Spreading the word on 20FPs.

I knew it would take some time, but we are beginning to get some feedback from folk trying to assemble that rarest of Stunt-specific models, a Cool Thing Profile.

It's not that it's a hard thing to do, Brett laid it all down for us, including things he has seen others attempt and which he put under a not-to-do listing. There is even a "Starter Package" section on Heman's AeroManiacs site, although I have not taken the time to look at it yet.

Still, there are a couple things at play here and I think it might serve all of us well to discuss them.

First, it's almost 100% about the 20FP and following *exactly* the Brett Buck Tune-Up. Deviate from this tune-up with any single piece of equipment and at the very least you have compromised your model/engine package. At the worst it is not useable at all and you think some of us are just plain crazy, have gone back to what we have already proven time and time again is nothing more than a Pukey Profile.

Secondly, this seems to me a unique opportunity to get a whole bunch of people operating to the exact same benchmark of performance, properly evaluating and refining whatever comes after we burn up all the loose 20FPs floating around out there.

Think about it. We know for certain there is a real good set of numbers for the 40VF, much of this setup developed by Paul Walker. He can recite the entire setup from one end to the other and it is a combination which he has proven works *every time* and at some rather interesting flying sites around the world. But even with this plug-and-play approach, it is not perfect. Hand-made pipes and props, just as two examples. And of course slight tuning changes made by each owner once basic package is up and running.

The O.S. 20FP ABC, per the BB T-U, does not suffer these compromises, small though they may be. The O.S. pipe, ooops, sorry, the *muffler* is fixed in place, cannot be adjusted in any meaningful way. Internal baffle, ditto. The APC props are all the same. My gallons of SIG 10% Champion fuel are exactly the same blend as Brett's and your own. Thunder Tiger RC long glow plugs are as close to identical as any modeling product I can name.

Thus Steve Fitton, Bill Little, Bob Reeves, Brett, Derek, Mike Hazel, myself and a whole bunch of others can easily and quickly assemble the *exact same combination* and fly it to the same high-level results no matter where we live. Even Norway if memory serves...

Once we do this, if we start fiddling with different stuff, CF props for example, maybe even other engines which might actually be available in a hobby shop or from our tuners, we can all do so from an established, fully understood benchmark.

For example, Steve and Bill and others are impressed by Steve's 25FP. I don't doubt them anymore than I doubt Doug Moon and the results he saw with a 25FP on his Primary Force.

My only question is, Compared to what? I am really anxious for these guys to bolt a 20FP in place on that quite light Tomahawk of Steve's. I could even be coerced into shipping off one of my known-to-be-good 20FPs for a few days of loaner duty. If it's better, which is what I am predicting, we all learned something.

If the 25FP is the better powerplant, maybe Brett and I have some work to do in finding out why. (I'll ask the questions, he will provide the answers.)

What then? Well, if nothing else comes of all this, we can claim more than our fair share of cleaning up the planet in recycling a whole bunch of aluminum, certainly in a more enjoyable way than just collecting pop cans. Better, it will become common knowledge the exact type of power delivery one would like to see in an engine for a profile model, precisely how to get it.

From there? I don't know, although there are ideas floating around in my head.

First let's all get on the same page. Then we'll talk further.

As a minor contribution, I have found the Hayes 3-ounce clunk tank to be quite the nice piece. It is exactly three inches long, will nestle between motor and LE on most ARF Flite Streaks. (I did have to relieve the LE by about 1/4", this being the better option to moving engine forward.) One of my ARFs has been fitted with this tank, this replacing a left-side mounted RST-4 clunker. Thanks to Bob Smiley, (ex-)Lancaire flier, for mentioning this tank as a good option for the short-nosed FS.

I like the tank enough that Skyray 20 will get one installed soon, even though an SS-4 clunker is working just fine mounted 1/16" high in relation to engine centerline.

Hey Dan, great post and thanks for sharing It with us! Sincerely-- Paul

So Dan, why haven't you found a .40 version of this most perfect combination. Say, a scaled up Skyray and a "?" .40 that will be the perfect stunt plane? Come on, I'm sure that your meticulous development skills and keen eye can find this gem?

