A 17" Hand Launched Glider, designed by Mike Chapman

 

 

 

 

 

The Beginnings.

Mick, the local Scout leader, approached me about the possibility of putting together the ground works for a Hand Launched Glider building and flying project for his local Scout group. At that time I though the Harry Johnson glider would make a suitable model and accordingly built one. I really didn't like the look of it but continued through to the flight testing stage. Maybe it's my flying style, but I didn't like the Harry Johnson glider, I decided to start from scratch and design a 'universal' glider.

Design

Firstly I wanted a glider that would be immediately interesting from an aesthetic point of view, I felt that a model that looked like a toy wouldn't have long lasting appeal. I also wanted it to look like the competition models that I intended to demonstrate. It had to be uncomplicated (no polyhedral or d/t's), carbon booms were ruled out due to their cost but would be suggested as an option.I also considered the possible flight characteristics of the model. The launch phase of any HLG is critical so I wanted a model with a forgiving nature. I've had very good results indoor with the Polka Dot design and considered that the vee dihedral would be an ideal starting place, I used short moment arms to give the glider a bouncy forgiving flight performance.

I drew up the design and called it Thermal Scout.

Materials

Mick was quite happy to leave all the pricing and acquisition of the materials to me and I therefore ordered most of the tools and materials that we required from Flight Hook (UK) some items such as non-shrinking Dope and modelling knives were bought locally.

The initial pricing suggested that the project wouldn't cost the Scouts more than 3.50 each ($5.00).

A Prototype

I built a prototype exactly to my plan, two coats of non-shrinking dope were given, the scales showed that it had an all-up weight of 16 grams. An evening test session at the local park lasted for about an hour, flights with Thermal Scout were mostly above 35 seconds and the best was 49 seconds. I had thought before the test session, that upon completion I would probably have to redesign part of the model but that wasn't the case. I immediately built another Thermal Scout for myself.

Building

To save the Scouts time and balsa wood I made templates to mark out the wing / tail / fin shapes onto the wood and roughly cut out 25 of each.

I made up about a dozen sanding blocks from the left overs of the 3/16 sheet. Modelling knives were a problem as the cost prohibited me from providing one per scout. The same was the case with the balsa planes, I had bought one plane for the Scouts and I also took along my own .

I had tried to anticipate the problems I would encounter with 25 Scouts all of whom had no experience of handling Balsa / modelling knives and reading plans. But after the first session with the lads (now 26 of them) my head was in a complete spin. The simple fact is that they will all start building together and all (some more than others ! ) will want help in some form or other and the questions come thick and fast. A two hour building session seemed to pass in about 15 minutes !

The availability of a blackboard was very useful, any anticipated problem areas were illustrated using coloured chalks. These were changed as we progressed through different stages of building.

Before each session I used the blackboard for a 'pep' talk to clarify the forthcoming building techniques.

There were some accidents during the building stage, all of which I was able to rectify by gluing or reshaping, in a few cases I had to issue new blanks.

The biggest surprise to me was the amount of non-shrinking Dope that the lads were able to make disappear ! - where it went I don't know - but I needed twice as much as I had anticipated !

Flying the Thermal Scout

It took three evening sessions to complete the gliders and on the fourth evening we went along to the local sports center to fly the models. A quick distribution of plasticine (modelling clay) and a demo of how to trim the glide and they were away. (I had provided diagrams but no one seemed to have read them !)

The quality of the flights varied but everyone had a model that flew and all the Scouts had showed great enthusiasm throughout.

The Scouts were particularly enthusiastic when I demonstrated my Hybrid competition model. I can see now the field full of circling and whirling Scouts, yelling and shouting as they chased after it - they didn't realise it would circle around !

In total I think we built about twenty six models and that was from materials intended for twenty. If you should have the opportunity to organise such a project, do so, it's good fun and promotes the sport of aeromodelling, also in this case each scout was awarded a Craft badge.

Finally I also gave the lads a pile of my old modelling magazines to use as a 'library' - you never know !

Mike Chapman Nov' '99.


If you would like a Thermal Scout plan

Go to the Download Page.


Building Instructions

Start by cutting out a ‘kit’ of parts.

Cut out the wing in one piece - plane and sand it to shape before cutting at the centre and then rejoining with Epoxy (50mm dihedral each tip).

Cut out the tailplane and fin, sand their edges to about .5 mm thickness, leave the centre 4 mm of the tailplane untouched (flat) as it will be glued to the underside of the fuselage.

Cut the fuselage from 5 mm balsa sheet (hard), cut it accurately as there is incidence built into the wing seat. If you measure the wing seat position (on the fuselage) you will find that the rear of the wing is 1 mm lower than the front.

[More experienced builders will perhaps like to build up the fuselage as follows:- From the bottom up - 1.5 x 5mm spruce strip, 5 mm x 5mm hard balsa strip, the upper part of the fuselage can be Medium/Soft grade balsa. This method will result in a strong/stiff/ light fuselage.]

Before sanding the rear of the fuselage to an oval section, glue (Cyano’) the spruce strip to the bottom of the fuselage. It is shown on the plan as 2 x 5 mm but 1.5 x 5 mm will suffice. Round all the edges of the fuselage.

Join the wing to the fuselage with Epoxy glue.

Before fitting the tailplane sand the bottom of the fuselage rear end to accommodate the tail tilt (3mm). Use Cyano’ glue to attach the fin and tailplane. Ensure that the fin is vertical.

Cut the finger grip from 5 mm balsa - bevel and taper to fit the underside of the right hand wing - ensure a good fit between the wing and fuselage as this will impart added strength to the wing / fuselage joint.

Finish the model with 2 to 3 coats of non-shrinking dope, sand with fine ‘wet and dry’ paper between coats.


Test Flying

Build your model exactly to the plan, the scales should show an all-up weight of around 16 grams. A visit to the local field (with long grass) will be required for testing, calm evenings are the best times for first flights.

Using Plasticine stuck to the nose, an initial balance point at around 50% of the wing chord should be established. Check also that neither wing is heavier than the other - add a little plasticine tip weight to balance if necessary. Test glide using shallow gentle hand launches, add or remove Plasticine until a flat shallow glide is achieved.

Once a flat glide is established - ensure that the model is also turning to the left. If it is not then gently bend the rear of the fin to encourage a left turn. When all is correct Thermal Scout should be launched up at an angle of about 40 degrees and to the right of the wind (in your face). Launch by trotting forward a few steps and use a whipping arm action to launch.

Happy flying,

Mike Chapman.