So now it's 2002 and a new Wedge has started to terrorize the skies around RI. This Wedge was much more of an accident than the previous models- I happened to stumble upon a small gasoline engine at a price too good to pass up.
This is the engine, an MVVS 1.60 cubic inch (26 cc) gasoline model.
The engine, complete with ignition system and box muffler. Overall weight is just under 40 oz., complete.
An absolute jewel of an engine. Overall performance and running characteristics couldn't be better although there is a definite learning curve when moving from glow to spark ignition / gasoline engines. The symptoms of miss-tuning aren't the same at all- what appears to be a rich condition in this engine is more often a lean condition. Further, the Walbro's carb. adjustments (high speed, low speed) are far more intertwined with each other than glow engine carb.s are. Both needles, H.S. and L.S., are effective across the engine's entire speed range and this allows the needles to to be grossly miss-set with one circuit 'sort of' compensating for the other. Of course, something ends up terribly rich or lean- usually it is the low end and this really hurts transition. I don't mean this to be critical of either the engine or carburetor, merely an observation that these systems are very, very different than glow engines and require a different approach.
This Wedge is based on the ~.60 size Wedges as previously built with a few exceptions: the size is considerably greater of course, the wings are tube mounted and removable, and the ailerons are split (flaps and ailerons). This last modification made it very easy to install (4) aileron servos but also served to allow the ailerons to be split for braking (called 'butterfly'). Also, the rudder uses a pair of servos to actuate it; I choose the twin cable method unscrupulously stolen from Roger Forgue's page. I don't think it was Roger's idea originally but that was my source for the idea. One other major deviation is that the ribs for this plane are made from individual parts assembled in a fixture. This is the first time I've tried this method and found it to be fast, easy and far, far better than cutting ribs out of solid sheets. I'll use this method for rib manufacturer all the time now, no matter what the size of the plane.
As the plane neared completion, I began to realize that it was going to be much heavier than the original target weight of 8 to 9 lb.. In fact, it ended up weighing a little over 11 lb.. This required the poor MVVS to put out as much power as was reasonably attainable so I drilled out the carb. venturi from its original restrictive 7 mm to a still relatively small 9 mm. Also, I scrapped the original box muffler in favor of a better exhaust system. A couple of MCM's were tried (mousse can muffler) with good results but I eventually went with a Mac's full length tuned pipe for optimum power output. The engine is still quite new and certainly not broken in but early figures are as follows: Menz (standard) 18-10 7,120 RPM max., APC 16-8 8,900 (with occasional trips well above 9K RPM while tuning the pipe) but these numbers come from an un-tuned system with a header that was far too long. With an optimized pipe length, best power of all props tested so far has come from a Mejzlik 17-10 turning 8,490 RPM, but best flight performance has come from a narrowed, thinned and swept Zinger 18-10 turning 7,400 RPM.
Spec.'s are as follows: Wing span, 76 inches. Wing chord, 20.8 inches. Wing area, 1973 Sq. In.. Length, 76 inches. Fuse side area 891 Sq. In. All-up weight (including fuel) is 11 lb. 4 oz. All controls are pull-pulls and use steel cable with the single exception of the throttle which uses Kevlar. The rudder is operated by a pair of servos coupled with the operating pull-pulls and can just barely be seen in this picture (inside bottom of the fuse, just behind the right aileron). The two rudder 'connectors' are separated by a piece of 1/16" balsa to prevent them from touching, and that too is visible in this picture. Two (5) cell, 1,100 mah NiCd battery packs are used with a pair of JR charge jack / switch harness (redundant system). A JR FM (PPM) (9) channel is used and yes, I know that a non-PCM receiver can't work on a plane with spark ignition but fortunately the receiver doesn't know this and works flawlessly :-) Oh yeah, and Monocote "X" hinges are used on all flight control surfaces (Note: there are no hinge gaps anywhere on the plane). Servos are a mix of JR 507 (w/ BB), 517's and Hitec 425's with a total of (9) servos being used in the plane ((4) ailerons, (2) rudder, (2) elevator, (1) throttle). The elevator is split so that each half moves independently- this allows the use of 'ailevators' or 'tailerons' where the elevator halves move in unison with the ailerons and is very helpful in 3D flying.
As this was my first gasoline and ignition engine, it required a slightly more elaborate approach to engine mounting. Well, the engine mounting itself was the same but the ignition unit required some additional space, wiring, a battery pack, and switch.
