Shrike .10-OS .25 vrdf project
#76
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RE: Shrike .10-OS .25 vrdf project
Besides raising the liner, which may or may not do any good, there is one item that all engines can benefit from. Removing as much weight as you can from the piston and rod. This will take a lot of strain off the crank and the load bearing points on the piston and rod. The factory is only able to do what can be done quickly and they do a heck of a job, but there are always micro-grams to be found. They multiply out to ounces when the piston starts going up and down 400 times per second. The skirt can even be notched to unshroud the front boost port as the piston swings over the counterweight. This might already be done on your engine?
The value is not just porting, but reducing weight. Same goes for the rod, the entire beam can be shaped to an oval cross section. If these parts lose enough weight, then you'll need to chuck up a fine carbide cutter and put a divot or 2 in the crank counterweight to get the engine running smooth again. If your engine doesn't already have a hollow wrist pin, it should...that's a significant amount of weight right there.
This engine of your's being high output already doesn't mean it can't be tweaked, it just means you got something much better built than average to begin with. I think it would be really cool to come here someday and read about you ripping off some 180 mph passes with it. [8D]
The value is not just porting, but reducing weight. Same goes for the rod, the entire beam can be shaped to an oval cross section. If these parts lose enough weight, then you'll need to chuck up a fine carbide cutter and put a divot or 2 in the crank counterweight to get the engine running smooth again. If your engine doesn't already have a hollow wrist pin, it should...that's a significant amount of weight right there.
This engine of your's being high output already doesn't mean it can't be tweaked, it just means you got something much better built than average to begin with. I think it would be really cool to come here someday and read about you ripping off some 180 mph passes with it. [8D]
#78
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RE: Shrike .10-OS .25 vrdf project
ORIGINAL: smoknrv4
180 mph? yeah you and me both CP, BTW MJD the theoat Dia. is .281''
180 mph? yeah you and me both CP, BTW MJD the theoat Dia. is .281''
RVman and I were both blown away by a couple of the good passes he got on his Picco .45DF SD the other day, one in particular - the "magic pass". It was clear that he was freaking moving.. I would happily bet 5 bucks he was kissing 180. But we'll see when we can get it radared. When it comes together you can just tell..
We need to hook up and fly!
MJD
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RE: Shrike .10-OS .25 vrdf project
ORIGINAL: smoknrv4
BTW the theoat Dia. is .281''
BTW the theoat Dia. is .281''
So please disassemble your entire engine (you also could measure the exhaust timing before that using a [link=http://www.rcgroups.com/forums/showthread.php?p=12658256#post12658256]degree wheel[/link]) and then measure the crankshaft bore. After that you can determine the correct speed venturi carb bore diameter. For example if the crank bore of the OS .25 VR-DF is 8 mm, then you should take 7.5 mm venturi bore dia...
I suggest that you send the OS .25 VR-DF engine to CP. He will increase the exhaust timing of the brass liner to 180 degrees and will make a well working speed venturi carb for you. Below a certain degree shimming a liner mildly works. But you will be required to adopt the compression ratio from a certain degree, see [link=http://www.rcgroups.com/forums/showthread.php?p=12590124#post12590124]here[/link] for example.
After increasing the exhaust duration to 180 degrees a pipe length of about 23.5 cm between plug and middle of the tuned pipe's belly (e.g. MACS 1120) will work OK for the OS .25 VRDF. This setup will allow rpm of at least 26K in flight.
As for lighten the piston and the conrod, the OS .25 VR-DF is not worth that IMHO. Better suited for a complete internal mod job would be the JETT .35 BSE FIRE or the OPS .29 VAE # 83600 (see pics below) which represent engines that – even after heavily modded - will last long running at WOT only.
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RE: Shrike .10-OS .25 vrdf project
I build model IC engines for display as another hobby, with all this info I would have no problem doing these Mods, thanks for all the help.