Author Topic: FP 40 gone wild (Read 13537 times)

Chris Fretz · « **on:** July 08, 2017, 05:27:47 PM »

So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should. Flew it and it just ran away wild. I've seen on here about adding a head gasket. So I pull the head gasket of the motor and put on a different FP 40 that was R/C. Took the needle and venturi off, the venturi was .290. I've read to use a FP 20-25 venturi. I've got a new one laying around, it measures .260. So I put that on. It has a 843 muffler, maybe I should of used a 892. I have no idea what the right muffler is. Both FP 40s are the steel ones. Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean. Basically the head shim and smaller venturi didn't do anything different. What can I do now to tame it?

I've got 2 FP 40 abn engines as well, I assume they run wild as well?

I could chuck up the head and remove materal but I have no idea how much...

Chris

Tim Wescott · « **Reply #1 on:** July 08, 2017, 05:37:13 PM »

DO NOT cut up your engines.

What prop (brand, model, diameter, and pitch)? What fuel? What launch RPM?

I was just flying with a Tower 40 today, which as far as I know is an FP clone. It flew great on an APC 11-4 and some Omega 10% Nitro that's been doctored up with some extra castor oil to bring the oil content up to 22%.

If you try to run an un-modified FP like a Fox 35, with a 6-pitch prop and a 2-4-2 break, then it'll run away every time.

Chris Fretz · « **Reply #2 on:** July 08, 2017, 05:47:21 PM »

Quote from: Tim Wescott on July 08, 2017, 05:37:13 PM

DO NOT cut up your engines.

What prop (brand, model, diameter, and pitch)? What fuel? What launch RPM?

I was just flying with a Tower 40 today, which as far as I know is an FP clone. It flew great on an APC 11-4 and some Omega 10% Nitro that's been doctored up with some extra castor oil to bring the oil content up to 22%.

If you try to run an un-modified FP like a Fox 35, with a 6-pitch prop and a 2-4-2 break, then it'll run away every time.

APC 11-4, 10% 11.5 11.5 Brodak fuel. I didn't tach it, I just cranked it up till I heard it break.

Chris Fretz · « **Reply #3 on:** July 08, 2017, 06:03:46 PM »

Quote from: Tim Wescott on July 08, 2017, 05:37:13 PM

DO NOT cut up your engines.

What prop (brand, model, diameter, and pitch)? What fuel? What launch RPM?

I was just flying with a Tower 40 today, which as far as I know is an FP clone. It flew great on an APC 11-4 and some Omega 10% Nitro that's been doctored up with some extra castor oil to bring the oil content up to 22%.

If you try to run an un-modified FP like a Fox 35, with a 6-pitch prop and a 2-4-2 break, then it'll run away every time.

I just fired it up and it was sitting around 9800-9900. What are you launching yours at? I'm running muffler pressure as well.

Brett Buck · « **Reply #4 on:** July 08, 2017, 06:11:51 PM »

Quote from: #Liner on July 08, 2017, 05:27:47 PM

So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should. Flew it and it just ran away wild. ....

<snip>

Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean.

<snip>

That's just what they do, time after time. I despise 40FPs for many reasons, but mostly because the "engine rework industry" was kept alive by people trying to get 40FPs to run properly (and usually failing in one way or the other).

My advice - sell them to an RC guy and use the money to buy an Aero-Tiger.

Brett

Chris Fretz · « **Reply #5 on:** July 08, 2017, 06:54:12 PM »

Quote from: Brett Buck on July 08, 2017, 06:11:51 PM

That's just what they do, time after time. I despise 40FPs for many reasons, but mostly because the "engine rework industry" was kept alive by people trying to get 40FPs to run properly (and usually failing in one way or the other).

My advice - sell them to an RC guy and use the money to buy an Aero-Tiger.

Brett

Well that's no help, I wanna tear up the skies tomorrow with the old girl. Maybe I can put a pair of pantyhose or two on and not run for 20 minutes on 4.5oz's. Someday I'm gonna bring back the LA 25 post too cause I can't get a stock one to not be a disappointing dog either.

RandySmith · « **Reply #6 on:** July 08, 2017, 08:03:11 PM »

Quote from: #Liner on July 08, 2017, 05:27:47 PM

So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should. Flew it and it just ran away wild. I've seen on here about adding a head gasket. So I pull the head gasket of the motor and put on a different FP 40 that was R/C. Took the needle and venturi off, the venturi was .290. I've read to use a FP 20-25 venturi. I've got a new one laying around, it measures .260. So I put that on. It has a 843 muffler, maybe I should of used a 892. I have no idea what the right muffler is. Both FP 40s are the steel ones. Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean. Basically the head shim and smaller venturi didn't do anything different. What can I do now to tame it?

I've got 2 FP 40 abn engines as well, I assume they run wild as well?

I could chuck up the head and remove materal but I have no idea how much...

Chris

What needle are you using? Do you have a tongue muffler that will fit it? Fuel ? are you sure the crankshaft is straight?

Randy

Tim Wescott · « **Reply #7 on:** July 08, 2017, 08:13:45 PM »

Quote from: Brett Buck on July 08, 2017, 06:11:51 PM

That's just what they do, time after time. I despise 40FPs for many reasons, but mostly because the "engine rework industry" was kept alive by people trying to get 40FPs to run properly (and usually failing in one way or the other).

My advice - sell them to an RC guy and use the money to buy an Aero-Tiger.

Brett

So I am wrong in thinking that they're similar to the Tower 40?

Maybe the answer is to sell 'em on eBay and get one or two 46LA's -- which are known-good.

Tim Wescott · « **Reply #8 on:** July 08, 2017, 08:17:08 PM »

Quote from: #Liner on July 08, 2017, 06:54:12 PM

Well that's no help, I wanna tear up the skies tomorrow with the old girl. Maybe I can put a pair of pantyhose or two on and not run for 20 minutes on 4.5oz's. Someday I'm gonna bring back the LA 25 post too cause I can't get a stock one to not be a disappointing dog either.

On my Tower 40, and my 46LAs, I launch at somewhere between 9600 and 9800 depending on the plane. If they run away, I put on pantyhose and launch at a speed that'll get them through the pattern. If they thin out at 45 degrees and in the overheads, I remove pantyhose and try again. Eventually this stopped working on the Tower 40, but a night in the crock pot with some antifreeze cured that very nicely.

If Brett's right, though, you're out of luck -- I can't say, because the only 40FP I have is on a carrier plane.

Tim Wescott · « **Reply #9 on:** July 08, 2017, 08:18:51 PM »

Quote from: #Liner on July 08, 2017, 05:47:21 PM

APC 11-4, 10% 11.5 11.5 Brodak fuel. I didn't tach it, I just cranked it up till I heard it break.

You didn't say what plane. I'm using an APC 11.5-4 on my Tower 40, and a ThunderTiger 11x4.5 (which is more like 11x4) on one of my 46LAs, and an APC 11.5x4 cut down to 11.25x4 on the other.

Chris Fretz · « **Reply #10 on:** July 08, 2017, 08:49:17 PM »

Quote from: RandySmith on July 08, 2017, 08:03:11 PM

What needle are you using? Do you have a tongue muffler that will fit it? Fuel ? are you sure the crankshaft is straight?

