Mini-500 MRGB Thoughts/Findings/Solutions

GA Rotor Guy

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Greg,

I think Barry (Ultracruiser1) has a mini-500 and it may (or may not) be fore sale. When we were up there in Nov, selling it was being tossed around. As far as I know... it is airworthy... but do not take my word for that.
 

bryancobb

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Greg,

Come over and look at my brand new project one. I will finish it, get the airworthiness, fly off Phase I and balance the rotors and work all the bugs out. Then sell it.

It would be a great starting point for you and your intentions, or if you are not over 200#, I will prove to you that the Rotax 582 with PEP is an OK setup by demonstrating it to you as much as you'd like.
 

GA Rotor Guy

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First let me say I am asking questions because I really do not now...

Seems to me; If the mini-500 was designed to run with a 582, then how much HP will the gearbox handle? Not trying to start a fuss... however with weight being an issue in all flying machines, was the gearbox designed to handle excess HP, or is it 'just beefy enough' for the output of a 582?

I read somewhere in this thread the design is similar to a Robinson R-22... which I am sure is higher HP than a 582...

Just curious... THX for any replies.
 

bryancobb

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John,

There is a LOT of variables to properly engineering a helicopter's drivetrain. It must be done a "system." Ability to carry the input torque of the selected powerplant is only one of many variables.

Since the Mini-500 is Experimental, you can TRY anything you'd like, but I'd be real nervous changing anything without a proper engineering study be done on that configuration. I feel pretty confident in the stock drivetrain if properly setup and installed, in its stock configuration. I have no way of knowing what caused it but one of the ears of the front flex-coupling drive flange on John H.'s Yamaha equipped helicopter broke in flight. It didn't break in a weld-joint. Maybe the bigger engine that caused it? Or its harmonic characteristics?

Dennis Fetters did design the 2-seat Voyager around this gearbox, so I would suspect he made sure the MRGB would carry the increased input torque. However, I don't know what else was changed on the Voyager drivetrain to come up with a "system" that would also work with a different engine?

Experiment-on! Just be prepared for success or failure.

Just remember...A 500# Mini-550 A 500# Mini-550 with a Rotax 582, A 500# Mini-550 including its Lycoming 180HP, will both make the same HP go into the gearbox. Add more weight to one, not true.
 
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GA Rotor Guy

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THX Bryan. I had not thought 'outside the box' far enough to consider the entire system, and the vibration issues. Did the 'voyager' (I am assuming it was an expanded version of the mini, capable of carrying two people), have a 582, or a larger engine?
 

scott heger

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Were any Voyager's ever built (except in Dennis Fetter's photo-"shop" version) by any customer that had placed down payments/deposits on them? Are the two supposedly built in the China business fraud scheme around? I believe the answer is NO to both. Seems like a pattern here.....None flying, lots of screwed customers.

Scott Heger, Laguna Niguel,Ca N86SH
 

bryancobb

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THX Bryan. I had not thought 'outside the box' far enough to consider the entire system, and the vibration issues. Did the 'voyager' (I am assuming it was an expanded version of the mini, capable of carrying two people), have a 582, or a larger engine?
Voyager had a water-cooled 3-cylinder 2-stroke watercraft engine. I am not sure of the horsepower.

 
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bryancobb

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Were any Voyager's ever built (except in Dennis Fetter's photo-"shop" version) by any customer that had placed down payments/deposits on them? Are the two supposedly built in the China business fraud scheme around? I believe the answer is NO to both. Seems like a pattern here.....None flying, lots of screwed customers.

Scott Heger, Laguna Niguel,Ca N86SH
I reckon that ONE was the only one that ever existed. They did end up getting it flying a few months after the (widely criticized) PhotoSHOPPE'd picture. It didn't fly very much before they padlocked the factory so I guess that's the reason there's no video.
 

GA Rotor Guy

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Voyager had a water-cooled 3-cylinder 2-stroke watercraft engine. I am not sure of the horsepower.

THX, I did not know about that heli.

The flier says the engine was developed to be capable of 165HP, it was derated to 135 for this application. Also says something like 105HP is all it needs to fly, so there is-like-30 reserve HP.

Now if this was designed to be fed into the current MRGB (main rotor gear box???), then I guess (?) one could assume a 125-150 HP engine could be substituted... given proper attention to vibration analysis...

