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Many questions about tuned pipe set up. Experienced help please

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

Many questions about tuned pipe set up. Experienced help please

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Old 11-14-2013, 09:48 AM
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CafeenMan
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Default Many questions about tuned pipe set up. Experienced help please

I have never run a piped engine. I've had one pipe for years that was never used. It was a .29-.40 pipe for I don't remember what engine. Maybe my old OS .28. Irrelevant.

I now have two OS .15 CV-A engines. These are the most fantastic engines I've ever had. Went to Tower a couple months ago to buy four more just because and found out they're out of production.

Anyway, I have a header and a tuned (not muffled) pipe for one of them. I don't plan to pipe the other but know I can get pipes and headers even if the engine is discontinued.

Yesterday I received three (3) NovoRossi Rex RFX-15TC engines from Planet Hobby (http://www.planethobby.com/collectio...ducts/rfx-15tc).

I want to put all three engines on one plane so am willing to give up extreme performance in exchange for more reliability. If I build this plane I am strongly considering mixing the two wing mounted engines to the throttle from a separate channel. When it comes time to land I can cut the wing engines and come in on the fuselage mounted engine thus taking out the risk of an engine dying on approach. Don't know if it's a good idea or not but something I'm thinking about.

I plan on using 15% fuel even though I have some 30%. Again, I want reliability over speed. Allen at Planet Hobby assures me that the plugs that came with the engine will like the 15%.

All three of these engines are rear-exhaust. I have identical headers and muffled pipes for all three engines.

Now I may make a twin with two of them and use the third on something else. But I really want the three-engine plane so I might buy one more.

OK, on to questions.

The OS has a header that is a little over 5-1/2" from the center of the plug to the end. Seems WAY too long as a starting point.

Question 1) Is there a safe header starting length so I can pre-cut off a chunk or do I start tuning with it as is?

Question 2) Are head shims always a necessity with pipes or is it a "maybe I need them and maybe I don't" situation?

Question 3) How do I even know if I need to add shims? What are the symptoms I will see?

Question 4) I didn't get any silicone coupler tubing. I looked around Tower and they gave some I.D. dimensions but what is the rule for choosing the tube size? I assume if it's too small it will seal but have a short life.

Question 5) If I build the triple engine beast then I will get the engines as close to the wing root as possible. I'm assuming I will never use a prop larger than 7" so will put the centerline of the engine 4" from the fuselage side giving me 1/2" clearance. Sound reasonable? The question is more about appropriate props than engine location. What size props should I be experimenting with? I can buy several sizes to try but at least want to be in range. I guess I could actually read the instructions that came with engine. They probably tell me.

Question 6) I've read about pipes since forever and recall that when tuning the engine you keep cutting a small amount off the header as long as the RPM increases with each cut. When the RPM goes down put the last cut in the tubing with the header. Is that still the way it's done or has that been updated?

Question 7) Do the pipe and header touch inside the silicone or is a small gap left?

Question 8) Is silicone coupler something I'll go through a lot of or does it last for a few seasons?

Question 9) How long should I break in the engine before trying to tune the pipe?

If I didn't ask something it means I probably didn't know to ask so don't hesitate to share your wisdom.

Thanks!

Last edited by CafeenMan; 11-14-2013 at 09:56 AM.
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Old 11-14-2013, 11:35 AM
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Goog morning CafeenMan.....
3 of these engine will allow you to use smaller than usual props on each one.
Typically a APC 6.5x5 is a good choice for a CVA.15 with stock timing on a speed plane. These engines respond nicely to tuned pipes with stock exhaust timing and this size prop. If you want more than that you will need to get out the carbide tooth rotary files and start modifying the ports and passageways inside the engine. At the very least the exhaust port gets raised to yield a total of 180 degrees of "duration" [the amount of time it stays open].
Do you want to mess with going this extreme..? If so, then matching the correct amount of prop load to the engine becomes a seperate hobby almost and you might find yourself either buying custom carbon speed props or making your own from scratch.