>I knew it would take some time, but we are beginning to get
>some feedback from folk trying to assemble that rarest of
>Stunt-specific models, a Cool Thing Profile.
>
>It's not that it's a hard thing to do, Brett laid it all
>down for us, including things he has seen others attempt and
>which he put under a not-to-do listing. There is even a
>"Starter Package" section on Heman's AeroManiacs site,
>although I have not taken the time to look at it yet.
>
>Still, there are a couple things at play here and I think it
>might serve all of us well to discuss them.
>
>First, it's almost 100% about the 20FP and following
>*exactly* the Brett Buck Tune-Up. Deviate from this tune-up
>with any single piece of equipment and at the very least you
>have compromised your model/engine package. At the worst it
>is not useable at all and you think some of us are just
>plain crazy, have gone back to what we have already proven
>time and time again is nothing more than a Pukey Profile.
>
>Secondly, this seems to me a unique opportunity to get a
>whole bunch of people operating to the exact same benchmark
>of performance, properly evaluating and refining whatever
>comes after we burn up all the loose 20FPs floating around
>out there.
>
>Think about it. We know for certain there is a real good set
>of numbers for the 40VF, much of this setup developed by
>Paul Walker. He can recite the entire setup from one end to
>the other and it is a combination which he has proven works
>*every time* and at some rather interesting flying sites
>around the world. But even with this plug-and-play approach,
>it is not perfect. Hand-made pipes and props, just as two
>examples. And of course slight tuning changes made by each
>owner once basic package is up and running.
>
>The O.S. 20FP ABC, per the BB T-U, does not suffer these
>compromises, small though they may be. The O.S. pipe, ooops,
>sorry, the *muffler* is fixed in place, cannot be adjusted
>in any meaningful way. Internal baffle, ditto. The APC props
>are all the same. My gallons of SIG 10% Champion fuel are
>exactly the same blend as Brett's and your own. Thunder
>Tiger RC long glow plugs are as close to identical as any
>modeling product I can name.
>
>Thus Steve Fitton, Bill Little, Bob Reeves, Brett, Derek,
>Mike Hazel, myself and a whole bunch of others can easily
>and quickly assemble the *exact same combination* and fly it
>to the same high-level results no matter where we live. Even
>Norway if memory serves...
>
>Once we do this, if we start fiddling with different stuff,
>CF props for example, maybe even other engines which might
>actually be available in a hobby shop or from our tuners, we
>can all do so from an established, fully understood
>benchmark.
>
>For example, Steve and Bill and others are impressed by
>Steve's 25FP. I don't doubt them anymore than I doubt Doug
>Moon and the results he saw with a 25FP on his Primary
>Force.
>
>My only question is, Compared to what? I am really anxious
>for these guys to bolt a 20FP in place on that quite light
>Tomahawk of Steve's. I could even be coerced into shipping
>off one of my known-to-be-good 20FPs for a few days of
>loaner duty. If it's better, which is what I am predicting,
>we all learned something.
>
>If the 25FP is the better powerplant, maybe Brett and I have
>some work to do in finding out why. (I'll ask the questions,
>he will provide the answers.)
>
>What then? Well, if nothing else comes of all this, we can
>claim more than our fair share of cleaning up the planet in
>recycling a whole bunch of aluminum, certainly in a more
>enjoyable way than just collecting pop cans. Better, it will
>become common knowledge the exact type of power delivery one
>would like to see in an engine for a profile model,
>precisely how to get it.
>
>From there? I don't know, although there are ideas floating
>around in my head.
>
>First let's all get on the same page. Then we'll talk
>further.
>
>As a minor contribution, I have found the Hayes 3-ounce
>clunk tank to be quite the nice piece. It is exactly three
>inches long, will nestle between motor and LE on most ARF
>Flite Streaks. (I did have to relieve the LE by about 1/4",
>this being the better option to moving engine forward.) One
>of my ARFs has been fitted with this tank, this replacing a
>left-side mounted RST-4 clunker. Thanks to Bob Smiley,
>(ex-)Lancaire flier, for mentioning this tank as a good
>option for the short-nosed FS.
>
>I like the tank enough that Skyray 20 will get one installed
>soon, even though an SS-4 clunker is working just fine
>mounted 1/16" high in relation to engine centerline.
>
>Dan
>
>
>
Dan, the GRW 3-3/4 oz. Chicken Hopper Tank fits the ARF Flite Streak also. I have a couple extras if your in need of one.
Regards,
John Jolley

Danny Dirt wrote: "Thunder Tiger RC long glow plugs are as close to identical as any modeling product I can name."

Surely, Dirt meant Thunder-BOLT RC long glow plugs. They're the good ones, made in USA by Ohlsson, no Rice. Steve

Dan,

If your really curious about the apples to apples comparison of the FP25 vs FP 20 on a known to be good airplane, I think we can manage before too long. I'm pretty sure one of my flying buddies (who is locally infamous for his considerable horde of motors, kits and general stuff(- ask Ron B sometime...)), has an FP-20. I'm pretty sure I could beg some flight time on the motor. If memory serves correct, this motor has already seen service this fellows flightstreak, at least enough to break it in. From what I recall, it ran great, but it was too long ago to help out with this experiment. Nonetheless, I think we can get some test data without having to resort to sending stuff cross country-at least yet. I'll take it out and do some quick swaps back and forth and see what we find.

Steve,

It will be interesting to see your results/findings. I did a similar test on my Ringmaster with a 20 and 25FP, and a 25LA and the only thing I could find is the 25LA has slightly less power than the FP's. The other thing I found out is they all ran excellent. However, I have several LA's and they have more than enough power.

My "test" engines all used the stock venturi's, OS needle valves.

>Steve,
>
>It will be interesting to see your results/findings. I did a
>similar test on my Ringmaster with a 20 and 25FP, and a 25LA
>and the only thing I could find is the 25LA has slightly
>less power than the FP's. The other thing I found out is
>they all ran excellent. However, I have several LA's and
>they have more than enough power.
>
>My "test" engines all used the stock venturi's, OS needle
>valves.

I think what Dan is up to is the FP20/25 comparison. Do you remember much difference between them? They need to be on the APC 9x4 and the factory mufflers for it to remotely compare to the West Coast setup.

I bet the LA is a bit weaker than the FP-with no boost port, it would lack some of the top end needed to get the most out of the prop.

>I bet the LA is a bit weaker than the FP-with no boost port,
>it would lack some of the top end needed to get the most out
>of the prop.

That's been my observation, too. Airplane that the 25FP would have no problem with like Twisters, Noblers, etc, seem to be at or very near the limit for the LA. The LA seems to work OK for the smaller models like the Skyray and Primary Force, but there appears to be very little reserve power. Note that this is based on obervations, to experiment, so take it in that vein.

I would imagine that the optimum setup is going to be different with the LA. Likely a larger prop to make more effective use of the reduced HP/torque at high revs (like other blocked-boost-port modified engines) could turn out to be superior.

Steve,

I saw no difference between the 20 and 25FP. They seemed to have the same power, and running traits. I used APC 9x4 props, and the stock muffler with the cone removed.

