Need reviews or info on.

oldguy wrote:First one is the OS max .15[FP], the OS Max .25[FP], and a thunder tiger .15. I would be using them in control line planes. Also how much difference is there between the OS Max .15[FP] and the OS .20[FP] .... Also have to ask about the K&B .25 Sportsters. Thanks

oldguy, a good source of information to help get a handle on these engines is sceptreflight.com Model Engine Tests

These are magazine review articles done by the engine test authorities of the day such as Peter Chinn, HR Warring, etc. Most articles have horsepower and torque curves and a list of test propellers used.

Perhaps a typo? K&B made a .20 and .28. One of the prolific old timer CL flier who goes by the name of Dennis on CL forums refer to the Sportsters as the poor man's 4-cycle, because they could turn larger props easily and were good replacements for the .35 cross scavenged engines of the day. There are various venturis and NVA's available if one wants to dispense with the RC carb. These engines have a chromed plated piston running in a special hard aluminum alloy crankcase (crankcase bore is sleeveless). Although you might get trolled, overall there are good experienced posters in Stunt Hangar and Stuka Stunt Forums who can tell what venturis work best and who has, set up, and etc.

Fliers have mistakenly treated these engines by running them in todays lower total oil content (i.e., 16% of total volume) with lower Castor oil content (i.e., 2% of total volume) fuels for ABC engines. They can be easily damaged by a lean run, eroding the piston's chromed surface, thus gaining it an unfair reputation by these that didn't know how to treat them. Thus it is best to run them in adequate Castor (10%) fuels. Mecoa instructions mentions no longer available K&B 505 (5% nitro) or K&B 510 (10% nitro) fuels of the day.

Here are excerpts from the FP instructions for specifications and props.





Opinions have changed over time with the newer fuels, general concensus is at least 20% oil with 10% as Castor (i.e., Sig Champion fuels). Use of synthetic oil helps to keep down the Castor varnish (except in worn out steel cylinder, iron piston engines 40+ years ago).

roddie wrote:Jim, Are you able to post photos of the subject-engines? The "FP" series description on the OS engines helps.. but are any/all of the engines in question; control-line versions? Some RC engines work ok for control-line use.. but I'd recommend using engines that were designed for the type of control-line flying that you'll be doing. Keep in mind though; that some control-line activities may use RC (throttled) engines.. such as "Scale" and "Navy-Carrier".

The OS Max FP-series were quality engines.. from what I've heard. Others will likely chime-in with their experiences and advice.

These are r/c engines.

The Fp.15 is pretty hot for a older .15. When I say older, I mean it was a 80's series engines which was designed for early r/c entry. It also has ABN construction which makes for easy starts compared to the vintage iron/steel.  Very good quality even though it was a inexpensive engine. On APC 6.3x4's and 7x4 Master Airscrews, we get 20K and above.The only other .15 that I know that comes close to this is a BB AME Norvel .15.  F2D .15's are excluded here as they're a different animal. I'm just saying that 20K is very decent rpm's for a bushed engine and it will do it all day long. The FP .15 will work terrific as a control line engine provided you have the proper spraybar and venturi if using a tank. The Fp.15 needle and spraybar is still available if you don't already have one.

      The Fp.20, it's a good engine equally. It was the "Rage" a few years back. Personally, I never thought much of them. I have 3 of them and these were available in ABN or iron piston configuration and I have both versions. I prefer the iron over the ABN myself. I don't use the stock muffler because it really is a POS. Some claim it offers tuned pipe like performance. It really just overheats the engine and adds tons of nose weight to the plane. It muffles the noise effectively but at the cost of losing power.Randy Smith tongue mufflers work very well with the FP engines from .15 on up to the .40. They do prefer a little back pressure. These engines want to run up so light pitch props not exceeding a 4 pitch are necessary. Keep the diameter in the 8"-9". They're not going to offer the mythical 2-4 break like older iron jobs. Your going ot have a much higher rpm engine and even with the nose pointed up audibly the engine doesn't change much in rpm's. This can be a new learning curve for flying. This is  due to knowing how much fuel your engine uses because it offers very little warning at the end of the flight.


     The K&B Sportster series are very unique. Mercedes utilized the same technology . Sportster engines don't have a cylinder liner. The piston travels in a high silicon cylinder head. Essentially on the sportster, the case is the piston liner. These engines although modern still require a bit more castor than the ABC/ABN version engines for longevity. Don't run them on less than 22% oil content. These engines are quite heavy but they offer a lot of torque. They can swing a larger prop diameter than other engines of the same displacement. My experience with the Sportster series is with the .20 and .28. Essentially all of the Sporster series are identical other than size. The stock muffler of these engines use the smallest outlet I have ever seen. This might work for the r/c crowd, not for control line. It's just too restrictive.

