Cracks in the Predator’s frame

[Arnie Madsen]

I will be there with my SparrowHawk and Bell 47 also. We should make sure to park the gyros together. 3 (hopefully 4) gyros will be a record for VC .

Marc

Marc Goroff You have one heck of a problem. How to get your Sparrowhawk and your Bell 47 to one place at nearly the same time. My mathematical calculations figure out that you have two very desirable machines and only one pilot.

If you are not able to explain how you will take care of it ..... please remember some of us guy's would much rather spend the next few days wishing we had such problems !

Thanks Marc, if you are able to handle one more thing , I would request you bring a camera and show some proof that you can do it.

I am sure I heard that helicopter pilots can do up to three things at one time. Pretty much everybody knows that by now.

But if we were ever to see a Gyro pilot who could also take pictures and fly helicopters ..... well ..... that would really be something.

Looking forward

Arnie

 

[Alan_Cheatham]

Vance,

In looking at the additional pictures it becomes clear there are multiple tubes in the front fuselage frame that are carrying bending loads and I'm sure you know that all the tubes in a truss structure should only have axial loads, preferably compression for a truss that uses welded joints. You are going to need to do some careful study of the problem and commit to a permanent solution otherwise this will be an ongoing problem with the potential of a catastrophic failure.

I surmise that most of the problem comes from landing and taxi loads magnified by the long lever arm of the nose gear struts. Although it would be best to use a structural analysis program to find the actual load each tube is carrying as a quick test try immobilizing the bottom of nosegear then push the frame from side to side and fore and aft to see the effect the load created has on the frame tubes.

.

 

[Dennis D]

Torsional loads?

Torsional loads?

Hi Vance.
I’m not an engineer so I have trouble explaining my thoughts, the location of the cracks and fact that there is no “horizontal" X bracing in the front of the frame would seem to create large torsional loading on the longerons at the location of the cracks.
I tried to divert those twisting forces by triangulating the longerons in the Viewmaster frame.
This is just an opinion based on observation.

Dennis

 

[WaspAir]

Marc Goroff You have one heck of a problem. How to get your Sparrowhawk and your Bell 47 to one place at nearly the same time. My mathematical calculations figure out that you have two very desirable machines and only one pilot.

If you are not able to explain how you will take care of it ..... please remember some of us guy's would much rather spend the next few days wishing we had such problems !

Thanks Marc, if you are able to handle one more thing , I would request you bring a camera and show some proof that you can do it.

I am sure I heard that helicopter pilots can do up to three things at one time. Pretty much everybody knows that by now.

But if we were ever to see a Gyro pilot who could also take pictures and fly helicopters ..... well ..... that would really be something.

Looking forward

Arnie

Marc and I will just harness up the two Bell 47s like a team of horses and tow in the three gyros in a long line like those multi-trailer semi trucks. Maybe we can get Discovery Channel to film the landing in 3-D.

 

[Alan_Cheatham]

Any type of spring (that includes a softer nose wheel) would lower the load on the upper cross beam.

Keep in mind that a spring or damper will only reduce spike loads and not static loads. If it takes X amount of force for the nosegear strut to support the front of the aircraft it doesn't make any difference if there is a spring in the sturut or not.

.

 

[Vance]

Where do you stop?

Where do you stop?

I am glad you found humor in it Pete.

Communicating over the sound of the engine with full face helmets requires some imagination.

I could see that he understood the message from the size of his eyes.

Braking was particularly difficult without the use of the right handlebar and I had to hold it with my left thumb so I could operate the throttle with my right hand.

The point was that I have learned through experience and mistakes.


Thank you for your concern Ed.

I am driven by passion and in the big picture that is exciting. There are moments that are less fun.

I looked rough because I had been rolling around on the hanger floor most of the day.

I looked tired because I was.

The business has been doing well lately so I have been able to manage it with just a few hours a day mostly by remote control.

I feel that Rotors Over the Rockies is the beginning of something very special and I would like to be there.

I want to fly to the Vertical Challenge even more.

My biennial flight review is scheduled and I would not want to disrupt that.

I love hitting the ground running each day and feeling like I have got the most out of it when I lay down at night.

If things always went smoothly and I always got my way I would become weak and board. I would need to find more worthy challenges.


Thank you for the input Juergen,

I am not well versed in the use of wire rope. This doesn’t seem like a good learning project.

I spent a lot of time with a replica DR7 and I found the rigging interesting but beyond my understanding.


I look forward to seeing you and your aircraft Mark.


Thank you Alan,

I will do the best I can with the resources and time frame.

I don’t think of this as an ongoing problem.

