Reduction drives

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slociviccoupe

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Been doing my research and wondering thoughts of dual mass flywheels. Even though heavy they are designed for the engines harmonics. With the hobmnda v6 there are versions that had single mass flywheels and others with dual mass. When running a psru with an auto conversion would you run a duall mass with the soft drive coupler together or just use a single mass flywheel and use the coupler supplied by the gearbox manufacturer.
 

wsimpso1

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Been doing my research and wondering thoughts of dual mass flywheels. Even though heavy they are designed for the engines harmonics. With the hobmnda v6 there are versions that had single mass flywheels and others with dual mass. When running a psru with an auto conversion would you run a duall mass with the soft drive coupler together or just use a single mass flywheel and use the coupler supplied by the gearbox manufacturer.
Please run an advanced search using the Advanced Search tool. I just searched on Dual Mass Flywheel. LOTS of cited posts on the topic.

Billski
 

pfarber

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Doing anything else is taking on the task of airplane designer (or in this case, powerplant designer), experimental fabricator, and test pilot for a new airplane (or powerplant).
Engineers make mistakes by the boatload. A quick search of the RV forums is FULL of builder fixes that have not been brought into the plans.

Also there are certified AC mistakes (Cessna seat rails, VAR cranks, splash lube cranks as far away from the oil as possible - Lycoming) that have required ADs to fix because they were safet issues.

Not to mention automotive screw ups that are historically bad: the F-150 motors have a laughably bad reputation due to these brilliant engineeers 'wisdom'.
 

Dana

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Engineers make mistakes by the boatload. A quick search of the RV forums is FULL of builder fixes that have not been brought into the plans.

Also there are certified AC mistakes (Cessna seat rails, VAR cranks, splash lube cranks as far away from the oil as possible - Lycoming) that have required ADs to fix because they were safet issues.

Not to mention automotive screw ups that are historically bad: the F-150 motors have a laughably bad reputation due to these brilliant engineeers 'wisdom'.
Yup, engineers make mistakes all the time. But there's a big difference between applying a fix proven in the community or making a change when you know all the design requirements and the ramifications of the proposed change, and making a change just because one "thinks" it will be an improvement without understanding all the engineering that went into the original design.
 

Saville

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It seems that 60-70 years ago designers like Allison and Rolls Royce could design and build robust pro reduction gear. So the know-how must be there.

Assuming money is not a big issue, is it that difficult to design and build a re-drive for one auto engine (say an LS3) that is reliable, durable, efficient and not priced out of this world?
 

Dana

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It seems that 60-70 years ago designers like Allison and Rolls Royce could design and build robust pro reduction gear. So the know-how must be there.

Assuming money is not a big issue, is it that difficult to design and build a re-drive for one auto engine (say an LS3) that is reliable, durable, efficient and not priced out of this world?
You know what the TBO is on a Merlin?

Automakers spend millions on drivetrain development and testing, because they can amortize it over millions of vehicles. Nobody in the homebuilt world can afford to do that.
 

wsimpso1

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It seems that 60-70 years ago designers like Allison and Rolls Royce could design and build robust pro reduction gear. So the know-how must be there.
Key words missing are analyze, develop, test, redesign, rebuild, and retest. I know the topic pretty well, and know a bunch of other engineers who also know the topic.

Assuming money is not a big issue, is it that difficult to design and build a re-drive for one auto engine (say an LS3) that is reliable, durable, efficient and not priced out of this world?
Unfortunately, the big issue IS money. It costs the time and efforts of the select folks who do know the topic, and it takes someone with adequately deep pockets to fund the work. The few people doing these things do already exist. EPI, airboat drive companies, AeroMomentum, the prop manufacturers, Lycoming, Continental, Pratt & Whitney, etc have people on staff with enough understanding of vibe, rotating parts, cases, seals, etc. to be successful. The money to be made has to be big enough to justify doing the engineering. At the tiny volume and modest prices the market will bear, you will not see me or any of the industry contacts I have trying to make money on airplane PSRU.

If all you want to do is run an LS, buy a Ballistic Drive or from one of the other reputable airboat drive companies, If you want to run a constant speed prop, buy an MT electric prop. They will help you select the right blades and hub.

Billski
 
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Saville

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You know what the TBO is on a Merlin?

Automakers spend millions on drivetrain development and testing, because they can amortize it over millions of vehicles. Nobody in the homebuilt world can afford to do that.

I would assume that the TBO for a Merlin is at least partly due to expected hard use in combat, no?

I see your point about amortization.
 

Saville

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Key words missing are analyze, develop, test, redesign, rebuild, and retest. I know the topic pretty well, and know a bunch of other engineers who also know the topic.



