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Jerry Schneider

CG Products - Engine Mount

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I received my engine mount for my Conical IO-320 the other day fro CG Proucts, (ie:The CozyGirrrls).

 

Gotta say, it looks good. There was some question as to whether there would be interference with the fuel pump. To avoid that, Chrissi asked me to take some high resolution orthagonal pictures of my engine and email them to her. She was able to put the pictures into some fancy engineering software, and create a "Virtual" engine with which she fitted "Virtual" tubing around everything. The result: Fits like a glove. (I should copywrite that. :D )

 

The Girrrls construct the jig, design, layout, and cut the tubing, and have a certified welder do the sticky stuff.

 

IMH (layman's)O, Top notch.

post-54-141090153747_thumb.jpg


"I run with scissors."

Cozy MKIV N85TT

Phase One Testing

http://home.earthlink.net/~jerskip

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I'm trying to plan my engine mount hard point locations.

 

Does anyone have 3D models of the various engines?

Engine mount hard point locations should be the same regardless of engine. (I think.:confused: )

"I run with scissors."

Cozy MKIV N85TT

Phase One Testing

http://home.earthlink.net/~jerskip

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I've redesigned the fuselage, and it's shallower than the standard MkIV tub, so the lower mounts need to be moved upward. By how much... not sure.

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...The Girrrls construct the jig, design, layout, and cut the tubing, and have a certified welder do the sticky stuff.

 

IMH (layman's)O, Top notch.

Great! But whose toes are those (bottom of the photo)?

Nathan Gifford

Tickfaw, LA USA

Cozy Mk IV Plans Set 1330

Better still --> Now at CH 9

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Jerry,

This engine mount is unsafe as it is designed. There will be bending forces where the four tubes are joined at the bottom. Fatigue cracks will develop there very quickly. Likewise, the top tubes are not properly supported. Bending loads will be present at the top firewall plates. The design of this mount is fundamentally flawed and it will probably fail with potentially disasterous results shortly after being placed in service.

 

I regret having to convey such a bleak assessment. Perhaps CG Products can solicit the services of a mechanical engineer and re-work the mount with a more robust design.

 

Aubrey

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I'm not an engineer, (though they seem to think I am at work).

 

I have to agree with Aubry. Without running an FEA on it, it does not look right to me.

 

The DF Long EZ mount was much beefier than this, with more and shorter support legs. When it was used for 320's it had to be re-enforced with 2 more tubes on the top mounting points.

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Jerry, I hear alarms going off... it's your decision, but having had the pleasure of meeting you on several occassions I am very concerned about "disastrous results".

 

I urge you to seek more feedback.


Jon Matcho :busy:
Canard Zone Member & Administrator
Now:  Rebuilding Quickie Tri-Q200 N479E
Long-term:  Building a Cozy Mark IV

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Originally Posted by Steve_Innova

"What is the advantage of a conical mount vs. the other types?"

 

---> A google inquiry, "dynafocal mount versus conical mount" turned up this from Sky Ranch and other sources.

 

---> The crankcases on the Lycoming 320 and 360 series engines were casted for three different types of engine mounts -- conical, Type 1 Dynafocal or Type 2 Dynafocal. Your engine can only take one kind of shock mount. It cannot be converted to any other type. Some builders have the mistaken idea that they can elect to use either a conical mount or a dynafocal mount with the engine they acquire. This is not true.

 

--> The conical engine mount came first. It is easier to fabricate than a dynafocal mount. If your crankcase pads are flat and if the mounting bolts are installed horizontally through the mount and engine, then it is a conical mount engine. The O-320-A and O-320-B engines use this mounting.

 

--> Next came the Dynafocal engine mount—now called the Type 1 Dynafocal mount. The mounting bolts and the larger rubber isolators are positioned at an angle of 30 degrees. The intent was to “focus” the mounts just ahead of the center of gravity of the engine/propeller combination. The focal point for each of the four slanted engine mount bolts is projected, for most engines, to intersect at some point inside the engine forming as an imaginary 30 degree angle to the engine’s centerline. This is the most commonly used system and is considered to be superior to the conical mount. Its large rubber discs cushion engine vibrations better than do the smaller cone shaped rubbers of a conical mount. Dynafocal engine mounts are much more difficult to design and to build because the engine mount must be around a precisely preformed dynafocal ring that has the correct 30-degree slant already built in.

 

--> When Piper introduced the Twin Comanche, the aircraft had long extensions to the propeller hubs. This gave an exceptionally clean cowling, but the center of gravity of the engine/propeller was moved ahead of the focal point of the Type 1 Dynafocal

mounts, so the angle was changed to 18 degrees to compensate. This is known as the Type 2 Dynafocal and is used on the IO-320-B1A engines.

