Part II - The story continues......
The plan for this next weekend is to tune in the other two engines and maybe do a two engine pass with the front pair just to see how everything is working and then maybe try for four again. I may have said it before but this is a very trying experience. Even my wife is feeling sorry for me! I certainly hope there is some sort of personal reward at the end!!!!! The power switch was replaced with a higher quality toggle unit and the front end damage repaired. All that appears to have happened is the bolt snapped off from the tank mount and the fiberglass sheet jammed back a quarter inch or so. A couple new bolts and everything was ready to go again. The plate is buckled but poses no problem as is. I need to get in the habit of two things when starting the car for a run.....the first is run the servos to make sure both the throttle and brakes are operable and the second is setting the failsafe mode in the receiver.
The other safety thing I need is a throttle return spring between the brakes and throttle servos. Both of this weekend’s accidents would have been avoided by these checks. On Saturday I would have seen that the brakes were unplugged and Sunday the brakes would have brought the car to a halt in short order. Live and learn!!!!! All of the problems I’ve had have been minor because of the low speeds involved. Had any of them occurred at the speeds I’m expecting each could have been catastrophic. Like the initial incident with the brakes unplugged...there’s no way the car would have gotten stopped without hitting something. Likewise with the defective switch. If the car had been at full throttle and THEN hit the drain wall........well, I’d still be sweeping up pieces. It all comes back to working out the bugs with one engine instead of four....four engines running badly enough to keep speeds low..... potentially dangerous incidents happening at low speeds....it’s like dad is watching, making sure its successful in its own time, keeping it from destroying itself.
In preparing for this next test I have plumbed up the remaining tanks and re-installed the front wing. I also disassembled the carb of the engine that didn’t rev up and there were no obvious problems with the exception that I was adjusting the idle and idle mixture with the wrong screws. I now have a good working knowledge of the engine so tuning should go easier. I have also changed all of the engine mounting nuts over to wing nuts, allowing for easier engine adjustments and changes.
I am so sure that this weekend is going to be successful that I’m starting to think about the body. The first consideration is what to make it out of. My four choices are lexan, ABS, fiberglass or carbon fiber.
The pros /cons are as follows :
clear so it paints well/ not sure it can be vac formed
keeps a nice shine/ not sure it can withstand 100+ mph
crack resistant/ expensive & I can’t form it
cheap/ not sure about crack resistance
can be vac formed /painted on exterior
I can form it /might be a bit heavy
fairly cheap /painted on exterior
WAY COOL /might be a bit heavy
I can form it /expensive
no need to paint /potential radio interference
can make either FG or CF with same form
Next thoughts are shape. I did a drawing of it but didn’t care for the tail. I will probably emulate Thompson’s Challenger tail..... since it worked for him it should work for me. I’ll have to hinge something so that I can start the engines and do fine tuning without removing the whole body. Maybe just leave a slightly enlarged hole in the top of the body. I would really like to use CF but there may be radio problems. I have a piece of CF in which I’ll drill a hole and then experiment with the radio’s range. If it works that’s gonna be the choice. I could even fake in a body with that sheet using hot glue....brilliant!
Jan 23, 2008- Got a lot of testing and tuning done this weekend. Prior to going I had to change the low gear on the front two-speed as it got chewed up. It appears that the engines move away from the gears and causes their failure so I’m going to set them up with no clearance and assume that some clearance will come in under power On Saturday I went to tune the left set of engines and they ran okay but again, not consistent.
There was one incident but fortunately the brake return spring I installed last week came into play and the car bumped the curb with no damage when the battery supply plug worked its way out of the receiver. I decided to pick up and head home in one piece. Sunday morning I was back out to test the right rear engine that I sealed up. It seemed to run better with a hotter plug but still not strong at top end. I decided to try to run two engines and installed the front pair. It pulled well but when the rpms got to the point of real power the second gear clutch seemed to slip. I had reduced the face to reduce weight in an attempt to raise the shift point but it appears there isn’t enough surface to provide sufficient surface area so I’m going to replace them with full face and stiffen up the springs. I got into the mid 70's (speedo locked up) with second gear going in and out. The gear with no clearance is still like new but the one with a bit of initial clearance is toast.... learned something there.
