Lap times

[cory colquhoun]

Can anyone please tell me how much 63 feet lines would increase lap time as apposed to 60 feet.i have a scratch built cougar stunt plans by T . Stoker, which I crashed and rebuilt as a profile weighs 34oz fuelled . Running .35 Merco 10x5 prop and at the moment doing 3.8 sec laps way too fast for me,but my son loves it

[Perry Rose]

Less than a half second. It sounds like the engine is running way to fast. Try 8000 rpm at launch.

[Brett Buck]

Can anyone please tell me how much 63 feet lines would increase lap time as apposed to 60 feet.i have a scratch built cougar stunt plans by T . Stoker, which I crashed and rebuilt as a profile weighs 34oz fuelled . Running .35 Merco 10x5 prop and at the moment doing 3.8 sec laps way too fast for me,but my son loves it

    The difference, to first approximation, would be about 5% (63/60 of 3.8, or to about 4 seconds a lap). It will be a bit slower in practice (maybe 4.1-4.2), but not nearly enough.

       I am not familiar with the airplane (is this the familiar Kenhi design?) but a much more effective way to slow it down would be to switch to a 10-4 instead of a 10-5.

    Having said all that, something doesn't sound right about this - with any reasonable airplane, a Merco 35 is *not* going to pull anything at 3.8 seconds on a 10-5, or at least, it will burn itself to a crisp trying to do it. It is either running *much faster*/leaner than is wise, or there's something wrong with the lap timing.

        If anything, I would expect difficulty getting it fast enough to fly patterns with a 10-5, or at least, would have to run it nearly in a two-stroke all the time to get it fast enough. I think there is something else going on here that we are missing. 3.8 sounds like a meltdown.

    Brett

[Dallas Hanna]

Can anyone please tell me how much 63 feet lines would increase lap time as apposed to 60 feet.i have a scratch built cougar stunt plans by T . Stoker, which I crashed and rebuilt as a profile weighs 34oz fuelled . Running .35 Merco 10x5 prop and at the moment doing 3.8 sec laps way too fast for me,but my son loves it

It's only a small model of 45" span Brett.  This is it from UK Aeromodeller Plans, not the Kenhi design.

Where are you located Cory??

DH

[Dennis Toth]

Cory,
General rule of thumb is 0.1 sec change for every 1 foot of line length added or removed. I agree with Brett, for a 5 pitch, on 60 ft lines in order to do a 3.8 lap time (which is around 67 is mph) you would need around 12,600 rpm. That is a bit much for the Merco. One would expect around a 4.85 ish lap time (53 mph ish) and even that with a 5 pitch is going to need around 9900 rpm (in air) which is going to push the Merco into a flat out 2 cycle. Check the pitch it might be in the range of 6.5 - 6.7 (check it at the 70% blade length out from the hub as a quick check) or just change props and see what lap time you get.

Best,   DennisT

[Paul Smith]

63 / 60 = 105%.  So your times will theoretically be 5% more based on increased radius.

Perhaps a bit slower yet due to more line drag.  Maybe not as much slower due to more slack and not as close to true radius.

[Sean McEntee]

1' line length= .2 seconds lap time

[cory colquhoun]

Thanks guys appreciate all the input , I think fuel mix could have a bit to do with it,local HS once mixed fuel and I used an 80/20 castor methanol mix for that engine.now all I can get locally is premixed synthetic with 5% nitro.also when I checked line length and they're closer to 59' as l forgot about kink repair. It never seemed to run that fast before ,I remember when it was a built up fuse it did 4.9-5.0 sec laps and I think I was using 10x6 prop.no cl in this area all info is gathered off net and help from you guys on forum equipment is a little hard to source locally most is bought Via post,think I need to stop playing around with this old engine

    Corey

[Larry Fernandez]

[quote author=cory colquhoun link=topic=47062.msg488754#msg488754 also when I checked line length and they're closer to 59' as l forgot about kink repair.

    Corey
[/quote]

Kink repair???
Do tell

Larry, Buttafucco Stunt Team

[cory colquhoun]

[quote author=cory colquhoun link=topic=47062.msg488754#msg488754 also when I checked line length and they're closer to 59' as l forgot about kink repair.

