Post by sean on Aug 12, 2009 18:01:28 GMT 10
Thought I'd post some pics of my new DS foamy design.
The pics above show it with some lead taped to the nose for the maiden.
As usual the hardest part of the design was coming up wth a name that suited the plane... anyway I've christened it the 'Brutale' (pronounced brew-tar-lee).
This plane was conceived to be a lighter knock-around version of my Hummer design. In the end it came out quite different to the Hummer - it shares nothing in common other than the general layout.
The wing is made from four EPP panels, which allows for a double-taper planform. The hinge line is straight to allow full span elevons and only two servos (Hummer uses four servos). The wing has quite strong taper on the outer panels. This does a number of good things - it allows the wing root to be wide and deep, making it easier to build a stiff strong wing. It reduces torsion loads at the tips. It also moves the centre of lift for each wing half inwards reducing bending loads and aiding directional stability. The downside of strong taper is the potential for the wing to be prone to tip-stalling. The planform and elevon shape were designed to minimise this tendency. This was my main concern with this design prior to maiden - that it might be a bit prone to dropping a wing. Thankfully the flight tests showed it to have absolutely no tendency to do this - the stall is very benign - it just does that classic 'hyperstall' bobbing up and down.
The aerofoil is a mildly modified PW51. Mods were made to improve inverted performance (at a slight cost to upright performance) and make it easier to build a stiff wing.
The spar is a 4mm carbon rod top and bottom, with a second 4mm rod doubler that goes about 1/3 span. Covering is 'burly' laminating film with no strapping tape. I bagged the elevons and fin in 75g kevlar, and also wrapped kevlar around the drag spar. The elevons are hinged with silicon. Built like this the wing is very stiff under bending loads - it feels at least as stiff as my Hummer which uses four golf shafts for spars. The burly does a good job of making the wing quite stiff in torsion, however the wing is nowhere near as stiff in torsion as the Hummer - the 4mm carbon rods contribute nothing to torsional rigidity whereas the 4 golf shafts in the Hummer make it incredibly stiff in torsion. Despite this there is definitely enough torsional rigity for some pretty decent DS speeds.
I wanted to keep the weight fairly low so it could be flown in a wide range of conditions, but not so light it got knocked around while DSing. It actually came out slightly lighter than expected at 1080g.
There are two ballast tubes in the wing, each one is positioned at roughly semi-span. Having the tubes at semi-span means the ballast won't increase the bending loads the wing experiences while DSing, and adds some inertia to the tips which should help it track straight through turbulence while DSing. Each tube takes about 200g so with full ballast it should weigh around 1480g. In contrast the Hummer weighs 2KG with no ballast!
The fuse bolts to the wing with 1/4" nylon bolts. All the radio gear is in the wing so all the fuse does is hold the balance lead and fin. The fuse is very similar to the fuse on the Hummer except it's a bit fatter. It's made from EPP with a golf-club shaft longeron, and finished with strapping tape and Profilm. I wish I could find something better to cover an EPP fuse... I tried PVC tape which at first looked to work well but heat from the sun affected the adhesive and made it shrink, so I ripped it off and went the old school Profilm path. The thing I don't like about Profilm on an EPP fuse is it gets ratty and the edges lifts up after a bit of knocking around.
I maidened the Brutale today at Brandenburg Rd in a light-medium northerly. A few test throws proved very little - it did what most planks do in test throws - plummet to the ground after a glide of about 3 metres. So nothing for it but to throw off the hill. After the throw it flew into massive lift and started tearing around really fast!! The pace was a big surprise! It needed very little trim and the CG seemed pretty close to ideal. It turned out that I'd launched into a massive thermal, and the lift was never as good again. This was a very good start - I couldn't believe how quickly this little foamy was flying but in the end that turned out to be more the massive lift than anything else... Once the lift settled down I was still very happy with its pace and it was making a satisfying howl. The handling proved very benign - it didn't stall once (just bobbled with full aft stick). The rolls are axial and true, tracking is good, and inverted performance also seems quite good. In the strong lift landing speeds were very high but once the lift dropped landings were quite easy. This plane was designed just for knockabout DSing but it proved to be surprisingly fun on the frontside today - fast, docile and quite aerobatic.
Unfortunatey on the first landing I hit some power lines and it toppled to the ground. Damage was very minor, requiring no repairs to keep flying. The only damage was a fold mark in the burly at the wingtip from the tip bending as it hit the ground. Looks like it was a bit of a design fault not continuing the spar all the way to the wingtip (it stops about 3cm short of the tip).
Unfortunately the strong lift subsided and I was left floating around in weak lift for an hour or two. The Brutale was quite happy to do that, though it certainly wasn't designed for such flying.
