Hand Launched Glider - A summer project

SteveOBHave · 15 Jun 2009 at 21:11

Being something of a lover of all things radio controlled and of things that fly I've always wanted a radio controlled airplane.

I have the small problem of living in a flat in the middle of London so I have neither the storage space nor the space to really fly a decent RC plane. I have also the minor issue of having to save for a wedding so I can't really spend any significant amounts of money on things that are considered by my better half as a toy. As we all know they are not toys but serious experiments in aerodynamics and a tool for learning.

A while ago I bought one of those foam faux RC planes that are shaped like an F22 Raptor and steers by changing the speed of a prop on either of the wings.

One of these:

Through a combination of crap skills and the aircraft being a pig to control I've given up on it and decided to try building my own. Looking around I came across these things, commonly know as HL Gliders (Hand Launched).

This particular one has radio gear in it and as such is a little beyond my means however it does interest me in as far as the design goes. It strikes me as both fairly customisable and also scalable. So the next trick was to hunt down some plans. It turns out that this is a pretty easy thing to find as there is something of a community out there for RC fliers and they seem perfectly happy to share them around.

I found a few on this site: http://f4bscale.worldonline.co.uk/hand.htm and decided to go with this plan:

It didn't seem too ambitious and being made out of mostly balsa I cautiously expect it to be fairly straight forward in construction. I'm going to take some liberties with the design, I will replace the main strut with a carbon fiber tube for some extra strength and am also considering cutting the guts out of the F22 Raptor thing and seeing what happens when you attach some motors to the wings.

Of course this is all extremely experimental and I have never done anything like this before so it might all end up with a poorly sculptured heap of crap that refuses to fly. I'll keep you all updated if you're interested.

SteveOBHave · 15 Jun 2009 at 22:19

Haha thanks - It's not built yet so it won't be flying anytime too soon.

SteveOBHave · 16 Jun 2009 at 08:45

I got started on the project last night. I have a hardware store across the road so it was a relatively easy thing to find most of the essential bits.

Sandpaper
Sanding Block
Balsa
Gaffer Tape
Masking tape
Knives
Balsa Glue
Carbon Tube (off the bay)

The first thing I did was cut out the basic shape of the wing from the plan - the scale is based on the size of the wood really - I wanted to be able to fit the entire wing surface onto one piece of the balsa and then cut it when I had finished sculpting.

After cutting it to the desired size I have marked out the High Point of the wing as a guide for shaping.

My chosen method for the sculpting was sanding with 180grit sandpaper - turns out that it is a ridiculously laborious task and I gave up after around an hour of sanding in preference for using the full length of the large knife blade and shaving thin slices off. I wish I had thought of it earlier as it would've save a large amount of time and copious amounts of inhaled balsa dust.

However I'm getting there and it's slowly starting to take shape. I've marked a grid on the trailing edge to ensure that I'm getting a relatively flat finish without major variations on the surface. One irritating thing that I have noticed is that the wood is slightly warped and I chose the wrong side to start sculpting on for a wing unless I was going for a symmetrical profile. Still this is stuff that can be fixed later.

SteveOBHave · 16 Jun 2009 at 08:53

After a little bit of investigation - it seems that one of these is the way to go - A razor plane. So that is now on order.

SteveOBHave · 16 Jun 2009 at 18:16

Well, another update.

After heading back to the hardware store and getting a MUCH rougher grit sandpaper I was able to make much more impact on the wing. The end result is looking not 'too' bad and considering it's my first wing not a bad effort so far.

Overall it took significantly less time than the initial work. I would say that any subsequent wings that I make will be far less time consuming.

Top of the wing

Profile

Leading Edge

Trailing Edge

Tomorrow I will be cutting the tailplane and finishing the wing.

SteveOBHave · 16 Jun 2009 at 18:25

Cheers - it's deffo getting there - it's quite an interesting project with lots of learning but not too steep a curve.

SteveOBHave · 16 Jun 2009 at 18:37

Ultimately this is the kind of thing I'm going for:

SteveOBHave · 17 Jun 2009 at 09:19

slylittlefox said:
The wing isn't symmetrical - doesn't it need to be?

/noob

It's a perfectly legitimate question and to be honest one that I had to quickly brush up on before answering.

