Another strange idea

Well, my “Holy Cr*p!” idea turned more into of a “Meh…” idea.  It works, but not as good as I'd hoped.  It’s more of a field expedient solution compared to a permanent solution.  But while I was laid up this last week I had another epiphany when I was lying in bed trying to fall asleep.  Since I’m feeling better and can get around now, I decided to try and implement the new idea last night.

I found that a 5/32” brass tube is a tight press fit in the Medallion NVA holes.  The standard fine thread NVA from a postage stamp backplate is a loose fit in the tube.  The first thing I did was take my calipers and measure across the sides of the venturi where the stock NVA goes.  It’s 0.375” across.  I cut a piece of tubing that width and then measured the venturi.  The width of the throat is about 0.175”, so I marked 0.1” from each side of the tube.  I then used my Dremel to cut out the center of the tube, leaving a thin strip between the ends.  This made a nice carrier for the NVA barrel.  Hmmm… the cuts were not too even.  Next attempt I will take more time cutting the tube to ensure everything is square.





I then soldered the NVA barrel into the carrier, ensuring the brass strip was opposite the hole in the barrel.  Afterwards, I took my jeweler’s files and smoothed and shaped the brass backing strip so that it was narrower than the NVA diameter to allow full air flow through the venturi.







Before installing, I took some coarse sandpaper and ran it lengthwise along the carrier to knurl the tubing so it wouldn’t rotate in the plastic.  Then I just pressed it in with the hole pointing down.  The hole’s a little off-center, but since it’s bladder pressure that doesn’t matter.  







So, the question is, does it work?   Well, no.  Or, at least not the first few times I tried it.  Seems the two Cox glow heads I tried were pretty weak.  I put on a Merlin adapter and insert, and Bazinga! (Chuck Lorre Productions, all rights reserved.)  






It seems a hair over-compressed, maybe.  I may try another glow head gasket.  But 18,650 or thereabouts seems pretty good.  It’s a Medallion, not a TeeDee.  Who knows what another gasket might gain or lose?  I’ll fly it when I’m able and see if I want to mess with it or just leave well enough alone.  Too bad Merlin seems to be out of the glow plug business.  When my current supply runs out, I guess I’ll just have to do turbo plug adapters only if I’m not going to use Cox heads.

Now that I’ve experimented and I know how I want to do this, I should be able to do the next one in about an hour.  I have six or seven of the fine NVA assemblies on hand for further experiments, if I want to do more of these.  I find that I am really liking the consistent RPMs of the bladder systems, and being able to do them with Medallions as well as TeeDees is a big plus.  The great thing is that this will also work for a Medallion .09 engine.  I don’t know about a Medallion .15, I’ll have to give that a try.

The Wizard Mark

Good job Mark ! Sounds pretty good in my book 18.5 K is good with a 6x3 prop I think even if it did come out with a couple imperfections You want see them in the Blur going by.

Yup,that's some wizzardy connections for sure! Very Good Idea and well planned out and nicely done. I hope whatever has been keeping you down is going away and lets you get back in full action.

Great picture tutorial Mark.

Gloved hand a necessity, those little APC? props can bite, sharp as a knife too.

Okay, I went to the flying field today.  I wasn’t up to flying, but I could start and toss for my son.  He’s been flying my Flip a lot, but I wanted to test out the Medallion.  Looking at the handle on the plane, I had 30 foot lines on it instead of the 35 foot lines I thought I had on there.  Fellow club member Jim Cameron first flew this on the existing 30 foot lines, and it flew slower than it did on the TD, which is what I wanted.  Then I put on 35 foot lines and it was just about right.  The engine is a little over-compressed, and it took a good bit of flipping to get it to start.  I'll add another head shim before the next time to the field to see how it goes.






Next, I have an idea for a handle I want to try to see if it will make flying smoother when I’m back on.


The Criminal Mark

The Medallion was Screaming way to go !! I have never flew a Skyray but that one with the built up wing seems to fly Great ! I hope you can get your health issues under control so's to get behind the handle again .

Found on my 049 TD engines if I want them to work really well on suction, I get a venturi from Matt or Bernie, get a standard Cox 049 spraybar. Drill the Venturi to take the spray bar, block the sprinkler holes in the venturi and fix the spray bar in with an Aluminum base epoxy and then screw it into the carb body either using standard glow plug washers (not Cox type) or the spacers Matt sells for them. Now it takes the standard long NV that the Surestart Grey backplates use as its the same spray bar I put in. I seal it all up with anaerobic permatex and also mount a short piece of piano wire parallel to the needle valve. I fix the piano wire into the Aluminum base epoxy, and then I put some fuel tube over the piano wire and wrap a rubber band around the NV and it doesnt change setting with vibration and such. You can also adjust the venturi position such that the NV is pointing well back away from the Prop. This also works very well with a TD spring and a Cox round muffler fits perfectly. Getting 22K with this setup according to Android RPM gauge. I should probably post a photo of the Venturi setup. Works fantastic on suction or pressure and everything fits. Spring and Muffler!

Yabby