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.


Go Back   VAF Forums > RV Firewall Forward Section > Propellers
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 07-07-2021, 01:49 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 403
Default do continuous RPM restrictions still apply after dynamic propeller balancing?

Hi All,

on my RV7 i installed a standard Hartzell 72" aluminum BA CS prop. the engine is an IO-375 low compression from aerosport which is kinda exotic. because of that i had an hard time to figure out the RPM restrictions for continuous cruise power with this engine/propeller combo. aerosport told me that the io375 has basically the same restrictions as the 360 but they can't say for sure.

i like more sedate power settings during cruise so the local A/P did the dynamic prop balancing at 2200 RPM. i don't recall the reached value in inches/second but he said that he never managed to get it that low before and the vibrations seem to me low at 2200.

info i have is that for a 360/hartzell continuous operation between 2000 and 2300 should be avoided. does that still apply after dynamic prop balancing in that RPM range and you're happy with vibration?

Kay

Last edited by KayS : 07-07-2021 at 03:00 AM.
Reply With Quote
  #2  
Old 07-07-2021, 04:52 AM
rzbill's Avatar
rzbill rzbill is offline
 
Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,745
Default

The rpm limits recommended by Hartzell are not affected by dynamic balance on the safe assumption the original tested prop was within reasonable balance. The restrictions come from different physical phenomenon (angular resonance vs power impulse frequency and amplitude for instance)
__________________
Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.

Last edited by rzbill : 07-07-2021 at 04:59 AM.
Reply With Quote
  #3  
Old 07-07-2021, 05:01 AM
Tankerpilot75's Avatar
Tankerpilot75 Tankerpilot75 is offline
 
Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 679
Default

I’ve never seen this prop rpm restriction for the standard Hartzell 72” CS aluminum propeller. I too like to cruise “comfortably” and usually set my flight rpm at 2350. Please give a reference for this restriction so I can read about it.
__________________
Jim Harris, ATP, T38, EC/KC-135A/E/R, 2008 RV7A, 2nd owner, N523RM (2015)
Superior XPIO-360, Hartzel CS prop, Dual GRT Horizon EX with ARINC, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level & auto-trim, Tosten 6 button Military Grips, FlightBox wired to EX, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
Retired - Living the dream - going broke!
Reply With Quote
  #4  
Old 07-07-2021, 05:58 AM
RVDan RVDan is offline
 
Join Date: Jun 2012
Location: Frederick, MD
Posts: 940
Default

The restriction is listed on the propeller type certificate and in the Hartzell Propeller manual, which you should have. It is not really just advice. If you stay inside of the RPM range, the prop stresses due to power pulses and blade resonance shorten the fatigue life of the blades drastically, potentially resulting in blade loss. The RPM limitation is 2000 to 2200 RPMs for the affected propellers.
For the affected propellers there is also a limit on the time you can spend between 2500 and 2700 RPMs.
__________________
Dan Morris
Frederick, MD
PA28-140
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Retired Aerospace Engineer and A&P/IA
Reply With Quote
  #5  
Old 07-07-2021, 06:31 AM
Champ's Avatar
Champ Champ is offline
 
Join Date: Apr 2012
Location: Kingsville, Ontario, Canada
Posts: 362
Default

I have the same engine as the OP with a non counter weighted crank and Hartzell CS prop. Hartzell said to use “Continuous Operation Is Prohibited Above 24” Manifold Pressure Between 2350 and 2550 RPM”. Hartzell have since recommended to not use an aluminum prop on this engine because of the crank. There are other threads discussing this. I have 240 hrs on it now with no sign of any problem but I’m picking up a new MT tomorrow.

I have not dynamically balanced the Hartzell and people have commented on how smooth they felt it was. I will dynamically balance the MT once I get it flying.
__________________
Dennis Enns
Bellanca Champ 7ACA since 1986, restored 1990.
RV-8 IO375, MTV-9-B/183-50a, PMags, OW Award Oshkosh 2017
2021 Donation In

Last edited by Champ : 07-07-2021 at 06:34 AM.
Reply With Quote
  #6  
Old 07-07-2021, 06:43 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,268
Default

Quote:
Originally Posted by KayS View Post
info i have is that for a 360/hartzell continuous operation between 2000 and 2300 should be avoided. does that still apply after dynamic prop balancing in that RPM range and you're happy with vibration?
As others have noted, dynamic balance and propeller operating restrictions have nothing to do with each other. Operating restrictions deal with blade vibration, not balance.