For now, I would run the engines with stock timing and look at "target" props that are readily available. I think 3 of these engines with 6 x 6 props would get a nice clean plane hauling real good and it would definitely sound *****in.
I do not know if APC makes a 6 x 6. MAS props can be cut down but their blades are bulky and need to be recontoured. Labor intensive.
At any rate, this is the "ball park" prop to set up the engines with.
Run the engines with open exhaust to get base line RPM. Do not throttle them, just make sure you are using 25% oil and control their temperatures with mixture control while doing the torture testing. Use "heavy element" plugs if possible.
Install the pipes now and be sure to open the needle a full turn before starting. Add a couple of head shims before getting started.
If the system is pre-tuned or [close to it] you will see a definite BOOST in RPM as you slowly lean the mixture and the sytem goes into resonance. If the system is too long, it will most likely fall short of the open exhaust RPM. Remove a head shim and try again, if you see no improvement put the shim back in.
Remove a 1/4" of the header with a fine tooth [32 count] hack saw, de burr, rinse and repeat the test. You should see a slight increase in RPM. Remove a shim, look for improvement in RPM..if not put it back. Keep cutting the header in 1/4" increments until the RPM improvements level off. Always leave 1/16"- 1/18" space between the header and pipe to avoid chafing..remember that the engine will ingest the mixture that is in the pipe, so you don't want any aluminum slurry in there.
I would like to see you try the 6.5 x 5 APC props as a safe "default" prop that I know works very well, but I think you should try to take advantage of this tri-motor set up by dropping down to 6 x 6 props if they are readily available.
I would expect to see 140 mph + set up like this and if you decided to use .15s set up like real speed engines with lots of exhaust timing and toothpick props who knows what the ceiling is..maybe more like 160-180..?
Oh....setting compression. Blowing plugs every run, even with adequate fuel mixture is a tip off.
Pitting on the piston and the head is a dead give away. It is better to sneak up to the highest compression that the engine can tolerate than visa versa. Dave Shadel of Performance Specialties taught me to run a stack of shims that barely allow the engine to start, then slowly subtract them like you would tune a model deisel engine. With your stock CVAs you don't need to be this vigilant but I would still run a couple extra shims until you get your combo sorted out. I would use 10-15% nitro for starters. The balancing act is between the load on the engine, the nitro, pipe length / volume and the compression setting..assuming that you always maintain adequate fuel flow. The pipe raises the dynamic compression and you should expect to wear out plugs more often but you never want to see obliterated plugs. You should always see smoke / spray and no audible signs of sagging and so monitoring 3 engines will be more of a chore than just keeping track of 1.

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Old 11-14-2013, 02:45 PM
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I was going to chime in with my tried and true method of tuning pipes but Combatpigg beat me to it. That has alwaws worked well for me. I prefer to break the engine in with at least two tanks of fuel before I start tuning pipe length, but that is personal preference. The only thing I do differently is tune my pipe length with one size larger prop than I will fly with, which lowers the RPM slightly. When I make the last cut that does not raise the RPM any the pipe is now too short for that prop. When I put the smaller prop on and the running RPM increases from the lower prop load the pipe length is now correct. Again, personal preference.

Good Luck
Scott

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Old 11-14-2013, 09:33 PM
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Another thought. When everything mentioned is in perfect harmony it is possible to get incredible performance without the engine getting too hot..or really too hot to touch after shutdown. Aluminum mounts are good because they pull heat away from the engine.
Remember all the elements that are part of this juggling act and pay attention to what the glow plugs look like after every run.
I think most "tuners" are lazy about getting the compression just right. The rule of thumb is you want the least amount that will get the job done. If you try to use too much prop, too much compression or too much nitro with these "supercharged" engines they WILL try to kill themselves. Melting the high temp silicone pipe couplers is a dead give away that the set up is too aggressive. RC Racing Car couplers are cheap and always good to keep for spares, but always be leery about why one failed.
A stock CVA will not be demanding at all to get tuned and maintained..what I've been talking about applies more to the next stage of power after the engine has had the exhaust timing raised. I've got a CVA that will always be left with stock timing because it is such a great all around performer just like that. I'm sorry to hear they are discontinued, but not surprised. They have been fairly expensive and I believe the Magnum .15 rivals them for less money.
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Old 11-14-2013, 10:06 PM
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Sorry for the delayed reply. I'm nocturnal and went to bed soon after my original post.

