How about an O.S. Max 61RF ABC for stunt?

[Scott Richlen]

Does/Has anyone flown one of these in stunt?  What did they have to do to make it work?

Thanks!

[M Spencer]

It might .

http://sceptreflight.com/Model%20Engine%20Tests/OS%20MAX%2061RF%20ABC.html

Short Nose tho , You must want to build my typhoon ! .



Was looking at the VF 61 for that. Used a OS 80 . 20 Oz . Flys good .

[John Lindberg]

Maybe it would work if you had an extremely tail-heavy plane. 

[Peter in Fairfax, VA]

Scott,

What about a Stalker 76?  Weighs less, seems like it could haul a pretty big stunter.

Peter

[Brett Buck]

My concern is that it's abn not abc.

   That is irrelevant for stunt, they are equivalent and will last more flights than you or almost anyone else here will fly with it.

 

It has a big crank and a brass liner, about 19oz.  Other wise looks made for stunt. I saw a few side exhaust versions on eBay.

   That is not entirely irrelevant, although normally you wouldn't choose engines based on weight.

    The real problem with this engine would be the complete lack of any experience, when there are an infinite supply of acceptable engines that are already known quantities. Harnessing the extreme power of these giant engines and having them generated only the 1/2 an HP without it going nuts in the corners is no small feat, and would not be a wise choice when you can get any number of other engines that are known quantities. Figure this - for any airplane you can reasonably fly on 70's lines, its little brother, the 40VF, is plenty and it is 2/3rd the size. Run in the first-generation type system, even the 46VF is more than you can easily use, and ended up with 3" of pitch and an ear-splitting scream.

     So now you are trying to run it in 4-stroke, that will probably require a year or so of experimenting if you really know what you are doing, during which time everybody else is going to be switching to electric, and that many more PA61s and 75s will become available.

  Of course, you could try it on a muffler, which just makes it harder still to tame. And, you can buy all the Saito 72s you want, which is a known quantity.

    Brett

     
   
   

   

[Mike Hazel]

About twenty years ago I saw someone setup one of these for speed flying.  Nearly 185 mph as I recall.  Worked good for that!

[Scott Richlen]

Hopefully, someone has had some experience with this engine.

The reason for my contemplation of this engine and not another is that I may soon come into possession of one.

I have a set of Windy's plans for the Typhoon with a nice short nose because it was designed for a 4-stroke.  19 ounces?  No problem!

[M Spencer]

It'd be worth a try , perhaps .

Bit like a SF . One piece case sorta of a VF .

The 144 / 114 means the mandatory 15 Deg. max. blowdown . Though the boost ports lower .

As the LA has none - boost port . and FP 40 can benifit from it blocked , might be a first priorty .
A bit of balsa or spuce tacked in would do it .

Theres a fresh ' old ' FP 40 post in the engine set up , with pictures of the renowned ' Big Art ' head .
That or maybe a narrow squish Hemi might help it along . Though a few gaskets to back off compression
most think is as much use .

The Crank close not late , and its a ' undersquare ' bore/stroke ration . So chances are it'd work .

Tho the cowl top vent & good cooling flow would be good,, as a runaway wouldnt .
Were some of Urtnowskis old props , 4 blades and suchlike , in classifieds a month or two back .
Narrow Tesstarossa  four blade C.F. etc . As it should swing something like that .

Id do a perforated tube muffler . Tube muffler with say 10 3/32 holes , as per tounge muffler .
Getting really carried away , a stack up the back to tubes to exhaust pipes on he cowls sides .

A lot of the OS'es DONT require nitro . a few % maybe . the 80 is steady on none .

A VF 61 is pretty much the same timing as the 40 / 46 . That tests saying the RF has better ' bottom end '
As in happier swinging a bit of propellor .

The 80 , I think Im running a 0.30 inch bore intake , with the 5/32 S T needle valve .Otherwise dead stock .
I wouldnt go over 0.33 intake on that RF .

[Scott Richlen]

what does blocking the boost port actually do?  Won't it reduce the engine's power?

[Lauri Malila]

It will lower the port area to an acceptable level, making it easier to control the engine at lower power setup.
But it also introduces a discontinuation to flow, making scavenging less stable and efficient. That's the downside.
I have made the same engine with and without boost port (same port area and same port height), and with boost port(s) it was clearly better.
L

[Scott Richlen]

It will lower the port area to an acceptable level, making it easier to control the engine at lower power setup.
But it also introduces a discontinuation to flow, making scavenging less stable and efficient. That's the downside.
I have made the same engine with and without boost port (same port area and same port height), and with boost port(s) it was clearly better.

Supposedly, the 61 RF was designed to operate at lower RPMs with more power since the engine designers wanted to lower propeller noise.  Is the boost port the main contributor to engine "run-aways"?

[Chris McMillin]

They work great on Classic Pattern ships. An 8 lbs Patricia with a 19 inch pipe on a 12x10 would probably be a nice longstroke set-up, I dont know why one would try that big thing in a Stunt ship.

[Scott Richlen]

I dont know why one would try that big thing in a Stunt ship.

uhhh, because I fly stunt and the engine is sitting there waiting for some use to be made of it....

[Steve Berry]

Sounds like the equivalent of using a Cummins diesel to deliver pizzas in the neighborhood. It can do it, but it'll be big, loud, heavy, cumbersome, and eat you alive in fuel costs.

[M Spencer]

" what does blocking the boost port actually do?  Won't it reduce the engine's power? "

THAT's The Idea ! .  Do you need 1.85 horsepower at 16.000 rpm. 

