MJD

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15k with a 12x12? I'd like to see that!

combatpigg

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The power calculator says it would take about 6 HP to do the trick.

speedracerntrixie

My Feedback: (29)

Depending on the condition of the engine when it arrives we will find out soon enough. Just out of curiosity what does the magical calculator say on HP figures to swing the 11X11 at 13,500?

MJD

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No 15cc engine I have heard of generates even close to that kind of horsepower at 15k rpm. A strong ducted fan 15cc at 20-22k rpm might be generating something like 4.5hp. But pull the rpm down that far and I'd never believe it.

No doubt the Rossi is a strong engine, all I'm saying is I think you're being optimistic - those props are some serious shaft load.

So you have a Rossi .60 that turns an 11x11 static at 13,500? That's 2.42hp according to one spreadsheet, FWIW.

combatpigg

My Feedback: (3)

2.8 HP and 140 mph

speedracerntrixie

My Feedback: (29)

That sounds fairly accurate. I will post numbers on the .90 when I get it up and running. Sounds like the same RPM numbers as the 60 but with the 12X12 will be more realistic.

Back to the 60, does that 140 mph figure account for the engine unloading in the air?

combatpigg

My Feedback: (3)

No. It's just the mathematical speed.
By saying, "fairly accurate"..are you telling me that you've already calculated the HP yourself and then verified it at a model engine dyno facility...?
How did you arrive at the conclusion that my 2.8 HP, or MJD's 2.45 HP figure is "fairly accurate"...?

speedracerntrixie

My Feedback: (29)

Knowing the HP figures of some of the .60 size engines knowing that the Rossi had a bit more punch then most engines of that time. The 140 MPH speed is really close to what the airplane did on radar. The last is just plain old experience of 35 years running 2 stroke glow engines.

C_Roundy

Just logging in. Do not mind me.

Edit: Combative pig, what does yer calculator say for a 16x15" wide blade @ 9100 static?

Edit: Edit: James H., I apologize for digressing. You actually have obtained some good pointers for your Mach Racer from the individuals above; (I have one too). Except for one thing- go straight to the 9x7" APC and let it rip. After that, we will talk.

I'm in your corner, Chuck

combatpigg

My Feedback: (3)

Chuck...I don't know if this calculator is as accurate on large models as it is on the smaller stuff I fly. I would think that the larger the model, the greater the error.
The HP figure is taken from standard formulae with hypothetical props...you can choose APC or MAS.

C_Roundy

Hmm. the HP figure I get agrees almost exactly (5.291360256). I have not flown it on this engine yet, the old DZ-1.70 that I gave to my buddy turned the same prop @ 8700 on the same 55% nitro fuel. All I did was re-work the airplane to a DZ-1.75 on spark ignition to get 9100. On the old engine it consistently radar-ed @ 186 straight and level, and would crack 200 out of a dive.

Here is a tidbit for you: We stuck a digital audio recorder in the airplane (having launched @ 8700), and found that it was turning exactly 10900 @ 186, and 11100 @ 200. Go figure..............

By the way, my airplane is not large. We made the molds off an ancient "Royal" .60 sized F-8 BearKitty kit.

James, H., again, I apologize for digressing so terribly.

But I'm still in your corner, Chuck

James c harrell

My Feedback: (18)

Ya'll di-gress! You lost me a page ago. Ran mine with all the props I got. All MS. 9-7, 9-8, 10-6. Gotta go by ear till I get a new tach but the 9-7 MS scares the mess out of me. Really turns up high and I feel like I'm gonna stick a piston out the top! 10-6 and 9-8 sound about the same. By the way, Temps get up a little sitting still. I quit at 230. For me that's a little high. Hope it'll cool when I get it moving, I'll see Wed. Again, Thanks for all the info!

airraptor

My Feedback: (66)

Get rid of those Master Airscrew props. A 10x6 MA = 10x4 APC ...

combatpigg

My Feedback: (3)

Is 230 degrees getting up there..?
Castor smokes at something like 400.
I would look into adding oil..like just take a full jug of any cheap [well, relatively cheap] store bought fuel and top it off with Klotz Benoil or Sig castor....then see what your results are. I've never ruined an engine from using too much oil.
1 quart of oil is enough to spike 8 gallons of "hobby store" fuel. I find 1 quart Nalgene water bottles at the thrift shops for $1 and fit them with the Dubro fuel can fittings. This way I can prepare a small batch of fuel for the day ans then see how it goes.
Commercial fuel suppliers generally put in the least amount of oil that a low revving sport engine guy needs, or that a RC car guys needs..[.which is hardly any for zero load RC car engines that see full power in 1 second bursts.]
Don't worry about "over revving" your engine unless there is a known history that your engine predictably breaks rods, crank pins, bearings, etc. at X rpm. I don't know of any modern sport engines that can't sustain 18,000 rpm if they are adjusted to run relatively cool, relatively smooth and allow the plane to land with an engine that isn't overheated.
Every .45-.50 engine I've ever handled likes 9x8 props on this size of delta and 140-150 mph is a pretty typical result.

I GLADLY take any RPM my engines want to give with the props that I figure will get the job done. It does help to have a way to verify speed to help make informed decisions about one prop against another but for general purposes I like any prop that launches the plane well and still allows the plane to get up to an impressive speed. The best all around prop is a compromise unless you have a specific goal that has no compromise.
Solid metal mounts can contribute to running cooler, BTW. Another way to look at that is vibration dampening is good, no matter how you do it. Metal mounts also sink heat away from the engine.
If your engine is still new, I'd run it with a 8x6 [well under-sized] prop at a slightly rich scream with 20%+ oil fuel for a couple tanks. this helps burnish the surfaces on the moving parts and makes the difference in "spec racing" classes where everyone has to run the same stock engine.
Check the feel of the bearings between runs by forcibly turning the prop back and forth to see if you can detect any "catches" or rough spots. Don't turn it through TDC, just rock it back and forth with some radial [side] force in your hand.

