The objective of Novembers article was to complete a 25 year old model Cambria Pioneer. Bumpy Green's Kevin (fastest builder in the west) kindly volunteered to rebuild the airframe for me as he was currently without anything to build. He completed it with his usual skill & precision. He even wired up the closed loop controls, fitted all the radio gear and installed the engine & fuel tank. As he had made such a perfect job on it, the original plan to use antique look Solar Tex was dropped in favour of more authentic (both in terms of the look of the plane and the age of the model) tissue & dope covering.

I got this Cambria Pioneer amongst a collection of 20+ year old models from a former aeromodeller who has since changed hobbies but had kept everything in case he had ever decided to return to the hobby.

Just looking at the model with it's open structure rear fuselage and highly exposed pilot position suggests the era this plane is from. Modern plastic covering would not have done justice to the look of the Pioneer or the excellent finishing job Kevin did on it for me.

Along with the various models I purchased came a box of covering materials, all 20 odd years old. The tissue was in pristine condition as it had been folded carefully and kept that way, I suspect since new. A variety of colours was available to use and the opaque white seemed most suitable for colour and texture. The chosen tissue is quite thick and has a very coarse weave which can be seen against the light when it is dry like a wood grain. The pictures I took didn't show this unfortunately.

I began by searching the net for 'tissue &dope' and came across quite a few articles which all gave good tips but seemed to be quite old and assumed that the reader knew exactly what all the terms used were.

	I read through them all and then spoke to Tony & Daren about how they would do it. All together I got a pretty good idea of what I needed to be doing and what I would require to finish the job. Dope comes in a variety of forms and can be made from different compounds. I did not investigate the differences and settled for the none shrinking type. Shrinking dope can be used but has been known to lead to warping of structures as it shrinks too much if not used correctly. It can also lead to what is referred to in the info I found as 'starved horse' effect - which basically means all the ribs stick out. This doesn't occur on sheeted models as there are no open sections for the tissue to shrink into.
	Using old jars to keep everything neat and as smell free as possible I made up one jar of 50/50 dope/thinners. Another jar of neat thinners to clean brushes and use if extra thinning is needed for a working piece and a third jar with just a little neat thinners to keep brushes moist while working. Dope left on brushes will turn rock hard but a little soak in some thinners and it dissolves easily. Thinners evaporates at an alarming rate into room temperature air so I had to make sure the room I worked in was always ventilated. I closed the window one evening as it was cold and forgot to re-open it once I started working again and nearly gassed myself half an hour later. I left the window open and the extractor running whilst retreating upstairs to download pictures.
	A water atomising spray gun can be used to wet the tissue prior to application. This provides an even covering of water for smaller parts. For the wing panels I did the first one with the spray but found it dried out too quickly so for the remainder I filled a washing up bowl with lukewarm water and dipped the tissue using smooth curves at the folds to cover completely. This was then left hanging to drip dry and allows the water to soak right through the material.

I decided to practice working with the tissue and dope before setting about my 25 year old model untried. I found a spare Mini Whizz tail assembly and some off cuts of coloured tissue.

	I began by painting the frame all over with 50/50 dope and this soaks into the wood and dries very quickly, becoming tacky after only a few minutes. Using the spray bottle I lightly soaked a piece of tissue and allowed it to dry for a few moments. This also gives the water time to penetrate the tissue completely. Starting at the back I secured the tissue to the frame by applying 50/50 dope over the tissue on top of the wood. Gentle persuasion with the brush ensures it soaks through and activates the dope underneath forming a good seal. Folding the tissue over the back edge starts off tricky as it will not stick but more gentle pressure from the brush as the dope begins to go off. I kept brushing over this area and checking the join as it does lift very easily to begin with when going round sharp corners. Patience is the key to success and there are not many right angles on most tail fins.
	Using a sharp scalpel I cut at a 45 degree angle away from the top corner to allow the tissue to fold round the edges without wrinkling. To make sure the first successful piece wasn't a fluke I took another off cut of tissue with a different colour and thickness. I applied this in the same fashion and found it just as easy as the first part had been. Finally I painted over the whole lot with 50/50 dope. I found if too much pressure is applied between the structure the tissue can stretch a little when soaked with dope, something I would have to watch out for on the Pioneer.
	The finished practice piece. The edges came out very well and the material became rigid and tight in the open sections just as I wanted it to. All the excess is removed with a scalpel. I was surprised how quickly tissue can blunt a surgical steel blade and fortunately had plenty of new blades to hand. I was very happy with the outcome of my first tests and cleared the bench ready for the Pioneer covering to begin in earnest.