CombatPigg asks, "Do you want to mess with going this extreme..?"

No. I have no intention of ever attempting to change the timing in an engine. If I ever do it will be with an engine I really don't care about and has no value and I don't care if it ever runs again or not.

I plan to use these engines as intended. The NovaRossi's are already pipe timed. Allen tells me there is one more in the line that is even more powerful but again, I don't want to get into temperamental engines.

What surprised me is how massive these NovaRossi .15s are. The three of them with pipes and mounts will be over 2-1/2 pounds. They are far bigger than my CV-A and almost the size of my Webra .35.

In fact, the .12 is bigger than my CV-A as well (I bought the .12 for a Sterling 1/2A Corsair but now that I have it I might use my old very worn bushing HB .12 instead).

So my plan is to pipe the .15s, use moderate nitro fuel, and be nice to the engines.

With those kinds of RPMs how long do you think a 3 oz tank will last?

I was looking at the Tettra tanks but at $24 each doubt I'll do that. It's hard to find 3 oz tanks at all. Wish I'd stocked up when I was in Germany but didn't realize there would be a problem. I have some Hayes 3 oz tanks but I'm really not a fan of Hayes tanks. Can't even say why.

So the three engine plane will be sort of a melding of my Shadow design that I've wanted to build two more of - one will just be the next generation with a single engine and one was going to be a twin. I love the fuselage for Dave Platt's Duellist so I planned to pretty much rip that off. Then it occurred to me that I could get another engine in the nose.

Now there's going to be a problem with getting a tank and a retract in there. I could always make it a tail dragger.

I have a Magnum .15 and it's not even close to the power of the CV-A. It was never intended to be. As far as I know the Magnum I bought is just a sport engine closer to an LA .15. I haven't run it much. I took the CV-A out of Great Gonzo and put in the Magnum and it was way different. Whereas the CV-A would lift off in less than 10 feet, the Magnum used a large portion of the runway before it had the speed. And I'm talking about a plane that was less than 2 pounds with a wing-loading in the 7-8 ounce range.
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Old 11-14-2013, 10:10 PM
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OK, I'm at the Tower site and looking at pylon props.

These are the choices for APC:

6.3 x 4
6.5 x 5
6.5 x 6
6.5 x 6.5

By the way, I forgot to ask Allen at Planet Hobby if there is a reverse crank for these engines. I'm going to have a lot of torque all going in the same direction. Should make for a wicked left roll rate.
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Old 11-14-2013, 11:58 PM
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As far as I know the NovaRossis are "re-purposed" car engines. They might work out OK in a speed plane, but I can not say. They will most likely [because of lost torque due to high timing] be harder to find suitable props for. Just my guess.
The 6.5 x 5 prop is the best one that I've used for the CVA .15.
I was hoping to see a 6 x 6 alternative if you were to build a twin or tri-motor.
APCs CAN be reworked [shortened] to help match the load to your engine, but it is of course more work that takes time away from flying.
You could try reworking the 6.5 x 6 just to see if trimming it down to 6 inches or less allows the engine to hit resonance. The 6 pitch in the mid 20K range ought to give impressive speed.
There is an invisible line that you can cross while reworking a prop. The engine will seem lifeless, unresponsive, growing hot, if there is just slightly too much prop, so recognize that early and don't make it suffer, just kill it. Take the back of an Xacto blade and scrape some meat off the prop blades' airfoils, give it another try and sometimes MAGIC happens.
There is another approach, but it still requires work because the props come semi-finished. Steve Wilk at Eliminator Props has an almost infinite selection of real carbon strand, hand laid speed props and props in this size range are probably $10 - $12 each. With a hot twin, you could roast 2 glow plugs, break 2 props and be out over $30 just for "consumables"........!
This would test your love for this sport.
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Old 11-15-2013, 02:22 AM
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OK, several photos here.

Included are the three NovaRossi .15's, a NovaRossi .12, an HB .12 (had a built in backplate mount that I cut-off many years ago and don't remember why but needed to for some reason), a Fox .19 CL and Webra .35 for size reference and the OS CV-A.