Steve,
I flew my orange plane all of last season with an FP.25 and switched to an FP.20 BBT-U this season. The .25 has noticeably more power than the .20, but the .20 has much better speed regulation.
I have enough experience with both engines to state that a .25 in BBT-U trim cannot be made to perform as well, in terms of speed regulation, as the .20 does. The solution to this lies in finding the right combination of venturi, muffler and prop. Again, I can guarantee it will not work with the stock (.267 id) venturi, stock muffler and APC 9-4 prop, which is the genius of the BBT-U setup. Mike Pratt has given us some clues in this regard. The venturi will be .250 or smaller; the prop will be a Bolly 9.5-4.5 de-pitched. My own contribution is I believe the muffler will be a Mac's 6300.
So be aware, we're talking $35 aftermarket mufflers and $10 venturis and $30 carbon props (rework labor not counted here) to make this work. Will it be worth it? Yep, but we're comparing apples to oranges.
Derek Moran

Is there any difference in performance between the iron piston versions of the FP20/25 and the later ABN versions and will the same fuel be OK for both?
Thanks

>Is there any difference in performance between the iron
>piston versions of the FP20/25 and the later ABN versions
>and will the same fuel be OK for both?

I only have experience with the ABN versions so everything I say refers to them. I would doubt that they like the same fuel.

You were running Sig Champion in your ABN's, right? 5% nitro?

I used Fox Superfuel in my iron piston FP-25. I imagine sig 25% all castor would be just as appropriate. Mine seemed to run great on the superfuel.

>You were running Sig Champion in your ABN's, right? 5%
>nitro?
>

I run whatever I have around at the time. That's never 5% nitro! Always either 10 or 15% SIG, Powermaster GMA, Powermaster regular R/C fuel, etc. I haven't found it to be critical.

>Is there any difference in performance between the iron
>piston versions of the FP20/25 and the later ABN versions
>and will the same fuel be OK for both?
>Thanks

For power, there is no difference. If I had my "druthers" it would be the iron piston version. They are older and the older ones are better made. They are also lighter! I prefer all castor--at least 20% on these babies, a little more is better. But, when treated right, they will run forever. The only reason I can figure for going to the ABN was the RC crowd wanting to use inferior oil in their fuel.

I would also guess that minimizing break-in time is always a popular selling point.

It's all well and good for the comparison between the 20 and the 25, but seeings how the 25 is what the average know nothing guy (you know, ME!) can walk up and buy, I'd be more interested in working with that. For some reason, the "Perfect" stunt engine always seems to be one that is no longer in production. Makes me wonder if someone doesn't have a large stock of engines to sell under a pseudonym on Ebay. I've always wondered about the Bett Bruck guy there.

Seriously though, I'm just spending my time with the 25 LA or the 40/46 LA's. Well, soon as my stock of 40fp and clones is gone I'll work with the 40' LA's. I'm going with a 46 LA in the Vector, soon as I get the covering on this Buster. Speaking of which, off to the showers after my 6 miles and down to the covering iron.

>It's all well and good for the comparison between the 20 and
>the 25, but seeings how the 25 is what the average know
>nothing guy (you know, ME!) can walk up and buy, I'd be more
>interested in working with that.
>
>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

Agreed. This nonsense of us Stunt guys "discovering" a good engine just about the time it is discontinued has gotten to be more than a little annoying.

However, and this is fact, until some unknown percentage of us actually knows, from personal experience, the capabilities of a stock 20FP we will continue to flop around in a 4-2-4 universe where old-school thinking rules.

Instead, let's establish a new, higher standard, a new benchmark, and shoot for that in working with engines which are more readily available.

I mean, how to replicate the power *and power characteristics* of a 20FP may well be a matter of bolting together existing engines and after-market products, a weekend of two of fiddling with details. But as long as the Fox 35 or the 25LA are seen as representing the state of the art in Stunt tuning, we're dead in the water.

.

However, and this is fact, until some unknown percentage of us actually knows, from personal experience, the capabilities of a stock 20FP we will continue to flop around in a 4-2-4 universe where old-school thinking rules.

I never thought that I'd be agreeing so totally with Dan on anything so relevant. Now if I could only get him to throw those Fox 35's out and get real motors that would indeed be an accomplishment.!
Dennis

> For some reason, the
>"Perfect" stunt engine always seems to be one that is no
>longer in production. Makes me wonder if someone doesn't
>have a large stock of engines to sell under a pseudonym on
>Ebay.

Well, when I started, it was readily available at any hobby shop. I think it would be a highly worthwhile exercise to apply the same idea to other, available, engines. There's nothing all that magic about the 20, and if they aren't readily available at any hobby shop, time to move on.

The "same idea", of course, is to take the engine out of the box, and make a very honest effort to *RUN IT AS IT COMES*. Instead of immediately "tossing in a few head gaskets, grab the Dremel tool, and ditch that heavy muffler". Most reworked engines I see are junk, because there are only a few people - very very few - who can do anything to the guts of an engine consistently and accurately enough to make them better. I finally got sick of telling people who grabbed me and said "hey, check my new Engine Guru 40" and then see it run worse than a $53 economy R/C motor. Witness the butchered up ST51 sleeve we saw a tew weeks ago.

So I went out looking for something that would fly a 35-sized profile without ANY modifications. And found it on almost the first try (with a few examples randomly acquired over the years).

Phil G. did the same thing with the Magnum 36XL. Took it out of the box, got the right venturi, the right prop - AND NOTHING ELSE. Now everybody thinks there's some miraculous magic inside it, when all he did was LEAVE IT ALONE.

I don't have any stake in selling 20FPs in any way. But I figure it's my duty to give something back to the event, and getting people to at least TRY doing something different and in this case, far superior, to traditional methods. Particularly when it's simultaneously cheaper, quieter, more durable, and far easier to use.

I have gotten more than the usual ration of crap for it, too, but I'm a big boy and can take it. I honestly don't care if people don't want to run it the way I think is best. But I do get a little annoyed when I get called a liar, cheat, moron, anti-Americanm, etc, for taking the basic ideas used to set up every single *current* competitive stunt plane and applying them to trainers and more modest competition models.

But I do get a little annoyed when I get called a liar, cheat, moron, anti-Americanm, etc, for taking the basic ideas used to set up every single *current* competitive stunt plane and applying them to trainers and more modest competition models. <\quote>

Ain't it GREAT to be popular?

