OS LA 25 Mount Bolt Pattern

[David Ruff]

What other engines will fit the LA 25 mounting bolt pattern exactly?

Thanks in advance.

[Brad LaPointe]

Brodak .25 , Thunder Tiger GP .25 , Magnum .25 plain bearing .

Brad

[Tim Wescott]

OS 20FP, I think the 25FP will, 25S but it has a shorter snout.

[Motorman]

Is you LA 25 worn out?


MM

[goozgog]

Funny how things happen.
I was asked that exact question
last week.

This drawing is reasonably accurate.

Cheers! - K.

[Geoff Goodworth]

For those who prefer to work with whole numbers, here is the page extracted from the LA Series manual.

[Steve Helmick]

For those who prefer to work with whole numbers, here is the page extracted from the LA Series manual.

Interesting that the factory .pdf says the fore/aft hole spacing is bigger (14.4mm) for the .15 than the 14mm shown for the .25. Based on that curiosity, I'd be reluctant to drill holes based on the factory data. The 14.4mm agrees better with Mr. Goozgog's data, FWIW. I learned a long time ago not to trust engineering drawings too much, especially in the CAD era. IMO, they don't look at the drawing long enough to spot their errors with CAD drawing. Steve 

[Tim Wescott]

Interesting that the factory .pdf says the fore/aft hole spacing is bigger (14.4mm) for the .15 than the 14mm shown for the .25. Based on that curiosity, I'd be reluctant to drill holes based on the factory data. The 14.4mm agrees better with Mr. Goozgog's data, FWIW. I learned a long time ago not to trust engineering drawings too much, especially in the CAD era. IMO, they don't look at the drawing long enough to spot their errors with CAD drawing. Steve 

I've taken to mounting my engines on aluminum rails with tapped holes, then mounting those rails onto the engine bearers with the usual T-nuts.  Within the accuracy of cheesy "milling machine" the holes have been spot on when I go from OS's drawings.

But then, I haven't mounted a 15LA.  You can always double-check with a good pair of calipers.

[Steve Helmick]

"You can always double-check with a good pair of calipers."

Good plan, Tim. Always double-check engineering drawings, 'cause they're too often wrong!  Steve   

[Tim Wescott]

Good plan, Tim. Always double-check engineering drawings, 'cause they're too often wrong!  Steve   

That's right.  Because the machinists always try to out-think the engineers and go off and do their own thing.

[Steve Helmick]

Good machinists always hope to make good parts, in spite of the engineers. Or maybe it's to spite the engineers?  Steve

[Geoff Goodworth]

I've measured the crankcase of an FP 25 and the hole spacing is 14mm.

Steve, in my extensive experience, it's the engineers and draftsmen who have never worked in tool rooms or on production machinery who make the most mistakes.

In my days as an engineer designing special purpose machinery, I often made mistakes but I usually found them. At one time I had to work with a particularly arrogant and pompous checker so to test him, when I found that I had made a particularly obscure mistake, I left it in but I kept a separate list so I could ensure that the drawings were correct when released for manufacture.

The existence of my lists became known when a drawing came back signed off with several mistakes undetected. I was 'sprung' correcting the drawing after sign-off and had to produce my list to prove what I was doing.

I was a checker for a time and the usual comment from some of the draftsmen—particularly contractors who were older and considered themselves better than me—would be something like 'see if you can find my deliberate error.'

I usually returned the drawings with a comment along the lines of 'Well I found your deliberate error, but what do you want to tell me about the other nine (or what ever the number) that I found?'  

As a complete aside, since I don't have access to a checker who can review my CAD model plane drawings, I always try to leave the drawings for at least a week without even looking at them after I think they are finished. If I have another design project happening, I will work on that.

After at least a week, I return to the previous project, and check everything again. Yes, I often find an error or two, but it's rare for a drawing to be issued for manufacture with errors except when I have to convert the CAD drawings to Corel files to drive laser cutters. The addage 'Use it or lose it' applies as I've forgotten more than I now know about CorelDraw because I have barely used it in 15 years.

[Tim Wescott]

On checking:

When I started at FLIR Systems in 1994, if a mechanical engineer wanted to get a drawing onto the floor he had to have a draftsman draw it up, then the draftsman had to submit it to not one, but two checkers before it could be signed off.  Thus, four sets of eyeballs had to look at the work before it was released.

If an electrical engineer wanted to get a schematic approved for production, he had to draw it up, then one checker would look at it before it could go to layout.  Then the layout guy would draw it up, the engineer would sign off, and it'd go into production -- so, three sets of eyeballs.

When a software engineer wanted to get some code into production, he would toss a floppy disk in the general direction of the ladies in Documentation, sign the line that said "responsible engineer", and off it'd go.  I always felt that if it were software, the line should read "irresponsible engineer".

I brought this up as a potential quality issue, as a software engineer, and was shot down.  I concluded that while mechanical and electrical engineering were, indeed, regarded as engineering disciplines, software was seen as magic.

