Author Topic: Tech Terror Progress (Read 2636 times)

Larry Renger · « **on:** October 20, 2009, 11:15:26 PM »

I am back on trying to tune in this model. I set it aside some months ago because of engine difficulties coupled with trim problems. Well, I decided to just use the tank in the Golden Bee and leave the internal tank empty for test flying to try to get the model tuned in. Several test flights later, the plane is flying quite well, and has done every maneuver in the pattern. Not great, but the power still in not what it will be. I am much encouraged! I am going to develop what is effectively a pressure feed Venom engine for the model.

To make a pressure tap, I took a short length of 3/32" aluminum tube and crimped it hard over a piece of .010 control line. That will be my pressure nipple/orofice. I have a spot located in the crankcase that should have enough meat for a secure mounting with JB Weld. Finally, I will file a small flat in the tank reed housing to allow the pressure to flow to the nipple. Should have a working engine by this weekend.

Running both tanks on the Golden Bee, I got over 9 minutes run. I really need less than 5, so I can go with a really hot "reedie" and probably high Nitro and still do the full pattern. I am currently on 40' lines, but if the power is good, may go longer. I fly the Sky Sport on 47, and Antone Kephart flies his baby Magician on 50'. I would hope to take this model out to 45' when all is tuned in.

(search Tech Terror for history and photos)

Larry Renger · « **Reply #1 on:** October 21, 2009, 06:26:01 PM »

Test engine completed after a couple of false starts (It's good to have junk crankcases around, this one had severe galling in the rear of the shaft bore, so I could try a couple of attempts)

The way I did the pressure tap jibes perfectly (after the fact) with a Warren Kurth and Larry Conover article. They turn a shallow taper into a piece of brass tube and drive it into an undersize hole in the backplate or crankcase. No solder or glue required! Then they clean up the inside as necessary. I used aluminum 3/32" tube and after seating and cleaning up burrs, crimped it over a piece of .010 wire next to the crankcase. The tube started 3/8" long, and lost just over 1/32" smoothing it to the inside of the case. I expect that the crimping operation helps seat it better. Sighting through it there is a perfectly round, teeenny tiny hole visible for pressure flow. Dang, it worked!

The venturi and backplate are drilled to .093, the piston and cylinder are Tee Dee .051. Head is Cox high compression with an extra gasket. I didn't go all the way and drill the crankpin, but I did grind away part of the crank web. In addition I polished the crankshaft in my drillpress as I usually do. It has one of those brass drive washers so I can use a starter if I so choose, though it does have the usual spring. More data when I have run it!

Robert McHam · « **Reply #2 on:** October 21, 2009, 08:57:11 PM »

I sure hope there are some pics on modding the engine soon. I grasp most of it pretty well but am having a difficult time getting a visual perspective on how and exactly where the pressure nipple goes onto the crank case and where you will be filing the small flat described. Also how is the brass tube crimped and by this I don't mean what too to do the crimping but how is the crimp applied?

Robert

Larry Renger · « **Reply #3 on:** October 22, 2009, 09:25:54 AM »

I use small round nose pliers to do the crimp, but the tube is aluminum, not brass, so it conforms beautifully. The crimping technique is a lot easier than the solder and soot covered wire described in the hop-up articles.

Larry Renger · « **Reply #4 on:** October 24, 2009, 10:05:07 PM »

It turnw out that Cox used 15/16" screws to assemble the long tank reed engines,and mine are 1" When I tried to fuel up this morning, it leaked all over the place, and when I tried to run the sysem, it would flood out with the needle all the way closed. I replaced those bolts with stock ones, and will try again tomorrow!

kenneth cook · « **Reply #5 on:** October 25, 2009, 06:07:11 AM »

Larry, is there enough meat along side of the tank/reed area? I'm imagining that the nipple is in the case where the reed holder of the tank protrudes into it. I'm curious about this set up because I had asked you some time ago if this was possible. You had mentioned it was a bit tricky due to no area for the pressure nipple. This does sound like a suitable way. The next question I have is, what effect will this have on the reed? I'm assuming your using the stock tank with a hole drilled in it for a external tank? Since I was just starting or at least trying to use pressure on some of my tee dee's , would this set up require the use of a one way valve? Ken

Larry Renger · « **Reply #6 on:** October 25, 2009, 03:18:40 PM »

The tap is in the area where the reed housing protrudes, and I have filed a small flat in the side of the reed housing to assure that the pressure can flow to the nipple. Probably not needed, but easy to do.