I feel I have received good service from the airframe.


Thank you Dennis,

As I told you at the lake, your aircraft is very nicely done.

I thought you did a fine job of explaining your reasoning.

There are a number of unresolved forces in the current design and it is hard to know where to stop.


The Predator was designed on a napkin and has held up remarkably well to considerable abuse from at least 5 different pilots and a more powerful engine. It has been through teaching a blind guy to fly.

If I simply put well made patches on it and the repair lasted another 2,500 landings and 11 years I would be pleased.

I would prefer a diagonal brace. It is always hard to know where to stop.

I am working with a fabricator, Max that I do not have a relationship with and I don’t know his limitations.

Max helped build the plumbing for the local nuclear power plant and he is restoring a rare 30s airplane.

Max is not comfortable with mild steel in an airframe and he is a TIG enthusiast.

I have not found a way to communicate well with him yet although he seems willing to approach this as an interesting project. He has been cautiously exploring my capabilities and knowledge.

He is two hangers down from the corporate hanger I share at SMX.

We will see what comes from the process.

My options for the repair are limited in a small farming community and I don’t work well with most fabricators.

When I first saw the way the frame was built I felt the loads were so small that the frame would not be one of the first things to crack.

I sent the pictures to Jim Belland and he wrote back, “You need to add pieces to carry the compression/tension loads into the top rails directly.”

Jim feels that he can see her flex in the video of her landing at San Carlos. I wonder what he would see if he saw some of my earlier learning to land landings.

On Mariah Gale we have increased the tubing one size and increased the section on the side frame.

The loads will be lower because of the front suspension and the larger softer tire but higher because of the increased fuel load and increased gross weight.

The goal is for Mariah Gale to last 4,000 flight hours and 15 years.

I will probably fly less in my 70s.

Thank you, Vance

 

[MikeBoyette]

Vance,
Why don't you give dad a call and he can probably give you some advice on what to inspect on the rotor head. He will be leaving for new Mexico on Tuesday so Monday would be the best day to reach him.

 

[RockyMeLad]

A crack by any other name is still acrack.

A crack by any other name is still acrack.

Mr. Vance,

I wasn't racing when I broke the right handlebar off an old Cushman scooter, but we were about 20 miles from camp across the desert... after dark. So I really respect your skill to finish a race.

As for the cracks... two things.
I agree with the parallelogram stress points.
Second, my buddy here that has the Legal Eagle found a cracked tube. We think it was vibration, since he and his son had both noticed first harmonic nodal vibration in the two front tubes. Other than in a long thin cable I doubt there would be any serious vibration higher than fourth harmonics. By putting a "damping" strut at other than 1/4 and 1/3 of the oscillating member, you should be able to kill any violent oscillations. Some designers use structural struts of careful length/placement to accomplish this. This technique also worked well on flying wires of old airplanes to keep them from "singing".

 

[kolibri282]

Alan Cheatham - Keep in mind that a spring or damper will only reduce spike loads and not static loads.

Although the material properties of a weld are far from those of the base material
welds stand up quite well to static loads. German design codes allow a plastic
deformation of 1% for a weld, which is five times the technical yield point (0.2%).
That's why, in all the years I worked as an FEM analyst in the railroad industry,
I have never seen a vehicle fail in a static load case. There may have been a little
warping in parts of the vehicle but the welds did not crack.
Repeated load cycles are another story. Especially with fillet welds you need a very
low number of cycles with a high stress level ( greater than let's say one half to
three quarters the yield strength) for a crack to develope. I therefore assume that
the crack in the predator is not from a static load and in my opinion it would be
worth while to bring down the peak load.

I have carried out a little sensitivity analysis for the structure, i.e I do not want to
find out the actual stresses in the part (you'd need much more data for that) but
to compare stresses for different load cases and design variants. In the attached
pictures the y-direction of the coordinate system is along the strut the z-direction
runs along the center line of the aircraft and the x-direction points sideways. For
each load case I applied a force of 1000 N in one of thedirections.

Results are:

A lateral load (x direction) causes negligible stresses in the T joint.

For the y direction this load gives a stress of about 12N/mm² in the T joint between
gear strut and upper cross beam. (picture 'BTR_Fy1k_dlt1.png'). A force of 1000N in
z-direction causes a stress of 40 N/mm², i.e. stresses are almost four times higher
for a z load than for a y load. The reason can be seen in picture 'BTR_Fz1k_defoScl1NN'
where the deformation of the structure is scaled to one hundred times the real value.
The picture shows that the two cross tubes are beeing bent and that the four longitu-
dinal tubes sag.
When the structure is braced like in picture 'BTR_Fz1k_ovw3.png' the stress in the
upper T joint is reduced to about 30 N/mm².