You can see how huge the NovaRossi's are compared to everything else. I didn't read the size specs on the engines before I purchased them and assumed they'd be about the same size as other .15's I have or have had.

I'm going to weigh them next.

The horses are ornaments I've been making for a while now. Started cutting out parts in July and now need to finish gluing on wheels, tails and handles. Then a couple coats of wax and ready for Christmas. They're made from cherry, maple, walnut, cocobolo, Brazilian rosewood, ebony and holly. I cut out 170 kits altogether and it's pretty much the only thing I've worked on since I started. I'm kind of over horses and ready to get back to my planes. I haven't finished a plane in five years.

Photo 1) All the stuff I ordered from Planet Hobby, some engines I already had and the horse ornaments. I have headers, pipes, pipe mounts and spare plugs.

Photo 2) On the left is the NovaRossi .12. On the right is a very old HB .12.

Photo 3) Back row is the three NR .15's. Middle row left to right is OS .15 CV-A, Fox .19 CL, Webra Speed .35. Front row is muffler for the CV-A, NR .12, HB .12.

Photo 4) Side by side CV-A & NR .15.

Photo 5) CV-A, NR .12, HB .12

Photo 6) CV-A & NR .12

Those should pretty well show the size comparison.
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Old 11-15-2013, 02:39 AM
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Weights of the various engines except the Fox:

From left to right.

293 g - Webra Speed .35 w/muffler

157 g - HB .12 w/muffler

230 g - NovaRossi .12 w/muffler. 2-1/2 ounces more than the HB. But then it probably has four times the power.

234 g - OS .15 CV-A w/header, pipe and coupler

367 g - NovoRossi Rex RFX-15TC w/header, pipe and coupler (over 2 ounces more than the Webra). Even the pipe is heavy. I may try to find lighter pipes.
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Old 11-15-2013, 07:06 AM
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As a reference point of questionable validity, from a piped OPS "Speed" .15 (which is actually timed for peak hp in the 23-24k-ish range, not really "speed") when I bench ran it for pipe tuning on a 90% diameter version of a 6x5.5 prop, I saw 24k. So in the air on the full prop I would expect to see about that. This is a good example of a .15 that weighs the same as a .25.. it's chunky as well. Maybe it has its roots in a car engine. http://www.youtube.com/watch?v=cH0OA5-VVgY

I looked at those NR .12's and .15's recently but when I saw the weight I recoiled.
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Old 11-15-2013, 07:27 AM
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I never even looked at any of that. I didn't even care about the RPM. First, I panicked when I saw the CV-A was out of production. I know good small engines of all sizes are hard to find.

Second, NovaRossi has a great reputation. I talked to Allen at length about it. He told me the two brothers developed the original Rossi line. Then one brother kept that (he's now deceased) and the engines became more sport type rather than high performance.

The other brother started the NovaRossi line and concentrates on performance engines. So the reputation told me it was safe to buy - even four of them - without knowing much else.

Rear-exhaust is a big plus.

But I would snatch up new in box CV-A's without a second thought. I'd love to have a half dozen of them.

Now this tri-engine plane I've been dreaming up was supposed to have a very thin wing (9-10% ish maybe even as thick as 12%) and have about 450 - 500 inches of area. I was hoping for four pounds or less. That's just not going to happen with the NovaRossi's.

I don't know jack about the Conquest .15 but I found the folks who are making it and it says they are out of stock but not discontinued. I have seen those in hobby shops and I don't remember them looking any larger than my CV-A. I'd take a handful of those new as well.

So now I have three NovoRossi's that I have no intention of returning but they may not even be paired up for a twin. I might just build three different planes for them and wait until I can get lighter .15's.

I have 2 CV-A's but one has a few hours run time on it and the other has never been run. The one that did run was on my Bride of Gonzo with a long, low-pitch prop and definitely never wrung out.

http://www.airfieldmodels.com/galler...onzo/index.htm

I have a vintage Top Flite 37" P-51 control line kit that will become an RC kit. Most of the wood will probably be replaced to make the model much lighter. I was thinking a .21 would be a good choice but I think one of the NR .15's would work well too.

