combatpigg

My Feedback: (3)

Thankfully the props in Eliminator's 6 inch family are $12 and the ones in the 5 inch group are $8.[Not many in the 5 inch family look hefty enough at the hub for a 5/16" hole though..so ask him before you order]]
It's kind of rare that APC does not have a pretty close to ideal prop for every application for a really fair price. As time permits I might take a 6.5 x 5.5 and try to do a complete "make over" on the blades to see what comes of that. The simple chop job of their 6.5 diameter props still gives a decent ride and they put up with most landings when chopped down to 5.5".

aspeed

As long as you have a shutoff, there is a better chance of saving a single blade prop on landing. It will stick straight up when the motor quits and be out of the way. Of course there is always a chance it may not. If you shed a blade for any reason, it will disintegrate the whole plane, not a good thing, but worth getting on video if you do ;-) That plane is really hauling now. Eliminator has a few single blade props to try.

MJD

My Feedback: (1)

The 3x6 (one side of a 6-6) is pretty common as an F2A prop and would probably work well on this. I will definitely run single blade on the forthcoming .15 machine.

combatpigg

My Feedback: (3)

Having the blade tend to park UP is something I never considered.
I think you guys are right...a single blade prop [especially in these smaller sizes] could put these projects over the top without shaking the planes apart.
Same goes for the .049 to .061 projects...if vibration seems excessive it will exhibit within a few seconds after fire up. In that case, just build a Mouse Racer to get some use out of the prop. There are lots of abandoned K Mart parking lots to fly C/L at nowadays.

aspeed

I was told the larger sizes vibrate more, like on a .29 size. The smaller ones are fine, that is unless you touch the tip on the ground for takeoff. Then you have a blurred plane on a shaft run.

combatpigg

My Feedback: (3)

No posts in this forum for the last 24 hours......and so not much to add except for a couple of props have been prepped and tached, ready for the next flying session.
Eliminator G7 is 5.5 x 5.25...this is the only prop of his that I do not see cutting down or reshaping the blades. It is a little toothpick. It runs at 27,000
The G8 is sold as 6.5 x 6 and I broke the first one and botched the video. I have another one RTF as 5.125 x 6 and it runs at 25,800.
If any props get this plane into the 160 mph range, these will be the ones [that I have handy].
I've also got a couple APC 5.25 x 6.25s that run at 25,500 to test. I think that APC props don't take well to modifying and this prop loads the engine down just a bit too much. I'll chop one down to 5.00" and see what happens. Hopefully it works well and then I have a nice low cost prop to get 150 mph out of this .15 with . Realistically, the blades are so thin [it is an electric prop] that it is very fragile and so it might not be so cheap to run if I end up with a piece of it sticking into my neck.

aspeed

The old speed props for the .15's were 6x7, and 6x8". They used nitro then, so a bit less dia. would be needed now. If you can get enough rpm with a 7 or 8" pitch you might get some good speed. Even 25,000 on the ground may pick up to 30,000 in the air. Good luck finding an old wood Revup or Top Flight prop though, and then kiss it goodbye every landing. We used a cheap wood 7x6" prop cut down to about 6" or something for test props, and then when it was on the pipe, and needle adjusted, go for the single blade expensive prop. We didn't even thin out the blades and would go 140 on the old Rossi's. A good 10 mph would be had on the single blade. Maybe a 7x6 MA could be a good starting point to cut down for economy. Wood blades are lighter and strong if you can find them too.

combatpigg

My Feedback: (3)

I would have to be willing to spend much time hitting swap meets, garage sales, on line parts surfing, etc. to come up with bags of the old wood props. Who knows how many of these props got tossed by widows.
These carbon props from Eliminator are based on record holding wood props after those wood props had lots of work done to make them winners. Steve and his Dad were active C/L racers, so their selection is based on more than just their life time in the hobby.
I have reworked MA props for combat to make a OS .32 keep up with the .36s better. The material is pretty workable but the blades get rubbery when thinned down

MJD

My Feedback: (1)

I'd be surprised if anything over 6" pitch was any help. These engines are revvers, and make best power 32-33k. I expect you'll find the Bat's top speed somewhere in the range of 5.5" - 6" of pitch and corresponding blade area to get the in flight rpm up there. Just my SWAG.

