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  #1  
Old 10-25-2010, 08:53 PM
tonyslongez tonyslongez is offline
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Default Berkut 360 build

Well gang for those of you who followed my posts on canard zone. I have good news we have another Berkut project going, this one is in much better shape than the first project, however it will require far more parts to be fabricated. With the new HAAS VF-2 in the shop, machining custom parts will no longer be a problem I will begin posting pics this week.

Tony
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  #2  
Old 11-05-2010, 11:33 PM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

First I want to start with landing gear. For the last 3 years I have been studying and reading every book I can find on landing gear design, most of which was written in the 50's and 60's. The latest print publication that I own is Pazmany's book and even that was published in 1986. My prized possesion to date is a book from H. Conway printed in 1958. Now in the last year, I have accumulated a mass amount of landing gear parts (mostly retractable parts).
Now most of you know that I'm building Berkuts so alot of the discussion will be for the Berkuts, however in the landing gear department, the Berkut is not what I would call the best landing gear design. We will have to start discussing other types of aircraft with retractable gear. I hope that what I've learned in the last few years will help with a new design of landing gear. I would like to share some pics of the latest victim to fall prey to the Berkut landing gear: Misha Kasyan. I will not go too far into the accident itself, only to say that he had a forced landing due to the rear canopy not being latched. Despite what you see in the pics the landing itself was uneventful that is untill the gear collapsed. Misha reported that the landing wasn't that hard a little fast maybe but not "hard" the gear he thought collapsed during heavy breaking. Now keep in mind this was an emergeny with lots of adrenaline so maybe harder than he thought. but certainly less than 3 g's



1) Aircraft departed runway centerline due to collapsing gear

2&3) Both legs (right and left) failed at trunion

I have in the last year collected no less than 3 sets of Berkut legs that have all failed in the exact same place. I will explain why in the next few posts.

Tony
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  #3  
Old 11-06-2010, 12:09 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

These are pictures that I will share so that we understand what a stock Berkut gear install looks like before bulkheads or plumbing. In these pics there are no other layups or chapters to perform, these gear are ready to be used per factory plans.



Pic 1) Basic Berkut gear installation

Pic 2) Top view Berkut installation

Pic 3) All bolts showed signs of being bent do to landing stress.

Pic 4) These are the failure points for the Berkut gear. All examples of failed
Berkut gear are indicated in red. keep in mind these are catastrophic
failures of either one leg or both legs at the same time

Tony
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  #4  
Old 11-06-2010, 02:12 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

Pic 1) you can clearly see the A-arm has failed. Now keep in mind this is a
fairly stout piece of linkage, (billet A-arm no slouch in the strength
department) So why did it fail?

Pic 2) Landing loads are as followed Up, Back, Torsion. in its simplest form
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  #5  
Old 11-06-2010, 03:42 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

O.k if we start to look at how certified aircraft are built. (I know, boooo)
its easy to see how the engineers at piper and cessna delt with landing loads.
I will verifiy my findings as I go, but I'm pretty sure talking with my engineer friends, I have it correct. Ok first things first. The original berkut gear legs where an all carbon gear leg but due to manufacturing techniques the all carbon legs experienced gear creep over time. Though the original gear legs where proned to creeping they where actually a better leg than the now cast gear legs. There are 3 parts to the berkut gear, upper, leg, and lower talon. The issue with the gear is the upper for several reasons, the biggest being that it's made of cast aluminum. Cast aluminum is not the material you want to use to make any landing gear pieces. The other problem with the upper is its not designed for landing loads. In other words, part of the landing loads are trying to deflect the upper portion of the gear, it's cast in such a way that the upper doesn't deflect (that's bad). So we have to do away with the upper or replace it with something else.

The next issue to look at is the area below the upper. You'll notice in the picture that there's nothing supporting the bottom of the uppers.
What has to happen here is, we need a saddle to put the gear in when they are extended. This saddle will have to be tied into the lower longeron (oh wait we don't have a lower longeron ) crap we need a lower longeron to help out with the landing loads.
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  #6  
Old 11-06-2010, 04:13 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

If you look at the pic with the failed A-arm I asked (what caused it to fail?)
Well without a lower saddle and lower longeron to dump the torsional loads into, what we have is a cast upper that fails during heavy torsional loads. once the upper has failed those torsional loads are immediately transfered into the A-arm and into the H-arm this becomes a point of very high stress so much so that the A-arm fails. The only way to prevent this chain of events from happening is to take the landing loads out of the upper. We start by first adding our lower longeron/ saddle. The saddle will transfer the loads going aft into the lower engine mount and spar, also the bulk of the torsional loads that causes the upper to fail. The minimum with of the saddle is six inches. Next we get rid of the cast upper. Now we could machine a new upper out of billet aluminum which is how the Mobius gear are, or instead of throwing metal at the problem we redesign the upper to retract the gear leg only, then minimize the loads that are transfered into the new upper.

Pic 1) Lower saddle handles the aft and torsional loads.

Pic 2) Mobius gear leg billet aluminum
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Last edited by tonyslongez : 11-06-2010 at 04:24 AM.
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  #7  
Old 11-06-2010, 04:50 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

Next up lets look at the A and H arm. The H arm is pretty stout, heavy but stout. The H arm is the linkage that actuates the gear, it also provides the over center lock. Now, all of the examples of certified gear that I have do not use bolts to transfer loads. In some cases it can't be avoided but for the most part bolts in landing gear are more of a means to hold things together not to transfer landing loads. The other problem with the A and Harm is they are much heavier than they need to be, also the over center locking portion of the linkage doesn't touch. Once The A-arm has traveled five degrees over cente it should positively contact the H-arm, most of the berkut linkages I have seen do not, this puts a hudge load on the bolts connecting the A-and H arms together the results are usually bent bolts.
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  #8  
Old 11-07-2010, 02:59 AM
tonyslongez tonyslongez is offline
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Default Re: Berkut 360 build

Here is a pic of failed berkut gear legs, notice that only one side has failed.
This is due to the torsional loads during landing, icorporating a gear saddle will eliminate this problem, However the upper can still be compromised because of its cast aluminum makeup.
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  #9  
Old 11-11-2010, 11:08 AM
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Default Re: Berkut 360 build

interesting, your study feels like my study of electronic fuel injection, spark and turbo charging, but i have no one to study, doin it my self with A LOT OF help from others.


keep on a goin

are those aluminum parts cast or machined?

dah - i see, cast.

You going to machine them?
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  #10  
Old 11-14-2010, 12:36 PM
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Default Re: Berkut 360 build

Quote:
However the upper can still be compromised because of its cast aluminum makeup.
You're doing great on your research but don't bash cast aluminum yet. Many suspension parts on cars are now cast aluminum and do very well. Being the backyard builder its probably best to do one-on parts with billet although it can be pretty heavy. Consider a wider stance at your pivot point - putting the "A" in A-arm instead of the H-arm. Here's a couple different designs to consider.
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