fit90

Has anyone had any luck installing a fuel pressure tap on a sure start type of engine? I have been thinking about drilling a hole in the case and installing a small solder filled piece of brass tube to drill out and use for pressure. My biggest question/concern is where to drill the hole to get a consistant positive pressure.

I think that these little engines have some untapped potential if they can be fed a reliable source of more fuel.

Any ideas or comments.

Thanks,

Bob

aspeed

I don't know if a pressure fitting would work with a reed valve motor. I don't know that it wouldn't either.  Many moons ago we had an event that Sam Burke made up   Reed Speed.  He took a baby bee and hooked up a Tee Dee needle valve pressed it onto the inside 1/4" dia. of the tank and hogged out the outside of the tank to fit the needle through.  The venturi was drilled to 1/8" and it was run on a bladder.  I can't remember the exact speed, but think it was over 90 mph.  (It was the 1970's  man)  A Surestart would likely be easier to drill out if there is enough meat left for needle to stay on and if the needle is removable.  I don't have one handy to look at but I think the needle goes through the middle of the bore. We used about 3/32" surgical (latex) thin walled tubing for a bladder, but there is a Red Cap used for caulking tubes that is supposedly available now that is suitable for 1/2 A.  Forget the throttle though.  Use the 2 port cyl , high compression head and lots of nitro.  It was a little tricky to start but no worse than anything else with a bladder.   If you want to try a pressure fitting, the only place I could think of is the boss on the crankcase where the screws go in.  I would put it where the relief for the con rod is and solder up the pressure fitting with a piece of .010" wire so there is some resistance to the backpressure and it doesn't flood.  Make sure it doesn't come loose though.  The wall is pretty thin on the case and I can't think of anywhere else that it could go.

Big Al-RCU

Yes they respond very well. This engine was installed in a Jr Falcon and would not run out a tank. This mod cured it. It would run the entire tank very consistant.
Al

Jim Thomerson

A uniflow tank will be a big help. I haven't tried pressure on a reed engine, but routinely run TD's on various pressure systems.

aspeed

Uniflow is pretty good, but if you want to go faster you have to open up the venturi a bit and it could need a little more help than a uniflow tank.  It is worth a try though. Even if it doesn't work consistantly the pressure tap can be attached to it.  I don't even bother with the reed valve motors any more,  the Tee Dees, Norvels and even the AP .09/.15 are more bang for the buck.  (I'll not mention electrics here)  I am even thinking about a Fora .049, not too hard though$$$$

fit90

Thank you for all the advice and opinions.. Big Al, thank you for the pictures.  They truly are worth a thousand words.  I think I will try the pressure tap like in the pictures but with a piece of pressed fit tubing.  This should allow me to open up the venturi more than before and still get a reliable fuel draw.  If I get lucky I might get a chance to begin playing with it this week end.  If so I will keep you posted.

Thans again,

Bob

iskandar taib

My Feedback: (5)

No need for a pressure tap - get some bladder tubing and use a bladder tank. I've done it, it works very well on a SureStart. You won't actually see any sort of speed inrease unless you bore out the venturi, though.

Iskandar

fit90

Iskandar,

I agree.  That is the simplest way to get a reliable fuel feed; but my thumbs are too dumb and fat to do the bladder start up dance.  I just thought that since I have had good luck with pressure taps on front rotary engines that it should work well on the reed valve engines also.  Plus I get the added bonus of the experimentation with the little engines.

Thank you,

Bob

Big Al-RCU

Bob, I should have explained that I didn’t add pressure for performance gain, but rather just to get it to hald a steady needle for the entire flight. Some of the product engines didn’t like external tanks. This was one of them. They were pretty hot and ran well on the plastic planes that they came with but had fuel draw problems with an external tank. This engine came out of a Bush Master. It was a good fix for this plane, no effect on performance, still easy/simple to fuel, start, etc. Going rich-lean-rich-lean-rich at the end of the tank in a single channel is a bit exciting. This cured it.
Al

Andrew

Nice job, Al. Good design and good work.

andrew

aspeed

That is kind of wierd.  Some people call me Big Al too.  Why do big guys fly 1/2 A ?

Big Al-RCU

Thanks Andrew, That was done some 35 years ago long before I acquired my Sherline lathe and mill. It was done painfully with needle files and drills in a pin vise. Sure would be easier and to do a neater job today!
Al

Big Al-RCU

Hah, I’m definitely not a big guy. It’s just a handle that the guys in our club hung on me years ago and it stuck. (I think it came from a reference to Big Al in Disney’s Country Bear Jamboree, and was NOT intended to be flattering)
Al

fit90

Big Al,

Thanks for the explanation.  What I hope to do is to enlarge the venturi to increase performance.  But, as I have found on Tee Dees, once the venturi is enlarged too far the fuel draw begins to suffer.  A little "push" of the fuel from crankcase pressure usually fixes that easily.  It also makes the fuel tank placement a little less critical.  On the downside, it typically requires that the needle valve be replaced with a fine thread needle valve to make setting the needle easier with the increase in fuel pressure.

If I can get my weekend work done in a timely fashion I will try it out tomorrow,  I will run the engine before the mod and after using all the same pieces, fuel, prop, etc. to gat a relatively close comparison.

I will post the results.

