News:


Advertise Here

  • May 23, 2022, 09:08:11 AM

Login with username, password and session length

Author Topic: I. C. Engine vibrations.  (Read 1705 times)

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1704
I. C. Engine vibrations.
« on: April 09, 2021, 04:01:32 PM »
Has anyone pondered about vibes from an I.C. engine contributing to it's aerodynamics?
I know there is some evidence that hinge lines benefit by shaking loose stiction but that's not what this is about.
Perhaps a rough shark skin surface combined with 10,000 micro movements a minute may help flow.

Now that I have thrown the meat into the lions cage let's see what comes up.
Chris.
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Online Ken Culbertson

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4477
Re: I. C. Engine vibrations.
« Reply #1 on: April 10, 2021, 12:58:52 AM »
Has anyone pondered about vibes from an I.C. engine contributing to it's aerodynamics?
I know there is some evidence that hinge lines benefit by shaking loose stiction but that's not what this is about.
Perhaps a rough shark skin surface combined with 10,000 micro movements a minute may help flow.

Now that I have thrown the meat into the lions cage let's see what comes up.
Chris.
The only thing that I personally feel that vibration *adds* is that you can see all of the loose balsa you forgot to get out of the canopy bouncing around.
I have 57 years flying IC and only 4 invested in electric.  Once I learned that the controls needed to be free of all binding because of the lack of vibration all I found was a plane that flew better, even the ones I converted.  So if vibration adds to aerodynamics then the high frequency vibration of the electrics must be even better.  I do miss the sound....
AMA 15382
If it is not broke, don't fix it.
USAF 1968-1974 TAC

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 12583
Re: I. C. Engine vibrations.
« Reply #2 on: April 10, 2021, 01:40:21 PM »
Has anyone pondered about vibes from an I.C. engine contributing to it's aerodynamics?
I know there is some evidence that hinge lines benefit by shaking loose stiction but that's not what this is about.
Perhaps a rough shark skin surface combined with 10,000 micro movements a minute may help flow.

Right off, I don't know. My gut feeling is that it doesn't matter, but I would be open to contrary evidence.

    Brett

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1704
Re: I. C. Engine vibrations.
« Reply #3 on: April 10, 2021, 03:18:25 PM »
It would be interesting to deliberately get away from dead flat high gloss finishes and try something similar racing yatchs riblets skin developed at Langley by NASA.
It's available in tape form and designed to reduce subsonic flow.
Chris.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.nasa.gov/centers/langley/news/factsheets/Riblets.html&ved=2ahUKEwiJuq6j0_TvAhVegtgFHWSjASsQFjAFegQIDhAC&usg=AOvVaw1vxl2Mw_pHMwVav5k19ngh&cshid=1618091171943
« Last Edit: April 10, 2021, 03:47:19 PM by Chris Wilson »
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 12583
Re: I. C. Engine vibrations.
« Reply #4 on: April 10, 2021, 04:16:42 PM »
It would be interesting to deliberately get away from dead flat high gloss finishes and try something similar racing yatchs riblets skin developed at Langley by NASA.
It's available in tape form and designed to reduce subsonic flow.
Chris.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.nasa.gov/centers/langley/news/factsheets/Riblets.html&ved=2ahUKEwiJuq6j0_TvAhVegtgFHWSjASsQFjAFegQIDhAC&usg=AOvVaw1vxl2Mw_pHMwVav5k19ngh&cshid=1618091171943

   Or, as a smaller-scale experiment - festoon it with VGs , trip strips, turbulators, and zizag strips.

     Brett

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1704
Re: I. C. Engine vibrations.
« Reply #5 on: April 10, 2021, 04:36:29 PM »
   Or, as a smaller-scale experiment - festoon it with VGs , trip strips, turbulators, and zizag strips.

     Brett
The issue I see there is that site specific application suits only a small range of use and having it applied generally with out regard of trip zones  maybe of greater benefit.
Coupled with ribs that resonate with I.C. engines would drastically increase the effective rlb size and take this discussion well outside of known research.
Ultimately I would like to see an equivalent product like Solarfilm made with a herringbone pattern on it and cover the entire model.
Such a film exists but not on a commercial level and comes from wind turbine research.
Chris.
« Last Edit: April 10, 2021, 08:59:28 PM by Chris Wilson »
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Air Ministry .

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 4419
Re: I. C. Engine vibrations.
« Reply #6 on: April 10, 2021, 08:34:19 PM »
Could be the ' boundary layer ' effect would produce less drag but more / better ' LIFT ' , as the airflow wouldnt fall off / break away from the aifoil / flaps as easily. Maybe .

You might have to vary the surface to suit the temperature / atmospheric density . VD~ S?P

Online Ken Culbertson

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4477
Re: I. C. Engine vibrations.
« Reply #7 on: April 10, 2021, 10:42:15 PM »
The issue I see there is that site specific application suits only a small range of use and having it applied generally with out regard of trip zones  maybe of greater benefit.
Coupled with ribs that resonate with I.C. engines would drastically increase the effective rlb size and take this discussion well outside of known research.
Ultimately I would like to see an equivalent product line Solarfilm made with a herringbone pattern on it and cover the entire model.
Such a film exists but not on a commercial level and comes from wind turbine research.
Chris.
You raise an interesting point.  None of this has anything to do with vibration but I have never had shiny clear coating and rubbing out make any plane fly better.  Score higher, yes but fly better?  It might be interesting to take a nearly finished electric and fly it with a fresh coat of unsanded filler, then sand it smooth and fly it again.

