Ozprey new build

[thevon]

I'm retiring my Ozprey and have got some new cores and fuse from Gerard to build a new one. I've started pottering with it and have glued the roots, and using my angle grinder (!!) have cut a deep trench and glued in a full length 5.5mm carbon tube spar. Not a bad job if I say so myself. Since the wing's higher in the centre the trench is a lot deeper there.

I'm trying to make it a simple build, fairly light, but very bouncy/durable. The full-span centred spar will be a big help. I've also marked out curves to fit a pair of quite thin 2.5mm fibreglass rods, curved towards the nose, with one directly above the other.

This kit is the last of Gerard's "old" kit. He's currently working on a revision with a pre-cut full span spar slot which will make life lots easier.

I was hoping to make do with what I have in the shed, and not buy anything, but I'll need to get some aileron stock, or some thick sheet to shape some. I'd like to try this one with wider ailerons than last time.

I'm planning not to use filler. Going to lightly Goop the whole thing so the Profilm will stick well. Then a few thicker coats of Goop around the LE's and tips.

Also I'm planning to put the Rx and beeper in the wing this time, and just the batteries in the nose. (Like the Reaper). I'll again use the balsa tail fin idea with the boom slid into a coreflute plate, stuck on with double sided tape. Works very well.

I'm so impressed with my faithful Ozprey - I reckon it's the funnest Shorncliffe plane I've flown. Having had one I know what tweaks to do (such as the C/F ribbon spars along the nose). Such a great tough little plane that is pranged and pranged and keeps flying with very little work. It's such a stable and well behaved flyer, and when you drop it into a dive, it's quick! Had to get another one.

[Vanders]

Andrew, why no filler, does it normally add much more weight?
Are there any posts around regarding the tail in the coreflute design?

Saw one of these Ozpreys at SC last week, looks like a fun plane!

[atmosteve]

Hi Andrew, I thought your Ozprey was a real sweet bird down at SC, nicely balanced, so I'm going to try one of the first of the next generation shortly if all goes well.

Going to borrow your tailfin design, and i have a number of other build ideas to incorporate into it too, one of them being a pull apart design, maybe. Thinking of going a different route with the goop, need to experiment first.

Please keep us posted, looking forward to another of your well composed build posts, i always learn something new from them.

[thevon]

Thanks guys. Vanders, there's a bit of info about the tail fin method in the modded bat thread - way down the bottom - it's a huge page!!: windsock.proboards76.com/index.cgi?board=general&action=display&thread=1189079175&page=1

Not planning to do a big build thread this time. It takes soooo much time! But I'll try to get a few pics.

[thevon]

Actually I've changed my mind on the covering method. I've been following Predator's talk about using thick clear iron-on coverings. He's really rapt with it as a fast and strong (and ugly) and cheap method.

See www.rcgroups.com/forums/showthread.php?t=790302

Ezza and Swoopdown and Kahnx have all imported some, and reports so far are good.

I was waiting to try it on some crappy cores sometime. But I've decided to get stuck in and have a go. So I'm buying some of the Ballisticover heavy from one of them (not the super-heavy Burrly) and will try it out on this Ozprey. It's a good size and shape for it.

I'll update when I've got it.

[thevon]

This is the whole wing with a 5.5mm tube spar PU glued in, and the 2 thin rods curved in and glued with CA.




This shows the wingtip closeup on top



and this shows the wing front-on. You can (just) see how the 2 thin fibreglass rods are directly laid one over the other. For maximum rigidity it's important. After the centre 5.5mm tube spar was glued in, it felt very bendy compared to the Reaper, for example! But once these 2 rods were glued in it immediately feels vastly more rigid.

[atmosteve]

That flat spar arrangment is intersting. But going by the Bat's torsional strength it sure must work along with other factors.
Hey that looks how my vice PU sets for the tube spar.
Andrew are you considering building any Horner into the wingtip foil? Have been playing with the idea in theory lately.
EDIT; I will be doing a standard build to start with though.

[thevon]

What's Horner?? It does have some washout ( I think that's what you call it) built in ... ie the angle of attack of the tips is lower, which probably helps with its stall resistance.

[sean]

Hey Andrew, Horner tips are a bit like the tips on my Skua and Reaper, but they are a bit different. A Horner tip is supposed to decrease the drag caused by wingtip vortices.

[atmosteve]

It has some pros and cons apparently, for the most part a curved or crecent wingtip wont effect lift and turn performance at regular to high speeds because that part of the wing provides practicaly no lift usually, depending on many wing design variables, so some wingtip curve may help reducing inherent drag.

But it can have some drawbacks too, again depending on those design variables. When a wing approaches a stall, thats when having a full chord/square and full (chord tapered) wingtip can provide lift that the rest of the aerofoil, from the chord root out, cannot, so i'd be careful giving some wingtip curve and Horner to a model such as say a fast Bat, but the Ozprey seems a very solid performer that might possibly benefit from some in terms of speeding around turns and gaining speed, that would be the only reason to try it.
There seems to be some variation in the interpretation of what Horner, or Hoerner design is!! I'm hardly an expert, just read stuff from time to time and used to experiment a lot with design (with varied success). There are guys here that might really know their stuff.



www.aerodyn.org/Drag/tip_devices.html#hoerner

selair.selkirk.bc.ca/aerodynamics1/drag/page8.html

www.rcgroups.com/forums/showthread.php?t=584087&highlight=Horner+tips

This is a bit heavy, some interesting stuff from the archives though;
ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19870013194_1987013194.pdf

Its hard to get good web info on the subject, but chances are the local public library has books on aeromodelling aerodynamics.

