# Torsional Vibration and Resonance - Basic Theory and Issues

Discussion in 'General Auto Conversion Discussion' started by wsimpso1, Nov 20, 2012.

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1. Apr 22, 2019

### gpetty

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As spelled, that looks like it could be Dutch. The closest German equivalent would be Geschwindigkeit, which is a general word for “speed.” I believe the Germans use “Drehzahl” (“turn number”) for RPM.

2. Apr 22, 2019

### wsimpso1

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Interesting. I have seen Drehzahl too, but Geshwenderheit more often. The LuK folks (LuK is in Buhl) told me that the long word is specifically RPM...

3. Apr 23, 2019

### PIK-21

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Geschwindigkeit means speed. Drehzahl is the more common word for RPM also Umdrehungen could also be used for RPM. It is more commonly used when describing a turning action ie 3 turns =3 Umdrehungen

4. Apr 23, 2019

### h_zwakenberg

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5. Apr 26, 2019

### pfarber

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Well, "3. Torsional Vibration Survey of the Packard Rolls-Royce V-1650-1 Engine. Army Air Forces Material Center. Report # EXP-M-57-503-632, June 5, 1942." is not a formal Army-Navy specification. When the AAF procured the engines, there would be a contract number (aka specification/purchase order) to do so.

What that article did was reference some test data, unless you can provide the report, it is NOT a formal specification.

I'm not saying TV isn't a thing, but that the Army/AAF didn't have a specific limit it was looking for.

There are airboat AND airplane PSRUs that have logged many thousands of hours without major issues (all mechanical devices can/will fail). But there are large, high HP belt based PSRUs that have run for decades without issues.

https://www.centurydrives.com/
http://www.beltedair.com/

comes to mind.

At best they are using nothing more than the dampers installed with the auto engine (possibly crank and pulley).

The use of gears and their inherent lash seems to be the TV issue... although its been said that belts don't offer any inherent dampening seems to be contraindicated by the above units.

Last edited: Apr 26, 2019
6. Apr 26, 2019

### pfarber

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Kitplanes today is about assembling parts from the 51%-ist kit you can buy. Rarely do they have auto conversion articles, and most 'how to's are watered down to almost nothing because no one wants to calculate bend allownce, just pop rivets and fly.

FWIW my E-AB can be ordered as a series of $35k kits, or source the materials only for less than$8k (both less avionics/motor/interior). Which one do you think would get an article in Kitplanes?

Last edited: Apr 26, 2019
7. Apr 26, 2019

### rv6ejguy

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Plenty of belt drives have disintegrated in short order from TV. I can think of 3 examples off the top of my head.

TV doesn't differentiate between gears or belts.

8. Apr 26, 2019

### pfarber

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Was it the engine/PSRU combo? Poor PSRU design?

Dude, don't just do a hit-n-run and leave us hanging. If PSRU blowing up are common I'm not having that kind of impression from what I can find.

9. Apr 26, 2019

### pictsidhe

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Get the design right, a belt redrive can last many thousands of hours. Get it wrong, it can fail in seconds. Since so many are designed using TLAR engineering, their life is completely unknown until tested. Often, the testing is done by customers...

Just because something can be successfully done, does not mean that it is a foregone conclusion.

10. Apr 26, 2019

### pictsidhe

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Bede went through a long and difficult development process to get their redrive to stop blowing up.