Randy

A stock OS needle, 20-40 FP .135 thick spray bar. I do have a couple tongue mufflers around. Brodak 10% 11.5 castor 11.5 synthetic. Both used 40FP I have tried vibrate a bit. Cranks appear to be straight.

Chris

Chris Fretz · « **Reply #11 on:** July 08, 2017, 08:51:15 PM »

Quote from: Tim Wescott on July 08, 2017, 08:18:51 PM

You didn't say what plane. I'm using an APC 11.5-4 on my Tower 40, and a ThunderTiger 11x4.5 (which is more like 11x4) on one of my 46LAs, and an APC 11.5x4 cut down to 11.25x4 on the other.

ARF Primary Force, where do you get thunder tiger props? I can't find them anywhere.

Air Ministry . · « **Reply #12 on:** July 08, 2017, 09:37:02 PM »

If This Dosnt Cure My FSR , I'll tear its head off . $:-\$

Said to MAINTAIN SQUISH BAND CLEARANCE Whilst Lowering C.R.

the clearance is required for the shock wave for the turbulance for the mixing / C R ' Shock ' , at t d c .

-------------------------------------------------------------------------------------------------------------------

Tho OS FP injun tests on sceptre flight , the Combustion Chamber Volumes are differant , C/L to R.C.
So Presumeably the R C head & the C L head are NOT the same ?? on the FP 40 .

any comparisons there ?

RknRusty · « **Reply #13 on:** July 08, 2017, 10:31:12 PM »

Chris,
Bob Z also posted a similar picture of his mods to the FP.40 head, so you can compare the two if you can find it. He posted it within the past year either in the open, or more likely the engine forum. It changed mine in my full fuse Oriental from running away after the first few stunts, and it ran a nice dependable 4-2 after that. You don't have to run it with a 4-2 break, I don't believe it was intended to anyway. FPs are notorious for running great on every flight except officials.

Mine had a stock FP.25 venturi and NVA. I ran an APC 10-1/2 x 4-1/2 prop with 10/22 Powermaster fuel. Tongue muffler an extra row of holes and pressure to the uni vent. Adding head gaskets did nothing to improve mine before I gave up and turned it over to Bob.
Rusty

EDIT: I found the picture he gave me, and that is it above in Matt's post.

Target · « **Reply #14 on:** July 08, 2017, 10:51:12 PM »

My buddy reworked my fp40, and it starts on the first flip, never runs away, and 4-2-4's perfectly.
I believe he changed the timing a little, added a shim, and puts on a (I think) .240 venturi. It's got an ST nva. Edit- this engine has a .256" venturi.
Whatever he's done, it works. Launch is in a mode between 2 cycle and 4 cycle, and we are running a uni-flow tank.
Hope you get yours sorted.
R,
Chris

Chris Fretz · « **Reply #15 on:** July 09, 2017, 12:48:36 PM »

Quote from: Matt Spencer on July 08, 2017, 09:37:02 PM

If This Dosnt Cure My FSR , I'll tear its head off . $:-\$

Said to MAINTAIN SQUISH BAND CLEARANCE Whilst Lowering C.R.

the clearance is required for the shock wave for the turbulance for the mixing / C R ' Shock ' , at t d c .

-------------------------------------------------------------------------------------------------------------------

Tho OS FP injun tests on sceptre flight , the Combustion Chamber Volumes are differant , C/L to R.C.
So Presumeably the R C head & the C L head are NOT the same ?? on the FP 40 .

any comparisons there ?

Perfect just what I needed thanks!

Chris Fretz · « **Reply #16 on:** July 09, 2017, 12:50:11 PM »

Quote from: RknRusty on July 08, 2017, 10:31:12 PM

Chris,
Bob Z also posted a similar picture of his mods to the FP.40 head, so you can compare the two if you can find it. He posted it within the past year either in the open, or more likely the engine forum. It changed mine in my full fuse Oriental from running away after the first few stunts, and it ran a nice dependable 4-2 after that. You don't have to run it with a 4-2 break, I don't believe it was intended to anyway. FPs are notorious for running great on every flight except officials.

Mine had a stock FP.25 venturi and NVA. I ran an APC 10-1/2 x 4-1/2 prop with 10/22 Powermaster fuel. Tongue muffler an extra row of holes and pressure to the uni vent. Adding head gaskets did nothing to improve mine before I gave up and turned it over to Bob.
Rusty

EDIT: I found the picture he gave me, and that is it above in Matt's post.

Good to know Rusty thanks! Do you know with your head mod still has the extra head gasket or just one now?

Chris

Chris Fretz · « **Reply #17 on:** July 09, 2017, 12:53:07 PM »

Some R/C guy is gong to be sad to know there is one less stock 40FP head left in the world. Pantyhose didn't help so screw it, in the lathe she went.

Sent from my SM-G920V using Tapatalk

RandySmith · « **Reply #18 on:** July 09, 2017, 02:23:12 PM »

Quote from: #Liner on July 08, 2017, 08:49:17 PM

A stock OS needle, 20-40 FP .135 thick spray bar. I do have a couple tongue mufflers around. Brodak 10% 11.5 castor 11.5 synthetic. Both used 40FP I have tried vibrate a bit. Cranks appear to be straight.

Chris

The 290 venturi with a FP 20 needle is WHOPPING TOO big.. This is the equivalent of about a 325 Venturi . The normal OS NVA diameter was .157 before they started to use the FO 20 Needle, you should try a 255 to 260 venturi maximum .
The ones I set up, and I have setup over 300 of them use that size, if you use a PA, ST , Enya, OLD OS Needle assembly use a 280 venturi .
The STOCK head does NOT need to be cut, This is normally just a way to reduce power by cutting the compression out of it , it works very well as is with 1 or 2 head shims, it needs no more.
I use a 11x4.5 , 11x4, 12 x 4 11.5 x 4.5 prop, 5 or 10 % nitro and 20% oil fuel with at least 1/2 synthetic oil.
In many ships this setup will launch about 10,7 to 11,100 RPMs, launch in just barely a 2 stroke or cackling back in forth in 4-2
The engine will unload and richen as the first lap goes... if it does not check your tank, Do NOT run pressure, or the 742 muffler, Use a tongue or open tube type that has an exhaust of at least 310 ID
Also it is not normal to have that much vibration, the most common cause of this is a slightly bent crank, and no you cannot see it with your eye. You need to check the run out with a dial indicator

Randy

Chris Fretz · « **Reply #19 on:** July 09, 2017, 03:08:23 PM »

Quote from: RandySmith on July 09, 2017, 02:23:12 PM

Also it is not normal to have that much vibration, the most common cause of this is a slightly bent crank, and no you cannot see it with your eye. You need to check the run out with a dial indicator

Randy

Do you have a picture of the set up to check it with a dial indicator?

Chris

RknRusty · « **Reply #20 on:** July 09, 2017, 04:25:40 PM »

Quote from: #Liner on July 09, 2017, 12:50:11 PM

Good to know Rusty thanks! Do you know with your head mod still has the extra head gasket or just one now?

Chris

Just one.

Brett Buck · « **Reply #21 on:** July 09, 2017, 11:21:52 PM »

Quote from: Matt Spencer on July 08, 2017, 09:37:02 PM

Tho OS FP injun tests on sceptre flight , the Combustion Chamber Volumes are differant , C/L to R.C.
So Presumeably the R C head & the C L head are NOT the same ?? on the FP 40 .

