Moving the " Mains " back a bit

tomhall

Member
Joined
Apr 27, 2004
Messages
211
Location
Rochester, MN
Total Flight Time
200
Guys. Tom Hall in MN here : I have 12 years and 210 hrs. on my 2002 ( completed in 2004 ) RAF. I changed to Sportcopter blades and rotor hear about 7 years ago. I extended my keel 18" to accommodate my Don Parham HS and I also have his suspension system. Time to move the mains back. I am nose light/ tail heavy ; everyone who has done this mod. seems happy. I am looking for input from anyone who has done this, or can offer advise. I can see where I can mount the support bracket, but am not sure where to mount the support tubes. I would like to go back 4 - 5 - 6 ". Any tried traditional aircraft gear, as in Cessnas etc. Thanks in advance. Tom T.
 

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Tom, for a long time I resisted my husbands offer to

Tom, for a long time I resisted my husbands offer to

move the axel back a bit on my Bensen gyro.

The nose wheel was on and off the ground as I taxied, depending on how smooth the surface of what I was taxiing over was. I was stubborn and didn't want anything changed but had to admit something needed to be done. Taxiing wasn't a joy with a bouncy nose wheel and besides the wood pad brake on the nose wheel didn't work with the nose wheel in the air!

So I said , go ahead ,and he moved the axel back I think, 2 inches and made a baby buggy out of my gyro as far as taxiing goes. No more bouncy nose wheel, and always able to use the wood pad brake on the nose wheel . And it made taxiing so much easier and safer.
Marion
 
Jim Vanek urges that mod, and eddie likes it.
I'll do this to mine as its next moderately large project.

Glad you've the SC rotors and head, as well as some main gear suspension.
Looks like a nice RAF.

Regards, Kolibri
 
I moved my axle back 5",the new down tubes are attached to the motor mount plates

on the mast,if the engine is still mounted then you will need a close angle drill to drill the

3/8" hole near the bottom of the plates,use heim fittings to attach the down tubes

I used 1" tubing with a .125" wall thickness,and I ordered a piece of 3/4"

solid aluminium to make the new inserts at the top of the tubes,these are from AC spruce

I now have more than 500 hrs on my mod without any problems.

I am in the process of installing my 2.5 turbo engine mod on a friends RAF and the first

thing I did was move the gear back. Before I moved my gear back it was just a matter of

time before I flipped over on takeoff,after 200 RPM's are reached on the rotor things

happen really fast on takeoff with 230 HP,having the nose wheel come back in contact

with the runway after it lifted off was not a desirable feature to have. My landings are still

the same as before,I can still set the tail wheel first, land and keep the nose wheel off of

the runway until completely stopped.

In the picture of your RAF it looks like your mast is moved as far aft as possible,even

with the heavier DOHC 2.5 my mast position is as far forward as it will go,and I fly level

when in the air and my cyclic is centered in a mid position.I weigh 178 lbs,when two are

on board lifting the nose on takeoff requires a little more aft cyclic,however in the air a

very slight nose up trim is all that is needed for level flight.



Beat regards,
 
I find rather than guessing where to position the mains, you are best to get 3 sets of cheap bathroom scales (the old spring type not digital) and put a set of scales under each wheel. Move the mains back what you think, then sit a couple of buddies in the machine and see how much weight is on the nosewheel (rotors on the machine). then with just one person in it. Depending on how strong your nose wheel is, you want about 50-60# on the nosewheel one up in my own opinion.

To me, this is better than guessing 6" and moving it 6" only to find now there is too much weight on the nosewheel:drama:

Also, I would make the brace tubes adjustable until you are happy with the suspension position, then button It up with permanent tubes. Don't ask me how I know all of this :censored:
 
If you have added so much weight to the rear of the aircraft that it is falling back on the tail then you are long overdue for doing a complete weight and balance analysis of the airframe.
Moving the wheels aft is treating the symptom, not the cause.
Your problem is that the CG has shifted aft considerably and may very well be at or behind the rear safe limit.
The balance relative to the Wheels is only cosmetic.
The balance relative to the Rotor is what is critically important.

Verify your CG range with full and empty fuel tanks and light and heavy pilots.
If you do not know where the CG is, and where it is supposed to be, you are playing a very risky game.
An excessively rear CG can cause the craft to go uncontrollably nose up without warning one day.
 
The balance relative to the Wheels is only cosmetic.

An excessively rear CG can cause the craft to go uncontrollably nose up without warning one day.

In my experience the balance relative to the wheels affects the takeoff process a lot and it not just cosmetic.

In my opinion an excessively rear cg will make a gyroplane fly nose high and will not go uncontrollably nose up without warning one day.

I feel there is value in knowing where the center of gravity is under various loading conditions.

If the gyroplane flies fine but is challenging during takeoff moving the mains may have value.
 
In the picture of your RAF it looks like your mast is moved as far aft as possible,even

with the heavier DOHC 2.5 my mast position is as far forward as it will go,and I fly level

when in the air and my cyclic is centered in a mid position.I weigh 178 lbs,when two are

on board lifting the nose on takeoff requires a little more aft cyclic,however in the air a

very slight nose up trim is all that is needed for level flight.



Beat regards,

I found that my mast's magic bushing had turned to goo when my upper mast shifted rearward like this.
 
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Uncle Willie,the RAF set with its tail on the ground when its properly balanced, when the

pilot exits the RAF the tail go's to the ground. That's one reason I have moved my mains

back 5",its the balance on the gear that's not balanced right,not the flight balance.

I think that landing gears are placed at the keel/mast junction because it appears to be

the strongest place to attach the gear,my mains have no attidional gussets placed 5" back

and after several hundred hour of flight and no telling how many landings there is no

signs of wear,fatique.or damage on any kind. The gyro community overall can be hard to

accept change in design,engine options,body design(or even a body at all).When I built

my 230 HP Subaru,i received warnings about torque roll,the engine ripping itself from the

engine mounts,reliability,to much speed,etc.so far with more than 600 hrs of run time I

still have a very reliable Gyro that I fly without worries.



Best regards.
 
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