OS engine ?

Thank you Jason for the information. Appreciate it.
Jim

No- there are major differences in footprint between the two: weight-25FP 244g 35FP 335g length-25FP 3-1/2 inches 35FP 4 inches
crankcase clearance 25FP 1-1/8" 35FP 1-1/4" muffler length 25FP 4-1/4" 35FP 5"

All actual measurements taken from my own examples-with regard to the weights quoted-these are the R/C variants-with a standard C/L venturi and NVA they would be slightly lighter.


the 20/25FP have comparable footprints-as do the 35/40FP but not the 25FP vs 35FP

ChrisM
'ffkiwi'

Thanks Chris for that information on the differences between the OS engines?

Is this a FP engine? I don't see the FP marking.

https://www.ebay.com/itm/164436440373?ul_noapp=true

Looks like an OS 25 FSR series engine. Ball bearings and the older style muffler.

Thanks Jason, is it as good as a Fp .25? Looking for one to put on a sig Skyray.

FSR was probably OS best engines.

Here are the mounting lug cards for the 20-25 FP and 35-40 FP.

oldguy wrote:Thanks Jason, is it as good as a Fp .25?  Looking for one to put on a sig Skyray.

Comparable-but a bit heavier, being a twin BB engine. 254g (FP) vs 279g (FSR)....the FP might well have a slight edge on top end power, being a later design.

ChrisM
'ffkiwi'

Here is a OS max FP.40 example. Is this an early iron piston, or the newer ABN version FP. I would think the FP .25 would look the same is that right. So the ABN newer version FP's would be the one's to look for?



https://www.ebay.com/itm/OS-40-FP-RC-model-airplane-engine-40-glow-fuel-/143762234910?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=%252FHR5gGl5cHU5mC2rWj4xZ9733Vo%253D&orig_cvip=true&nordt=true&rt=nc

So then I'm looking for the ABN version FP .25 for a sig skyray and a super Satan. I have two of the ABN FP .40, but there too big for these two planes i will be building this winter.

How does the OS MAX 25 SF stand up to the .25 FP?

If you have an iron lunged FP 20 or 25 with the correct muffler and venturi it will run like the Brett Buck setup for the box stock LA25.  The OS website calls out the muffler and venturi in the LA25 parts list.  The older muffler will not provide the desired run.  

While I am sure the ABN vs iron has other differences, for flying pattern on a Flite Streak or Skyray the power and performance will be there.

http://www.aeromaniacs.com/brett.htm
APC 9-4
11,300 rpm

The "2030" muffler (silencer in the instructions) is the important part of this system as it is a tuned pipe.  (the 871 does NOT perform) the venturi diameter is not listed on the osengines website.

The footprint is close enough to a fox35 that it should bolt right up unless there is no wiggle room in the bolts.

Phil

how does the OS MAX .20 compare to the OS max FP .20?

Similar physical size and weight-but a cross flow engine compared to a schneurle-so somewhat less powerful. Timed for a lower rpm peak-so might in fact be a better choice for your proposed CL stunt use than an FP. You can find the engine test on the Max-20 here: http://sceptreflight.com/Model%20Engine%20Tests/OS%20Max%2020.html

Tens of thousands of them in use during their day....I still have three or four in my inventory. They were the direct successor to the OS Max-19-so the design dates to the mid 60s....though-as the engine review points out, it didn't appear on the market till quite a bit later-in the early 70s

Unfortunately there is a bit of a dearth of data-in terms of english language engine tests-on the smaller FP engines-the 10, 15, and 20-so you have to rely on the manufacturers figures....which are often...how shall I put it...optimistic....

If the intended purpose IS for CL stunt-then I would happily recommend the Max 20-and running on a 10x3-1/2 or 9x5 (depending on your preferred flying style-slow or faster) which it should turn around 10.5K.....and they are still plentiful on the second hand market. Spares of course are entirely another matter....

The FPs do have something of a reputation for not being entirely tractable when use for CL stunt-ie a reluctance to hold the 2-4-2 break reliably...and a tendency to 'run away' once they get a bit warm during the flight. You would probably have to drop the prop size slightly compared to the Max 20 to get one in its power band....which might or might not affect the way the model flies as a consequence...on the plus side-being more recent, spares are more available-but I should qualify that by saying that earlier OS designs were much better supported in terms of spare parts than more recent ones...I suppose thats a simple result of the OS range having proliferated vastly over the decades-and the more engines and variants you have, your spares requirements increase exponentially....as does the time required to both produce them and manage inventory..

ChrisM
'ffkiwi'

ffkiwi wrote:Similar physical size and weight-but a cross flow engine compared to a schneurle-so somewhat less powerful. Timed for a lower rpm peak-so might in fact be a better choice for your proposed CL stunt use than an FP. You can find the engine test on the Max-20 here:  http://sceptreflight.com/Model%20Engine%20Tests/OS%20Max%2020.html

Tens of thousands of them in use during their day....I still have three or four in my inventory. They were the direct successor to the OS Max-19-so the design dates to the mid 60s....though-as the engine review points out, it didn't appear on the market till quite a bit later-in the early 70s

Unfortunately there is a bit of a dearth of data-in terms of english language engine tests-on the smaller FP engines-the 10, 15, and 20-so you have to rely on the manufacturers figures....which are often...how shall I put it...optimistic....

If the intended purpose IS for CL stunt-then I would happily recommend the Max 20-and running on a 10x3-1/2 or 9x5 (depending on your preferred flying style-slow or faster) which it should turn around 10.5K.....and they are still plentiful on the second hand market.   Spares of course are entirely another matter....

The FPs do have something of a reputation for not being entirely tractable when use for CL stunt-ie a reluctance to hold the 2-4-2 break reliably...and a tendency to 'run away' once they get a bit warm during the flight. You would probably have to drop the prop size slightly compared to the Max 20 to get one in its power band....which might or might not affect the way the model flies as a consequence...on the plus side-being more recent, spares are more available-but I should qualify that by saying that earlier OS designs were much better supported in terms of spare parts than more recent ones...I suppose thats a simple result of the OS range having proliferated vastly over the decades-and the more engines and variants you have, your spares requirements increase exponentially....as does the time required to both produce them and manage inventory..

ChrisM
'ffkiwi'

Chris thanks for all the breakdown on the differences on the OS eng. I'm looking to put a .20 on a Super satan combat, so i would be wanting the Fp series.