Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Mach racer and engine thrust

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Old 11-09-2006, 06:59 PM
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Default Mach racer and engine thrust


It appears that the engine thrust line is excessive. Has anyone changed this closer to zero, zero? My shrike was at zero, zero with my Jett 46, it flew ok.

Just wondering if the angle of thrust is needed? I know at slow airspeeds and quick throttle up, r thrust helps.

thanks,
rcs
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Old 11-10-2006, 11:03 AM
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Default RE: Mach racer and engine thrust

The plane is very short, having no fuselage. It also has a closely spaced landing gear.
Add to that, it has no rudders. I think the right thrust is necessary. Normally I don't
incorporate much right thrust...a tad perhaps with a tail dragger.

I maidened my Mach Racer a couple weeks age, and it seemed dead-on.

....I would leave the right thrust the way it is.

FBD. [sm=regular_smile.gif]
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Old 11-10-2006, 02:09 PM
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Default RE: Mach racer and engine thrust

I built mine with the right thrust, but without the gear. I launch from a PVC launcher from a slanted table. Seemed to take off fine. There's not much right, anyway.
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Old 11-10-2006, 02:56 PM
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Default RE: Mach racer and engine thrust

Yo, Ed....

....does yours sound like a snare drum when it is flying ? [X(]
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Old 11-10-2006, 04:25 PM
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Default RE: Mach racer and engine thrust

No, it didn't. I didn't notice any noise, but I was using a small prop and a tuned pipe so the frequency would be up there.

I had an elevon come loose or something. It started rolling and ended up meeting the concrete. Concrete-1, Mach Racer-0, engine-0, radio-0. The wire hook that I held it to the launcher with was OK.

I gotta get me another one of those planes and a couple of pylon props. I have an OS .50 and another of the Rossi mini-pipes waiting.
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Old 11-10-2006, 06:21 PM
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Default RE: Mach racer and engine thrust

I'd leave the right thrust alone... it seems dead on to me also.

Flyboy dave,

Mine also sounds like a snare drum as I throttle up and down and if it fly around at say half throttle... haven't exactly figured out where it's coming from to fix it... besides I usually only hear the noise 2 times during a flight

John
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Old 11-11-2006, 01:16 PM
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Default RE: Mach racer and engine thrust

Mine is the same way....it makes that "noise" at throttle up, and just about half throttle.
I never got it above half throttle, in fact I backed it off until that horrendous "noise"
quit, and I just flew it around like that....working on the trims. Then I played around a
bit with the dual rates on the ground and flew it again, but just below half throttle.

The covering on the ailerons is not tight, and when I tried to tighten it up with the iron
it got looser. I was gonna hit it with the heat gun, but I decided to leave well enough alone
rather than destroy the ailerons. They are built-up, and not strong looking. I really didn't
want to go full throttle with the baggy ailerons and destroy the plane because of flutter.

So basically I just got in a couple good "up and downs" and got it trimmed, ect.

The plane was very stable, and actually surprisingly slow on the aileron roll, I thought
it was going to be super quick, and nasty....it was not. I did have it on low rates. I'm sure
that it will be really responsive at speed, and at high rates.

FBD. [sm=regular_smile.gif]
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Old 11-23-2006, 06:01 PM
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Default RE: Mach racer and engine thrust

The vibration (drumming) usually comes from an out of balance prop and or spinner, both balanced an the plane is quite quiet.
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Old 11-23-2006, 07:02 PM
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Default RE: Mach racer and engine thrust

Dave,

Mine rolled so fast you couldn't count them. The guys were laughing because the rolls were a blur. I did have the ailerons sealed with clear tape and was using JR Sport Digital servos. I think I ended up with 75% expo to tame the roll down. I also used 4-40 rods.
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Old 11-23-2006, 08:16 PM
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Default RE: Mach racer and engine thrust

after 3 rolls per second I even get a bit dizzy.
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Old 11-24-2006, 01:35 AM
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Default RE: Mach racer and engine thrust

The plane was very stable, and actually surprisingly slow on the aileron roll, I thought
it was going to be super quick, and nasty....it was not. I did have it on low rates. I'm sure
that it will be really responsive at speed, and at high rates.
....whoops....my bad....when I posted this I was thinking about my Sonic Q-500. [sm=red_smile.gif]

The Mach racer was very quick on the aileron rool with the stock recommended throws,
in fact when I rolled it for the first time it suprised me when it completed a roll before I even got
the stick all the way over....