I went on line and found a site with info on the Picco engines and they recommend sealing them up with silicone. I have done one but am working my way through the rest. I am optimistic that this will help in the tuning department. I have also ordered some new gears, some regular nylon R/C type and a couple pairs of delrin gears. They will be stronger and may chip before they bend over like the nylon gears. There may be some brass ones in my future...... It’ll be a couple weeks before I test again. The engines need to be gone through, new gears and clutches installed and a headliner kit needs to go out. I am optimistic that big speeds are right around the corner.........
1/29/08 - So far I have sealed up two of the engines and repaired a broken exhaust manifold. I also put epoxy beads on the mufflers so the couplers won’t slide off. The new gears showed up yesterday and I’m anxious to see how those made of delrin hold up. New clutch shoes have been purchased and are ready to install. Tuning wise, I have spoken or emailed a few folks in the know and feel like I have a better working knowledge of how these things run. Hopefully I can go through one more tuning session and then run all four. The overriding problem right now is weather....nothing but rain, rain and more rain. Maybe I can get the gears and clutches in and the engines sealed in time to run this weekend..... and maybe not. Not gonna kill myself to get it done. The starter box was also starting to act up again. The box uses a very simple washer to contact two tabs to switch the engines on but there is considerable arcing at start-up which has rendered them toast. I am going to install a Ford starter relay to run the starter motors and then the washer switch will only activate the relay’s very low amperage. Supposed to rain this weekend.....no running happening then!
It’s been several days since I even worked on the car. My wife's 50th birthday party was a LOT of work and fun and worth every minute. I am going get back to work on the car tonight and maybe be able to run tomorrow (2/12/08) I’m anxious to see what difference the sealing, my newfound knowledge, new gears and new clutches will make. One of these days the combination will work and success will be mine!! All mine!!!! Bwwwaaahaaaahhhaaaaaa
I got one night to work and hooked up the solenoid in the starter box ... it works great but the contacts are still a little inconsistent. When contact is made power is there. I also installed the new clutches and found a bad bearing in the front high gear housing so exchanged the bearing from another damaged housing. I also changed out the rear gears to delrin in anticipation of their success. Still waiting to work on the car. Every evening there’s something to do or its just too cold. Tonight I’m taking my wife out to dinner so I don’t mind missing tonight for that. I’m off tomorrow and for the next 17 days so I’ll be able to get a lot done. I’m going to get it back together on Sunday while I watch Daytona so I’ll be ready to maybe do some practice on Monday if there’s no traffic out at the test site. I’d also like to get started on the body since the basic layout of the car is finished. Maybe I can get the plug cut out of plywood and finished....maybe even get a rough mold pulled off of it. Gotta figure out how to vacuum the form also. Also need to repair the rear wing mounts, maybe make a nose out of stiff foam.
Well, back from vacation and a lot got done! I replaced all of the nylon gears with delrin and spent some time tuning each engine. All four are mounted and ready to run! The throttle servo started going wiggy, and eventually got stuck at wide open. Fortunately, the car wasn’t running at the time and I replaced it with a new one. The brake servo also started getting weird so I replaced it also, both servos being much stronger than the originals.
The side by side pairs of engines are now tied together with a brace between the heads. Under power the engines actually twisted away from the spur gears but now they’re very stable. I hooked up the four front tanks to the front engines (two each) and mounted two new tanks at the rear for the rear engines. This has allowed much shorter fuel lines which has made the engines run more consistently.
