sigrun

Having acquired a second hand O.S. MAX 20 which I bench tested yesterday and now intend to put into service in a TF Flite Streak ARF ASAP, curiosity of comparitive performance begs the inquiry as to what props those of you using the more recent, widely available and more powerful Schnuerled (?) O.S. 20FP/S are running on your Flite Streaks that you consider "Jus perfec !" - and in particular what RPM you might be taching with them if known?

I'll kick off with my results. Bench ran 6½ Imp. ozs through the engine yesterday over two lengthy peak RPM engine runs of around 10 mins ea. Previously, this engine hadn't been started or run in > 16 years (known) - most probably even longer. [:@]

Engine: O.S. MAX 20 C/L (baffled piston) fitted with OS-702 muffler
Plug: O.S. #8
Prop: Bolly Clubman 8.5 x 4 - didn't have an APC 9 x 4 or Bolly 9.5 x 4 to hand [&:]
Fuel: Home brew. Approx. 24% (by volume) Klotz Techniplate and Castor @ 1:1 + 3% nitro (was R/C leftovers to which additional methanol and oils were added sufficient to run it ensuring a high oil, adequate castor and low nitro content.)
Tacho: 13,300 peak, 13,000 stable 2 clicks rich. Consistent.

Have to admit most of the noise on the bench was consequence of prop noise & tip speed.

I don't seek speed in the Flite Streak, just good acceleration through sustained aerobatic manouvre in sequence with minimum RPM variation under load and good line tension at the end of 60' lines. So I'm thinking (1) Bolly 9.5 x 4, (2) APC 9 x 5 or (3) APC 9 x 4 on this engine in the Flite Streak. Still expecting it to static between 11.5 - 12.5k RPM unloading to 12.5-13.5k in the air on those props. Sound reasonable on 60' x .012 or .015?

Plan on using 20 to 24% oil by volume, 1:3 ratio of Klotz synthetic:SIG AA Castor. Unsure about nitro content yet. Probably 3-5% 'for the needle', but happy to up it to 10-15% if it sags under load and needs the additional 'pump' through vertical. Have an spare head gasket/shim if necessary. We'll see.

Please post your prop choice, preferred fuel brew and tach results if known. Thanks.

Edit: spelling

Jim Thomerson

I've been fiddling with ST G20-23's on a Flite Streak. Have had to go to a 1/8 in venturi to slow it down to flyable speed on 60 ft lines. 9 x 4 APC, the 9 x 5 was just too fast regardless. I suspect an APC 9 x 4 will be about right for you.

sigrun

Thanks for the suggestion Jim.

3.2mm!! That's tiny...weeny even! Bet suction is great. Smallest venturis I have are regulation max. 4mm ID for my TBR F2D 30+k screamers for FAI combat models.

I'd previously read your comments on the G20-23's which brought a wry smile to my face.

From my remaining suitable C/L powerplants, I'd considered a PAW .15 TBR diesel - similar performance to the G20-15 diesels, but with a bit more tug and poke - or a Cipolla Master 2.5 SE Schnuerled (true) ABC TBR glow as alternatives, but shyed away from the diesel because of the local problems and cost of obtaining the necessary fuel components. The Master isn't a bad alternative potential option to the MAX 20 as its the mildly timed heavier reciprocating mass steel piston version with the conventional head and throws a larger diameter prop at revs than its cubic capacity would suggest.

I also have a VGC OS 40FP with an 35FPS stunt venturi and N/V assembly available which I could use, but decided I didn't want to fly Flite Streak combat. Nah, from reading what you and the others have said, sounds like my venerable MAX 20 will be just about purrfec and lightweight for a ~400 sq in and 41½" span TF Flite Streak ARF.

I had used MAX 15's and as recent as last year a 15 FPS' in the 300 sq in 36" span "Peacemaker" for sport flying and slow combat, and either had gobs of power and speed on .015 x 52' lines. Even carrying their 2 oz bloat, a venerable ENYA 15 IV had more than enough grunt to aerobat them respectfully and gracefully about the circle. The TBR PAWs were just power overkill and flew them at ridiculous speeds! It's been a long time since I flew a "Flite Streak", but I've always had a soft spot for their smaller brother the "Peacemaker", of which I've built many, so I'm a kinda' excited about this project in a nostalgic sort of way. [:-]

gcb

sigrun,

The MAX-I, II, and III .15's, and probably the Enya should match up well with the Flite Streak Jr. which is a little smaller than the Peacemaker. Don't have the MAX .15 baffle with liner. The .20 and .25's seem to be good runners.

Good luck with your Flite Streak.

George

sigrun

Thanks George. Having re-considered all the pros and cons again overnight I'm committed to trying the MAX 20 in it first now. From all user reports, I suspect it'll be the best powerplant from those I have available for what I want to do with my Flite Streak.