I am just thinking out loud... :)
 

MH1FLYER

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John,

There is a LOT of variables to properly engineering a helicopter's drivetrain. It must be done a "system." Ability to carry the input torque of the selected powerplant is only one of many variables.

Since the Mini-500 is Experimental, you can TRY anything you'd like, but I'd be real nervous changing anything without a proper engineering study be done on that configuration. I feel pretty confident in the stock drivetrain if properly setup and installed, in its stock configuration. I have no way of knowing what caused it but one of the ears of the front flex-coupling drive flange on John H.'s Yamaha equipped helicopter broke in flight. It didn't break in a weld-joint. Maybe the bigger engine that caused it? Or its harmonic characteristics?

Dennis Fetters did design the 2-seat Voyager around this gearbox, so I would suspect he made sure the MRGB would carry the increased input torque. However, I don't know what else was changed on the Voyager drivetrain to come up with a "system" that would also work with a different engine?

Experiment-on! Just be prepared for success or failure.

Just remember...A 500# Mini-550 A 500# Mini-550 with a Rotax 582, A 500# Mini-550 including its Lycoming 180HP, will both make the same HP go into the gearbox. Add more weight to one, not true.
The mini transmission was very poorly designed in several ways. First was the bolt pattern was not equal all the way around on the mounting points. This led to frame cracking and other issues. Second is the pinion gear it has no front bearing support so you add more horse power – torque and that pinion deflects and it burns up which there is no fix for this problem. Most of the time, the ring gear has very little damage. Now you add improper heat treat and that’s just fuel for the fire. These transmissions just want hold up to a bigger engine in the mini!! Even the Ford 9” has a front pinion support bearing.. Plus you’re adding more weight on the same rotor disk which puts the pounds per square inch way over… I’m riding the fine line with the 120 engine with the rotor diameter. As far as the tail drive coupler failure I had was due to a pin hole in the weld and poor nickel plating. The pin hole let moisture in, and corrosion set in along the grain of the material, which just happened to be cross ways and the tab broke off and resulted in a full down auto and I’m glad that’s what I performed, had the other ear broke too, well I’m pretty sure I wouldn’t be here.. Just happen two years ago this month on the second day of December. Buy the way,, DF even said on my Forced Auto thread if you add any more power other things would start to happen wonder why!! The voyager would have never made it with that transmission in it. My 2 cents worth for now..






Full Down Auto - YouTube
 

HobbyCAD

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The mini transmission was very poorly designed in several ways. First was the bolt pattern was not equal all the way around on the mounting points. This led to frame cracking and other issues. Second is the pinion gear it has no front bearing support so you add more horse power – torque and that pinion deflects and it burns up which there is no fix for this problem.

John, I was waiting for you to chime in, and so you did, but you spread utter hogwash !!!

The transmission bolt pattern and frame cracking have got absolutely no relation to each other. You have heard the bell ring, but have absolutely no friggin idea where the gong hangs.

The transmission bolt issue. There were no transmission dowel pins in the Alpha model gear case halves. Without the mast support, the massive moment arm of the mast would be able to deform the transmission, sliding the case halves. This loaded up the old style pinion bearing, popped the carrier, and the pinion bearing failed. The repair was to insert dowel pins into the design. These 5 dowel pins stopped the case halves from deforming under severe loading. Problem solved.

The frame cracking issue. The frame design load path did not line up. Look at the frame from a side view. Follow the 4 vertical members up to the top transmission frame. Look at where the 4 transmission mounting points are. Now load up the top of the mast, as if you are maneuvering in flight. Imagine how it loads up the transmission mountings. The load path does not follow through into the vertical frame members, it forms a Z. It thus rocks and flexes the original thin upper member, especially in it's rear section. To solve this, the upper member was replaced by a thicker 0.063" tube, or an insert repair was place into the original tube, to stiffen it up. The frame design stays a weak point, the correct method would have been to have the vertical frame link in at the transmission mounting points, a perfect load path. Problem solved.