RC and CL are the same part, including part number, as is the case with almost all of these engines. Virtually all of these engines are exactly the same as the RC version, with the carb removed and venturi put in.

Excess compression can cause many problems, but "running away" is not one of them.

By the way, "running away" is a misnomer. The engine is running *exactly as designed*, and if you try it on an RC carb, you can easily see it has absolutely no problem running at even 2000 RPM with stock compression.

The solution to excess speed is clear- run it at reduced throttle (i.e. a much smaller venturi). Then, you will see if there is any secondary problem with maneuvering. Of course, there is a still easier solution - since you only need about half the power of a 40, maybe you need a 20. And a 40FP will require a *much smaller* venturi for the same amount of power than a 20FP.

The suggestion of a .240 sounds like it could be about right, and I recall people using as little as .225.

Brett

Target · « **Reply #22 on:** July 09, 2017, 11:28:55 PM »

Brett- just for the sake of accuracy, my buddy that set up the FP .40 says my engine has a .256 venturi (with the .156" ST needle valve running through it.
Boost port not blocked.

R,
Chris

Brett Buck · « **Reply #23 on:** July 09, 2017, 11:47:37 PM »

Quote from: Chris Behm on July 09, 2017, 11:28:55 PM

Brett- just for the sake of accuracy, my buddy that set up the FP .40 says my engine has a .256 venturi (with the .156" ST needle valve running through it.
Boost port not blocked.

That's about the same as a .240 with a 3.5mm/.138 spraybar, which sounds like it is about right.

Brett

Chris Fretz · « **Reply #24 on:** July 10, 2017, 12:55:08 PM »

Anybody know how you check for a bent shaft? I could put a dial indicator on the end of the prop shaft and turn the motor through but it's not going to be much of a reading bouncing up and down on the threads.

RknRusty · « **Reply #25 on:** July 10, 2017, 02:00:07 PM »

I'd like to know too. we have a professional machinist amongst our regular video hangout members, so I'll bring it up in tonight's session. I would guess it'll amount to something like chucking it in a precision milling machine and using a sensitive gauge to feel and measure it as it's hand turned through a revolution.

RandySmith · « **Reply #26 on:** July 10, 2017, 04:53:03 PM »

Quote from: #Liner on July 10, 2017, 12:55:08 PM

Anybody know how you check for a bent shaft? I could put a dial indicator on the end of the prop shaft and turn the motor through but it's not going to be much of a reading bouncing up and down on the threads.

Yes I spin mine, by hand on the lathe, or setup in bearings, and then use the 1/4 x 28 sleeve I turned over the threads , or I use one of my Spinner couplers (that are cnc and true) over the threads, then just slowly turn it with the dial indicator on it.
Other way is to chuck up the entire front threaded part and indicate off the of the main journal
If I get time I will try to take a photo

Randy

Chris Fretz · « **Reply #27 on:** July 10, 2017, 06:37:50 PM »

Quote from: RandySmith on July 10, 2017, 04:53:03 PM

Yes I spin mine, by hand on the lathe, or setup in bearings, and then use the 1/4 x 28 sleeve I turned over the threads , or I use one of my Spinner couplers (that are cnc and true) over the threads, then just slowly turn it with the dial indicator on it.
Other way is to chuck up the entire front threaded part and indicate off the of the main journal
If I get time I will try to take a photo

Randy

So something like this with a snug fitting sleeve? I get about .001 spinning the engine through on both my 40FP.

Sent from my SM-G920V using Tapatalk

RknRusty · « **Reply #28 on:** July 10, 2017, 10:09:18 PM »

Maybe Randy can tell us what an acceptable tolerance is. Do you get any change when you apply side pressure back and forth?

Chris Fretz · « **Reply #29 on:** July 11, 2017, 02:50:58 AM »

Quote from: RknRusty on July 10, 2017, 10:09:18 PM

Maybe Randy can tell us what an acceptable tolerance is. Do you get any change when you apply side pressure back and forth?

One of the 2 has a bit of a sloppy shaft bushing, I think it was about .010-.015, probably some jerk that didn't balance his props.

RandySmith · « **Reply #30 on:** July 11, 2017, 09:44:12 AM »

Quote from: #Liner on July 11, 2017, 02:50:58 AM

One of the 2 has a bit of a sloppy shaft bushing, I think it was about .010-.015, probably some jerk that didn't balance his props.

Hi
001 run out will not make it vibrate and is OK, that said , with that much bushing slop you cannot test it that way, you would need it out of the case. I assume you are keeping the motor still and turning the crankshaft?
If you test that way you would need to remove the head, and try to spin the crank consistently without moving it up down or side ways in the bore, also if you have any drag in the piston sleeve then remove it too before testing

Randy

Chris Fretz · « **Reply #31 on:** July 11, 2017, 10:08:11 AM »

Quote from: RandySmith on July 11, 2017, 09:44:12 AM

Hi
001 run out will not make it vibrate and is OK, that said , with that much bushing slop you cannot test it that way, you would need it out of the case. I assume you are keeping the motor still and turning the crankshaft?
If you test that way you would need to remove the head, and try to spin the crank consistently without moving it up down or side ways in the bore, also if you have any drag in the piston sleeve then remove it too before testing

Randy

Yes keeping the motor still and turning the crankshaft. I had noticed the crank pressure caused the rod to push on the crank giving an inaccurate reading, I just turned it slow to keep it from pushing the crank up and down.

What is an unacceptable amount of bushing slop? What is an unacceptable amount of run out?

Chris

Brett Buck · « **Reply #32 on:** July 11, 2017, 10:10:26 AM »

Quote from: RandySmith on July 11, 2017, 09:44:12 AM

Hi
001 run out will not make it vibrate and is OK, that said , with that much bushing slop you cannot test it that way, you would need it out of the case.

I am far from an aerospace machinist but I would be tempted to remove the crank, put the thread in a 1/4" collet, then put the dial indicator on the smooth part of the shaft. That will tell you if the crank is bent WRT the threads.

What it won't tell you is if the plane of the drive washer it perpendicular to the crank, which might be just as important.

Brett

Brett Buck · « **Reply #33 on:** July 11, 2017, 10:18:25 AM »

Quote from: #Liner on July 11, 2017, 10:08:11 AM

What is an unacceptable amount of bushing slop?

You will get plenty of arguments about that. My observation, for what it is worth, is that at least some aspects of the 4-2 brake are greatly improved as the bushing loosens up, and the best seem to be with alarming amounts of slop (like 1/8" or more of slop at the prop tips). With very tight bushings, they tend to "smear" back and forth from 4-2 and even more so, from 2 to 4, where when they are very free, it's like flipping a switch. The Discovery-Retro, while ball-bearing with no detectable slop, it also astonishingly free through the slack portion of the rotation. The only way you get that with a bushing is with a lot of slop, because tight fits = lots of oil drag.

It was almost an article of faith that the Fox 35 was best after you were on your 3rd piston/liner, because by then, you had enough run time on it to get the bushing sufficiently worn.

Brett

Chris Fretz · « **Reply #34 on:** July 11, 2017, 10:22:14 AM »

Quote from: Brett Buck on July 11, 2017, 10:10:26 AM

I am far from an aerospace machinist but I would be tempted to remove the crank, put the thread in a 1/4" collet, then put the dial indicator on the smooth part of the shaft. That will tell you if the crank is bent WRT the threads.