Unfortunately, the big issue IS money. It costs the time and efforts of the select folks who do know the topic, and it takes someone with adequately deep pockets to fund the work. The few people doing these things do already exist. EPI, airboat drive companies, AeroMomentum, the prop manufacturers, Lycoming, Continental, Pratt & Whitney, etc have enough understanding of vibe to be successful. The money to be made has to be big enough to justify doing the engineering. At the tiny volume and modest prices the market will bear, you will not see me or any of the industry contacts I have trying to make money on airplane PSRU.

If all you want to do is run an LS, buy a Ballistic Drive or from one of the other reputable airboat drive companies, If you want to run a constant speed prop, buy an MT electric prop. They will help you select the right blades and hub.

Billski

What I was trying to ask is:

If money is not an object, can a rugged dependable PSRU for something like an LS3 be designed and built in a reasonable amount of time?

I'm trying to learn if it's the technology or know-how that's the issue. I've read many times that PSRU development is "really hard".

But I'm trying to pin down, from the people here who seem to be in the know, if it's really that hard or if it's a question of money and payback.

Seems to be the latter.
 

Dana

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I would assume that the TBO for a Merlin is at least partly due to expected hard use in combat, no?
Partly, maybe, but shortcuts were doubtless taken as the engineers knew the expected life of the entire aircraft in combat wasn't that long.

Push the throttle past the gate to "war emergency" power and you're replacing the engine when you land.

What I was trying to ask is:

If money is not an object, can a rugged dependable PSRU for something like an LS3 be designed and built in a reasonable amount of time?
Depends on how you define "reasonable". Part of the process is reliability testing, and that can take time.
I'm trying to learn if it's the technology or know-how that's the issue. I've read many times that PSRU development is "really hard".

But I'm trying to pin down, from the people here who seem to be in the know, if it's really that hard or if it's a question of money and payback.
It's both. Designing a robust PSRU takes some serious engineering and in-depth knowledge of torsional resonance, etc. Even so, there are a lot of uncertainties so you'll probably break a few during testing. And, since weight is such an issue in aircraft you don't have the luxury of the large(er) safety factors that you can use in other industries.

Then all the work and cost to make a reliable unit, you have something that looks deceptively simple and people want to know why it costs so much when "it's just some belts and pulleys, I could make one myself."
 

TFF

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It’s both. How many iterations can you afford, to hone in on good, even if you had a legitimate good design? I say five. Four will be door stops in the end. How long does that take in a small shop to find out if it’s good? Off the bat, 1000 hours of testing is very legitimate. How fast can you test 1000 hours after iterations? We can talk about being lucky not needing any extra fixes, possible. There are engineers missing a challenge to design something complex. Somebody out there can afford to fly two hours a day every day for a year and a half. There are master machinists twiddling thumbs wishing they had something to make. Idle machines, tooling and materials. Can all these come together? Not easily. Not without dispersal of money.
The mad scientist in the garage is the only way where drive wins out over everything else. Even that guy needs a fairly hefty budget if just materials.
 

wsimpso1

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I would assume that the TBO for a Merlin is at least partly due to expected hard use in combat, no?

I see your point about amortization.
Nope, just a design pushed up near the limits on all sorts of things. High Power, Low Weight, Low Cost, Long Life - You only get to pick three, and long life was just not required. The big issue with short life on WWII combat airplanes was that the airplanes themselves became obsolete so quick that long lived engines just were not important.
 

wsimpso1

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What I was trying to ask is:

If money is not an object, can a rugged dependable PSRU for something like an LS3 be designed and built in a reasonable amount of time?

I'm trying to learn if it's the technology or know-how that's the issue. I've read many times that PSRU development is "really hard".

But I'm trying to pin down, from the people here who seem to be in the know, if it's really that hard or if it's a question of money and payback.

Seems to be the latter.
Yes, it can be done. Heck it is already done by several outfits selling PSRU to customers running LS3's in airboats. Nothing magic about turning a prop on an airplane.

I have difficulty imagining some billionaire itching to make a good PSRU and not caring if the enterprise will run out of money.

Gears, shafts, seals, cases, and vibration management are all known engineering topics, combined into successful products of many types all over the globe. No magic. Just a substantial engineering task and money sink (mostly in prototyping and testing) to serve a tiny market without much potential for making any money.

Billski
 

Dan Thomas

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I would assume that the TBO for a Merlin is at least partly due to expected hard use in combat, no?
The typical light aircraft engine makes about one-half of a horse for every pound of weight. The Merlin weighed around 1640 pounds and produced nearly 1600 HP. Nearly a horse per pound. The means a lot of stress on everything, a lot of pressure on bearings and pistons and cam and lifters and all the rest. Lots of load on the reduction gearing. It's a wonder it went 600 hours.