(To their credit, FLIR did, eventually get their act into shape -- you didn't even get to send your code off to SQA until it had been reviewed by your peers, then SQA tested the snot out of it before it went into production.  The system still wasn't perfect when I left, but it was better and getting better yet.)

[Steve Helmick]

"Steve, in my extensive experience, it's the engineers and draftsmen who have never worked in tool rooms or on production machinery who make the most mistakes."

Yep, when I did layout checks during my 10 (miserable) years in QC, I had a few guys test me to see if I would catch their error. Apparently the guy before me didn't catch some errors. I didn't ask to see if they were testing him or not. Nobody in that shop could do Trig but me and the boss, and I wasn't sure about the boss. At another shop, I had to start doing 1st Article inspections across "the rock" from an older guy who was very good. I didn't like messing with compound angle plates and all the calculations, but showed him an easy way to get to the same place with a simple work-around. Blew his mind, it did. 

At one time, here in the USA, engineering students got some machine shop class time in their schedule, and spent some time making chips. From what I've heard, that requirement has generally been eliminated about 20 years back. High Schools no longer teach "Mechanical Drafting" and there are no more "Wood Shop" or "Metal Shop" classes or even sewing classes. Where we are now is that young folks graduate from HS with no work skills, no problem solving abilities, and no ability to do anything but flip burgers.    Steve

[Tim Wescott]

Steve, it's slowly getting better on the school front.  Folks realized that (A) not everyone is ready to get a degree in English Lit with a minor in public administration, and (B) that sooner or later all of the baby boomers in all of the machine shops were gonna DIE (or at least retire).  So there's a lot of noise about bringing back shop, and in at least a few places (like the Oregon City school district), some serious work being done.

[dave siegler]

"Steve, in my extensive experience, it's the engineers and draftsmen who have never worked in tool rooms or on production machinery who make the most mistakes."

Yep, when I did layout checks during my 10 (miserable) years in QC, I had a few guys test me to see if I would catch their error. Apparently the guy before me didn't catch some errors. I didn't ask to see if they were testing him or not. Nobody in that shop could do Trig but me and the boss, and I wasn't sure about the boss. At another shop, I had to start doing 1st Article inspections across "the rock" from an older guy who was very good. I didn't like messing with compound angle plates and all the calculations, but showed him an easy way to get to the same place with a simple work-around. Blew his mind, it did. 

At one time, here in the USA, engineering students got some machine shop class time in their schedule, and spent some time making chips. From what I've heard, that requirement has generally been eliminated about 20 years back. High Schools no longer teach "Mechanical Drafting" and there are no more "Wood Shop" or "Metal Shop" classes or even sewing classes. Where we are now is that young folks graduate from HS with no work skills, no problem solving abilities, and no ability to do anything but flip burgers.    Steve

IDK. 
No they don't get wood shop or auto shop ( s few here still do)

Now, many get 3d CAD classes, 3 d printing, advanced math, 2 or 3 programming classes and if they get involved in FIRST, they can do a lot of metal fabrication, software engineering, electronics. 
Not a lot of time in the schedule for the other stuff.
The ones who's parents are involved and push the kids a little are coming out of high school very very well prepared for an engineering program. 

[Steve Helmick]

I got "Mechanical Drafting" in Jr. High (Pullman, WA), and seem to recall it being required, along with Jr. High Wood Shop. I took Wood Shop as a HS Freshman, Metal Shop as a Sophomore at Desert HS, Edwards AFB, and Wood Shop and/or Drafting for Junior and Senior years at Sammamish HS. I thought I'd do fine in Freshman Engineering Drawing at Wazzu, but it was not easy. I can read a drawing, but I'm not ashamed to say that making a good one isn't easy. But then, nothing worth doing is easy, nor should it be.  Steve

PS: I'm still not sure what the bolt pattern is for an OS .25, but do I know the .21FP, .25FP, and .25LA are the same!   

[dave siegler]

screen shot from the pat johnson cad file of engines.   

[Tim Wescott]

I took drafting in high school, and all it got me was a comment, the first time I took a drawing to the model shop "you're not a mechanical engineer, are you?"  (Cuz the drawing was too nice.  It turned out the guys preferred sketches, because without multiple passes you'd always get something wrong anyway, so it was better to just tell 'em what your goal was, and turn them loose.  Then, if you asked nice, you'd get a nice drawing back.)

[David Ruff]

back to my issue; i am just looking for more power without messing with current mounting holes in my Oriental.  Maybe if I run pressure?   

[Brad LaPointe]

While not a perfect fit an Enys SS .30 is a definite power up grade . I have a porky Sig Skyray that isn't very happy with the LA .25 . A bit of relief work on the mounts to bolt it in and instant power upgrade .

It went from a dodgy sliding down the lines trainer to a almost combat plane . Allows me to do vertical eights at will .I used a 3 oz. Hayes tank and muffler pressure . Stole a tongue muffler off an Evo .36 and it works very well.

Brad

[Geoff Goodworth]

David, have you tried an FP 25?