I would sum up results like this:

- the design has quite some potential for improvement.
- bracing helps a bit but does not solve the basic problem
- forces in y and z direction must both be considered in the design of the joint.


Cheers,


Juergen

 

[Vance]

How far do you go for the repair?

How far do you go for the repair?

Thank you Mike,

That is a good idea that may make Phil feel better.


Thank you Rocky,

We used to play with weights to make the parts of a motorcycle that touched the rider seem smoother.

For example we used to put lead weights in the handlebars of certain three cylinder two strokes to make the handle bars feel smoother and keep the rider’s brake hand from going to sleep.


Thank you Juergen,

I feel the peak load that caused the problem has to do with the contact point being behind the large tube to allow the wheel to castor for the steering to be done by differential braking. I agree that the peak load cycle is at the heart of the failure.

There are no braking loads on the nose wheel.

I feel that the members are much larger than they need to be if the structure was a better design.

I will post pictures of the structure of Mariah Gale, when she has one, and I would be very interested in your structural analysis if you would continue to be so generous. This again becomes a question of how far to go.

Less than 10% of the weight is carried by the front wheel in a static condition. In an inelegant landing the nose wheel can slam down and the peak loads are much higher.

When we repaired the collapsed front end with the next size thicker 4130 instead of the thin mild steel we moved the problem to the next weak link.

I don’t know about the repeated stress from the two per rev shake and other undefined vibration.

The plan is to make the repair stronger than it is now and we feel it will have a satisfactory life.

I hope Mariah Gale will be flying in less than a year and this is the time frame for the repair to last.

I would like to again point out that she lasted for 11 years, more than 2,500 landings and 770 hours that would be reasonable expected to take more than 15 years to accumulate. She had less than 200 hours on her at 8 years of use when I purchased her. At that rate it would take over 30 years to accumulate that many hours.

In our non engineering sort of way we will be trying to improve on a satisfactory life cycle in building Mariah Gale with larger diameter 4130 steel with deeper sections for the truss. I hope our experience will allow us to overcome our engineering ignorance.

In my opinion, if you did a structural analysis of a Harley Davidson Racing frame it would make your head hurt with predictions for immediate failure.

When I was last in Jim’s shop there were at least two Harley Davidson dirt track frames that were being converted to street bikes that Jim had built over 40 years ago and had not experienced a single failure. They had been raced continually on a national level. There are no direct load paths and the entire structure is too narrow. They weigh 27 pounds including the swing arm and rear axle. A production frame weighs well over 60 pounds.

Thank you again Juergen, it would be fun if Maria Gale was an international design with some engineering expertise.

Thank you, Vance

 

[kolibri282]

Vance - ....I would be very interested in your structural analysis...

Vance,

it would be great to analyse a real gyro frame and I feel I can learn quite a bit from
participating in a project with people of considerable practical experience. As I pointed
out I will not be able to come up with a statement like 'This part will last 657 hours.'
I am not an aircraft designer by profession and have no training in that area, yet I think
that beeing able to compare stress levels throughout a structure under a given load and
studying deformation plots might still be somewhat helpfull in the design process. I will
be glad to contribute what little I can to Mariah Gale.



Cheers,


Juergen

PS: a three view sketch with dimensions is probably more helpful than pictures
of a frame since I'd have to guess the dimensions from a pic and any error there
would make the results less useful.

 

[Vance]

That is very exciting Juergen!

That is very exciting Juergen!

Hello Juergen,

I feel that this will be an exciting and instructive interaction.

I have great admiration for what you do to become an engineer in Germany. I feel it gives you a wider range of capabilities.

If you send me an email address I will send both pictures and dimensions when we have them.

The current fantasy is Ed and I will visit Jim on June 26 and the sides of the frame will be tacked together and we will be defining the connections between the two sides around ergonomics.

There are multiple things that could delay this plan. This is not what Jim, Ed and I do for a living either.

Thank you, Vance

 

[Alan_Cheatham]

I hope Mariah Gale will be flying in less than a year and this is the time frame for the repair to last.

So what are your plans for Predator Vance, retirement?
.

 

[Vance]

Plans???

Plans???

Plans would be too strong a term Alan.

The current thinking is using the Predator’s engine, Propeller, rotor blades, main wheels, brakes, master cylinders and some of the instruments on Mariah Gale.

I feel it would cost close to $25,000 to replace those items to make the Predator airworthy. That may be a future project but for now she will be retired to a corner of the hangar because I don’t have an extra $25,000 dollars.

