THE BEAST!

[Terry Keeley]

Is this it?

 

[Terry Keeley]

What Dave said.    Your picture is close to what I'm considering for my new dyno.  Thanks.  Watch the flywheel diameter if you plan to test nitro engines.  We melted the piston on all (3) 11 cc nitro engines we tested. 

The first inertial dyno for model engines was designed and built by Marty Davis and Brian Callahan.  John Ackerman built the dyno.[SIZE=10pt]  [/SIZE]I found an article on it at https://web.archive.org/web/20030205134346/http://rcboat.com:80/dyno.htm   and https://web.archive.org/web/20030209190150/http://www.rcboat.com:80/dynotech.htm It has calculations and mentions that they used a 3.75 inch diameter by .75 inch thick flywheel for .45 cubic inch engines.

Why did you melt the pistons?  Too long a run up time?

 

[shoboat]

John,

How much would the bearings cost?

It would be nice to get that Dyno back to work?

Could you ask Marty or Norm what it would take to make this happen again?

I would be willing to pay for whatever it needs to get it back in service.

I think there is a lot of useful information that a good Dyno will provide us all.

Thanks,

Mark Sholund

 

[LohringMiller]

Why did you melt the pistons?  Too long a run up time?

I think the load from a 5" flywheel was too high.  We saw around 4 hp just before the peak when the engine failed.

Lohring Miller

 

[John Beardslee]

John,

How much would the bearings cost?

It would be nice to get that Dyno back to work?

Could you ask Marty or Norm what it would take to make this happen again?

I would be willing to pay for whatever it needs to get it back in service.

I think there is a lot of useful information that a good Dyno will provide us all.

Thanks,

Mark Sholund

I’ll ask and go from there. It’s been awhile and I don’t remember where we left off.

 

[shoboat]

Thanks John it would be awesome to get that dyno back up and running. I know there is still a lot more performance to learn about in our little engines. Pipes and head buttons are my main interest.

Mark Sholund

 

[David Ashcroft]

Thanks John it would be awesome to get that dyno back up and running. I know there is still a lot more performance to learn about in our little engines. Pipes and head buttons are my main interest.

Mark Sholund

With names likes Ackerman,Martin,Doer and a few  other engine gurus  ,I would think all that testing was allready covered years ago.

 

[shoboat]

David,

Don’t you think our engines have changed quite a bit the last 20years?

I know we have found more power in our tuned pipes, fuel, and head button designs.

Do you know how much horsepower, rpm, and torque your engines put out currently?

It would be nice to know what changes make a difference? A few years ago I had a chance

to have one of my 12-engines tested on a Dyno, and we found almost 1/4 more horsepower

and 10 more ounce/inches of torque from just a head button change. I thought that was a lot

of power with just a head button change?

Thanks For Reading,

Mark Sholund

 

[LohringMiller]

In an afternoon of dyno testing you can test changes that would take a year of on the water testing.  Once you get the engine and pipe right, you just need to work on props and hull changes with water testing.  An onboard data logger really helps with this, but a peak reading tach and GPS or radar gun to get matching speed works too.

Lohring Miller

 

[Terry Keeley]

In an afternoon of dyno testing you can test changes that would take a year of on the water testing.  Once you get the engine and pipe right, you just need to work on props and hull changes with water testing.  An onboard data logger really helps with this, but a peak reading tach and GPS or radar gun to get matching speed works too.

Lohring Miller

What exactly were you looking for when you did your testing?  Just greater peak HP?  Flatter torque curves?  More over run? 

 

[DaveMarles]

Better peak hp and most important over-rev. but trying to maintain a decent torque curve at the same time

. 

 

[Terry Keeley]

Better peak hp and most important over-rev. but trying to maintain a decent torque curve at the same time

. 

By "over-rev" do you mean you want to keep making decent torque past the HP peak?

Why not just prop the boat to rev to the peak and not past it?

 

[DaveMarles]

Terry,  When your boat is running at it's maximum speed it is well past the rpm point of peak hp. 

 

[Terry Keeley]

Oh, see I didn't even know that.  My fastest recorded run with the Eagle Tree is 118 mph and just about 29K rpm, so you're saying the hp peak could be say at 25K?

So you want to try and flatten the HP curve past the peak and not have it fall off sharply?

 

[DaveMarles]

Oh, see I didn't even know that.  My fastest recorded run with the Eagle Tree is 118 mph and just about 29K rpm, so you're saying the hp peak could be say at 25K?

So you want to try and flatten the HP curve past the peak and not have it fall off sharply?

Yes to both. 

 

[LohringMiller]

Below is a very early series of tests we ran.  We hadn't solved the scatter issues with our dyno but you can see the basic information.  The flat M&D and Quickdraw curves are the kind of power curves that are easy to prop to and give great heat racing performance.  It's mostly about the pipe.  We actually depowered a CMB to shift the power curve to higher rpm for SAW runs.

Lohring Miller

 

[dwilfong]

Over rev is the holly grail if you ask me. at top speed the boat is light on the water and has inertia to keep it going. Dose not take much to keep the revs going.

I have always thought of it as taking the governor off the eng as fare as RPM potential.

So what is holding back the RPM's on a eng in a boat with a optimal set up?

At what point do harmonics take over the eng and every thing just gets in the way?

What will hold it back from free spooling at top RPM?

Just a few questions??????

 

[DaveMarles]

Over rev is the holly grail if you ask me. at top speed the boat is light on the water and has inertia to keep it going. Dose not take much to keep the revs going.

I have always thought of it as taking the governor off the eng as fare as RPM potential.

So what is holding back the RPM's on a eng in a boat with a optimal set up?

At what point do harmonics take over the eng and every thing just gets in the way?

What will hold it back from free spooling at top RPM?

Just a few questions??????

On nitro engines....

1. On a rigger the pipe is being cooled by the airflow as you go faster. That is just what you do not want. 

2. Pipe design. In general,  a short steep angled rear cone will cut off the power after peak. A shallow rear cone angle will allow more over-rev.

On gas engines the same applies but you can also extend over-rev more easily by severely retarding the ignition after peak.

 

[LohringMiller]

With the right pipe mechanical issues are limiting.  The CMB 35 is a good example.  First the AAC piston and sleeves failed.  Even one of the ringed piston and sleeves failed due to out of roundness at the exhaust port.  Then we got flywheel strikes from crankshaft flexing.  An additional front bearing and electronic ignition solved that.  Finally the wrist pin hole in the piston started to elongate after runs to 25,000 rpm.  In most other engines the big end rod bearing is the limiting factor.  Stock Zenoah rod bearings start to have a short life over 20,000 rpm.  Bushed rods fail frequently in nitro engines.  Piston speed is probably the best indicator of mechanical stress, not rpm.  None of our engines get close to the 5000+ feet per minute (35+ meters per second) piston speeds of full size race engines.

We ran water injection to broaden the power curve on a high rpm pipe.  It worked really well giving flat power from 18,000 rpm to 23,000 rpm. We could have run faster but for the above mentioned mechanical limits.

Lohring Miller

 

[dwilfong]

Yes wrapping the pipe dose a lot to keep things going.

Also found that opening intake timing on the nitro eng at BDC help a lot. 

Tested a duel rear cone pipe and this also helped.

Looked at the AB fat pipe for inspiration on my 1.01 pipe.