combatpigg

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It's been ages since I posted anything here except for a bunch of static [], so here is a small contribution to the forum. It's been so long since this project was started, IIRC it was a Top Flite .20 sized model? I saw a video link posted here of the same plane about a year or 2 ago and thought it was impressive.
This model was thinned down slightly in the fuselage [from the stock kit], but the wing is built "as is".
The engine has a home made venturi and will run off of a combat bladder for now. I made an exhaust extension to help keep the hot goo out of the engine compartment, but there will be no exhaust system.
For starters I'll try it with 8x8 and 8x7 props.
Oh ya, there is one of those "How Fast" gizmos in the wing. Let's see how long those air sampling tubes last down at the hay field.

Flyboy Dave

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....that looks like a nice little plane CP....[sm=thumbup.gif]

[sm=teeth_smile.gif]

Lomcevak Duck

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Oh my, I think I've got another project on the list...

vicman

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One of the guys in my club did the same engine in a HOB P51. It zipped along pretty good too.

combatpigg

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Those Mustangs are faster than they look sometimes [or maybe I got that backwards?].
I've seen what look like new, "from the ground up" Mustangs being built at the Chino Airport. That place is a must see for all airplane nuts traveling through the area. They've got a little bit of everything there.
A OS .32 sat on display at the LHS for several months at $107 until the news that they got discontinued. Some lousy%&*@ bought it before I could [&o]. Probably one of those guys who will use it once, crap his pants, then let it sit in his sock drawer for the next 20 years .

Lomcevak Duck

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My LHS still has one in stock. I was thouroughly surprised when I saw it this past Saturday. He's a high volume shop, and I bought one of the only two he had at the beginning of last month.

I guess everyone is waiting for that new .35AX racer engine...

Have you run that .32 like it is yet?

combatpigg

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I ran it last Summer with about 2 weeks of practice time for AMA Fast Combat [The Bladder Grbber]. I had the usual .36 Fox Combat Specials ready to go and just ran the OS.32 out of curiosity. The .32 became the pick of the litter and ran best with 8x7 MAS props that had the blades thinned way down and shortened to about 7.5". It was keeping up well enough with the Nelsons to be competitive.
I could kick myself for walking past that other .32 at the LHS now [&o]

combatpigg

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Here is the flight report......kind of fast and a little bit tail heavy and very loud. It is running a 8x7 prop at 18,000 on 30% Wildcat heli fuel that has 8 ozs of castor added.
The plane takes quite a bit of effort to hold in my left hand while I fumble for the TX. The problem is that it dives to the ground on every launch...you have to give it full up and hold on til it starts flying.
My little .049 Cyclon powered Mustang does the same exact thing. Seems like the plane should just blast off straight up like a rocket?
Anyway, it flys just fine and takes forever to land. I'm going to add some weight to the nose for a less touchy elevator, I don't like having to use dual rates.
The plane weighs 38.4 ozs, which is surprising if you knew how much fiberglass, bondo, paint, etc. is on it.
I'm using a Berg 4 channel RX, HS 225s for aileron and elevator. I thought about using an engine kill, but it's only .32 powered. The battery is 350 mah.
The "How Fast" says it did a best of 174 mph, what do you think about that? NFW?
The .32 did about 110 mph clocked [over and over] on 60 foot lines, towing a CL fast combat plane, I expected about 130 mph on this RC plane.

Strykaas

Nice
Actually, when you add up the free exhaust (power and missing draggy mufller), and the sleek lines of the aiframe, well, I think it could be true... Where were the pitot tubes mounted ?
A 60 ft line is very short for timing a 150 mph aircraft [&:]

combatpigg

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The tubes are mounted in one of the rib bays near the wing tip. The How Fast is recording the fastest speed measured, so the readings will always be from a dive. I'll try it again today to compare results. The makers of the HF will replace it unconditionally up to a year, even if you crash!
The fun part of having it is being able to make changes at the field and getting an instant read out of the results. So far those tubes have survived plowing through the grass when it's time to land.

freakingfast

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That's realy, realy cool CP![sm=thumbs_up.gif]

combatpigg

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Thanks FF......you too could be the first kid on your block to build one, because I just found the plans after doing an archeological dig on my building table. The plane is made by House of Balsa, not Top Flite. It is .20 sized.
I crammed an oz of lead in the nose and will do more serious R&D work today.

combatpigg

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Just got back from some serious R&D with the Stang. I was wearing the white smock, had the clipboard, WD40 pen holder and big thick "no poon" glasses on.
The first flight was with a 8x7 and the read out was 129 mph. It was just slightly rich, but not a bad needle for the first run.
The 2nd run was with a 8x8 and I didn't have to touch the needle, the extra load cleaned up the mixture and it sounded great. The read out was 137 mph, and it did seem some what faster.
The next step will be to rig up the tuned pipe and set the spinner up to accept the 7.2x8.6 prop.
Is the tuned pipe worth the extra money and drag? Stay tuned.
This How Fast doodad is fun to have. It's like having a cheap tach, you have to learn to dismiss the garbage readings I guess.
The extra oz. of lead in the nose really smoothed the plane out, but it still likes to zoom towards the ground every launch [X(]!!

Strykaas

Sure it's worth it.

combatpigg

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......but with open exhaust you can fly the plane at night [X(].

