Gary, I just got home from our Fun Fly, where I flew a new prop on my .46VF. I'm running 10% and a Randy Aero pipe, but hold on, there's something in common here. I was using an 11.5 x 4 APC, and it worked pretty well, but I had to launch around 10.2-10.3K to keep the speed about right. Dave Gardner suggested the 12.25 x 3.75, but the plane doesn't have enough ground clearance for more than 11.5". So, I clipped one down to 11.5" and reshaped the tips last night. I was looking to raise the launch rpm to about 10.6k, and this reworked 12.25 hit it dead nuts. The airplane is flying slower, the engine running faster, and the pilot is a lot happier. Hang in there, and keep working at it.

I also added a 1 oz Great Planes spinner weight, and improved the way the plane flies a lot!   Steve

Edit: I was rushed (dinner!!!)...IMO, the 12.25 x 3.75 is a LOT of load for a .46VF. The trimmed prop works real well. When I did the first prop, I made a stiff card template (stencil material for painting crates labels) with a 1/4" dowel pin at the center, that allowed me to reshape both tips to the same shape. I used the belt sander to get the profile to a scribed line, and scraped most of the airfoil refurb work, then sandpaper. They came out very close in balance, so I guess it worked well. The plane sure liked it. With the extra 1 oz spinner weight, that makes it 67 oz dry.  

Hi Steve,
Thanks for your reply. My problem with the carbon pipe was that I couldn't get the engine to slow down. She wanted to turn 11,000 to 12,000 rpm's and lap time was around 3.8 second laps. When I would try to slow her down she would just go rich and quit. So I went to a different pipe set up hoping I could get her to slow down. With the Mac's pipe system I can run her in the 8,000 range and she act like a super tigre 60, 4 cycle to 2 cycle. This range is to slow but I'm able to run her in many different ranges. The problem I see is that she wants to change is variation to much and on the up hill let I'm afraid she'll want to go to fast?? When I hold the nose up there is a variation of 900 rpm's, is this to many, I thought there was only need about 50 to 100 rpm variation??? I guess I'll find out at the field tomorrow. The engine is a great motor just a lot of power to tame. She doesn't have a problem with the 12 1/4" x 3 3/4" prop, I believe she could handle more prop??? Might help bring the variation closer??

Thank You
Gary

Gary

You have it set wrong, There have been hundreds of people use the VF with carbon pipes, The pipe doesn't make the RPM run away, try setting it at 18.5 inches from glo plug to the first baffle, use 5% nitro fuel and about 4 inches of pitch

Randy

Hi Randy,
You're correct, the carbon pipe I was trying to use on the 46 is small in diameter pipe and the engine just wouldn't run in the low rpm's. I tried using the same props as I use on my FSR engines. The engine ran very well, no run away, just couldn't get the rpm's down with that pipe. I have a carbon pipe from Jett that would probably work well but its set up with the RoJett 61. Not sure the diameter of the pipe makes a different but I would think it would. The distance I'm using is the 18 1/2" and it works great with the set up I have on her. I was just trying to slow the rpm's down to slow lap time down. I wish I knew who made the carbon pipe, it also has a pressure tap on it?? I'm just worried that the nose up rpm's is to high?? Probably if I was using the correct pipe the rpm's would only be varing around 50 to 100. I believe 900 is to much a difference??
I appreciate your input
Thank You
Gary

This topic has made me wonder if there is a way to tell how big an engine matches up to one of Randy's pipes, by measuring the OD of the chamber? All the pipes I have are Aero Products, except for one "Utah Pipe". That thing is huge...and they only make one size fits all...beautiful and light, however. I'd think that the chamber and outlet would both be bigger for a bigger engine. It sounds like Gary bought an engine here and a CF pipe there, and perhaps has them mismatched?  Steve

   Those revs make a lot more sense than what we were discussing above. I would be launching at about 10200 with 3.75" of pitch, too. It goes up to about 11,000 in the air, btw.

    Brett

Hi Brett,
Thanks for your input, Yes most of my FSR Engines like to run around 10200 to 10400. I knew the rpm was to slow, I was just testing to see if the engine would perform at that low rpm and she did with the different bigger diameter pipe. Yes Steve I have several different type pipes and for some reason the smaller diameter pipe wouldn't let me run the OS 46 or the OS 40 at a low rpm, it wanted to run close to 12000. When I tried to add length to the smaller pipe, the engine didn't like it at all, neither the 40 or 46. Maybe its just a bad pipe?? Maybe if I hooked up the pressure tap thats on the pipe it would work?? I wanted the smaller pipe to use on my Lark, easier to hide than the larger pipe, just didn't have any luck with that pipe. I purchased the smaller pipe and the OS 46 VF off of Evil-Bay as a package and the person that sold me the engine told me it was to powerful for him and be careful ya don't get hurt. Well, if he was trying to use that small pipe, guess what, the poor OS 46 was probably doing about 14000 rpm's. I have not had a run away problem, just couldn't get the r's down. Today was a great day cause I ran her way to slow and she acted like a champ, I'm proud of her and looking forward to flying her in my Lark. I fly electric also and its great but give me my RoJett, OS's over electric any day. What ever you fly, if it works, its great! I appreciate all your input.
Thank You Guys
Gary

