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-   -   OS .15 CV-A question. (http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/9410208-os-15-cv-question.html)

Mr67Stang 01-12-2010 04:17 PM

OS .15 CV-A question.
 
I posted this in the glow engine forum but I then thought all the small engine tinkerers are right here!:D

I have owned an OS .15 CV-A for some time now and love the little engine. It is based on OS's popular buggy engine the .15 CV-X. If you look at the specs between the two engine you will see a gross difference.

CV-A:
RPM range: 2,500 - 19,000
BHP: .50

CV-X
RPM range: 3,000 - 30,000
BHP: .68

Why?
It could be a safety thing that they don't want us trying to spin our rotating razor blades in the mid to upper 20K rpm range (if that's possible?) Maybey it's the different carburetor... It's not the bearings because both engines call for the same bearings for replacement. Then I saw something. I looked at both engines replacement piston and sleeves. They have different part numbers. Now my curiosity is about to boil over. I am thinking about that little plastic card in my wallet. Somebody save me so my wife dosn't kill me and tell me if you all aready figured this one out?

combatpigg 01-12-2010 04:21 PM

RE: OS .15 CV-A question.
 
I run my ancient CVA with a 6.5x5 at 133 mph on a little delta. Now go to your rpm/speed chart to see what this little hummer is turning......[:-]!

It barely gets hot, is very easy on plugs, it gets rode hard and put away wet every time.

Mr67Stang 01-12-2010 04:32 PM

RE: OS .15 CV-A question.
 
Quote:

ORIGINAL: combatpigg

I run my ancient CVA with a 6.5x5 at 133 mph on a little delta. Now go to your rpm/speed chart to see what this little hummer is turning......[:-]!

It barely gets hot, is very easy on plugs, it gets rode hard and put away wet every time.
Okay, I came up with 28089.6 RPM with NO SLIP (100% prop efficiency (impossible) Likely turning in excess of 34,000 RPM???

So, are you saying the CV-A is under rated?

MJD 01-12-2010 04:37 PM

RE: OS .15 CV-A question.
 
On a similar note, if one had one of the OS .15 DF fan units en route via a marketplace purchase.. do you know which .15 it would be? I would guess it would be the high timed sleeve like you show in the CV-X version. Check out the torque drop versus rpm rise with the X P/L set, 36% more hp with 58% more rpm, so that's only 14% less torque at 30k versus 19k, not bad for a wee .15.

It is most likely simply a higher timed sleeve and may breath through a larger carb, if the CV-A version isn't maxed out on the crankshaft passage:bore relationship already that is. If not then a larger carb would be logical with that timing change and subsequent max power rpm range.

.50 hp at 19k is a pretty good number for a .15 actually, that puts it in the honkin' sport engine category. If it has manners to go with it, I want one! I might own one already actually, I'll find out when UPS arrives this afternoon.. :D they called you see.. and I'm in Christmas withdrawal too. I have an Xacto with a fresh blade ready on the table to cut the tape soon as it arrives.

MJD


combatpigg 01-12-2010 04:51 PM

RE: OS .15 CV-A question.
 
67S, I haven't dopplered this set up to answer your question about inflight rpm, but it doesn't sound anything like 30,000 to me...I'd guess a little lower. I'm running it open exhaust on bladder.
Some of the speed planes are flying at real close to 100% according to Doppler and onboard sensors.
This engine has conservative timing, internally you see no tricks, nothing fancy. It's kind of a mystery to me how these engines can be Jack of all Trades and pretty good all the way around.

Mr67Stang 01-12-2010 06:14 PM

RE: OS .15 CV-A question.
 

Quote:

ORIGINAL: MJD

.50 hp at 19k is a pretty good number for a .15 actually, that puts it in the honkin' sport engine category. If it has manners to go with it, I want one!

The OS .15 CV-A is a classic example of no-fuss set it and forget it OS reliability.

I am wondering if there is more power in this .15 CV case that OS is not giving to us airplane guys.

My plan:
1) I will buy a $100 OS .15 CV-X engine
2) I will tach my OS .15CV-A with 2 or three different props
3) I will take the back plate/NVA, carb off of my CV-A and put them on the new CV-X
4) I will break in the CV-AX as I would any other OS engine
5) I will tach the OS .15 CV-AX with the same props used on the CV-A
6) It may take some time for me to get the CV-X so don't expect results in the near future
7) Maybey CP will beat me to it:D

MJD 01-12-2010 07:01 PM

RE: OS .15 CV-A question.
 