The switch, charge jack and ignition light (L.E.D.) are mounted on a removable plate on the left side of the nose. The ignition itself is mounted directly above and slightly behind the battery pack in its own well (follow the ignition lead from the spark plug back to the plane- the ignition ends right at the edge of the fuse.
The wing follows the latest geodesic design with the single exception that each side is tube mounted and removable from the fuselage. This presented a bit of a problem due to the wings' being swept but I ended up mounting an additional set of <false> spars to carry the tube into the main spars. This system allows the tube to be mounted straight through the fuselage as well as straight into each wing panel and greatly simplifying wing / fuse alignment during construction. The wing panel's dimensions are span, 35 inches (each side), chord 21 inches.
This picture shows the right wing panel removed from the fuse. The wing panels are retained by a set of rubber bands that pass through the fuse and pull each panel toward the other one. The system is a little bit crude but very light, strong and simple- and it works great.
The fuse end of the right wing panel. The wing tube sheath is captured between a false set of spars and reasonably well supported. There is a 3/8 inch birch dowel near the trailing edge that serves as an anti-rotation pin. All necessary electrical connections are made via the electrical plug located near the top center of the wing. The right wing panel only has connections for the two servos but the left panel also carries an RX battery pack. The pack is located about 12 inches from the wing root and balances the plane laterally.
There is a small piece of 1/8" lite ply to stiffen the wing around the locating pin but otherwise, all wing materials are balsa. The ribs, sheeting, leading edge, trailing edge plates and cap strips are all 3/32" thick balsa while the spars are 3/8" square balsa.
The fuse with the wing panel removed. The front rubber band is just visible with a piece of scrap balsa retaining it. This view also shows the header, pipe and velocity stack. I don't know if the velocity stack really changes performance but it was cheap :-)
Note the piece of brass tubing in the pipe's stinger, the one that looks like it has been crushed with a pair of pliers. That tubing is being used to find the ideal size of the stinger diameter and I did this by...... crushing it with a pair of pliers :-) The exit area is amazing small but that's what the engine runs best with. Of course I'll replace the brass tubing with something more respectable but it was the easiest way I could think of to make a 'field adjustable' outlet.
The exhaust header is made from a Krumsheid kit, and is custom fitted to this plane and engine. Made from stainless steel, the tubing is very thin and light (0.020" wall thickness). The pieces are cut as necessary, assembled and brazed together using nothing more than a propane torch. A very nice product at a very reasonable cost although shipping from Germany was slightly more than the price of the header itself.
This view shows the fuel tank (mounted on the CG), the RX switches, one RX pack, the throttle servo and the on-board voltage monitor.
My original goal was a plane significantly larger than the .60 size with an all-up weight of between 8 and 9 lb.. The size is OK but the weight is far beyond my original expectations- all-up weight is 11 1/4 lb. as shown in these pictures. Performance is still very good however as the engine produces more power than I had originally hoped for. Normally a tuned pipe is a mistake for 3D flight but this combination doesn't jump on and off the pipe constantly; this may be due to the pipe's relatively mild characteristics or the engine's relatively small air passages. Whatever the cause, the results so far are great.
A few thoughts about oil- I was originally intending to use a synthetic oil at the 'de rigueur' mix of 100:1 but have researched this a bit and now find that mix to be a little thin. Even the synthetic oil manufacturers recommend a minimum mix of 50:1 for 'hard-use' engines as well as almost all air-cooled engines. Another interesting thing is that those who really lean on engines, such as motocross riders, find even a 50:1 mix to be far too little oil and use at least 32:1 and sometimes even heavier mixes. My current mix is Pennzoil at 35:1 which I will continue for at least the next couple of gallons. I may then move to a full synthetic mixed at 50:1 although the Pennzoil is working out so well that I have little reason to change.
That first start up in mid January, 2002. My brother is holding the plane and I'm trying to teach the engine to turn all by itself :-) This actually went much better than I had expected- about 10 flips and it was off and running. We managed to get three short flights out of it that day and while none were long or particularly impressive, it was sufficient with a new design, a new plane, a new method of construction, and a new and very different engine type to deal with.
And it really did fly!
I've flown the plane perhaps another 1/2 dozen times since but all for relatively short periods due to the low temperatures and the constant need for adjustment of the plane- the CG had to be moved twice, the landing gear beefed up, etc., etc.. The part I was worried about being reliable, the engine, has proven itself to be a rock and not missed a beat except when badly mistuned by its owner.
More information and pictures will be posted as time allows..... assuming the plane survives, of course :-)