If you put a 74 1 litre Honda Civic exhaust system , on a Hemi 426 , it may have difficulty producing 600 horsepower ,

if you put a 426 Hemi N A S C A R exhaust system , on a 74 1 litre Honda Civic , it may not produce 600 horsepower .

=========================================================================

Basically , the Scavage / back-flow / Charge Density .  ( for the port mod )

Say it had five intake ports , and produced five horsepower . If you wanted ONE Horsepower and blocked four ports ,
the one remaining would be working as it did , previously .

Gross oversimplification . But pertinant .


a.k.a. the Big Port heads on a 351 , it comes off idle at 80 mph .

If you put realy scrawny port bore heads on , the power'd come in much lower .

The Gas Speed & therfore distribution , would be more effective at low rpm.
Might not work worth a damn at mega revs , but who gives a toss .
They are positively not desireable  . In a aerobatic ship .

============================================

For Tourque , mid range , and throttle response , you require smaller port & exhaust volume than big hairey
Max Output , nothing bellow 3/4 revs , Max output ( top end = Revs ) system .

There ya go


===============================================================

essentially there differnt porting requirements for differant power requirements .

theres certain gas speeds where even distribution of fuel vapour occur .

So the port area needs matching to the rpms. bunging the boosts a easy way .

sofisticated , would be halving area through thickeners on the liner with gas flowed ( curved/blended ) exit & entry. Not sharp edges .

But keeping it basic, as in the case of a axe or sledge hammer , which predate office nerds & computors , is often as more , effective.
After all. A boomerangs the most efficent aerodynamic device known. On this planet .

Might get a replica head for two FP 40s in the Comet .
H-35C's , Enya 35 PB, ' 'Big ' FP's , all match mounting screws to prop face . The 35-S's are short .  and lighter .

For a ' Tecnical ' mod . , youd perhaps raise the transfer port upper edge . To lower blowdown .
They all recon 30 o/a, 15 seperation - is max , for a 4-2-4 run. Or Even to ' Drop ' from rev pick up .

SO. The Fred Flintstone trip , is to run it on the bench . RICH . Tank c/l level with N V A .
Pinch the fuel tube .( to inrease revs .)
RELEASE.
It should drop back to RICH .
Instantly .
A slight hesitations not unusual .
a second and a half is querulous.
3 seconds, your doomed .

Instantaeneous & your in clover , so bunging it & a bench test & comparison , & you know if youve got it.
Also the ' Pick Up ' in revs . Should be slight- measured - and consistant . Fine if it is .

Otherwise some kind of restriction somewheres called for . which we've just done .  bunging the boost port.

Also cause weve tooned it for tourque ( rather'n rpm's ) itll swing a bigger prop . If youve got it right .
So now youll need a Rabe rudder .
 




The ' FLAT ' goes opposite the outlet ( exhaust port ) .

[Scott Richlen]

What was that?

[M Spencer]

Would you like me to repeat that in english ! ?

RUN IT ON THE BENCH .

Pinch the fuel tube .( to inrease revs .)
RELEASE.
It should drop back to RICH .
Instantly .
A slight hesitations not unusual .
a second and a half is querulous.
3 seconds, your doomed .


Also the ' Pick Up ' in revs . Should be slight- measured - and consistant . Fine if it is .

=====================================================

OH ! the Picture ? A ' Big Art ' Adamisson Schnurle 40 Two trans. Port HEAD INSERT .

https://stunthanger.com/smf/engine-set-up-tips/os-40-fp-set-up-q's/

And yer typical ' full hemi ' job . Say a 1 or two mm squish band , full radius to mate plug face .
so as ' squish Band ' clearance can be optimum for Compression Ration to suit use .

https://stunthanger.com/smf/open-forum/flight-report-spring-practice-at-the-zambelli-aerodrome-taming-a-runaway-fp-40/



Chances are you can get a ' Jett ' / p. A. type run , from it . Like a L. S. stalker 61 with twice the power .
so youll need good flying lines, connectors , and a firm grip . as That typhoon is a bleedy great Pattern Master . essentially .
Whereas mine is designed by Sidney Camm . With a few modifications by me . & is light on the lines . & turns Tight.
With the Low Polar Moment .

[Lauri Malila]

No, with correct port areas and duration it would be better with boost port than without. What causes runaways is that the engine is designed to higher power output than what cl people needs.
But eliminating the boost ports lowers the power to acceptable level.
Port timing and area makes power.
Scavenging geometry makes efficiency.

L

[Scott Richlen]

Thanks Lauri.

According to the engine review that "Air Ministry" referenced, this OS engine was designed to generate power at lower RPMs (to reduce prop tip noise) for the RC guys.  I'm hoping that that should prove usable in the CL arena as well.

[Curare]

The RF's were decent pattern motors, and designed to be on pipe, swinging big, pitchy props, this was the era of "long-stroke" motors, where torque was more important than BHP  (and keeping noise down was critical).  While that sounds good for a stunt motor, I think the amount of power there would be waaaay more than we need, I'd bet you'd need a 14" three blader to absorb that torque.

Personally I think it'd be a waste of a good motor if you had to start butchering heads and timing to get a 'stunt run' out of it.

[Scott Richlen]

Personally I think it'd be a waste of a good motor if you had to start butchering heads and timing to get a 'stunt run' out of it.

Good point.  However, in ten years this stuff all goes into the dumpster when everyone has gone electric and the fascists have banned fuel because it has "nitro" in it, and who knows, some modeler might go berserk and start blowing up everyone using Sig 10%.   

[Curare]

Scott, if and when that happens, I'll take it off your hands! There's still a few of us who play with those "old" pattern motors!