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?

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

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?

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.

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

"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.   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

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

   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.

  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

 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.

Short story is not this year, maybe next!

That's what I keep saying about VSC.  I look forward to seeing you at both.

I'm not sure VSC is ready for a party animal like Howard.  Steve

 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

  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

  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

   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

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).  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

Thanks, Steve!

AFAIK, The AT.36 and Magnum .36XLS will swap mufflers.

BIG Bear
RNMM/AMM