Ooh yeah, my Profi pipe is a couple of weeks away.

combatpigg

My Feedback: (3)

Yes, the break in prop was a APC 7x3 cut down to 6 [IIRC] and it was honking...just a hurricane of thrust at well over 30,000.
I'll run through all the prop possibilities on 10% nitro, then mix up a batch of 20% to see how well the engine handles it. The color of the exhaust and glow plug life a dead giveaways. This head button would take about as much skill as I've got to copy with a double bubble chamber thrown in to handle the higher nitro blends.
There are too many other things to do around here before tackling that.

MJD

My Feedback: (1)

I got an FAI and a 10% nitro head button with the Profi. I asked those in the know and they encouraged me to run 10% nitromethane. I'm just putting together a prop list for Steve Wilk, this time I get to include 3x6 SB counter-weighted props, never had occasion to order those before. At $20 a pop, the ***** better stop with the blade up! I need a bench prop too, but I haven't broken any small CF props lately so no feed stock. I bet a CF 5x5 would be close, with some trimming. I will also try some small 2 blade, but I want to one bladers to work.. too cool not to..

combatpigg

My Feedback: (3)

The advice not to exceed 10% is based on lots of bad experience I'll bet.
Lots of experimentation goes into combustion chamber design. I do not know if anyone has figured out a rule of thumb for chamber volume to displacement ratio that can be applied to all engines. I'll bet that there is some consensus amongst engine designers.
The easiest way to increase nitro is to copy the hard work that someone else has done with chamber design..so somebody who has successfully run a piped Profi .15 on 40% nitro ought to be chiming in here soon....
What you really need is a variable compression head to quickly find the sweet spot, or else plan on spending Saturday and Sunday looking for just the right combo of prop, compression, nitro% and pipe length.
This is how some petro-chemical engineer students re-wrote "The Book" on how to run high nitro in Top Fuel..then they dominated the class until their driver Mike Sirotka had a driveline failure and was killed.

MJD

My Feedback: (1)

A lot of what I got from those conversations was actually encouragement for wanting to run a bit of nitro instead of FAI fuel - saying it makes life much easier. But yeah, also that 10% was plenty, more starts to mess up the mojo within the highly strung F2A engines. But 10% = good. I thought it was interesting how foreign these guys thought the concept of wanting to fly an F2A engine RC was. I did sense some skepticism at first until I assured them that I had thought this out quite thoroughly already.

I bet a lot of speed engines have been passed down or over to modellers wanting to tinker, meaning I bet only a small percentage of sport RC speed projects ever started with a call to a speed engine guy to order a new .15 with 359 degree exhaust timing and a pipe that starts at the diameter of a pencil and opens up to the size of my son's latest badly hidden hookah. These odd little projects just happen/happened, and the odd one got reported or documented but not many I think until more recent years.. hooray for phone cameras and yootoob. I only ever saw c/l speed flying courtesy of YouTube, starting maybe two years ago when one day I thought "duh, I can search for control line speed videos on yootoob".

combatpigg

My Feedback: (3)

Yes, this forum and Youtube has accelerated / expanded my learning 1000%

This video should be titled, "Nothing to See Here Folks".
I tried 2 very different Eliminator props and a APC 5.25 x 6.25 today.
The results were very similar, all 3 props registered mid 150 mph passes. A slight edge goes to the 5.5 x 5.75 Eliminator prop. This is the E8 that starts out at 6.75 x 5.75...so the blades look pretty stocky after a simple chop job. http://youtu.be/j0EmiMOmjoE The APC prop is just so fragile, I think your Profi would blow it apart.

klord125

CP.. Absolutely amazing!!!! That thing really hauls the mail...Wow!!!!!

MJD

My Feedback: (1)

Sounds like you are converging on top speed, maybe potential there for 160 and a bit. What are you seeing for inflight rpm now, are you over 30k?