1 Attachment(s)
This is the CV that UPS brought me an hour ago. I like it already. Do you know which version this would be? The carb throat is bigger than my old Max .40 I think.

MJD

Edit - I looked at OS's site, I imagine this is an "A".

Mr67Stang 01-12-2010 07:22 PM

RE: OS .15 CV-A question.
 
I think you have the OS .15 CVX-DF. Follow this Tower Hobbies [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBZ30&P=7]link[/link] and go down the page to near the bottom where it says "Comments" and you will see the CVX-DF is a dirivitive of the CV-X with an OS CV-A head and an OS #2F carburetor. Notice it does not say anything about the back plate as the CVX-DF was/is a pull start engine for ducted fan use. I think you have what I want to experiment with. I would be very curious if you carb is the #2F required for conversion. If you intend to convert this for regular propeller use and remove the pull start and instal a regular [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXXD34&P=Z]back plate[/link], we could do a close comparison of tach numbers.

Also a picture looking straight down the carb venturi with a metric ruler across the bore would be great!

Mr67Stang 01-12-2010 07:51 PM

RE: OS .15 CV-A question.
 
1 Attachment(s)
Some pictures of a CV-A.

You will see my carb ventri is right about 10mm at it's widest and roughly a 5mm bore at the barrel.

MJD 01-12-2010 09:20 PM

RE: OS .15 CV-A question.
 
Yes, it's a 2F carb - I checked that out.

On that subject of breathing, if you recall my comment about the breathing maybe being maxed out as is - I took a quick look inside, and the crank passage appears to be 6mm (I'll get an exact measurement soon) and the carb throat just a hair under that, I mean it is at least 5mm and maybe 5.5, I'll try to measure more accureately later when I'm more patient. But in any case ther are not drastic gains to be had there, I think that's getting close to it for intake with the exception of a venturi and pressure versus the carb.

I am looking at the starter drive pin on the crank pin, and thinking how nice it would serve as the drive for a rear drum intake.. [&o]

I DO like the tight radius header/adapter, kind of like the nice cast Al unit on my old G.15-RV that I always croon about. It certainly gets lighter without the starter and whatnot.

How much nitro are these happy with stock? I'll go look at the OS site for the manual of course.. now..

MJD




MJD 01-12-2010 09:38 PM

RE: OS .15 CV-A question.
 
Is there a CV-DF amd a CVX-DF I wonder, older and newer marks of the same engine? The CVX buggy engine has a black anodized case. But I see that the buggy and DF engines are the same, so it does have a high timed sleeve relative to the I guess. Cool.

I have Graupner Speed 6x5.5 and Eliminator 6x5.5 and 6.5x5.5 CF props I can run on it. I think it should be happy on 30% nitro. Gotta change the backplate. What about the starter drive pin on the crank.. does the regular backplate clear that?

I'll measure up the carb bore better than I did and let you know. And the crank passage.

MJD


scale dail 01-13-2010 01:42 AM

RE: OS .15 CV-A question.
 
1 Attachment(s)
When I saw the specs I had to get FOUR of those CV's for my old Stafford B-24D. They start right up and yes start and forget about it! I only need half power to take off! I needed reliability for competing in the Scale Masters Championships and they worked perfect!!!!!!! They are great engines!

Mr67Stang 01-13-2010 06:23 AM

RE: OS .15 CV-A question.
 
These CV-A engines run great on 15% and turn 8x4-5 in props with ease for sport flying. So based on what you have vs me we would have a hard time doing any real (fair) comparisons. Honestly, I don't know if the starter drive pin will or won't be an issue in replacing the back plate.

MJD 01-13-2010 08:13 AM

RE: OS .15 CV-A question.
 
Yeah, but I guess we can see the difference in the two, which is an education in itself. I had paid little attention to OS .15's other than the FP and old MAX III that I have/had respectively, so this is interesting to me.

One thing that intrigued me was the plastic mount that is evidently designed to mate with the Kyosho F-86 fan shroud assembly. It could easily be incorporated into a neat and aerodynamic nose fairing. Mounting would be different, one bolt each side through the engine bearer, and a couple in the nose ring, but it would blend nicely into a 1.5" spinner. I'm sure it will sit in my engine drawer gathering dust while I think about how well that would have worked, but you never know.