Strykaas

combatpigg

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OK, we're on the pipe now. The plane sounds much nicer, it seems quiet now. The pipe is musical, open exhaust is just harsh.
I needed to open the needle somewhat, to accomodate the extra fuel demand. The engine really needs to consume a lot more fuel for a modest jump in rpm.
The first run was with a 8x8 and it hit 139 mph....and it blew a plug.
2nd run was with a 7.2x8.6 competition prop and it slowed to 135 mph, also blew a plug.
3rd run with 8x7 and it ran 130 mph but really sounded good and flew fast laps.
Switching down to 15% nitro didn't effect the speed much on the rest of the runs and eliminated the blown plugs.
This combo really flys great, I don't remember who to thank for posting the video last year of this set up.
I guess the last thing to do here would be to reinstall the stock carb and see if this C/L venturi was worth the trouble.
Installing the pipe is a plus, it didn't throw the CG off or make the plane feel heavy. It is kind of expensive though, I think you could pick up a used Q40 engine for about the same total cost and have a real raped ape on your hands!

vertical grimmace

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CP, you are flying .32 sx and Foxes in fast combat over your nelsons? I have been away from CL combat for a little while and was wondering is everyone backing off a bit? Those N36 engines sure are fast.
How did the Bladder grabber go? Great looking Mustang. Don't mean to hijack the thread, you can keep your reply brief.

combatpigg

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VG, It isn't worth it for me to run Nelson .36s for 1 fast combat contest a year [if that] any more. There used to be 5 or 6 contests within 300 miles per year and running a Nelson made sense then.
The 80 mph event took over in popularity...a LA .40 will do that number with a 9x6 and the action is real good.
The sport looks to be on its' last legs [this time, really] any younguns' that are in it are there because of their Dads' full ride sponsorship, but I don't think there are enough of them to keep AMA Fast going. FAI is a different story, I hope it stays around for a long time because there are all those very cool .15s still being made.
I think I saw the Bladder Grabber on the contest calendar for this year. It isn't for at least another month yet. In the mid 80s to mid 90s the turn out was from 50-100 flyers each year. Bob Carver used to bring over the best Soviet pilots and set them up with engines that they adapted to their FAI models.
The Nelson is still the engine that 99% of the guys and gals run. The Jett .35 has been tried but it doesn't put out enough. The Foxes were great in their day but don't have it any more.
I might swap a Fox .36 into the Mustang if I can find a low timed liner laying around.

Strykaas

CP, I quite can't understand why it blew a plug with a 8x8 and that it did not with a 8x7. To me, when propped with a 8x8, it was maybe too lean, or the 8x7 setup was too rich... A 8x7 will turn faster and as such it would burn plugs more easily...

Are you refering to this video ?

http://uk.youtube.com/watch?v=DKHIFDW7VoA

combatpigg

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Strykass, the difference between the props is the load, which effects the heat generated. After a hard run with the 8x7 the engine is cooler, even though the rpm was higher. The engine developes more HP with the 8x8. How do I know this? Because the 8x7 runs with the needle closed 1 click or 2 from the optimal setting with the 8x8. Fuel demand and power output go hand in hand. The 8x8 will make the needle much more critical [compared with the 8x7] and increase the chances for a blown plug because of over leaness, but over leaness isn't always caused by just a bad needle setting.....it can be the result of the engines' fuel demand increasing on its' own during the run as the conditions optimize. I see it as a run away condition that too much nitro or compression can cause. You can set the needle for a very clean sounding run if the nitro and compression is right without blowing plugs every run.
The 8x8 continues to prove that it is the fastest prop for this engine/plane, but the 8x7 might be the best on the race course.
I'll have to leave this computer idle for an hour to watch that video link, but it is probably the same one I saw. His rating system is inflated......pretty fast is 160 to 175, pretty damn fast is 176-185, Pretty f&*%#$%^& fast is 186, 195....and so on

combatpigg

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I ran my oldest Combat Special today, a MKIII. It came out in the 70s [I think] and was iron piston / steel sleeve. They were known for breaking cranks, rods, eating circlips, you name it. I bought it used and through the years changed every part in it with after market stuff. Brasher crank, Athens ABC P/L set, RPM rod, Glen Dye head button. The neatest add on is a home made diaphram actuated pressure regulator that cost $20 each....made by a local genius [Norm McFadden]. You can set the needle on the ground the way you want the engine to sound in the air and it only allows fuel to pass through the check valve if the engine is pumping. It is like taking a 128 thread per inch needle and making it a 600 thread needle.
The first run with a 7.75x6 combat prop netted 20,800 rpm on 15%. Not bad for combat.
Next run was with a APC 8x7 and it gave 17,900. Not bad, but not worth the effort to put into the P-51.....
Maybe after a couple of beers........

vertical grimmace

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I sure love my MK III combat special. I also have several MK IV as well. For some reason I always stuck with the MKIII for contests. Never let me down.

Strykaas

Thanks CP for your explanation

combatpigg

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You're welcome, Strykass. Running a high pressure bladder takes the fuel tank level problem out of the equation..it works in reverse actually. As the bladder empties, the walls of the latex tubing return to their original thickness and fuel pressure goes up slightly, plus it is less affected by G forces. This can back fire if you over inflate or use an old bladder........or get "sold" on a needle setting before the engine is warm.
Finally, I do believe that not running enough oil compounds the problems and you might as well keep adding oil to the mix until you see ill effects, then back off.
VG, one of the local "greats" has MKIIIs with so many miles on them he has to Locktite the bearings to the case. An old guy gave me a box full of olden Fox engines and there was an ancestor to the 36X in there. It had the square intake, but kind of looked like a genetic mutant 35 stunt [baffle] engine. It totally screamed! It wore itself out because of rust, but was easily capable of 100 mph way back before I was born.