11. Apr 26, 2019

### Vigilant1

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You can believe as you wish, but I think you are about 6 years out of date.
- Here's a breakdown of the contents of a recent Kitplanes.
- And here's what the May issue contained.
- Review of the Whisper X350 aircraft: 6 pages. This is the kind of article you are complaining about-- A kit that will be \$120K by the time it is finished. Fine.
- An article about re-engining an existing aircraft: 6 pages
- Custom designing a DIY Helmholtz-tuned induction system: 6 pages
- A continuing series on building a Bearhawk LSA. 4 pages. Not an ad for the airplane. Discussion of covering options, etc
- Antenna mounting: 6 pages
- Designing and constructing streamlined gear fairings and wheel pants: 4 pages. Drag considerations, carbon fiber fabrication, etc
- Tools: Choosing and using Japanese-style pull saws: 4 pages
- Buying a used homebuilt: Another in a series. 5 pages. Not a penny of "paid placement" evident.
- Building a double-flash LED strobe system: 3 pages, includes schematic and mounting info.
- Tips of performing preflight checks, commonly missed items etc: 3 pages
- Use of dollies under acft wheels to ease moving planes/projects around a hangar/shop (not high-tech, but handy)
- Selection and mounting of floating nut plates: 1/3 page
- Use of pulled rivets with stacked flanges: 2/3 page
- Account of a recent Dawn Patrol gathering: 4 pages
- Design and DIY fabrication of a muffler for a Piet: 3 pgs
- Completions: 6 planes
- Jim Weir article on LED technology: 3 pages
- Choosing a project: Consider the plane you'll likely need by the time it is done (2 pages).

So, I guess if someone is expecting pull-out plans to build a plane from scratch, they might be disappointed. But this magazine is no longer 40 pages of paid advertorials for expensive kits.

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12. Apr 26, 2019

### wsimpso1

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if you go to somebody else's replies and grab their picks, you may not get to the things I posted and was trying to send you to. Try this page http://www.enginehistory.org/engines.shtml and scroll down to the stuff on No Short Days. They cited a 0.5 degree torsional vibe at the prop, as called out in AN-9504, and that is what the engine makers were going for in the 1930's. I did not cite the article to prove the need or lack thereof in an AN spec, I cited the work as how the issue of TV is real, and took big efforts to solve back when.

in 1980, DuPont Engineering Services Division guys taught a class I attended that include words to live by:

"In God we Trust. All others must bring data"

There have been crappy PSRU's sold. There is a guy selling geared PSRU's right now who got all pissed off online claiming that the guy with one of his drives was pulling g's. Airplanes pull g's, will spin, etc. These gadgets should be able to do that. I am trying to help folks be smarter consumers. If you think that you can just go on the seller's nice words, then go ahead. I say we should be telling the sellers to bring data.

I like history. If someone says they have a great history, I want to know how many are flying, with which engines at what power, how many hours on the fleet, and how many failures have occurred, and if certain engines, props, or other things should be avoided. MTBF would be great. Good words but no data means little reason to hang it on the front of your airplane. 60 flying, 12000 hours, one engine at 900 hours and none broken tells a decent story. 3 flying and 30 hours and one guy had an elastomeric isolater self destruct is a horrible record and that builder might not want to publicize that record.

If they have no fleet history yet, wouldn't you want to know that its design has been analyzed, what the testing looked like, and that it is expected to have a 1000 hour TBO with: Prop inertia below X, Four cylinder engines below Y hp and Z rpm, and no combined yaw/pitch rates greater than W degrees per second? It would also be helpful to know if there are limits on how heavy or light we can go on flywheel and prop MMOI.

Billski

13. Apr 26, 2019

### pfarber

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Dude, Mays issue is out for a few days...

I get the magazine. I know whats in it.

Re-Enginging AC: Titan AC is the Continental E-AB version... so yeah, SALES PITCH
Tuned Induction: AD for SKY DYNAMICS. No way in heck this is a DIY article. A narrative at best.
Building the Bearhawk: ITS AN AD FOR AN LSA. LSA must be made as per manufacturers instructions. Its not an E-AB.
Antennas: rehash of every other how to mount an antenna article
Fairings: resash of every other how to build a fairing with composits
Tool/Saw: some dolt wearing a headband.
Buying a used E-AB: Rehash of every other crappy 'how to buy a used plane' article. Talks down about auto engines. really?
LED Strobe: rehash of every other article about flashing an LED.
Dollies: really? REALLY? This is filler and not worth addressing.
Preflight: rehash of every other article about pre-flights
Nut-Plate: Hmmm... I may have read about that in an Airframe handbook somewhere.. I think someone called the 'FAA' printed it. IT never addressed any sort of set back though.
Pietenpol exhaust: FINALLY!!!!!!!!! An article that is useful!!! One out of ELEVEN. Not even 10% useful magazine.
Completions: kwel.
LED article: rehash of every other LED article.

