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Engine basics => Engine set up tips => Topic started by: Howard Rush on June 14, 2012, 07:13:55 PM
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A local guy stopped by today. He has an Impact with a .46VF. It has a largish Randy pipe with a fairly flat back on it, with the marked baffle 18.5" from the plug. He is using a Mejzlik 12-something-4, 3-blade prop. The engine had a .284"-ID Scott Riese intake. It has a needle valve assembly I didn't recognize, but it looks kinda like a Supertigre with a little knob on the outside end of the needle valve. I forgot what the diameter is, but it looks about like the Supertigre. He is not using pipe or any other pressure. He was using a Fireball hot plug. The tank vent is above the tank and to the inside of the circle. The engine shows no sign of leaking fuel and is clean as a whistle. It blasts off at 10,200 RPM (as I remember), and sounds and feels fine when he's flying. The problem is that it burns or does something with 7.5 oz. of Powermaster GMA 10-22 or 5-22 in 4.5 to 5 minutes. I taped his flaps and sent him home with a Thunderbolt idle-bar plug and a .275" intake, but I can't imagine either of those will change the gas mileage much. What do you reckon is wrong?
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I think you've already solved the problem with .275-inch venturi. Assuming the bar being used is .15625-inch. If nothing else, use of venturi you have supplied will eliminate this as being a problem.
Is this engine stock internally? Might want to look under the head for a huge stack of shims.
Dan
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A local guy stopped by today. He has an Impact with a .46VF. It has a largish Randy pipe with a fairly flat back on it, with the marked baffle 18.5" from the plug. He is using a Mejzlik 12-something-4, 3-blade prop. The engine had a .284"-ID Scott Riese intake. It has a needle valve assembly I didn't recognize, but it looks kinda like a Supertigre with a little knob on the outside end of the needle valve. I forgot what the diameter is, but it looks about like the Supertigre. He is not using pipe or any other pressure. He was using a Fireball hot plug. The tank vent is above the tank and to the inside of the circle. The engine shows no sign of leaking fuel and is clean as a whistle. It blasts off at 10,200 RPM (as I remember), and sounds and feels fine when he's flying. The problem is that it burns or does something with 7.5 oz. of Powermaster GMA 10-22 or 5-22 in 4.5 to 5 minutes. I taped his flaps and sent him home with a Thunderbolt idle-bar plug and a .275" intake, but I can't imagine either of those will change the gas mileage much. What do you reckon is wrong?
I don't know. Uncle Jimby has a 40VF, set up just like mine, that burned something like 7 oz a flight while mine was using something more like 5-5.25, with apparently about the same performance.
The only thing I can imagine is that there is something binding up and making it use more fuel with no more HP delivered. The 20FP does that when it is new - the fuel consumption goes down by roughly a factor of two over maybe the first 15 flights. Jim never flew his enough to see if that would happen, he went straight for the PA61. That had other interesting effects - like moving the stalls from the third corner of the triangle to the first.
Brett
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Thanks, folks. He thinks the new intake and glow plug might have done the trick, based on a ground run. He disassembled the engine and reassembled it in the meanwhile, which could have fixed a bind. Yes, he does have two head gaskets, but he thinks that adding a second gasket improved gas mileage. We await flight data.
Correction: his blast-off RPM was 10,500, rather than 10,200.
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Don't mean to hijack the thread, but I have a similar issue with my RO-Jett 76. Before the line broke, I was using six ounces of fuel in about 6 1/2 minutes. After the crash, we put it back in the air, and it ran much shorter time, around 5 minutes. We took the engine apart and saw the connecting rod was bent a couple thousandths of an inch. We straightened it, thinking that was what was wrong, and put it back in the air. It still ran the same amount of time, about 5 minutes. This time the tank was leaking, so that got fixed, and now the run time improved to 5 1/2 minutes. I stopped flying it last year after one thing after another was breaking on the airplane (landing gear, crankshaft stud broke in half sitting on the ground).
This year, I took it up once and one thing I noticed was my lap times were varying between 5.2-5.7 without moving the needle a great amount (less than 1/16 of a turn). My fuel consumption is still really poor around 5 1/2 minutes. We changed nothing to the setup of the motor after the crash, so could there be something like what Brett said that could still be binding in the motor?
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Not sure how valuable it is to this conversation but...I had a similar fuel consumption many years ago with a 46 VF using a fat long pipe set up like you described.
On reccommendation from someone (don't remember who but it could have been Bill Byles) I switched to a "skinny" 40 pipe and shorter length (around 17.5 in I think) and fuel economy nearly doubled. Don't ask me why?