Okay guys, when it comes to this ongoing discussion concerning the merits of the O.S. 20FP ABC/ABN (pick one) it's game over.

No, I mean ***Game Over!***

Up until now I have first taken advantage of Brett's advice, this applied to existing models plus one new Skyray 25. And fiddling with tanks, where to put them, what kind to use, worthless non-stock plumbing of same. More fiddling with trim on the models, all the usual stuff.

All coupled closely to more than one example of that most dreaded of all phrases uttered by the males of our species, "Watch this!"

But can we agree that a great many trick pieces and techniques fail utterly when we drag our rear ends to a contest?

I have now flown two 20FP-powered models in a NW contest. Truly, it's game over...

New site, Puyallup airport, formerly known as Thun field, hence Steve Helmick's cute play on words, transforming "Stuntathon" into "StuntaThun." A fair amount of wind, even a little rain at times on Saturday. Same deal on Sunday, although more velocity. On both days the wind speed picked up throughout the day, so while this was not a big factor in the mornings it became much more so as afternoon came around. All of the air was coming over buildings which were pretty close to the two circles.

The conditions were not conducive to properly sorted PA models, let alone Pukey Profiles.

On Saturday we flew OTS first, some whack job, not sharing his model with another this time around, won in relatively mild conditions, not too much unlike OTS at the NW Regionals but with a few bumps.

Classic was won handily by Don McClave and the wind was starting to get fairly nasty. I lost a "down" leadout, and the Oriental, shortly after take-off. (Details not now, totally my fault, even had a warning. And, yes, it had been pull-tested.)

As Bob Emmett quickly pointed out there was no reverse wingover, thus only an attempt, I could drop down the order two slots and take another shot. Which I was already preparing to do, although I had assumed such would take place in second round.

Yep, pulled out the better-looking of my two ARF Flite Streaks, O.S. 20FP with the "Brett Buck Tune-Up" in full force, told the judges to delete appearance points.

No practice flight, of course, and while I have a fair amount of time on this and a very similar model, neither had been flown since a week prior to this year's Regionals.

Don't remember the scores, finished fourth, not too far off what I was counting on getting from the Oriental.

No matter, the ARF FS/20FP just *punched through* at least as much of the bad air as the best models and a lot better than some of others. While few of you have actually seen this model, it is even draggier than most profiles as it is packing a Du-Bro S-4 (four ounce) tank on the *inboard* side of the fuselage.

There were no changes at all made to the model/engine package from back when I was flying it at Arlington, WA. In fact, other than "creative" placement of the tank, and use of an ARF, no changes whatsoever from Brett's suggestions.

A Big Deal: There was no time for a test flight. Fired it up off the end of the pits, set the needle for 12,600 (left-side tank, remember), a setting which had been the best when test flying. And it was *perfect* this day as well.

As Bruce Hunt and I work together at contests, I suggested he enter P-40, we could share my model. There was a period of acclimation required, as Bruce was flying a mildly chunky Shark 45, ST 60 power, in both Classic and Expert PA, so it was off to the practice circle.

Took about 1 1/2 of the three total practice flights Bruce got for it all to begin coming together, his **puhlenty low** pull-outs and all. I put up one more flight, not once did the model do anything weird, get blown out of a maneuver--Ooops, I did have opportunity for a do-over on two tricks--or in any way act as if was a mere cheap profile with a too-small motor.

We each easily and with confidence got in our officials even with worsening conditions, had a great time.

Minor Bonus: 10 flights total on this model, good results at the scoreboard, didn't scare ourselves over losing months of effort, burned substantially less than a quart of SIG 10% fuel.

Sunday morning. Didn't look that great. A lot like Saturday, just more of everything. I spent about 30 minutes debating on what to do, finally decided things could only get worse, I was not going to risk the Impact. As the ARF was a known quantity it could be used if I had to but as I have been planning on using my Skyray 35/20FP in a 2004 Expert PA contest anyway, this seemed like the time.

As my Skyray was (intentionally) bulked up with non-contest wood (34.5 ounces all-up, no fuel) and the airfoil fattened 1/8" I saw the distinct possibility of wanting more power. Removed the air filter (90 rpm on the ground is about what they cost) but no other changes, still with SIG 10% Champion.

First flight was fine, and I wish to emphasize that setting the needle to 11,200 (right-side tank)--a setting which has always worked for me in practice flying--was all that was required to nail the needle.

However, with more wind on the way I mixed my "Fox Kool-Aid," 20% nitro with SIG 10% 50/50 to get a 15% brew which was decidedly to the side of more castor than Klotz. Leaving the needle alone, just switching to more potent fuel raised the revs several hundred rpm. Taking a chance, and knowing the setting would have to be backed off some anyway, I set it to 11,400 rpm.

That was the last time all day I touched the needle. While the engine sounded just a very little bit richer than it had in practice flying, and certainly would have withstood harder running, there was no need. Even in the winds we had the engine would pull model up and over with authority. Not an excess of same, but I was not going to take the chance of going over-lean at the top of the circle toward end of patterns.

Issues of trim were not quite so easy, as a couple weeks ago I had added 21 grams of lead to the nose, wanting to try a 15% balance point, also had a full 14 grams of lead in tip weight, knowing it was too much. After test flights I removed 7 grams from nose, but the rest of it wasn't going to be quite so easy, adding 5 grams to tail instead of fighting it. Began whacking away at tip weight, although I never did got as much out as I wanted.

No complaints, but Bruce and I both saw some yawing taking place, a little bit of tip-banging. No in perfect trim by any means.

While it would be so easy to end with "I won!"--and I did--there is a little more to the story. A lot of our Expert PA fliers were scared off by the weather, Randy performed the coolest airborne antics I have ever seen and passed on flying for maybe another month or two.

