Another Reaper!

[thevon]

You can get the opposite of adverse yaw too. Greg's Starling Pro the other day doing corkscrew rolls, and you could see it pull the inside wing back when you banked. I found it had almost no down ail and plenty of up. The design of the ailerons was funny and they were being restricted from down movement by their wood cutout so we trimmed it back with a knife and hey presto - it got us the down ail and the straight rolls too.

[sean]

Despite what I said in the last post I really like planks too! They're so pure, they have only what's needed for efficient flight and no more -- two wings, a fin, and the CG in the right place! In the past I've considered adding a rudder to help dial out the adverse yaw, but it'd spoil the simplicity I guess. The thing is it's not just adverse yaw at play, there are also pitching issues caused by slight differences in aileron throw, tiny inaccuracies in aileron movement end up having a big effect, and I believe the TE reflex needed to make a plank fly also contributes to the awkward rolling behaviour. I use my throttle stick to control elevator trim on both my current wings, the elev movement from throttle full forward to throttle full back is almost imperceptible, a fraction of a millimeter I reckon, but it has a big effect in flight.

Carl told me he'd post the kit today, so hopefully its on its way now... I went for the normal fuse option cause it's cheaper, and I won't be using it anyway, unless I have a sudden change of heart! The pine nose will be a pain to build cause I only have hand tools at home but I want something a bit different so I'll persevere.

Sean.

[sean]

The Reaper kit arrived on Friday. It looks pretty nice! First impressions weren't good because it came with no box, just a bit of bubble wrap and tape around the parts! But I guess the parts are tough enough so everything survived the trip. Second impression: holy cow, those spars are huge! They look absolutely awesome, and there's a massive alloy rod that slips in between the carbon spars at the centre section -- the whole unit is super stiff. The tail boom is the same as the wing spars with a slot machined in the top to fit the fin.

The wing cores are accurately cut with no blemishes, although the TE isn't perfectly straight or square, but that's being pretty fussy. I took a photo of the wing root and superimposed some aerofoil sections over it in Photoshop and found that Carl has used the PW51 section on this wing, The PW51 seems to be the plank racer aerofoil of choice right now and the shape of these cores appear to be an almost perfect reproduction of this section. This wing is going to be a goodun!

The ballast tube is well engineered, the lead slugs appear to be cast inside brass tubes, which is nice, it means you don't have to touch the lead when handling the slugs. The finish on the slugs needs a bit of cleaning up with a file to remove burrs, I found without being cleaned up they don't slide in and out of the tube too easily.

I'm still going with a wooden nose but have been playing round with ways to build a break point into the nose. I want the nose to break off from a heavy hit without inflicting damage on the rest of the airframe, and then be easy to fit back on. I've got a few ideas on how this can be done but need to refine them before I have an effective design. I'm going with a longer tail too, in the hope that it will improve yaw tracking. The wooden nose will also be longer than standard to balance the longer tail and to generally look sleeker. The wingtips will be pointier than the standard Reaper which is just for aesthetics, I really like the pointy wingtips on my Bat and to my surprise they've stood up to many big hits with barely a mark. When finished this thing isn't going to look much like a Reaper! But I've been wanting to build a plank in this way for a while now, and I really bought the Reaper because it looked like a good kit to hack to these specs. I nearly bought an M60 a couple of months back for this purpose but after learning about the Reaper I realised it'd be better for the job.

I'll upload some photos soon!

[ezza]

The spars are quite impressive aren't they.

I thought the ballast slugs were a little tight as well. You don't want to drop or dent the tube as the slugs would not slide in.

Winds were pretty light down here but, still managed some ds laps with the Reaper.....you will like it!

I look forward to the photos/build.

[sean]

Here's a few pics for starters:

This shows the PW51 section (in red) superimposed over a photo of the Reaper wing root. The PW51 was generated in Profili 2, and it matches the Reaper wing almost perfectly! I'm not sure, but I believe the Drongo uses this section?



These two are a preview of how it should look when finished. These are from a model made in 3D Studio Max... wouldn't it be nice if you could get that kind of finish for real A glass version would be quite desirable I reckon

[ezza]

Sean,
That 3D model looks more like a weapon! Very cool.

Looks like the same airfoil as the Drongo.

Yeah, relaxing is definately the key, let it do it's thing, just like on the frontside. If you are ds'ing these tricky places....you will have no problems at a decent site. A good site is about 80-90 percent of the battle. They are soooo hard to find. The one I flew today was the first time I have tried it. I am sure nobody has done it there before. I found it after talking with a truck driver the other day. The only problem is that it works in an Easterly, which usually aren't that strong. The hard part is finding a good, high, sharp ridge, with minimal trees, facing SE or NE, near the coast, with easy access and a good LZ.

[sean]

Hey Ezza, the other problem is finding somewhere where you have the owner's permission! There are some amazing looking hills about an hour inland from where I live (they're near the township of Somerset), really tall, unusually pointy for this region, with no trees and face NE. I reckon they're the best looking DS hills I've seen. But, they're all on private land!

[ezza]

Yeah, most of the best spots are on private land. Often it is hard to tell who owns them as well.
The easy ones are where a road runs along the ridge top. That way you can launch from the road and fly 'over the the land' = no trespassing.
Somerset, yeah, the area surrounding Brisvegas has alot of potential ds sites I reckon. Wish I lived closer.