BiggerDanno

For what it's worth, I'm currently having fun with my Mach Racer with a West 50.
Couldn't get it tuned right on a 9 x 7, I think the pipe is too long. It loves the 8.8 x 9.25 pylon prop though. Turning over 20k static, appears to be around 120-130 mph.

If I were you, I'd remove that pipe mount from the fin and attach it to the fuse. Those fins break easily and don't need the extra vibration from the engine going thru the pipe. When the fins do break, replace them with solid wood, they last longer and are easier to repair. The weight difference is very small and needed as ballast as the plane is nose heavy.

I've also found that the plane likes the higher rpms of the West vs. the Magnum 46 I had on it previously. The lower rpms of the Magnum would create harmonics in the covering that would cause it to blow a piece of covering off every flight. Have not had that problem since I put the West on it.

MJD

My Feedback: (1)

You're actually taching over 20k on the ground with that prop...? I can't argue with measurements but that seems high.

Eventually I ran the 8.8 x 9.25 props trimmed to 7.9"-8.0" diameter on my West .50.

Of the APC sport props, I think 9x7 is too much shaft load for that engine, but 9-6 is a good test flight prop. Pulls like a mule but keeps the speed in check (as in only about 120 on a clean airframe).

I'd be surprised if your Mach Racer didn't pick up some speed if you dropped the pitch a bit - have you run 8.5, 8.75" pitch? I could be wrong, but it's comparatively draggy to a Demon and maybe the Magnum R and the 9.25 seems like a lot of pitch.

vicman

My Feedback: (10)

Definately!

James c harrell

My Feedback: (18)

All-right guys. MS out the door . Put the APC 10-6 (all I had) on it and it almost came off the table. So I shall start over with them. Also found out why my tach wouldn't work. They don't work indoors! Light bulbs it seems. Befor you ask I have my table set up indoors with a vent system and all. Guess you all knew about the indoor thing with the tach but like I said befor I just keep learning. I'll check some RPM's outside in the morning, with an APC.

vicman

My Feedback: (10)

Why aren't you going with the 9x7, 9x8 as has been repeated numerous times? They really aren't that rare and are what you will most likely end up using.

MJD

My Feedback: (1)

I'll bet it did. You will get all kinds of static thrust with the 10-6. But static thrust is meaningless when it comes to speed potential. Flying the Mach Racer on a 10-6 is equivalent to leaving your car in second gear. It will accelerate hard from a hand launch or slow flight, vertical will be outstanding, but top speed will suffer. Good test flight prop is about all. Putting a positive spin on it, if your eyes & thumbs aren't happy with the speed of the aircraft it is a good prop choice to limit the speed to manageable levels while you get used to it.

James c harrell

My Feedback: (18)

I got to test top three planes wednesday. Been cooped up in the house to long! I figure it like MJD said and think it best for the first couple of flights. I will have a couple of other APC props by that time(9-7) (9-8). That and the Previous owner shipped her to me with this prop and said it flew it pretty good and he has been a great help. I have moved the pipe mount, the rudder mount didn't look rigid to me. Through the wing is better I think.

MJD

My Feedback: (1)

It'll fly fine on the 10-6, no doubt about that. But remember this is a forum for speed junkies, so if you mention any potential impediments to top speed you'll get an earful about it [8D].

Get it trimmed out, get used to it, then try the other props. Expect a little less acceleration from the hand launch, but don't sweat about it, those props still pull well. And as far as top speed, you have a throttle.

As an example of the difference, I fly a 32" span 4.25 lb delta on a piped ducted fan .65 with a control line speed prop - 8.2x11. At launch/ground rpm it is probably producing north of 3hp. But.. static thrust is little more than the weight of the aircraft and hand launches are a total b as it crawls away with little to no control authority and threatens to torque roll into the ground. However, as airspeed increases and the prop starts to work more efficiently, it's off like the roadrunner. Yet, I could probably hand launch the same aircraft vertically on a sport .46 with a 10-6 prop, but it would cap out at maybe 100mph.

BTW anything lighting powered by AC is a problem as they fluctuate at 60Hz which is the same signal as a 2 blade prop at 1800 rpm (or higher for compact fluorescents). Daylight or a strong flashlight best. In the days of Heathkit build-it-yourself tachs, calibration was done on indoor lighting.

James c harrell

My Feedback: (18)

Yea I figured out about the AC bulbs but figured it should read 60. Could understand 120 on 2 blade setting but mine reads a steady 360 when put to a house light.

MJD

My Feedback: (1)

60Hz = 60 cycles per second.

Each AC cycle (sine wave) has two zero voltage points and two peak voltage points, so the flickering occurs 120 times per second, or 7200 per minute.

When the tach sees 120 flickers per second - and is configured for two blades - it interprets that as 120 blades per second, or 60 revolutions per second, which is 3600rpm.

Voila!

James c harrell

My Feedback: (18)

AAHHH! Makes sense. In that case, my tach is working fine, and with a APC 10-6 it turns 15100. Best I can get. Motor does have some age and I have a newer one with little run time I can try. Also have a Rossi 53 I could try. Have no idea how to set that one up. Has two different carbs and two different exaust. I flew it on a very heavy Great Planes F-15 a couple of times but not much. But it ran good and turned hard with the tuned exaust.