 

GLG (gotta love google)


Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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A conical engine CAN be converted to a dynafocal engine, but the cost is prohibitive. There's a Long EZ out there with a converted O-290 that ECI changed - welded up pads, machined them, bored them. It's cheaper just to get the right engine.

 

On the Berkut, when we went to the 540 - the 540 engine mounting points are bolted onto the case. To reduce their size we made our own conical mount bolt on ears. The result is a little more vibration getting to the airframe, but no big lumps on the cowl.

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Jerry, I hear alarms going off... it's your decision, but having had the pleasure of meeting you on several occassions I am very concerned about "disastrous results".

 

I urge you to seek more feedback.

The concern is appreciated. Due dilligence has, and will continue to be conducted.

 

As to the warning, I appreciate that as well.

Aubrey: Since you chose to open this can-o-worms on a public forum, would you please let us all know your bonafides? (Due dilligence goes both ways.) (ie:background.) Your Forum profile is pretty much vacant. You've made some pretty serious statements here, and I need more source data to evaluate their validity. In any case, I appreciate you taking the time to type them in.

 

I understand Chrissi IS a mechanical engineer.

I know she has spent a lot of time researching engine mounts.

The design is standard, and has been in use for many years.

 

Richard: I'm not an engineer as well, (and I didn't stay at a Holiday Inn Express either.:D ) but I'm guessing an FMA is some sort of analysis. What "doesn't look right" to you? I'm guessing you're echoing Aubrey's comments as to robustness.

 

Funny thing though, checkout http://pages.sbcglobal.net/ccanedy/chapter23.html . Clark Canedy's mount looks exactly like mine, (except for the Dynafocal ring). Is he in danger too?

 

In closing, I appreciate any and all comments/suggestions offered here. If any of them turn out to save my life, I'll buy you a beer. If it doesn't, I'll buy you a beer anyways.:)


"I run with scissors."

Cozy MKIV N85TT

Phase One Testing

http://home.earthlink.net/~jerskip

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People:

 

In the interest of accuracy, I would like to amend my previous post. Don't want to be responsible for spreading bum dope.

 

As I understand it, Chrissy of CG Products is not a mechanical engineer as I previously stated. She's a Mechanical Designer. My Bad :o . But the design she used was taken from a well respected and widely used source. Namely Tony Binglelis's book "Firewall Forward" page 78 & 79. I would guess Tony Binglelis IS an engineer, or equivalent.

 

Secondly, with regard to the statement "probably fail with potentially disasterous results shortly after being placed in service" , I have opinions, from more than one source, indicating failure would most likely be manifested by vibration which would necessitate premature ending of flight (ie: controlled), rather than "disasterous results". Potentially? Yes. Likely? Not in my present opinion. (I reserve the right to change, though.:D )

 

And oh yes.... It's bona fides. Never have been a speller.:irked:


"I run with scissors."

Cozy MKIV N85TT

Phase One Testing

http://home.earthlink.net/~jerskip

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Jerry,

I appreciate your skepticism. My background includes BS and MS degrees in Physics. Before retiring last year, I taught physics, hydraulics, engineering mechanics, and electronics at the college level for many years. During the 8 years preceding my retirement I was the Chair of the Science and Math Department at Cape Fear Community College in Wilmington, NC. My department employed about 50 faculty and served typically around 4000 students per semester. I am an applications oriented physicist and have taught the Statics and Strength of Materials courses that cover the design of these structures many times. These courses were actually not offered by my department, but, by our Engineering Department. Cape Fear Community College engineering students have participated in several competitive international engineering events (human powered submarines, remote controlled underwater vehicles) we have always placed first, second, or third and we usually win the secondary "best design" award. Not a bad performance, especially considering that MIT and CalTech are usually in the competition. So,...we know how to build mechanical "stuff".

 

What does the engine mount need? This mount should be designed as a truss type structure. In a truss structure the tubes or truss members should experience forces that are only either tension or compression. No bending forces are allowed. The four engine mount points must each be independently fixed in 3-dimensional space by tubes that transmit only tension or compression back to the firewall mount points. Fundamentally, this means that each of the engine mount points must be contacted by at least three tubes. In this instance the engine case cannot be part of the structure because the rubber bushings allow motion. The dynafocal type mount you mentioned is an entirely different type of structure because the engine mount points are connected together by the (fairly heavy) ring system. I've attached a marked-up version of your photo. We need tubes where I've marked lines. The yellow and red tubes will fix points "a" and "b". The lower X structure should consist of straight tubes that lie in a plane. I would replace the existing tubes with the green tubes. Finally, on composite aircraft, I worry about how "hard" the hard points on the firewall actually are. So, although this is probably optional, I would tie the four firewall mount

points together with the blue tubes. These would be tension members and could be made of 3/8" tubing. They would represent very little weight penalty and may save a major airframe repair at, say, 1000 hours or so. (guessing here) Of course, what I've penciled in may interfere with existing components on the firewall or with engine components, etc. In that case, some other tube configuration may be needed.