Perhaps the big pipe is wasting fuel????
Randy Cuberly
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I wondered about that. I would have let him try one of my wee pipes, but he uses a really long header, and I would have had to cut the pipe to have it fit his engine. I guess I could have him cut the header to fit my pipe. There's a sex-change-operation metaphor here somewhere.
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I wondered about that. I would have let him try one of my wee pipes, but he uses a really long header, and I would have had to cut the pipe to have it fit his engine. I guess I could have him cut the header to fit my pipe. There's a sex-change-operation metaphor here somewhere.
Now that's funny... LL~ LL~ LL~ LL~ LL~ LL~
Randy C.
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The setup he has normally uses about 6 ounces, I setup 100s of those for people, His is a strange one, I spoke to him on the phone about a week ago and gave him some things to try.
Another thing would be to remove the 10mm exhaust deflector, and install a 9mm deflector, this will make the venturie act effectively smaller, and will give a little more milage, more break in may change that also.
Randy
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"He is using a Mejzlik 12-something-4, 3-blade prop."
Seems like a LOT of prop for a .46VF. I run a 12-4 BE 3-blade on my PA .51, and that's about too much, and the fuel economy is bad, as a result. The .46VF runs well on a 11.5 x 4 APC, and around 6 oz. of 10%. Yes, the APC is ugly and grey and is far too cheap to suit some, but it works, is easy to obtain, and I don't give a crap about how heavy it is. y1 Steve
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"He is using a Mejzlik 12-something-4, 3-blade prop."
Seems like a LOT of prop for a .46VF. I run a 12-4 BE 3-blade on my PA .51, and that's about too much, and the fuel economy is bad, as a result. The .46VF runs well on a 11.5 x 4 APC, and around 5 oz. of 10%. Yes, the APC is ugly and grey and is far too cheap to suit some, but it works, is easy to obtain, and I don't give a crap about how heavy it is. y1 Steve
No that is NOT a lot of prop for a 46 VF, the prop he is using my PA 40 will turn, it is a "N" narrow blade and was made for this size pipe engine, It has no where near the load or drag of the eather prop.
The prop is a 12 x 4.33 N 3 blade, the Aero Tiger turns this prop cut to 11 inches on many many ships, and the VF 46 has many people that use this prop. The other prop that works very well is the 2 blade Majic 12.2 x 4.2 , it will turn it easy as is or cut to any lenght down to 11.5.
Both of these were Originally Bolly props I had made, we made new molds for the new CF props from those older props.
Bill Rich ,Bill Werwge and dozens more people used the wide blade 12 x 4.25 Bollys on VF 46s years back, I shipped those all over the world for the Piped VF 46 engine.
The 40 VF would never come close to turning that one, but the 46 has much more power than the 40 does.
Regards
Randy
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I thought that on the west coast getting a .46 to burn 8+ ounces of fuel for a pattern made you a hero?
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I thought that on the west coast getting a .46 to burn 8+ ounces of fuel for a pattern made you a hero?
Oh, that's helpful. I think we have explained why we do what we do sufficiently in the past, so I won't bite.
Brett
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Other props that work very well on the 46 VF are:
12 x 4 n 3 blade Bolly
12 x 4 N 3 blade Bill Lee prop
11 3/4 x 4 1/4 , and 12.2 x 4.2 Bolly 2 blades
and the majic clones of those
plus the 12.1 x 4.5 majic
Randy
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Oh, that's helpful. I think we have explained why we do what we do sufficiently in the past, so I won't bite.
Brett
No worries, that was supposed to be tongue in cheek and not a troll attempt. The SN Special edition pipe tuning article is something I read and re read frequently, and explains what you guys do and why.
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I doubt anything is wrong I flew my OPS the other day with a big Eather #7 pipe, high compression & big venturi it used well over 7 ounces & the time was under 6 minutes I feel as long as its good in the air there ain't nothin wrong. This thing was on par with one of my PA.51s I care less who believes me.. if you want power you need fuel pretty basic.
john
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I doubt anything is wrong I flew my OPS the other day with a big Eather #7 pipe, high compression & big venturi it used well over 7 ounces & the time was under 6 minutes I feel as long as its good in the air there ain't nothin wrong. This thing was on par with one of my PA.51s I care less who believes me.. if you want power you need fuel pretty basic.
john
HHHMmmmmmmm....
