Two different OS FP 25s

[Robert Zambelli]

Looking at some of my FP 25s, I came across these two.
I really don't have much experience with them but I know that some of you are quite familiar with them.
Note from the photos that they're different.

So, how do they compare? Are the differences cosmetic or is one an improvement?
Running characteristics, weight, reliability, etc?

Thanks for any help,

Bob Z.

[Dan McEntee]

  Just off the cuff, they are just like the FP-20 and .40, with an early model and a later model. I think the earlier models of each had a steel liner and iron piston, and later model had the ABN construction. You can see in the photos on the differences in the way they look on the outside, and that is how to tell one from the other. I just can't remember which is which. Performance between the two is similar. I think Leonard Neuman over at Stuka Stunt Works preferred the earlier version as having just a bit more  power. I think the ABN lasts longer.
   Type at you later,
    Dan McEntee

[Fredvon4]

Not weight reduction...the left one with noticeable bypass hump is old iron liner and the one on left is ABN variant later...they both are within grams of each other

[Brett Buck]

Looking at some of my FP 25s, I came across these two.
I really don't have much experience with them but I know that some of you are quite familiar with them.
Note from the photos that they're different.

So, how do they compare? Are the differences cosmetic or is one an improvement?
Running characteristics, weight, reliability, etc?

  Left = ABC, right = iron-liner. I only have extensive experience with the ABC. David has an iron-liner version that Eric flew at the NATs, he said it runs OK as long as you have enough oil in it. The ABC runs on whatever fuel I happen to have a lot of at the time. My impression from watching other people is that the iron-liner versions are not as consistent from day to day or individual engine to individual engine, but that might have more to do with the state of the piston/liner fit, which you would expect to be more variable from engine to engine, based on how it had been treated before you see it.

    For my money, the 20FP runs a lot better, but there is no question that the 25 is much more powerful, and there have been numerous examples of people not being able to tame the power even in airplanes like Noblers. It's plenty stable, but keeping the airplane at a reasonable speed has been an issue with common commercially-available props (like the APC 10-4 or 11-4).

    It's also much more powerful than many/all of the old B Team race engines, with some people reporting 20 mph more using a 25FP over the sainted Dooling or McCoy 29 (at much less weight). ST X29 - probably not.  During the "revival", good thing they didn't allow modern ball-bearing engines, because the 25SF and 25VF are much more powerful than a 25FP.

     Brett

[Phil Spillman]

Hi Bob ET Al. The iron piston and liner is correct as Bret says. I've found these to run quite well accordingly as long as you use no less than 22% total oil. these engines are not a finicky as the Foxes used to be. The other one with the smooth intake side is an ABN alloy. OS didn't use chrome in their cylinder.
Again use at least 22% total oil to maximize wear. Many years ago Willis Swindell told me that he thought that the older iron pistons and barrels gave better performance.

Tally Ho!

Phil Spillman

PS I am flying a Brodak issued Sterling Yak-9 with an LA .25 which has been giving me many many hours of flying fun on "60'" instant use lines! I imagine that they're likely to be 58' eyelet to eyelet. Haven't measured them as yet. Suggest that you use a 6mm id venturi insert. My LA likes the 9.5 X 6 MAS prop!

[M Spencer]

Now to put the pidgeon amoust the cats , and perhaps get coffe spilt . ( Move any papers from desk etc before proceeding ) .



This Ere's a Adamisin FP 40 case . Their theory is the exhaust exiting at the casting gets it a bit hot there , so if its not there, it dosnt .So it dont - warp .

Stated they got a extra 1.000 rpms !, Th FP 25s were elidgable for B' T/R here in Aus. Mutch butchery . Nelson Plug Heads ( Said to gain 1.00 R P M s )
plus cranks gougedpassage exit , retimed shaft , ' gas flowed ' , rods faired, and cases butched  et al .

I got a bag of junk with a Nelson Plug Head ( Now  suited to my 21 FSR ) 2 cranks - 1 ' modded ' , a good std. piston & liner , and two cases with pices removed ,
The ' lathed ' one haVING THE EXHAUST STACK MISSING ENTIRELY .oops. plus passages gouged larger lower- tapered even .A right mess. But faster .

The moral of this story , is ; if you had a case with the muffler lug ' modified ' by inadvertent landing , whacking it off - the rear corner of the case - would clean it up.

It may even run better .
As the ' Big Art & Sons ' FP 40 has a bunged bypass ,so is effectively the same as the LA 25 ! , plus a 'wedge ' head ; My GP 25 FP clones may well get ' the treatment ' to the bypass at least .
As A vice,drill & file may not be good enough to replicate the head .

ALSO the FSR 25 is essentially the ball race version. Top End from rod up are intechangeable . Have a unrun unmolested late FP 25 for one day . Maybe for a mini Patternmaster of mini L J .
Would put in dual holes for FSR & FP for same spinner location . 
Pirated picture of FSR 25 , similer to early case FP 25 .