Before I set about the model covering proper I will give a quick overview of the steps taken whilst I learned the best methods of applying the tissue to the structure.

	I began by spraying the tissue to be used with the water atomiser. Ensuring an even covering of spray was not hard with this tissue as it turned very translucent when wet. The wing sections being very large required a lot of spraying to get wet through and in places the water collected and ran. I decided to use a method I had read about whereby the tissue is dipped into a bowl of water and left to soak for a minute or so. Using this method is much easier for larger sheets of tissue and creates less mess from dripping.
	Once the water has penetrated the tissue evenly throughout excess water can be wrung out. I did find however on the larger areas of the wingpanels that as the tissue dries - if it has been squeezed out too hard - the wrinkles left behind can be hard to flatten out. On the tail surfaces however this made little difference as it was easy to keep the tissue pulled tight. Using the bowl method for the wing sheets allowing the piece to hang and drip dry has 2 advantages. First there is no wrinkling which on such a large area of open structure is a blessing. Secondly as the water runs down the tissue it soaks completely and evenly and the top begins to dry slightly sooner. This keeps the remaining tissue from drying too quickly when dealing with a large panel or sheet. The second, third and final wing panel were done this way and I found it much easier to work with and far less wrinkling occurred.
	Tissue being left to dry slightly before applying. If the tissue is too wet the dope tends to turn cloudy and this leaves marks on the open section of the structure. The drying times will vary according to the tissue type used, size of the pieces used and how wet it is made to begin with. There is not set time and experience taught me to judge when the tissue was ready for application. Testing on scrap pieces can help determin the best time to begin applying dope.
	Using a fine brush I painted 50/50 dope onto the frame as I had with the practice pieces. Allowing this to go tacky I dampened the tissue and laid it onto the framework. Using the same brush and 50/50 dope I began at the middle of the area and made sure the tissue was straight. Brushing quite firmly along the entire length of the starting piece. I allowed a few moments for the dope to penetrate and activate with the dope beneath. Dipping the brush into the cleaning thinners I brushed over the length again until I could see the wood grain in a uniform colour beneath. This again ensures the dope is activated and soaks right through from the wood and into the tissue but may not always be required.I gave the first doped part a few minutes to set before pulling the tissue around and finishing the piece. The first attempt at this revealed that the tissue will move if A) it is pulled too hard before it has begun to go off & B) too much fresh dope is applied over the area causing it to soften and become moveable.

Removing the rudder for covering was just a matter of unclipping the control cables as it is held in place by the long pins of the hinge.

	Another must when doing this job is a pair of sharp scissors. This saves blunting all the scalpel blades when only a rough cut is required. I learned from a mistake at this point. The first piece of tissue I cut was a good fit but I found I hadn't left enough overhang to handle the tissue easily once it was applied to the rudder. I overcame the problem as it is such a small piece to work with but I saw from this any larger pieces would have been difficult to keep straight and tight with not enough tissue to grip.
	With the first side covered I allowed it to dry completely to ensure there weren't going to be any warping or sagging problems. These pictures show the single finished sheet from both sides allowing the frame to be checked before continuing.
	The finished product. I know I could never have got this effect with Solar-tex covering. I turned off the camera flash to exaggerate the opaque transparency of the covering against the light. Close inspection looks like there is no tissue over the frame as it has gone almost completely transparent. Once finished another couple of light coats of 50/50 dope all over. Any stubborn areas or wrinkles can have neat thinners brushed over them and rubbed down with finger tips.