[thevon]

In this instance because I'm trying out the stiff film (which doesn't go around compound curves) I'm happy with it being square ... will be easier to cover. I've liked the way the Ozprey flies for Shorncliffe so I'm hoping it retains its characteristics ... don't really want to experiment with it.

[windsock]

Been away from the forum a bit, busy with getting ready for the baby - 5 weeks to go. But I've been lucky enough to squeeze one more glider build in before the baby.

I've been working with Pete from Wowings to develop the latest OzPrey. This will be the forth prototype that I've made. There are some slight changes to the airfoil & wing layout (positive changes - so far) but one of the major changes is the full-length pre-cut spar tube. It makes such a difference compared to the previous prototypes.

I took it for it's first test flight yesterday and I'm really happy that it's retained the overall flight characteristics of the Ozprey design. I will post some photos soon on the site.

Gerard

[thevon]

As mentioned above, Karl (Predator) has been testing and promoting “The New Stuff” on RC Groups, as a new covering for EPP planes. I've been talking with him about it and watching his thread on developing it. He has primarily been experimenting with coverings around 250 micron thick. I played around with coverings of 125 micron (also called 5mil which Karl's calling Burrly Light) and also 80 micron. When I initially tried it on EPP I melted foam, and I gave up!. I’ve been using it to cover fins very successfully. It’s comprised of a tough clear gloss front, and a layer of heat activated glue on the back. When ironed, it’s totally transparent.

But as you can see by Karl's thread he's been having success so I decided I’d cover the Ozprey with New Stuff. Swoopdown sent me some samples of his Burrly and the Ballisticover Heavy (BCH) to try. I ironed some onto EPP. Both are very thick, similar weight, and hugely strong. The Burrly is very stiff, whereas the BCH is just as thick, but more “floppy”. It seemed to me that the BCH wouldn’t add as much wing stiffness, and would follow the bumps more. But it would be more rubbery. However I was surprised, when I scrunched it, the BCH seemed to hold stay wrinkled more than the Burrly.




So I ordered some Burrly from Swoop, but meanwhile I tried covering a paperback book-sized bit of EPP with the 125 I already had, more carefully than last time. It worked. I was very impressed at how stiff it is.

The Burrly was still a few days away, and with the 125 looking so good, I decided to take a leap and have a crack covering the Ozprey with it, rather than with the Burrly. So I did! I gooped the LE and tips and TE and centreline. The film was pretty easy to put on. Easier than Profilm really, but since it’s clear you’re not worried about neat straight edges or gaps!! You have to be careful not to stop with the iron or it will melt your foam, but it’s do-able. The Gooped bits seem more resistant to melting. I've found it useful to have a dry and wet rag handy, and iron a section quickly then rub it with the wet rag to cool it faster, so it bonds. Best to crease along the folds/ bends first, then iron, then press to set the glue.




I covered the elevons in the 80 micron film, which is all you need. Excellent stuff.




When covered … well, it’s ugly! Hard to get used to it looking like it’s not covered at all! I'm pretty impressed. Monstrously stiffer than Monokote. The all-up-weight when balanced was 732gm.




This arvo after being totally calm a huge S/E came thru! So Gerard, Tom and I met at Woody Point. It looked pretty scary for a maiden – a gale force wind! But I did anyway. After a bit of CG adjustment, it flew perfectly.

Gerard had his new version Ozprey there and really, the performance of the 2 planes was identical. It penetrated great, performed perfectly. We climbed to great heights and had dive races, and did “pylon races” over the trees on the beach. Nothing in it. I was totally happy with mine. We had various wing touches … such close flying! But then in front of the big pines, Gerard hooked my wing and the plane flipped into a dive and it went arcing at great speed through the trees downwind, and into the solid concrete corner of a hi-rise! Whack! Bits flew and I thought, well that’s the end of that model. But the only damage was that it tore the fuse off (easy) and a put a little scrape in the film!!

There’s no doubt, this stuff is tough. It won’t puncture and tear easily like tape or monofilm. For Shorncliffe type planes, I’m sure you wouldn’t need film any thicker than 125. But I also have to point out that this plane has a 5.5mm central full span spar, and 2 thin fibreglass rods one above the other, curved. One benefit of Karl’s thick Burrly is you could build with no spars.

NOTE: yes, I am going to put some colour on it! Using strips of coloured tape - that's the simplest way as paint etc doesn't stick to it well.

[ezza]

Great report as always Andrew. Enjoyed. Glad to hear about the crash resistance as I never got a chance to find that out!

I really like this covering. Here is a link to a rebuild I have done to my old Reaper using Burrly; www.rcgroups.com/forums/showthread.php?t=821598

I found that putting it on with low heat seemed better. I had the iron set just over 200 degrees. One of the best things is that you don't have to use strapping tape. ;D

Eric

[atmosteve]

Thanks for pics and words Andrew, we dont have much in the way of laminating businesses up here, but i will have a bit of a hunt. Failing that there is always the serious goop treatment etc for Ozprey.