RAF PSRU aluminum mount plate (which cracks) -- replaced it with CNC 4140 steel

Kolibri

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RAF2000 old vs. new steel rear mount.png


As any long-suffering RAF owner has learned, there are many design/material issues to the gyro.
The engine/PSRU mount plate has been known to crack, and it happened to me last year.

When my TIG welder friend repaired the OEM mount, he cautioned me against relying too heavily on rewelded aluminum (which loses its temper),
and forecast that it would probably crack again in about 25 hours. Well, his forecast unfortunately proved correct, as it cracked after 22.9 hours.
I found it on a post-flight inspection, having felt/noticed nothing in its previous half-hour flight. The mount could not be further repaired.

I've vowed to never order anything from RAFSA, as our USA owner experience has often shown that a local part can be made
better, stronger, faster, and often cheaper. (RAFSA parts are still made in Canada, but shipped to South Africa to prop up the
dwindling fiction that RAFSA does their own mfg. Thus, USA customers pay for the bloated shipping costs involved.)

So, I cast about for a local CNC machinist, and a pilot buddy knew of a reputable fellow who had a home-based shop who wasn't nervous
about making aeronautic parts. I sent along the mount, horseshoe, and jackshaft.

While 7075-T6 aluminum would have certainly sufficed (for a long while, at least), I and others (including Jim Vanek) thought that the vitality
of the mount deserved chrome moly steel. Such would probably never fail, and if it did, it could be repaired. There would be a moderate weight penalty,
but with its location near engine cg (while also reducing RAF propthrust vertical cg), the effect would be insignificant.

I wished that the mount thickness (designed for aluminum, but not needed in 4140 steel) could be reduced, but standoff dimensions had to be
maintained for the jackshaft and crankshaft bearing plate bracketry.

The machinist and I agreed that the horseshoe should also be made of 4140, to maintain like heat expansion with the mount.

I asked that all bolt holes and surface edges be radiused, to reduce odds of stress risers. (I believe that the OEM mount's sharp edges all around
contribute to its frequent cracking. Also, IMO, the pinch bolt force places too much stress on the lower horseshoe bolt holes, and the mount usually cracks there.)

It's rather a complex part to design in SolidWorks, but within the capability of most CNC guys. There is a LOT of trig to input!
There were 22 small holes to be drilled, a few of them tapped, plus the larger holes for the jackshaft, starter, and flywheel area.

MODS: He widened the top area from 4.875" to 5.25", requiring a longer pinch bolt (AN8-60A).
Cross-section was increased for the two lateral horseshoe bolts.
His weight-reducing measure was a very nice looking "bow-tie" 0.5" deep inset, handsomely rounded out inside with a ball mill.

My machinist estimated its strength as "
about quadruple" the OEM aluminum mount. I think that'll do, heh.
His plate bolted right up; evidence of high-quality work. Workmanship was first-rate.
I just landed today after 0.7 hours, and all's well. Feels great to be rid of that crack-prone OEM mount!

Anybody who has a failed RAF mount and wishes to replace it with something far superior (either in 7075 or 4140) may PM me for a price quote.

Regards, Kolibri

P.S. I'd briefly considered going to a geared redrive at this point, but it would have taken longer, been more expensive, and required a
reverse pitch prop. Also, had I been thinking of going to the EJ2.5 motor and flipping the redrive, this would have been the perfect time
to have a mount plate made for that. But, since I'm getting a Sport Copter M2 this year and selling the RAF, I hadn't time or will to convert
from carbed 2.2. That can be the next owner's project if necessary. (I think that my RAF would make a great first gyro for a newbie, as nearly
all the bugs have been worked out, or a good training ship for a CFI who wants to add the RAF to his stable. I'm about to do its 500 hour
checklist. All components are strong and reliable, and its engine is 80/80/80/80 making no metal. Asking price will be mid-$30k.)
 
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AirCommandPilot

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What did the difference in weight end up being? Machining a one off part like that must have cost a fortune.
 

CLS447

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Very nice ! Ballpark figure......$1000 ?
 

Kolibri

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I wish it were merely $1000. (Material and tooling cost alone was $800.)
Design time was extensive at 30+ hours. I should be able to offer them for ~$2000.
Weight penalty in 4140 is 15lbs. Or, have yours made in 7075-T6 without the "bow tie" cut-out
(the beefier horseshoe bolt hole cross section should be prove sufficient).

I've no idea what an RAFSA OEM part costs delivered, but my CNC guy thought the stock design lacked in strength.
If yours ever cracks, you'll probably want a better part in stronger material . . .

Regards, Kolibri
 

eddie

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I had never heard of a mounting plate crack before,it appears that the cross bolt was overtightend,I only snug the cross bolt up.