My only experience of the LA 25 is an LA piston and liner in a Thunder Tiger GP 25 crankcase and I don't think the engine produces as much power as an FP 25. The FP drops straight in so maybe, if needs be, you could borrow one to try it out.

I started with a Fox 35 in my ARF Oriental but replaced it with a Brodak 40 so I can't help any further.

[Tim Wescott]

back to my issue; i am just looking for more power without messing with current mounting holes in my Oriental.  Maybe if I run pressure?   

Pressure affects the quality of the engine run, but not the amount of power delivered.

There are, apparently, at least two versions of the 25LA.  The original one was gutless compared to the later one.  I don't have personal experience, but Brett Buck has written about this a few times.  As far as I know (and this is all based on hearsay) the 25FP has the power of a "new" 25LA.  So changing to an FP, or trying out some different 25LA's, may help.  (I seem to have lucked out and only ended up with the "new" ones -- and no, alas, I have no idea how to tell the difference).

Experiment with props and nitro content.  Russel Shaeffer runs a 25LA on a Fancher "Medic" with a 9-4 APC.  The 9-4 definitely puts out more power than a 10-4.  An 8-4, or a trimmed 9-4, may put out more power yet (at a higher RPM, of course), but I suspect you'd lose the nice "stunt run".

[Air Ministry .]

Asa they say , the 21 & 28 & 25 FSR & clones , manum royal and chunder tiger . The Olde OS max 20 & 25 from the 70s I think may have the same nose length ( to prop driver )

The ETA 15 & commie ' Falcon tbr diesels are   within half a bolt space , as is a 21 series supertigre , if you want to strech a point , and open the bearer at the crankcase .

[Steve Helmick]

back to my issue; i am just looking for more power without messing with current mounting holes in my Oriental.  Maybe if I run pressure?   

Ah...now we find out it's all about an under-powered Oriental!

Are we to assume that you've already tried an APC 9-4, 9.5 x 4.5 and 10-4? If you're using a Zinger or Master Airscrew, that's likely your problem. Have you tried 15% or even 20% nitro? Pressure only helps if you open up the venturi bore. That's easy enough to try...the .35/.40FP and .40/.46 venturi will bolt in. If you are using the rear NV assy., then you might want to change to a .156" (K&B, Veco, ST, ST Clone, Randy Smith, Double Star) NV Assy, and still might want to put some pantyhose mesh over the venturi to adjust the effective bore downward. I ran a .272" bore venturi on my early .25LA with a .156" spraybar. I wouldn't want it in an Oriental, however. 

From what we've been able to uncover, the early .25LA's (if I remember correctly) had no boost port, so were not as sporty as the .25FP. So, I'd suggest looking at your .25LA and seeing if it has 3 ports in addition to the exhaust or only two (bypasses). If only two, then maybe you could look for a .25FP or newer .25LA (look in the exhaust stack or remove the head if you must). Personally, I'd plug a Magnum XLS .36 into it, but then I've got some. I'd shove in a Brodak .40 if I had one, but I don't. The Enya .30SS that Brad suggested sounds good.  Steve

[David Ruff]

Well I have not flown it yet.  I do have two Brodak 40s I could use.  It is very light, however.  I run the front NVA setup.  The engine is strong.  I will try it before making any mods.

[Tim Wescott]

Well I have not flown it yet.  I do have two Brodak 40s I could use.  It is very light, however.  I run the front NVA setup.  The engine is strong.  I will try it before making any mods.

Post a weight when you get it put together.  Or better, pile up the airframe, tank, engine, etc., onto a scale and get a weight before you go to the trouble.  I wish I knew just how heavy a plane the 25 could handle; I'm sure you'll be fine with up to 40 ounces if you've got a strong engine, maybe quite a bit more.  Someone should know -- you'll get all sorts of "I've flown that on a 25LA and the results were..."

Don't give up on it until you've experimented with props.

And -- keep us posted.

[Steve Helmick]

A few problems with Tim's suggestion. 1) Novice fliers really need more umph up front than a really good experienced flier, who can back off the corners, place the maneuvers better to require less thrust, etc. B) Folks tend to forget to mention what altitude they fly at, how long the lines are, how hot it is where they live (another good reason to include your city & state in your profile),  how windy it typically is in your area, what propeller (MA, Zinger, APS, CF), etc. III) Tim    Steve

[Tim Wescott]

III) Tim    Steve

Hey!

[Mark Scarborough]

NEVER underestimate the power of a GOOD prop (pun intended) or the absolute disaster a bad prop makes...

especially on an LA or FP 25....

us an APC,, NOT a master airscrew, NOT a Zinger, NOT a * ibnsert other brand here*
either an APC 9x4 or 10x4,, although ( I dont recomend this) Pat Johnston has flown very effectivly with an 11x4 on the FP 25 as I recall,,

[David Ruff]

The Oriental comes in at 32 oz.

[John Park]

The Oriental comes in at 32 oz.

Definitely try a 25FP, then.  Mine (an early steel 25FP-S, on 5% nitro with a 9x5 Graupner prop.) flies a 500 sq. in. flapped profile very well at 36 oz.