hi all,

i currently have returned to flying after a 15 year layoff......have 3 planes that are air ready (sport planes), but have this godawful itch to return to pattern flying as was when i quit 15 years ago.
my pattern planes back then were the Super Kaos and the Dirty Birdy..........both were grossly overpowered with a Rossi.61/tuned pipe. not to say they weren't fast and fun, but they were in my opinion, too fast.

i wanting to build a new Dirty Birdy, and want to keep it light, and i will use an OS.61FSR for power.

it would seem to me that the OS will have plenty of power, but what prop?..........
the Dirty Birdy will be finished with epoxy finish, and although monokote would probably be lighter, i feel i'll get a longer lasting finish with paint.
are Spring Aire retracts the way to go?

I too am returning from about a 15 yr lay-off. If you can, go with paint. The new OS .61 engines are very strong. You can use a 12x7 or 11x8 with ease.

i know the newer OS engines are designed as long strokers, but the engine i am going to use is the FSR series..........they were more of an RPM motor back in the late 70's.....can't remember if i use 11x7 or 11x7.5's.........and even at that, i was using the Rev-up props................

The thinking years ago was that one needed very high rpms in order to get near the peak of the horsepower curve - hence tuned pipes and relatively small props. The planes relied on high entry speed and momentum to get through the vertical maneuvers. A major lesson from the early turnaround era was that one could go to higher pitch props at lower rpm and get good - or better - performance. Technically, although this puts the engine in a lower horsepower range, it is closer to where the peak in the torque curve is since horsepower is proportional to torque times rpm. More torque results in better vertical performance. This was especially true of the long stroke engines which were designed for the lower rpm region. The lesson holds true today. Build a light airframe and put a bigger prop on it. I am flying a 7 1/4 lb Cutlass Supreme with an OS 61 FX running an 11x8 or 12x7 prop and I get excellent vertical performance using 15% nitro fuel. I would expect a similar result for your Dirty Birdy and OS 61 FSR. The FX is just now getting broken in (~30 flights) and I get around 10,700 rpm with the 12x7 and 11,500 with the 11x8. At these rpms the plane is relatively quiet compared to many sport models. So, don't be afraid to experiment with larger props.

Jeff
Skylane N9214G
SPA 243

Actually, the OS 61 FX is not really a long stroke: Bore=24 mm, Stroke=22 mm. I think that you'll find that my comments will pertain to your engine, too. But the fun part is experimenting!

Jeff
Skylane N9214G
SPA 243

i wonder, is the FSR series 61's even worth fooling with for pattern?
perhaps i should focus more on getting an SF series and swing the larger props?

fsr is a great engine I had one buti its matched with a 11-7 or 1/2 prop

The best prop I found on the FSR was a Rev Up 11x 7 3/4. The second best was the APC 11x8 on my old Dirty Birdy. By the way the FSR ans the SF were higher quality and longer lasting thany of the newer engines that OS is putting out. As an example it was not uncommon to get 14,500 rpms on the ground with the APC 11x8 as opposed to the 11,500 your getting with the FX on the same prop. The only advantage that I can see with the FX is that you can get parts for them. But as cheap as they make them now, you would be beeter off going with a Tower 61 and getting better performance.

Just my 2 cents for what its worth.

I say go with the FSr if you have it. No other engine unloads in the air like an FSr/VF.

Hiya...Just getting back after a (little shorter) lay-off too...(My how things have changed)...I vote you stick with your FSR!!

I've recently been buying a few used OS engines off eBay and such...Up to this point I had never owned an OS engine...I must say I am really impressed!! I don't have an FSR...Just a few in the SF and RF series...But they are really nice!! Most of the ones I have purchased have required some TLC to whip into shape...I've defiantly over rode the cost of purchasing a new (modern) OS engine in rebuilding these Old School guys...But they are worth it IMHO...Time will tell if they are going to hold up...I'm just going to try and take care of them the best I can...

You can still find some nice looking FSR's on eBay from time to time...You may keep an eye out for a spare (parts) engine if you feel the need??

To me...It just feels a little more natural mounting one of these era engines to most of the aircraft I'm interested in building...I think (hope) they are gonna look and sound "right" if you know what I mean...

Good luck with your build!!

Have some Fun...

Chuck

thx for the feedback .........
here are the 2 FSR's i won recently off ebay,

http://cgi.ebay.com/VINTAGE-NIB-ORIG...QQcmdZViewItem

http://cgi.ebay.com/OS-FSR-61-Engine...QQcmdZViewItem

i found most of the parts needed to completly rebuild the ABC version, and the rings for the Ringed version are also still available, as are the rods, bearings, pistion pins etc.....

further reading on here has me looking at the UFO as well.
next item on the list is a good set of retracts.

