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Post by atmosteve on Jan 14, 2008 19:57:35 GMT 10
Sean it sounds like your version of the Skua kind of flies how it looks it might fly, the stall induced spin (flat spin- the best!!) sounds like a result of good to rear CG balance with wingtip wash and lift properties, maybe due to your re-profile. It sounds very promising.
Thats one thing i just found with the 8-15 knots (or about that) at Pt Cartwright Saturday also, surprisingly clean and steady lift that let me play around with total ease on the bee, the LZ for a Bee is fairly generous though as even i could catch mine as it floated in from behind. No wonder guys parasail there, Cartwright has a nice mix of features that seem to give a predictable S to E lift.
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Post by ding on Jan 14, 2008 20:00:50 GMT 10
One interesting manoeuvre it can do is a true, perfectly controlled spin! A true spin is where one wing is stalled while the other keeps lifting, causing the plane to autorotate straight down, while airspeed remains low. This usually requires a rudder so was a nice surprise with the Skua. With the Skua it's entered by gradually slowing the plane down, feeding in more and more elev to maintain (or very slightly gain) height. When the plane reaches its stall speed you can see it bobbing back and forth in pitch. At this point, keep the ailerons centred and feed in full up - one wing will drop and the plane will begin to quickly autorotate heading straight down with no aileron input required as long as you keep holding full up. To stop the spin simply release elev back pressure, wait for the spinning to stop and pull out of the dive. I tried this with the Bat a couple of times and it didn't recover, kept spinning to the ground . Also many years ago I deliberately put a powered model into a flat spin but unfortunately was a unable to recover - it kept going all the way to the ground turning it into balsa confetti . Sounds like the plane is going well Sean. It certainly looks great I might get motivated to re-cover mine one day. I might make a couple of points on this that may be of interest to everyone.... the fact that it's spinning with the wings level (this is critical) at full elevator means you have a tip stall. I'd be interested to know if it favours a particular direction or not. If it is consistent you might check that the elevator throws are identical. This can also point to a wing warp or wing weight issue. If it can go either way perhaps putting in some washout on the tip will fix it. If one wing is at all low when performing this type of test you will get an insipent spin. This is caused by the lower tip traversing a smaller arc and therefore having a lower airspeed. Hence, the low wing will always stall first. In full size gliders this is critical and is drummed into students as when landing it can combine with wind shear to make dead pilots. "50 is flying 40 is dying". Wind shear isn't generally a factor in models due to their smaller wingspan. Lastly recovery from spins is primarily a function of centre of gravity. The further back they are the harder they are to stop. Design also plays a factor but CG is the main influence. Re your powered plane..in my experience they are always recoverable if the CG is good. I spent many afternoons getting various planes into lomchevacks and deep flat spins and a combination of controls (principally full opposite elevator, rudder, and varying power) will get the most stubborn plane out. Sometimes it takes longer than you like but
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Post by sean on Jan 14, 2008 20:26:10 GMT 10
Atmosteve, maybe one day I'll pluck up the courage and throw the Bird off Pt Cartwright. With crow I don't think it'd be hard to bring down on the grass patch. Ding, I thought you'd bight on this one . Yeah, I've spun, lomcevaked etc powered RC planes a lot, as well as full size planes and gliders (with an instructor ). With the Skua there's no wing warp or wash-in, if anything there's a little wash-out. I believe the spin is caused simply by having a rear CG and excess elevator throw, enough to get into a deep stall. When held deep into the stall like this, thanks to wind buffets etc one wing is always going to stall first, enough to cause autorotation to commence. A plane held deep into a stall will never keep its wings level all on it's own, but of course not all planes will spin as cleanly as the Skua does with no rudder. Interesting I did the same thing with Pete Loftus' Skua on Sunday - he flies with lots of elev throw so it was very easy to do with his, infact with so much elev throw it took a bit of concentration to not spin his Skua! The plane I spun into the ground was an own design thing, I was about 14 at the time. I never had anything else that spun so easily, infact you could do a perfect lomcevak flying straight and level at full power by just chucking both sticks into the top left corners!
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Post by sean on Jan 28, 2008 12:11:28 GMT 10
Thought I'd update on how the Skua's going. Basically I love it! In the few weeks since it was finished it's had more time in the air than all my other planes' combined. I've thrown it off all kinds of different hills I wouldn't risk my other planes on, used it to test DS conditions on hills I've never DSed before, had it up to about 90mph DSing a couple of times with no sign of flutter (it's surprisingly stable DSing, I think the tail helps a lot there)... and pranged it lots! Amazingly the tail has held up through all those prangs including a number of cartwheels - a couple of collisions with powerlines and some very fast heavy landings on sharp rocks at a spot with no decent LZ.
The only complaint I have re durability is the light density EPP cuts easily - one collision with a powerline at fairly modest speed cut right into the LE - but if I'd used bi-di tape on the LE that wouldn't have happened. A few days ago it was looking pretty beaten up - I gave it an iron, applied a couple of patches and it looks as good as new ;D.
To sum up the Skua - I reckon it's a really good blend of plank and combat wing. Tough, manoeuvrable and easy to land like a combat wing, but faster with decent DS ability. IMO it's definitely not the fastest plank out there but on dodgey sites with no LZ that's a point in it's favour.
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Post by atmosteve on Jan 28, 2008 18:20:18 GMT 10
Thanks for the reports on the model Sean, really starting to lean this way for next foamy, maybe the 1500mm. Sounds like it fits my needs better than the more highly strung DS type models, which i'd be pressed to find a suitable site to fly up here, not much point if i cant fly them on a day trip. Seen some vids of the Skua's, they are nothing Earth shatering BTL, but sure look quick enough to be fun and basically aerobatic enough for someone at my foamy flying level to enjoy and twist about in the sky.
I will be happily pinching some of your and other peoples ideas on the build too. I wonder if WW use the 20Kg/m^3 or the 30Kg EPP? At any rate bi-di on the LE sounds fair. If i'm going to have a crack at some basic DS then it will be needed!
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Post by sean on Jan 28, 2008 18:47:34 GMT 10
Hi Steve,
The 48" Skua uses the 20Kg foam while the 60" uses the 30Kg. Pete has a prototype 48" Skua flying at the moment with extended twin fins - they're a bit bigger than standard and extend about 30mm aft of the standard fins, seems to help the tracking as far as I can tell.
Sean.
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