Learn something every day, thought I had ruined my ignition modules. Lucky I did this now before I finished the design of the Pod. The bottom cylinder plugs filled with gas and shorted out both ignitions. I guess there is a reason one never sees these engines mounted this way. Oh and that 6 or 8 oz of fuel container was used up in about a minute.
Still playing with the engine. The short version, the engine was impossible to time properly with the prop reverser without modification of the location of the ignition trigger. Broken shaft key, 6 broken prop bolts. Need to modify the hub and change the bolts from 5mm to 6mm and tap another hole for the ignition trigger. The good news when the engine did run in the proper direction, it appears the baffles cool it.
Ordered wrong bolts, and it looks like I did not need the extra trigger tapped hole,.....I was given the whole set of Tony Bingelis books, he has a whole chapter called "Make Haste Slowly".
Got the taps, modified the hub to 6 mm, the prop drill jig, and prop to 6 mm.
Waiting for crank key and new bolts. The key is only 2 mm , the hub is tapered but it is aluminum and the crank is steel. It looks very weak for 20 hp. , ...there is a steel hub available, if I have more problems I may have to spring for that.
The whole aircraft/concept is designed around this engine or one about the same size and weight, so I hope it works better than it has, although the problems are probably of my own making.
Made a tool to properly torque the prop hub, after the 2ud key failure. I did not even use the the recommended Locktite 638 this time, as if it breaks I want to remove it without heat. The torque spec. is 65NM from 3W but recommended torque for an 8 mm 12.9 bolt is 47 max. I did a calculation and went with the 47 NM figure. The temperature spec is either 212 F or 212 C depending on which 3W reference you read. I talked to the model shop owner and he said the gas models run 180-212 F, so that is what I am going with. The baffles keep it there when running but it goes up to 270 after I shut down. I was seriously thinking about searching for another engine but today things went better.
Engine is running good ....went through a gallon of fuel in the last two days. I am getting 5600-5700 RPM WOT, and was told only to expect about 5800 static. Temperatures are 180-205 F when running but it shoots up to 270 F after I shut down. So the baffles are working fine. Playing with the mixture, had an experienced model guy listen to it and he said it sounded great. Today I was able to check the timing, and yes it is at 30 BTC but I do not think it is very gradual as at low idle it vibrates very badly. It also will start backwards I think because if flipped fast it exceeds the 400 rpm advance threshold and fires at 30 BTC instead of about 1 -10 ATC (after top dead center). The engine has a very bad reputation I find out now. It is from 2001 and an early model, I would assume they have corrected many problems, this engine is no longer sold but I can still get parts so kudos for 3W on that. The recommended timing is supposed to be the middle of the black sensor, I have pictures here to show how far off from that I had to set it, and it will still start backwards 25% of the time. The funny thing is the little round piece of medal on the bottom is close to or right on TDC (top dead center) so I have to wonder if it is again something lost in translation from German to English. I am learning lots and will have to secure much better, things just vibrate off. Sheared some pop rivets, and broke some electrical wires in less than 1 hr running.
Also shown is my portable hanger for the engine, (55 gal garbage bag) , and every two days I have to clean off the work table.
Working on gallon 4 of 6 gal. break-in. Had a .016 baffle attach tab just shear off around a bolt. Inspecting plugs to see if I can get tan color, so far no joy. Can not get to the adjustment screws while running because the exhaust is in the way. Thinking about various schemes to be able to adjust them while running. Looked at my chain saw plug and it had a beautiful tan color.
Guess I should have used the Locktite....the top layer of the aluminum was sheared off of the inside of the taper...the key sheared and the prop unscrewed and flew off. It looks like a pusher prop is a better solution in that the hub bolt will want to tighten if the key shears.
The attractiveness of the prop reverser is that I can use standard propellers to find the best pitch as their are lots more and less money.
I ordered another and will use the Locktite on the hub bolt and taper and key, and see if that is a reasonable solution. But I do not trust glue, might work though.
If anyone knows if that is a standard taper in the 3W that I can get a ream for, I am considering designing a better hub. Please PM me.
so far I have sheared one key...in the correct direction the engine went far advanced and I broke all the 5mm prop bolts. Or the engine kicked back and broke the bolts...not sure which. (changed to 6mm bolts)
I have sheared one key in the reverse direction and prop unscrewed and flew off.
This design concept may only be suitable for a powered glider with a large field off the end of the runway.....I have about 1 hr break-in running, and am learning the problems associated with this concept. I get a great satisfaction in solving engineering problems. (having loads of fun)
valve compound lapped hub...ordered new standard prop...will see if the Locktite makes a difference....In the end I will have a pusher prop but right now a standard prop for testing makes sense. ... That is assuming the hub stays on going in the wrong direction.....forgot to add that the prop bolts were loose when I first broke the 5mm bolts. the charred prop is the giveaway, so maybe with proper torqued 6mm bolts even if the key shears the bolts will not brake. I have decided I will make this engine work or one like it and I have moved on to building the fuselage.
Plot of the Gussets, cutting on vintage table saw with carbide blade, all cut and drilled (holes not shown) in one morning.
Decided to run with existing hub.....removed and purchased new magnet, shrink fit at 350 degree the aluminum hub and used Locktite 638. I will spend the extra for a pusher prop, (about $30) and see if going in the proper direction with the enhanced install procedure will still cause hub slippage. I hope the worse will be that it goes slightly advanced (which can be checked with marks on the hub), and I will not be able to start it. I was able to sell the new standard prop I just got. Shown here is drilled Socket Head Bolts, and safety wired....makes it look almost aircraft. Torque fixture still attached to the hub as I have decided not to disturb the item for the full 168 hours Locktite calls out for full strength.
Had -2 Cherry-Loc, but the tolerance build up required -3.....Found some Monel Cherry Max on e-bay. How to find the center of a tube, Rivets installed........ boom 2/3 assembled.
Trying to bend wing attach fittings, my bending tool (water pipe) and parallel bar die were not strong enough. The press and parallel are not mine so I had to quit before I broke it. Will reinforce the parallels with tractor test attach fittings and get a solid piece of bar to finish off the bend. This stuff is really tough,...have to over-bend 12-15 degree to get it square.
Problem with this type of project, everything is "first time"......and what exactly to do next to minimize wasted effort is sometimes difficult. Here is a picture of the aft structure less 4 ft. of boom and the tail feathers. The big plates are the wing attach to structure. They still have to be trimmed which means I have to go back to my unfinished wing drawings to check the dimensions. Lots of scratches of the Alclad ....clean up and prep is often more time than the fabrication.
As said last post, how to properly approach the next step is taking some time. The plan is to load test this assembly, and the proper way to do that is to attach at the wing attach fittings shown "un-drilled". Well the proper way to attach the wing is to have the wing spar finished....so perhaps you see the problem here. Anyway I did level it up to look at it and think.....I have decided to finish the spar design before I go any farther. With a finished spar design I should be able to locate the holes for the wing attach unless I change my mind and test this assembly without the fittings and test the fittings and whole assembly after they are located with the spar, which is more work. Another option is to set it aside until the spars are built, but if this fails the load test the spar could change.