What it won't tell you is if the plane of the drive washer it perpendicular to the crank, which might be just as important.

Brett

Why not indicate the front of the drive washer wile in the collet then? Good idea though, I always forget about collets.

Chris

Chris Fretz · « **Reply #35 on:** July 11, 2017, 10:26:55 AM »

Quote from: Brett Buck on July 11, 2017, 10:18:25 AM

It was almost an article of faith that the Fox 35 was best after you were on your 3rd piston/liner, because by then, you had enough run time on it to get the bushing sufficiently worn.

Brett

All 7 of my Fox 35's have a ton of bushing slop. I wouldn't be surprised if there wasn't a lot when brand new.

I use to just a engine at a swap meet by how much bushing slop it has, and still do. Maybe I shouldn't worry about that anymore.

Chris

Fredvon4 · « **Reply #36 on:** July 11, 2017, 10:54:37 AM »

Because I do have a good dial indicator but no good way to fixture these cranks to check run out.... I have never tried

BUT if I did, I would probably gut the engine down to only the crank and bearing(S) ...super clean and dry, then very slight coat or ARO and indicate off front drive washer that the OD should be concentric with a prop tightened down

last year, I had one engine that vibrated a lot more than I thought was right >>>compared to several other of same lineage

I set to get one good prop properly balanced and each tip in plane....convinced myself the hub was flat and square to the blades
This was on an Enya 5224 .35 with collet compression drive washer.... tried several different prop clocking and still vibrated
When I checked for the prop tips in plane, now on the engine, I discovered the drive washer was not perpendicular WRT the crank shaft...swapped drive washers and vibration went away.....

FWIIW I now have a robust collection of OS LA/FP/FX engines from .20 to .46 and so far all of them seem to run the smoothest of any of my other similarly sized engine brands

BUT a year ago I did a bench run with brand new APC prop one time with a NIB OS FP .25, and learned a lot about a badly out of balance prop.... OR was it that horribly off center placed drill hole....hummmm

Yes Virginia I did remove the sticker and glue

and yes, NOW I do check the balance and correct for all my to be in use props

Funny how for years I got away with never balancing a Top Flite/Torpedo/Grish 1/2a prop or any Rev Up .35 / .36 combat engine propellers

RandySmith · « **Reply #37 on:** July 11, 2017, 12:23:51 PM »

Quote from: #Liner on July 11, 2017, 10:08:11 AM

Yes keeping the motor still and turning the crankshaft. I had noticed the crank pressure caused the rod to push on the crank giving an inaccurate reading, I just turned it slow to keep it from pushing the crank up and down.

What is an unacceptable amount of bushing slop? What is an unacceptable amount of run out?

Chris

Hi Chris
The bushing should have no more than .005 thou slop on a OS FP, they have less when new and run very well, as far as how much runout, I would not use the crank if it has more than .003 to 4 thou

Still, as I said the best way to test is to remove the crank, and test it that way, you can also load the drive washer with spacer rop washer nut and test the runout on it too, I would put the spinner back plate on just to have another point to run the dial indicator on

Randy

Chris Fretz · « **Reply #38 on:** July 11, 2017, 04:25:56 PM »

Quote from: RandySmith on July 11, 2017, 12:23:51 PM

Hi Chris
The bushing should have no more than .005 thou slop on a OS FP, they have less when new and run very well, as far as how much runout, I would not use the crank if it has more than .003 to 4 thou

Still, as I said the best way to test is to remove the crank, and test it that way, you can also load the drive washer with spacer rop washer nut and test the runout on it too, I would put the spinner back plate on just to have another point to run the dial indicator on

Randy

Thank you for the information Randy!

I assume the same tolerances apply for the LA series engines?

Chris

Air Ministry . · « **Reply #39 on:** July 11, 2017, 08:05:22 PM »

Crank Out and between centers'd sound like the way .

Liner - one often sets the " Squish Band Clearance " or at least measures it . Just Depth to Piston at TDC , minus amount of head ' pluged in ; .

About 10 Thou, on a .40 .

-------------------------------------------------------------------------------------------

Just aword on the Venturie Dia Issue . Altitude & Temperature .

A Magnum 40 ( Identical bar spraybar Posn ) at 3.000 somethingas altitude and 30 + degrees , drilled the straight thru / pherical jet
factory thing out to 1/4 in , for adequate oomph .
Back in NZ at sea level Temp around 15 , About 80 mph was the result .

Somebody talks of ' Tuning ' to site ( Comps ) by changing Venturie so Needle Stays The Same Setting .

Anyway , Venturie Dia Equates to Atmosphereic Density . The Red Sea isnt going to be the same as pikes peak .

Air Ministry . · « **Reply #40 on:** July 11, 2017, 08:07:08 PM »

looks Marvelous . theres half a dozen heads in the mail on the way .

Brett Buck · « **Reply #41 on:** July 11, 2017, 09:04:37 PM »

I know I am going to regret this, but can anyone explain why you think lowering the compression will keep the engine from running away? Compression has pretty predictable effects:

more compression = more power, bigger difference between 4 stroke power and 2-stroke power (stronger break), faster transition from 4-2 and 2-4
less compression = less power, less difference between 4 stroke power and 2-stroke power (weaker break), slower transition from 4-2 or 2-4
too much = misfiring, random quitting

none of which seem to apply here. If you assume it's a compression problem, if anything, it doesn't have enough compression - it breaks to a 2 and *never* comes back.

It's also clear that the engine would run fine as slow as you wanted if you had a throttle on it, also suggesting that the compression is OK even at low revs. If not, it would be a fuel suction issue - again not the compression.

If the issue is too much power with a still-needleable system, you would want a smaller venturi, not less compression. If the system is *not* needleable, then you *still* need a smaller venturi (and possibly a change to the lateral tank position, i.e. you are trying to suck fuel too far uphill on a profile with a 2" wide tank, or it's too thick).

It's running too fast. The most direct solution is to reduce the power and increase the fuel suction. So no matter how you cut it, to first approximation you need a smaller venturi, not a lower compression head or 50 head gaskets, etc.

Brett

Chris Fretz · « **Reply #42 on:** July 12, 2017, 03:53:44 AM »

Quote from: Brett Buck on July 11, 2017, 09:04:37 PM

I know I am going to regret this, but can anyone explain why you think lowering the compression will keep the engine from running away?

Are you asking me? I just read a bunch of people had problems with the engine and everyone's cure was a extra head gasket or if that didn't work getting the head machined. I have 4 of them and I'm willing to give anything a try when I run out of ideas. I really have no idea what more or less compression does. I'm just trying what has worked for others, if it don't work for me I just waisted my time and move on to something else. I think most of my problem is a weak fuselage causing vibration.
After running the engine with a machined head it seemed to be breaking from 4-cycle to 2-cycle at 8300rpm so that seems to be following what your saying.