             Dennis has posted some very good info on the Sporster engines. This was way before most were trying to use them. He had used them on profiles and full bodied planes. He's a encyclopedia of knowledge on many of these engines. Sadly, Dennis suffered some serious neck and shoulder issues which essentially meant he had to stop flying.

GallopingGhostler wrote:

oldguy wrote:First one is the OS max .15[FP], the OS Max .25[FP], and a thunder tiger .15. I would be using them in control line planes. Also how much difference is there between the OS Max .15[FP] and the OS .20[FP] .... Also have to ask about the K&B .25 Sportsters. Thanks

oldguy, a good source of information to help get a handle on these engines is sceptreflight.com Model Engine Tests

These are magazine review articles done by the engine test authorities of the day such as Peter Chinn, HR Warring, etc. Most articles have horsepower and torque curves and a list of test propellers used.

Perhaps a typo? K&B made a .20 and .28. One of the prolific old timer CL flier who goes by the name of Dennis on CL forums refer to the Sportsters as the poor man's 4-cycle, because they could turn larger props easily and were good replacements for the .35 cross scavenged engines of the day. There are various venturis and NVA's available if one wants to dispense with the RC carb. These engines have a chromed plated piston running in a special hard aluminum alloy crankcase (crankcase bore is sleeveless). Although you might get trolled, overall there are good experienced posters in Stunt Hangar and Stuka Stunt Forums who can tell what venturis work best and who has, set up, and etc.

Fliers have mistakenly treated these engines by running them in todays lower total oil content (i.e., 16% of total volume) with lower Castor oil content (i.e., 2% of total volume) fuels for ABC engines. They can be easily damaged by a lean run, eroding the piston's chromed surface, thus gaining it an unfair reputation by these that didn't know how to treat them. Thus it is best to run them in adequate Castor (10%) fuels. Mecoa instructions mentions no longer available K&B 505 (5% nitro) or K&B 510 (10% nitro) fuels of the day.

Here are excerpts from the FP instructions for specifications and props.





Opinions have changed over time with the newer fuels, general concensus is at least 20% oil with 10% as Castor (i.e., Sig Champion fuels). Use of synthetic oil helps to keep down the Castor varnish (except in worn out steel cylinder, iron piston engines 40+ years ago).

thanks for posting this info.

I'm pretty sure your aware of this, the FP .15 flies a 230 sq inch plane very well. Some claim that they use this engine on full size Ringmaster's claiming it has too much power. Well. I don't subscribe to that page and unless your getting a full size Ringmaster down to 20oz's, it isn't going to fly it worth a ding dong using a FP.15. The Fp.20 flies planes like the Ringmaster quite well. It would fly a Sterling version however they're ounces heavier than the newer offerings by Eric Rule and Brodak which the FP.20 would suit much better. The FP .20 is much more suited for 400 sq. inches so you can see the differences in the planes these engines support just in wing area from one to the other.  They do want to rev and even looking at the offerings of prop sizes on the instructions, I must say I don't agree with all of them in terms to what works best. That being said, the iron piston versions do rev but they're not as happy through the run doing so. Knowing which version you have is important. The iron piston version of the FP.20 has a large bump on the case from the mounting lugs to the cylinder fins vertically. In addition, the OS logo on the opposing side is taller whereas the ABN is somewhat italicized.

Ken Cook wrote:I'm pretty sure your aware of this, the FP .15 flies a 230 sq inch plane very well. Some claim that they use this engine on full size Ringmaster's claiming it has too much power. Well. I don't subscribe to that page and unless your getting a full size Ringmaster down to 20oz's, it isn't going to fly it worth a ding dong using a FP.15. The Fp.20 flies planes like the Ringmaster quite well. It would fly a Sterling version however they're ounces heavier than the newer offerings by Eric Rule and Brodak which the FP.20 would suit much better. The FP .20 is much more suited for 400 sq. inches so you can see the differences in the planes these engines support just in wing area from one to the other.  They do want to rev and even looking at the offerings of prop sizes on the instructions, I must say I don't agree with all of them in terms to what works best. That being said, the iron piston versions do rev but they're not as happy through the run doing so. Knowing which version you have is important. The iron piston version of the FP.20 has a large bump on the case from the mounting lugs to the cylinder fins vertically. In addition, the OS logo on the opposing side is taller whereas the ABN is somewhat italicized.

Great info Ken. Would say this is a non iron piston version? Would the Fp .25 be a good match for a 35 size planes like the ringmaster or others? Or is the .20 plenty of power, I like to fly my planes faster than most.