Theres a rag under the sink, if youd clean up that spilled coffee , NOW . 

[Dave Hull]

Air Biscuitry,

If you are going to run a stock .25 FSR fur stunt, ya better be sure whut it's getting puttin on is bigger than a Nobler....or make arrangements for two more blokes to join in and call it something else. So don't make yur Mini-PatternMasher too mini....

Other follow-up comments,

The current US BT-R rules allow any type of engine up to .28 cu. in. Or, a single bypass engine up to .29. Which means that no one would run a 29 unless they had an heirloom hanging on the wall. (ie. the rulesmakers didn't want to obsolete someone's equipment and turn away an entry.) But no full wave or tuna pipes. As written, it is definitely a horsepower event. And unless you can make a very light airplane, the pilots have to be strong and agile, cause those dudes are movin'....   On the west coast, the B-TR revival by Ken Smith and Dave Braun was going down a different path. The current rules managed to retain the original flavor of the event as regards the airframe, but racers being racers voted for all the engine they could get. Anyone that ran a period-correct engine would be blown away. And were. As I recall, some of the best performers under more restrained rules allowed the Aussey's to run modified Brodak .25s (plain bearing, but modern materials and design) in very light airframes. They seemed to like that combination.

The Divot

[M Spencer]

Yea, my T/R leaning is Early 70s Kiwi , ST 21/29 , ETA 29, Enya 29 , OS H-29 R . Saw them at touching 120 in practise & think Mr Brown got ' The record ' at that Taranaki meeting . They were mid-20s . The Blokes .
Times were around 6.00 tops , for 140 laps = 10 miles .
Had the FSR Clone in a 47 Oz 50 span thing , thinking 48 in LJ & 40 ish PM , so the FP will hack it . Had a 10 x 6 Tornado , when worn to 9 1/2 was good . Tho a black 9 x 6 or 9 x 4 flying in gales was necessary .55 feet of .018 Laystrate for steering .
Might ( semi ) replicate that ' Phantom F4E ' bigger & Twisted , for a FSR 45 . one day. , , , maybe .  Was good value , but dont think a bigger one'd take the hits . The Drained swamp in winter , Vertical, if square , was acceptable . 

This was Staples ( Wanganui ) 21/29 ABC Ship . The Then record holder ,

Being 15 , watching these 3 up , the footwork in the centre was the Top of the Pops . Their Then . Other perhaps did not quite have the technique down pat . First Nats. a ' B ' flat out , over grass , lost a up line . The suden cessation  soundwise
was abrupt . Incedents Aplenty . Survivers generally had themselves sorted out by the FINALS .
After All , suposed to be a rewarding persuit, not neccesarrily regarding the Trophy Pot . Cool Calm & Collected . Drama quite puts me off . A lot cooler & calmer after the ' B ' went in , and the pilot collected the pieces .

Kenny Steves would rival the Marxs Bros , piloting . Generally a B was 1/4 lap ahead , on take off . B a ' Lft Turn ' on take off , across the centre , Hard Left at the other side & It was in the race & on the pace . Unless ' Wires were Crossed .' .

Pity theres no video of any of it . 

This is my Classic FAI ships , ST RV left, Eta 15 Rt. Under refubishment & full repaint at the moment . Plus a Super Nova - ETA 15 . Id better pull the finger out , ' B ' Wise. A olde 1/2 A Hawker Tempest scaled 5/3 for the ETA 29 , likely . 



Back to the FP / FSR . Dead Stock , YES Brett . But butchered remains can be obtained for a pittance . The EX ' B ' FP crank & cases are free to a good home . More the nostalia trip , Why, a 64 GTO'd be far nicer than a current one . 

[Trostle]

Had the FSR Clone in a 47 Oz 50 span thing ,

Sort of off topic here, but did not, or does, New Zealand have three classes of team race:  Class A for .15's, Class B for .29's, and Class C for .60's?  I think it would be something to see two or three .60 powered racers in one circle.

Keith

[Brett Buck]

On the west coast, the B-TR revival by Ken Smith and Dave Braun was going down a different path. The current rules managed to retain the original flavor of the event as regards the airframe, but racers being racers voted for all the engine they could get. Anyone that ran a period-correct engine would be blown away. And were.

   I suggested changing the name from Vintage B Team Race to "Simultaneous Sport Flying Demonstration for Gentlemen of a Certain Age" and then having 100 appearance points (split between workmanship and adherence to prototype) and 50 points for winning, 49 for second place, etc. Basically to make it objectionable to people who wanted to win by ratcheting up performance - basically, trying to prevent it becoming Slow Rat, part two.

   I also suggested limiting it to modern plain-bearing engines up to a 21 (to let the 20FP be legal) but I assumed that someone would figure out how to put a NovaRossi liner in a 20FP crankcase soon enough.