    Corey


Kink repair???
Do tell

Larry, Buttafucco Stunt Team

WTF

[Brett Buck]

It's only a small model of 45" span Brett.  This is it from UK Aeromodeller Plans, not the Kenhi design.

   Nonetheless, I can't see a Merco 35 pulling even a Ringmaster at those kinds of speeds, not with a 10-5, at least, without operating in "meltdown mode". Particularly on FAI fuel. If it is, it won't be doing it for long, I am afraid.

     I think the engine is probably running away, or it is being peaked out. Either case will resolve itself pretty quickly when something in the engine fails.

      Brett

[Russell Bond]

Here you go........

[cory colquhoun]

   Nonetheless, I can't see a Merco 35 pulling even a Ringmaster at those kinds of speeds, not with a 10-5, at least, without operating in "meltdown mode". Particularly on FAI fuel. If it is, it won't be doing it for long, I am afraid.

     I think the engine is probably running away, or it is being peaked out. Either case will resolve itself pretty quickly when something in the engine fails.

      Brett

I could be running it too lean What would be the best setting as I'm still learning.also I have a fan twister I got off Walter,which will be powered by os.35 max what would be the best line length for this

Cory

   

[Tim Wescott]

I could be running it too lean What would be the best setting as I'm still learning.also I have a fan twister I got off Walter,which will be powered by os.35 max what would be the best line length for this

Someone correct me if I'm wrong, but I believe the Merco wants lots of oil, and lots of castor.  25% oil?

Run it richer.  I'm guessing that you want to stick with the 10-5, and either run a really wet 2 or a 2-4.  Ditto -- on everything -- for the OS 35.

[cory colquhoun]

Someone correct me if I'm wrong, but I believe the Merco wants lots of oil, and lots of castor.  25% oil?

Run it richer.  I'm guessing that you want to stick with the 10-5, and either run a really wet 2 or a 2-4.  Ditto -- on everything -- for the OS 35.

          Thanks Tim will rich it out a bit next time ,one day I will get everything right so much to learn

      Cory

[Brett Buck]

I could be running it too lean What would be the best setting as I'm still learning.also I have a fan twister I got off Walter,which will be powered by os.35 max what would be the best line length for this

     Assuming that you are talking about the older OS35S (baffle piston version) for the Fancherized Twister, I would suggest starting with 60' (eyelet to eyelet) and then expect to cut it down. Or make up 60, 58, and 56, and see which you like the best.  Note that the OS35S is also pretty notorious for meltdown runs, unless you use the smaller of the two venturis that it came with. Unfortunately, people tended to use the large venturi to "Get More Power" and lose or toss the small one. Randy probably remembers the right bore diameter.

        I think you may be struggling a bit with some of the explanations here, and there is likely to be something else going on. Dallas was hinting at it, but it would be very helpful if you could find someone with experience to check out your airplane and engine, and help you get on the right track. Even if it takes some travel, it might be worth it to save some frustration.
       
    Brett

[cory colquhoun]

Yes guys struggling with it all,I think I need a new engine these older ones have been giving me grief for a while now,after all the input I'm running engines way to lean , thought that was the go, also I bought the OS second hand so it only came with one Venturi which looks to be a small one.

[Dallas Hanna]

Yes guys struggling with it all,I think I need a new engine these older ones have been giving me grief for a while now,after all the input I'm running engines way to lean , thought that running at peak was the go, wanna go out on weekend and try a bit richer before I go new.i won't give up just yet, so much more tech involved.

"Dallas was hinting at it" 

Sure was Brett!!  If Cory can let us know what area he is living we may have someone near to give him some help. N.S.W is big but not that big.  Not many model fliers west of the mountains.  I have a Merco 35 in a "Stingray" and another in a T-Bird II. They are all the early 1970s red head vintage. Usual fuel is minimum 22.5% oil and maybe 5% nitro. All ok for "sport" flying with 10 x 5-5,5 Eather CF props which I have tried but certainly not sub 5 sec laps on 62ft lines.  I use Castor (Castrol M) in them but mainly because that's what they had as a diet years ago.