There is an expectation over time to replace some of those parts with new.

Mariah Gale may not be a satisfactory aircraft in which case the parts will be returned to the Predator until a suitable replacement can be constructed.

Thank you, Vance

 

[Hognose]

Ed is going to try to get some better pictures tomorrow.

Vance (&Ed), you either need to back up a little and then blow up the resulting picture, or get a Macro lens ($$$$) or a spacer (¢) if her camera has interchangeable lenses like a DSLR. Those pics were shot too close for the optics to focus.

You can still see some of the cracks. Good catch, and not a bad idea to double check the rest of it.

This is a good example of how valuable an annual condition inspection is.

Amen brother. Also a good example of how safety-by-inspection works, and the practical-infinitely-renewable nature of steel tube construction.

I have never understood those guys who dread their annuals (or 100-hours), as if they're better off somehow having a mechanical problem and not knowing about or fixing it. Kinda like the guy who won't go to the doctor because he thinks the lump is cancer. (If it is, going to the doctor isn't going to make it worse).

Of course the same guys who don't want to inspect in the first place are the ones who then who squawk about repair costs, and want to keep flying with unairworthy stuff. "But I flew in here with these!" Yeah, and you could fly out with 'em too. But how far?

cheers

-=K=-

 

[Vance]

Inspections are important!

Inspections are important!

Thank you Kevin,

Ed has a Macro lens on layaway.

My camera is a Cool Pix and I have no options that I am aware of. There may be a different setting that I am not aware of.

That is just what I was trying to get across. You are very succinct.

I spent some time today getting ready for tomorrow.

I tied the brake hoses out of the way of the welding and stripped the powder coat.

The two big cracks were even worse under the paint.

What appeared to be cracks in the tabs may have just been cracks in the paint.

I will go after it tomorrow with a lighted magnifying glass.

The lower corners appear to be just paint cracks as well.

I finished up the repairs on the propeller.

Ed stuck the fabric back down on the vertical stabilizer.

Ed took a lot of frame pictures and inside the tower pictures and is going to put them on a disk and send them off to Jim Belland.

I will post pictures of the finished repair when it is finished.

I have sharp little wire things sticking out of my cloths, hair and any exposed skin. Shortly they will be everywhere in the bed. It is worse than crackers.

I bought a new face shield to protect my one good eye during the paint striping process.


Thank you, Vance

 

[Vance]

Another long interesting day.

Another long interesting day.

I had spent some of Sunday cleaning the paint off the frame around the cracks so the welding could commence as soon as Max showed up.

Max and his friend showed up a little after 10:00AM.

He had the cutest little TIG welder I have ever seen and a very old very small gas torch setup.

We spent a lot of time tying the tanks to the hanger and positioning several fire extinguishers around the aircraft.

We decided not to put diagonals in because we were concerned about moving the problem somewhere else. With the curve in the top tube we felt that strengthening the side would move the entire load to the joint between the side rail and the curved tube.

We decided to go with what Max called finger patches.

They are formed pieces of sheet that allow the repair to go down the tube and cross it in a curve.

The two long cracks were in the front tubes but there were a lot of little cracks to manage and some weld beads to smooth out.

We cut a v into the cracks and welded them first and then put the finger patches over the top.

My trepidation was elevated as I cleaned the rust off the welding rod.

We spent most of the day checking each step of the process with light and a magnifying glass.

I have spent the rest of the evening cleaning and sanding the burned paint.

I just checked and found that Max and I forgot the body mount crack.

Rotors Over the Rockies is looking more and more distant.

Phil came by the hanger and pronounced the repair good to go in his best IA voice.

We hope to finish up the condition inspection and repair the heat damaged brake line tomorrow.

I have two new friends and a mostly repaired gyroplane. Life treats me well.

Thank you, Vance

 

[RotoPlane]

I liked his use of joint doublers or finger patches on those curved tube joints….good way to smooth out the stress-lines in that area. One good thing about cracks….they are a pretty good indication of a highly stressed joint and a good guide for where doublers or gussets should be used .

Have you noticed one can become more fatigued by watching someone work on your bird than if you did the work yourself?

 

[Gyro_Kai]

Vance,

on a different subject. You better delete your e-mail address in post 32 or you will get all the spammers' attention. Better send it via personal mail.

Kai.

 

[Heron]

Vance
Get a new owner for the Predator, he can buy you brand new stuff for Maryah Gale.
Two ships in the air is better than one in the docks.
And it also can be a great deal for some new gyronaut.
Do I hear credit card buying a good gyro?
Heron