Spent all afternoon playing with my Cox.....

Engine that is.
This Hyper Viper thing is going to kill me!
I run a Black Widow cylinder and piston and could get 15,500 RPM with a COX 5x4 prop. Changing to a .051 Tee Dee piston and cylinder reduced the rpm's too 14,600 with the same prop. Changing to the stock HV cylinder and piston reduced the rpm's too 11,500, again same prop.
About ready to give up on the Cox engines and try a Norvel Big Mig .061.
I tried all the mods spelled out on this forum short of the anodized case, and 15,500 is the best I could get.
Any more ideas before I pull the plug on Cox and go Norvel?
Rob Johnson
Orange,Ca.

What are your target RPMs?

Would like to get 19,000 out of it.
Rob Johnson
Orange,Ca.

LAST EDITED ON Mar-13-04 AT 09:46 PM (CDT)
 
Have you tried Mike Pratt's recommendation -- a 5.7 x 3 from APC?

No, kept going smaller, trying to get the rpm's up. Ended up with a 4.75x4 APC which gave me the same rpm's as the stock Cox prop.
Rob Johnson
Orange,Ca.

>No, kept going smaller, trying to get the rpm's up. Ended up
>with a 4.75x4 APC which gave me the same rpm's as the stock
>Cox prop.
>Rob Johnson
>Orange,Ca.

Pitch of 4" is a kiss high; too much 'bite'. You might still want to give the APC 5.7 X 3 a try.

I'm curious as to why the worry about the RPMs, the Viper is a cute little airplane, and I'm sure a very good 1/2A ship, but how important is a few 100s of RPM?

By now I'd be just flying and enjoying the ship, I wouldn't even have my tach out of the flight box.

It's RTF, right?

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"My wife said she wanted to have sex in the backseat of the car. With ME drivin'!" -Rodney Dangerfield

Correct, but... I've had nothing but problems with this plane from day one. Fuel tank plugged up, stuff entered the engine, etc. Changed engines to get more preformance from this plane. Now just trying to get the most out of a Cox engine before flying her again.
I'll try the x3 APC tomorrow and see what it adds.
Also, mines not so cute. 25% nitro takes the finish right off!
Rob Johnson
Orange,Ca.

Hi Rob,

I don't have a Cox Viper but I do understand the frustration that
you may be going through.

It sure would be nice if the darn thing just flew and
you would be happy with it, right?

From my own experience of feeling frustration and continuing
to make effort sometimes causes more problems because
of my bullheaded ways of trying to "FIX" everything and make it
work.
So step back, take some time away or fly something else
and then begin your testing with a fresh outlook.
Before giving up on the Cox engine, simply and slowly go over
all your procedures and see if they make sense to you, make
notations and then do your comparisons.

At least then you will have given yourself the chance to see clearly
what you have done and then it will be time to make your decisions.

I know this sounds elementry, but everything we do in life
is a series of little steps.

Quit trying to fix stuff. I have a 1972 Greeves QUB Griffon 380 (motorcycle) that I am constantly diddling around with. The old beast runs, rides and drives- it will really crank on dirt when all goes well.
So do the best you can with what you have and use and enjoy the time and the place. Life is short, and death is REAL long...

Jake

Man guys....I wish one of you guys that are having troubles with the HV's engine lived near me. I do alot of work with Cox engines and would like to see first hand the problems with these things!

Later,

Tim Wiltse

LAST EDITED ON Mar-14-04 AT 02:05 AM (CDT)
 
The problem lies in the fact that I pull a cox motor out of a box, strap on a 5x4 prop or the APC 4.7x3 feed it 25% nitro and I get 15,000 rpm tops out of the motor, then under 14 flights later there is a hole in the top of the piston.

OR

I pull a Norvel engine out of the box, feed it 10% nitro on the same props and its getting 18,000 rpm AND I've got several with hours and hours of running on them. My buddies LMH Helicopter engine has over 32 hours of run on one piston/sleeve assembly even though Norvel rated them at 5 hours originally.

But I have plenty of time with Cox engines and I have flown several summers on a Black widow with a Teedee assy flying a Baby Flightstreak until it was more glue than balsa, and man did it fly.

This product engine though, man, what a piece of junk this one was. Well, I've got a different engine in there, the ball seat is in and the plane is flying again. It still could use some rpm. Dead calm it didn't really like doing the eights and going over the top on a wingover, forget it. Even on 30 foot cables.