Well that may be "pretty basic" but not all that logical. Especially if the "Big Pipe" is simply sucking all the fuel into the header and not really putting it back into the cylinder. The result is cool running, high fuel usage and not really one iota more power except in some folks imagination!
If this theory were correct all one would have to do to increase "power" is to increase fuel pressure and usage...definitely not so!!!
Randy Cuberly
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Hi Randy,, dont you find with the more powerful engines you use more fuel? I mean 90% of the time.
John
PS Randy ,, didnt you retire? And if so is there any chance you'll be in Muncie Mid July?
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Hi Randy,, dont you find with the more powerful engines you use more fuel? I mean 90% of the time.
John
PS Randy ,, didnt you retire? And if so is there any chance you'll be in Muncie Mid July?
Hi John,
Yes I did retire...unfortunately I seem to be working harder than when I was working...does that make any sense? Well you see I have this lovely wife that...oh forget it! Short story is not this year, maybe next!
Good news is I am getting some airplanes built and finished. Sowly but surely! As the stooges said...Slowly I turned...
Good luck in Muncie.
Randy C.
PS: To answer your question...Sometimes. However more power can come from a leaner mixture and that may actually use less fuel...probably will all things equal.
Pipe geometry can, if not correct for the job required, waste fuel by actually pulling the charge into the pipe and not increasing the actual charge in the engine. I know you know that, and I'm not trying to talk down to you, however if you consider that coupled with a fairly large volume engine like a 60/75 something, the power may still be more than adequate to fly the airplane nicely but not efficiently use the fuel. This can sometimes result in a very nice sounding, constant, fairly powerful mid-range four stroke...however at the cost of lousy fuel efficiency.
Bottom line is that pipes work on thermo-dynamic principals with several variables and can sometimes be difficult to give predictable results when different geometry is tried with different engine parameters. Maybe that sounds like gobble-de gook, but there are a lot of variables at work and un-managed changes can give unpredictable results.
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Randy C.
PS: To answer your question...Sometimes. However more power can come from a leaner mixture and that may actually use less fuel...probably will all things equal.
Pipe geometry can, if not correct for the job required, waste fuel by actually pulling the charge into the pipe and not increasing the actual charge in the engine. I know you know that, and I'm not trying to talk down to you, however if you consider that coupled with a fairly large volume engine like a 60/75 something, the power may still be more than adequate to fly the airplane nicely but not efficiently use the fuel. This can sometimes result in a very nice sounding, constant, fairly powerful mid-range four stroke...however at the cost of lousy fuel efficiency.
Bottom line is that pipes work on thermo-dynamic principals with several variables and can sometimes be difficult to give predictable results when different geometry is tried with different engine parameters. Maybe that sounds like gobble-de gook, but there are a lot of variables at work and un-managed changes can give unpredictable results.
Sounds about right to me. For example: both of my PA 65s on a Randy high torque pipe run 7+min. on 6.5 oz of 10% nitro. I have to take a little fuel out of my 6.5 oz tank, usually about .25 oz. So it will do the full pattern on 6.25 oz of 10% nitro with plenty of time to spare. I could get away with 6 oz if I wanted to. By the way, it makes TONS of power.
Derek
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Short story is not this year, maybe next!
That's what I keep saying about VSC. I look forward to seeing you at both.
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That's what I keep saying about VSC. I look forward to seeing you at both.
Thanks Howard...
Don't give up on either one!
Randy C.
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I'm not sure VSC is ready for a party animal like Howard. ;) Steve
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I'm not sure VSC is ready for a party animal like Howard. ;) Steve
Given the crowd that is here, Howard will just be one of the Boys!!! y1 y1 #^ #^
Randy C.
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Randy C. , what I am seeming to do ( without optimum results) is run a big prop at lower rpm in order to not let these PAs charge. I end up with a big venturi & high compression , high nitro. The run & result is pretty fair but I end up not on the powerband , so entry into a manuver is sometimes sluggish. I use lots of fuel & its runs quite well at hte expense of lots of fuel & running about 60% power. When I put on a lesser prop the thing wants to unload in the air & go. True enough big pipe most likely pulls a lot of fuel into the engine & blows out a lot of unburned fuel also. This is the payoff for a real strong 4 cycle run at least this is what I've found. Going back to my OPS .40s next year .
john
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Randy C. , what I am seeming to do ( without optimum results) is run a big prop at lower rpm in order to not let these PAs charge. I end up with a big venturi & high compression , high nitro.
