HI all, I just finished a BVM Aggressor ll ducted fan, all though I fly turbines ,I had to finish this kit. My question is which pressure was more successful ,pipe or puffer and with the 91 do you put the insert in the carburator on puffer or was that just for the 82.
Thanks for your help
Rcpete

Puffer pipes were considered more reliable and consistent especially diring aerobatic maneuvers.

The other for speed.

Insert was not used on the .91.

Some of the 91s did not like puffer, not enough pressure, I have one of those. The only draw back of pipe pressure is that you have to be carefull to not pull the power back during some manuevers. If you where to pull the power back in a split-S after you got the nose pointed down, the higher pressure in the fuel tanks would push fuel back through the vent line into the pipe, and with the nose pointed down that fuel might go back into the engine and put the fire out. I have allways felt it was easier to set the needle on a pipe pressure set up, it was more controllable on the rich side. It will really come down to how well your engine runs on puffer as to if you should use it. If you have trouble getting a reliable rich setting on puffer you might want to try pipe pressure.

Steven

I'll have to disagree with bvmjethead. My BVM 91 came new with the carb insert already installed. The engine instructions said to remove it if you weren't going to use puffer pressure.

You will find that most DF fliers will swear by their system of choice. I prefer pipe pressure and have had that on all of my DF's. I have never experienced the problems during aerobatic maneuvers that some attribute to pipe pressure.

One plane that I bought already built had fan pressure. What I didn't like about it was it's narrow range of authority. I would have to turn the radio knob to max. lean, then adjust the needle to peak the engine. Once in the air I would end up turning the knob to max. rich and on some days it was not enough to get a good contrail. I ended up converting it to pipe pressure. With pipe pressure once it is set up I never have to touch the needle. It has sufficient range of authority to go from too lean to too rich using the radio knob. Once the engine is started I just have to peak it with the knob and take off.

Puffer pressure probably has slightly better range of authority than fan pressure. The reason I never tried it is because I preferred to stick with what worked well for me and I didn't want the few hundred rpm penalty due to the restrictor in the carburetor.

Joe

Although I have never used puffer pressure, I can certainly say that pipe pressure has always worked for me. I did however have a few flame outs with my aggII in the beginning due to chopping the throttle with the nose up. It's just part of the learning curve, it was something I always did with my prop jobs. My aggIII so far has been 100% reliable on pipe pressure.

Chris

HI, I started up my Aggressor this morning with a 91 on puffer and no insert.The first couple of runs on the bench I could not get it to maintain a half throttle setting, it was too rich and the low end would guit on a lean setting.
I leaned the midrange one turn and richend the low end, it ran great and would idle for over 2 minutes.
I know pipe pressure is great for all out flying but not so great for a person that flies at half and three quarter throttle because of the none linear throttle curve of the pipe pressure.
But if I do have problems when flying with puffer pipe pressure I"ll go back to Pipe, at least I am familiar with its bad habits.
Rcpete

I built an aggressor II last winter and have about 25 flights. I've been using a puffer pipe and it runs flawlessly in the air. I have had it die on my landings but it's probably because I bring the idle down lower than I really need to. I had to richen the low setting a little to get a better throttle response but otherwise it really throttles up nice from 1/3 to 2/3 to full power. Jim