Thursday though I built one of those Manwin trainers off of the Balsa Beavers site. Stuck my Norvel on it and WOW, that is fun for free right there. We were flying them in the park today with over 20 mph gusts. Made flying upwind really interesting. I threw the handle down once and yelled "RUN away, Run away' as it was tumbling in at me. It was the first airplane I've ever see make a roll and keep on flying, and it did several of them.
From somewhere near Parkville, Mo.
William Crane
AMA 6733

I could UPS it to you!!!
Rob Johnson
Orange,CA.

We don' need no stinkin' 4" pitch! Do not pass go, do not collect $200.00, go straight to a 5x3 Cox black nylon or an APC 5.5x2. See how you like it then.

I have a 5.5x2 APC. I'll give it a try. As stated, the Cox 5x3 gave the same RPMs as the APC 4.75x4.
Rob Johnson
Orange,CA.

To answer Larry's question---Another 100 RPM is darn important on small engines.

If you are at the point where 100 RPM makes any noticable difference at all in the way it flies, then your airplane is simply too much for that particular powerplant. It's either too heavy or too big or a combo of both...

Jake

>To answer Larry's question---Another 100 RPM is darn
>important on small engines.
>
>Jim

On a 1/2A RTF? This is a $40 model that comes WITH the engine, right? If this were a cutting edge 1/2A combat ship, I'd be inclined to agree.

If you're farting with it, it's because you WANT to, not because you NEED to.

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"assive activity income does not include the following: Income for an activity that is not a passive activity." -IRS form 8583, Passive Activity Loss Limitation

And I would say you have a real safe bet there.

Jake

Drilled out the venturie one more drill size and changed to a 5.5x2.5 APC prop. The engine now hits 17,000 rpm. I'm happy and done farting around with the thing! Big improvement over the starting point of 11,500 rpm.
One odd thing is I can get more RPM's out of a Black Widow piston and cylinder that I can get out of a Tee Dee piston and cylinder.

LAST EDITED ON Mar-14-04 AT 05:29 PM (CDT)
 
Yeah, It's all in how much you want to dink around with 50+ year old technology.
My old Griffon (motorcycle) will really crank; I can get some 44 HP (crankshaft) out of a 380cc motor that is 32 years old- when it is tuned properly- so what? And you guys who haven't ever ridden the "stone ax" of dirt bikes need to try one sometime- it will lift your scalp- no joke.
I still think electric motors are the wave of the future in C/L...

Jake

Jake,

Finally some commonality: I have owned two Greeves, 250s both, Killer Deal back when new.

But, my man, no Griffon has ever made 44 horses at the crank, certainly not one which is both a production piece and 32 years old.

Ya know, one can drop by most any race track during a track-day deal for motorcycles and come across at least one trailer-mounted dyno. Roll up there, whack it on, show me the readout. Even corrected for drive train losses, there is no way...

LAST EDITED ON Mar-14-04 AT 07:28 PM (CDT)
 
Dan, got ya' on this one. Standard garden variety 380 Griffon was listed at 38 HP at 7000 RPM. The Q.U.B. (which stands for "Queen's University. Belfast" and was named in honor of the teaching residence Doctor Gordon Blair and his staff who developed the special porting and (muffled!) pipe technology will pull 44 HP at 6750 RPM.
See Motor Cycle News (British) for April 19, 1972 and Popular Cycling (US) November 1972 (among others) for reference.

Jake

Larry,
we were under the impression that this little $42 Arf might be able to do a full pattern (hmm, maybe because Mike Pratt designed it and Cox does include the full pattern instuctions with the plane). Unfortunately the supplied engine seems a little anemic (and/or the plane is a little too heavy) to do very much. Also for $42, and Larry Renger's instructions, it gives us all something to play around with as we wait for real flying weather to get here!

If you want to just go round 'n round, it is fine.

That's what weekends are for, messing with things.
I have a 1946 Willy jeep that for years I messed with. Bigger engine, lower gears.... The best I could afford. What did it get me? Two spreads in two very big off-road rags. Top of the heep for a couple years anyway.
If one were to take things as they are, then this hobby, sport, profession would be stuck in the fifties. We would all be flying 10 lb. profiles. That venturie is fine, that muffler is sure to be OK. Wing loading? Who cares! 4-2-4? What is that?
I'll be a tinkerer till the day I can't. That's how things progress.
Rob Johnson
Orange,CA.

No, that's how you enjoy a hobby- progress hasn't a thing to do with it.
I like Jeeps too...