There is no effect on the reed as the engine cycle is completely normal, and only a tiny bit of the fuel mix flows through the pressure tap hole (.010" diameter is pretty darn small!).

I tried again to run the engine, and was just about there, but there is enough pressure in the tank to blow off my pressure cap. I will have to make the tubes larger and longer to hold the pressure sealing caps and fuel hose from the external tank on.

I am running an external tank, but it flows to the lower tank tube on the engine, thus I can use the capacity of both tanks. Photos soon!

Larry Renger · « **Reply #7 on:** October 25, 2009, 10:08:12 PM »

Here are the photos. Pressure tap inside and out, the flat filed in the tank (oops, wrong place the first time, but no harm done) and the fuel pickup system I use.

I put some .050 weed-whacker line inside the tubing and bend it over a dowel, then pull the line out. Then I trim it to fit. Final bends can be done without the weed line inside if you are careful.

minnesotamodeler · « **Reply #8 on:** October 26, 2009, 02:36:29 AM »

I suppose you're running the pressure line to the exterior tank? Is there no change in fuel flow when the auxiliary tank empties and you're feeding from the integral tank only? I guess I'm having a little trouble visualizing this whole setup. It sounds well thought out but not exactly clear to me. I'm also guessing the main point (other than increased fuel capacity) is to run a larger diameter venturi, you said you drilled it out to .093? That ought to increase power for sure. I wonder what the limit is for a reed valve? Somewhere there's got to be a point of diminishing returns so to speak. Very interesting project.

Larry Renger · « **Reply #9 on:** October 26, 2009, 10:03:21 AM »

One limit on drilling the venturi is that you run out of venturi to drill, at the very least! .093 is cutting it pretty close.

The whole point of this excersize is to get greater fuel capacity than I have in the integral tank without modifying the outlines of the model. The plane was designed to fly with just the Golden Bee for power. However, the stock engine doesn't have enough capacity to do the competition pattern, and is marginal on power for that anyway. So, I added a tank inside the plane, but it is also too small due to the limited room. The two tanks together have all the volume I need. Fuel pickup from the rear tank goes to the bottom tube on the engine tank. The top tube on the internal tank is capped as is the top tube on the engine tank. I guess I better shoot a photo of the whole works (or did I do that in the original thread? but I'll do it again with the pressure line in place)

In my initial runs, I could not get a single needle setting that worked with both tanks. Thus the quest for a pressure system.

minnesotamodeler · « **Reply #10 on:** October 26, 2009, 11:36:27 AM »

Oooohh, you had the dual tanks working, even sort of, on suction? That is impressive, I wouldn't think it would draw from that far. Seems like the pressure setup ought to do the trick, sounds like plenty of pressure if it blows the lines off.

Yup, I'd like to see a pic of the whole shebang.

Larry Renger · « **Reply #11 on:** October 26, 2009, 07:00:10 PM »

As the Jewish baker said: "Your Knisch is my command!" Here is the setup. Actually, the venturi and fuel pickup are at the firewall, so the fuel draw from the rear tank isn't all that bad. But one behind and one in front with all that piping turns out to be just too much difference.

minnesotamodeler · « **Reply #12 on:** October 27, 2009, 04:13:39 AM »

Larry, thanks for the picture, all is clear, very nice installation. Keep us posted on how well it works, how steady a run, etc.