Eric

[thevon]

Sean I was thinking you could just have the wooden nose butt-joining onto the chopped EPP nose stub (just with say 1cm of EPP projecting in front of the wing). Sort of like an engine nacelle mount, but with a long nose attached instead of an engine! That way when it gets a bad whack on the pine nose, the EPP can distort without the pine cutting into the wing.

[sean]

Hey Andrew,

I've decided I'm going to use the EPP fuse just where it holds the carbon tail boom, and then build the nose around that using 8mm timber epoxied together (easier to accurately cut than one big chunk, using basic tools). Once shaped I'll glass over the whole shebang and mount it to the wing with 5mm nylon bolts. That way the bolts should shear in a big hit, and the wings can be removed for transport. I posted a message on RC Groups to see if anyone had experience with solid wood noses, and one fellow answered saying he's used a glassed solid wood nose on one of his slopers and its almost indestructable

Sean.

[ezza]

Hey Sean,

I reckon just make the fuse out of one block of wood......for simplicity. It should be bullet proof. An old or broken baseball bat would be a good starting point. I would even consider gooping the wing and fuse together, like the epp fuse on a standard build. This eliminates any 'wiggle' between the two, and is ultra sleek. It only lets go on a really nasty crash, and then just re-goop back together. I guess it depends if transport is an issue?

I like the wingtip and fin design, fuse looks great as well.

I saw your post on rcg. How do you do all these beaut drawings etc,?

[sean]

Hey Ezza, you put across a convincing case Transport's not an issue but it would be nice if it could come apart to take on trips, but its certainly not essential. So you reckon if I use goop (or Shoe Goo) it'd separate in a big crash? If so it sounds ideal.

How do I do the drawings? I'm a graphic designer by trade so these piccies are very quick for me to do

[ezza]

Sean,
I have only had mine seperate once. After a lot of landings, it had a little bit of 'wiggle' between the fuse and wing. Then in a flat but extremely hard (104mph) crash the wing and fuse seperated. It was not a perfectly clean seperation (small pieces of epp stuck to wing and fuse) but it keyed back together perfect with goop. Seems to be even stronger than before.

I suspect it would be the same with timber.

[sean]

OK, sounds like it might be the way to go. Although I keep changing my mind so I guess it will depend on how I feel on the day...

A 104mph crash eh! Must be a pretty tough bird.

[sean]

The build so far:

This pic shows the basic wings. The cores are very nicely cut with a round channel for the carbon spars. My modified wingtip shape is marked on the foam with a texter. In ths pic the spar is below the wing, and the ballast tube is above it. For those who like numbers (like me ) keep reading, for those who don't skip to the next pic ). The span is 1500mm, the root chord is 210mm, the claimed aspect ratio is a healthy 8.07 (but if you use the formula span squared divided by area is comes to 8.3) and the taper ration is about 0.65 and as stated before the aerofoil is the PW51. These specs all point to a well designed high performance wing with good handling.




The spar: "Grand Slam"... yeah baby!




The spar joiner... solid alloy.. more than adequate for the job!




Ballast Tube with ballast. All up weight is about 300g.




The pine nose is progressing. I decided to go with one solid piece of shaped pine for simplicity. This all seemed like a great idea until I actually started shaping my chunk of 30mmx65mm pine... it was at this point that it really dawned on me how minimal my tool collection is. After considering a trip to the local hire centre to pick up some choice power tools, I decided to go for broke with basic, mostly hand, tools.

Step one was sawing the timber to the basic shape with a hand saw, then using a sanding block and files to get it close to the right shape. Once this was done it was necessary to make the slot for the carbon golf shaft tail. For this I used my trusty dremel with a small sanding bit, which worked quite well but did take some time. The slot is quite rough and much larger than the carbon, but I'll use PU glue or maybe epoxy with microballons to glue it in place.





This pic shows my rough pine nose next to the stock EPP nose for comparison. Mine's longer and much thinner (ahem). Carl apparently has two new EPP fuses you can choose from that both look a bit sleeker than the one in this pic.




Here is the rough nose with the tail shaft in place.




The first bench flight, complete with paper fin. ;D The carbon tail boom needs to be shortened.




Time to start rounding the nose. First I drew some contour lines to shape the nose to an octagonal shape.




After wittling away the corners with a stanley knife, then a rasp, a bit of a go with an orbital sander (which wasn't much good thanks to only having a fine grit disc) and finally a sanding block it came out quite nicely, and only 133g. Less than expected!





As I write this the nose is drying after a couple of coats of primer. I was going to fibreglass it but that seems like a lot of bother for little return so I'll see how it goes with only an enamel spraypaint finish. At least that way repairs will simply require some filler and a respray. It seems very strong and I'm sure the nose will rip away from the wing before it breaks. I can see chunks being dug out of the timber if it lands/crashes on something hard (like a rock), but that would be a pretty easy fix.

All up it took maybe 6 or 7 hours to shape the nose ready for painting. Not too bad but it would have been less than half that with a bandsaw, sanding disc and sanding belt. It was pretty satisfying doing it all by hand though.

Now its time to start on the wing, and once the primer is dry on the nose I can check for low spots and get the shape just right with some filler and more primer.

Sean.