No way I'd run any APC prop on the Profi. CF one blade, and CF two blade bench props. Might look at two blade flight prop later - likely 4.75x4.75 or 5x5 or so, not sure. Probably base the decisions on eCalc and see what 1300-1400 watts will spin at 36-38k. Or base it on the front end of the model shaking off. Eliminator has Cf versions of some of the small lekkie props.

aspeed

That is pretty fast for a motor with no pipe. You may find the brick wall at 160 something. (only?) Every little gain will multiply other gains though. The 10% nitro recommendation is likely from control line speed guys as all the classes are limited to this now. It saves motors for sure, and keeps the speeds under 200 mph which seems to scare the AMA for some reason. The 1/2A's really don't like the 10%. The piped F2A models are revving about 40,000 rpm on pretty much the same props (single blade ones are like magic), so there is a possibility of some good numbers there, maybe somewhat over 200 - 240? There are no lines to slow you down.

combatpigg

My Feedback: (3)

Klord..it's a tough little bass turd..too! The swept leading edge and solid 1/2" thick balsa help it to roll with the punches.

MJD, yes the "wall' has been met with regular props and open exhaust. More fiddling might produce 160 mph with a nitro head and hotter fuel.
The easiest thing to try will be a single blade prop. I'll just order 1 to see what the vibration level is before committing to them. The AMA contest book has single blade DIY hub construction specs, so I should save some broken props and look into making my own SBers. It'll still be well worth it to see how Steve Wilk makes his as an example to follow.

combatpigg

My Feedback: (3)

I might pipe this engine after getting some more fun out. of it as is, but then it will need a bigger venturi for sure. This venturi is a complex looking part that extends down to the crankshaft....so it would be a big deal for me to make one.

iron eagel

Your getting some darn good performance out of a fifteen from what I see.

combatpigg

My Feedback: (3)

I've never flown this class of C/L Combat, but this is what is flown everywhere else in the World [FAI] and you can see why it is popular. 0% nitro, lively performance with very light planes that can survive pretty severe impacts. These engines have been designed over decades of experience to "crash well". Even though they seem expensive at first glance, they run like Swiss watches for lots of pretty thrilling flights.
I've stayed tuned to FAI Combat activity through Rich Lopez's columns in Model Aviation magazine and remembered him mentioning the ZALP as a good alternative to the "bigger names" in the FAI engine World.
Mr. Lopez has been such a huge asset to the C/L Combat community over the years and has always been a great guy for me to talk to for the past 20+ years for his wealth of knowledge.
He's an AMA Hall Of Famer in my book, first ballot, no doubt about it. Ironically, I think he could not care less but he deserves as much recognition and thanks for all he has given to that great sport.

MJD

My Feedback: (1)

Just leave me two or three of the 3x6 CW Profi style and I'll be happy.. That's probably the size you need too.

aspeed

The .15 size is probably the best size motor overall. No .049 miniature problems, and cuts through the wind, and can go 200 mph. I will not post this in the gasoline engine forum threads though. Bigger is better in most peoples eyes. When going single blade, I think a few mm larger dia can be used than on a two blade. It will rev the same, and the tips do most of the pulling IMHO.

combatpigg

My Feedback: (3)

I enjoy the big gassers too..[.when it's someone else who is putting on the show and footing the bill......]
3D is an example of where size helps make it easier for wet power, but the ultra-light electric indoor 3D guys can make it look easy.
I've dabbled with .15 powered 3D and 8x3 props but they just don't have the brute strength and hovering stability of a set up that can make good use of a 12 inch or larger prop.work. I did see an awesome demo by Walt Morris' .15 size Pen Knife Profile plane. It had a piped MVVS .21 and could do real tight knife edge loops....so tight that he called them pinwheels, or lollypops if they ended the pinwheel with a tail slide.
The .15 is pretty versatile though. You can power the 1/12 scale warbirds that were designed for .049s...you can power 5 or 6 foot span RC Combat designs for towing and chasing streamers and a pair of them would make plenty of power for any fairly large bomber project that I'd ever be game to take on.

MJD

My Feedback: (1)

It's hard to characterize but .15's are just a "nice size". Small enough to be cute, but large enough that they deserve a bit of respect, and a hot one is a gnarly little animal.