I have run outside pressure on a reedie (Black Widow, bladder tank to outside vent, fuel line from inside vent to fuel nipple, so bypassing integral tank, gives a good solid run by the way) but never thought there would be a way to use crankcase pressure. I may have to give that a shot myself. No more fiddling with line clamps, etc.

Great contribution to the world of reedies!

minnesotamodeler · « **Reply #13 on:** October 27, 2009, 04:30:55 AM »

Further musings: Apparently the pressure tap location could be most anywhere in the crankcase, right? If a fella needed more meat to hold the pressure tubing, he could even drill through one of the bosses ahead of the tank screw hole. Or vertically right beside (behind) the cylinder, for a little more protection from damage.

Larry Renger · « **Reply #14 on:** October 27, 2009, 11:03:29 AM »

Any place the pressure gets to is as good as any other. The wall I drilled through seems thick enough for a sturdy mounting. The screw boss area would be even better, I guess. I'll have to experiment with that scrap crankcase I still have.

minnesotamodeler · « **Reply #15 on:** October 27, 2009, 03:28:07 PM »

I'm thinking in terms of a slightly undersized hole, then heating the case while keeping the fitting on ice, then insert and let cool. Unnecessarily complicated procedure? But using aluminum tubing a guy couldn't exactly drive it in.

I should stop asking questions and just go try it.

Larry Renger · « **Reply #16 on:** October 28, 2009, 12:11:38 AM »

If you go back to earlier in the thread, drive it in is exactly what I did. But, I reamed the hole till the tube almost fit, then taper filed the end of the tube so it entered the hole easily and locked up as it was driven home. Dremel tool to level it inside the case, then the crimp on wire bit. Of course you could just drill the hole to .093 and JB weld the tube in place. (Too easy?)

Heating and chilling should work too, but sounds pretty hairy to me.

minnesotamodeler · « **Reply #17 on:** October 28, 2009, 01:20:51 AM »

I have a hot air gun (hair dryer on steroids) that's safer than a torch on the object being heated. Really great for de-warping wings too. Have to be careful when heat-shrinking plastic film with it, just quick passes and not too close. My planes occasionally acquire patches before they're ever flown.

I'll probably try your trick of tapering/driving first. If I mushroom the end a little seems like that actually would be good, help hold the fuel line on.

Robert McHam · « **Reply #18 on:** October 28, 2009, 07:36:28 AM »

I have been following closely to all of this from the beginning but sad to say have not been able to add anything till now.
The picture below shows an early production engine with a Goldberg radial mount adapter (the reason I saved the picture) and later I noticed it also sported a pressure nipple! The engine was for sale on Ebay a while back and I had no real interest in it at the time other than it shows how the Goldberg adapter fits on the back plate. There are those who have never seen one of them before.

The pressure nipple. looks cleanly done and since there are no flats near the base for a wrench to grab onto I would have to say this was pressed in.
This is the only other reedie I know of to have a pressure tap

For your consideration gentlemen.

Robert

minnesotamodeler · « **Reply #19 on:** October 28, 2009, 03:32:06 PM »

Man, that appears to be right in the race for the bottom of the rod...very thinnest part of the crankcase.

Larry Renger · « **Reply #20 on:** October 30, 2009, 08:45:05 AM »

Going through the boss like that there is probably plenty of "meat", but I would move forward as far as possible to get ahead of the thin spot.

minnesotamodeler · « **Reply #21 on:** October 30, 2009, 03:07:18 PM »

OK my heat/cold trick failed miserably (hot enough to burn my fingers, no appreciable expansion), so I drilled a 3/32" hole and (gently) drove the 3/32" alum. tubing in, then swaged it around a piece of wire as per your description. It's fairly solid but I wonder what the vibration of running will do to loosen it. I may put a fillet of JB Weld around it for insurance.

Oh and I put it in the same general location you did, Larry, after all the thinking about using the boss, etc.