Randy's advice is right on.  I flew a Tom Lay 46VF for several years in my original Ephesian at 710 squares using Randy's pipe set at 18" and the APC 12.25 X 3.75.  With the drag of the big ship I launched a little over 11K and flew 5.4 second laps on 65' lines.  Never had a problem with the run on 10% with 22% lube at 50/50.
The only reason I left the VF was when I went to higher drag airfoil and it kept asking for 15% on the windy days.  It became time for torque!  (Can you say PA?)
The VF is a super fine engine in my books.

Hi Gary,  what you find with the pipes is what caused me to go to fatter pipes way-back-when.  Not that I'm so knowledgeable, and I can't even remember  who clued me in to do that, but my pipe engines have been a lot happier and much more reliable since doing that.  'Course, I just set them the way Randy says and forget all else.  Life is easier that way.

In reading through all of this it seems to me that one basic principle in using a tuned pipe for stunt has been ignored.  It's very important to set the pipe for a certain RPM Range and ADJUST THE SPEED OF THE AIRPLANE WITH PROP PITCH.
Most of what has been said is simply trying to slow the engine down to reduce speed.  This never works very well, especially with an engine like the 40VF because of high exhaust duration.  With high exhaust duration in a two stroke engine the power stroke length is greatly diminished at lower RPMs.
This is a given premise that can be helped with a tuned pipe but only if the pipe volume and length is correct for the given engine.
Randy Smith noted earlier that many many stunt fliers (like a world Champion) have successfully followed this premise with 40 VFs and tuned pipes, even many of us middle of the pack experts have managed to grasp this concept and sucessfully use this engine using this "standard method" of set-up and obeying the basic physics of IC engines.  
I'm surprised Randy S. didn't mention this earlier because it's always been his Mantra!

Randy Cuberly

Hi Randy

I do try... :-)
I have written and posted this many many times, below is an excerpt from the basic setting of an IC motor article..pinned at the top of this forum


