rcportal - dsm excelsior 188 review

Dave Smith Excelsior 188 by Martyn Uttley
Why Build an Aerobatic Model ? My interest in aerobatics started to develop after progressing from a trainer to the well-known Acro Wot. I then became a bit bored of flying the Acro Wot around with no real purpose, just the odd roll and loop etc. After watching fellow clubmembers Bert Caton and Ian Pilton flying their aerobatic machines, I tried to fly the Acro Wot in a similar fashion with mixed results. After a phone call to Bert, followed by a visit to his loft, I was the proud owner of an early 80’s aerobatic design Pacemaker. After a few teething problems with the engine, she was in the air. I was totally astounded on how smooth she flew compared to the Acro Wot and was now totally hooked on flying Aerobatics. During that summer Bert invited me up to Rakesmoore to watch his son Kevin, on one of his visits to Barrow, practising for the UK Nationals and European Championships. I was totally amazed by the skill of his flying and how quite his aircraft was. The aircraft was powered by a YS Fourstroke engine. I went home totally inspired and thinking of what I could build during the winter.
The very affordable Dave Smith Models - Excelsior 188
The Purchase..... After much research on the fourstroke kits which were available (I’m still shell-shocked on the prices!!) and many phone calls to Bert, I purchased a Dave Smith designed Excelsior 188 suitable for a YS120 fourstroke engine. The design is dated now (although this was once a competitive championship design in the early nineties) compared to the current crop competitive designs ZN, PL etc. The deciding factor, not surprisingly came down to cost, at £150 for the kit, it was by far the cheapest and afforded good value as even the Fuz came pre built. The Kit...... At first sight the kit seemed to be ok, the wings and tailplane were balsa sheeted which looked to be of good quality and straight. The fuz came pre built and again was of good quality with balsa sheeted foam deckings. The canopy was of clear plastic and the cowling was of the moulded epoxy glass type, but a bit on the rough side. Also came what appeared to be all the balsa required to complete the kit. (I subsequently had to purchase additional balsa strip to face the leading edges of the ailerons). On the down side there was NO PLAN and a very badly photo copied instruction leaflet, which gave a set of very vague instructions to say the least, these had to be clarified with a number of phone calls to Dave Smith Models. The building was going to be a long-term project and would only be ready when I had a bit more experience flying aerobatics and had a few competitions under my belt.
The Fuz...... The engine installation was the first job recommended to be completed. I purchased a second hand YS 120AC fourstroke (you don’t have to buy the latest engines to get good performance) and mounted it using a Gator Soft and Safe mount. This was a tricky operation, as there were no datum lines or dimensions to use for position. Side and down thrust were built in to the fuz according to the instructions and the engine was to be positioned using the cowl for reference, but after careful measuring of the fuz and cowl the engine mount had to be packed out to fit and the cowl was modified to suit.	Motor of choice was a used YS 120AC
The fuel tank (Tetra 16oz) was positioned over the CG, which left little room for mounting the servos and receiver etc, which was quite surprising for such a large model. I used Futaba 9202 coreless servos for the elevator and rudder and a 3001 that I had spare, for the throttle. It was at this point that I decided to use mechanical retracts as I now had nowhere to site an air cylinder. As there was going to be quite a long run for the elevator push rod, I elected to use a carbon fibre rod supported in the middle and an MK dual elevator crank, which I hoped would be a lighter set-up and stiffer under load than a conventional balsa push rod. Although difficult to set up, in the end this worked out quite well, but I also ended up using the MK Ball raced clevises and servo ends, which were quite expensive and not budgeted for. The rudder used a closed loop system. Setting up the tailplane and fin were straight forward with no real problems encountered, although I did find a slight twist along the length of the pre-built fuz, which had to be taken out by off setting the tailplane.
Not enough room for an air cylinder meant thatmechanical retracts had to be used	The Wing...... The wings came pre-sheeted in balsa, with carbon reinforcement and NO cut outs for retracts or Aileron servos. A box section was fabricated from light ply with beach ply bearers for the retracts and set into the wing. EZ Supra DX 60 mechanical retracts were used with a Futaba 136G servo, which made a very light but strong set-up. The retracts are operated using a separate 300mah battery and switch harness, so if the retract servo stalls in flight the main receiver battery will not be drained by the retract servo.
Futaba 9201 servos were used for the ailerons, which have a lower profile and can easily be set flush with the wing. I did not want to cut into the balsa skin of the wing and possibly damage the carbon reinforcement, so holes for the servo leads and mechanical retract linkages were made using the sharpened end of a length 15mm copper tube, being careful when boring down to keep the tube inline with the wing and servo/retract cut outs. The wing was joined and three layers of 100 gram glass cloth was used to reinforce the joint out to the retracts cut-outs. This was done because I had heard a few reports of the wings failing across the retract cut-outs during snap rolls. Finishing...... The instructions recommended that the Fuz be epoxy glass skinned, with the flying surfaces covered with film. Much research was done on various methods and techniques of epoxy glass skinning before opting for the method used by Phil Williams of Probuild. This method, which is not much different from any other was outlined in the June 99 Edition of R/C Model World. The key to successfully finishing any model is to use good quality materials and use as little resin as possible (weight is the enemy!). By following the steps outlined in Phil’s article, I found it was quite easy to apply, but the sanding afterwards was very laborious. The finished surface was sprayed using a combination of Hobbypoxy and automotive two pack paint. This type of finish added a total weight gain from bear wood to finished-sprayed surface of 5oz. (Bear in mind that the Fuz is 78” long!) The flying surfaces were covered using Profilm, which is a little thicker than Solarfilm, but produces a very durable finish. Set-up...... The CG of the aircraft came out about 20mm in front of the optimum balance point and as the batteries were as far back as practically possible, I had to use tail weights. Control throws were set up according to the instruction sheets. As a final check, I asked Kevin Caton on one of his visits to Barrow give the set-up a final check and with a few minor mods the Excelsior was ready to take to the air, if only I had some fuel. YS engines run with 20% synthetic oil and anything between 10%-30% Nitromethane, which can be mixed or made to order. I decided to use 20% nitro, and at £20 per gallon from Probuild it's not cheap. (I have now run out of excuses Bert!) Conclusions...... At first sight the kit looks easy to build, but there is quite a lot of work involved particularly with the fuz. Being a pre-built fuz you would be mis-lead to believe that all the work has been done, wrong. This is a kit for the experienced builder, as much is left to the individuals discretion, “no two Excelsior’s are the same”. However, as a competition aerobatic model, you do get value for money, which was the main criteria for the purchase. Span: 72” Length: 77” Weight: 10lbs 4oz Power: YS 120Ac *Many thanks to Martyn Uttley for the review* [back to the reviews page]