Larry Renger · « **Reply #22 on:** October 30, 2009, 09:59:49 PM »

I thought the 3/32 hole was a bit too loose a fit, so thus the smaller hole and taper on the end of the tube and drive it in. I think JB weld is in order for you.

minnesotamodeler · « **Reply #23 on:** October 31, 2009, 07:06:49 AM »

Yah, it's simple insurance, and holds on these little engines very well. I have 2 different Norvels with the venturis JB-welded in. Just redid one after about 3 yrs' service.

minnesotamodeler · « **Reply #24 on:** October 31, 2009, 06:58:04 PM »

OKAY, here's the fruit of my labors...

first few pix, pressure tap, thoroughly anchored in JB-Weld;
Next, fuel/pressure line arrangement;
Finally, the plugged overflow.

Not as pretty as Larry's, but then my stuff never is...I'm just a throw-it-together, try-it-out kinda guy.

I think it'll work.

Incidentally, this engine also has the drilled-out venturi per Larry's description.

ray copeland · « **Reply #25 on:** October 31, 2009, 10:05:43 PM »

My tries at crankcase pressure have been unsuccessful with a stock tank, crankcase pressure is way higher than muffler pressure and on inverted flight even with a one way valve has resulted in a rich run to the point of engine cutoff. The hole in the Norvel crankcase pressure backplate is very small and may work . Will try it this week on my remodelled Hyper Viper. Hope you have better luck than i have, am looking forward to flight reports.

minnesotamodeler · « **Reply #26 on:** November 01, 2009, 01:12:59 AM »

I've already realized and corrected one mistake: The pressure line must go to the bottom vent (which extends to the top of the tank) to avoid flooding when starting--otherwise it will suck fuel back into the crankcase at every upstroke...the vent I have it hooked to in the photos goes to the bottom of the tank and is immersed in fuel. I finally recalled from my RatRacer days, that's a no-no.

The last time I ran crankcase pressure was in about 1965! So some of the subtleties are a little slow reviving in my mind.

Larry Renger · « **Reply #27 on:** November 06, 2009, 12:01:19 PM »

I have been making some progress, but I think I have TOO MUCH pressure. I can't get consistent needle settings. I will try several smaller size holes. Andy Borgogna pointed out that I can just make restrictors to throw in the pressure line, it doesn't have to be IN the engine! DUH! (on my part)

I also want to try a lower compression head. I have the High Compression with an extra gasket, and that still may be too much.

minnesotamodeler · « **Reply #28 on:** November 06, 2009, 08:13:31 PM »

I ran mine, and apparently have WAY too much pressure...about one click of the needle from sagging lean to flooding rich...I made a (further) restrictor from smaller tubing that fits inside the tubing on the engine, squished down even more. Seems pretty limited now when I suck on it. I plan to test it again tmw (Sat.) But, it's encouraging that the system does work! And to think I wasn't sure a reed-valve engine would put out enough pressure to be useful.

Robert McHam · « **Reply #29 on:** November 06, 2009, 09:18:05 PM »

I will be glad to see how this will be solved.
I propose a needle valve to regulate the air flow.
Or if you remember the Perry pumps and regulators, a smaller version?
This came to mind from my working days: http://www.toolsource.com/inline-flow-regulator-p-65530.html

Robert

Larry Renger · « **Reply #30 on:** November 07, 2009, 10:25:42 AM »

I plan to make restrictors with .004, .006 and .008 holes. The tap currently is .010, but I have wire in those smaller sizes. News at 11 (some day or other).

minnesotamodeler · « **Reply #31 on:** November 07, 2009, 03:13:25 PM »

I'm thinkin' you better go with the .004--with the further restrictor in mine I got it running well enough to fly today, but it still is very touchy, just seems to put out way more pressure than it needs. I can hardly see light through the tap now and it's still too much.

Larry Renger · « **Reply #32 on:** November 08, 2009, 02:31:18 PM »

I agree and will start with the .004 hole restrictor. Sadly, I have a cold and couldn't go flying this morning.