Week 83 - 23 June 2004 |
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This evening Rick and I worked with the engines as Gary and family are on vacation discovering Missouri. We mounted the engines on an engine stand where Rick had also rigged up a pull meter for us to check the thrust. For an 18cc engine various engine to propeller charts recommend a 16-6 or a 15-8 propeller. We used a 16-6. With the tachometer at the ready, we proceeded to start Engine 4. After some issues with the fuel lines, the engine started easily with a starter. Engine 4 ran up to between 6100-6300 rpm at full throttle, so we called it 6200. We could not get the thrust meter to work. We worked with the thrust meter awhile and gave up on it. I remembered reading information on various thrusts from propellers from J & Z Products (best known as ZINGER PROPELLER on their website at www.zingerpropeller.com ) so we decided to give up on making the thrust meter work and continue with the engines. We wondered about the air cleaner being on it, so we took it off and tried again. 6200 rpm was it. So we proceeded with Engine number 3. On this engine we had shaved the block that separates the carburetor from the engine to move the carburetor closer. With the carb assembly closer to the engine, we had hopes of fitting it inside the nacelle. We started this engine. 5900 RPM was it. Nothing we did could squeeze out any more RPM’s, remember the carburetors on these engines do not have high or low speed adjustment screws, the mixture is what you get. We were concerned that maybe cutting the block closer may have disrupted something. We also thought we just may have a weak engine or the carb spacing is an issue. Before moving on, we thought how would a smaller prop do? We attached an 11-7.5 on it. This prop turned in 8700 RPM’s. On to Engine 1, all this one would do is 5800 RPM’s, Engine 2, 5800 RPM’s. We began to realize that Number 4 was a strong engine and the rest were probably normal. As we pondered options with Engine 2 sitting on the stand, we realized that we may not be matching the propeller quite right. A 15-8 may be a better choice; we also feel a little more break-in may up the RPM’s 200 to 300. Just for one last shot we took the stock muffler off the engine and started it up. It really was rather quiet. Definitely not as loud as one would imagine, or maybe rock music has finally caught with us. Anyway, we gained 800 RPM’s. We then tach'd the idle. The idle seems high, too high, about 2800-3000 RPM’s. Rick believes that if we plug the idle hole in the throttle butterfly valve it may slow the idle speed some more. He will also run the engines more this weekend to determine if the RPM’s increase. I went to the ZINGER website and estimating from their thrust chart, I determined that at 6000 RPM’s with a 16-6 prop we are getting about 5 lbs of thrust per engine. I took an IOU to determine if we could get different carburetors that would have high and low speed adjustments or a bigger bore. I know that a lot a R/C race car modelers know various conversions of carburetors for these size of engines. All of three of us will probably have a good discussion about these engines during the week. We called it a night. One last note, the retractable main landing gear have arrived at NRC Hobbies. It is going to be a busy July.-- Greg Golden |
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Week 84 - June 30 2004 |
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Tonight should have been a joyous night, our main landing gear and the rest of the actuators came in last week while I was on vacation. First business was to take the gear out of the box and admire them. The Robart Mains are a nice piece of work, however I don't see the $360 retail price tag for them. Robart includes a nice explicit drawing of the mounting envelope. Robart states the distance between the rear bracket and the front bracket "Has to be 9-3/4" with an offset of 5/8". If these dimensions are not maintained the gear will not "lock" properly, if at all. Full of excitement we held the gear in the wing. Some thing does not look right. A quick check of the dimensions proved we can not acquire the 9-3/4", the best we can do is 9". We lay the gear on the Don Smith drawing and every thing is perfect. Back to the wing again and double check things.....yep.......still 3/4 short. How in the Heck did that happen? After much investigation we found out the problem is the distance between N2 and N3 should be 3-1/4". Ours measures 2-1/2" which proves our 3/4" short coming. Further investigation proved we mounted N2 & N3 right on the laser marks provided. Guess that means the Kit Cutter screwed this up. A double check of the outboard motors proved they were correct. Only the inboard nacelle is screwed. Months ago, we modified the firewall location to accommodate our gas motors. While doing this we based our adjustments off the N2 former. So...........this means our inboard motor is also 3/4" closer to the wing than it should be. After much discussion, we decided to cut the the rail between N2 & N3 and splice an extender aircraft ply piece. This will fix both the motor and main gear problem. Out comes the razor saw and we make the cuts required to extend the N2 former. Problem solved and once again happy, we decided to build the rear mount before we splice the N2 back to the assembly. Simple.....right.......wrong! Again the parts provided do not match the drawing plus there seems to be at least one extra part.. Being a draftsman for a living, I always thought I could figure out any drawing no matter how poorly it was drawn. I am pulling my hair out over this one! From the drawings we know the gear mounting needs to be on a plane square and parallel to the nacelle formers. The parts provided would be a "Mickey Mouse" mounting at best. Experience proves to me the top & bottom wing spars must be tied together. So after wasting an hour trying to figure it out, we decided to scrap all the pieces provided except the one piece with the landing gear mounting holes in. We will buy 5/8' thick bass wood and cut to tightly fit between the top and bottom spars. Next we will taper the part to the required angles, drill lightening holes, then glue in place. This did not get accomplished tonight as by this time the Sponsoring Hobby Shop was closed. Being once again totally disgusted we called it a night.-- Gary Himes |
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