Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 129757 times)

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #435 on: February 19, 2020, 04:06:06 AM »
James,
You know you could put the adjustable ballast you made on a ball screw of some sort and a 360 degree continuously rotating servo and not need adjustable trim tabs. But consider using the stuff that actually does something in the boat as a ballast because in the long run that will save you some weight.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #436 on: April 06, 2020, 05:30:58 PM »
Starting to get the shop back together. New LED lights & power to all machines is complete. Next comes the 12,000 BTU mini split.

Jim Allen

Offline nj111

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #437 on: April 06, 2020, 06:08:06 PM »
Good to see this as it has been a most informative thread!
Nick

Offline CHP

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #438 on: April 10, 2020, 02:29:46 PM »
I have no idea where to begin when discussing the hydraulic dynamometer. Maybe if some engine

More to come.

Jim Allen
great article, thanks, any chance of getting plans, or more specification.
i'm in the process to get as much info as possible to build a Dyno for chainsaws.
Thanks
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #439 on: April 10, 2020, 03:08:52 PM »
Inertial dynos are the easiest to build and are especially useful for two stroke engines.  See my article at namba.com/content/library/propwash/2019/april/16/ for my experiences and advice for new builds.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #440 on: April 10, 2020, 10:18:49 PM »
"great article, thanks, any chance of getting plans, or more specification.
i'm in the process to get as much info as possible to build a Dyno for chainsaws.
Thanks"

Sorry, there are no plans available. However any & all question would be answered as to specifications. Take a close look at the Kahn Hydraulic Dynamometers. While an inertia dyno is easier to build, you probably would prefer a constant load type for testing a chainsaw.
Jim Allen

Offline CHP

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #441 on: April 11, 2020, 02:29:57 PM »
Inertial dynos are the easiest to build and are especially useful for two stroke engines.  See my article at namba.com/content/library/propwash/2019/april/16/ for my experiences and advice for new builds.

Lohring Miller
Thanks, I already have the copy you did in  Model Engine Builders in 2008 :ThumbsUp:
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #442 on: April 11, 2020, 05:00:06 PM »
One of the few areas where Jim and I disagree is on the subject of inertial vs brake dynos.  An inertial dyno is not only easy to build, it is also easy to get a full power curve in a matter of seconds.  That way you can see what part of the power curve your change affected.  You can test a lot of different things in a short time.  We often ran 50 dyno runs in an afternoon.  You can argue about how accurate the readings are, but comparisons are what you need, not absolute accuracy.  We did compare our Quickdraw readings with the readings Quickdraw got on their brake dyno on the same engine.  They were very similar.  That said, A brake dyno is superior for endurance, fuel consumption, and similar tests that require a significant time at a fixed power level.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #443 on: April 13, 2020, 01:31:10 AM »
I agree in part with what Lohring has written. However, the main reason I chose a hydraulic rather than an inertia type dynamometer is the maximum RPM speed possible with a water brake & the ability to open & close the throttle while the engine is under under load. For example the Kahn #101-030 has a max HP rating of 70 at 35,000 max RPM & 14.7 ft lb max torque. I have used my hydraulic dyno many times, testing my .90 cu in engine at 7.6+ HP, 32,000+ RPM &  1.25+ ft lb of torque; throttling the engine up & down during the 4.5 minute dyno run. I should note that I have run this engine at 35,000+. Can an inertia dyno duplicate throttling an engine up & down while still under Load? Can an inertia dyno survive at these RPM's? Why do high performance two stroke engine builders use hydraulic type dynamometers?

Jim Allen

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #444 on: April 13, 2020, 04:55:54 PM »
You need to check the stress on an inertial dyno wheel for the design rpm.  Even though the original design was for 20,000 rpm, we ran to 25,000 rpm many times.  I used heat treated 4340 steel for the flywheel which had a respectable safety factor.  It isn't a problem to design flywheels for higher rpms.  I have a spreadsheet that does this as well as guessing at the time for the run up.  The stress calculation method was checked by an engineer.  You still need to be very careful in the manufacture of the flywheel. 

We only did full throttle runs.  The flywheel we used was sized to simulate the run up  to the traps for speed runs.  The acceleration out of a corner down the straight is similar.  In racing you nearly always run at full throttle at these times and the inertial dyno simulates this very well.   I believe there is a place for brake dynos for testing a variety of things like Jim said.  We even used a water brake dyno Mike had for our electric hydro.  It took around the same time to get a few points on the power curve as 50 inertial dyno runs.

Lohring Miller

Offline CHP

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #445 on: April 13, 2020, 07:50:34 PM »
the underdogsracing.com isn't available anymore.
any chance your dyno would be big enough for chainsaw up to 80cc.????
I also have a 1.5 induction ac motor???
thanks
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #446 on: April 14, 2020, 02:08:51 AM »
My hydraulic dynamometer was designed for engines up to 16.4 cc (1.00cu in). A typical single disc type hydraulic dyno can absorb 180 HP at 25,000 RPM with 60 ft lb of torque. The rotating disc is usually made of hardened stainless steel with the entire rotating  assembly dynamically balanced. My rotors were made of aluminum & they were not balanced. The single perforated disc rotates in a housing between perforated stators. The amount of power absorbed by the dyno is a function of the water level in the housing & the rotor's speed.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #447 on: April 14, 2020, 06:12:10 PM »
High speed, high HP hydraulic dynamometers contain the basic parts shown in the illustration. They are extremely durable, very easy to operate, have light weight & have full power absorption in either direction of rotation. The illustration shown is a typical Kahn high speed dyno which I used as a model for my miniature hydraulic dyno.

Jim Allen

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #448 on: May 19, 2020, 05:41:02 PM »
A purpose built eddy current or brushless motor turned generator for this application with braking load can work as good or better than either of these executed correctly at any rpm. It can be used in inertial or steady state mode. The inertial wheel safe speed can be enhanced by a properly designed CFK or Titanium retention sleeve. Even Inconel might work for you needs. You have to design and test it's limits. The sleeve needs to be pressed fit so you make an undersised mandrel by a few thousandths to facilitate an extended no contact speed and wrap it with CFK and high temperature epoxy then vacuum bag it. Turn the sleeve and part it off on the lathe. I have a paper with reference numbers but surely a masters in ME can determine your sleeves needed strength at the proposed surface speeds at you wheel diameter. You could also wrap the wheel with titanium thread with some type of pre tensioning apparatus you build for it. You can look up and mimic that process.



@ you both.....
What differentce would it make if you are only looking for improvement in your motors with no reference to anything else on a particular dyno? The only time youd run into trouble is when you try to make direct comparisons of your data if your machines aren't calibrated or read to the same level of accuracy.  If calibration reporting IEEE  sensors aren't used academically speaking there's not the concurrence from the body you'd wish for anyway. These style sensors do live calibration updates with the central body as it pertains to calibrations etc. So basically it provides colleagues and the IEEE the assurance your stuff read correctly. It is updated through the technology better know as the world wide web.

BTW have you seen this James?
https://pelz-motorenentwicklung.de/wp-content/uploads/2020/03/Gravierende-Vorteile-T-Motor_-20200218.pdf

Thanks,
Hubert
« Last Edit: May 19, 2020, 07:28:30 PM by DRT »

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #449 on: May 19, 2020, 06:13:09 PM »
 :LittleAngel:
« Last Edit: May 19, 2020, 06:19:17 PM by DRT »

 

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