Holy smokin' pipe Batman, lemme see that for a sec..
 

A couple of young ruffians from the city came up for the afternoon and we played put-the-pipe-on-the-engine. Specifically they had a Lanier Shrike .10 I guess it was, with a GMS .32 in the nose. Apparently they had been bombing it around on this engine for a bit and wanted more snap, so got a Macs header and "nitro pipe". Whaddya know, second airplane and certified speed junkies already. There is hope for this world after all.

So we yanked the engine and plumbing out by rhe roots, with step one being to bench run it with the stock muffler on a target prop and get a baseline. The OPS .65 was still fitted up, so what the heck we decided to give that a run first to get warmed up. After two shrieking runs we headed back to the dungeon for warmth, me leading two pairs of saucer plate eyes and babbling grins. Next we fired up the GMS .32, on an 8-6 APC which I planned to use to set the pipe up on the bench, having suggested an 8-7 is likely the prop for them to get the best top end out of the aircraft. I really did not know what to expect on the 8-6, but muffled on 15% nitro it peaked at about 16,300-400 and settled in nicely at 16k or so backed off a bit. So I figured cool, we ought to see 17 and change with the pipe.

After trimming the header to 3.75" based on reasonably useful similar data in the chart provided plus 1/4" for added measure off the top, we fitted it up the stand with the pipe. Fired it up, warmed up a bit, pinned it - pinch, tweak, pinch, tweak etc.. there we go, up in the 15's, and clearing up and.. zinggggg.. would you believe it hit 18,300. And, like the comments I stirred up on the 'net the nigth before, there wasn't enough turns in two needles to get it opened enough to richen it up. It ran like a bear, not past dead lean I am sure, but very close, and spun up over 18k and singing like a canary - it seemed really happy. But without adjustment left I shut it down fast, and looked for fuel system issues. Blew out the plumbing, checked it all over, hmm.. add fuel and try again. Same deal. They were delighted - the darn thing just came alive on that pipe and header and the power increase was noticable and substantial. So back inside to check for elaks etc.. none found. I had fiddled a bit on the stand before shutting down and found I could force it rich easily with a little help on the pressure side. So one possibility was that the stock header mounted pressure tap wasn't giving enough for even this rather short and efficient setup. But.. folks had spoke of similar troubles. Maybe GMS never tested them on aftermarket pipes? Anyhow, I poked arund and the 4A carb off my Max .40 fit perfectly and appeared to be idenitcal or a few thou larger in bore, so I suggested one way to determine carb or pressure system is to try a known functional carb. So back outside, and after a few wet starts due to the airbleed being screwed in much to far - whereby I showed them how to run off a crankcase full of fuel - I got it running and opened the throttle, and lo and behold it was in a fast 4 cycle.. a few clicks in and up it went on the pip eand singing a nice smoky song. ran like a bear, and in fact gained a couple of hundred rpm over the prior runs. So, since this was a bit over the supposed peak hp number of 18k, on went the 8-7 to see how that held it back. Better ground load, now it needed just a little more urge to stage onto the pipe, but it jumped on with a pinch and off it went again, this time pulling the 8-7 up to 17,400 or so, and I backed it off to 16,800-17,000 for a bit of a bench run.


Anyhow, it was a cool, very orange and yellow rustling maple-leafy afternoon of repeated open piped engine runs - IOW, a fun afternoon. The gain in output was tremendous, I was very pleasantly surprised by the repsonse of the engine to the new set-up. This was my first chance to handle a .32 sized engine; I do not own one. I can see how it would make a great power plant choice for a Screamin Demon delta in particular as an example, and for other stuff too, esp. .25 sized sport aircraft.

In the end, I loaned them the OS carb (drop in replacement, kind of plink - plunk it's in) for now while I fiddle with the GMS unit. After they had the chance to hold the aircraft with the piped engine reinstalled and running full bore, they realized it was ready for near vertical takeoff and seemed to approve of the retrofit. The 8-7 seems like a good match for the set-up, and I think a tad more needs to come off the header to get it right for flight, probably that 1/4" I left on for good measure is about bang-on.