Jake

Want to see a Viper do a pattern? Hand it over to Bart Klapinsky!

Bart used to fly the plastic Cox ships at Disneyland, I've heard. And LOOP them! Imagine what he would do with a Viper..

Instructions are not a valid argument. That little Wen Mac Bonanza my brother, father and I had came with instructions (for flying!) as well!

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"It rubs the lotion on its skin,
it does this whenever it's told..
It rubs the lotion on its skin,
or else it gets the hose again.." -Buffalo Bill, in "Silence of the Lambs"

Hey Larry,
Even the Box says it will do the whole pattern! You mean I shouldn't believe the Hype??

Besides, like I said, it is fun fooling around with an ARF with a price tag which is only a factor of 4 more than the price Cox charges for a glowhead! Which reminds me of the great deals I got from Tower on the Cox StarWars plastic junk, about $7 a piece, even cheaper than the glowhead--as a matter of fact, that is my main supply of glowheads for the Cox engines.

What % Nitro fuel are you using? On my first outing the engine was turning 14,000 rpm and that was with 10/22 fuel.

I tried 25% right off the bat but I guess you do need to break in a .049 engine to some degree.

I tried 25% again today and this combo did showed some promise.

I'm using 25%.
The 5.5x2.5 APC made the biggest differance in RPM's.
Going to go fly this engine on a Combat Wing today, then it's getting sent out for some machine work and anodizing. Has to look good too!
Rob Johnson
Orange,CA.

Dan, got ya' on this one. Standard garden variety 380 Griffon was listed at 38 HP at 7000 RPM. The Q.U.B. (which stands for "Queen's University. Belfast" and was named in honor of the teaching residence Doctor Gordon Blair and his staff who developed the special porting and (muffled!) pipe technology will pull 44 HP at 6750 RPM.
See Motor Cycle News (British) for April 19, 1972 and Popular Cycling (US) November 1972 (among others) for reference.
Jake

Jake,

I didn't say no one claimed 44 hp, I'm sure they did. They may even have been involved with the guy who wrote advertising copy for Bultaco. Remember the Sherpa and Mettise?

Gosh, I don't seem to have those particular magazines in stock at this moment. You are referring to dyno tests from these sources, correct?

I still don't believe it.

Dan, yes that is affirmative. I will copy and mail the articles to your snail mail addy (it is still same as in PAMPA directory?).

Jake

Go Norvel!

Dan, yes that is affirmative. I will copy and mail the articles to your snail mail addy (it is still same as in PAMPA directory?).
Jake

PAMPA directory has current address, I look forward to seeing your documentation.

So I am clear on this, you continue to maintain that the engine in your 380cc motocross bike develops more horsepower than 350cc engines used in roadracing during the same period of time.

Fascinating.

Dan, I "maintain" nothing. This is what the factory specs stated and what magazine articles of that time frame stated. You have a beef with that, take it up with Bert Greeves or Dr. Gordon Blair. My personal old Greeves has been "tweaked" several times for desert racing in California back decades ago- what the power output is today only heaven knows, but the puppy will still rock. The QUB was the last of the Greeves line and the swan song of British dirt bikes. They didn't build very many QUB's and they aren't exactly common today.
Articles in the mail to you by this weekend.

Best,

Jake

Replaced the Product engine with TeeDee .051 piston/sleeve assy. APC 4.7x3 prop. I need to dump the stainless steel reed, it seems to stall out when the engine unloads, but after a couple needle set runs, it started to work better. Launched on 39 foot spider wire lines and it whipped around in the light breeze just fine. Up and over the reverse wingover, loops, horizontals, inside squares, jumped to the overhead eights because my buddy was asking about them. At this point, the motor started running lean inverted and rich upright for the rest of the tank, which wasn't too long. If I can ever get that figured out, it'll be a pretty good deal. Didn't tach it, but it was howling almost as good as my buddies stock Norvel BigMig .049.

Was pretty fun today.

Also flew the Manwin with the other Cox engine till I knocked the intake line off, I have to take the tank apart. It has a Teedee .049 piston/sleeve on Blackwidow mounts, wokring pretty good. John Bender, my flying buddy, designed a launcher for his, which I copied. Works just like the combat guys and their stooges. Little coro thing is folded up, then with a couple spacers, has another piece of coro on the top. Just slide it in, start it up and pull on the handle. Manwin hovers right away.

Norvel one is working a tad better.