Cory, you never know, there could even be the odd ST 46 or similar engines sitting in cupboards somewhere which aren't used for comp flying now. (wink wink!!)

DH

[cory colquhoun]

"Dallas was hinting at it" 

Sure was Brett!!  If Cory can let us know what area he is living we may have someone near to give him some help. N.S.W is big but not that big.  Not many model fliers west of the mountains.  I have a Merco 35 in a "Stingray" and another in a T-Bird II. They are all the early 1970s red head vintage. Usual fuel is minimum 22.5% oil and maybe 5% nitro. All ok for "sport" flying with 10 x 5-5,5 Eather CF props which I have tried but certainly not sub 5 sec laps on 62ft lines.  I use Castor (Castrol M) in them but mainly because that's what they had as a diet years ago.

Cory, you never know, there could even be the odd ST 46 or similar engines sitting in cupboards somewhere which aren't used for comp flying now. (wink wink!!)

DH

woops Dallas I didn't realise you are from Aus I just pm you

[Dallas Hanna]

woops Dallas I didn't realise you are from Aus I just pm you

Good to hear from you Cory.  You are only 500km north of me but hope to catch up in the future.

DH

[Tim Wescott]

Yes guys struggling with it all,I think I need a new engine these older ones have been giving me grief for a while now,

OS 25LA or 20FP for the size plane you're talking about.  OS 46LA for bigger planes.  Neither are in production, both show up on eBay.  Search on the "Brett Buck Tune Up" (BBTU).  The 20FP is sweet for the right-sized plane, the 25LA is probably a bit more versatile.  Either one is more available as an RC engine, and will work fine with the carburetor wired open, or you can make a venturi.  Tower Hobbies still sold venturis for them the last time I looked, but I don't know how easy it is to get stuff from them into Oz.

There's a new Enya 25 that's supposed to be good, and a 45 that's purpose-built for CL stunt.  But I have no personal experience, not even to the point of watching a buddy fly one in competition.  There are also various higher-dollar Russian engines (Stalker is a name that comes to mind), and you can always put off buying a new car for a month or three and get a PA from Randy Smith.

after all the input I'm running engines way to lean , thought that was the go, also I bought the OS second hand so it only came with one Venturi which looks to be a small one.

Lean and fast is what you want for speed events.  For stunt you want consistent power.  Two-stroke engines tend to act like they're leaning out the more load you put on them.  So you adjust them really rich -- way too rich for an RC plane -- and you get more power when you need it.  This applies whether it's an old engine or a new one.

[cory colquhoun]

OS 25LA or 20FP for the size plane you're talking about.  OS 46LA for bigger planes.  Neither are in production, both show up on eBay.  Search on the "Brett Buck Tune Up" (BBTU).  The 20FP is sweet for the right-sized plane, the 25LA is probably a bit more versatile.  Either one is more available as an RC engine, and will work fine with the carburetor wired open, or you can make a venturi.  Tower Hobbies still sold venturis for them the last time I looked, but I don't know how easy it is to get stuff from them into Oz.

There's a new Enya 25 that's supposed to be good, and a 45 that's purpose-built for CL stunt.  But I have no personal experience, not even to the point of watching a buddy fly one in competition.  There are also various higher-dollar Russian engines (Stalker is a name that comes to mind), and you can always put off buying a new car for a month or three and get a PA from Randy Smith.

Lean and fast is what you want for speed events.  For stunt you want consistent power.  Two-stroke engines tend to act like they're leaning out the more load you put on them.  So you adjust them really rich -- way too rich for an RC plane -- and you get more power when you need it.  This applies whether it's an old engine or a new one.

yeah starting to get the picture, awesome Tim , thanks , really keen for another try this weekend and hoping for light winds

[Tim Wescott]

yeah starting to get the picture, awesome Tim , thanks , really keen for another try this weekend and hoping for light winds

Everyone who's new to stunt goes through this.  The correct engine adjustment for stunt is just plain wrong for everything else -- particularly RC, where an engine that's rich enough for stunt wouldn't be able to run below mid throttle.  With the exception of the 25LA and the 20FP, that's not how you want to run 'em.

[Air Ministry .]

1 / 20 th .

Of the 5 seconds odd, or thereabouts .