It's probably best to start with the basic theory behind why a wing works and how lift is created.

A wing fundamentally works by causing a pressure differential between the top and the bottom of the wing. The way this is normally achieved is by making the air travelling over the top of the wing travel faster by making it cover a greater distance.

Thiefed from http://science.howstuffworks.com/airplane6.htm

When you get a symmetrical wing you have the same profile across the top and the bottom of the wing and as such when the wing is 'flying' straight on then the air is moving over both the top and the bottom at equal rates thus not creating lift.

So as Khan stated, a symmetrical wing needs to have it's Angle of Attack (AOA) changed in order for it to start creating lift.

This has a couple of effects on the airflow across the wing, firstly it causes a deflection of the air down or up (depending on positive or negative AOA) and secondly it shifts the point at which the leading edge of the wing hits the air up or down having the end effect of making the wing effectively asymmetric again and creating lift.

Clear as mud?

A symmetrical wing has severl uses of which I don't really have application, the most noted of which is improved aerobatic performance, i.e. the wing flys just as well upside down as it does the right way up.

EDIT: Since I am making a glider and it is unpowered I ideally want the wing to work at a 0 Angle of Attack. If I made the wing with a positive AOA then it would introduce added drag and reduce the efficency of the aircraft.

SteveOBHave · 17 Jun 2009 at 19:10

Small update.

I got the razor plane today so I put it to good use and flattened out the bottom of the wing since it wasn't entirely flat due to wood warping. It was a slightly nervous experience because I've already invested quite a bit of time into the wing, I didn't want to have to start again. End result:

The other thing I did was cut out and sand down the tail - it will be a 'V' shaped tail both because the plan says so and because it will be lighter and the less weight on the back the less I will need to balance it out on the front.

I've layed it out in the basic configuration with the carbon fibre tube running down the middle. It's next to a DVD for scale.

SteveOBHave · 18 Jun 2009 at 11:57

YZFAndy said:
I have several gliders and mostly slope fly, using updraft to stay up for hours and no need for any kind of motor power.

Yeah I'd love to get into a bit of slope soaring but because of my current living situation, i.e. in the middle of London, both slopes and storage space are at something of a premium.

YZFAndy said:
A nice bit of care gone into that wing section very impressed but the is a couple of things.
The wing section is very thin which isn't a bad thing but will make it fly very fast.

The other thing is without ailerons and a total flat wing it will equal want to fly on it side as the right way up. Most wings without ailerons will need quite a bit of dihedral in them to come back to a level. You will notice the glider you have picture has a split wing that is a slight V angle. This split and v angle is your dihedral and because of the large wing spans of most of these have this allows you to split the wings in two for east transport.

Maybe look at cutting the wing in two, and having a small v brace to join them.

As you will see with the plans posted at the start of the thread not only does it call for the thin wing section but it also has provision for dihedral. I'm actually thinking of altering the plans a little to make it a double dihedral, one at the wing root and the other further out similar to this as I think it looks a little more graceful than the one the plan calls for:

Cheers for the comments - I appreciate the positive feedback from someone in the know

SteveOBHave · 18 Jun 2009 at 12:06

Monkey Puzzle said:
Looks very elegant.

Yeah it does - now all I need to do is get mine looking like that

SteveOBHave · 28 Jun 2009 at 21:38

Update:

I've done more work on the wing and it's closer to being finished. Weight wise it's quite even and I think airfoil wise it works fairly well. The only thing I can think of that might be an issue is that it's quite thick and as a result possibly heavier than ideally desired.

I've also spent a bit of time sculpting the body of the glider. I'm completely playing it by ear and it's not quite what I am thinking of as a final shape.

It's constructed from 3 sheets of balsa wood glued together. I'm not entirely sure why but it's something that is repeated in plans quite often. Initially I used the razor plane to carve it up and then sanded it to refine the shape. For a first attempt I'm fairly happy with the result but there are a couple of things I need to take into account. One is that there needs to be provision for weighting in the nose, and two that there is provision for mounting the carbon fiber rod into the back of the body. My initial impulse is to take a drill to it but that is still a little further down the line.

So things left to do - I need to create the dihedral in the wing to create stability in the glider which will be a nervous time because I will have to cut it in half. It would be a shame to wreck it.