Lack of front pinion support a problem? Bull, there are many transmission designs which do not have a front pinion support, and they work just fine. The problem is that the transmission oil has no proper heat dissipation, it only whirls down in the bottom of the case. Nothing splashes around a lot, cooling it down against the upper transmission case. To add insult to injury, this all sits in an enclosed space, with no proper airflow. It overheats the transmission, tolerances go for a loop, the rest is history. Find a way to cool the transmission oil, implement that into a well set up transmission, and your problems go away. No need to case harden the gears, just implement oil cooling. Problem solved.

That original transmission, with location dowels, properly set up, with transmission oil cooling, will work just fine.

Merry Christmas all.

Cheers,

Francois
 

bryancobb

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...The frame cracking issue. ... It thus rocks and flexes the original thin upper member, especially in it's rear section...
Francois,

That's almost verbatim what dozens of us were telling Dennis F. in 1997. He always blamed us and said it was because we didn't balance our rotor well enough.

Finally when his "perfectly balanced" factory demonstrator had frame cracks just like ours, he started listening and came up with the mast support tube assembly and as far as I know, the cracking stopped.
 

bryancobb

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...The transmission bolt issue. There were no transmission dowel pins in the Alpha model gear case halves. Without the mast support, the massive moment arm of the mast would be able to deform the transmission, sliding the case halves. This loaded up the old style pinion bearing, popped the carrier, and the pinion bearing failed. The repair was to insert dowel pins into the design. These 5 dowel pins stopped the case halves from deforming under severe loading. Problem solved...
That's exactly right except I wouldn't say "deform." The two case halves just simply migrated and slid around in relation to each other, at the joint.

My pinion bearing never failed in the Alpha configuration but many folks' did. Maybe I just didn't yank my helicopter around and "cowboy" it very hard? I was aware of the weakness of the pinion bearing arrangement, but not the case-sliding problem, at the time so I'm sure it affected the way I flew.
 

bryancobb

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... it only whirls down in the bottom of the case. Nothing splashes around a lot, cooling it down against the upper transmission case. To add insult to injury, this all sits in an enclosed space, with no proper airflow...
I intend to jury-rig a mock-up transmission case out of clear lexan and spin it at 546 RPM so I can video what's going on, lubrication-wise. If no splash is getting to the upper bearing, I will do something about it.

Vance Breeze gave me some hard numbers on heat generation in meshing gears with load applied. I assume he got this knowledge from the education he got at the application level as his "gear-gurus" helped him tweak his motorcycles?

The information he posted seemed to indicate that the temperatures the Mini-500 gearboxes ran at were in the range of what should be expected an should not be a problem. I think he mentioned that you shouldn't be able to comfortably lay your hand on the case very long after landing without getting burned.
 

HobbyCAD

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Bryan,

The crown gear sitting over the splashing pinion, and the diameter of the crown gear blocking the complete upper half of the transmission off from the bottom, to me this traps the oil in the bottom half. The upper part of the transmission is supposed to act as the heatsink, but there is no effective way of getting the bottom oil to dissipate it's heat into the large surface area of the upper casing. This is where it is supposed to be transferred out. The only thing now is the bottom heats up a lot, the heat transfer into the bottom case metal has to rise up and transfer into the upper case metal, only then dissipate out. Imagine how hot the bottom gets, by the time the top can get rid of some. I'm not too keen to introduce additional splashing functionality internally, as it may lead to foaming. The best seems like to circulate the oil out, cool it down, then stick it back in. This ensures an efficient dissipation of heat out of the transmission.

Cheers,

Francois
 

GA Rotor Guy

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Just thinking out loud here... Concerning the lubrication issue in the tranny...

Could one design and install a system with a small oil pump, that moves oil from the sump to the upper gear... then the excess draining down would land on top of the crown (ring?) gear and be thrown to the sides of the upper half of the case... thus using them for cooling radiation. If this oiling system had an external line to the top bearing, that line cold be tapped for an oil cooler if chosen to do so later.

Again, thinking out loud here.
 

MH1FLYER

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John, I was waiting for you to chime in, and so you did, but you spread utter hogwash !!!

The transmission bolt pattern and frame cracking have got absolutely no relation to each other. You have heard the bell ring, but have absolutely no friggin idea where the gong hangs.

The transmission bolt issue. There were no transmission dowel pins in the Alpha model gear case halves. Without the mast support, the massive moment arm of the mast would be able to deform the transmission, sliding the case halves. This loaded up the old style pinion bearing, popped the carrier, and the pinion bearing failed. The repair was to insert dowel pins into the design. These 5 dowel pins stopped the case halves from deforming under severe loading. Problem solved.