MJD

Mr67Stang 01-13-2010 08:28 AM

RE: OS .15 CV-A question.
 
I just looked up the replacement crank shafts for both the CV-A and the CV-X and see that pin you are talking about on the CV-X. I do think that will get in the way of a "normal" aircraft engine back plate. So, you could likely get away with cutting off the pin or just get the $22 CV-A crank shaft for it.

DeviousDave 01-13-2010 02:40 PM

RE: OS .15 CV-A question.
 

Quote:

ORIGINAL: combatpigg

67S, I haven't dopplered this set up to answer your question about inflight rpm, but it doesn't sound anything like 30,000 to me...I'd guess a little lower. I'm running it open exhaust on bladder.
Some of the speed planes are flying at real close to 100% according to Doppler and onboard sensors.
This engine has conservative timing, internally you see no tricks, nothing fancy. It's kind of a mystery to me how these engines can be Jack of all Trades and pretty good all the way around.
Probably isn't 30k. Props don't go thru the air like a solid screw. The blades are airfoiled and provide lift.

Doc.316 01-13-2010 10:18 PM

RE: OS .15 CV-A question.
 
Hello,
My friend (that happens to own a hobby shop)...has two of the CV-A engines. They run good! But we haven't been able to get them to really run. (I am kinda sore since I got beat in a .15 race by a fox). When I say that I mean that they run (smoothly, good idle, good transition, etc) but they would not keep up with the fox! Now we tryed the pipe/ran them in/ the plane was actually smaller than the one the "fox" was on...but it blew us away....(sigh). So, how do we get these engines to really turn up and produce some power? To give you some background we tried a multitude of props (heck the guy owns a hobby shop)......pipe lengths...fuel (we boosted the nitro up a bit....ok a bunch)...shimmed the head (for the nitro)....everything we could think of...and it was a nice non finiky engine that didn't really produce....

Now I had a fox .15 that would run faster than the one that beat me...(it was a friend that we used to fly combat with)....it was to be honest pretty hot...the carb was junk...(kept hanging up and needed to be relapped to even get it to remotely work) but it would run.... Oh, (btw) I hate foxes (they were bad back when I was a kiddo and seem to be not as polished as other engines...all other engines)

So...is there any way to get the os to really run??

Steve

combatpigg 01-13-2010 11:28 PM

RE: OS .15 CV-A question.
 
Steve, the 7x5 props are a good place to start. If the air frame isn't small, clean and light enough, going to racier props like the 6.5x5 won't speed things up any. If you are flying something along the lines of a 36" Mustang kit, then you are on the right track for this engine.

The FOX .15 schnuerle was always considered pretty good in it's day, I've never seen one used for RC.

I haven't tried this myself with a CVA, but generally you tear the engine down after degreeing it and marking the sleeve where 180 degrees of exhaust duration occurs. Do the same with the crankshaft port, mark the closing side of the port at 60 degrees . Grind the sleeve and crank back to these marks. While you are at it, look for excess metal to be removed from inside the piston.
Check the fit of the crank in the case. The whole rotating assembly should spin for a few seconds after just flicking the prop and coast to a gradual stop. If not, the distance between the bearings can be off, the crush fits are too tight, do what it takes to get it freewheeling without any slop. Nothing else you do will matter until the lower end is correct.
Reassemble the engine and shim the head. The next step is to tune the pipe for the prop that you want to see burn. I would go with the 6.5x5. Start with an open exhaust reading to get a baseline and then start removing 1/4" lengths of the header as long as you see steady improvement. At some point you should find a length where there is an explosive jump in rpm. At this point you will see plugs blow if the compression is too high and of course if the fuel system doesn't ramp up enough to deliver fuel on demand. In this case, a back plate pressure tap and a C/L type venturi are your best bets fpr a maxxed out system. Plugs will also blow if the prop load is too high, going to a lighter prop with the thinnest blades really helps. Too short of a tuned length also blows plugs and will bounce hot air way back into the engine.
If you don't want to go through all this......you don't want it badly enough......:D

MJD 01-14-2010 12:20 AM

RE: OS .15 CV-A question.
 