In a nutshell:
Remember the needle is for setting the fuel mixture,(ie. needle setting) ....NOT..... for setting the plane speed.
The prop .....pitch ....is for setting the speed of the airplane.
The prop diameter is for loading the engine properly and getting maximum thrust from the motor.
Nitro is for controlling how much or how little break you have,either coming on in a 4\2 or an all 4 cycle, this is to say how strong the motor will come on in the maneuvers. The other 2 items that work with this are compression and venturie size.
This is not all there is to getting perfect engine runs. Many things work in conjunction with each other to achieving this goal, and most everything I am going to mention affects the others to some degree or another.
Please do not think of the following as an oversimplification, it really is not. It would take a volume of text to try to explain all the relationships that one item has to another, this is just to try to add a little clarity, and to give you a place to start.
The 8 basics to helping yourself to a better engine setup are:
1. Engine: Pay careful attention to matching the engine to the airframe. Don’t overpower or under power your plane. Make sure your power plant is an acceptable weight for the ship it is in and matches well with it
2. Correct Fuel: Fuel is one of the most important things in tuning an engine. You must make sure that you have the correct oil type and percentage for the engine your using. For example Fox 35s, OS 35s, older McCoy’s and such need high oil content fuels 24 to 29% are common percentages.
Modern ABC and AAC engines will use much lower oil, 18 to 22 % percentages are the norm here. Nitro percentage is also key to getting the best from your power plant, There are so many ways to run stunt engines it is impossible to print anything but guide lines.
I have written many times about fuel. You can get a copy of my Care and Feeding of a Stunt Engine from the PAMPA archives
Typical stunt engines will use 5% nitro in cold weather going to 10 or even 15% in hot months. You can get in trouble using, say 15% in January, this setup would need 25% or more to be the equivalent in August. So unless you really have this working it is best to setup your engine for lower nitro in cold months and higher nitro in hot months. This will help keep the run constant thru out the year. Also it will help control power in your motor.
3. Correct Props: Props are also critical for achieving good engine runs; a prop needs to “load” the motor correctly without over or under loading the motor. It also needs to be the correct size and pitch to pull the airplane. This is somewhat of an over-simplication, but generally the diameter will be what you use to “load” the engine and the pitch will be what you pick to set the plane speed
Some of the things you will run into when over propping an engine are; hard to set the needle on the ground; the engine will unload a lot and go rich in the air; the engine will run hot, or not cycle very rapidly.
When under propping generally you will notice the engine will also not cycle correctly. They at times will just 4 stroke thru everything, sometimes going into a 2 cycle at weird times.
A properly loaded engine will use a prop that if running a 4-2 break, will come onto a 2 stroke a 10 O’clock and back to a 4 at 2 O’clock. There are variations on this; You can have a strong motor just beep 2 stroke at the tops of maneuvers, but you shouldn’t have one that 4 strokes uphill and switches to a 2 stroke on the downhill parts of maneuvers. You can setup the run with a very strong 4 cycle that doesn't break anywhere, but will still cycle and increase/decrease power in maneuvers somewhat, don't try to get so deep into a 4 cycle that the engine goes even richer when starting a maneuver, or slows ans speed in weird places, generally this setup should still be in a high power setting that is close to the 2 cycle beep without going into a 2.
4. Needle setting: Don’t try to use the needle to set the speed of the airplane; the needle is for setting the fuel-air ratio that goes into the engine. Typical settings are so the motor will be in a very fast 4 stroke when in level flight. If you set the needle too rich it will delay the engine switching and make the engine come on late in the maneuvers. If you set it too lean, you can sometimes run the risk of too much 2 stroke and going sagging lean in the tops of maneuvers, killing your drive and over heating the engine. Once you get this set, you will have a little leeway in tweeking the needle in or out for conditions.
5. Airspeed: Most all planes like to fly at the airspeed they work best in, even exact or what is supposed to be the exact same design , will a lot of times want to fly at different lap times. Example: I have flown many SV-11s, at the same weight that fly at different speeds. Try to find the optimum speed for the plane your flying. This will depend a lot on the weight of the plane and also the power of the engines
6. Compression: Setting the correct compression for you motor isn’t a simple thing and will vary with nitro and prop size. Try to set the compression so when your engine hits into a 2 stroke it doesn’t come on too hard or too soft. This will work in conjunction with nitro and venturie size. Generally you will use higher compression for low nitro and lower the compression when using higher nitro fuels.
7. Venturi : Venturi size is one of the keys to get a proper switching 4-2, while not coming on too hard or too soft or too late or too early. If you are constantly accelerating too much when your engine cycles you may need to go down on venturi size. If you are not cycling much or have too soft of a break or a late break , you may need to open the venturi up a size or 2. This will work in direct relationship to nitro and compression.
8. Fuel Tanks: A large portion of engine problems I see are really not engine problems. They are fuel delivery problems that many times relate to fuel tanks, Tanks are maybe the most critical component of your power train. Make sure you have a solid mount, and a tank with no leaks or cracks in the tubing, inside or out. When in doubt I suggest trying a new tank, if there is a difference, you may have bad tank. Don’t forget to use a good filter and make sure there are no holes in the fuel tubing. It is also advisable to try to keep the tank as close to the engine as possible
These are just basic suggestion to help you tune your engine, and by no means covers it all. There are literally thousands of engine setups that would take volumes to cover.

Randy Smith
 


PS for Randy C.  " basic physics"   ....some of the people don't believe in that sort of thing... :-)

Hi Randy and Brett,

Both of you are correct. I don't know why the small pipe didn't work?? Maybe something wrong with the pipe?? Anyway, what I have found is that when you get the pipe length close to where the engine is happy, you have a lot of needle to play with. My OS 46 VF was happy running is the 8000 range to the 12000 range. Of coarse it wasn't developing the power needed in the 8000 range but what was interesting is that she acted happy, she would pick up around 100 rpm's when ya held the nose up and would come right back to it setting when I leveled her out. Like I said earlier was that I set her at a lower rpm (9600) which was to slow but when I pulled the nose up she would still go into a 2 cycle mode and return when level. With the high compression engine, I'm using 5/22 with great success, (100 Plus degree weather, with no problem). If the cancer lets me, I'm going to try her at my usual setting of 10200, which has been the magic number for my FSR's and my RoJett 61. Tomorrow I'm planning on going to Mr. Bob Ellis funeral, some probably remember Bob & Kathy from the seventies to ninties. Bob and Gid ran the Golden State Contest for several years and was a great Advanced Flier. Bob was a great friend and I will miss him. Rest In Peace Bob.
God Bless
Gary

Both of you are correct. I don't know why the small pipe didn't work?? Maybe something wrong with the pipe??

  Something wrong with the pipe *length*, as noted. Jumping to the wrong node.

   Brett