It takes an inverted engine and if I can find a short, muffled pipe or a short muffler it can probably be mostly hidden in the underside "cheek".

Point is I now have several engines and no concrete plan of what to do with them. I'm not complaining and no, you can't have my engines just because I don't know what I'm doing with them yet. I know you were thinking it.
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Old 11-15-2013, 01:45 PM
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It would be smart to build a plane for one of those NR .15s [to get acquainted with running the engine] but I would just build a bare bones high wing plane with a skinny airfoil that is easy to hand launch and land on grass. Flat aluminum skids can be inlaid in key spots if you have to land on fabric or pavement.
The idea here is to get one of these engines airborne with the least invested in the airframe but with a sleek plane that will allow a 6 inch prop to do it's thing. To save weight, ditch the carb [if it seems too heavy] and use a fixed aluminum or nylon venturi. Dedicate a mini servo to pinch off the fuel line.
What I visualize for one of these engines is a "scaled up" version of a .15 Class Control Line speed plane that has ailerons and elevator tied to mini servos and a mini RX.
Mustangs with the low wing and high thrust line [inverted engine] are difficult to hand launch because they zoom towards the ground until the wing takes over. Throwing them as hard as you can seems to exacerbate the problem. They were still very popular for WWII RC Combat but even at 1/12th scale [36" span] they weren't what I'd call extremely fast with CVA.15 power. The standard wings were too fat and the fuselages had more girth than what was necessary to gift wrap the onboard equipment.
One picture is worth 1000 words and just to give you a good idea for what a NR.15 powered plane should ressemble it would be worth your time to look at pictures of .15 Class Pylon Racers and some Control Line Speedsters to glean some insight.
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Old 11-15-2013, 02:18 PM
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Hi Combat,

Hand launching planes is no issue for me. I've been doing it since forever - all types. Even hand launched my own ukie combat planes a few times when nobody was around to help. Ate dirt more often than flew but eventually I could get it in the air then run and get tension on the lines and save the day.

The Mustang will most likely have retracts. If I can't find anything I like then probably no gear. I'll have to see how the scoop looks. This was supposed to be a scale plane so the outlines are fairly accurate. But I have no intention of making it a speed plane. I will put on a higher diameter, lower pitch prop but start off with something I know has enough speed to fly it. It's probably not a good choice for the .15. My initial plan was to give the kit a good look over and figure out how much engine it will need after conversion to RC and replacing wood as necessary. I've been thinking a .21 would be the perfect engine but I'd have to buy one. Thus if the .15 will work and my other plans for the .15 get ditched then it would at least fly.

I know exactly the style shoulder wing you're talking about. I made a plug for a hobby shop owner when I was in Germany for a .15 speed plane. He showed me the prototype and it weighed give or take a few grams, at least a ton. It had some rear-exhaust piped .15 that I believe was Russian. Couldn't tell you what it was. He showed it to me in his shop. I never saw it fly. I took the fuselage to measure to make the plug.

Anyway, I've got lots of decisions to make but a couple things come first. I have to finish those horses because last year they didn't go out for Christmas until feb this year. I have no excuse for not getting them done. But there are 38 of them so as little word as there is to do on them it's still a lot of pieces.

Then I have a plane I started on years ago and pulled it back in the shop last year. It just needs to be finished but the weather isn't cooperating. Too humid to spray dope.

Then I promised a good friend two roofs for the steam tractors he's machining. Any time I asked him to make anything for me he had it done in a couple days. I promised him these roofs almost two years ago and keep putting them off.

I also need to make some fixtures because I'm almost out of one size. Everything else I have at least a year's worth of so after that I'm clear to start playing with whatever I want.
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Old 11-15-2013, 03:11 PM
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It's not easy to build both thin and light...then hope that it's strong enough.
The prop, engine and plane all have to compliment one another with these specialized engines. The speed engine is like a spoiled, bratty rich kid who dictates to his friends [in this case the prop and the plane] exactly what works with him and nothing else will do.

