MJD

My Feedback: (1)

Thought I'd post new thread on this and a quick progress report. The model is a Boomerang from Soaring USA, 118 sq in., weighs nothing.

I've chopped the nose, fitted an engine mount plate, blended the plate into the fuse sides with epoxy filler. Mounted the tail group, that took a lot of jigging and fussing before I was settled on the stab incidence. It is a precision molded model, but even so the stab could slide back and forth a touch either way which alters the incidence angle. Total weight as it sits here is 202 grams. Add nose and cowl and gear and should come in at or under 10oz. That's a 4-1/8"x4-1/2" prop on there now, I am prepping a couple of 4-1/8"x5" as well, probably have to go down to 3.9"-4.0" dia.

The big job will be the cowl plug and mold, but it is midwinter..




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Mr Cox

I'm working on a sheet wing racer...
Haven't decided yet between a Norvel or a VA .049 MkII RC in the front.

MJD

My Feedback: (1)

Nice. And it has a turtledeck and canopy too?

This pylon model has wing so thin it may as well be an SWR. Even the vertical fin is made in a CNC two-part mold - the maximum thickness is 0.075"! It is a clean ship - and the inside is about the perfect cross section for a bladder and 1/2A gear.

aspeed

I've been thinking about the sheet wing racer (Killer Buzz) with the Fora, but need to develop my flying skills or at least get a mini throttle or shut off. I'll probably just use it on a 1/2A combat plane that is sitting around. I should have got the motor you did, my Fora won't work with a pipe or rc carb at all.

combatpigg

My Feedback: (3)

Looks like a couple exciting projects brewing...!
Don't forget to tether the engine to something solid in the heart of the plane.

MJD

My Feedback: (1)

For reference, it took about 30 minutes to deflash, shape, detail, and smooth sand one Eliminator E-6 4.125" x 5" prop today. Maybe I'll get faster with practice. Still haven't balanced it yet, I'll batch that job. I sure hope they don't break on this thing as often as on deltas*. With the inverted engine and small props on this thing compared to the size of the jug, they are only in big danger if they stop close to vertical.

(*What's the sound of a delta with a carbon fibre prop landing? "$nap")


I wonder if I could turn down the fins on the head a bit.. maybe match the cylinder diameter and taper the od.

Man I am itching to see how thing will perform.

Mr Cox

Yes, the idea was/is to have the aileron servos on top of the wing, so a canopy will allow for that. I'm just making things up as I go along though. It ended up a little too small perhaps, but I wanted something fast...

What wing-span (and thickness) does the Boomerang have?

MJD

My Feedback: (1)

Here are the published specs:

[TABLE="class: product-properties, width: 907"]
[TR]
[TD="class: property-name"]Wingspan[/TD]
[TD="class: property-value, colspan: 2"]30 in[/TD]
[/TR]
[TR]
[TD="class: property-name"]Wing Area[/TD]
[TD="class: property-value, colspan: 2"]118 sq in[/TD]
[/TR]
[TR]
[TD="class: property-name"]Wing loading[/TD]
[TD="class: property-value, colspan: 2"]15.9 oz/sq ft[/TD]
[/TR]
[TR]
[TD="class: property-name"]Airfoil[/TD]
[TD="class: property-value, colspan: 2"]MH42 Mod[/TD]
[/TR]
[TR]
[TD="class: property-name"]Length[/TD]
[TD="class: property-value, colspan: 2"]23.5 in[/TD]
[/TR]
[TR]
[TD="class: property-name"]Weight[/TD]
[TD="class: property-value, colspan: 2"]13 oz RTF[/TD]
[/TR]
[TR]
[TD="class: property-name"]Controls[/TD]
[TD="class: property-value, colspan: 2"]Ail-Ele-Throttle[/TD]
[/TR]
[/TABLE]

The numbers above vary +- a few % depending which website you look at. When I get back home tonight I'll measure the wing thickness. Considering the flying weight will be 50-60g less than electric, it ought to turn okay.

MJD

My Feedback: (1)

Not sure mine will either - it is not the pipe timed version. I have been trying to get one of those too, they were supposed to be available Jan 2013, but they have not materialized yet - I ask again about every 3-4 months. Independence movement in Ukraine causing problems so I am told.