Ken
AMA 15382
If it is not broke, don't fix it.
USAF 1968-1974 TAC

Offline Dave Hull

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1473
Re: I. C. Engine vibrations.
« Reply #8 on: June 15, 2021, 12:30:28 AM »
A bit more to add to the thought experiment:


(Ok, can't remember how to link one thread to another. Go look at "Energized Boundary Layer" in the engineering section--while I try to figure this out again.)



Offline Jim Hoffman

  • 21 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 483
Re: I. C. Engine vibrations.
« Reply #9 on: June 16, 2021, 05:58:45 PM »
It’s been my experience that hunting (low frequency pitch limit cycle)  is more often seen in E powered stunters than IC.
There are two theories (IMHO) that may explain this……

1)   Higher inertia effects from the rotational mass of the motor, crankshaft, prop and spinner in E-power planes.
2)   Some boundary layer disturbance that may exist more in IC than E-power due to vibration.

I have been able to trim both IC and E-power stunters to a reasonably high level.

Online Dennis Adamisin

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4132
Re: I. C. Engine vibrations.
« Reply #10 on: June 17, 2021, 07:26:20 AM »
It’s been my experience that hunting (low frequency pitch limit cycle)  is more often seen in E powered stunters than IC.
There are two theories (IMHO) that may explain this……

1)   Higher inertia effects from the rotational mass of the motor, crankshaft, prop and spinner in E-power planes.
2)   Some boundary layer disturbance that may exist more in IC than E-power due to vibration.

I have been able to trim both IC and E-power stunters to a reasonably high level.

I vote for #1.  I have been having great luck with thrust line adjustments to cure hunting on several E-birds lately...
Denny Adamisin
Fort Wayne, IN

"Dear Lord, please keep your arm around my shoulder - and your hand over my mouth..."

Offline phil c

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2363
Re: I. C. Engine vibrations.
« Reply #11 on: June 30, 2021, 09:16:23 AM »
It’s been my experience that hunting (low frequency pitch limit cycle)  is more often seen in E powered stunters than IC.
There are two theories (IMHO) that may explain this……

1)   Higher inertia effects from the rotational mass of the motor, crankshaft, prop and spinner in E-power planes.
2)   Some boundary layer disturbance that may exist more in IC than E-power due to vibration.

I have been able to trim both IC and E-power stunters to a reasonably high level.


Not anything to do so resurrect an interesting one.
Just looking at the planes, I'd opine that electrics may no have enough vibration to keep the controls from sticking around neutral.  Particularly, electrics may be too smooth running, and not generate really sharp vibrations that IC engines are known for. 
phil Cartier

Offline PJ Rowland

  • AUS - 29541 AMA - 809970
  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2056
  • Melbourne - AUSTRALIA
Re: I. C. Engine vibrations.
« Reply #12 on: July 06, 2021, 10:22:24 PM »
Your actually asking 2 different questions.

Firstly..


Perhaps a rough shark skin surface combined with 10,000 micro movements a minute may help flow.

Well it will.. its about pressure and creating a change in the pressure of the airflow. You suggestion is similar to the golf ball dimple. Not all about drag reduction but about micro pockets of pressure differences.

Many people felt open bay wings were giving some improvement vs a perfect foam wing. Again this is explained by the pressure changes that occur along the chord line.

In the past much of this has been speculation but with programs like Ansys you can see how airflow reacts to different objects.

Micro scales, if you look.at a shark skin under electron microscope they look closer to a formular front wing crossed with a 3 way vortex generator.

Even if you wanted to copy the technology,  I don't know how you might even come close to it.

I hate agreeing with brett because it happens to often.

Having studied boundaries and how they interact within certain conditions,  im not convinced that there is anything to be gained by "vibrational resonance enhancing boundary layer efficiency "

I dont think the airflow molecules stay attached long enough to the surface to be bothered by a vibrating surface. The issue is the plane is flying through a very dynamic environment with à HUGE amount of pressure change.

Im not a rocket scientist, but I figure they vibrate ALOT more than our IC or electric ships do, if vibrational resonance was a "thing" they would see it there, and Ive not read anything to suggest its even close to "a thing"


The emergence of hunting in electric is simply solved by thrust line adjustment. Electric motors deliver power to the airframe differently thus might need a tweak.. not every design hunts .. some do it worse..

There is more vibration loosening control systems than electric does.. so that's a "thing"
If you always put limit on everything you do, physical or anything else. It will spread into your work and into your life. There are no limits. There are only plateaus, and you must not stay there, you must go beyond them.” - Bruce Lee.

...
 I Yearn for a world where chickens can cross the road without having their motives questioned.


Advertise Here
Tags:
 


Advertise Here