The underslung tailplane presented an unusual next step as the lower side can be covered in one go.

	Again the frame is painted with 50/50 dope and allowed a moment to go tacky. Measuring and checking of tissue size should be done before this to avoid sticking problems. The screw holding the elevator control horns in place was seized so I had to work around them, but this was not a problem.
	Laying the damped tissue in place to align with the trailing edge. I began at the centre of the tailplane brushing on 50/50 dope with quite heavy brush strokes. Once this is begining to go off it allows the remaining tissue to be pulled tight over the rest of the tailplane.
	The lower tailplane finished and looking very transparent with the dope still glistening wet. The curved ends were not as difficult as I feared, starting at the centre of the leading edge and working in a fan shape across the tailplane keeping the trailing edge pulled tight as the curve is made. Small cuts help reduce wrinkles at the corners.
	The top tailplane covering is done in two parts for left & right making sure that no tissue sticks to the sides of the fuselage. I started from the middle edge of the wing and worked outwards, keeping the tissue tight with one hand and brushing with the other. I took it slowly at the corners so as not to create any wrinkles and you can just see how much the tissue moved back onto the elevator as I kept it pulled tight. This is carefully trimmed to allow free movement and the excess tissue seen here is left in until the dope is almost set before trimming. The trimmed edges are then worked down slowly with pressure from the brush and finger tips to eliminate all wrinkles.
	The finished tail end reassembled. If I say so myself, I didn't do a bad job of it either.

Now comes the real challenge: - a built up wing with a flat bottom, a very curved upper surface and loads of dihedral.

	The wing had to have a few spots of surgery by Kevin, including an entire rear rib section on one side. Most of the damage was caused by the brittle wood but all defects were repaired or worked out before I got it back. I decided to start on the bottom first as it would be an easier approach to the curved top and any overlapped covering from the top would not be seen easily on the ground.
	Having soaked the tissue with the spraygun I laid it over the underside of the wing and pegged it in place at the tip. The whole underside of the wing was liberally brushed with 50/50 dope. Beginning at the main spar at the root of the wing using firm strokes I worked along the wing re-adjusting the ends to keep the tissue tight. Allowing it a few moments to begin to dry I pulled the tissue tight once more and re-pegged it in place. Then working from the main spar forwards I carefully brushed over each rib and riblet ensuring an even pressure was applied to each. Brushing round the leading edge again using firm strokes and going back over a few areas to ensure the tissue stuck properly. Once I had finished the leading edge I began on the long rear rib sections. Working back to the second spar initially to keep the centre section tight and to ensure the tissue didn't get bunched anywhere.
	Working back from the second spar and onto the trailing edge sheet I began at the wing root again and worked outwards. Only one cut had to be made on this section, right at the corner. This was to be expected and I had planned for this by placing the peg on this corner. A slight overlap was created but is all but invisible unless held up against the light. The tissue on this wing panel began to dry before I had reached the end and the result was the white patches in the open sections you can see in the picture on the left. To counter this I dipped the brush into the 50/50 dope then into the neat thinners making the dope very thin. This was able to penetrate very easily.
	For the second lower panel I wet the tissue by dipping it into a bowl of lukewarm water. This gave a much more even soaking without any water logged areas. I used the same order of application beginning at the main spar, working over forward to the leading edge, backward to the second spar and finally over the trailing edge. The curved tip I found easier to apply this time as the tissue had not dried out as before. In this picture you can clearly see the stain which is the only non removable damage. After a quick attempt to sand the wood back revealed the stain went right through the wood I decided to leave it. As I worked on the piece and it began to show through the tissue I thought it looked quite striking.
	The centre section of the lower wing I reinforced with a piece of tissue that covered the entire sheeted section. Using a large brush I coated the area thoroughly and applied some neat thinners over the area also to make sure the dope already on the wing became workable. Placing the tissue in position I worked from the centre outwards and with the large brush soon had it finished. I trimmed off the excess and then gave the whole lower surface another good coat of 50/50 dope. Taking care not to press too hard between the ribs as this can stretch the tissue and create sagging.