I managed to get the plug done and am ready to make the mold. I bought all of the fiberglass, resins and gel coat. Hopefully this weekend will provide the time to do the mold. The plug is made of two 4x4's of fir and three pieces of redwood between them, ending up with a body 9-3/4 inches wide, enough to cover everything. The two different woods has caused a problem by causing the joint between the woods constantly show up on the plug. If I fill it and paint it right away it’s invisible but as soon as it sits for a couple days its visible again. Minor, but irritating!
It turned out nicely and is very reminiscent of Mickey Thompson’s Challenger...can’t wait to run it! My goal is to make everything as aerodynamic as possible. This is an area that other racers have discounted as not important but I can’t believe that it doesn’t have the same effect as it does on full scale cars. There will be very small gaps between the body and chassis pan and the mounting screws will be as flush as I can get them, maybe small dzus fasteners. Hopefully this will counter balance any horsepower shortage I may have.
There are already claims of 100 mph so I’m going to set my sights to 110. This may require new gearing but I’m not changing anything until I run at Willits airport and get a true idea of the car’s speed. As I’ve been working on these engines, I really have no idea what RPM they’re running or if they can pull full power at full speed. I also have a question about the mufflers....are they a help or a hindrance? Once I get some nice runs on the engines I should pull one out and set it up on the bench, put a prop on it and run it through it’s paces. I could test venturis, carb settings and mufflers while checking its rpm range. Sounds like something I definitely have to do before going south!
03/09/08 - Got to run today! Put all four in and went to the site . I was rushed and left the radio at home, had to go back and get it then later realized the temp gun was sitting on the bench also. Gotta make a check list. Have I said that before? Prolly......
Started all four and set it down for a few slow passes. It was running great but came in on three so I thought I’d give it a run anyway. The rear wing mount broke a while back and I hadn’t repaired it yet thinking it was heavy enough so made the passes without it. All was well until decided to go for broke on a run and hit the brakes to slow down. At 87 mph it started spinning down the road, fortunately the road had enough dirt on it to minimize traction and it didn’t flip. After gathering myself up I packed up and went home.
Yesterday, I picked up a couple propellers and I’m going to build a bench test rig to allow me to tune the engines in at speed one at a time. I tried doing it in the car but it’s difficult to discern what’s happening as it drives by. It’s also time to step up to the 9 mm venturis. The 7's seem to be holding it back so let’s open it up. The clutches worked great, shifting and staying in gear. I’d like the shift point to be a bit higher so I’ll experiment with tightening the screws more. The delrin gears held up nicely except for the one where the screw backed out so I replaced it and put loctite on the screws (shoulda done it the first time). I fabbed up a four plug starter pack so I can run all four plugs at the same time. It’s much easier to keep them all running that way. My ampped up starter box worked great all day, never failing me once. All in all, it was a fun couple of hours. Again there were lessons to be learned....like the back wing......and the checklist.......and the temp gun.
Over the last couple evenings I designed and built a jig to allow me to bench test my engines under load out of the car. I thought that using a propeller for the load was pretty simple but one of the problems was how to mount it on the engine. I decided to mount the prop on a shaft and drive it from a gear on the other end of the jig, keeping fingers away from the prop blades. It also eliminated the need to remove the clutch from the engines, instead just meshing the gears as in the car. The plate that all this is mounted on will be bolted to the top of the starter box to allow easy starting of the engine while tuning. Can’t wait to try it out! Pretty simple and it should help me tune in the top end on the engines since that’s where all of my interest is. I’ll be switching over to the 9mm venturis and 25% nitro so it’ll be nice to be able to tune the engines before making any runs.
I also want to compare a Macs tuned pipe to the pipes presently on the car to see if there’s a significant difference. I don’t want to start changing the body to accommodate some new exhaust but in light of new competition I may have to. A lot of progress made this week..... I got my engine test stand built and it works well. I mounted it right to the starter box making the tune up procedure easier. The first engine on there runs good but doesn’t seem to be revving very high. I think this is going to be very productive as far as top speed goes.