Hyper Viper progress

I finally am getting really excellent engine runs on the HV. I figured out that when I moved the tank upward and glued it in, I had caused the fuel to foam, and I could not get a good setting.

So, I installed a balloon tank, and now the engine screams happily and steady through the entire flight, driving a Master Airscrew 5.5x4 prop. The tank plumbing extends out the fuselage on the outside so I can access the tube to fill the tank. A bit involved, but worth the trouble.

The plane is now too fast on 40' lines, so I will make up a set of 45's. That should give me some much needed room to do maneuvers closer to competition size, an a little more time to allow accuracy.

Incidentally, one wheel lost its little washer and fell off. I soldered a new washer on, and will do the other too, now that I think of it.

The current setup, then, is a Killer Bee crankcase/shaft, Tee Dee piston and cylinder, Norvel plug, 3 washers and the original backplate, drilled to 11/64". One nickle added to the tipweight, clear packaging tape covering up the bottom rear of the plane. The pushrod is in the middle hole of the control horn. I am using one of my handles with line spacing around 2". There is more than enough control authority to stall the plane, so I may cut the sensitivity still more. It does fly pretty smoothly as is.

I can do the pattern on 20cc of 25% Sig fuel with plenty of margin. Once I have the longer lines, I may need more fuel, but I actually have enough capacity to do over 200 laps (the pattern is 60 laps) so no problem.

I need to repaint the black stripe on the top, the fuel ate it! I think black Urethane will do the job.

Just a "thank you" Larry, for continuing to post changes to your HV. It is very helpful. I am in the process of getting an original Killer Bee myself...
Nick Vanmatre

I finally got my HV out this noon with Alan Hahn acting as 'stooge'. Alan is really good at that (hee hee - I should get flamed for that one)! My setup was an original Killer Bee engine with standard Cox head; 5.5x3 and 5x3 Grish Black Magnum props. I have been running my 'stunt brew' from last year (10% nitro and 23% mixed oil). It has Armoral added as an anti-foaming agent. First I tried tying the 2 vents together with a brass T going into the fuse. That way I'm drawing from 'dead' air in fuse. Then I tried the standard 'stunt' venting supplied, with the vent angles cut down per your suggestion.

On the bench the KB was holding a steady 20.5K rpm with the 5x3 Grish (same fuel). Also, the needle setting was very linear. In the plane, it is difficult to needle. It jumps quickly from too rich to too lean.

With the 5.5x3 prop I managed to get a couple of approximate settings, got it in the air and it would shut off lean. If I set it rich (4-stroke), it would stay rich. If set slightly leaner it would come off the ground rich, lean out for a couple laps and quit.

With the 5x3 prop I managed to get closer settings but it still went from rich to lean very abruptly on the ground (not at all like bench running). I managed to get a fairly lean setting, launched (thanks Alan). The setting held for a few laps. I got some inside and outside loops, then it went very rich again.

Alan believes this is a fuel foaming problem and I tend to agree, even though there is Armoral in the fuel. The bottle does not foam when shaken! Does this sound like your balloon tank might be the cure? We also discussed the possibility of an in-line fuel filter curing the problem as it may break down the bubbles and provide a small in-line reservoir. Thoughts??

Alan took some pics. If they turn out, we'll post them tomorrow.

Fred

You are having exactly the type of problems I did, and I did try Armorall in the fuel too. No good.

The balloon tank TOTALLY cured the problem. The engine needs to be set rich on the ground, as the balloon plasters itself to the outer wall of the fuselage, and tends to slide rearward till it hits the landing gear mount. But, once you find that good setting, it stays there the whole flight

And I really did 200 laps when I filled the balloon to capacity. I hit nearly 100 on 30cc of fuel, and still too much at 20cc. But getting there.

BTW, the engine will get over lean about 1 or 2 laps before it quits as the balloon finally begins to totally collapse. I would aim for at least 5 laps over completing the pattern and your two unwinding outside loops. That is a total of about 70 laps needed.

Ya know Larry, a picture is worth a bunch of the constanents and vowels.

But come to think of it, that's probably my problem I discussed with you too. When the motor finally gets revved up, it cuts out until the prop spins down, then its off again. I though this might be the reed sticking, but it could very well be foamy fuel.

YES pictures of the aforementioned balloon tank would be greatly appreciated.

Tell us, please, about the balloon tank. What is it? Where can one get one? How frequently do you need to change them? Etc???

Nick Vanmatre

Well I may be a good stooge, but a lousy photographer. My digital camera is just too slow to capture the Hyper Viper in flight. But here is a photo of Fred and the HV.

I have posted a separate thread on making the balloon tank. I figured more people would see it there.

LAST EDITED ON Mar-22-04 AT 08:17 PM (CDT)
 
My engine should be ready soon. Can't wait!
Rob Johnson
Orange,CA.

So do you just pull out the present tank and stick the balloon in without any other modifications?

Hello Larry,
Need to see about an e-mail address for you please, send it to this address: [email protected]
Thanks, Gil

I did cut a hole in the outer side of the fuselage to allow a loop of tubing that lets me get the tank filled. It needs to be unplugged from the engine to fuel it up. The hole is about 3/4" long and 1/4" wide, right on the centerline, and starting even with the needle valve.

Flew the plane some more yesterday, and it is getting better.