Preparing myself for the final task for a day or so as I was quite worried that having made a pretty good job of all the flat parts I may not be so successful with the curve of the wing upper surface.

	The difficulty of the upper wing is even worse when I realise the second spar doesn't reach the tops of the ribs so I have an even bigger area of tissue with only the ribs to bond to. You can see the whole rear of the first visible wing rib has been replaced. Plenty of dope was painted onto the framework again and I went over each rib twice to ensure full coverage.
	Allowing the dope a bit longer to dry than before I damped the tissue and prepared it for fitting. Once the tissue was ready I placed it onto the wing and spent a few extra moments getting it all lined up perfectly before pegging it into place. Beginning at the root of the wing and again working along the main spar first I kept re-checking the tissue and pulling it tight as I moved along. The forward part of the ribs and leading edge went remarkably well
	Pulling the tissue tight as I went along after each rib I did tear the tissue towards the end as I was pulling it quite tight for that trailing edge curve. The only wrinkle I had to deal with was on the leading edge tip corner as it is quite a sharp angle. A few generous coats of 50/50 dope and a couple of brush overs with neat thinners in a few tricky spots and it all looked great.

A few pictures of it finished and ready.

The overall look has come out exactly as I had hoped and I am indeed glad I took the plunge and gave tissue & dope a try. I will certainly be using this method again. However I don't look forward to another headache like I had when I forgot to open the window. I'll take this final chance to say to anyone who intends to try this, get a decent breathing mask. Ventilation is all well and good but the fumes and vapours are slow moving and build up quicker than the air can carry them away. I will feature the mask I choose sometime in the future.

With very few days available to fly at this time of year, a brief break in the weather proved too much of a lure and we headed for the nearest Bumpy Green flying site.

	I readied the Cambria Pioneer and checked everything was moving in the right directions. Filled the tank with 5% nitro 15% castor fuel and fired her up. I asked Daren to test fly it as he has the quickest reactions of all of us and the most experience with all types of aircraft. He handed me the controller after only a few laps and I thoroughly enjoyed my first flight. Bringing it low for Tony to get pictures it became a little sluggish at slow speeds. It stalled once when I turned too sharply but it just dips it's nose and a little extra on the throttle soon brought it level again.
The original plan was to try to hop it off the ground as there had been a question of the Thunder Tiger GP15 having enough power. It did take off after a long run and had to be kept on quite high throttle to maintain altitude. With additional weight added to the front for balance I fell that a larger engine will be beneficial to this model. Not only will the additional weight be working for it's living but it will enable a larger diameter prop so lower revs will be needed to maintain flying speed.
A couple of nice shots of it overhead showing the structure through the translucent tissue. It looks amazing when flying. The sound is not so realistic being a small high revving 2 stroke. A suitable 4 stroke or diesel replacement will be investigated for the summer season.
The sun soon headed down the back of the houses in the west and I handed back to Daren for him to land it safely.
Keeping the speed up to maintain positive control as the Pioneer touched down it bounced and Daren had to blip the throttle to hop it over the Long Cabin parked at the side of the landing strip. I'm not sure I could have managed that so was thankful Daren was at the controls. I will be waiting until the better weather arrives as the cold made the tissue pick up condensation. The harsh landing also knocked out a few joints at the rear of the fuselage so I'll be having the epoxy out at some point to put it all back into shape.

My thanks go to Kevin for restoring the airframe, Tony for putting up with the smell of dope while I finished this project & Daren for helping me out with the first flight.

Article by Chinman from Bumpy Green Model Aerodrome
1st January 2002