RandySmith · « **Reply #43 on:** July 12, 2017, 08:11:36 AM »

tHE vast MAJORITY of problems of OS 40 and 35 fps came from TOO large a venturi, OS swapping the .157 diameter Needle assembly out for a 20 size assembly at .135 or so, and then putting out a muffler (742) that was extremely restrictive . It had nothing to do with over compressed head.
The same problems plagued the LA series , I cannot tell you how many people I have seen trying to use the tiny OS FP Needle assembly with a 290 venturi,The problem with this is it is massive in size and equates more like a .325 venturi with the tiny needle assembly , all the above cause runaway and low fuel suction, and will almost never be stable.
If your going to use the tiny OS 20 NVA you need to use a 250 to 255 venturi max. or use a more standard size , Old OS , Enya, ST, PA etc that are all .157, with this size NVa you can use a .275-.285 , The tweek from there .
Other things that help are a solid motor mount, stiff frontend, well made tank mounted to help minimize vibration, keep the tank close to the engine, stay away from muffler pressure, use a good fresh fuel with mostly synthetic oil, or at least 1/2 synthetic oil, of at least 20% total (22 seems to be used by most) , use nitro that fits what the weather is..don;t under or over nitro your fuel , use what is needed... too much is not better...too little is not better try to alway use fuel filter on the feed line

Randy

Chris Fretz · « **Reply #44 on:** July 12, 2017, 08:31:18 AM »

Quote from: RandySmith on July 12, 2017, 08:11:36 AM

The tweek from there .
Other things that help are a solid motor mount, stiff frontend, well made tank mounted to help minimize vibration, keep the tank close to the engine,
Randy

Randy could you show me a good example of a padded tank mount that will minimize vibration for a profile?

Thanks
Chris

Tim Wescott · « **Reply #45 on:** July 12, 2017, 08:53:05 AM »

Quote from: RandySmith on July 12, 2017, 08:11:36 AM

... I cannot tell you how many people I have seen trying to use the tiny OS FP Needle assembly with a 290 venturi,The problem with this is it is massive in size and equates more like a .325 venturi with the tiny needle assembly , all the above cause runaway and low fuel suction, and will almost never be stable.
If your going to use the tiny OS 20 NVA you need to use a 250 to 255 venturi max. or use a more standard size , Old OS , Enya, ST, PA etc that are all .157, with this size NVa you can use a .275-.285 , The tweek from there ...

I'm no Randy Smith, but I can personally attest to the whole thing about a too-large venturi causing runaway on an OS (or Tower) motor. I've had it happen to me. You get it slowed down well past its natural speed on the ground by running it rich, you launch, and either in the first few laps, or after you've been at 45 degrees a few too many times, it "hits the step" and jumps from 5+ second laps to 4.5 second or less. It's the basis of the tuning procedure that I outlined close to the top of this thread, which is only different from what someone like Randy might advocate in that I prefer to use layers of nylon mesh instead of a handful of different venturis to arrive at the right venturi size.

I think the only place where I really differ from Randy is purely a matter of personal preference -- he likes to use a 0.157 needle; I just hate having a motor that's had holes drilled out, so my tendency is to make a venturi of a size that's proper for the OS needle assembly, and run with that.

But he's telling you pretty much the same thing I was.

Dang. Now I need to go get a 40FP and give it a whirl in a plane...

Chris Fretz · « **Reply #46 on:** July 12, 2017, 10:05:43 AM »

Quote from: Tim Wescott on July 12, 2017, 08:53:05 AM

I think the only place where I really differ from Randy is purely a matter of personal preference -- he likes to use a 0.157 needle; I just hate having a motor that's had holes drilled out, so my tendency is to make a venturi of a size that's proper for the OS needle assembly, and run with that.

But he's telling you pretty much the same thing I was.

Dang. Now I need to go get a 40FP and give it a whirl in a plane...

I'm reluctant to drill mine out as well. However lately when I see 1 click almost change 300rpm I think it might be nice to have a more fine adjustment. Looking on "list your LA46 setup" almost everyone is using a PA needle valve.

Target · « **Reply #47 on:** July 12, 2017, 04:14:33 PM »

It's only @ .010" off each side of the hole. Practically nothing. So much easier than what you did (a beautiful job of) putting the head on the lathe, for sure.
It's worth it alone for having a needle valve without "clicks" at all. We like the Brodak NVA's as well.
Any needle valve with an adjustable tension collet on a smooth needle is awesome, they seal wonderfully and have infinite adjustment. Just what you want in a needle valve.

DO IT! :-)

Hope you come back with a happy result!

Try my sized (.256") venturi and the .156" NVA, and see what happens. I believe we are running 8% nitro, and 11/11 oil, so aim for 5% or 10% nitro with that same venturi and needle and your results should be close.

Chris Fretz · « **Reply #48 on:** July 12, 2017, 08:14:39 PM »

Quote from: Chris Behm on July 12, 2017, 04:14:33 PM

It's only @ .010" off each side of the hole. Practically nothing. So much easier than what you did (a beautiful job of) putting the head on the lathe, for sure.
It's worth it alone for having a needle valve without "clicks" at all. We like the Brodak NVA's as well.
Any needle valve with an adjustable tension collet on a smooth needle is awesome, they seal wonderfully and have infinite adjustment. Just what you want in a needle valve.

DO IT! :-)

Hope you come back with a happy result!

Try my sized (.256") venturi and the .156" NVA, and see what happens. I believe we are running 8% nitro, and 11/11 oil, so aim for 5% or 10% nitro with that same venturi and needle and your results should be close.

Thank you! I'll hack up a 40FP without much heartache, buuuut I have a hard time cutting up my beloved LA46's. They seem to have increased in price a lot on eBay lately. Plus then I have to turn around and buy all new needle valve assemblys. This hobby will make you broke fast. Maybe just maybe I'll take the giant leap in the near future and try one but I may need someone to pull the trigger on the drill for me

Chris

Tim Wescott · « **Reply #49 on:** July 12, 2017, 09:53:33 PM »

Quote from: #Liner on July 12, 2017, 08:14:39 PM

Thank you! I'll hack up a 40FP without much heartache, buuuut I have a hard time cutting up my beloved LA46's. They seem to have increased in price a lot on eBay lately. Plus then I have to turn around and buy all new needle valve assemblys. This hobby will make you broke fast. Maybe just maybe I'll take the giant leap in the near future and try one but I may need someone to pull the trigger on the drill for me

Chris

If you're handy with that lathe you can make your own needle assemblies. Just sayin'...

Steve Helmick · « **Reply #50 on:** July 12, 2017, 11:27:09 PM »

Not long ago, I posted part of Leonard Neumann's (sp?) venturi chart in another thread. No, I don't recall what size engines the section of the chart was for. But in general, .272" bore with a .156" spraybar (AKA 4mm) is a good start, which can be easily toned down with a few layers of nylon mesh trimmed from 2nd hand pantyhose. Tim does this, himself.

The interesting thing is that a .272" bore with .156" spraybar through on center is a good start on .25 to .76 engines, because the bigger engines pump more air through the same throat area. Perfect, no. But it saves a lot of math. I've used .272"/.156" on .25LA, XLS .36, and .46LA engines. My PA .51...dunno. OS .46VF...dunno. PA has the offset spraybar like a lot of Super Tigres did, so the bore is much smaller, and I don't recall what it is, but I think the .46VF is .272", but it's a Randy Aero engine, and I haven't checked the venturi bore.

