More rambling on the 20FP, the engine which delivers enjoyment in so many ways. One of which is in actually flying the little sucker...
Beginning with Andrew, May 31st:
Yep, the cases from steelies and ABN engines are interchangeable; it's the internal parts which are of importance.
As to the cost of getting the proper assembly of parts, I must admit that was not a high-priority item when writing about the 20FP ABN with Brett Buck Tune-Up. At that time--and this is still the case--emphasis was placed on first putting together a piece known not only to haul the mail but to do so with amazing consistency.
Not to the total exclusion of dollars spent, but almost. Look at it this way: For approximately the cost of a new CF pipe, certainly less than a pipe and a CF prop, one can discover what approximately 50% of the Top 20 at the Nationals each year is talking about when going for the correct--and winning--style of run.
And, like Brett, I was interested in seeing those with no interest in engine work, presumably along with lack of interest not having the skills nor the tools to do the job.
Related, I have heard back from quite a number of guys who fly alone, have only limited opportunity to see proper engine runs. They need the Right Stuff and they need it the first time through.
So it is that with one's first 20FP w/BB T-U, it is real important to eliminate as many potential pitfalls as possible, as this single engine will be used to establish a baseline of performance.
In my view this eliminates used ABN engines, as without the history of use (abuse in some cases) one just never knows...
With a known quantity in hand, there are lots of options in coming up with more engines, some are less costly, even if we are not talking about saving a lot of money.
I do not know what to say about Bill Little's comment on the steelies and ABNs. The man clearly knows what he is talking about, note the very favorable comparison 20FP to 40VF. However, my back-to-back tests, while inadvertent and taking place early on in my testing of 20FPs (I had mistaken a steelie for an ABN), showed a definite preference for the ABN unit.
Were I to do these tests again, in a more controlled manner, I might even agree with Bill. But I strive to eliminate as many variables as possible and so all my motors have ABN parts, the only style currently available new.
Brett's comments, 31 May:
As with a lot of things from Brett, this deserves a second or third reading. And it needs to be noted that a few short years ago I am not so sure I would have agreed as enthusiastically as I do today.
This deal of "engine experts" selling to us whack-job conversions of various sorts is really quite annoying, and I say that as a flier who did indeed once buy a custom engine, a Fox 35, from Larry Foster. Look, it was a real good engine. Indeed, it was a better Fox 35 than I had been able to build and I have had some success in this area. So it's not as if all the tuners are frauds; it's just that the number of true experts is really quite small. And note that not only did Larry do his homework on the Fox 35, he specialized in this engine. Exclusively, I believe...
And sure enough, with the engine which begged for mods when forced to act like a larger Fox 35, the 40FP, now gone tuners are looking around for more fertile ground, this currently being the LA series of engines when from what I have seen Brett's approach to the 20FP is the only approach to the LAs which makes sense.
I'm pretty sure that I am familiar with the engine and the parties involved to which Brett alludes as to working on "improvements" to 40LAs and 46LAs. This is of a piece with a comment I made on SSW, that of being told a large-bore muffler-pressure fitting delivers "more pressure" to the fuel tank, in turn this being one of the keys to the puzzle of converting an LA series engine to CL Stunt.
This is a clue. This is nonsense. I don't mind overmuch if a customer swallows this line, even if he should know better. But when the seller--a self-declared expert, remember, one who expects some cash in exchange for his expertise--puts something like this forth as fact, you can pretty much cross that guy off your list.
But this is also an area where the 20FP w/BB T-U again demonstrates its worth, why a proper engine almost no matter what it cost to put together is a good investment: It gives one a real good benchmark to use in evaluating the custom engines which show up at the flying field from time to time. These sorts of comparisons can be quite enlightening...
Still with Brett's comments, it is true the 20FP has not been produced for years, although engines and parts are readily available. So as long as we have a repeatable base line of performance for small-bore engines, it does make sense to find a current engine to use in the stead of the 20FP.
Brett says he is not interested. I am not interested either, and not just because Len at SSW promptly established himself as a rather obstinate block to spreading around some real good ideas. Should I be bothered to retrieve a 20FP on loan to a friend and his son, I think I've got six of the things. All have fresh parts, with a single exception** all are interchangeable one with the other. I'm set.
What about the HB 20 Gold Cup, now made by or available from RJL? (Sorry, I don't know which it is, although Mr. Google pointed me in the right direction using search words "HB 20," "Gold Cup," and "RJL.") I recently got a note from Mikey (Mike Pratt) and not only has he settled in at a new job, he's back on board and designing a new model, the competitive fires having come back.
That in itself is Great News--details never--but Mikey says the HB 20 is a good 'un. It's a ball bearing engine, is still in production and can be had for a good price. He is using a tongue muffler on his, Bolly 9.5 - 3.4, revs set at 12K. "Big time power and punch," according to Mikey.
Reading between the lines of the note, it seems as if the HB 20 might not be ideal for things like Flite Streaks, but more suited to larger models, possibly something like the SIG Primary Force, in itself a Design by Mikey.
Or maybe his current design project, although you will not get any other hints from me! While I have not been sworn to secrecy, friends are friends, and if you have a friend like Mikey one treads real lightly without being asked...
Again with Andrew: Agreed, there are certain aspects to the tune-up which can be changed without changing the run. Plugs and fuels, for example. While I am sure you understand this, in the beginning it most important to first make every effort to experience the exact sort of run being described. I have no problem with those who set aside a proven tune-up, going off the res in trying to make a differing tune-up better.
