View Full Version : To New Hornet Builders. Warning.
08-21-2009, 08:49 PM
Re: landing gear rod stainless steel attachment bracket.
We have been doing some taxii check on our Hornet with the gear built as per Don's plans. During these I also checked the disc brakes, which work extremely well. Stuart however noticed back in the hanger that the plates holding the Delrin block in which the axle is housed had twisted forward.
The lower rod leading from the axle to the attachment point near the cluster plate at the base of the keel is fastened there by the stainless steel bracket as called for in the latest plans. This only has one bolt and this will not prevent the twisting force applied when braking.
We will be changing both ours.
Roy Freeberg had not liked the plans for the gear and done his own had also seen this potential problem and had attached his to the base of the mast by a bracket with two bolts and this prevents any twisting.
08-22-2009, 06:59 AM
I thought you mounted 4 plates on the outside of the axles struts?
(1 on each side for a total of 4 plates)
I am going to do this to my gyro because I know that the axle tubes have to be twisting when I apply the brakes. I try not to apply to hard until I make them.
I can say this I love my disc brakes.
08-22-2009, 01:01 PM
Chris those two plates in the photo sandwiching the block through which the axle passes were tilted forward because the twisting motion imparted by the brakes grabbing the disc was not arrested at the end attached to the plates by the keel. That point on Don's plans is by a single bolt stainless steel clamp which will allow rotation.
On Roy's Hornet this was replaced by a two bolt clamp which does not rotate. The strength of the structure as planned is all about forward backward and upward forces, it left out the rotating forces due to brake engagement.
During the taxi trials they were tested for stopping ability at probably higher speeds than one might normally use them at. It however highlighted a potential problem which we will be attending to.
08-23-2009, 02:05 PM
I had the same problem I had to build a piece to attach to the Axle tube to stop it.
I built it out of steel so I knew it would be strong enough.
Of course I still have to build my plate like you did on the 2 tubes to help hold it. I don't plan on using the brakes except to stop the bird on a real slow roll or to turn around. other than that it is there for looks.
Landings use the blades to stop the rolling.
08-23-2009, 05:43 PM
Chris, plan on using brakes and using them quite hard. It may well be in an emergency and not very often but when you need them it's nice if they work as intended.
If by any unfortunate circumstance the blades were already trashed they won't be there to assist in braking. I tend to try and look at worst case.
Glad you spotted it and sorted it out.
08-23-2009, 07:09 PM
You might have to go to a steel land tube then so it will not twist off with you.
08-23-2009, 08:49 PM
I think that modifying the clamp will probably do fine.
Like your rock guard.
08-24-2009, 05:26 AM
Is this the same clamp you are having problems with? :confused:
08-24-2009, 05:49 AM
Chris the steel U clamp at the keel held by a single bolt is the one giving the problem. That clamp will be replaced by a clamp held by two bolts. It then will not be able to rotate.
08-24-2009, 08:37 AM
This brings up what I perceive as not best practice that I see on many gyroplanes.
I see A arm suspension without a bottom to the A.
In my opinion an A should always have a bottom in order to manage torque from the brake.
In my opinion it is not good to manage torque at the axel joint because the torque has leverage on the joint.
In my opinion it is nice to manage torque with a long lever between the front and rear pivot. I feel that things can be made lighter if the load paths are optimized.
I have never seen the plans for the Hornet so I don’t know if this is the problem you are describing and I apologize if it is unrelated.
Thank you, Vance
08-24-2009, 09:20 AM
I just looked at the plans for the Hornet and that is an example of what I am talking about.
The axel attachment cluster could also use a little beefing up. Putting a bottom on the A would exacerbate the weakness of the cluster as it is.
To me it appears that the torque is being managed by the shock tube and I feel that the pivot is not strong enough or precision enough to manage this torque well. The load path appears to be somewhat convoluted.
The torque can be managed with a tube between the A arm pivots but only if the axel is better attached to the A arm. Tubes are very strong in torsion and I would like to see the axel plugged solidly into the A arm tube.
I can see why increasing the strength and precision of the cluster would help.
I have never designed a gyroplane that has flown so please keep that in mind when considering my opinion. I have fabricated a lot of race car suspension and that is the experience I am drawing on. I realize that there is a lot less torque from a gyroplane’s brakes.
I am off to Smokey’s shop to work on the Predator which has a similar design on the A arms. I have not yet addressed it and I can see it flex when I apply the toe brakes. It is something I check carefully on every preflight.
Thank you, Vance
08-24-2009, 10:33 AM
Resasi and Vance :
I am going to change out the shock that I have on my Bird right now as well as the axle tube. I am over the 254 and going for the S/P/Lic. It might be ok but I have already thought about changing it out! Something just a little more thicker.
08-25-2009, 04:29 PM
Just spotted this thread...
Brent and I discovered the same thing. This isn't even strong enough to keep from turning while rolling our mock-up frames around in the garage....
I made some quick little anti-rotation device for the time being...I'm pretty sure this will not be sufficient however.
We are going for 103, so after it is all done, I will see how much weight we have to play with and then come back and start making some mods to the axle cluster...
Good comments from everybody.
08-25-2009, 05:29 PM
Dennis ours held quite well and we have done a lot of moving around.
It only showed this weakness when I was applying really quite fierce braking from around 30kts to check out what the brakes would do, but yes it will have to be replaced.
Vance your present knowledge is very relevant, the fact that it this is on a gyro very secondary. I will admit that one is unlikely to want as much braking or at very high speeds, however it is something that does require a better solution.
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