition and to corroborate what I think is it's length, but this is encouraging.
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Donald
Unregistered
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Posted Sunday, June 5, 2011 @ 05:03 PM
My visit to the local microlight strip this morning equipped with notebook and GPS revealed several things of interest.
First, the grass strip has been realigned a little which has allowed it to be cut tighter into one corner of the field so the useable length, allowing for tail behind me and the need to climb over the far fence, is probably now around 320m instead of 300.
Next, they have cleared a concrete roadbed for use as a hard surface strip, about 30° off the grass strip direction and with a length maybe around 280m but with the possibility of being extended by a little over 100m to around 400m, perhaps even more.
Lastly, the guy who founded the strip has a two seat, high performance weight-shift machine and I gather he finds the grass strip a little neat for it so he tends to operate from the hard surface. For his own benefit he has already been in discussion with the landowner about lengthening the grass strip as well as the concrete track. All this is good and makes me hopeful.
A quick comment on my last post when I estimated my shortfield takeoff run, out of a strip with grass long enough to be full of buttercups and daisies, at around 140m. The ruler tool in Google Earth measures it at 141m! I think that's pretty damn good and is almost exactly half of what I used to take at the same strip. It's also not a heck of a lot different to the 130m written in my Alpavia Flight Manual.
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Jorgen
Unregistered
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Posted Sunday, June 5, 2011 @ 06:05 PM
Nice to hear ou are beeing thorough and meticulous about it, Donald. Just be sure to try it first time with as many factors working to your advantage as possible.
May the 4's be with you/ Jörgen
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Donald
Unregistered
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Posted Friday, June 10, 2011 @ 05:54 PM
Today I got in some short field practise and found that I could certainly get in and out again within my target field length of 300m. With my digital camera set to movie mode and mounted on the cockpit side pointing along the starboard wing I could capture my previously paced-out markers as they went by, so while the movies are not great and hardly riveting viewing they do let me time and estimate where things occur.
Pretty consistently I got off the ground in 12 seconds from a standing start. Perhaps more relevant was I got airborne earlier than my previous best of 140m. It varied a little but it was definitely before my 140m marker went by and my estimate is somewhere around 125 - 130m.
The other side of the equation I also had to verify was the landing. That varied a little more, dependent as it is on nailing the landing point and ranged from about 180m to about 140m. That's not landing roll but distance in from my marker for the start of the strip.
Conditions weren't flat calm but they weren't flat calm the last time either, there was about 7 kts of wind down the runway but I was sufficiently encouraged to go look at the microlight field where the wind wasn't lending a helping hand. I'd fly the pattern and I'd throw it away if it didn't look or feel right. Even so I can now tell that I have landed into and taken off from the local microlight field, both without taking a fence with me. Going in I used just over half the field length and coming out almost exactly half.
OK, it can be done and I'll do it again and thanks to Bob's short field technique it's a lot less marginal than it might have been, but I'd still like another 100m. However, I am given to understand that might just be possible.
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Bob Grimstead
Unregistered
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Posted Friday, June 10, 2011 @ 07:20 PM
Hi Donald,
Very well done!
Your meticulous, step-by-step approach paid off, and I'm delighted to hear that it did so.
Obviously, like us, you'll have to accept that there will be days that you just can't fly from that strip, perhaps because of the wind or other weather, or more likely because you're just not feeling 'on the ball' enough. We'll assume here that Fourniers never develop faults!
Great stuff, and I hope you have many years of successful operation from your local strip (preferably lengthened, of course).
Yours, Bob
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Donald
Unregistered
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Posted Saturday, June 11, 2011 @ 03:59 AM
Thanks Bob, couldn't have done it without you.
Anyway, my short strip landing was just the start of what I hope will become a relocation of my RF3, and you are, of course, right when you say that there will be times when I just can't use it. C'est la guerre.
To return to a more general consideration of why your short field technique works, I've been thinking about that and have come to these tentative conclusions:-
With my former technique of raising the tail so that the fuselage went pretty much horizontal I would wait until I could feel she was about to fly then I'd ease back and off she'd come into a good positive climb. In retrospect that alone probably indicates that she was already on the front side of the drag curve. If I looked at the ASI at all it was just a quick glance for confirmation as I was about to unstick, but really it was done by feeling her 'buoyancy'. Even then the ground roll wasn't for a lot longer than about 13 or 14 seconds so I think that method let the aircraft accelerate fastest but because the wing would be at a low angle of attack she needed to cover more ground to get the lift.
Conversely, tail-off-but-held-low puts the wing at a higher angle of attack so although the acceleration may be slower due to higher drag, she's ready to fly very much sooner, and I'm still doing it by feel. We know that even sitting on her main and tail wheels she's not in a stall attitude so flying off at a shade less than that attitude doesn't endanger the take off by pecking at the stall. Sure, she's a little on the back side of the drag curve but not very far away from the transition and a couple of seconds gentle handling of the stick and we're clear.
That's where I am with this but as always I'd love to read what others think of this. These developments show to me that this old dog can still learn a new trick so I'm open to modifying my view of why this works.
Donald
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Bob Grimstead
Unregistered
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Posted Monday, June 13, 2011 @ 06:01 AM
Thanks Donald, although I have to say at the outset that this is not 'my' technique, but Matthew's.
We were both taught the 'conventional' fuselage-level taildragger take-off method that you describe, and we both still use that on runways which are not limiting (hard or grass), also for formation take-offs of course.
But, making lots of take-offs from short grass strips, many years ago Matt decided to experiment, to see if he could find a repeatable way to make the shortest possible take-off in any tailwheel type. He established that this works for most, of not all the tailwheel types he then flew, from Turbulent to T-6 Texan/Harvard.
Some years later he convinced me his method was preferable for short strips by getting me to fly overhead and observe in my Champ while he used the different techniques in my Maule on the field below. Believe me, watching such a demonstration is a very powerful persuader.
Since then, I've always used Matt's 'tailwheel skimming' technique for performance-limited take-offs.
Obviously your wing generates lift even at very low airspeeds, but it stalls because that lift is way exceeded by the aerodynamic drag.
But there is also the wheel drag to consider.
I reckon that lifting the small tailwheel, which rides low in the ground due to its small footprint, significantly reduces the wheel drag, while having the wing at its greatest feasible angle of attack provides a little lift to raise the main wheel(s) out of the grass a bit, thereby minimising that drag too.
It seems that this wheel drag reduction is greater than the aerodynamic drag increase from the greater angle of attack, although this is merely an empirical observation, and we have no true theory to back it up.
As an addendum, when the grass gets really long and we’re flying a three-wheeled taildragger, we’ve found that lifting one main wheel out of the grass shortens the ground run, just as you would lift one float out of the water in a performance-limited floatplane take-off.
Just another tip. That’s what all this grey hair is for.
Maybe see you at Husbands Bosworth?
Yours, Bob
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Donald
Unregistered
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Posted Monday, June 13, 2011 @ 03:31 PM
Bob, wherever and whoever it came from it works and I'm delighted to have been introduced to it.
That small diameter tailwheel must have a hard job climbing out of the hole in the grass so, yes, picking it up must reduce the drag significantly. However I hadn't considered the progressive lightening of the load on the main as the wing carries more and more of the weight, but logically you must be right. Perhaps with the wing being both low to the ground and at a positive angle of attack we're benefitting from a ram air ground effect too.
I plan to make the Husbands Bosworth event so with luck, and if the weather plays nice, we'll meet and you will find that my hair has gone beyond grey to white! I'm looking forward to it.
Donald
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