Actually that bolt only serves to hold the pulley shaft in place so the horseshoe collar can be installed,the horse shoe collar piece

clamps the pulley shaft flange against the mounting plate,its held in place by 3 bolts and the motor mount rods running from the

attachment plate on the mast. If you wanted to really tighten the 1/2" cross bolt make sure that the pulley shaft fits really snug inside

of its mounting hole,that way little movement of the plate will be caused by overtightening and lead to cracking.
I apply 230 hp on takeoff to my 5 bladed prop that is pitched to 14.5 degrees at the tips and have never had it come loose or
lose the belt adjustment setting and I have more than 750 hrs on it.
 

FRANK'S

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All I can Say is that Kolibri Help me in not buying a RAF2000 I liked it was made in Canada and there was a local man selling one for 19K Can
It's was all updated with proper parts and was made a safe Gyro.
But after reading and education my self about the RAF2000 mostly reading Kolibri rants and info post I did not buy it and bought a Continental powered Bensen instead.
 

eddie

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Sorry you didn't buy the RAF they are probably the best buy for the money on the market,kolibri took a hosing when he bought his RAF and has been tearing

down the reputation of the RAF ever since. He is just one person who flys the RAF, if you really listened to his rants you would never fly anything ever,you would

just sit at home and fly your armchair.
 

Vance

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I have several friends with RAFs that have had very positive gyroplane adventures Frank.

Based on the pictures this cracked plate looks like a maintenance issue to me rather than a design flaw.

Good assembly technique is to break all sharp edges and deburr all holes.

RAF was trying to meet a price point and I feel doing some extra finish work on a low cost experimental aircraft is to be expected.

Many builders were carless about finish work and maintenance creating problems for themselves that they blamed on RAF.

Please understand I am not suggesting there were no problems with RAF.

I am suggesting that many of the problems were caused by poor assembly and maintenance.

I am happy to train someone in a well built, well maintained RAF.

I feel a proper preflight is very important in any gyroplane.
 

Kolibri

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I had never heard of a mounting plate crack before
Well, eddie, here ya go:


I had the same thing happen as did a few others without any kind of accident. Luckily, they found it while I was having the AAI conversion done. They machined me a new one. I also had the prerotator assembly crack both at the top and the bottom. Check all your RAF aluminum machined parts often and carefully.

I can't comment knowledgeably on this because I know almost nothing about machining, but I was told that some of the cracks are due to stress from improper machining techniques, like not radiusing inside corners and cutting them square. I can't recall who said it, but it was after someone posted photos like Gary's on the old forum a few years ago about the same problem on their drive-plate. I do know that the lower bolt-hole assembly of my prerotator cracked because the hole was grossly miscentered. One side wall was almost paper thin.
KenSandyEggo 04-14-2004


Sorry you didn't buy the RAF they are probably the best buy for the money on the market
A safe and moderately priced RAF is possible to find, but the buyer must really know what to look for, and be able to trust the seller.
Good luck . . .


kolibri took a hosing when he bought his RAF and has been tearing down the reputation of the RAF ever since.
He is just one person who flys the RAF, if you really listened to his rants you would never fly anything ever,you would
just sit at home and fly your armchair.
eddie, it's funny how you've somehow time to allege things about me, yet ZERO time to educate RAF owners about
how not to install Sport Rotors, or apologize to Sport Copter for falsely accusing them of a botched product.



__________
Good assembly technique is to break all sharp edges and deburr all holes.
RAF was trying to meet a price point and I feel doing some extra finish work on a low cost experimental aircraft is to be expected.
Many builders were carless about finish work and maintenance creating problems for themselves that they blamed on RAF.
Vance, then take it up with Dofin Fritts who co-built my RAF, and many others.

Based on the pictures this cracked plate looks like a maintenance issue to me rather than a design flaw.
That assumes that I or somebody before me overtightened the 1/2" pinch bolt.
All I can say is that it wasn't me. That area always struck me as one not to overtighten.
What others did during its pre-Kolibri 267 hours I do not know.

(And, somehow, without the benefit of your remarks, I knew to radius the bolt holes and edges last year on the TIG repaired aluminum plate.)

My machinist commented that the plate was designed without ample cross section where needed.
I had the idea of making the new plate with a 7/16 AN7 cross bolt, to increase the material there (and because brutal AN8 compression wasn't necessary).

Regards, Kolibri
 

Kolibri

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Below is from my RAF2000 Construction Manual.
No torque values are given, but there should have been.

RAF redrive belt tensioner assembly2.JPG
 

Kolibri

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, , , rather than a design flaw
I can point out the most obvious design flaw right now: the asymmetrical portion of material between the two bottom horseshoe bolt holes and their respective edges.
The right side is less than the left, and my machinist and I agreed that such was a problem. He added to the right side in his improved design.

Also, his increased width of the pinch area moves the vertical edges past the bolt holes, and without any concentrated stress of the
OEM drop-down rounded inset junction of the horizontal edges to the vertical.