However, Bruce Hunt was there, as was Jerry Eichten. I have generally managed to come in ahead of Jerry, the NW Regionals being an exception I believe, Bruce has come in ahead of me two or three times in recent contests. So we're pretty closely matched.

After my two practice flights, making it clear that I was going to fly the Skyray, I overheard Jerry saying something to the effect of, "Well, we've been hearing a lot about these 20FPs and profiles, now we'll see if they work."

It is with no malice or evil intent that I mention Jerry, flying a quite nice SV-11 with a piped 40VF, now has an answer, even if not a definitive answer, the margin being well within a minor bobble being noticed. Or not.

There's more to say, as I was able to make some comparisons of interest, but this posting is already too long.

But as far as I am concerned, even under fairly challenging conditions, a spare Cool Thing Profile is a pretty good thing to have tucked into the odd corner of your van.

Dan,

>>A lot of our Expert PA fliers were scared off by the weather, Randy performed the coolest airborne antics I have ever seen and passed on flying for maybe another month or two.<<

I do hope that Bruce managed to miss my performance with his video camera. Bad enough I was flying while running away from a knife wielding maniac.

Circleburner,

It has been my experience that if you are running the 20FP without the insert--referred to in O.S. instructions as a "mute"--plugged into the muffler you are not getting the best performance from your engine.

Sorry to dominate the conversation, but I continue to think the elimination of Pukey Profiles to be a worthwhile cause...

During Stuntathon (StuntaThun) I was finally able to match a 25LA-powered ARF Flite Streak up against my nearly identical model, the only difference being my use of a 20FP.

Bob Smiley had the same piece used at VSC this year, it having been a last-minute replacement for a Stills Stuka he lost just a week or so prior to VSC. Bob flew this model to what I believe was a 14th-place finish in Classic, meaning he stuck it out through some heavy wind.

Bob's 25LA is a stock engine to which he has fitted some sort of tongue muffler. Tank is a Hayes 3-ounce unit, wedged in between leading edge of wing and engine. Bob mounted his tank with the "tongue" against fuselage, while I chose to rotate tank 90 degrees, tongue side down on my beater ARF FS. As my installation places clunk closer to NVA, theoretically it should be a little better, but Bob reports no problems.

In the air Bob's model seemed to handle well, especially after I got him to add 1/2 ounce of lead to the 1/2 ounce already bolted in place. These things really do fly better if the balance point is 1.5 inches back from leading edge of wing.

The problem, from my perspective, and being able to watch both models several times, was that Bob's 4-2-4 setup alternately delivered just barely adequate power while in a four-stroke, only to immediately yank the model forward when breaking into a two-stroke.

Yeah, yeah, hard break and all that, but it was to my eye much more pronounced than I have ever seen, for example, with Fox 35s. I can now see and feel the difference in break, still with a Fox 35, when going from 10% to 15% fuel. Bob's situation was a lot more extreme than that.

How better to describe it? From watching the model, and remember we had some character-building weather patterns last weekend, it looked as if one should have been whipping it up to better speed when the engine was in a four-stroke, that there was simply no way to hold it back enough when it clicked into a two-stroke.

This wildly varying airpseed meant Bob had a lot more trouble keeping the model pointed in the proper direction, while my 20FP-powered ARF FS just motored through it all with a much more constant airspeed.

The real problem is I see little in the way of fixing this--remembering we are talking about achieving Cool Thing Profile status--as softening the break to some minimally-acceptable standard would require enough added head clearance that nobody would be left at home in the Dept. of Torque.

The 25LA is a nice sport motor. Can probably even be a decent contest motor if one is real careful about selecting an appropriate model and/or event.

But it is nothing like a real good 20FP as to power delivery, certainly weaker than a 25FP.

A quick question: Does anyone know why engine makers dropped the .20 size in favor of the .25?
Is there perhaps an event of some kind (possibly RC) that caused this?

Thanks,
George

> A quick question: Does anyone know why engine makers
>dropped the .20 size in favor of the .25?
> Is there perhaps an event of some kind (possibly RC) that
>caused this?
>
> Thanks,
> George

The bottom line, nobody was buying the 20 when the 25 was the same size, weight, and 25% more power. These are made primarily for the RC crowd, after all. Thunder Tiger didn't even make a 20 when they cloned the FP. I, too, favor the 25 for the same reason for CL purposes. I stock 25s and don't mess with the 20.

If they come out with a 26 next year, the RC crowd would stop buying the 25 and go for the 26, even if the only difference was say, the color. Could be the exact same engine on the insides. Really, it's a doggy engine for RC. Nowhere near the power of the lighter Norvel 25, but takes a lot less maintenance too. Put a Mouse can muffler on a Norvel with the 9x4 prop and say 15% nitro and stay behind the prop.

>If they come out with a 26 next year, the RC crowd would
>stop buying the 25 and go for the 26, even if the only
>difference was say, the color. Could be the exact same
>engine on the insides. (snip)
>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

Sometimes "new" goes in reverse. Magnum/ASP dropped the .53 and went to a "new" 52 with the (now in rage) square finned case and head. I think the change is size designation was made just to let the people know it was a new engine.

We don't need the square case and head with its extra weight (a full ounce difference) but the RC crowd will buy it because "its the thing to get."

You know, I really don't think the RC crowd is to blame for everything. Engine manufacturers know what car manufacturers know, and that is "new" sells--and that manufacturing economies help with profits--nothing wrong with that.

The main differences (I think) in the RC and CL is the size of the markets, and the fact that the CL application is trickier than the RC application. A muffler-pressure throttled engine is more easily adaptable than our fixed (during flight at least) venturi system.

Considering that "nobody" was buying 20FPs when the 25FPs were also available, there sure are a lot of 20s floating around out there.

I've mentioned this before, but the first time I asked Mike Conner about 20FPs he pulled out two used pieces he had just bought. (We were at a swap meet at the time.)