BMatthews

That sounds like one of those "don't ask me how I know" sort of statements....

MJD, I'm curious why you mounted the engine inverted? It's likely to lead to a lot of dirt and grass packed into the head and cylinder fins as well as dirt and grass up into the intake.

I understand the desire to save on prop breakage but I think I would have gone for an upright engine with a single leg or maybe double wire whisker off the engine mount as a landing skid(s).

aspeed

We damaged a lot of plugs with inverted heads on speed planes. I would go sideways or upright myself. It doesn't look as nice though. One spec. you missed on the carbon fiber plane was the $200 price tag. Yikes!!!

MJD

My Feedback: (1)

CP does indeed have a story to go with that recommendation, I think it's titled "Where's the #$%@&$%g $175 Cyclon that used to be on the front?". I plan to follow that lead about safety lanyards.

Prop clearance wasn't my goal. I wanted to keep the airflow around the center of the wing as clean as possible so I fit it inverted. The engine will have a full cowling with intake air and cooling air inlets, and the cylinder won't touch the grass. I fly off grass fields so I am not worried about mucking up the engine, but I'll check the intake and cooling passages anyway after each flight. I plan to avoid wire whiskers, too draggy, but had thought about those at one point. Although this started life as a pylon racer, the goal is top speed on an .049, this model seemed like a good start.

Aspeed - yeah I left the price out. The aircraft at $199.00 still cost $16.00 less than the engine. Add Rx, battery, servos, and a few CF props and yer talking about a $550 1/2A sport plane. But - it ain't no ACE Whizard with a TD. And the build quality on this thing is out of the world. Honestly - I have the choices of (A) $75 kit (of what?) + 40 hours + finishing materials, (B) build from scratch at $50 materials plus 80-90 hours, or, (C) $199 prebuilt insanely clean ARF + 25 hours of mod work. I liked this idea, made sense to me rather than dreaming all winter about finishing a dedicated speed model plug and mold - I have other priority projects to finish.

If I can't crack 140 - then I'll feel like I spent too much. To that end I'll be trimming those props until I get about 35-36k in the air and watching performance gains/losses in the process. What I can't figure out is if it might be faster if I clipped the wings down to 95 - 100 squares, or left the funky tips as is. IOW I wonder if the big hit will be on turning performance or top end, I suspect the former. But for now - as is.

DeviousDave

If I might make a few suggestions, as a former manufacturer of planes like your Boomerang:


1) get a 30mm spinner from MP Jet-that's what the airframe was intended to have on it.
2) With that 30mm spinner, you are free to mount the engine further back in the fuselage, which will mean not having to deal with balance issues
3) Rotate the cylinder head so that it lines up with the wing/fuselage junction-it's already a draggy area where the wing and fuse meet, why have the jug sticking up or out in the breeze in addition to that drag?
4) build a speed bonnet to reduce the drag behind the cylinder head.
5) I'm not telling you to use Electric pylon props from APC for safety reasons, but they are very worth looking into. Start with the 4.1-4.1 and go up from there until gains aren't realized anymore.

MJD

My Feedback: (1)

Good stuff. I thought about a spinner but reasoned that I could be using props as small as 3-3/4" diameter - of which a 30mm spinner would be 35% of the diameter - and wanted to preserve the inner blade area. I looked to the F3 speed models for inspiration - many of them taper their cowl nose down sharply after the crankcase, and go right down to a spinner nut. And they go real fast. Others do use small speed spinners and a more gradual nose taper. So on this one, I intend to build the lower cowl onto the fuse, and taper it smoothly down to the groove in the prop driver OD. I think I can soften the transition a bit on the top half.

As far as balance goes, I believe it is going to come out alright, I have already roughly dry fitted the components and checked it out. It definitely was not going to work with the engine out front on the stock nose ring, so that's why I went back the distance I did. I'll use a 250mAh 2S LiPo, they're skinny, and get it far back in the boom as I can, with the elevator servo directly in front and Rx opposite that. If I end up with - worst case - 10 grams at the end of the tailboom, I'll still have a sub-10 ounce aircraft. But of course I hope to avoid that.

