Hornet build update

[Mike Jackson]

Don,

I have tried to understand the merits of a redundant vs single mast. I think Gary's 2 examples of rollovers are valid. Are two data points enough? Maybe not, but they are convincing with the data given. The design characteristics/flaws of the nose gear is not relevant to the dual mast debate. The point is these gyros did roll over and what happened to the masts is relevant.

It would be interesting to hear from those with similar rollover incidents.

Cheers,

Mike

 

[donshoebridge]

No, I don't think two data points is enough, and no, I don't think they're convincing either. You two are trying to draw a connection between blade strikes and mast failures. A mast is not designed for blade strikes. Masts are designed to carry a useful load into the air, which is a great deal less load on the mast than a blade strike.

As far as I'm concerned, the information given by gyrodude is technically inconclusive. It's always unfortunate when a gyro rolls over and returns itself back to kit form. But if the root cause of the mast failing was due to a faulty design of a nose wheel assembly, and subsequent ground strike of the rotor blades, fault can not be aimed at a mast design.

The redundant mast design was not a product of blade strikes. A rotor blade of sufficient speed striking a heavy enough object, fixed or otherwise, such as the ground, will cause the mast to either twist to destruction, or snap right off, regardless if you have one, two, or three 1x2 tubes, period! Regardless if you have a redundant mast or not, simply because of the close proximity of the pilot to the mast the chances of pilot injury are pretty high.

The primary reason for a redundant mast is/was to provide greater strength for flight loads, and increased fatigue resistance. It was not the primary design intent to provide roll over crash survivability of either the mast, aircraft, or pilot.

Hence, the mast/diagonal combination on the Hornet is designed for strength in the lift and drag directions, ie, flight loads. I rather doubt that ANY square tube, or redundant mast structure flying today would ever survive a blade strike from a roll over event, to include a Magni which is made from 4130N.

I have ran FEA's till I'm blue in the face on the Hornet mast, and in the lift/drag directions, the Hornet mast is over-killed by a substantial amount. Computer models indicated that with a gross weight of 500 pounds, and rotor drag of 100 pounds, that the Hornet mast can withstand a G-loading in excess of 23 G's! Why? Because the diagonals are in tension during normal flight. In a vertical decent, the mast is in tension. With 2-per-rev pulses being present, the drag load provided by the rotor blades is increasing then decreasing, effectively shifting the RLV fore and aft, which then shifts the loads from the mast to the diagonals, and then back. Even if I were off by a factor of 10, I'd still be much better off than someone flying a mid-span supported mast, regardless if there were holes drilled in it or not. If you would like to see one of the FEA studies that I did, go check out the technical library area of my site.

If you take into account the total amount of material in both diagonals and the mast tube, the cross-sectional surface area of a redundant mast design is only slightly greater than that of the Hornet. But because I triangulated my aluminum, I've better distributed the loads and greatly increased the load carrying capacity and fatigue life of my mast.

So in reply to gyrodude's initial posting about holes in the mast, the farther down the mast the FIRST holes are, the worse off you are. By placing the first set of holes in the mast where I did, I've greatly reduced the leveraging forces applied by the rotor blades during flight.

 

[gyrodude]

Masts

Masts

Don You keep talking about flight loads. A 2x2 mast is plenty strong enough to carry any and all flight loads. We are talking about what happens in a blade strike now. First of all go back and read my post again. With holes drilled in my mast when a blade strike occured the first thing that happened was the mast broke off at the bolt holes!!!!! On Ora Cooks machine with a redundant mast and clamped cheek plates the mast did not break off but was bent considerably. There was reports of some Air Command masts drilled at the factory inproperly and the inner walls were scored meaning that the mast was a fatal accident waiting to happen. I checked mine and they were not scored so that did not cause the mast to break off.

 

[CLS447]

I would say that this is not a faulty nosewheel on the AC, but improper adjustment of the steering spring tubes. One time, while doing sharp steering on the ground, my tubes got over-extended & popped apart. This caused wheel lock.

After readjustment, I can't make them come apart. If this still would have been a problem, I would have grounded the machine.

So , those with the older AC steering, check to make sure you can't get into this situation!

 

[donshoebridge]

Don You keep talking about flight loads. A 2x2 mast is plenty strong enough to carry any and all flight loads.

I once thought that too. But after running FEA's on 2 x 2 tube, I can't say that now.

