VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.






VAF on Twitter:
@VansAirForceNet

  #11  
Old 08-25-2022, 01:50 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 6,012
Default

If done properly, it can be done and it will work.

Having said that - I'm an engineer by trade, a tinkerer and gearhead by choice, and I love turning wrenches on my plane almost as much as I love flying it. I installed a Lycoming.
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2022 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
Reply With Quote
  #12  
Old 08-25-2022, 02:01 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 11,054
Default

Quote:
Originally Posted by Robercom View Post
Performance is not good... It drinks 10.5 at a best of 143kts.
Brian, what seems to the cause (or causes) of the performance loss?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #13  
Old 09-07-2022, 04:07 AM
Lufthans's Avatar
Lufthans Lufthans is offline
 
Join Date: Dec 2017
Location: Hilversum, The Netherlands
Posts: 224
Default

Quote:
Originally Posted by DanH View Post
Brian, what seems to the cause (or causes) of the performance loss?
Thermodynamics and sub-optimal engineering Dan.

Liquid cooling has advantages and disadvantages.

The disadvantages are clear - added complexity, added failure points, possibly added weight.

The advantages include better temperature control and thus the possibility of running closer engine tolerances. So less oil consumption, less blow-by and thus longer lasting oil. Furthermore no shock cooling, and - and here’s the kicker - the possibility to transport heat to have it removed from the system to a more suitable place than the up-front-in-the-nose location that you are forced to with air cooling.

Turns out that right behind the prop is not the best place for cooling. No good flow due to disturbances from the prop, no room to create a smooth path for air to flow without having to navigate all sorts of turns and around objects. As a result, with our air-cooled engines, cooling drag can form a significant part of the total drag of the airplane. As high as 40%.

The P51 Mustang is also known for its “Meredith effect” of its cooling system, which according to many actually produces a little thrust. While this is debatable, what its cooling doesn’t do is create 40% of the total drag of the Mustang. 

The Spitfire and BF-109 with their wing-mounted radiators don’t do so bad either.

The secret is the smooth ducting that they can have, slowing down the air to hit the radiators at a significantly reduced speed, and then once through the radiator, the air can be accelerated again to exit at roughly the same speed as it entered. Thus posing very little drag. And enabled by liquid cooling, which transfers the heat from the engine to that place in the rear fuselage or wing.

One thing that air cooling has going for it is that you need less air over an engine than you need through a radiator. Simple thermodynamics - heat transfer is proportional to the difference in temperature between the media. And the cylinder heads of an air cooled engine get hotter than the coolant in a radiator. And so you need more air through that radiator than you would over an equally powerful air-cooled engine.

Now for the Eggenfellner.

Presumably for reasons of simplified installation, Eggenfellner chose to not take advantage of the option of moving the heat to a more suitable place for cooling. In stead, he stuffed the radiators in the nose. Worst of both worlds - bad cooling location, no way to create a smooth airflow with an engine sitting right behind the radiators, and to add insult to injury you need more air through them than you would have needed with an air cooled engine.

Result - massive air resistance and mediocre cooling.

And there’s your answer…

As an aside - an excellent read on this subject are the (now ancient but still valid) Hans Mayer articles:



http://www.glasairproject.com/Glasai...ngSystems1.htm
http://www.glasairproject.com/Glasai...ngSystems2.htm
http://www.glasairproject.com/Glasai...ngSystems3.htm
http://www.glasairproject.com/Glasai...ngSystems4.htm
__________________
Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.

Last edited by Lufthans : 09-14-2022 at 06:50 AM.
Reply With Quote
  #14  
Old 10-02-2022, 02:48 PM
dlomheim dlomheim is offline
 
Join Date: Sep 2006
Location: (2OK2) OK City, OK
Posts: 400
Default 800 Hr. Subie!

Robercom: From watching the Egg in RV fiasco play out from the beginning, one of the biggest issues was always the "factory" PSRU, as seen by the requirement to keep coming out with new "Generations" (1, 2, 3, etc.). Great to see a Subie out there with 800 hrs. on it, but sadly more than one RV ended up "off airport" when their PSRU failed, safe flying with yours.

Doug

RV-9A Mazda 13B/FWF

Last edited by dlomheim : 10-02-2022 at 02:52 PM.
Reply With Quote
  #15  
Old 10-02-2022, 08:08 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 6,012
Default

How did the Gen3 fare? Did it finally have a good torsional vibration analysis done on it?
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2022 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
Reply With Quote
  #16  
Old 10-04-2022, 08:21 AM
Lufthans's Avatar
Lufthans Lufthans is offline
 
Join Date: Dec 2017
Location: Hilversum, The Netherlands
Posts: 224
Default

Quote:
Originally Posted by airguy View Post
How did the Gen3 fare? Did it finally have a good torsional vibration analysis done on it?
It seems like it really depended on how lucky you were. Some units were doing perfectly fine, others ran very hot.

I've seen a Gen 3 taken apart. It had some questionable engineering practices inside. Gears WELDED onto an axis. Ball bearings doubled up and slid up against the weld. That kind.

Seemed like there was plenty of room for unit-to-unit differences.

Some people have reported issues with severe fretting on the splined output shaft.

Having said that - For a friend, I've built a Robin with a 6-cylinder Egg engine and gen 3 gearbox coupled to a 3-bladed MT prop. The unit has over 500 hours with no issues.

I seriously doubt if a torsional analysis has ever been performed..
__________________
Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.

Last edited by Lufthans : 10-04-2022 at 08:24 AM.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 11:24 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.