I think the internal arrangement where the LS needle intersects the spraybar is too restrictive, I don't like how it feels in the "blow through an 8" scrap of fuel tubing" test. I think it becomes the bottleneck soon after normal rpm and exhaust system fuel demand levels. I even swapped the GMS RNB for the JEtt unit I had just run on the .65, figuing it ought to flow enough fuel, right?.. no change. I did bevel the pressure tap inlet - the one in the header flange. I wanted to move it to the pipe fat point, but the owner was waffling. "drill a hole.."? So I proposed the carb swap test, and it passed with flying colors. I think I might carefully bore the spraybar a bit to reduce fuel flow restriction at higher throttle barrel positions. I may bugger up the mixture somewhere in the middle, but I'll risk it for science.

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

Nice going! I have heard good things lately about GMS from the combateers. I had totally written them off after buying a weak .25 several years ago.

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

I think the only thing that is a major vs minor complaint, if it proves out, is this fuel restriction issue. According to his descriptions of flights to date with the muffler, he has constant problems with it cutting out, but I suspect the old needle fingers and ears just aren't seasoned enough yet to back the needle off to where it ought to be. However, when I googled the engine for info ahead of time, I found forum reports of fuel draw issues. So.. maybe.

I found two things that concerned me off the top:

One was that the remote needle assembly continued to meter the flow until I backed it out enough to drop out of the threads, and by that point there was still noticable restriction in the system relative to removing the needle and plugging the hole for free flow. So to eliminate that variable, I swapped in the Jett needle assembly that had only an hour before worked on the OPS .65. IOW fuel flow was not restricted in this RNV for the likes of a .32. Aha! No change in it's behaviour on the pipe, I could not open enough to crack into 4c. So the RNV was not the bottleneck.

The second was that - subjective though this is - I thought that the fuel line "blow test" through the fuel inlet - spraybar assembly was a little bit restrictive. I strongly suspect that piped operation on the stand and in a an aircraft is not part of the R&D and QC process at GMS. This could easily be a problem that surfaces primarily with the increased fuel demand of an aftermarket piped system. To prove this out, I rooted around in my drawers - my engine drawers - and found the carb from my old Max .40, a drop in fit (.511" I think, or the other standard just bigger, .550" or so I think) and with this carb being visually virtually identical in throat diameter (I wasn't that worried about the few thou diff) I expected similar performance. It ran great, and I could easily needle it to a smokin 4c. So.. yup, the carb is restricting fuel flow, or not sucking enough in the literal sense. I think I might drill the spraybar out carefully a few numbers larger, and hope the mixture stays workable in the mid to low range. At worst, we'll have a carb we don't want to use that works more poorly than it did prior.

Beyond that, with it;s own carb on the muffler it throttled well, and ran pretty strongly. With the pipe it took off, and sounded very pleased with the accessories. The owner was concerned with the slight lloss of throttle smoothness, and I fixed him a beady eye and mentioned he had just dropped $90 on an open pipe and header for an $80 engine and got over 17k on the 8-7 prop.. you just don't get extra gravy with that! Actually, it can clean up a bit more, the major thing is that it is nicely overpropped a hair with the 8-7, ad it takes a tweak to get it to stage. This bodes well for the in air performance on the same prop. It wa dark by the time we got it running on the aircraft, but they got the picture holding it with the engine pinned. Grins all around, so flight reports to come. Not a bad little aircraft, I have never had the opportunity to handle a Shrike in person. Now I wanna fly it too.

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

We are flying a couple of GMS 47s on reasonably clean airframes. I will try a pipe on one of them. If it gets those extra 2K ypu got with the 32 it will be a pleasant surprise, running a $70 engine @17,000 rpm.
Thanks for the tip!!!

