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Blocks Away

Old 27th Jul 2011, 13:48
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Blocks Away

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Old 27th Jul 2011, 15:34
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Oooops!

Bllllaaaaaaady ell!! - Who didn't do their external check then??!!
Suprised That wasn't noticed during taxi.

AA
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Old 27th Jul 2011, 21:23
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An innovative way of moving the CofG further aft? I don't suppose the airfield operator thought too much of it though, after it left a groove down the runway!
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Old 27th Jul 2011, 21:27
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This shows just how much use these pathetic little tie-down blocks are. For some reason, people seem to think that a few kg of concrete will magically stop an aircraft blowing away as long as said concrete is attached via rope; I bet if you put the equivalent weight in extra fuel into the wings instead these same people would be equally convinced that the plane was less secure than with the blocks

Thanks for sharing, Tony.
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Old 27th Jul 2011, 22:33
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Must admit that was my thoughts as well Katamarino.
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Old 27th Jul 2011, 22:45
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With the ever-increasing cost of AVGAS, moving the C of G aft to reduce Trim Drag (* la Airboosse) was seen by Scroggs Aviation to be a viable cost reduction feature.

Shame about the subsequent crosswind landing!
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Old 27th Jul 2011, 23:24
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Is that a tie-down block, Katamarino? It looks more like a chock to me, but not too clear. Anyone got better pictures.

Either way, a pretty big miss to make on a pre-flight. I'm only a few hours into learning, and I think even I would spot something like that!
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Old 27th Jul 2011, 23:36
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I agree it looks too small to be a concrete block. But back to basics, the C172 wing will produce enough lift, at a certain angle of attack, to lift circa 1100 kgs off the ground at around 60 knots. Tying a couple of hundred kgs of concrete to it will not do anything if the wind is strong enough.

It just gives you an increased level of protection on the usual stormy days in the UK where winds gust to 30 or 40.
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Old 28th Jul 2011, 04:51
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Wow!

When I read about a C 150 having done this with a 50 pound concrete block, I though it was an urban legend. I suppose it could have happened.

For reference, the much older Cessna Pilot's Handbooks specify 700 pounds as the appropriate capacity for a tiedown. I once landed in Manitoba, right after a windstorm had gone through. I saw a dozen or so aircraft on their backs with concrete blocks, and screw in anchors still attached to the aircraft by the ropes, but otherwise utterly useless.
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Old 28th Jul 2011, 08:18
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It just gives you an increased level of protection on the usual stormy days in the UK where winds gust to 30 or 40
Realistically it gives you virtually no protection with anything that a normal pilot can move.

The 700 pounds per tie down is over 300kg per point so your going to strap a ton to your aircraft before its going to do any good. The volume of concrete alone is going to make it interesting getting the aircraft to the tiedowns.

All that Sub 100kg for a tie down is going to do is fatigue your structral load point as it jerks it. It will only make 1-3 knts difference in the wind speed thats required to cause the aircraft to go flying by itself.

The only thing that really works is perm inverted mushrooms installed under apron concrete and once you have them all you do is transfer the failure point from the tether to the bit of rope that you have used to attach the plane to them.
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Old 28th Jul 2011, 08:58
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A lot of airfields in the US use wires that lie across the ground and are anchored to it, the planes are then tied to the wire using tie down rope. Not sure if that is any better?
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Old 28th Jul 2011, 11:06
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A lot of airfields in the US use wires that lie across the ground and are anchored to it, the planes are then tied to the wire using tie down rope. Not sure if that is any better?
We use wires at White Waltham (line 2 and 3) and it's very efficient.
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Old 28th Jul 2011, 11:08
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surprised noone has entered it on the G-INFO picture database yet.......
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Old 28th Jul 2011, 13:07
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Wires are connected to perm mushrooms under the apron and the tape from what I can remember that they used was the same tape as rockclimbers use to attach themselves to their gear which from a distant memory has something like 2 tons working load and 3.5 ton failure load.

Which is completely different to the old shite bit of washing line blue rope that seems to be in favour in the UK.

So contacttower I would say its orders of magnitude better than the UK.
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Old 28th Jul 2011, 13:42
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Just thinking what the result might be if he got a bit dutch roll going!
D.O.
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Old 28th Jul 2011, 13:46
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If you think about it, its no different to banner towing or tugging a glider.

Anyway you can only get dutch roll with a swept wing aircraft.

They had 30-40 lump hanging off the back they wouldn't have noticed, and obviously didn't.
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Old 28th Jul 2011, 14:53
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If you think about it, its no different to banner towing or tugging a glider
I can't agree. A banner, or glider on tow, is much more acting as drag to the aircraft, than directly as weight. The nearly pure weight force (as opposed to drag) of the concrete hanging from the tail would very certainly act to put the aircraft way out of C of G limits, and make it very dangerous, should it have been allowed to stall.

The determination of this is based upon the angle of the "tow" rope. Down = weight, aft = drag. Obviously, both cases have elements of both forces, but clearly the weight is evident as the primary force with the concrete.

I'd say that pilot was very lucky to get back to the ground safely.
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Old 28th Jul 2011, 15:01
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Mad_Jock, you can get Dutch Roll in any configuration of aeroplane - the Chevvron 2-32c for example which is a straight wing microlight motorglider DRs constantly, albeit with too small an amplitude to be more than mildly irritating. The flying flea family all have DR problems, and all are straight wing.

(It is true that some swept wing aeroplanes have or had Dutch Roll problems - the SHAR particularly springs to mind and there's that infamouse Tu154 video...).



At my flying club we had a PA38 tied down to 3 large concrete blocks. In a storm it got airborne on its own and cleared a 10ft hedge. It is widely rumoured to be the best rate of climb ever achieved from a Tomahawk.

G
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Old 28th Jul 2011, 21:31
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I was thinking more of structural loads DAR and as nobody would ever try and land with banner or glider still attached its not really the same. I suppose its how long the bit of string is 30-40kg in a 70 knt wind isn't a straight down force and on the departure roll its pure drag behind the aircraft. Although to be honest looking at the photo the bit of string is very straight up and down.

I would be more worried with it bouncing and it hitting the tail on landing while breaking.

I would have agreeded with you Genghis two years ago until a rather well educated empire test pilot of my aircraft type told me otherwise when I was bitching about the aircraft with the yaw damper U/S. I must admit I got a bit lost half way through the different modes of various divergent oscillations, and which control you belted with a rubber hammer to set them off.

But as you know way more about these things than I. If you say its possible thats good enough for me.

I was very happy with the principle that if the arse waggles and the nose pitches up and down a bit it and its uncomfy it was dutch roll.

Last edited by mad_jock; 28th Jul 2011 at 21:48.
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Old 29th Jul 2011, 04:09
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Hmmm, structural loads;

As I think about it, using an unsuspecting block of concrete at the tail, to balance your aircraft in flight, might well, on the whole, reduce structural loads.

We know that the tiedown itself is good for 700 pounds or so, so we're not worried about loading that. We know that the tail produces a balancing down force at all times the aircraft is in level flight, so if the aircraft is flying level, the loads through the tail boom must the same.

That just leaves the loads carried by the H stab spar, which normally provides all of the down force. Now, the need for an aerodynamic downforce from the H stab, is greatly reduced. So the load on that is relieved!

But to have though of that, I must have too much time on my hands tonight! Back to a bit more work!
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