    Brett

[Brett Buck]

Sort of off topic here, but did not, or does, New Zealand have three classes of team race:  Class A for .15's, Class B for .29's, and Class C for .60's?  I think it would be something to see two or three .60 powered racers in one circle.

  Yes, three airplanes powered by K&B or OS 60 VF DF engines at the same time would be something to see. From behind a strong barrier or closed-circuit TV from a bunker!

     Brett

[M Spencer]

Sort of off topic here, but did not, or does, New Zealand have three classes of team race:  Class A for .15's, Class B for .29's, and Class C for .60's? 

Kiwi Land , early 70s ; was the tail end of ' A ' ( .15 cu. in. ,2.5 c.c. ) 1/ A  , Oliver Cub 1.5 c.c. was popular . and safest . B was 32 Oz Max , 5 c.c. engine , 30 c.c. tank . 60 foot lines ( .016 ? ? ) 70 lap 5 mile heats & 140 lap 10 mile finals .



May not be to scale .

Over here in Aus. at the moment / last decade . Ive seen a ' C ' 70 Ft. .018s . But was K&B 40 powered . so not earth shattering .
Olde Dayes , when men were men , and six foot , and 20 stone ( some ) They ran ' C ' here , but was much like early American ' B ' , Vintage of equipment at least .
Scarceity wouldve meant use what you had . Doolings  Mc Coys and suchlike Id think. Most found a .40 was less irrascable & could be counted on to finish .

I couldnt say if it were ever flown as a Nats Event , but there mustve been a dozen or so built . First T/R events here apparently the ended up with a 44 gallon drum . ( 50 US Gal. ) for the lone Country Boy entrants ,
so there wernt six pilots standing on one spot rotateing , apparently . So they could get past three laps tops .  I think the ' C's were topping out around the ton , from recolections of observes / particpants .

[John Park]

While we're on the topic of the early steel-cylinder .25FP, can any of you clued-up gentlemen tell me whether there was any difference between the .25FP and the .25FP-S (apart, of course, from the replacement of the carb. with a C/L venturi insert and NVA)?

John

[Brett Buck]

While we're on the topic of the early steel-cylinder .25FP, can any of you clued-up gentlemen tell me whether there was any difference between the .25FP and the .25FP-S (apart, of course, from the replacement of the carb. with a C/L venturi insert and NVA)?

John

  No difference. And that is very good, you *want it* to run just like it runs for RC.

    Brett

[Dennis Moritz]

I've run both extensively. Fun engines. Nickel engines peal the liner if abused, iron piston steel cylinder engines eventually wear. We run them up in the rpm band, not much break, but consistent high power. They work well on Phil Cartier combat wings of a certain size, Flite Streaks, CG originals and knock offs, Sterling warbirds and knock offs. We use them with Philly tongue mufflers, meaning chips with a lotta holes. Usually loud and nasty. Excellent Ringmaster engine. Very reliable feed, chicken hopper, bladder, clunk. Way easier to tune than an Fp40 or 35. Fun. Almost every one I've run has been fuel, ignite, flip and fly.

Yes. Left is ABN, right is iron piston/steel liner. The bump from exhaust port down means iron piston. The iron piston engines I've used have been consistently machined accurately. Needing not much break in. I would do a few runs on the ground making sure engine is not tight. Then take it easy before you kick the rpm up high. I have run the ABN engine without much caution. A few 2 stroke flights fairly easy. Then. Whatever. Combat fliers around here like to run these in speed limit events.

[Steve Helmick]

I would think the weight reduction in the case and drive washer would off set the difference between the iron piston and aluminum piston so same weight but an attempt at weight reduction none the less.


Motorman

Don't forget that the brass cylinder is heavier than the steel one!  Steve

[Robert Zambelli]

I finally had the opportunity to try the iron sleeve FP 25, thanks to the help from Keith Trostle, who was kind enough to give me a backplate.
I made a Torlon venturi with a .200 inch bore and used a universal NVA (1/8 inch diameter)
After modifying the backplate to fit, I fitted a 9-4 Master Airscrew and mounted the FP on an ARF Flite Streak.
I was really impressed by the performance and now I understand why the FP 25 is so popular.

Thanks to all for the help and suggestions.

Bob Z.

[Brett Buck]

I finally had the opportunity to try the iron sleeve FP 25, thanks to the help from Keith Trostle, who was kind enough to give me a backplate.
I made a Torlon venturi with a .200 inch bore and used a universal NVA (1/8 inch diameter)
After modifying the backplate to fit, I fitted a 9-4 Master Airscrew and mounted the FP on an ARF Flite Streak.
I was really impressed by the performance and now I understand why the FP 25 is so popular.

   That is a *very small* venturi for that engine, less half the choke area of stock unit, so there is *very much more* power available.  But I bet it needles nicely even at low revs.

   For reference, with that spraybar, you need about .246" to match the stock choke area, but you will need to make sure in-flight revs are sufficient to draw fuel that way.


     Brett