The APC 4.2x4 1/2A prop is a good performer on these engines. I need to prop in the 35-36k range for maximum power output, which precludes anything bigger than the 4.2x4 which will not quite get there. The 4.1 x 4.1 is right in that sweet spot. There are several good candidates available in CF from 1/2A speed prop manufacturers. Since this is not a piped engine, I have more latitude in prop choices for experimentation. I've considered a dump on the pressure bladder for engine kill, triggered with full up travel, or something along those lines.

So you figure that it would be less draggy to rotate the engine to put the head in line with one of the wing/fuse junctions? Hmm. I wondered if I could smooth things out in that area by adding more in the way of wing fillets.

Anyhow, I am committed to this path for now, so I'll see what happens.

DeviousDave

Half of the fun is in the experimentation, but FWIW, Matchless incorporated my suggestions when he when from his original Caliente to the second version and there was a significant increase in speed.

On a related note, I know everyone has their own ideas about props, engines, and how to prop engines... But hear me out. You want a 'square' prop, one that has the same pitch as diameter. One with thin blades. IMO, the APC's that are available for 1/2A engines-while available and fast enough for sport flying-just aren't up to what you want to do. One of the bad things about 1/2A sized airplanes is that prop efficiencies fall off a cliff under 5" so conventional wisdom sometimes goes out the window when basic things are less than optimum. You can't just prop for peak hp on the ground-especially when the engines have so much overrev capability like these F1J motors do.

Long story short, you might find an electric pylon prop with a little more load to be better than a 1/2A prop that makes peak power on the ground. A clean airplane is going to unload a lot in the air. Again, others won't agree, but I know that a Cyclon will turn a 4.7-4.7 at 27,500 on the ground and the F5D's at the time the Cyclons came out were doing 155-160 on that prop at that rpm. A little less load that that would be a good place to start. A 1/2A has a big advantage over an F5D airframe because the electric planes weighed 3 times as much back then so the induced drag was considerable.

DeviousDave

Or, put another way, you want the engine to unload to the peak hp RPM number. Revving faster than that is past peak torque, meaning you could be running more pitch.

MJD

My Feedback: (1)

That was indeed my intention in terms of prop load - to have it unload to peak hp in the air, not static. I have yet to systematically bench run the engine and get a feel for it, so even though I am merrily deflashing and balancing props, they might all end up back in the drawer, who knows depending what I find out about this engine's prop turning abilities. I'll take a look at some of those lekkie props for sure. I've never flown 1/2A proto or speed or the like, so this world of tiny props is new for me. This airframe ought to both glide well, and fly well on greatly reduced power - so a poor prop choice or rich run shouldn't have to end in a powered descent into terra firma. At least I hope not. Just thinking about the virtue of injection-molded props.. and again, about a means of pulling the plug on the engine.


A big part of this project for me is getting a taste of 1/2A performance potential without excessive work. The cowl will be a pain but the rest of the hard work is done. I just wish there was a 95 square inch all composite lekkie pylon racer like this out there. Another part of it is testing out the viability of these lekkie to glow conversions for sport speed - I would love to build a model for an F2A .15. This sort of thing has gone on in Europe for a while, with mixed results as I hear - but I believe it came down to the fact that dedicated IC designs were the way to go for all out straight line speed results. Me, I'll be happy with what I get, it will be maneuverable as heck, and a fun learning platform. Handled right these engines just go and go, the airframe is more than up to the weight and power, so after trimming and debugging this should be a fuel-and-go 1/2A maniacal sport model.. sounds like a winner to me.
.

MJD

My Feedback: (1)

The prop I had in mind to start with - after a couple of trim and checkout flights on a combat prop - is the 4.25 x 4.5". I compared blade thickness to an APC 5x5E - the CF prop was 0.005" - 0.010" thicker across the high point across most of the span, but tapered down closer at the tip. About 0.070" near the hub, 0.035" at the tip just before it tapers off, where I measured 0.030" on the APC.