Prior to the NW Regionals Mike called and I asked for more 20s if he had them. No problem, two more came south with him, although one has ended up being a parts motor.

Mike thinks a fair number of 20FPs were sold for RC twins.

It is true that there are a lot more 25FPs out there than 20s. Even I have a 25FP! But it will soon be converted to a 20 with new piston/cylinder set ($24.95 from Tower) and related parts from above mentioned parts motor.

Regardless of how many are available used, the 20FP is **easily** the better of the two engines. For one thing, 25s don't typically come with the "mute" insert for the muffler, and this piece adds substantially to the effectiveness of the 20FP.

Ya know, some of you, maybe all of you less only 10-15 people, are gonna laugh, but if I were to be one to two years into a full-on effort in CL Stunt, casting about looking at PA models, 60 and 65 two-strokes, small-, medium- to gargantuan-capacity four-strokes, the best advice possible would be to buy a fresh 20FP--even if assembled from new parts, this probably costing something on the order of $125.00 for a motor complete with muffler.

To continue, the new piece should be bolted to a SIG Skyray 35 and flown. A lot. And then flown some more.

One would then know quite a lot concerning a certain style of power delivery which is quite effective.

From there it would be a matter of looking for a suitable power plant in the 36 to 65 range.

With engine in hand the model to build would be the next question and the answer would be to build a proven design which appeals. Get it straight, stiff, and light.

At the end of the day our imaginary up-and-comer would be money and two to several years of frustration ahead of the game.

As to other engines, I think Brett is right in that we can do something similar to the 20FP and Brett Buck Tune-Up with pieces tucked into hobby shop display cases all across the country, and I believe he and I both have some ideas on how to proceed.

But my real point is that until more of us get recalibrated as to what *really* works there is going to be a lot more mindless debate going on, the more aggressive being folk that haven't even tried a 20FP, are totally clueless as to what we may be talking about.

I most certainly made believers out of some NW people this past weekend, some of them watching either the ARF or Skyray 20 fly and then coming by the van to shake their heads in amazement.

Minor points to add:

Early on Randy asked why I haven't found a 40-sized version of this "most perfect combination."

The answer is that PTG got there ahead of me. Way ahead of me. Magnum 36. John Leidle was using one of these engines in his Nakke at Stuntathon, I had never seen it powered more appropriately. And of course Mike Haverly is flying one in his Oriental.

A tip of the hat to John Jolley, but I have surplus GRW chicken hopper tanks myself. Appreciate the offer. More appreciated was the subtle dig.

Derek has shown an ability to post very clear photos here, how about some pictures of the 20FP-powered model you had at the NW Regionals? I continue to think it is a pretty cool design, like the back-door motor mount and other features. Worth showing to one and all. Especially the fact that you have yet to fully accept the mounting system.

Dennis, I have not tossed my Fox 35s, but you may be pleased to know that with loss of my Oriental, and the L&J Fox 35, and the PA crank, and an irreplaceable Real-Deal B-Y&O 10-6 I am prepping something (sorta) new for Classic competition.

I built a Super Combat Streak several years ago just for fun. Has not been flown much, still in real good condition. Am now fitting it with a 20FP, model previously having a 25FP installed. Even bent up some two-wheel landing gear last night.

We'll see how it flies, I am predicting goodness and light, you may get your wish.

For those trying to do the right thing in following BBT-U exactly, the "mute" insert improves the run. And is not available as a replacement part, from inquiries I made it seems as if it was never sold as a replacement piece.

I was told that replacement mufflers for the 20FP are available and that they come with the "mute," but at twenty bucks for the assembly it will surely be worth calling around first.

In order to retrofit a 25FP into an 20FP using parts, you'd need:

20FP piston/cyl set - p/n 22303010, $24.95
20FP wrist pin - p/n 22406001, $5.79
20FP cylinder head - p/n 22304000, $9.99

I believe all other parts are common to both engines (well, the 25FP crankcase would say "25" and the 20FP crankcase says "20" but they're the same dimensions).

>In order to retrofit a 25FP into an 20FP using parts, you'd
>need:
>
> 20FP piston/cyl set - p/n 22303010, $24.95
> 20FP wrist pin - p/n 22406001, $5.79
> 20FP cylinder head - p/n 22304000, $9.99
>
>I believe all other parts are common to both engines (well,
>the 25FP crankcase would say "25" and the 20FP crankcase
>says "20" but they're the same dimensions).

If you're going to the trouble of a retrofit, and it is worth doing, might want to order up a new gasket set for the 20. You'll certainly need the head shim, and it can't hurt to install a new gasket on rear cover.

Dan,

Is there any chance you have a picture or illustration of the muffler with the mute you are talking about in your posts?

Thanks,

>Dan,
>
>Is there any chance you have a picture or illustration of
>the muffler with the mute you are talking about in your
>posts?
>
>Thanks,
>
>Tom

Tom,

No, sorry. I'm still a film guy who has just enough time and money invested in current camera and accessories to strongly resist new technology.

The "mute" insert is aluminum and in overall shape looks a lot like the rear plate of a factory muffler, although not as smoothly tapered as the O.S. muffler. But it's got a hole in the middle, just as one would expect, a convergent shape to it.

With muffler halves separated it plugs into forward shell, rear shell traps it in place.

Or. It looks amazingly similar to baffles I have seen in some 2- and 3-chamber tuned pipes we used in RC Pattern models back in the days of 60 two-strokes. It may even look like baffles used in CL Stunt tuned pipes, although my understanding is they are flat instead of cone shaped.

A nice bonus to use of these mutes is that one can talk back and forth between flier and Pit Dude while flying. Of course, this is not always seen as a positive, especially when I yell out cutting comments about the quality of most recent maneuver...