We are talking about what happens in a blade strike now. First of all go back and read my post again. With holes drilled in my mast when a blade strike occured the first thing that happened was the mast broke off at the bolt holes!!!!! On Ora Cooks machine with a redundant mast and clamped cheek plates the mast did not break off but was bent considerably. There was reports of some Air Command masts drilled at the factory inproperly and the inner walls were scored meaning that the mast was a fatal accident waiting to happen. I checked mine and they were not scored so that did not cause the mast to break off.

I'm not arguing the fact that a hole in the mast will weaken it. What I'm saying is that every mast is too weak right from the beginning, regardless of holes. A blade strike is bad no matter how strong or weak the mast, and it if breaks off and leaves the general area, good! What scares me more is having the mast wrapped up around me, pining me to the seat, or tearing my head off. To avoid either situation, you need to make sure your aircraft is functioning mechanically as it was intended, which requires good build, set-up and pre-flight practices. It's all part of the risk assessment, management and prevention process. But there's still a chance bad things are going to happen, and that fact alone scares enough people to keep them from building their own aircraft.

To expect a mast of ANY design to act as a roll bar, especially for ultralights, is asking more from the mast than is realistically possible, because all of the gyro weight would be in the mast design. This has about the same logic as flying a Mac powered Bensen across Lake Michigan from Ludington to Oshkosh. Besides, what would a strong mast buy you? So your mast doesn't break off from a blade strike... So what! The incident shouldn't have happened in the first place. To expect the mast to somehow make up for other failings is avoiding the root cause of the accident in the first place.

I've seen the product of "hole paranoia" before, and it's ugly, time consuming and eat up a bunch of money. But most importantly, it's HEAVY! Machined brackets and clamps come with a weight penalty, and for an experimental it's not so much of a problem. But for ultralights, all weight is bad!

 

[GyroRon]

Don what is wrong with a plain jane 2x2 tube for a mast? Neither of my dominators had the so called redundant masts.

 

[birdy]

Heh heh .
You stick with it Don.
Your simple,light weight frame has strength overkill.
This machine I flog around the scrub is much the same as yours,except for your diagonal angles.And I consider my frame to be more than adequate,seeing as it has over a thousand hours of rough strips and rough air.
But it don't matter,if you smack your blades on the ground,your go'n to damage the machine,end of story.
I'v wrecked two sets of blades and two masts with the same setup,and only BENT the masts.[with loaded rotors at high rpm]

 

[donshoebridge]

Ron,

Did your seat tank bolt to the mast? And if so, how far down from the rotor head were the first set of bolt holes for the seat? Also, looking at one of the pictures I have of you and your Dom, it looks as if the mast is fairly short, which is a plus with regard to mast strength.

Don what is wrong with a plain jane 2x2 tube for a mast? Neither of my dominators had the so called redundant masts.

 

[GyroRon]

Don in either of the two Dominators I have much experience with there was NO holes - not a single hole - from the cheekplates at the rotorhead all the way to the cheekplates at the keel cluster.

Everything is clamped on the mast including the upper seat brace. I just want to make sure I am ok.

 

[cgmg]

Chris,

Interesting you mentioned the steering tube problem with your Air Command. While my wife and I were practicing taxiing during our lessons, we had the same problem. The only times the tubes popped apart was in front of the hangar, where we were doing low speed tight turns, or pressing the rudder pedals while sitting still. It took our instructor a couple of attempts to correct the problem. Since then, we've never had the problem again, and we fly off of grass for 95% of our flights. And, like yours, our airframe is an older generation which has been upgraded to centerline thrust.

 

[donshoebridge]

Ron,

Seeing how the mast isn't as tall as any of the Bee's, mainly above the seat, there wouldn't be nearly as much stress to the mast. With everything clamped on like it is, at various locations up and down the mast, I doubt there is a problem.

Don in either of the two Dominators I have much experience with there was NO holes - not a single hole - from the cheekplates at the rotorhead all the way to the cheekplates at the keel cluster.

Everything is clamped on the mast including the upper seat brace. I just want to make sure I am ok.

I need to set the recond straight. There was a small but important detail that seems to have been overlooked, mainly by me. The FEA’s that I ran were based on a worst case condition. In other words, the bolts have loosened, or were not properly tightened, and the result is that the bolts are carrying all of the loads. Any bracing, cluster plates, etc, have no contact with the mast and the bolts are being loaded in shear. Obviously, the bolts will not fail in this condition because the loads are not great enough. But the forces are now focused on one side of the hole(s) that are drilled.