 

I don't know about Chrissi's engineering qualifications. I meant no offense. All I can say is that everybody makes mistakes occasionally. I am reminded of a machinist who worked on the 2nd shift at a textile mill who, when I was a kid, would help me with my "build it" projects. "Red" Thompson was his name; his favorite saying was: "Don't worry about making mistakes,

I've never made one I couldn't fix".

 

Aubrey

post-622-141090153846_thumb.jpg

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Gentlemen,

Before things get ugly lets take a look at a few things.

Have any of you actually seen a Long-Ez or Cozy III Conical engine mount in real life? Recently? hmmmmmm?

Jerry sent us the one that came with his engine off of a Cozy III, been on there awhile I think. They are not what I would call confidence inspiring.

NOT being an aircraft engineer or a structural engineer I would not presume to pull a design out of my rear end and pronounce it Good and Holy by all things I hold sacred, for that matter I'd be reluctant to listen to anyone with a casual opinion on the subject unless they had specific and pertinent information with the experience and the history specifically with this subject, this includes certain self-proclaimed experts on some other list who sent me a marked up version of the 3D rendering from our own web site of the dynafocal engine mount... proclaiming imminent and certain catastrophic failure (as he always does). I did not have the heart to inform him that the very clearly rendered drawing was an exact representation of the plans Cozy Mk-IV Dynafocal mount.. I guess we all need to get the word out huh? :D In fact I'd just stay out from under them altogether.

But we were talking about Jerry's engine mount. You guys sure have a knack for telling a mother her kid's butt ugly.

Hoping that the pictures come out in the right order...

Lets take a look at Jerry's mount, then the following two pictures are scans from Tony Bingelis's "Firewall Forward" ISBN 0-940000-93-8..sixth edition printed in 1998, lets see, the EAA has in fact been printing this same book since 1983.

Now, is there anything in common between Jerry's Conical mount and the Conical mount illustrated in Mr Bingelis's book?

Any resemblance at all? I'd sure hate to be accused of doing something original.

I'm also smart enough to not presume I know how to design an airplane, I have no training or experience in doing so, that is why I defer to people who have the qualifications, information and experience. If you want to design cardiac catheters, endoscopes, surgical cameras, semiconductor test equipment or yacht hardware, I'm your girl.

Manufacturing airplane hardware? I know nothing, its just a hobby I picked up so I strictly follow the plans, Randi and I would strongly suggest you do too

;)

Christine

post-11-141090153826_thumb.jpg

post-11-141090153828_thumb.jpg

post-11-14109015384_thumb.jpg


CG Products

www.CozyGirrrl.com

Cozy Mk-IV RG 13B Turbo

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...Finally, on composite aircraft, I worry about how "hard" the hard points on the firewall actually are...

I am just wondering have you ever examined EZ engine hard points? The first VariEzes have been around for decades and all the descendants have used the same system. Are you suggesting or suspicious that there is a flaw in composite aircraft hardpoints and what do you base this on? If there is there are plenty of us who would like to make those corrections before we get too far into the build process.

 

Chrissi, as you have shown how common this mount is, is there any difference between this pusher system vs. a tractor system?


Nathan Gifford

Tickfaw, LA USA

Cozy Mk IV Plans Set 1330

Better still --> Now at CH 9

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I don't think you need to fret about the Cozy hardpoints, Aubry. They're pretty bulletproof on the Cozy IV. I do agree (political science major talking here) about the need for the yellow tubes with the conical mounts. If you imagine twisting the engine around a vertical axis, i.e., the same kind of forces the mount would see in a rapid pitchup or pitchdown, it appears to this poly sci eye that you'd impart lateral bending forces to the upper tubes.

Most of us Cozy builders are using the same tube layout as Chrissi is using, but with a dynafocal ring welded in, I imagine the ring imparts a little more rigidity to the upper tubes. Not sure the green tubes you're suggesting would clear accessories on the accessory case. Could be why they're as they are.

--Kent

Cozy IV N13AM


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Aubrey

Have you ever designed a engine mount before? I saw nothing in your analysis of the HP of the engine, the weight of the engine, the torque of the engine, the type of isolation mounts and the total application of the engine mount. Your credentials are very impressive but you are way off base in your analysis of this perticular mount. This type engine mount has been around for over 40 years in one form or another and I have never heard of a failure. I have a very similar engine mount on my E Racer only closer to the firewall because of the weight and balance of the AC. I have pushed my engine to 448 Hp with 59 inches of MP. The problem I have come across in the last 5-6 years developing my electronic fuel injection system and supercharging system, is when I talk to the trained proffesionals for the systems I am working with, they have absolutely no knowedge as to what the application is. It seems to me your statements follow this exact line of thought. The CGs in my opinon are producing the right product and the right quality products for the application. Also about the hard points, where did you come up with that statement? There has never been a engine hard point failure , ever. The same hard point is used on AC with 85 HP to 448HP. Cozy Girrrls, keep up the wonderful work.