I prefer the FP .25 over the .20. They're pretty close in power, I find that I like a bit in reserve whereas the .20 seems to be nearing it's limit. Many say that the .25 doesn't work as well. They have their heads up the rear ends. It works better. They're a great engine for .35 size planes. The Sig Skyray was being mentioned on another forum to use with blah blah blah setup. It lacked power and performance. One of my club members tried to make the supposed setup work and spent 3 months doing so. I refused to help him anymore as I had enough explaining to him how restrictive and counterproductive the stock muffler is. I have witnessed this setup many times and was not happy with it at all. The FP .25 took all this out of the picture and it worked flawlessly.

Ken Cook wrote:             I prefer the FP .25 over the .20. They're pretty close in power, I find that I like a bit in reserve whereas the .20 seems to be nearing it's limit.  Many say that the .25 doesn't work as well. They have their heads up the rear ends. It works better. They're a great engine for .35 size planes. The Sig Skyray was being mentioned on another forum  to use with blah blah blah setup. It lacked power and performance. One of my club members tried to make the supposed setup work and spent 3 months doing so. I refused to help him anymore  as I had enough explaining to him how restrictive and counterproductive the stock muffler is.  I have witnessed this setup many times  and was not happy with it at all. The FP .25 took all this out of the picture and it worked flawlessly.

Ok that's what I want to know. I will look for the Os  .25  and the .15.  Is this the Fp version I should looking for the non iron piston.

https://www.ebay.com/itm/OS-25-FP-RC-model-airplane-engine-with-muffler/123280891563

And is this the iron piston version?
https://www.ebay.com/itm/263861398084?_trksid=p2471758.m4703

Ken can you give me any comments on the Thunder tiger engines?
https://www.ebay.com/itm/Vintage-Thunder-Tiger-GP-15-Model-Airplane-Engine/253803080459

The first link the .25 is a FP. It's hard ot tell because I can't get a good look at the exhaust side of the case. It appears to be the ABN version but as I said it's hard to tell. Both versions work very well. The ABN possibly hot starts easier and it's said they're more tolerable of a lean run due to the difference in materials, the liner expands away from the piston when hot.  

The second link of the .15 is not a FP .15 but the second version offered after the MAX-S.  Thunder Tiger engines were essentially designed by the same individual who designed the FP series for OS. When this individual left OS, he took his designs with him and elaborated on them. As you notice the box says ABC, ABC is superior to the ABN plating and generally offers a touch more power. In addition, longevity is increased. Thunder Tiger is a Taiwanese company. Rumor has it that these and engines like the early Tower Hobbies engines were made under high quality control in a factory that produced sewing machines. I was always pleased with any of the Thunder Tiger engines I own. I have some very nice engines from them. Many of the parts swap to the OS Fp engines. For instance, the Tower Hobbies .40 is the FP OS .40 just in a ABC version.

Ken Cook wrote:The first link the .25 is a FP. It's hard ot tell because I can't get a good look at the exhaust side of the case. It appears to be the ABN version but as I said it's hard to tell. Both versions work very well. The ABN possibly hot starts easier and it's said they're more tolerable of a lean run due to the difference in materials, the liner expands away from the piston when hot.  

The second link of the .15 is not a FP .15 but the second version offered after the MAX-S.  Thunder Tiger engines were essentially designed by the same individual who designed the FP series for OS. When this individual left OS, he took his designs with him and elaborated on them. As you notice the box says ABC, ABC is superior to the ABN plating and generally offers a touch more power. In addition, longevity is increased. Thunder Tiger is a Taiwanese company. Rumor has it that these and engines like the early Tower Hobbies engines were made under high quality control in a factory that produced sewing machines. I was always pleased with any of the Thunder Tiger engines I own. I have some very nice engines from them. Many of the parts swap to the OS Fp engines. For instance, the Tower Hobbies .40 is the FP OS .40 just in a ABC version.

Thank you Ken I do appreciate you taking the time to share your knowledge.

Here are some pictures



The FP.15 was only made available in the ABN version. Case also says FP on the exhaust side as pictured here.


This is a iron piston FP .20 ( Note the way the casting letters are written on the case, all iron piston versions share this ).

All ABN versions use this logo on the case

FP ABN version on the exhaust side of the case ( Note that it's smooth)

Iron piston versions FP .20, .25, .35, and .40 all have this bump as I call it which is recognizable over the smoother rounded case above.

Ken Cook wrote:            Here are some pictures



        The FP.15 was only made available in the ABN version. Case also says FP on the exhaust side as pictured here.


           This is a iron piston FP .20  ( Note the way the casting letters are written on the case, all iron piston versions share this ).

          All ABN versions use this logo on the case

           FP ABN version on the exhaust side of the case ( Note that it's smooth)

           Iron piston versions FP .20, .25, .35, and .40 all have this bump as I call it which is recognizable over the smoother rounded case above.

Got it.