Friction between the mast and cluster plates, cheek plates, and diagonal braces is really where the loads and forces are transferred. The nuts and bolts only provide the necessary pressure to hole everything together so that there is enough friction between everything.

Now, with that said, proper nut/bolt torques are critical. Too much torque and the tube compresses and flexes away from the plates or braces, resulting in reduced friction and decreasing the maximum load bearing capacity. Too little torque and the bolts are in constant shear against the holes of the mast tube and the plates and/or braces.

I wouldn’t think that too much torque is a common problem. However, too little torque I’m sure happens more than some people would like to admit. There are a lot of bolts on a gyro, and it’s easy to miss a couple.

With diagonal braces added, any mast will be stronger, and will better deal with loads. What’s important is the location of the diagonal braces. The attached images are sample studies to show that brace placement can effect the loading needed for a failure to occur. Neither study is completely accurate because of the absence of cheek plates, rotor head, seat, engine, etc. But you can still get an idea of what can happen.

Almost forgot... In the images, I cranked up the FOS value so you can see where the highest stress point is. The number above the input window is the important number (the number with all the digits behind the decimal point that is).

 

[gyrodude]

Air Commands

Air Commands

What I did was the same thing. Adjust,adjust,etc. It always worked for a while and then unexpectedly it would lock up again. My machine was an old one with a lot of miles on it. Wear plays a big part in it.

 

[willbow]

As a Hornet builder, I've studied the Hornet documentation exhaustively and have no concerns about the holes in the mast or diagonal bracing system nor the single tube v/s the redundant type mast tube systems.

IMHO, the holes are not there for the sake of having holes here and there but to accomodate necessary fasteners. Presuming that one did not score the tube wall when drilling through-and-through holes and that all fasteners are present and tightened properly, structural integrity should not be significantly compromised.

Also, IMHO, one has to look at the integral structure of the airframe. The seat is more than just a seat bolted to a structure but indeed is part of the structure itself. An appropriate description of the airframe itself (main tube/mast/diagonal braces/seat/engine mount) might be a "pre-stressed truss". I could easily believe that it would take forces in excess of 23g to force a catastrophic failure of the airframe. Or at least the main mast system. Way before that point though, I would think that some other vital component failure would have doomed the pilot to whatever his/her fate was going to be.

As far as a blade strike goes, it's gonna be bad news whether it be a single tube mast or redundant tube mast. Consider this notion, you have a 20+ foot dia rotor directly over your head rotating at 200+ rpm, a 40+hp motor directly behind you swinging a 60 inch or so 2 bladed prop spinning about 4000 rpm. No mast tube of 6061 single or double configuration is going to fare very well in a blade strike.

I think that all considerations have to be weighed with respect to the performance envelope expected of an aircraft of this type. At least in, for lack of another term, this "mk 1" version, Don wants to keep the craft within part 103 specifications which is very wise IMHO, personally I think that the craft is well capable of performing well outside those limits but were talking about sanity here Point being that, as Clint Eastwood would put it .. "A man has to understand his limitations".

Without a doubt, especially where it comes to flying machines, I hope not to ever take things for granted and will endeavor to take a close look at my bird, stem to stern, before each and every flight.

Really though, whether you are talking about the Hornet, RAF, SparrowHawk ... the ultimate question comes down to "are you willing to bet your life on it?"
Well, I dont expect to ever see 23g

Sort of OT but I was watching some WW I stuff on The Histor Channel and often wonder of those who survived a day of suicidal charges in the face of enemy mahcine gun fire. If you managed to survive that day, what would it take to really bother you and make you feel really put out on after that?????

And though it might not be scientific ... I dont think it's my fate to die in a gyro

 

[GyroRon]

" And though it might not be scientific ... I dont think it's my fate to die in a gyro "


You better be knocking on wood! I would never say something like that, it is like placing a Spell on myself.

 

[scottessex]

Sounds like the same kind of thing all of those 44,500 people killed in car accidents last year thought.

 

[Dean_Dolph]

Yeah, and the rest of us keep on driving!

 

[birdy]

There's only one other place ,besides me gyro,I'd rather die, and it don't concern you lot.

 

[willbow]

I'm not sure what that means David .... Your bird has built-in handles just in case 6 of your best friends need to carry you around??

Just kidding

Will

 

[CLS447]

Hey Birdy, If she's lucky, rigormortis(?) will set in quickly !

 

[birdy]

I'v heared that rigormortis lasts longer than Viagra to.