Just as long as the known tune-up is used to evaluate further evolution, even though the 20FP can so easily be devolved...
Yes, the 20FP can indeed be boring! I was almost excited to see mufflers coming adrift. Aha! An item which needs to be dealt with in coming up with modifications. Even if it is only cap screws and a suitable hex key. Sigh...
As to more current tricks, I am really liking the Hayes 3-ounce tank mounted to the left side of the fuselage. While it might not be a common complaint, more often than not I found the needle to of a sudden go non-linear on me. And the motors would take too long to get up to temp, this being handy when getting a setting. Uh, we're talking about contest flying here.
It seems to me that with some models and engines, ground revs in the range of 11,200 to 11,400 see the setting go just a little bit too rich as the needle is wound open. One more click is all it seems to need, this is just a touch rich, back in one click. Again, this does not happen all the time, but with the inboard-mounted tank and revs in 12,200 to 12,300 range it never happens.
And at the higher revs/leaner setting the 20FP builds heat faster, this hurrying the process along, sometimes a factor in contest flying.
Still with tank issues, the Hayes tanks don't seem to be a full three ounces. I have not actually measured one, other than using one of those ubiquitous "ketchup pumps" as part of my fueling rig, but they pretty reliably deliver one ounce per stroke. It seems as if these tanks were rated as three ounces prior to stuffing the plumbing inside, leaving us with something like 2.75 ounces.
If you find yourself with range problems, the 4-ounce Hayes tanks are probably interchangeable as they are only .026 taller, less than 1/2" longer, just over 1/8" wider. The length is probably a deal-killer on a Flite Streak with outboard tank, but in most other cases should not be a problem.
However, before giving up on the three-ounce tanks, notice that during fueling there is an air pocket in the forward-protruding tongue. Tip the model on its nose to get rid of it. And if you are seeing foaming in the top of the tank during fueling, this merely slowing the process, two or three drops of Armor-All in your fuel will eliminate the foaming.
Said with a conspiratorial tone and behind the back of a hand: "Modifications to the 20FP."
As you might assume, head clearance is slightly variable on the 20FPs. Using the squished-solder technique of measuring head clearance on assembled engines, I got readings of .029, .029, .033, .031, .028, .030, a variance of .004.
Far, far from something to worry about in the beginning. All of these engines ran well, although my notes indicate some minor issues with the engine running at .033, mostly in the area of getting a good setting for the first flight of the day.
Still, some of us revel in excess and so...
**With one engine/model combination I have been fiddling as of late, contest flying being the ultimate goal. And I wanted more grunt when winging across the top of the circle.
The first "modification" was to switch from SIG 10% "Champion" fuel to 15% "Champion." Stealing a tip from the crowd (Brett and Crew) which flies on the left coast and at low altitude and then tromps off to Muncie once a year, that was the only change and ground settings of 12,300 with 10% are also used for the 15% fuel.
In my view, this is worthwhile as the model is a plans-built Flite Streak which, uh, came out a little heavy as I insisted upon 1/64" ply laminated to both sides of the fuselage, this leading to quite a slug of lead in the nose when going for the 1.625-inch balance point I like. My first whack at using LustreKote on the fuselage didn't help in any way I can see, although the finish looks good...
Wanting some more grunt and remembering the issue of getting heat in the motor while on the clock during official flights, I measured head clearance at .031 and reduced this to .025, using a stack of .001, .002 and .004 heads shims a friend cut for me.
This was a guess and nothing more. Well, I was interested in making a change in squeeze large enough to see any negative characteristics, fine-tuning to come later.
So far, I like this setup. The model goes across the top with more authority, the needle didn't go all wonky on me, the motor gets hotter faster, the runs are still superb. Whether or not I will lower the head further, probably not with the engine on this particular model.
It might be worth noting that I am taking a cautious approach here. On hand is a proven model/engine combination, The World's Most Labor Intensive ARF Flite Streak (TWMLIARFFS) and I will sometimes fly the two models back-to-back in order to avoid any wild claims as to improved performance...or to simply demonstrate that I have screwed up a good thing.
Lines: I have been going back and forth between .012s and .015s, suggest you do the same. In general I prefer the lighter .012s, but one does not really know until testing both sizes with the attendant changes in trim to the model.
The only thing I am comfortable in stating is that on an ARF Flite Streak without adjustable leadouts you are probably stuck with .015s. The leadouts are too far to the rear, but they are even further off when flying with .012s.
Brett has suggested the .012s stretch too much in flight, but I am hard pressed to see this as a negative, at least when used in conjunction with a hard-point handle, Ted's design and from Carl Shoup. More often than not the .015s with their increased drag show me an annoying "belly" to the lines while flying and with some models I get mild to "What was that?" hints of line whip in the maneuvers.
If you don't understand what is meant by "line whip," (cautiously) try a set of .018s. Back when I was flying Combat and we were still using .015 lines Show Biz square eights were pretty easy. When we went to .018s line whip meant this maneuver was real sloppy, which was why some of us at all times had on hand cheater lines for sport flying and general showing off.
Again, try both .012 and .015 lines, although I have had less than stellar results when going much beyond 60-foot line sets, measured centerline to centerline.
Dan
Topic: FP.20 by Dan (Read 4316 times)