You guys have a great weekend,

Bob

fit90

I got time to play today.  The original engine ha an older style Golden Bee crank case assembly, Killer Bee back plate with mylar reed, Tee Dee .049 cylinder with a Xenalook SPI lightened piston, Galbreath head and Nelxon plug.  I ran Sig Champion 25% with one ounce castor added to each quart and an APC 5.7X3 cut down to 5 inches.  It would run 17,900 RPM occasionally blurping above 18,000 RPM and often blurping down to 17,000 RPM.  While installing the pressure tap I damaged the threaded portion of the crank case where the cylinder attaches.  I then removed the crank shaft and drive plate and installed them in a Babe Bee crank case that I had installed a pressure tap in.  I then reassembled the new engine with the same parts from the old engine.  While running with the same fuel and prop I learned that I needed a check valve in the pressure line.  After installing the check valve the engine ran at a super steady 18.550 RPM with very few very small deviations in RPM.  Start up required a very specific procedure but was very easy and easily repeatable. The engine ran out several one ounce tanks with very consistant performance.

All in all, I think it is a great mod that should provide the possibility of enlarged venturis and easier fuel tank installation.  I am looking forward to using it in future planes.

My computer, camera and I are currently not getting along well.  If we are able to sort things out soon I will include the pictures I have taken.

If anyone else tries this I wish them the best of luck.

Bob

nekked_man_2000

when I used to fly my old Cox Black Widow on my Baby Ringmaster, I hated that the prop wash over the the fuel tubes on the top of the tank worked like a venturi and sucked fuel out of the tank. I had seen some of the slow combat guys run a fuel line from the vent on their tanks to a brass tube pointed at the propellor, so I made litte tubes to do the same thing on my tank, on both vent lines, I had to lean out the needle valve, so presumably it increased the fuel pressure. I've done similar things on larger engines that didn't have a pressure tap on the muffler, I think some of the DF engines derived tank pressure this way also.

Austin

Big Al-RCU

I’m curious, what were the symptoms that tipped you off that you needed a check valve?
I did not need one. But again I forgot to mention another detail. The inside end of the nipple was covered over with a thin film of solder and a small hole drilled. Then the nipple was placed over the end of a drill and the solder hole peened to close the hole. It looks to be completely closed to the naked eye, but is still enough of a ‘leak’ to do the job. My thinking was that without a small orifice the effect would be to vastly increase the effective crankcase volume, which I deemed undesirable. Others have stated that the size of the orifice was not critical, which I found surprising, but maybe they were also using a check valve? That would eliminate the entire tank & line volume except that from the orifice to the check valve.
Al

aspeed

We always used a small hole in the pressure fitting so the fuel in the tank wouldn't trickle in accidently, and to keep the crankcase backpressure inside the motor a bit higher.  We used about .008" to .015" wire with wax or oil on it inserted through the fitting hole and then soldered up the pressure fitting. I guess a check valve works too, but the pressure may be higher than needed. The small hole worked well for the .15 sized goodyear motors for restarting as too much pressure would flood it quickly, especially if fuel got in from the pressure fitting into the crankcase. An electric starter wouldn't work at all, likely, if it didn't fire up right away. 

fit90

Bib Al,

The engine would occasionally just stop and the line from the crank case would be filled with fuel.  I do not know if this was caused by the large amount of SPI or that I drilled too large a hole in the solder filling the pressure tap tube (I used a #60 bit and held the tube in my hand causing it to move while drilling the hole).  Also, if I stopped the engine after only using part of the fuel then the tank pressure caused the fuel to fill the crank case making a quick and easy restart impossible.  After installing the check valve the engine would run out a one ounce tank easily  or restart easily if I shut the engine down part way through a tank of fuel.  I do not need a check valve on my Tee Dees or Norvels that use a pressure tap so I think it is probably a combination of the huge amount of SPI and the huge gole in the pressure tap.  Just a hunch.

Bob

fit90

When the engine just stopped and the line from the crank case filled with fuel the fuel was coming from the fuel tank, not the crank case.

Jim Thomerson

I have always run check valves in backplate pressured TD 049s and 09s on stunt airplanes. I've flown the 09 a few times without check valve and found it to be occasionally unpredictable. I didn't use them on Goodyears or TD mice. We did a lot of practice and had starting/restarting down pretty good.

fit90

aspeed,

I am terribly lazy and as such always use a full size electric starter.  Knowing what these can do to little conrods and other parts I tend to typically be a bit cautious, especially when I see that fuel could possibly be in the crank case.  The check valve just allows me to indulge my laziness.  I have not had this problem with other engines and have not had a need to use a check valve except in three line fuel tanks.  In these set ups the check valve prevents fuel from going from the tank into the crank case during refueling.  It tends to be a little complex for a 1/2A set up though.

Bob

aspeed

Maybe keeping the pressure line tube up high in the tank would be better.  And yes they were unpredictable and would flood easily even just from flipping by hand.  What did you use for a check valve?  It may be a good thing to use with a T fitting on a control line combat plane I have for filling it easier.

fit90

I used a Perry check valve for this.  It is a really nice aluminum body valve.  I do not think it can be opened but I am not sure about that.  Kavan also makes a nice check valve that I think can be opened for cleaning.  Tower hobbies also carries a relatively low cost plastic check valve.  With any and all of these make sure the valve wil work with whatever you are going to run through it.

danilo-2

My Feedback: (1)

As an alternate to adding pressure.. at least as an intermediate step.
Use a Balloon tank. Just  fit a simple plain balloon with a fuel line and clunk in it.
 No bladder pressure  needed, mount it in an old 35mm film can.. if you can find one :-)
This gives a very consistent fuel supply, regardless of the model's orientation.