Quantcast

Angular Velocity/Acceleration

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

PMD

Well-Known Member
Joined
Apr 11, 2015
Messages
242
Location
Martensville SK
I am a bit hesitant to start any thread right now, as rumour has it I might be called out on my Covid shutdown for an international job - that means a lot of long days in travel and work - but I suspect this one might survive long enough with or without me.

I have been fixing and building engines for 54 years at last count, including building a lot of direct drive and a few reduction drive airboat engines. I actually did my first airplane engine work on a direct drive VW (Evans) pretty close to my first highly invasive motorcycle engine days. Over all of those years, I have become extremely wary of the elephant looming in every engine's bedroom: angular velocity variations and the harmonics that can result. In my airboat days, I was extremely happy to find Rotax (Kodiak) had built such a good gearbox that it would tolerate the violent torsional velocity reversals of a 2 cylinder 2 cycle, and I was always fascinated at how severe the biggest offender of all (big singles) could be (BSA Gold Star) and how they dealt with the still rude parallel 4 cycle twins (BSA A-10 pre-unit) with a bloody great cam/ramp connection ("cush" drive in m/c vernacular of the day). I have also seen truck drivelines torn up by an extremely common engine with a major manufacturer that did not fully appreciate the torsional resonance problems in the crankshaft/flywheel caused by their ineptitude in fuel systems.

So what's the big deal? Well, I am one of the first (for the reasons above and a million more) to warn enthusiastic homebuilders that just codging up a re-drive is NOT a good idea. Well, it's a good idea, but it's not an easy one. I like to cite Frank Thielert as a good example: here's a guy who built his business and reputation designing and building extremely high performance engine and driveline bits (Formula 1 being one of his areas of expertise) took one of our favourite E/AB things - a little automobile engine - and made a little certified aircraft engine with a HUGE redrive that literally killed the company. He never managed to get it right.

So, can we discuss the theories, facts, experiences and idea around what the angular velocity and resonant frequencies of engines, propellers and gear trains in aircraft look like, how to measure, quantify, calculate, modify, dampen or eliminate them? These things not only are a big deal to the engine/drive/propeller, but have significant implications to an airframe. Anyone who has worked with riveted aluminum structures for a long time can tell you that the peaks and nodes of vibration in an airframe can show up where rivets loosen and cracks propagate not only from flight loads, but propeller vibration.
 

PMD

Well-Known Member
Joined
Apr 11, 2015
Messages
242
Location
Martensville SK
Geez, never thought of myself as a Billski Troll, but I guess in light of his background and my interests, that's what I have become.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
Hmm. Maybe you should check out the following thread. If we left any cards to be played, we can talk about them.

 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,778
Location
97FL, Florida, USA
Darn. Was looking for a summer rerun.

“Tell them three times, then let them learn in the school of hard knocks.”


BJC
 
Top