Run in stand/dyno build.

[John Beardslee]

Bad, bad, bad, harmonic vibrations. Don't know what is causing it. But something is not happy.

I’d take a look at your drive shaft, I’m no expert but it would be were I’d look for an harmonics problem.
Thanks John

 

[Terry Keeley]

Here's an rpm plot of the "event".

 

[Steve White]

Hmmmmm....

The above curve is consistent? That's amazing, I thought it was just the torque dropping off - but, RPM drops out as well. That's gotta be vibration to dampen the RPM like that. Could be bearing chatter. The RPM drop rate is significantly steeper than the torque curve.

Red flag, danger Will Robinson - extreme caution.

You'll figure it you.

 

[Terry Keeley]

Could this be it? Watch carefully what happens at 7 seconds.

Hmmm...

 

[dwilfong]

Nitro need load to burn.

Could this be it? Watch carefully what happens at 7 seconds.

Hmmm...

Nitro needs load to burn..............
Not enough will act just like to much.
Fickle little thing this Nitro is.

 

[Mike Rappold]

Terry,
What did the glow plug look like after the run?

Mike

 

[Terry Keeley]

Terry,
What did the glow plug look like after the run?

Mike

Pristine. And I definitely started out on the rich side...

 

[Steve White]

What does the rundown slope look like when you chop the throttle? Same slope?

 

[Ken Retallick]

Terry, watch the exhaust gasses change when it does that. Almost as if its running out of fuel. Fuel tank vibrating ?

 

[Terry Keeley]

Terry, watch the exhaust gasses change when it does that. Almost as if its running out of fuel. Fuel tank vibrating ?

Thanks, I really don't think it's going lean even tho it sure sounds like it. The first time it happened I thought I burned the plug.

Dave Marles said this was a normal event on the dyno well after the power peak. I later talked to a buddy that ran karts and he said it was almost like you reached down and turned the needle full rich, then Brian Spitzer reminded me about nitro needing load to burn and we both had the light go off thinking about fuel cars.

Did you ever see anything like this when you ran your dyno?

 

[Chris Davis]

Jim Wilson on multiple occasions during testing used to actually show me the effects of load and the ability to burn nitro. On as extremely well tuned boat he would reduce the load and results were similar to what you are experiencing. The boat would pull hard out of the corners. Come up to rpm and just drop off as if brakes were applied. Jim's boats ran so much fuel that he ran an onboard glow plug to keep things lit when the load dropped off and on the bench

 

[Brian Spitzer]

Terry,
Awesome work Terry. Watching the videos, looking what you've posted on the data, and the plug is pristine and nothing else shows an signs of detonation, I'm confident you're too rich and it started 4 cycling which caused the harmonics.

 

[dwilfong]

So Terry if it did run out of load what are you going to do?
How are you going to add load as you test for more power from the eng?

 

[Terry Keeley]

So Terry if it did run out of load what are you going to do?
How are you going to add load as you test for more power from the eng?

I think it ran out of load only because it was 2K past the power peak, for the way it was set up.

I've seen this in a boat at the end of the SAW when the motor starts "4 cycling", thought it was too much cooling so I cut the water back and it cleaned up. In hindsight I probably could have propped up a bit and gone faster.

I think that how much power our little motors make is closely tied to how well this nitro stuff we run burns, and optimizing the timing of that burn. This is effected by the needle setting, type of fuel, plug, head, cooling, pipe & piston fit to name a few.

I'm doing some work now to move the magnet pickup for the wheel and should be running it again tomorrow or Wed. I'll try again as is and let it go a bit longer to see what happens, then I'll lean the needle slightly to see if it cleans up.

I was wondering all along how to get an optimum needle setting with this thing, I just didn't think it would be the first thing I'd havta figure out, lol.

 

[Ken Retallick]

Terry, too long ago to remember!

I would try the pipe at different lengths to see if the 'Glitch' moves up and down rpm with corresponding pipe lengths.

Look like your real testing of nitro engine behavior has already begun.

 

[brad nichols]

Have you tried leaving the glow plug hooked up? When I use to balance band saw wheels 4 to 8 feet in diameter, sometimes you would get one that would go through that harmonic stage on it spooling up but would go away at run speed.

Brad

 

[dwilfong]

I think it ran out of load only because it was 2K past the power peak, for the way it was set up.

I've seen this in a boat at the end of the SAW when the motor starts "4 cycling", thought it was too much cooling so I cut the water back and it cleaned up. In hindsight I probably could have propped up a bit and gone faster.

I think that how much power our little motors make is closely tied to how well this nitro stuff we run burns, and optimizing the timing of that burn. This is effected by the needle setting, type of fuel, plug, head, cooling, pipe & piston fit to name a few.

I'm doing some work now to move the magnet pickup for the wheel and should be running it again tomorrow or Wed. I'll try again as is and let it go a bit longer to see what happens, then I'll lean the needle slightly to see if it cleans up.

I was wondering all along how to get an optimum needle setting with this thing, I just didn't think it would be the first thing I'd havta figure out, lol.

Reduce the nitro % and see what happens.

 

[Terry Keeley]

A little diversion, my Consigliere's "in-line four" on a test stand with a Byron fan:

https://photos.google.com/share/AF1...?key=Tzcyc3NGUEc0VktPVDB6emk5T2NLTHFhelhydjZR
The output shaft is belt over driven 2:1, rpm is the motor.

 

[DaveMarles]

Terry, try changing the pipe length or better still change to a different pipe but keep plug to start of stinger the same length then see if the dip is still there or moved to a different rpm. That way you will know if it is a problem in the drivetrain. My experience is that it is all in the pipe design. Don't overthink it . (As if you would)

 

[Terry Keeley]

I changed the pickup location for the wheel and upgraded to the Pro version so you can input better wheel data and do a "Coastdown" test to check friction in the system. It also graphs torque in oz.in which is better for our little motors. The result was the calculated HP went up and I should I be very close to actual numbers now.

I think the surging at high revs might be the load decreasing as mentioned but also the clutch slipping a bit, or a combination of the two. It definitely slipped once when it got hot and looking closely at the rpm plots I can see it slipping slightly.

Here's the last run of the day (no kidding), I didn't change the needle or anything else from the runs a few days ago. I think that since it was the third pull of the run plus the tank being half empty caused the motor to lean out a bit and there's no surging. I thought I blew the motor but it's OK, the collet unscrewed as I was closing the throttle, I have some ideas to fix that including just closing the throttle quicker to let the one-way bearing take over. I'll also add some tungsten weights to the clutch to (hopefully) get it to lock up better.

My buddy Mikey Ross (Suicidal Engines) said I was "starting down the rabbit hole", he was right, lol.