I'd kinda like to post the whole chart once and have it "pinned", but it's not up to me. I have the file, if anybody can pin it someplace. I've reworked it some to try and get the columns straight and the column headers lined up. Frustrating, the computer program used didn't like that, but it's better than it was. Numbers are the same, all I did was put a lot of time into fine-tuning the chart a little to make it easier to read...multiple pages of it. <sigh>

Frankly, I strongly dislike "clicker" type NV assemblies, most especially the OS ones. Yes, they work nice while they work nice. But they can be damaged, look ok, but don't work worth a spit. I'd rather have them look broken when they're broken! I'm hoping you'll play with the ones you have, if you like them. Randy's are the best!

Steve

Brett Buck · « **Reply #51 on:** July 13, 2017, 12:42:14 AM »

Quote from: Steve Helmick on July 12, 2017, 11:27:09 PM

I'd kinda like to post the whole chart once and have it "pinned", but it's not up to me. I have the file, if anybody can pin it someplace.

I really wish you wouldn't. It happens to be in the ballpark in this case (because its in the center of the range) but it is wildly wrong at the ends. The premise is faulty as well.

Brett

Tim Wescott · « **Reply #52 on:** July 13, 2017, 09:59:51 AM »

Quote from: Brett Buck on July 13, 2017, 12:42:14 AM

I really wish you wouldn't. It happens to be in the ballpark in this case (because its in the center of the range) but it is wildly wrong at the ends. The premise is faulty as well.

Brett

We need the Brett Buck chart. Or the Brett Buck/Randy Smith chart, if you two agree.

Chris Fretz · « **Reply #53 on:** July 13, 2017, 06:51:17 PM »

Ok we are looking at .008 up and down slop on the bushing. The crank is reading. 001-.002 runout.

Sent from my SM-G920V using Tapatalk

RandySmith · « **Reply #54 on:** July 13, 2017, 07:56:53 PM »

Crank is good , the bushing is worn, may work or maybe some of the vibration problem, I would be happier with .004 thou

Randy

Chris Fretz · « **Reply #55 on:** July 13, 2017, 07:59:58 PM »

Ok crank #2 was reading .003 runout. However my lathe and cheap China collet was giving me inconsistant readings I would get one time reading .006 runout and then another time I would get get .003. On the backplate I would get anywhere from .008 to .004 pretty much on both. So the inconsistent readings are rather disappointing. But it's an old lathe too.

Sent from my SM-G920V using Tapatalk

Chris Fretz · « **Reply #56 on:** July 13, 2017, 08:03:13 PM »

Randy I couldn't get the 1/4 in backplate adapter to fit any of my 1/4 28 shafts. Got a good fix for that?

Sent from my SM-G920V using Tapatalk

Dan McEntee · « **Reply #57 on:** July 13, 2017, 09:21:28 PM »

Way back when in the early 90's I think it was, there was a bit in Stunt News about the best set up for an OS FP.40. This was the era of the desk top published newsletter that Windy or Mike Keville or one of the other early editors put out. It consisted of the smaller of the two venturis that came with the control line version at that time, one head shim, and as little exhaust restriction as you could get and still use a muffler, and no more that 4" pitch or something like that. I pretty much followed that recipe and always had good luck, once I got the idea out of my head that I could make a Graupner 10-6 three blade prop work on it! I had a bone stock FP.40 in a SIG Mustang Stunter back then that I never had a bad run on. I found and used some Tornado 10-6 three blade props on that model and they worked well, mainly because they were actually a 4" pitch. I also remember reading then that others had good luck with them when mounted inverted in a stunt model. Some weird quirk of physics helps with things in that position. I have read where guys dislike the LA.40 for stunt and do all sorts of plugging a such to bypass ports and head shims and such. I used one of those on my Dusty profile model in bone stock configuration following the same recipe that was in Stunt News all those years ago and I think I have a .250" Russ Gifford venturi in it with a OS needle valve assembly when it is in stunt rim, and I was very impressed with the power it made when I have the stunt set up on it. Uses right at 4 ounces of fuel for the pattern and uses a MAster Airscrew 10-5 three blade for a prop.. For scale flying with throttle, that venturi comes off and a carburetor goes on with electronics pack with receiver, servo and battery. The prop is a very important part of the equation, and you may have to try several brands to find what works best on a particular airplane. It is just a matter of experimentation and test flying.
Type at you later,
Dan McEntee

Carl Cisneros · « **Reply #58 on:** July 13, 2017, 11:07:34 PM »

Chris
The tank set up on the PF is pretty much fool proof.
Solid run from start to tank finish.

Carl

RandySmith · « **Reply #59 on:** July 13, 2017, 11:08:28 PM »

Quote from: #Liner on July 13, 2017, 08:03:13 PM

Randy I couldn't get the 1/4 in backplate adapter to fit any of my 1/4 28 shafts. Got a good fix for that?

Sent from my SM-G920V using Tapatalk

yES TAKE some alum or brass tube and use it over the shaft to bush it to fit the backplate hole, or just turn a bushing on your lathe easy ..

Randy

RandySmith · « **Reply #60 on:** July 13, 2017, 11:09:27 PM »

Quote from: RandySmith on July 13, 2017, 11:08:28 PM

yES TAKE some alum or brass tube and use it over the shaft to bush it to fit the backplate hole, or just turn a bushing on your lathe easy ..

Randy

Or ream the adapter out till it fits

Chris Fretz · « **Reply #61 on:** July 14, 2017, 02:50:06 AM »

Quote from: RandySmith on July 13, 2017, 11:09:27 PM

Or ream the adapter out till it fits

Plenty of options, thanks Randy.

Chris Fretz · « **Reply #62 on:** July 14, 2017, 02:51:26 AM »

Quote from: Carl Cisneros on July 13, 2017, 11:07:34 PM

Chris
The tank set up on the PF is pretty much fool proof.
Solid run from start to tank finish.

Carl

Who makes that tank? I've never seen one like it.

Chris

Carl Cisneros · « **Reply #63 on:** July 14, 2017, 08:07:12 AM »

Chris
I can not remember who makes that tank.
Got it a long time back.

Carl

Chris Fretz · « **Reply #64 on:** July 14, 2017, 09:46:16 AM »

Quote from: Motorman on July 14, 2017, 09:14:51 AM

It's not as easy as you might think. I've made a good number of the SuperTiger style and I prefer to buy. It's a good pet to have if you need a custom length or diameter but allot of work.

MM

I was thinking the same thing. Some things just aren't worth making.

Dennis Moritz · « **Reply #65 on:** July 18, 2017, 07:30:36 PM »

We fly lots of FP40s and Tower40s in our club. We like them. Cheap power that can be made to work. Our formula differs some from Randy. In many ways we overlap. Runaway has many causes. Vibration, wrong fuel, bad choice of prop, restrictive muffler, attempting to run the engine in a bad rpm range, usually too slow. Which is why I cringe when this topic comes up. Hard to diagnose at a distance.

Here are a few starter points. Good running FP40s and Tower40s burn 4.5 to 5 ounces of fuel when running right. Sometimes even more. If you're not burning that much fuel, open up the muffler. Use a bigger venturi, if the plane you are flying is over 40 ounces. I also wonder why none of the folks who offer advice here, ask, what plane, what weight. Model weight, design drag, hugely effect these engines. I had a 27 ounce magician that flew very well with a stock Tower 40, two extra head gaskets, and a mid size .273 venturi. Broke in right places. That plane went in when the controls let go after a way over spec pull test. My immediate next model was a somewhat porky Prowler, 45 ounces. Engine set up greatly changed.