So AT BEST you got ONE ACTUAL homebuilder-esq article and 8 garbage articles that are little more than regurgitation of every other filler article and three MASSIVE advertising articles.

If you think this is good then you have much lower standards than I.

14. Apr 26, 2019

### pfarber

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What a great read. Its amazing to read how they could rework an entire crankshaft so quickly.

15. Apr 26, 2019

### pfarber

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So when it can be pointed out that there are multiple belted/geared PSRUs with thousands of hours of flight time, that data is ignored?

I posted two companies that have successful designs. I agree that TV is a thing, and can seriously shorten component lifespan.

But have you looked at the two companies, that take WILDLY different approaches, and offer a reason for their success?

Thanks for the tutorial. You remind me of that Epi-Eng web site.. everyone is wrong about PSRUs except them... except for all the other working units lol

16. Apr 26, 2019

### Vigilant1

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Great, "dude", I'm glad you believe it is worth the subscription.

17. Apr 26, 2019

### pfarber

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Not going to renew. I thought I would get the 1990s version of a useful magazine... not filler articles and sales pitches. I'll buy some back issues of CONTACT! magazine instead of kitplanes.

ts just not the same magazine. Really.

18. Apr 26, 2019

### rv6ejguy

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It's always a relationship between engine, PSRU and propeller.

I've been involved in this game for over 25 years now so I suspect I have somewhat wider experience than you. Examples: BD-5, Dan Horton's Geo Metro, Eggenfellner's belt drive design- all suffered catastrophic failures where everything appeared to be going swell for a while. Ignorance is bliss. We've tried to educate you here but you don't seem to be absorbing the info. Your choice.

Nobody is saying that belt or gear drives can't work. There are plenty of examples of both types with hundreds or thousands of hours on the fleet collectively. I have hundreds of customers flying both types. The devil is in the details. Get it wrong and a forced landing awaits you...

Use one that's been well flight proven on the same engine, same flywheel and same prop and you're likely going to be fine. Change even one of those aspects and you're in unknown territory again. Might work fine, might explode on you.

When the system reaches resonance, peak loads as high at 8000 lb./ft. have been measured or calculated on auto engines which put out less than 200 lb. ft.- 40 times the peak torque of the engine. In these cases, failure is almost immediate.

I agree with your comment on EPI. Jack Kane is a smart guy but fails to accept that many drive which have been flying for years and thousands of hours are in fact reliable despite that fact that he doesn't like their designs. Applied engineering can help us avoid many problems in the design but in the end, only thousands of trouble free hours validates those designs or TLAR designs.

Last edited: Apr 26, 2019
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19. Apr 27, 2019

### BBerson

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I don't think I will renew Kitplanes either.

20. Apr 27, 2019

### Toobuilder

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I just let my subscription to KP lapse recently because it's not quite up to the technical resource I'm looking for. But I admit that my interests are not mainstream. Besides, most of the contributors are regular members of VAF so I get the content anyway.

That said, if the induction article is by Dave Anders, I can personally attest that it is NOT a fluff piece for any manufacturer. I have spent countless hours discussing airplanes with Dave and you will not find a more passionate "experimenter" than him. He has reams of data to validate the effectiveness of his many modifications. He is a true "put up or shut up" guy and is very happy to share his research with anyone who will listen.

I know what he's doing with induction tuning and if you dismiss this as a fluff piece it's your loss.

Dave is the real deal.