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The thinking years ago was right on the money for the models they flew in the patterns that existed then. Trying to fly a choked down FSR with a 12x7 in the same models and in the same pattern will quickly reveal a huge loss in performance.

Two things keep emerging when those that did not fly in that era comment on models and engines of the era:

1. Noise. It was of no consequence then and shouldn't be today. When was the last time that you heard of a NASCAR event where noise levels were being measured? This is a European problem. Let them keep it. If we are really concerned about noise in SPA, then muffled tuned pipes should be legal - not banned. Muffled pipes are far quieter than mufflers. Even the noise of a high rpm prop is much less aggravating to the human ear than a muffled (barely) engine. Give the two-strokes back their muffled pipes and I'll quit *****ing about the .91 four-strokes burning 30% nitro. While we are at it, give back the retracts too. Or divide the classes into retract and non retract classes.

2. Comparing old models designed for old pattern flying against turnaround pattern is comparing apples to oranges. What works in Turnaround would be at a severe disadvantage in the pre-turnaround era. No, turnaround props on ballistic patternships and typical engines do not work "better". In fact, they don't work well at all. The planes become slow sluggards with no vertical performance. Then remove the pipe to match SPA rules and you might as well be flying a K&B .40 powered Senior Telemaster. PC has nothing to do with the actual physics encountered in flying - thank God.

I'm not angry with you, just the mindset that rewrites history to suit the current PC aspects of the hobby.


Ed Cregger

I remember when I was experimenting with the new concept of big, high pitched props in pattern, and wanted to get with the the times. I switched to a YS long stroke with whatever prop Hanno was using, I think it was something along the lines of 12x11. I immediately noticed a severe loss in vertical performance where the aircraft would noticeably slow down in an upline. It was disappointing to me at the time, and If I had stuck around in pattern, I would have gone back to the fast Rev-Ups.

Any thoughts as to why my experience stunk?

My thought is that the higher the pitch, the less efficient it is under a direct load, similar to the gearing in a car.

Ed,

Been there, done that. I've been building models since the late 50s, flying RC since 1970, and flying pattern since 1977. I am not rewriting history, but rather commenting on my own experiences in going from a Cutlass (muffled Enya) to a Kaos (muffled Kraft) to 2 Deceptions (piped Super Tiger, Webra, and Rossis) to a Tiporare (piped Rossi then YS) to an Escape (piped YS FR then YS longstroke) to a Cutlass(muffled OS 61 FX). The Cutlass performs far better with the modern engine and larger prop than did my old Cutlass, which was my point. And I have been impressed with the results of experimentation which has shown to me that I can get better performance in some situations by going to a larger prop than I used to use. The key is experimentation, as noted in one of my earlier posts. No single solution works best for all airframes and all engines.

However, I do agree with you about the noise factor. It is certainly possible to make pattern planes with pipes very quiet. My planes are almost always the quietest at the local field and I usually can't hear mine when another is in the air.

Jeff
Skylane N9214G
SPA 243

Stiletto

Perhaps the problem was pipe tuning. The lower rpms require a much longer pipe setting. I have used both a YS FR (round head, short stroke) and YS long stroke (square head 61-R) in my Escape. When the pipe was properly tuned there was no loss of vertical - quite the opposite. And I was running an 11x11 usually on the long stroke.

Jeff
Skylane N8214G
SPA 243

Vertical performance is like driving a car uphill - you have to use a lower gear.

Lower pitch/larger diameter is better. Think helicopters.

A 13x6 prop at 14k rpms will have unlimited vertical for an 8# plane.

I looked at the 75 Masters results in my December 75 RCM. I think these were the tryouts for the WC. (??) I wanted to get a feel for prop sizes used at the time. 11x7s seemed the most prevalent. Dave Brown won with an 11.5x7. All the engines were muffled. This was pre-tuned pipe.

I assumed the props were small by today's standards because engines were weaker back then. However, maybe it's because the engines were designed for RPM, not torque.

Tom

You hit the nail on the head, Tom.

We had 12x6 and 12x7 props back then and I tried them myself. On a very light model, you might get away with it, but none of my leadsleds were light enough to benefit from them. Besides, to what end?

Folks didn't start running other than 11" props until the noise requirements were being strictly enforced. Large, slow pattern props are a noise thing, not a performance thing.


Ed Cregger