FBD.
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Old 11-24-2006, 04:12 AM
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Default RE: Mach racer and engine thrust

I have one converted to electric, it is quicker than IC versions with tuned performance engines, flight times 10 minutes plus. Using 2250 5S 2P lipos and turning a 9x9 prop.
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Old 11-26-2006, 10:03 AM
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Default RE: Mach racer and engine thrust

My original question--It appears that the engine thrust line is excessive. Has anyone changed this closer to zero, zero?

I have answered my own question. I removed the right thrust and maidened with a Jett .46.
No wheels, moved the elevon servos topside, sealed the gap on the control surfaces, used a 10 oz. fuel tank and it weighed in at just under 3.5 lbs. I also changed the control surfaces to solid 1/4inch stock. Only beveled the LE.

Good flying plane.

When I purchased my Jett at the Toledo show, I was asked if I wanted to go Fast, Very fast or Really fast? Their .40, .46 and .50

I first placed the SJ .46 on a GP Viper. 3.5Lbs -- Very-fast
Second plane was a Shrike 40. 5Lbs-- below Fast. It was a tub.
Now on this Mach Racer it is Really Fast.

On the bench I see 17,500 rpm with an APC 9X8. We are estimating 125mph.

rcs
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Old 12-12-2006, 12:59 AM
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Default RE: Mach racer and engine thrust

I didn't mess with the thrust angle... seems to fly just fine like it is.

I don't know why, but I never seem to pay attention to the recommended throws. I just follow the TLAR method - "Eh, That Looks About Right". But, I wish I had with this one... my gosh, the first roll was absolutely BLINDING fast and actually startled me. I just took it easy and got 'er down, then promptly tuned the throws down to 70%... now that's better.

I am having fits with the motor on this plane... I'm running a Magnum 46XLS with a 9x9 prop and the Tower muffler. No matter what I do, the darn thing leans out about midway through the flight.... loss of power, then usually a blown plug.

I can think of several reasons:

1) Air leak (Mags are known for this)
2) Tank position... the tank stopper seems to be about 1 or 1.5" below the carb spray bar on this plane... certainly can't raise it easily.
3) Seems to be worse with the Tower muffler. I notice that the pressure fitting hole seems smaller than the stock one? Enough pressure going to the tank?

The airleak option just got handled with a fair amount of RTV around the carb base, needle valve seat, backplate, and everything else I could think of. I'll test that this weekend. But, the tank position... has this been an issue for anybody else?
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Old 12-12-2006, 01:23 AM
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Default RE: Mach racer and engine thrust

Mine doesn't seem to mind the low tank, and the upright engine....

....but then, I'm not pulling high G's with the plane.

FBD.
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Old 12-15-2006, 03:16 AM
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Default RE: Mach racer and engine thrust

Not pulling high G's? C'mon FBD, I've seen too many of your posts to know better than that!

Well, the Magnum 46 ended up blown anyway. Running it on the ground, after a few mins the engine leaned out badly didn't respond to the HS needle at all (started backing that thing out like crazy till it darn near fell out), and ended up overheating so badly it smoked the oil residue off the head. [X(]

I pulled it off the plane yesterday and found no compression without the plug, a very badly abused liner with no TDC taper left at all, and a missing backplate gasket (odd that the parts breakdown shows one, but it certainly didn't come on my engine). I suspect a major air leak was the culprit, as it seemed to only happen after it warmed up... perhaps that unsealed backplate?

Just broke in a new TT 46 Pro... seems to be a great little engine, we'll see how that does on Sunday (weather permitting).
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Old 12-16-2006, 12:31 AM
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Default RE: Mach racer and engine thrust

....sorry about the fried Magnum....[]

I've only had mine up and dowm about 4 times, and it is dialed in....

....now I might cut her loose a bit....
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Old 12-19-2006, 08:48 PM
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Default RE: Mach racer and engine thrust

Well, I can honestly say I did NOT miss that Mag 46 on Sunday. I've now officially swore off of their 2-strokes for good (their 4-strokes are pretty decent IMHO).

The TT Pro 46 with the Tower muffler ran flawlessly and really hauled the Mach around very well.... spins a 9x8 APC on Powermaster 20/20 fuel at 15,700 rpm. On my last few runs, broke out the Cool Power 30% heli fuel... oh wow. Didn't tach it as I lost my flying buddy (what do you hold onto to keep this plane still during a high power?), but had to be in the 16k range for sure... it was screaming.

Just based on prior radar clocking of some of my YS-110 fitted warbirds, I estimate somewhere in the 130mph range straight and level with plenty of vertical.

What a nice engine... now I know why everybody seems to like them so much. Certainly not a Jett 50, but at $85 from the LHS, a real bargain in my book.

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