 

Jack

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Richard

You are right looking at the photos that it looks spindly and I agree, looks can be deceiving, especially the toe in. But seriously, this design is not new. It has been a proven design. I wil say though that I added some additional supports to my mount but only because of the additional HP and torque I was using in my application. I made my mount myself(like design) and consider myself a good welder, shipped the tacked mount to Shirl bolted in position on a 1/4 in steel plate and had a certifided welder do the final welding. Really do not know for sure if it was necessary, but I always like to stay on the safe side with the airspeeds I am running. Would like to touch base with you sometime, I spoke with you several times when Berkut was still in business. Berkut is a great AC, best of the canard design.

 

Jack

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Folks, let's be very careful about the generalizatiions here. As I stated, the dynafocal type mount with a ring structure that ties the engine mount points together is NOT "similar" to this mount. It is a frame type structure. My comments are directed toward this particular configuration. It was as incorrect in 1983 as it is now. It could probably be made correct by the addition of a dynafocal type ring structure. But, then it would be a different mount and not "similar" to this one.

 

Chrissi, EAA publications are not peer reviewed. The fact that this design was published does not necessarily make it correct.

 

Jack, I did not consider tubing diameters and wall thickness. So, there was no need to mention engine weight, torque, hp, "g" loads, safety factors, etc. That is a separate set of issues. I have read of numerous firewall hardpoint repairs. I did not say "failure". I agree with you that a failure is a remote possibility. Your mount is probably some variation of a dynafocal type. Do you have a photo you could post?

 

You will not find this particular mount configuration on a certified aircraft.....for good reasons.

 

Be safe,

Aubrey

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...As I stated, the dynafocal type mount with a ring structure that ties the engine mount points together is NOT "similar" to this mount.

I will agree with this statement. Having the ring substantially stiffens the structure, and having some cross-members as you sketched would substantially stiffen the conical mount design. Since the back side of engines with conical mounts is not substantially different than engines with Dynafocal mounts, what you've proposed would be possible.

 

However, all that said, no amount of cross members will turn an engine mount of this type from an indeterminate structure to a determinate one - unless you were willing to use ball/pin joints at every tube intersection.

 

... It was as incorrect in 1983 as it is now. It could probably be made correct by the addition of a dynafocal type ring structure.

There's "CORRECT" and then there's "ADEQUATE". While I will certainly agree with you that this design is not optimal from a load paths standpoint, without a stress analysis, it's not possible to claim that it won't work. It IS possible to claim that it MAY have bending moment issues, but that's something that can be addressed by looking at the population of non-cross-braced conical mounts and obtaining the failure rate.

 

If the imposed bending moments, even under vibration loads under "G" loading, are lower than the fatigue limit of the 4130 steel, then it doesn't matter that the mount would be structurally more efficient with different load paths (and the claim of structural efficiency is dependent upon the increased thickness of the existing tubing weighing more than the extra tubes for bracing would have weighed). It would work - that's all that anyone will care about.

 

Chrissi, EAA publications are not peer reviewed. The fact that this design was published does not necessarily make it correct.

Absolutely true. But 23 years of experience without failures would make it ADEQUATE, if not optimal.

 

I have no idea if that's the case, but it might be. It's one of the things to consider.

 

Jack, I did not consider tubing diameters and wall thickness. So, there was no need to mention engine weight, torque, hp, "g" loads, safety factors, etc. That is a separate set of issues.

A seperate set, yes, but intimately tied in. If the engine attached to this mount put out 20 HP and weighed 40 lb., I don't think this discussion would have occurred. Conversely, if it put out 2000 HP and weighed 1500 lb., it would be fairly obvious that the mount was inadequate.

 

We're somewhere in the middle, and that's why you had the gut feeling that there MIGHT be a problem. And there might - as I said before, I'd feel better about it with some more bracing on the top, but IF O-320's have been mounted to this design for 20-40 years, and have worked, then my gut feeling was misplaced.

 

Here are some pics of mounts used for lower power engines that have similar configurations:

 

http://www.greatplainsas.com/scengmounts.html

 

 

You will not find this particular mount configuration on a certified aircraft.....for good reasons.

Well, you bring up some good points, but using certified GA aircraft, most of which were designed 60 years ago by folks who may or may not have done any analysis or much testing, and which, by and large, have failure rates of systems and components that would NEVER be tolerated in a consumer or automobile marketplace as an example of something to emulate is not one of them.

 

Be safe,

Always.

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