Piped Stunt engines

After watching some FAI speed ships, R/C Piped planes and some recent views of piped stunt ships I am a bit confused (almost a daily life pattern at this point, but I degress).

Piped speed ships take several laps at very rich settings before getting "on the pipe", and when this happens one can easily see and hear the great difference the pipe makes in speed.

I never hear this in R/C ships or in stunt planes that are fitted with a pipe. Carrier fliers have given up the idea of using a pipe on their planes as it takes too long to get the benifit of the pipe and by then the first seven laps in that event are over without any big time increase in speed.
So, my question is this. How can a tuned pipe in stunt be working other than a muffler when there is no obvious increase in speed or sound?
PLEASE do not surmise that I am against pipes in stunt, I am not! I am simply trying to justify my observation that there is some rather wildly different results happening with piped engines in the different modes. Also, please keep the answer to a level that dosn't involve mathamatical equations or a PHD in Astrophysics.
Joe

Joe:
The big difference, as I understand it, is that pipes in "speed" events BOOST power, while in Stunt, they limit power.

I would question a couple of your observations......I believe that pipes are illegal in Carrier?

I also believe that there is no noticable "spool up" with a pipe.......the motor may be a little "saggy" until it reaches designed resonence, but they sure seem to wind up quickly to me.

See Ya

>Joe:
>.
>
>I would question a couple of your observations......I
>believe that pipes are illegal in Carrier?
>
Yes, pipes are not legal in carrier, however in inticapation of a possible rule change some carrier flyers tried pipes and determined they were not suitable for this event.

A few contests in Navy Carrier have allowed a new rules proposal to be tested- pipes ok but limited to 10% Nitro. Mike Greb is at the forefront of this activity- he's the only one I've observed trying out the pipe. He is very well known locally for his piped Ringmaster which pretty well cleaned my clock in Combat at the DMAA FishFly this year. I was flying a non-piped Skyray and suffered a severe speed disadvantage. The real problem flying against Mike is his height advantage. His fisted handle pummels his opponent's noggin. Many of you all may know of what I speak! All the best,

LAST EDITED ON Dec-09-03 AT 06:29 PM (CST)
 
pipes in
>"speed" events BOOST power, while in Stunt, they limit
>power.
>

Ron B.
F4Fguy

This is a common mis-conception about tuned pipes.A(properly designed)tuned pipe will always boost power AT THE DESIGN CONDITION.It will always limit power at other conditions.Depending on the design the power range can be fairly broad or extremely narrow,but it will always produce more power than the same engine unpiped.The reason speed models "stagger" into the air isn't lack of power,it's because the prop is operating at post stall until it gets up to a reasonable speed to allow the prop to unload.

Brett:I flew speed in the late forties and fifties and even back then you had to"tow"the plane into the air and up to speed.I don't recall anything as radical as a 9-16 on a .29,but,you're right conceptually.Common props were;
ClassA(.19)5 3/4"to 6"D x 5 1/2"to 7"P
" B(.29)6"to 7 1/2"D x 9"to 10 1/2"P
" C(.49)8"to 9"D x 9 1/2"to 10 1/2"p
" D(.60)9"to 10" x 10"to 14"P
From the time I started until I quit in 1953,speeds had gone from 90-100 to over 160,all unpiped.

I remember pipes on speed planes in the 70's and they did indeed take two or three laps before they "came on to the pipe". In fact the first one I ever saw was Jim Rhoades "Rapid Apparatus" in Salt Lake City in 1971. It went snarl, gurgle, snarl, gurgle, crackle, weeeeee. Or kinda lika thata. It seems they are installed opposite those in CLPA models. Backwards if you will. I may full if it, but it looks that way to me. Maybe I was upside down and looking at it wrong.

>I remember pipes on speed planes in the 70's and they did
>indeed take two or three laps before they "came on to the
>pipe".

Something not dissimilar used to happen back in the late 40's (as relayed by my dad, who flew speed competitively back then) - but of course without the pipe. Since the engines were incapable of revving up to any great extent, they used some amazing props. For instance, a 9-16(!) on a .29. WIth a little math, you get a blade alpha of no less than 29 degrees at the tip (and of course much higher everywhere else). That's probably 2-3 times the stall angle for the blade. So, needless to say, it was pretty gutless on the ground. They would whip and whip until the forward motion started unstalling the prop, and then gained thrust, which sped the airplane up, which unstalled more of it, which made gain more thrust, on and on, until off it went. From barely flyable to speed in half a lap.

Of course, power was not in abundance, and my dad set the last "B" speed record below 100 mph - beaten the very next day by someone who broke 100 for the first time, or so he, uh, remembers. Phantom P30 motor, 9-16 prop, some sort of "hollow log Mustang with the fuse hollowed to "paper thin", and the radiator cut off. At least parts of the story seem to be validated by photographic evidence. I can't tell if the pitch is really 16, but it's very clearly *really high pitch".

> How can a tuned pipe in stunt be
>working other than a muffler when there is no obvious
>increase in speed or sound?

The difference between an FAI speed plane and a stunt plane is how the pipe is tuned. The FAI model is tuned to 40000 rpm, and the launch rpm is far lower than this (maybe 15000?, but I am not an expert), and then you count on a combination of unloading and whipping to get the RPM to the point where the HP curve begins to rise, and assuming it does, you get the same runaway RPM effect we discussed in the previous thread, and up it pops to 40000.

A stunt plane is tuned to an RPM close to the ground launch rpm, if not lower. So, it's already close to or past peak before any unload happens - so no tremendous "burst" like you get with a speed plane. In fact, the RPM is prevented from going higher, and in fact the peak HP is clearly reduced from the maximum. I mean, if you are capable of generating 6 hp, and the airplane only needs 1/4 HP in level flight at 5.2 seconds a lap, you better do something.

It's interesting to watch, say, Carl Dodge, fly a F2A. Takes off staggering into the air, really rich, wing bowed like a rainbow, and then after some whipping, the RPM suddenly shoots up to 35,000 RPM, and the plane bolts forward. You think it's on the pipe at that point, but then, all of a sudden, it jumps another few thousand and goes up a note. Only then does he put the handle in the pylon for the attempt.