Hello All,
I was fortunate enough to buy an OS 46VF for a reasonable sum. It has been used, but not a great deal (reminder to buy a P/L from Randy for the future!). I was intrigued to note that the spigot on the backplate was tapped, to presumably run crank case pressure! Now what discipline would use such a set up rather than muffler pressure? Whenever I have tried to use crank case pressurisation, it has been a merry dance ending in failure!

Regards,

Andrew.

Hello Randy,
Thanks for the information. The backplate is numbered 5407 and it has a cast tube integral with the backplate, the tube is about 3/8" long and this has a fairly large nipple screwed (?) into the tube. It all looks to be a very professional setup, quite unlike most DIY pressure nipple set ups that I have seen.
So this was some kind of pressure outlet to drive a fuel pump? If it is the P version you speak of, then I presume it is a stock 46VF in terms of timing etc? Or have I just got myself a paperweight as far as a stunt engine goes? It obviously has a few hours on it looking at the piston, but it still has a noticeable nip at TDC and the bearings are very smooth in operation, lots of after run oil by the look of it.

Thanks,

Andrew.

Hello Randy,
Thanks for the information. The backplate is numbered 5407 and it has a cast tube integral with the backplate, the tube is about 3/8" long and this has a fairly large nipple screwed (?) into the tube. It all looks to be a very professional setup, quite unlike most DIY pressure nipple set ups that I have seen.
So this was some kind of pressure outlet to drive a fuel pump? If it is the P version you speak of, then I presume it is a stock 46VF in terms of timing etc? Or have I just got myself a paperweight as far as a stunt engine goes? It obviously has a few hours on it looking at the piston, but it still has a noticeable nip at TDC and the bearings are very smooth in operation, lots of after run oil by the look of it.

Thanks,

Andrew.

That will make a good stunt engine, it is the same timing as the 46 VF

Randy

Thanks Randy,

   But don't use crank pressure!
   
   Brett

Hello Brett,
I am not that stupid! I really need to find the pump to go with it, then I will have some awesome fuel feed! Hm can't seem to get the smilies to work, there doesn't seem to be one for tongue in cheek!

I would consider just plugging the pressure tap and running it off of pipe pressure or or ambient pressure.  I would also reccommend checking the size of the venturi/restrictor.  The pumps that come with these engines produce a lot more fuel pressure than ambient or pipe pressure and may come with a larger venturi area to take advantage of that to produce more power.  This is not typically conducive to a good stunt run.
A venturi larger than .280 - .290 with a ST size (.156 diameter) through it would be too large as a starting point and most likely would be better at about .270-.280 to start.

Randy Cuberly

Thanks Randy,
I purchased the OS 46VFP as an R/C engine and will obviously be changing the R/C carb for a stunt venturi and NVA. I have an OS 40VF set up on pipe and I have never yet found the need to run this on exhaust pressure. I am not a particularly good stunt pilot (read pretty damn awful!), so maybe a top class pilot would find some advantage running pressure, but it is probably way over my head!

Regards,

Andrew.

Hi Andrew,
The only real advantage in running pressure (muffler or pipe) in my opinion, for stunt, is that it avoids the slight richening effect that occurs sometimes when flying in wind.  Some setups with the uniflo tube facing into the airstream (typical ambient setup) will cause a richening as the airplane goes into the wind due to the increased airpressure on the tube caused by the relative increase in airspeed into the wind.
Running pipe pressure or muffler pressure avoids this.  I really don't think there is any other advantage for stunt.

Randy Cuberly