The smaller the engine, the more exacting this 3 way relationship tends to be.
Not only will the NR.15 act like a "spoiled rich kid", but as you already know it is also a spoiled FAT kid.
Without any hands on experience with the NR.15, I might be over-blowing what I think about it.
It's just that car engines work with much less load, so the designers can give them lots of exhaust timing to produce super high RPM without worrying about the loss of torque. If you can work it into your busy schedule, get it running [singing] happily with a few "target" props to play with just to see what size prop it is capable of turning in it's designed RPM range.
I've been curious about these engines but have never heard any "real world" feedback. The North American Speed Society" [NASS] is all about C/L Speed and they've most likely got some guys at that forum who can give you as much info as you need. They've always been very helpful with me and generous with their time.

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Old 11-16-2013, 05:05 AM
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All these engines will go on a stand before going into anything. More to learn about them than to break them in but I plan to be careful with them so not to cause any damage. As you're saying, I really do need to run them and see what I think about their performance. Unless the plane is powered by a Cox .049, I don't plan to ever not use a throttle. I'm not after all the speed I can get no matter what. Just all the speed I can get and still enjoy the plane.

I have a nice stand. It's the PSP stand bolted to a fuel-proofed board on a bolt-together Craftsman tool stand. So far I haven't put an engine on it that can even make the stand wobble but if I ever put some big ass engine on it's easy enough to sandbag. The .15's aren't going to move it anywhere. My YS .91 didn't even bother it and that's the biggest engine I've put on it so far.
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Old 11-16-2013, 05:10 AM
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By the way, I was a spoiled kid. Very spoiled and had really nasty temper tantrums growing up. I have to say that I'm amazed they never took me to the back woods where nobody would ever find the body.

My mom used to tell me she hopes I have a kid like me one day. So maybe she is getting her wish and I just got three of them.
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Old 11-16-2013, 05:12 AM
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Forgot to ask. Can I cut a big chunk off that header for the CV-A? Did you see how long it is? I don't mind cutting bits off, but if I need to remove 4" one-quarter inch at a time including taking off the header, cleaning it up and putting it back on it will take a very long time.
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Old 11-16-2013, 08:48 AM
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I could tell you what the header length is on mine, but we could have different bend radius, differing tubing diameters and who knows what else. It's just safer to go through all the motions yourself with YOUR target prop, YOUR timing, YOUR compression, YOUR fuel and YOUR pipe.
Change any combo or any single one of these mentioned items and it will change your results....the exact prop and pipe being the most heavily weighed factors. You are tuning the exhaust for a specific prop and pipe..it's not a one size fits all deal..so be sure to save those cuts
From the center of my header's exhaust flange opening to the end of the header pipe, it is 3.5 inches. So, IF we share the exact same pipe, choice of prop, etc. that is your "end point". I'm fairly certain that I run 6.5 x 5 APCs or 7 x 5 Rev UP wood pylon props.
Some piped engines with radical porting are an unpredictable mess to throttle once they hit resonance you just let the engine run the tank dry wide open. The CVAs wont be like that, but they wont hit the pipe very hard, either.
I can't imagine a .15 sized plane with relatively small props for speed being able to "Get On Step" if you weigh the plane down with retracts. In the case of a twin you get more leeway of course so maybe retracts wont be such a deal to over come but usually for small speed projects to be really successful you need to have a militant attitude about any dead weight that measurably changes the wing's and the prop's AOA.
A wing that is thick enough to house retracts will also present more drag. The airfoil should only be 5/8" to no more than 3/4" thick where the retracts are to be stationed.

Last edited by combatpigg; 11-16-2013 at 09:04 AM.
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Old 11-18-2013, 10:15 PM
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I don't plan to pipe the P-51. It's just a sport plane. The only reason I would use a pipe would be if I do use the NovaRossi with a rear exhaust and can find a pipe that will hide in the chin. The only reason I brought it up was in case I decide that the three engine beast isn't doable with these heavy .15's and I need to find another use for them. I want the Mustang to fly like a Mustang, not a pylon racer.

Honestly I think a good sport .21 will be the best engine for the Mustang.

The three engine plane will be larger and I think the wing will be thick enough to get some retracts in it - especially if it's a tail-dragger (which is probably a bad idea for other reasons such as ground handling a small three engine plane on rough fields). But for argument's sake, a tail-dragger gets the gear mounted in a thicker part of the wing up in front of the main spar rather than much farther back where the wing will be way thinner.