It's always a good feeling maidening a new design. Really looking forward to trying it on the back.
Sean.
The pics above show it with some lead taped to the nose for the maiden.
As usual the hardest part of the design was coming up wth a name that suited the plane... anyway I've christened it the 'Brutale' (pronounced brew-tar-lee).
This plane was conceived to be a lighter knock-around version of my Hummer design. In the end it came out quite different to the Hummer - it shares nothing in common other than the general layout.
The wing is made from four EPP panels, which allows for a double-taper planform. The hinge line is straight to allow full span elevons and only two servos (Hummer uses four servos). The wing has quite strong taper on the outer panels. This does a number of good things - it allows the wing root to be wide and deep, making it easier to build a stiff strong wing. It reduces torsion loads at the tips. It also moves the centre of lift for each wing half inwards reducing bending loads and aiding directional stability. The downside of strong taper is the potential for the wing to be prone to tip-stalling. The planform and elevon shape were designed to minimise this tendency. This was my main concern with this design prior to maiden - that it might be a bit prone to dropping a wing. Thankfully the flight tests showed it to have absolutely no tendency to do this - the stall is very benign - it just does that classic 'hyperstall' bobbing up and down.
The aerofoil is a mildly modified PW51. Mods were made to improve inverted performance (at a slight cost to upright performance) and make it easier to build a stiff wing.
The spar is a 4mm carbon rod top and bottom, with a second 4mm rod doubler that goes about 1/3 span. Covering is 'burly' laminating film with no strapping tape. I bagged the elevons and fin in 75g kevlar, and also wrapped kevlar around the drag spar. The elevons are hinged with silicon. Built like this the wing is very stiff under bending loads - it feels at least as stiff as my Hummer which uses four golf shafts for spars. The burly does a good job of making the wing quite stiff in torsion, however the wing is nowhere near as stiff in torsion as the Hummer - the 4mm carbon rods contribute nothing to torsional rigidity whereas the 4 golf shafts in the Hummer make it incredibly stiff in torsion. Despite this there is definitely enough torsional rigity for some pretty decent DS speeds.
I wanted to keep the weight fairly low so it could be flown in a wide range of conditions, but not so light it got knocked around while DSing. It actually came out slightly lighter than expected at 1080g.
There are two ballast tubes in the wing, each one is positioned at roughly semi-span. Having the tubes at semi-span means the ballast won't increase the bending loads the wing experiences while DSing, and adds some inertia to the tips which should help it track straight through turbulence while DSing. Each tube takes about 200g so with full ballast it should weigh around 1480g. In contrast the Hummer weighs 2KG with no ballast!
The fuse bolts to the wing with 1/4" nylon bolts. All the radio gear is in the wing so all the fuse does is hold the balance lead and fin. The fuse is very similar to the fuse on the Hummer except it's a bit fatter. It's made from EPP with a golf-club shaft longeron, and finished with strapping tape and Profilm. I wish I could find something better to cover an EPP fuse... I tried PVC tape which at first looked to work well but heat from the sun affected the adhesive and made it shrink, so I ripped it off and went the old school Profilm path. The thing I don't like about Profilm on an EPP fuse is it gets ratty and the edges lifts up after a bit of knocking around.
I maidened the Brutale today at Brandenburg Rd in a light-medium northerly. A few test throws proved very little - it did what most planks do in test throws - plummet to the ground after a glide of about 3 metres. So nothing for it but to throw off the hill. After the throw it flew into massive lift and started tearing around really fast!! The pace was a big surprise! It needed very little trim and the CG seemed pretty close to ideal. It turned out that I'd launched into a massive thermal, and the lift was never as good again. This was a very good start - I couldn't believe how quickly this little foamy was flying but in the end that turned out to be more the massive lift than anything else... Once the lift settled down I was still very happy with its pace and it was making a satisfying howl. The handling proved very benign - it didn't stall once (just bobbled with full aft stick). The rolls are axial and true, tracking is good, and inverted performance also seems quite good. In the strong lift landing speeds were very high but once the lift dropped landings were quite easy. This plane was designed just for knockabout DSing but it proved to be surprisingly fun on the frontside today - fast, docile and quite aerobatic.
Unfortunatey on the first landing I hit some power lines and it toppled to the ground. Damage was very minor, requiring no repairs to keep flying. The only damage was a fold mark in the burly at the wingtip from the tip bending as it hit the ground. Looks like it was a bit of a design fault not continuing the spar all the way to the wingtip (it stops about 3cm short of the tip).
Unfortunately the strong lift subsided and I was left floating around in weak lift for an hour or two. The Brutale was quite happy to do that, though it certainly wasn't designed for such flying.
It's always a good feeling maidening a new design. Really looking forward to trying it on the back.
Sean.