I made up a set of 44 foot lines, and it holds line tension well.

I think I may need a bit of noseweight, as the balloon tank is probably lighter than the plastic one. The plane hunts slightly, even though I desensitized the controls a bit more since last week.

It also tries to float after the engine quits, and is more difficult to land well than I remember from the first flights.

More as it develops!

undoubtedly fuel foaming.

I've seen some really weird things, playing around with Sullivan tanks on combat planes. In one setup the tank would run fine unless it slid slightly and contacted the rubber band hook. Then a huge cloud of bubbles would come off the contact point.

another one would run fine, except at a certain rpm the molding ridge on the tank would touch the fuse and generate a cloud of bubbles. you could stop it just by touching the tank.

So, Armorall can help, but it ain't a cure all. Makes you wonder if Cox did any real test flying before they started production. An RTF plane that needs a special tank doesn't bode well for successful flights by newcomers.

I don't think the stock tank foams with the stock engine. When you go from 12K to 18K some problems are likely to appear....

The plane flies nicely, and will loop, do eights, fly inverted etc. in stock configuration, but a clean pattern - no!

Just for the heck of it, I am being entertained by seeing how far you can take the plane.

AND, I haven't put a Norvel .06 and monoline in it yet <VBG>

To keep it legal for competition you could install a Fora engine from George Cleveland with a CF prop and see what problems you have at over 30K, and longer lines will be needed.

Can you say "melted plastic"?

Larry or others. I've got a new Hyper Viper and I've not flown c/l for many years so I want to start with the HV. OK, I've read most of the forum notes on the HV but I'm not sure where to start. I would like to condense all of the ideas so I have a plan.
First of all I would like to stay with the existing Cox engine to do basic loops until I have better control.
Do I re-adjust the engine to have a right angle thrust?
Do I bore the venturi before first flight?
I have 2 props sizes, these were the only ones from LHS, a 6X3 and a 5X4, would these be OK? Where do I order others from?
Do I put on extra weight on the outboard wing?
Do I change out the Cox tank to the Balloon tank before my first flight?
I thought about putting packing tape on the fuse and leading edge of wings, would that help for strength and fuel proofing or would that be too mush extra weight?
Do I run with the control line provided or get new .008 line and at what length?
Do I open the Cox engine apart to check if the con rod seems tight, (which I've never done Cox repairs)?
I have a new Norvel .061 with integrated fuel tank, should I not use the Cox and modify the bulkhead for the Norvel .061?
Do I use the Norvel fuel tank?

I'm open to any design modifications on the Hyper Viper. If anyone wants to reply to my email I would appreciate that. I'm sure once I start assembly of the HV I'll have more questions. My email is: [email protected]

Marvin,
It all depends on what you want to get out of the airplane. There are some guys on this forum that will tell you that their HV flies great in its stock configuration. Before you do any mods, break in the motor per instructions, inspect all parts for functionality and give it a try. You can always modify after. Who knows, you may love it as is.

1. The thrust line is fine, and I am happy with the leadout position as specified in the instructions.

2. Do bore the venturi before flying. The plane definitely needs more power than the stock engine provides.

3. For your first flights, you will probably be satisfied with the dacron lines and use the 5x3 prop that came with the plane. Later you can switch to .008 x 40' cable and your 5x4.

4. Add 1 Nickle to the hole in the outboard wing.

5. The C*X tank is OK until you really hop up the engine and get the rpm over about 17K, then you will get fuel foaming. Switching to a balloon tank immediately will prevent any possible problem and works just fine with stock or modified engines.

6. No packing tape required for strength unless you fly over weeds, then a little on the leading edge to prevent getting chewed up might be good. It probably is worth covering the hole in the bottom rear of the fuselage (I did, and Mike Pratt, the designer, recommended it)

7. As long as you have the engine apart to drill the venturi, you might as well go ahead and tighten the rod socket. This would be best done after a couple of break-in runs, though. Now that I think upon it, break the engine in a couple of runs, then pull it apart to do the work.

8. If you go with the Norvel .061, I would plan on 50' lines, a Master Airscrew 5.5x4 prop and definitely the balloon tank.

Tower ( towerhobbies.com ) stocks both APC and Master Airscrew props, I think. You definitely can get the MA props from masterairscrew.com
Control-line can be had from Brodak.com.
Good luck and keep us posted on how you do!

Thanks Larry and Chris for the info. Much appreciated. I forgot to mention that I fly at about 3500 ft so the alitude is sometimes a concern. But I still keep my feet on the ground.
I thought for sure the offset for the thrust angle would help, I would do it for all my other cl planes.

Prop2buster,
The Cox preformance bug is going to bite.
Learn for the Masters, Larry, Tim, Tony, amoung others.
I have a nice notebook on Cox Preformance thanks to these guys.
Spent over an hour on the phone with Tony just on Cylinder blueprinting. Spent 45 minutes talking with Davis Diesel about timing and reeds.
Open that engine up at your own risk!
Before you know it you'll be soaked in caster, tach in hand, trying to get every possible RPM out of the thing!
Going to run three engines this weekend, maybe four if my Witch Doctor comes in.
My Cox adventure started with a simple fuel tank problem with my HV.
Good luck with your HV! I've all but forgotten mine while being side-tracked with engines!