The TBOs for old small-aircraft engines weren't a lot better. Some were only 1200 hours or so. IIRC the Gipsy Major in my Auster was only good for about 1000 hours. Metallurgy and lubricants have made a big difference now. Just because a Lycoming "looks" like it did in 1950 doesn't mean that it's the same engine. There are hundreds of invisible differences and improvements.
 

Dan Thomas

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Engineers make mistakes by the boatload. A quick search of the RV forums is FULL of builder fixes that have not been brought into the plans.

Also there are certified AC mistakes (Cessna seat rails, VAR cranks, splash lube cranks as far away from the oil as possible - Lycoming) that have required ADs to fix because they were safet issues.
Please tell me when Lycoming used splash-lube cranks.

If you mean the camshaft, yes, the cams get most of their lube by oil thrown off the crank journals. And there's a LOT of it. There's a thick mist of oil in that case when the engine is running. Startup is when the wear happens, and even then it's not bad. It's corrosion that does the damage, and most of the corrosion is caused by owners ground-running the engine without flying it. I looked after dozens of Lycomings in my time as a flight-school maintenance manager, from O-235s to the O-540, and every one of them went to TBO, and still had compressions in the high 70s and no metal in the filter. We didn't ground-run them then put them away for the next month. No corrosion, no wear.

Cessna seat rails were just fine, They just weren't designed to last 20,000 hours. Or even 10K. None of those engineers figured that their airplanes would be flying decades after they had retired and died. The new rails are really skookum, not only to make them last long and not crack under the weight of modern Americans, but to get more idiot-proof latching. The seat belts are also attached to the seats now instead of the airframe, and the seat (which also weighs about three times what it used to) is good for 26G (front) and 19G (rear). So those rails have to take all the loads of a 300-pound pilot surging against the straps in a crash. The original design was never intended to do that. And the seat/rail failures were due to a lack of maintenance as per the manuals, and due to the longstanding 1987 AD requirements being casually applied (87-10-03. Superseded by 2011-10-09). I have spent hundreds of hours correcting such problems the first time I encounter an airplane I haven't worked on before. It's horrific. Lazy mechanics and/or cheapskate owners.

So what is Cessna's fault in that? I'll tell you. They were reluctant to make the airplane a lot heavier for no good reason. They didn't have those reasons in 1956. Now a 172 grosses at 2550 instead of 2300 (1970s) or 2200 (1950s and early '60s). Its empty weight has gone up by around 400 pounds. It needs 180 hp instead of 145. You pay for every ounce of that. I flew the oldest airworthy Cessna 180, serial number 4, built in1953, for a few hours in the 1990s. Its empty weight was less than the empty weights of our 1970s 172s, and it performed like crazy.
 

rv7charlie

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if it's really that hard
It seems really hard because it is really hard, for the 99% that fail, largely failing because they aren't mechanical engineers. Most of the failed alt engine stuff in general was built by a 'that looks about right' builder. (This is a trap I've tried very hard to avoid with my alt engine installation by shamelessly copying the successful stuff by actual engineers, and asking the advice of a couple of close friends who are engineers. I'm still managing to mess up stuff periodically. I hope I or someone more knowledgeable catches the important ones before I fly.)
 
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Saville

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Yes, it can be done. Heck it is already done by several outfits selling PSRU to customers running LS3's in airboats. Nothing magic about turning a prop on an airplane.

I have difficulty imagining some billionaire itching to make a good PSRU and not caring if the enterprise will run out of money.

Gears, shafts, seals, cases, and vibration management are all known engineering topics, combined into successful products of many types all over the globe. No magic. Just a substantial engineering task and money sink (mostly in prototyping and testing) to serve a tiny market without much potential for making any money.

Billski

Got it.

It seems that while it's time consuming and money consuming it's known how to do it and it seems to be an iterative process. It can be done but since there's no money in it, no
serious manufacturer will do it.

So the impression I'm getting is that PSRU difficulties, problems and failures resulted from back of the envelope calculations and "that looks about right" designing. And not from a task that is extremely difficult.

Thanks!
 
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rv6ejguy

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The Merlins used in Canadian Northstars were often lasting 800 to 1000 hours and some went to the 12-1400 hour range. These had beefier gearboxes with different ratios and are the ones used exclusively on race Merlins at Reno which can produce up to 4000hp. RR knew what they were doing here. They had extensive previous experience with 2000hp class engines on the Schneider Cup racers and other geared engines before that.
 
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