Pukey Motors for Pukey Profiles

LAST EDITED ON Feb-27-04 AT 03:35 PM (CDT)
 
As should be clear by now, I have kinda gone overboard in fiddling with a couple ARF Flite Streaks and a plans-built Super Combat Streak. (Latter built from Barry Baxter's excellent plans.)

Thus it was that a couple days ago I was out running two used O.S. 20FPs which had been disassembled, cleaned up and reassembled.

There is not much to report when it comes to the 20FPs as I neglected to put any meaningful time on them before getting the tach out. I assume certain parts were reinstalled just a bit off from original positions, plus I had cleaned some crud from pistons and cylinders, even made a quick dash down the bores with a brake hone.

They both seem to run fine, the better of the two hitting a peak of 12,270 rpm, the weak sister pulling 11,730. All runs with APC 9-4 prop; SIG 10%, 25% castor fuel; and stock muffler without that little insert which further reduces noise output. The motors themselves are, of course, stock.

Still, they both seem to be healing somewhat, whirring bits getting to know each other once again, thus some inconsistent readings, especially early on.

I did come up with things of interest on my 25FP. It too is stock, or at least is now, having several months ago discovered that at one point in time--probably two or three years ago--I had added a huge stack of head shims.

First, I had slightly modified an RSM tongue muffler to fit the 25FP. Seemed like the right thing to do at the time, especially with the aversion we all share toward stock and heavy mufflers. But it was still a dumb move.

The 25, with APC 9-4 prop, SIG 10/25 fuel, Thunderbolt standard long and RSM muffler pulled a peak of 13,400. Slipping on the stock muffler cut this back to 12,700. Installing noise-reducing doo-hickey in muffler dropped revs to 12,500.

The cool thing was that with tongue muffler the revs just went all over the place, made easier--and more disconcerting--by use of a tach which reads down to the 10s.

Installing stock muffler saw the motor instantly calm down, giving reliable and repeatable readings, whether at peak or at (approximate) launch revs of 11,000.

This follows exactly what I have seen in the air with this motor, although it is made more difficult by trying to read quiet and noisy exhaust notes, different levels of power and being 60 feet away at the handle.

There is no question that the stock muffler is the best way to go with these engines, same thing seen with the two 20s, especially toward the end of testing.

The quieting insert can be counted upon to drop peak revs another 150 to 200 rpm. And while I kinda thought readings varied just a bit more with insert installed it was nothing like the (nearly unworkable) variations seen with tongue muffler installed.

I have since added stock mufflers to all three engines, lead to the tail of one ARF FS and what I call my Soup Combat Streaker. Didn't even flinch when bolting on lead; the FS wing can pack a lot of weight, none of the models are even close to the upper limits of this wing in the first place, and a tunable/consistent motor is a must.

Interestingly enough, when installing an O.S. #8 plug in each of the three engines, power went up. This increase varied from 90 rpm to 150 rpm.

I know each of us--depending upon where we live and those with whom we fly more than any other factors I can identify--have our favorite glow plugs. However, I know the #8 to be an excellent plug in a great many different engines and am always surprised when CL guys act as if they have never even heard of them.

>The cool thing was that with tongue muffler the revs just
>went all over the place, made easier--and more
>disconcerting--by use of a tach which reads down to the 10s.
>
>Installing stock muffler saw the motor instantly calm down,
>giving reliable and repeatable readings, whether at peak or
>at (approximate) launch revs of 11,000.
>
>This follows exactly what I have seen in the air with this
>motor, although it is made more difficult by trying to read
>quiet and noisy exhaust notes, different levels of power and
>being 60 feet away at the handle.
>
>There is no question that the stock muffler is the best way
>to go with these engines, same thing seen with the two 20s,
>especially toward the end of testing.
>
>The quieting insert can be counted upon to drop peak revs
>another 150 to 200 rpm. And while I kinda thought readings
>varied just a bit more with insert installed it was nothing
>like the (nearly unworkable) variations seen with tongue
>muffler installed.
>

Almost like the little short length of chamber, maybe 1/4 of the length of a tuned pipe if measured along the centerline, with a tapered tail cone, had some sort of regulating effect, huh? How very odd.

>
> Almost like the little short length of chamber, maybe 1/4
>of the length of a tuned pipe if measured along the
>centerline, with a tapered tail cone, had some sort of
>regulating effect, huh? How very odd.
>
> Brett

Yes indeed. How very odd.

I forgot to mention that not every single engine manufacturer can be assumed to have developed mufflers which actually match and/or augment the power and its characteristics, but it is without question that anybody looking for that Cool Profile and running either the 20FP or the 25FP simply must try a stock muffler. No matter how much lead must be added to preserve balance.