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

But be aware that this comment about fuel flow has popped up with more than the .32. The GMS .32 with the stock carb is not functional yet. I have opened up the spraybay slightly, but have to get the engine back to try it out now.

But I think I did a good job convincing these guys the .32 was perfect for a Screamin' Demon. Captive customers, heh heh... [>:]

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

I have used that Harbor Freight aluminum solder to attach a thick pad of aluminum to where I wanted to tap the tuned pipe for a fitting. You could probably just go with a build up of the filler rod, then tap it. I've been told that the pressure tapping at the flange isn't the best place.
Recently I tapped a K&B.15 backplate hole for a #6 thread brass nipple and drilled a pin hole into the case. This works great, since this engine runs open exhaust.
If you are working with a system that has good pressure, you should be able to pull the fuel line off ahead of the needle [while the engine is running fast] and fuel will shoot out of the line like a little fire hose for a second.

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

I have no hands-on experience with header mounted pressure taps, I have never done one or bought one that way. We dremeled it so it had a wee bevel, to ensure there was at least no venturi effect happening. I think the pressure would be better on the pipe, something tells me it is marginal here. I'm going to have at it next time he comes by with the whole affair to fly, now that I've slept on it. I've never heard a complaint about a pressure tap in the pipe, I have heard questions about taps in the header or header flange, and I have heard some but not all people say it works perfectly. So I don't bother with them anywhere else except the pipe.

But.. should it not be able to be tuned on suction only on a test stand with everything level and the tank stuffed right next to the engine? If the pressure line is mandatory on the test stand with a pipe is that a sign that fuel draw is marginal or is that to be expected? I'd say it means the system is going to have trouble in the aircraft in the air, but..?

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

Oh btw CP, I have no qualms about tapping a pressure fitting into the pipe. I just had a hard time convincing the young protege we needed to perform surgery on his fresh out of the bag pipe. I think if it came in chrome he'd have one. Like I say, next time he shows up to fly I'm tossing the thing on the bench for some plumbing work and give him the choice of looking at it or flying it. Young bucks with bling in their eyes.. :) Just foolin', it actually got pretty late so we ran it up on the aircraft once with the header tap still in place, and terrifying the local trick or treaters with our high rpm nitro burning piped Freddy Krueger act in the pitch darkness outside my barn. Anyhow, I think it leaned a little too much nose up and I plan to see it changed next chance.

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

The wall thickness of some pipes might be too thin for a reliable tapping job, that's why I like to build the area up with filler.

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

Fer shure. I just swapped the black matte and very light OPS pipe on my boat with the Weston plated fancy muffled job that comes with the .50V1 package, coz it looks real sharp on the boat and it needs a muffler for goodness sake (ouch!) and the OPS pipe weighs almost nothing and I plan to fit that to the West .50 and back on a delta. But my point is, in the OPS pipe it has a real nice through the wall fitting with a nut inside the pipe. A bit fiddly but I guess with the right homemade laparoscopic tool and some patience it could be done that way. I usually make a tight fitting "tapped" hole then screw in the fitting with Permatex. So far they work okay but I sure like the fitting on the OPS pipe.

So that aluminum solder works and can actually be used by the average twit like me? I like the idea.

These cool fall days, with grey skies and all the maple leaves piled on the ground, take my mind back in a flash to when, as a kid, this season would find me in and out all day with all sorts of FF and Cl contraptions - when not messing around in the sand with firecrackers and my buddies - since the grasses and what not were all cut and/or flat by now, and a network of open fields was always calling for something, anything to come fly. I wish it would do this for three months, then dry up and get warm again. Well, I guess it does just that a few hundred miles south doesn't it? I have the sudden urge to run a Babe Bee on a yellow Tornado 6-3 and stand behind it..

MJD

RE: Holy smokin' pipe Batman, lemme see that for a sec..
 

Cleanliness is important with aluminum and never touch it with plain steel, use stainless steel wire brushes to prep the area. It is possible to burn through with a propane torch if you really try hard. If you have an old pipe to practice on, that's the way to go.