That's more-or-less what we were doing, but reducing the diameter and adjusting the pitch to get right speed accomplishes much the same thing without having to bog it down at low revs. The key it to unload it enough that it never gets into a 2-stroke under normal circumstances. Once you get that set up, you can throw all the nitro and compression that you want within reason, without getting the excess boost. Running it at low revs (say, launch revs in the low 9000s, in the air around 10,000) gives up a lot of power.
Brett
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Thanks Brett,
I launch mine around 9,400 give or take does this sound ball park to you?I'm pretty much fine with the whole thing ,,other than its really not up on the power band.I mostly use a very wide Eather prop & when I go to a more narrow Bolly it runs much faster & speeds up during manuvers a lot more.. I am fairly happy with it ..I suppose building a lighter plane would help a lot also. So, back to work got a wing to finish.
John
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John, what did you think of my .46VF runs yesterday? I'm launching at 10.4 ~ 10.5k and burning right at 6 oz of 10% Wildcat Premium on a stock 11.5 x 4 APC. Sounds like a fast 4 cycle to me, but could be wrong. Pipe is at 18.75". It's a fairly small Randy Aero pipe with a small (but short) rubber ducky, .272" venturi with one layer of nylon stocking. I have considered replacing the rubber ducky with a larger and longer one. I think the longer/larger should cancel and make it run about the same. I need to add a little nose weight already, tho.
No comments on my flying, please! I was pretty disgusted with myself to get beat by that sucky electron burner. :-[ Steve
PS: Your new/old Spacehound in Classic appeared to fly quite well. I recall that some of your maneuvers were way big, especially the rounds. Practice picking out 45 degrees at home, by just sticking your arm up at 45, and check with a drafting triangle or protractor.
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Hi Steve, I'm glad you wrote .I just saw this message this am, I was going to email you & ask what was the power in your plane. I didn't pay much attention to the running characteristics I was busy trying to concentrate on the flight. However I did notice when you started it up it sounded like a 427 Ford W/dump plugs out. I never heard a VF sound like that, of course I haven't witnessed many .46s either. It sounded pretty dam strong maybe I should scrap the idea of using an OPS in my new plane & use it . ( kidding)
John
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John...I think mine is running pretty darn rich at 10.4k...and still only uses 6 oz of 10%N. The noise probably is going to vary due to the pipe, the rubber ducky and the pipe tunnel's coverage of the pipe and header. This one has smallish Randy pipe, and a fairly small and shortened rubber ducky. The tunnel is perhaps rather shallow, as the plane was built for a Stalker .76 and changed midstream. It does sound a bit loud to me, but you still have me beat on dB production, I'm sure! H^^ Steve
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Steve? What my little Thundertiger ? Mkes more noise then the thunder of that .46? What I ment by what it sounds like is it sounded real powerful. Didnt mean made lots of noise.
John
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John...I'm not a fan on tongue mufflers, I'll admit it. Whether the dB's are more or the same, they sound bad loud to me. Most everything is loud when compared to my (now Tim's) XLS .36 (with the .46LA muffler). H^^ Steve
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John...I'm not a fan on tongue mufflers, I'll admit it. Whether the dB's are more or the same, they sound bad loud to me. Most everything is loud when compared to my (now Tim's) XLS .36 (with the .46LA muffler). H^^ Steve
HI Steve,
I didn't realize that the OS .46LA muffler was a "bolt on" for the Magnum .36 XLS. ???
That could help if nose weight is needed.
BIG Bear
RNMM/AMM
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HI Steve,
I didn't realize that the OS .46LA muffler was a "bolt on" for the Magnum .36 XLS. ???
That could help if nose weight is needed.
BIG Bear
RNMM/AMM
BIG Bear...First time I flew it, it had a Magnum muffler on it, and it would glide about 1/4 laps before it touched down. I knew right away that it needed nose weight. If you get out the calipers, you'll find a slight difference in spacing between a Fox .35, OS .35/.40FP, OS .40/.46LA and Magnum .25/.28/.32 and .36, but it's very slight, and all swap fine for me. If you're using a specialty muffler with 4-40 screws, there will be zero problems. Wondering now if the TT and AT .36 also are in that group? The Magnum .40/.46/.52/.53 and ST .46/G.51 and ST .60 are also super close, and I have used Randy Aero's CNC Tube mufflers on some of them. The 4-40 screws are smaller than 3 mm screws, so that helps. H^^ Steve
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Thanks, Steve!
AFAIK, The AT.36 and Magnum .36XLS will swap mufflers.
BIG Bear
RNMM/AMM