The frame cracking issue. The frame design load path did not line up. Look at the frame from a side view. Follow the 4 vertical members up to the top transmission frame. Look at where the 4 transmission mounting points are. Now load up the top of the mast, as if you are maneuvering in flight. Imagine how it loads up the transmission mountings. The load path does not follow through into the vertical frame members, it forms a Z. It thus rocks and flexes the original thin upper member, especially in it's rear section. To solve this, the upper member was replaced by a thicker 0.063" tube, or an insert repair was place into the original tube, to stiffen it up. The frame design stays a weak point, the correct method would have been to have the vertical frame link in at the transmission mounting points, a perfect load path. Problem solved.

Lack of front pinion support a problem? Bull, there are many transmission designs which do not have a front pinion support, and they work just fine. The problem is that the transmission oil has no proper heat dissipation, it only whirls down in the bottom of the case. Nothing splashes around a lot, cooling it down against the upper transmission case. To add insult to injury, this all sits in an enclosed space, with no proper airflow. It overheats the transmission, tolerances go for a loop, the rest is history. Find a way to cool the transmission oil, implement that into a well set up transmission, and your problems go away. No need to case harden the gears, just implement oil cooling. Problem solved.

That original transmission, with location dowels, properly set up, with transmission oil cooling, will work just fine.

Merry Christmas all.

Cheers,

Francois
Hahahahaha hogwash!!! I don’t think so!!! All that blabber mouth bull **** again! That still don’t change anything I said. Band-Aid fixes that you believe in, ok they work, but for how long?? I done some reality checking this morning and found out that almost every transmission manufacture has a front pinion support due to poor history of failed pinions. I guess you don’t have frickin Google or Bing to just check for yourself.. You’re just pissy because I busted out about lying to me and everyone else here on the forum. Once again I will say this! My helicopter fly’s and is flying! What’s yours doing smelling up your garage? I sure hope we get to meat one day, It will be a real ass kicker of a day!!!!! Experimental is actually two words one is for people to experiment with, the other is what you are. And that’s MENTAL. The transmission works for what we are doing, any more HP and it will fail!!!!!!!!!!!!! I’m trying to save lives not chance them!!!!! Here’s some of my proof enjoy..



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bryancobb

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John,

I'm pretty sure Francois is on that case. Someone (I think it was him) made an oil screw pump in between the pinion bearings that was so effective, it blew out the seals everywhere. He's probably got that fixed now.

Francois,
Doesn't 1/4 or 1/6 of the big end of the pinion protrude from under the crown?
 

hillberg

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The Kiss Jet Exec has a Racing rearend & no pinion nose bearing , Every gearbox has it's own desine criteria, To lump it all on Dennises mini you're flying & say all other have a poor history is Stupid as hell.
 

MH1FLYER

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The Kiss Jet Exec has a Racing rearend & no pinion nose bearing , Every gearbox has it's own desine criteria, To lump it all on Dennises mini you're flying & say all other have a poor history is Stupid as hell.
Hillberg,
You need to wake up and smell what you’re stepping in. I was a John Spurlings three years ago and he is the Rotorway KING. Every Trans I saw, and there were plenty of them sitting around and they all had front bearing pinion supports. All the winter race rear ends all have front supports as well. Next, is this is my helicopter I’m flying and no one else’s, I own it. This thing has a very poor history all the way around. That all happen way before I came along. I bought my helicopter from Bob Hubner in August 2008 as parts. I spent 2008 and part of 2009 rebuilding back to its original Mini 500 configuration. That’s when I found out about all the bad history and all the problems myself, that and my wife reading all of problems made me rethink what I was doing, or I was just going to be another number at the morgue. Then I spent four years of pure hell to get my dream up and flying. Not to mention the team and all their hard work that went into rebuilding and solving all the problems with the MH-1 build, my build. I have a lot of respect for you Don but what you said is just not true and don’t ever call me stupid. I think everyone is pointing there figures at me for the problems and the problems were already there long before I came to play. Making me want to go play helicopters!!! There will be four more MH-1s flying soon very soon. 2014 will be a great year!! Here’s how I found my dream...
 

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