I've attached two gifs (courtesy of Chrystal Instruments and Ziyuan Jiao, www.crystalinstruments.com) illustrating 1st and 2nd mode blade vibration. Running within the restricted range excites some mode (1st, 2nd, 3rd, etc) and pushes blade and/or hub stress to levels the manufacturer finds problematical. The simulation exaggerates the motion, but yes, this is really happening out there in front of you.

2nd mode on left, 1st mode on right. Blade twist and mass distribution complicates the mode shape, but basically the 1st mode is a bow, while the second mode forms an S-curve. A third mode would add another opposing curve.
-
Attached Images
  
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 07-07-2021 at 06:54 AM.
Reply With Quote
  #7  
Old 07-07-2021, 06:45 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 403
Default

Bill: this is what i also had in mind. that the propeller balancing does not sufficiently affect these strange harmonics that lead to some RPM ranges to be avoided.

Jim and others: i have no idea where the actual RPM restrictions are. if you use the search function to see what is recommended for an io-360 with a hartzell you'll find all kinds of limitations. Dennis here just came up with a new one i was not aware of. and when you look at some Cessna, Piper and Mooney forums they come up with even more restrictions. at the end we have no RPM at all where we can run the engine between takeoff and landing.

if there would be some reliable advice i would be happy to follow that recommendations. is there any way that we find out for ourself with our specific setup? i feel that (besides displacement, compression ration, ignition timing etc. etc.) these resonant frequencies are affected by the phase of the moon.

btw: i called Hartzell once adressing the issue and they basically said "you're on your own with that engine."

Last edited by KayS : 07-07-2021 at 06:55 AM.
Reply With Quote
  #8  
Old 07-07-2021, 06:49 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 403
Default

Dan: thanks for the great pictures!!!

would it be safe to say that below a specific manifold pressure you can run any RPM for extended period of time? let's say 24"...?

the one thing i am much more concerned of than an engine stoppage is when a propeller blade says goodbye.
Reply With Quote
  #9  
Old 07-07-2021, 07:14 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,268
Default

Quote:
Originally Posted by KayS View Post
is there any way that we find out for ourself with our specific setup? i feel that (besides displacement, compression ration, ignition timing etc. etc.) these resonant frequencies are affected by the phase of the moon.

btw: i called Hartzell once adressing the issue and they basically said "you're on your own with that engine."
Do you have one of the 375's without crank pendulums? If so, your best bet is to send it back and exchange the crank.

(Warning, soapbox mode ON)

EAB has become way, way too cavalier about propeller vibration. Knocking Hartzell for saying you're on your own is, well, not good. They, with MT and a few others, actually conduct the necessary testing with instrumented props, and if they have not tested your particular combination, their truthful answer is "We don't know". Other vendors simply guess, parroting Hartzell et al based on what they perceive as similarity.

None of this is new. Note the date on the blade mode illustration. Mr. Lurenbaum traveled here from Germany to present his research. Good thing he did.

BTW, you'll hear claims about wood, composite, and wood/composite props being immune to blade vibration. Fact is, everything vibrates. The real issue is amplitude. The maple prop below resonated and failed when excited at a particular RPM in a dyno cell, with poor glue lines being a contributing factor. A blade with different mass distribution and stiffness would behave differently.
-
Attached Thumbnails
Click image for larger version

Name:	GlueFailure2.jpg
Views:	109
Size:	102.1 KB
ID:	13374  Click image for larger version

Name:	Propeller Vibratory Modes.JPG
Views:	91
Size:	16.6 KB
ID:	13375  
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 07-07-2021 at 07:20 AM.
Reply With Quote
  #10  
Old 07-07-2021, 07:22 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,268
Default

Quote:
Originally Posted by KayS View Post
would it be safe to say that below a specific manifold pressure you can run any RPM for extended period of time? let's say 24"...?
There is no such blanket assurance.

Quote:
the one thing i am much more concerned of than an engine stoppage is when a propeller blade says goodbye.
As you should.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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 11:57 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.