RknRusty · « **Reply #66 on:** July 18, 2017, 11:18:33 PM »

Don't you have a box of metal tubing bits?

Chris Fretz · « **Reply #67 on:** July 20, 2017, 08:39:40 PM »

Quote from: Dennis Moritz on July 18, 2017, 07:30:36 PM

We fly lots of FP40s and Tower40s in our club. We like them. Cheap power that can be made to work. Our formula differs some from Randy. In many ways we overlap. Runaway has many causes. Vibration, wrong fuel, bad choice of prop, restrictive muffler, attempting to run the engine in a bad rpm range, usually too slow. Which is why I cringe when this topic comes up. Hard to diagnose at a distance.

Here are a few starter points. Good running FP40s and Tower40s burn 4.5 to 5 ounces of fuel when running right. Sometimes even more. If you're not burning that much fuel, open up the muffler. Use a bigger venturi, if the plane you are flying is over 40 ounces. I also wonder why none of the folks who offer advice here, ask, what plane, what weight. Model weight, design drag, hugely effect these engines. I had a 27 ounce magician that flew very well with a stock Tower 40, two extra head gaskets, and a mid size .273 venturi. Broke in right places. That plane went in when the controls let go after a way over spec pull test. My immediate next model was a somewhat porky Prowler, 45 ounces. Engine set up greatly changed.

On 4.5oz I could definitely have gotten about 3-4 full patterns in. I'll get back to messing with the FP40 in a week or 2, too much going on right now.

Chris

Quote from: RknRusty on July 18, 2017, 11:18:33 PM

Don't you have a box of metal tubing bits?

You mean for the spinner backplate? I do have some laying around, I just haven't looked to see if I have all the right sizes.

Chris

Target · « **Reply #68 on:** July 20, 2017, 09:20:57 PM »

My fp40 flies plenty long on 4oz. But my plane is only 38oz.

Dennis Moritz · « **Reply #69 on:** July 21, 2017, 06:26:08 AM »

4.5 ounces plus of fuel running through an FP40 and clones helps cooling. This will assist stabilizing the run.

Sent from my iPhone using Tapatalk

Target · « **Reply #70 on:** July 21, 2017, 07:28:57 AM »

Dang, I'll have to put on a bigger tank now....

Matthew Brown · « **Reply #71 on:** November 13, 2017, 06:00:25 AM »

Sorry for bringing this back up, but I was planning on making some venturis for my FPs and LAs. I was wondering if there is any gain or negatives to mounting the NVA higher in the venturi. Mostly I just didn’t want to drill out the case to accept a PA NVA. I figured easiest way was to mount the venturi like the RC carb with screws and put the NVA higher up in the body of the venturi.

Thanks, Matt

Dennis Moritz · « **Reply #72 on:** November 13, 2017, 08:58:40 PM »

Arf Primary Force has a weak nose. Probably complicating your run. I put a 1/8" rectangular aluminum plate on the inside of fuse of the one I had. Engine mounting bolts used were long enough to bolt through to the plate, going through a hole drilled in each corner. Plate slightly larger than engine mount outline. Lock nuts were cinched tight every few flights. If they were not, bad vibes and run run runaway. Cinched very tight. Washers of course were used under the heads of the mounting screws. Not uncommon for me to break the black screws after a few flight sessions. That's how tight. With this particular bird, doing that, calmed it down. Free flowing tongue muffler always important. In Philly we often run larger than 260 venturis when plane weight is above 40 ounces. It's necessary to flow sufficient fuel through engine to keep it cool. Look to burn 4.5 plus ounces in a pattern. Some FPs tolerate less fuel flow, most don't. Tower 40 is an excellent copy of the FP40. Not exact. Improvement over the FP. True chrome liner instead of the softer nickel in the FP40. I've had Tower 40s retain stall a starter compression season after season. Cylinder head has deeper cooling fins. Looks as though the compression dish is shallower on the Tower. Head gaskets of the Tower are 10 thou, head gaskets of the FP are 15thou. You might try a .273 venturi with the stock needle valve. That, along with a free flowing muffler, will increase fuel flow through engine increasing the cooling.

Weight of plane, drag of plane, vibes of the construction. And so forth. All play a role in engine run. We even had an FP40 calm down when the old needle valve was replaced. Tolerances had apparently grown over the years, needle vibrating in screw seat.

In Philly we work with these engines season in and season out. Almost always we get them to run effectively enough in competition. They are not PAs, RoJett's or good running Super Tigres. But they can be had cheap and can be worked with. Way more powerful than the older baffle piston 35s.

Fuel suggestions are similar to what we use. Powermaster 22%, 50/50, 5 and 10%.

What tank. Don't run uniflo if you are having any runaway issues. Uniflo can aggravate any fuel foaming issues.

We almost always run 10.5x4.5 APC props.

My Galaxy is posted. Shows the aluminum plate. A Tower 40 has powered this plane for ten years. Chicken hopper tank. For 7 years I ran it on muffler pressure and uniflo. One day that stopped working, solid engine run started to be a wee erratic. Taking it off uniflo fixed that.

Chris Fretz · « **Reply #73 on:** November 15, 2017, 05:27:20 AM »

Quote from: MattBrown on November 13, 2017, 06:00:25 AM

Sorry for bringing this back up, but I was planning on making some venturis for my FPs and LAs. I was wondering if there is any gain or negatives to mounting the NVA higher in the venturi. Mostly I just didn’t want to drill out the case to accept a PA NVA. I figured easiest way was to mount the venturi like the RC carb with screws and put the NVA higher up in the body of the venturi.

Thanks, Matt

That is a interesting idea to avoid drilling. Depending on what you are putting it in, you may not have a problem on a profile set up but you may run into a tank height problem in a full body airplane with the needle valve being so much higher up. However I am no expert on set up's. If I was you I would start a new topic in engine set up and tips to get more experts to help you out.

Chris

Matt Brown · « **Reply #74 on:** August 31, 2018, 05:34:13 PM »

Popping this back to the top. I’ve read through every post.
I have an FP40 in a Nobler arf. It has a nylon venturi with a .256 bore. I have a PA NVA mounted in the original location. Using Sig Champion 10% fuel. It has an RSM tongue muffler. The plastic tank it came with plumbed for Uniflow. I have tried both Xoar 11-4 and TT 11-4.5.
It does exactly like someone described earlier in the thread, running away.
Timed a couple laps before I did any maneuvers it sounded great and was running a decent 5.25- 5.30 lap. After just a couple maneuvers it leaned out and stayed that way the rest of the flight, running steady but fast 4.40 laps.
I assume it has only the stock head shim as I’ve never added any. Per most of what I have read through this thread, I should be getting decent runs but definitely not so far. The only thing that occurs to me is maybe the RSM tongue muffler is too restrictive.

What do the FP40 fans say?
Worst case, I can do the head mod but I tend to agree with those that feel that isn’t the way to go.

