How much fuel does it need to do the pattern.
Allan Perret
Allan Perret
Brodak 25
Stuka Stunt Main Forum · 8 of 8 known posts recovered
I'm sure that the answer depends a bit on how you run the engine and your fuel choice, but mine will do the full pattern on 2 oz of fuel. I'm running 10x22 Powermaster much of the time and an APC 9X5 prop with the engine in a 2 stroke for the whole flight. Engine is stock except for a "Big Art" tongue muffler. At VSC, I put 1.75 oz in the tank for OTS and ran just over 7 minutes on that. At sea level, it will burn a little more fuel, but when run lean it is very economical.
Steve
Steve
I reduced the compression on mine (a VERY early engine) by creating a hemi configuration and a narrow squish band. With a 9-6 Master Airscrew, it does a decent 2-4 but requires a bit more fuel - around 2 1/2 ounces.
The individual results will of course vary but I would leave room for 2 1/2 ounces, just in case you decide on some slightly rich runs.
Bob Z.
The individual results will of course vary but I would leave room for 2 1/2 ounces, just in case you decide on some slightly rich runs.
Bob Z.
Would it do a 2-4 break before you lowered the compression. Can you tell me how much of a cut you took on the head. What was the width of the squish band before and after the mod.
Allan Perret
Allan Perret
Allan asked: "Would it do a 2-4 break before you lowered the compression? Can you tell me how much of a cut you took on the head. What was the width of the squish band before and after the mod?"
Allan Perret
Hi, Allan - no, my particular engine wanted to run full out. Even if I set it slightly rich, it would soon go lean and stay there.
As I recall, the original squish band was around .10. Using a cutting tool with a .48 radius, I gently removed metal, bringing the squish band width to around .040.
I ran it on Powermaster 10/22 (50/50) and Brodak 10/23 (also 50/50). Both fuels yielded similar results.
I did notice that the Brodak .25 required a substantially loger run-in time than did the .40. I don't know if this was a unique instance or if there are some metalurgical differences between the two engines.
All the testing was done on my Cardinette design - cowled in, inverted, head exposed and using a single vent, non-uniflow tank.
Stock muffler. The plastic 9-6 Master Airscrew yielded the best results but I did not try a lot of different props. 52 foot .012 stranded lines.
I hope this helps,
Bob Z.
Allan Perret
Hi, Allan - no, my particular engine wanted to run full out. Even if I set it slightly rich, it would soon go lean and stay there.
As I recall, the original squish band was around .10. Using a cutting tool with a .48 radius, I gently removed metal, bringing the squish band width to around .040.
I ran it on Powermaster 10/22 (50/50) and Brodak 10/23 (also 50/50). Both fuels yielded similar results.
I did notice that the Brodak .25 required a substantially loger run-in time than did the .40. I don't know if this was a unique instance or if there are some metalurgical differences between the two engines.
All the testing was done on my Cardinette design - cowled in, inverted, head exposed and using a single vent, non-uniflow tank.
Stock muffler. The plastic 9-6 Master Airscrew yielded the best results but I did not try a lot of different props. 52 foot .012 stranded lines.
I hope this helps,
Bob Z.
Allan,
My stock B25 will not consistantly run a 4-2-4 breaking run. It does, however, run a very consistant 2 stroke run which is very easy to set. I have a couple of engines (Fox & Max S) that run the 4-2-4 run, but most of my other engine are happier running a constant 2 stroke with low pitch props. I have come to accept this as normal and actually like the consistancy of this type of run.
Steve
My stock B25 will not consistantly run a 4-2-4 breaking run. It does, however, run a very consistant 2 stroke run which is very easy to set. I have a couple of engines (Fox & Max S) that run the 4-2-4 run, but most of my other engine are happier running a constant 2 stroke with low pitch props. I have come to accept this as normal and actually like the consistancy of this type of run.
Steve
Steve:
Did you experience a longer than normal break in ?
I will try the constant 2 run first.
Allan Perret
Did you experience a longer than normal break in ?
I will try the constant 2 run first.
Allan Perret
Allan,
Actually I thought the engine was ready to fly before the suggested break-in was complete but I kept running it. I did have an early problem with wear on the connecting rod, but apparently this is rare with the 25. Since the installation of the new rod, operation has been excellent. It consistantly starts on the 2nd flip and it seems to be tolerant of slight needle valve errors. I have been experimenting with fuel mixes and am currently running 15% nitro, 14% castor, and 11% synthetic oil. This was developed for one of my other engines, but the B25 seems to like it too.
Back to your original question about fuel consumption, the 2.5 oz tank is also what I am now using although I never have filled it except for practice. I also got a 2 oz syringe from Lee Machine shop and it is great for this engine size where I'm never using the full 2 oz.
Steve
Actually I thought the engine was ready to fly before the suggested break-in was complete but I kept running it. I did have an early problem with wear on the connecting rod, but apparently this is rare with the 25. Since the installation of the new rod, operation has been excellent. It consistantly starts on the 2nd flip and it seems to be tolerant of slight needle valve errors. I have been experimenting with fuel mixes and am currently running 15% nitro, 14% castor, and 11% synthetic oil. This was developed for one of my other engines, but the B25 seems to like it too.
Back to your original question about fuel consumption, the 2.5 oz tank is also what I am now using although I never have filled it except for practice. I also got a 2 oz syringe from Lee Machine shop and it is great for this engine size where I'm never using the full 2 oz.
Steve