1 Attachment(s)
I partially tore down my CV15-DF or CV15-X or whatever it is - either I guess - and got a couple of measurements and pictures, so I'll put it here. I like the little plastic mount that goes into the F-86 fan shroud assembly.. it begs to be used in the front of a glass or craftily sculpted ply nose on a speed model. It could be secured easily with machine screws.

Note the crank bore to carb throat ratio.. even closer than I thought. 0.245"/6.2mm crank passage, 0.235"/6.0mm carb throat, or 96%. That's about the limit.. but a 0.245" venturi may give a last few rpm, who knows.

I wonder how fast this'll spin a break-in trimmed Graupner or Eliminator 6x5.5 prop.. we'll soon find out. I think they were regularly run on 30%+ nitro in the Sabres. I think I'll use something like SIG Champion 25%.

BTW re the prop thing above - props use airfoils, sure, but this does not change the nature of pitch speed nor is there any weird science going on. A prop moving forward sees an AoA based on the pitch angle of the blades, the rpm and the airspeed. Wings moving forward do not produce positive lift at AoA below the zero lift angle. Similarly, aircraft in level flight do not exceed pitch speed of their own accord, because the definition of pitch speed is the speed where the relative wind approaches the prop blade airfoil at zero lift angle. Why you see examples where these quickie calculations falter is for more than one reason, IMHO:

- Pitch ratings based on chord line or worse yet, the lower surface datum line like pitch gauges generally measure. These can easily be 2,3 or more degrees lower than the true aerodynamic pitch. A Clark-Y airfoil for example, flying with the chord line at zero degrees angle of attack, is actually flying at 3.52% positive AoA. A NACA 2415, like ACE wings, at 2.06 degrees positive when set up similarly.
- Rounding error, i.e. is that 7" pitch prop really 6.77"? Or pure error in mfg. pitch rating.
- Data error in measuring true airspeed, rpm, etc.

So a "10-7" prop can mysteriously fly an airplane at 103% of pitch speed - it's just GIGO effect. IOW the calculated figure carries more significant digits than the incoming data can support.

MJD

MJD 01-14-2010 12:21 AM

RE: OS .15 CV-A question.
 
1 Attachment(s)
the rest of the pics..


Oh yeah - check out the piston port in picture 3... [sm=confused.gif] What does it do?

MJD

proptop 01-14-2010 02:31 AM

RE: OS .15 CV-A question.
 
The hole in the piston lines up w/ the boost port in the sleeve. Take a look in the case...is there a boost port passage in there? I don't think there is...it's all in the sleeve IIRC.

MJD 01-14-2010 08:19 AM

RE: OS .15 CV-A question.
 
Darn, I buttoned it all up again.. :)

It looks like a nicely made engine, and seems robust internally. Next stop - the test stand. I wonder what rpm they set the pipe up for stock with the Kyosho fan unit. We'll find out.. soon-ish anyhow.

MJD

gkamysz 01-14-2010 10:23 AM

RE: OS .15 CV-A question.
 
Yes, that hole will line up with the boost port. Some versions of the car engines rely on this hole as there is no transfer passage in the CC. They could just be using an available piston. That header is part of the universal muffler setup. I don't think that muffler setup is offered anymore, I have one from somewhere. http://www.osengines.com/parts/images/72111000.jpg

MJD 01-14-2010 12:23 PM

RE: OS .15 CV-A question.
 
1 Attachment(s)
Here's the pipe I have with it. This is all Kyosho F-86 stuff AFAIK.

That muffler would be pretty cool for sport use on a CV-A or a reggler sport .15 with that adapter - you could tuck it back behind the engine with the inlet offset to the right and get it buried without much effort. So darnit, those headers don't exist anymore you say.

MJD

Mr67Stang 01-14-2010 01:11 PM

RE: OS .15 CV-A question.
 
Well, as I suspected the 2F carburetor is discontinued. I went to my LHS for lunch today and learned the bad news. On the upside though I learned the 2F carburetors were used on this little DF version of the .15 CV that MJD was so lucky to come across as well as the .25SF and the .40 FSR. I happen to own two .25 SF's so one may end up donating it's carby:D

For fun and for our good freind CP I think I will get some numbers with my stock CV-A on it's carburetor and then install the Carb from one of my .25 SF's so he can determine if it's worth hunting one down;)


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