He also reduced the tolerance between the jackshaft and the plate hole, which reduces the amount of pinch bending necessary.
He cautioned me against painting this area due to tight tolerance. I instead lightly coated it with XF7 gun lube (an excellent rust inhibitor
which according to the mfg. bonds to the substrate, and lasts a very long time). Navy SEALs used XF7 on their weapons, and it's quite effective
even against salt water. I've tested it extensively with great satisfaction.

I discussed with him my idea of eliminating the cross bolt, as I believe that the 3-bolt horseshoe is ample to anchor the jackshaft.
(The cross bolt is mostly an assembly aid to retain tension of the drive belt until the horseshoe is full tightened.) Not envisioning an
elegant solution for temporarily holding belt tension, I retained the cross bolt (although without enthusiasm). We discussed going to
an AN7 bolt, but my machinist thought the steel plenty strong enough for the original 0.5" hole.



Good assembly technique is to break all sharp edges and deburr all holes.

RAF was trying to meet a price point and I feel doing some extra finish work on a low cost experimental aircraft is to be expected.

Many builders were carless about finish work and maintenance creating problems for themselves that they blamed on RAF.
Really? It was too much to expect from RAF Canada to "break all sharp edges and deburr all holes" on this plate?

Really?

RAF Canada CNC manufactures the plate.
Do you know long it takes for an edge and hole radiusing additional CNC cycle?
Only 3-4 minutes, according to my machinist.

That RAF Canada chose not to bother radiusing the plate edges and bolt holes had nothing to do with their "
trying to meet a price point".
Rather, they were shoddy. They still are. Their gyro is replete with bad designs, poorly executed, and repeated years after public exposure.

On the OEM plate, I consider the weaker right side horseshoe bolt area especially deserving of preemptive attention.
One should definitely chamfer that hole, and also the left side.



I am happy to train someone in a well built, well maintained RAF.
Oh? Regarding this plate, how would you know if a quality builder had actually deburred the bolt holes?
The holes are concealed by the hardware, and those bolts are not removed for belt tensioning/replacement -- only loosened.

How would you know? You couldn't.

Until I had to remove the plate last year for TIG repair, I did not know what the bolt holes were like.
(Had I clarioned the discovered need to chamfer these holes, you likely would have accused me of "
crying wolf" and "bashing RAF".)

Regarding a "
well built, well maintained RAF", in my opinion after nearly 4 years of ownership, discerning such in another's machine is not as easy as you imply.
I'm confident that most-if-not-all RAFs you've flown hadn't plates with chamfered bolt holes.




___________
not buying a RAF2000 I liked it was made in Canada and there was a local man selling one for 19K Can
It's was all updated with proper parts and was made a safe Gyro.
FRANK'S, an all updated/proper parts/safe RAF for only C$19,000 is an oxymoron.
Unless the seller is truly dumping it at a monetary loss, I would suspect that it's not quite as "updated" as claimed.

Feel free to post some detailed photos, and we can comment on the gyro specifically. What was the tail #?

One final tidbit of wisdom: Nobody owns an RAF2000 because of alleged superior design or flight qualities.
Rather, they're owned because they're the most affordable 2-place enclosed gyro, period. I bought mine for less than 25% of a used Cavalon or Calidus.
For the money, it's been merely OK. I've learned a lot about gyros, logged in hundreds of hours, and greatly improved it for the next owner as I move up to a Sport Copter M2.


Regarding RAF shopping, here is a thorough thread on what to watch out for.

Regards, Kolibri
 

FRANK'S

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[COLOR=#008000 said:
FRANK'S, an all updated/proper parts/safe RAF for only C$19,000 is an oxymoron.
Unless the seller is truly dumping it at a monetary loss, I would suspect that it's not quite as "updated" as claimed.

Feel free to post some detailed photos, and we can comment on the gyro specifically. What was the tail #?

One final tidbit of wisdom: Nobody owns an RAF2000 because of alleged superior design or flight qualities.
Rather, they're owned because they're the most affordable 2-place enclosed gyro, period. I bought mine for less than 25% of a used Cavalon or Calidus.
For the money, it's been merely OK. I've learned a lot about gyros, logged in hundreds of hours, and greatly improved it for the next owner as I move up to a Sport Copter M2.[/COLOR]

Regarding RAF shopping, here is a thorough thread on what to watch out for.

Regards, Kolibri


That was over 3 years ago I don't have pics it was in Alberta and the owner lost his medical and needed to sell.
but it's been sold and probably someone here owns it now.
 

Kolibri

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You mean my "rants" were so effective even "over three years ago"?
That's when I joined the forum.
And I was so young and inexperienced then. :smile:
 
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JohnyWalter

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It is very interesting.Good advises..
I have a question, I saw in the description that you constantly mention a tig welder.Which good?for similar projects related to aluminum.I ask for myself, I want to buy for future work..
Thanks in advance!
 
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