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GNOTT 39" sport slope soarer

[A New Gnott]

 

Over the years I have made many of the Gnott Slope Soarers. A lovely mild mannered slope soarer that is capable of flight in lights wings through to pretty strong winds, depending on the all up weight (AUW) and has a good aerobatic performance.

 

Indeed, some of my models were particularly light but I always built in the option to add ballast, not much, but enough to improve penetration in windy conditions and allow for more energy retention during aerobatics.

 

It was back in March 1990, when reading one of the many modelling magazines, RC model World, that I came across the free pull out plan of the Gnott. Designed by Arnfinn Lie.

Although I didn't do anything with the plan for a while like so many free plans you acquire, until a couple of friends of mine stationed at an RAF base up in the north of Scotland said that they had built a couple of these models and had some great fun on the slopes. At a later slope competition that I had arranged in South Wales, these models were flown and an enthusiastic crowd gathered and shared their views of how good they seem to fly.

 

Well, it really appealed to me and others and then I remembered the free pull out plan in the magazine. Not wanting to be outdone on having some slope fun and only having larger thermal type gliders at the time, I duly made the necessary aerofoil templates for the wing and went to town creating a nice set of foam veneered wing and started to build. I was used to building from plans, powered models and gliders alike, so turning my hand to making the Gnott did not pose too much of a challenge. The result of which saw me cutting wings for a few others so they could also make one of these.

 

Nowadays I don't watch much Tv,  preferring time in the workshop, but even back then, I spent most of my spare time in the model room than in front of the Tv. Two weeks on I had a nice new shiny solar film covered model ready for a test fly, which was not to disappoint. If I was to be critical, it was a little light but I had a couple of thin pieces of Glider ballast and put these either side of the servos in the fuselage and it transformed the model - what a cracker.

 

Over the years I have made 4 or five of these for myself even my "Midge" model design has roots going back to the Gnott and uses a similar set of dimensions. I have made many sets of wing for the Gnott of the years some resulting in plug-in wings as per the plan, others with a one piece wings. The fuselage can be made to match, raising the wing towards the top of the fuselage so it sits almost on top of the fus.. Indeed, the fuselage design / shape is open to interpretation and change of shape to meet your requirements.

 

 I even tweaked the shape of the fuselage whilst maintaining the critical measurements of wing to tail dimensions etc and the later ones, I stretch the wing to 40" and used an RG14 or RG15 wing section all to good effect.  Recently I let a friend borrow my well used plan to build one for himself.

 

I cut him a set of white foam balsa veneered wings (vac bagged of course....) and I've heard he is putting the finishing touched to his new model. I hope

to get him to give me an update on his experience of building the model and also capture his first impressions once he gets it trimmed and flying on the slopes. and of course I'll bring you some photos.

 

John's New Model

Late 2017, Colin and I were talking about what would be a good aircraft for me to make the next step as a newbie to the slope soaring fraternity. I had already cut my teeth on a Weasel (foamie wing) and was tempted into purchasing one of Colinís second-hand machines (The Solange). Having seen Colinís Midge perform I thought something like this would be interesting as my next model. Colin stated that the Midge design had itís roots in an old slope soarer called the Gnott that first appeared as a free plan in a 1990 Radio Control Models magazine.

Having expressed an interest, the next time we met Colin had a set of veneered foam wings with servo hatches, vac formed coverings, the original plan and build article. Well that was it, a swift exchange of monies and I was the proud owner of this starter for ten.

Post acquiring the wing panels I had a number of decisions to make.


Wing location. Colin assured me that the wings could be seated low, mid or high to suit my preference and/or built as a single panel or in 2 halves. Any of these arrangements would work provided the aerodynamic relationship between wing and tailplane is maintained. I elected to follow the original plan and went for the mid wing plug-in arrangement.
 

Servo location. Colinís wing panels were already prepped for a two servo arrangement so this was a given. However; going for plug-in wings meant a decision had to made regarding the elevator servo location. I decided to mount the servo inverted with an access panel in the lower fuselage skin held in place by countersunk screws.
 