Now I am confused - I just went and looked at my FP20 mufflers and found I had 3 different types. First and smallest is the #842 (1.75oz), next is the one with the 'cone' insert but with a different number (E2030) and slightly longer body section and longer and more tapered rear cone (2.2oz) and finally the #842 again but with the 'quiet' section in the centre (this 1.25 inch insert also has its own baffle and weighs 2.3oz)
In the early correspondence I believe it was suggested that the muffler was acting as a pipe but now we have three different lengths of silencer, both in overall length and in terms of internal reflecting surfaces, does this affect the running speed or has all the test work been done on one particular thpe of muffler?
I have tried to include pictures but could not seem to get below 50kb!

Hooray, managed to upload files at reduced size! Pics show the 'cone' shaped insert for the E2030 and the 'quiet' section and baffle for the 842.

>Now I am confused - I just went and looked at my FP20
>mufflers and found I had 3 different types. First and
>smallest is the #842 (1.75oz), next is the one with the
>'cone' insert but with a different number (E2030) and
>slightly longer body section and longer and more tapered
>rear cone (2.2oz) and finally the #842 again but with the
>'quiet' section in the centre (this 1.25 inch insert also
>has its own baffle and weighs 2.3oz)
>In the early correspondence I believe it was suggested that
>the muffler was acting as a pipe but now we have three
>different lengths of silencer, both in overall length and in
>terms of internal reflecting surfaces, does this affect the
>running speed or has all the test work been done on one
>particular thpe of muffler?

I have only used the E-2030 muffler, without the extra "mute" but with the internal baffle. Take the internal baffle out, and it runs differently.

>
> I have only used the E-2030 muffler, without the extra
>"mute" but with the internal baffle. Take the internal
>baffle out, and it runs differently.
>
> Brett

Thanks,
looked again at my E-2030 it only has the cone shaped 'mute' fitted as described by Dan in message 38, there is no baffle. There are just three pieces, front shell, cone mute and rear cone. Have I got something missing?
thanks.

>>
>> I have only used the E-2030 muffler, without the extra
>>"mute" but with the internal baffle. Take the internal
>>baffle out, and it runs differently.
>>
>> Brett
>
>Thanks,
>looked again at my E-2030 it only has the cone shaped 'mute'
>fitted as described by Dan in message 38, there is no
>baffle. There are just three pieces, front shell, cone mute
>and rear cone. Have I got something missing?
>thanks.

No. What Dan refers to as a "mute" is actually just the cone-shaped baffle and is a stock part supplied with the engine. There is, available as a separate piece, something that OS refers to as a "mute" which is a ~1" long cylindrical extension between the from and back halves, with a flat plate at the rear end and a hole for the exhaust to pass through.

I have seen decent runs with the engine using the OS Mute (since the flat reflecting surface is at least in the ball park of the centroid of the conical tail cone) but I can't say it was any better than the stock muffler including internal baffle, nor was it signifcantly quieter. It didn't seem to hurt anything.

For reference, I have seen some 25FPs supplied with the internal conical baffle, and some not. When I was trying to see why the 25FP was "homing in" on a slightly-too-high RPM, I guessed that the problem was the baffle was missing. But when I added the baffle, it changed the run a little, but did not change the "homing" (i.e. tuned regulation) phenomenon.

Hi Dan,
This forum link shows some of last season's pictures of my plane http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=8121&forum=DCForumID1&viewmode=all.
Since then the tissue has acquired the patina of an old golden retriever and the FP.25 has been replaced by an FP.20. I've been shaving the mounting lugs, one stroke at a time, with a Swiss file to achieve the optimum CG. Hope I don't remove too much- I'd have to buy a new engine and start over.
Derek

>Hi Dan,
>This forum link shows some of last season's pictures of my
>plane
>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=8121&forum=DCForumID1&viewmode=all.
>Since then the tissue has acquired the patina of an old
>golden retriever and the FP.25 has been replaced by an
>FP.20. I've been shaving the mounting lugs, one stroke at a
>time, with a Swiss file to achieve the optimum CG. Hope I
>don't remove too much- I'd have to buy a new engine and
>start over.
>Derek

Derek,

Thanks, I had forgotten you had already posted pictures. Glad I got to see it at the NW Regionals, really slick model.

Reference above about shaving mounting lugs the result of very early conversations between Derek and myself on Friday at the Regionals. I told him something along the lines of liking the model but wondering why he had not taken full advantage of the back-door mount. He looked a little confused, so it was pointed out to him that if he was actually serious about stuff like this he would have removed the mounting lugs as they are no longer needed, thus are worthless weight being drug along on a model which was obviously built plenty light.

He took it well, we quickly became friends.

Dan

P.S. Derek's rear mount is a stock O.S. piece and it is still available.

Dan,
I'm setting up an ARF Flite Streak as you describe. I have a stock FP-20 with stock muffler, APC 9X4 prop, Thunderbolt R/C plug, and a 3 oz. Hayes tank. How did you plumb the Hayes tank? I don't see any way to make it uniflow.

Steve
The older I get, the better I used to fly!

On the Hayes, just mount the tank with the molded vent to the outside and it will work as a uniflow vent. I use the Hayes tanks on my profile carrier planes that are very sensitive to vent location and they work fine.

I insert a thin copper tubing into the outer vent that ended about a quarter inch ftom the back.

Steve,

My Hayes 3-ounce tank is plumbed per instructions with tank. No tricks.

However, details count. I am mounting these tanks such that the forward-protruding "tongue" portion of the tank is at the bottom of tank as installed on model. It sounds as if some are installing tank such that this tongue is placed alongside fuselage; locally, Bob Smiley is doing this as well and reports no problems.

I am not using uni-flo plumbing on any of my profiles, all of which are powered by 20FPs fed by plastic tanks. My Soup Combat Streaker has a 3.5-ounce hard tank which is plumbed uni-flo and gets muffler pressure.