For example, I am saving a square-head Magnum 36 for upcoming ARF Nobler. It has already been fitted with a tongue muffler. Methinks this was a real bad move, and the next time out testing will be running it with stock muffler. And maybe even a MACS muffler.

As I have told Brett once or twice in the past, I am continually stunned by not only what I don't know about Stunt (and should already), but by the things I learn.

Hi Mr. Dirt,
As a side note, I have a Byron Barker reworked OS 40 FP, and it definitely runs best on the stock OS muffler. Much more consistant.
Haven't tried the stock muffler on the square head Magnum, though. It just runs so good on the tongue that we haven't gone anywhere else with it.
Fixing up the old Flite Streak, and intend to use the FP 25. I'm sure it will be a good combination! Got to get in on the pukey profile thingie.
Bill <><

>>
>> Almost like the little short length of chamber, maybe 1/4
>>of the length of a tuned pipe if measured along the
>>centerline, with a tapered tail cone, had some sort of
>>regulating effect, huh? How very odd.
>>
>> Brett
>
>
>Yes indeed. How very odd.
>
>I forgot to mention that not every single engine
>manufacturer can be assumed to have developed mufflers which
>actually match and/or augment the power and its
>characteristics, but it is without question that anybody
>looking for that Cool Profile and running either the 20FP or
>the 25FP simply must try a stock muffler. No matter how much
>lead must be added to preserve balance.

Weight is NOTHING compared to good power. A few ounces will not make a difference, a bad-running engine is a disaster.

I am also continually amazed at how sophisticated these engines (not just OS, but a lot of those currently available) really are, and how well-though out they are even in the little details. That's why I get so frustrated by seeing people take them and toss out the mufflers and throw in a bunch of head gaskets even before running them, much less flying them, on the assumption that they "know better". It took me a fairly long time (year or two) to realize what was going on and the level of sophistication involved. There well may be improvements to be made to the engines, and certainly they need changes to run in ways for which they were not designed. But the chances of hitting on the right changes without first understanding how it worked as it came can only be sheer guesswork.

In this case, of course, it's just sort of luck it ended up tuned pretty close to right for our application. That's why getting exactly the right prop makes so much difference. A "better" prop, i.e. bigger, will result in too much speed in level flight and you won't be able to slowit down no matter how much needle-screwing-out you do. Ted and I spent an afternoon once trying to get the Coyote/25FP slowed down with a 10-4, but no matter what we did, it just popped up a little faster at some point once it came on the pipe.

Dan, For the last several years I have been using .25's in my personal Ukeys and have sold many to our customers. You are right on about how well the stock mufflers work! I have an ASP .25 that will give all the power I will ever need at 5+ sec laps. I did find out though that this particular engine prefers uniflow tanks, otherwize one must use muffler pressure. I also have been using either APC or Tiapan 9x4's as well. Ocassionaly I will use a Tiapan 9x6 and from where i am in the development stage (beginner) I can see little difference between the two props.
Joe

LAST EDITED ON Feb-27-04 AT 10:41 PM (CDT)
 
Dan, I know you are getting fidgity, wanting badly to test your FS with a 9-4 Taipan. I have some, and will bring one for you to test on your first official at the next contest! It's the thing to do, near as I can tell. Joe's right, the Magnum XL .25 (same as ASP) likes the Taipan 9-4 real well. I think 10-4's and 10-3's still have some potential, if only folks would consider trimming the diameters. Seems like not many are willing to chop the pretty tips off an APC. One thing for certain, if you are loading the engine too much, as it heats up, it will go too fast. Your old ST G.51 did that with a full 12-5 APC at Arlington last July, first time I tried a full 12" dia.
Steve

Dr Dirt, check your mail later this week. Im sending you a trick prototype muffler 24 grams. Close to the same size as a stock OS.Give it a try,flip and fly! Scott Dinger

>Dr Dirt, check your mail later this week. Im sending you a
>trick prototype muffler 24 grams. Close to the same
>size as a stock OS.Give it a try,flip and fly! Scott Dinger

Scott,

Oh goody! A new product to test, only this time I've actually got existing stuff to test it on.

To All,

I am hoping that the claims made on this thread are being taken as seriously as seems to be the case. There certainly is little effort required to refute or affirm what is being said. And if we're right, a great many of you will be pleased, even the jaded Stunt Pros who seem to think they have already seen everything.

Back when I was taking a more serious approach to CL Stunt, a couple years or so could easily have been whacked off my development time if only someone had forced me into using a package exactly like the one presented here. That my ego would not have allowed such a thing is not the point here...

Dan