Ballast tube. The plan does not show a ballast tube; however, I decided to fit one across the C of G position which again meant a slight design change and a second access panel.

The build of the fuselage went together as per the instructions provided; however, some build mods that I adopted were;
Formers 2 and 3, I had issues with the strength of the recommended balsa items so I replaced these with light ply of the same thickness.
 

The wing tubes that support the wing connecting piano wires I decided to ensure that the front tube was securely bonded to former 2 to add structural strength.
 

Cut holes in the fuselage sides for the aileron servo wires and to accept the wing retaining system. (See wing build)
 


The wing build

This was straight forward as most of the work was already done. Some points of note;


The wings are thin so the size of servo you use is critical. I originally tried to fit some micro Hitec servos which were too thick. So a quick call to Colin and I settled on Savox 0255.
 

The alignment of the wing incidence is tricky with plug-in panels so take your time and use an incidence meter. Wing incidence is about +1.5O
 

In order to obtain the correct dihedral I cut slots in the wing panels to accept the retaining tubes. The tubes were made into a sandwich with the upper and lower balsa infill. This tube sandwich was positioned on the connecting piano wires and the wing was then slide over the assembly. The wing dihedral was set and the wing position marked on the tube assembly. The wings were removed and epoxy applied to the slot and sandwich and then reassembled. The wings were held in position until dry.
 

Cutting the ailerons out after covering is beneficial and I used a finishing technique suggested by Colin which was to use micro balloons and epoxy to finish off the forward face of the aileron and the rear face of the wing. This was a new technique to me however, the finish did provide a close gap between aileron and wing.
 

In order to keep the wings on the mounting piano wires I decided to use a hook and band arrangement. I shaped a hook out of piano wire which was then bonded into the wing root. The wings are then held together using rubber bands (in my case cuts of tyre inner tube seem to do the trick). To pull the rubber bands through the fuselage you will need to fashion a small tool out of scrap piano wire to hook the band and pull through the fuselage and hook onto the other wing panel.

The Tail Feathers

posed a new challenge for me, I had never built an all moving tailplane. Some build notes from my experience.
 

The plan shows two vertical supports to build the fin around. Take care in getting these perfectly vertical to the fuselage and square to the wings.
 

I elected to put a horizontal support beam at the bottom of the fin which is mounted on the upper surface of the fuselage. This provided some additional rigidity at the base of the fin.
 

In order to get the tailplane at 90O to the fin I used the following technique. Cut out both sides of the fin and then laminate the bearing surface with thin ply to suit. I then dry assembled to the fin supports to obtain the correct dimension for the bearing tube. I cut the brass tube to length and trimmed One of the fin sides was securely pinned to the build board and the brass tube accurately epoxied into the pre drilled hole using a set square to ensure the tube is perfectly vertical in all directions. This was left to dry and then this side of the fin was glued to the fin support structure. The other side was aligned and glued to the fin supports ensuring that the brass tube is epoxied into the second side.
 

To ensure slop free support and rotation of the tailplane, strive to obtain the closest fit between support bearing and piano wire. I had many attempts before I achieved a fit I was happy with.
 

To ensure smooth operation of the tailplane and longevity of the bell crank. I bushed all three holes in the bell crank with the appropriate sized brass tubes.

Finishing of the structure was done by using fibreglass matting and acrylic resin. Although this process went well it proved to be too absorbent as a base for priming and painting. The amount of paint used added more weight to my finished model than I would have liked.

Fitting the battery, receiver and switch into the nose cavity is tight so prior planning is a must, particularly as there may be a requirement to add weight to the nose.

I now await a good day to take the GNOTT onto the slope and get some air under its wingsÖÖ..that will be another story.

 

John M

 

April 2018 - and the new Gnott has taken flight, I now await a few words from John on his thought and view of how it flew. I will save the detail for him, but a few photos wont hurt to give you the idea that everything went according to plan.

Back soon with an Update

 

I  have just found that Sarik hobbies are selling the Plan https://www.sarikhobbies.com/product/gnott/

 


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