I haven't even drawn the first sketch of this thing. My main plan was to take Shadow and decrease the chord 1", extend the span about 4", thin the wing a couple percentage points and then scale whatever that comes out to be to the size I want for this plane. Shadow was never as fast as I wanted it to be. I had no idea what airfoil to use (this was one of my first designs) and the guy who chose it was an aerospace engineering student. He told me to use a NACA 2412.

I think the proportions of the plane are very close to perfect but the more I look at it the more I think the wing chord is too much. Not by a lot, but enough.

So narrower chord, thinner, faster airfoil and maybe more span (or maybe not). For a sport plane I would make the fuselage rounder, slightly wider and much taller. For a speed plane I would leave it pretty much alone. The fuselage was originally designed to wrap around what had to go inside and nothing more.

The photo at the top of this page is when it was first finished. When I refinished it I added a canopy, huge wing fillets, a shorter fin and glassed the fuselage. The wing was stripped and covered with Koverall and dope and then sprayed with HobbyPoxy color. I already realized this wasn't going to be my speed demon so I decided to make her spiffier.

I joined the Army shortly afterward and never did get to fly the newly refinished plane. Movers pretty much destroyed the plane. It could be refinished but it would mean completely stripping the plane again, filling a lot of dents and repairing a lot of damage. I don't plan to do that but I do keep it around because without the plane I have no drawings or sketches so have to measure it out if I want another one or want to use it as a starting point for something else.

http://www.airfieldmodels.com/galler...els/rc/shadow/
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Old 11-18-2013, 10:17 PM
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OK, now that I'm looking at it again, I need to take more than 1" from the chord if I don't lengthen the span.
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Old 11-19-2013, 11:53 AM
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The full scale engineer designed a nice sport plane wing for your model plane, but he doesn't appreciate the limited amount of thrust that a speed model has to work with. You can develope your own airfoil patterns using arched music wire. You want to limit the thickness to 8%, but when you scale down to .049 power even 8% is kind of thick to get the most speed possible. That is how it works.
The airfoil should have a fully rounded LE but the radius is kept small. My .40 powered speed models have a 3/16" radius, my .049 models go with a 1/8" radius LE. The music wire is formed so that the high point is at the 40% chord line and so that you have no dips or flat spots, just a smooth arch back to a razor sharp TE.

Yes, your idea for both projects sounds good if you select realistic target props for both the intended engines and for the amount of drag. If the Nova Rossis can't be tuned to deliver the neccessary thrust that you will have on anything less than a purpose built speed plane, they might still be able to work in tandem on a twin or tri-motor plane design that pays close attention to minimalizing drag.

The use of these engines like this is uncharted territory for me. There is a speed forum in Europe that is attended by a more active community of flyers and their input are likely to be better grounded in real life experience about a project like this.
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Old 11-21-2013, 06:39 PM
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I looked in my prop box and found APC 6.5 x 5 and 6.5 x 6. I think I bought them for the CV-A a few years ago when I was working on my smaller versions of Thwing! Still need to build those. All the parts are cut but forgot something on the plan I need to add and make new copies before I start.

Oh... and I have a 5.5 x 2.
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Old 11-22-2013, 11:13 AM
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for the cv-a engines I would go online and find some c/l fast combat props..buy a variety of six or so and try them stock and then modify as needed, its likely that you will find that a 5 inch ish prop is whats right....the old rossi 15 engines used cut down and thinned 6x5 revup props..they aimed for 30k rpm on the ground..if it wouldn't turn 30k rpm it was to much prop....
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Old 11-23-2013, 06:09 AM
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OK, I'm only getting about 36K on the 6.5 x 6 prop. Isn't it supposed to be more like 42K??? The engine isn't broken in yet and that was only 15% sport fuel with lots of oil and run just a tad rich, but seems unlikely that breaking in, leaning and higher nitro is going to pick up another 6K RPM.
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Old 11-23-2013, 07:01 AM
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It's even more unlikely you are turning 36k on a 6.5x6. I'd like to see that!
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