I'm sure the small APC lekkie props are "fine" on the 1/2A motors - I have a hard time believing the intermittent power pulses of an IC engine are really so much harder to endure than the abuse heaped on these props by sudden applications of massive torque from a hot electric motor. I dunno. I hear a lot of stories of people using them on hot 1/2A motors and none of them ended with graphic descriptions of blades being shucked. Yet don't folks spin the 4.1 / 4.7 / 5.0" props upwards of 40k at times on electrics? Or have they gone CF by then?

aspeed

I would try the electric prop, but wear a face shield for a bit and stand behind it for a while and check for cracks yada yada. The manufacturer of the prop has a flyer that says the max rpm to go. My Fora .15 was well within that on the 7-5 prop that I used. I think I could have got up to 23,000 or 25,000 and it 'only' did 20,500. so even unloading 3,000 in the air would have been safe. It wasn't an electric prop though.

combatpigg

My Feedback: (3)

I'm curious what you'll find with a 4.2 x 4.5 prop. What happens with these engines if you overload them is the piston gets too hot and you'll never find a good needle setting.
I've tried going below 4 inches in diameter and couldn't find gains in flight.
Regardless of what I've found, those results were with my planes, my engines, my fuel, etc. and not your's.
I can not honestly say that I invested much time in experimenting with props after finding the 4.2 x 4, so my opinions are based on limited custom work with the pitches higher than 4.
I just got an impression that the 4 pitch was a "wall" for .049 - .061 engines to turn at any usable diameter and gave up trying.
I seem to recall trying the 4.1 x 4.1 but do not recall the exact results.

aspeed

I kind of recall a 1/2A speed guy using a 5" pitch single blade prop years ago, saying that just in case things go right, that that would be the ticket. He did go very well. Since then however the nitro was limited to 10%, so now I am guessing a lower pitch is used with higher rpm's, although I can't say for sure.

MJD

My Feedback: (1)

CP - I had every intention of consulting with you about your trials and tribulations with 1/2A sport speedsters and props. Like you and DD, I suspect there is little joy in much smaller diameter. But with the light wing loading of this thing I'll be able to try all sorts of things without fear of crappy launches etc. I'll start with a combat prop to trim it out and get a feel for it, then 4.2x4, then the 1/2A speed props.

aspeed - I do intend to try one bladers, this was part of the master plan. If I spring for the Profi Junior and do a similar project with that, it will be on an F2A prop of course. Typical 1/2A SB sizes are 2-1/2 to 2-5/8 radius x 4-1/4 to 5 pitch. That radius gives more disc area than the 4.1-4.2 diameter props.

aspeed

Yes, I think the tip does most of the pulling anyway, so having a little more dia. is a good thing. I had heard a little heavier on the blade side when balancing is good.

combatpigg

My Feedback: (3)

It's really important to use the least amount of compression that will allow the engine to operate while you are experimenting with different props. The "Combat Guys" will even pay some attention to this while running the toothpick props that they do.
The only thing close to extensive experimenting with Eliminator Props I've done was with a high timed G&Z .061. By saying "extensive" that meant I tried 5 or 6 different 2 blade props that sounded feasible.
Back then I didn't measure speed, I just was happy to see a complete run without frying any parts.
Back then I was several hundreds of dollars from understanding that setting the compression for the least amount that will get the job done is essential. I also learned [too late to save my interest in running G&Z engines] that it's possible to get a winning combo of load, compression and fuel mix..and still get half way decent service life from the engine parts.
Running the lower timed combat engines is really the best alternative unless you plan on setting a new official speed record. You can get hundreds of totally awesome runs from the same engine with standard sized APC props.
That's about as picked as my brain can get, I'm afraid. The results I got working with the G&Z were confusing because nothing was repeatable. I don't remember EVER getting 2 good runs in a row and a lot of that had to do with my lack of experience.
By the time I switched to Fora and Cyclon I was so thrilled with the APC 5x3 and 4.2 x 4 that I did very limited searching for anything that worked better.

MJD

My Feedback: (1)

My first E-6 4-1/4" x 5" prop ended up a 4"x5" after I dropped it and nicked the tip..

Are you kinda suggesting working through the props until identifying what seems to be the best performer, then looking at compression to optimize performance after settling on the load?