It is understood that a slightly better Stunt run can be gained through use of uni-flo. However, with my personal models I am trying to make the points that a really fine powerplant is available, that the capabilities of almost any decent profile can be increased markedly with use of the stock 20FP, and that off-the-shelf equipment (tanks, props, fuel, etc.) is all that is required.

Thus my Hayes tanks use stock internal plumbing, which means only a short line, clunk at one end, feed fitting at the other. Top vent is used for muffler pressure. Second hole down has been opened up and is used for refueling.

Works really well.

Mike Bennett,

Coincidentally I stumbled across the same sort of confusion just this last weekend. Two of my most recent 20FP purchases came with "842" mufflers, but only because seller was trying to provide complete engines.

The first two 20FPs I bought came with "E2030" mufflers and the little cone-shaped baffle. Which, working in conjunction with order support at Tower, I have managed to confuse as being a "mute" described--but not pictured--in certain 20FP instruction sheets.

Anyway, your pictures show the **correct** muffler and the cone-shaped insert, both of which I am using.

Further, one of my engines is a little weak. It is of course fitted to a junker of an ARF Flite Streak, mostly used as a demonstrator. However, this last weekend it was taking 20% fuel in order to haul the mail as expected.

So back in the shop I snag a piston/cylinder set, also used, to try. Hmmm... The one I don't like is obviously ABN. The replacement to try is ABC.

There are iron 20FPs, ABC 20FPs, and ABN 20FPs??!!

>There are iron 20FPs, ABC 20FPs, and ABN 20FPs??!!
>
>Dan

I am not aware of any true ABC FPs. To my knowledge they were all iron piston or ABN. They did go through a period where the plating was thin and they looked different. The ABN liners are plated on the inside and outside. An ABC liner is normally plated on the inside only and just shnows the brass liner on the outside. Is this the way this liner is made?

Okay okay I get it , you prefer the .20 to the .25.

Is this because it is the optimal size for your airplanes?,is a .25 over-powering the size airplanes you put it on.

Is the .20 an engine with a 'sweet' bore-stroke ratio along with a muffler that is matched, but the same muffler doesn't match a .25?

So the question is, why the difference?

To Len first, the piston/cylinder set mentioned above is clearly an ABC unit.

It must be mentioned that all four 20FPs I have bought over the last few months came in as used examples, and via a third party at that, thus I have no idea of the history behind each.

To Zeke, you're asking the wrong guy. While I have very definite opinions as to what I like in a powerplant, my approach is quite pragmatic and based upon flying experiences.

Still, I have found that bore/stroke discussions are mostly mental masturbation in that when someone (stupidly, in my opinion) cites a long stroke as being responsible for high torque in a given engine there are equally valid examples directly refuting what must be regarded as a half-baked theory.

The 25s typically over-power your average 400-inch profile.

But the big hit, in my experience, has been that they tend to run away on us. I think there is a fix, although just running the 20FP-specific muffler w/insert has not worked for me.

So the answer is, "I don't know."

But if you follow the BB T-U, you won't care...

>To Len first, the piston/cylinder set mentioned above is
>clearly an ABC unit.
>
>It must be mentioned that all four 20FPs I have bought over
>the last few months came in as used examples, and via a
>third party at that, thus I have no idea of the history
>behind each.(snip)

>Dan

I know that George Aldrich chromed a bunch of OS engines, maybe others did, too. George never liked the nickel plating, but then he did admit that all but two of the engines he chromed were rc versions that didn't hold up to the fuel (and abuse) they were used with. He kept talking about the nickel "peeling". With bad fuel I could see it happening. Anyway, maybe you got one of these??

>>To Len first, the piston/cylinder set mentioned above is
>>clearly an ABC unit.
>>
>>It must be mentioned that all four 20FPs I have bought over
>>the last few months came in as used examples, and via a
>>third party at that, thus I have no idea of the history
>>behind each.(snip)
>
>>Dan
>
>I know that George Aldrich chromed a bunch of OS engines,
>maybe others did, too. George never liked the nickel
>plating, but then he did admit that all but two of the
>engines he chromed were rc versions that didn't hold up to
>the fuel (and abuse) they were used with. He kept talking
>about the nickel "peeling". With bad fuel I could see it
>happening. Anyway, maybe you got one of these??

Doubtful. I liked George about as much as any of us did--and he was certainly an entertaining, while completely trustworthy guy to do business with. But he was also a champion maker of mountains, beginning with mole hills.

In my view, the stories of nickel stripping from O.S. liners falls into this category.

In any case, considering the tens of thousands of 20FPs out there, the very small likelihood your typical RC Newbie would even consider the possibility of a bogus cylinder and then sending it off to GMA, indeed even knowing of the man, makes this possibility remote at best.

Besides, there are no GMA markings on this engine. In fact, if there were I might not run it.

I also wish to make clear that all I am doing is swapping parts around, trying to get a demo motor that doesn't require 20% fuel to deliver the goods. It is far from clear the ABC set will prove advantageous at all, especially as I have yet to run the little critter.

Dan

Ooops! My mistake.

Last night I was so anxious to demonstrate to myself the piston/cylinder in question is of ABC construction that I left the engine bolted to model and merely removed the head, pulling liner straight out.

Clearly an ABN part when you get really close and start looking a lot harder than I did the other day.

What is funny about the liner is that it appears to have been masked top and bottom prior to nickel plating being applied. Thus the exterior of liner carries multiple clues of being ABC construction. And as I simply did not notice anything unusual until getting ready to fit the cylinder head, there was (sorta) bare brass staring me in the face.

For the record, my other 20FP liners have been plated all over, no brass showing at all, appear normal in all ways.

(Have I ever mentioned that prior to buying a 25FP a couple years ago I had never owned an O.S. engine? It's true. And when that first motor proved unsuitable for anything but sport flying my O.S. experience was rather low-key. Now I've got more motors and a whole bunch of flying time.)