Thanks, Matt

Dane Martin · « **Reply #75 on:** August 31, 2018, 06:06:46 PM »

Quote from: Matt Brown on August 31, 2018, 05:34:13 PM

Popping this back to the top. I’ve read through every post.
I have an FP40 in a Nobler arf. It has a nylon venturi with a .256 bore. I have a PA NVA mounted in the original location. Using Sig Champion 10% fuel. It has an RSM tongue muffler. The plastic tank it came with plumbed for Uniflow. I have tried both Xoar 11-4 and TT 11-4.5.
It does exactly like someone described earlier in the thread, running away.
Timed a couple laps before I did any maneuvers it sounded great and was running a decent 5.25- 5.30 lap. After just a couple maneuvers it leaned out and stayed that way the rest of the flight, running steady but fast 4.40 laps.
I assume it has only the stock head shim as I’ve never added any. Per most of what I have read through this thread, I should be getting decent runs but definitely not so far. The only thing that occurs to me is maybe the RSM tongue muffler is too restrictive.

What do the FP40 fans say?
Worst case, I can do the head mod but I tend to agree with those that feel that isn’t the way to go.

Thanks, Matt

My opinion....
If you're gonna leave the engine stock, but use a tongue muffler, you should start with a .200 venturi and a stock os nva. Now, if your nva is fatter, you'll just need to match a venturi to get the same choke area as that set up.
Set it screaming highest rpm you can get and back it off enough clicks to keep it from roasting in the air. Basically I ran mine like a 25 set up. High rpm low pitch. The setting remains the same from start to finish

Air Ministry . · « **Reply #76 on:** August 31, 2018, 08:27:36 PM »

Quote

Sorry for bringing this back up, but I was planning on making some venturis for my FPs and LAs. I was wondering if there is any gain or negatives to mounting the NVA higher in the venturi. Mostly I just didn’t want to drill out the case to accept a PA NVA. I figured easiest way was to mount the venturi like the RC carb with screws and put the NVA higher up in the body of the venturi.

Thanks, Matt

Like Wot Thisis Ere Eh .

Upright / Inverted , tankll need to be ' in line ' , so if close could hinder cooling airflow aft . Perhaps .

SIDEWINDER Fashion , . . .

This & a OS 40 Four Stoke I observed . . .

Both with TANK outer Edge / at / level / almost inside even , the Spray Bar Line . Longitudeinaly . Inside Laterally Rotationally

;

Good Rich ' Four Stoke ' ( What Else do you xpect of a four stroke OS 40 $:-\$ ) at ' level flight .

As the Full weight ? of fuels loading the feed , Higher you go the less ' head ' it has , so set for o.k. , not to lean , overhead ( 8's )
Lower you go the richer it gets . Which was basically a good set up for this ( 25 ) in a Nobler size sucker .

The Uniflow Vent was stright out the inboard side , whacked of at 45 degree or a bit flatter - into the airstream .

So it ' could ' be a Gun Set Up , for these nasty schneurle OS 40 things . of which I unfortunately have a few . Gotta New 44 GP Magnum now to , a clone .
NOW YOUVE DONE IT .
Might try this intake in that , as its ' cinch bar ' type & Im loath to cross drill the case .

RandySmith · « **Reply #77 on:** September 01, 2018, 05:16:03 PM »

Quote from: Matt Brown on August 31, 2018, 05:34:13 PM

Popping this back to the top. I’ve read through every post.
I have an FP40 in a Nobler arf. It has a nylon venturi with a .256 bore. I have a PA NVA mounted in the original location. Using Sig Champion 10% fuel. It has an RSM tongue muffler. The plastic tank it came with plumbed for Uniflow. I have tried both Xoar 11-4 and TT 11-4.5.
It does exactly like someone described earlier in the thread, running away.
Timed a couple laps before I did any maneuvers it sounded great and was running a decent 5.25- 5.30 lap. After just a couple maneuvers it leaned out and stayed that way the rest of the flight, running steady but fast 4.40 laps.
I assume it has only the stock head shim as I’ve never added any. Per most of what I have read through this thread, I should be getting decent runs but definitely not so far. The only thing that occurs to me is maybe the RSM tongue muffler is too restrictive.

What do the FP40 fans say?
Worst case, I can do the head mod but I tend to agree with those that feel that isn’t the way to go.

Thanks, Matt

Hi Matt

You should read my post about NOT using a .255 venturi for a ST or PA NVA, and NOT using a .281 for a OS 20 NVA, IF you use a PA assembly use the .281, a .255 is too small, and it is choking the motor down, cutting down the fuel/oil burn, and if using restrictive muffler, runaway.... if you use the STOCK OS 20 NVAs, then YES use the .255, it is about the same as a .281 with the St or PA OR the OLD OS 35 40 NVA

Randy

Dennis Toth · « **Reply #78 on:** September 03, 2018, 10:07:47 AM »

Chris,
The FP 40 likes to run pretty high rpm. I think you should try dropping the prop diameter first to 10 1/2"x4 maybe even go to 10" diameter. Most of the problem is heat. Use a good NVA that doesn't leak air (either an ST or one of Randy's PA NVA). Think low pitch/high rpm. Let it spin up to a rich 2 cycle and adjust your line length and pitch (could go to 3 3/4 or 3 1/2 pitch) to get the lap time you need. I like wood props (RMS or BY&O), they are light and can be heat pitch just like an APC prop does. Think about the way they run the FP 20, they launch at 11K. Stop trying to fight the engine and use the power to pull the ship.

Best, DennisT

rich gorrill · « **Reply #79 on:** September 04, 2018, 01:11:37 PM »

I realize this is an old thread, but just want to interject I have had the same problem with an FP20. I put it on a newly built ringmaster from Eric Rule this spring and the same thing happened as Chris describes with his LA 40. I had no vibration problem but it "ran away" as soon as the plane went airborne. My solution was to install an LA 25 and that solved the problem. My point is this problem also happens with the FP 20. I used a stock OS needle valve and the small OS venture and an 8-4 prop.

Brett Buck · « **Reply #80 on:** September 04, 2018, 01:19:55 PM »

Quote from: rich gorrill on September 04, 2018, 01:11:37 PM

I realize this is an old thread, but just want to interject I have had the same problem with an FP20. I put it on a newly built ringmaster from Eric Rule this spring and the same thing happened as Chris describes with his LA 40. I had no vibration problem but it "ran away" as soon as the plane went airborne. My solution was to install an LA 25 and that solved the problem. My point is this problem also happens with the FP 20. I used a stock OS needle valve and the small OS venture and an 8-4 prop.

Again, that is not an engine defect. The problem is that the engine is *way too much power* for a Ringmaster when running correctly, meaning, it goes way too fast in flight.

The needle is not a throttle and is only capable of tiny speed change range, if you want different overall power, use a smaller venturi or a smaller engine. Or use the stock RC carb and use that to control the speed.

Brett

phil c · « **Reply #81 on:** September 10, 2018, 06:09:42 AM »

Chris-
"This hobby will make you broke fast. "

You ain't seen nothing like going broke until you try quarter scale 3D RC flying, or getting a few of the Yatsenko PA models. Multiple thousands just to get in the air. And you lose it all in a bad crash.

Target · « **Reply #82 on:** September 10, 2018, 02:54:49 PM »

That's nothing.
How about 3K for a carbon fiber sailplane airframe, then 6x 80-100 bucks for digital servos? (X2 or 3 to compete)
1500 dollars for an f3b winch (x2), special 12v winch batteries, 400m spools of mono (25 bucks each, could last 1 flight or 5 flights).
All that and no fuel or motor.

Author Topic: FP 40 gone wild (Read 13537 times)

Matthew Brown