Razorback Tractor/Pusher hybrid

rtfm

Gold Member
Joined
Mar 24, 2004
Messages
531
Location
Brisbane, Australia
Aircraft
Robin R2120
Total Flight Time
105
Hi,
Well, it seems like things have taken a turn for the better at RTFMaero. After battling away in my double-garage workshop for over a year on the pre-prototype design of the Razorback, and recording mostly failures and dead-ends, I have finally secured some (modest) financial backing, enabling me to take the project to the next level.

Starting early next week, I'll be engaging a team of specialists to translate my ideas into tangible form.

To start with, my 2-D CAD drawings will be used to create a full 3-D model of the aircraft. This will allow us to have the entire plug shaped on a CNC machine, ready for the mold to be cast. Then I've secured the services of specialists in this area, and within a week or so of the plug being finished, we should have the first glassfibre/foam sandwich monocoque fuselage ready for bulkhead fitout.

There's nothing like a bit of money to oil the wheels, that's for sure.

I took this opportunity to tweak the Razorback design, and realised that by the simple addition of a nose cone, and by slightly altering the centreline of the fuse, I can either leave the prop at the back in the Pusher configuration or (if I wish) mount the prop up front in the Tractor config simply by reversing the engine, and re-routing the exhaust. Everything else (including CG) remains identical. The Razorback will be able to fly either as a pusher, or as a full tractor design. I think this is probably the first aircraft ever to offer this sort of functionality, and I'm very aware of the growing interest in Tractor gyro designs. In fact, my preference is strongly for Tractor designs, so this is the option I'll be configuring first.

I have also cracked the problem of how to add collective pitch control to a standard offset gimbal teetering rotor system, and will be getting a local engineering company to build it for me.

The single rotor RX-8 rotary engine will be ready by the end of the year, together with a matched reduction drive and 72" 3-bladed Bolly prop. The engine weighs 220lbs (a bit heavy, but @ 135hp, it's not too bad). On the positive side, the engine is extremely compact which allows it to fit easily into the heavily streamlined rear fuselage, and it is, of course, velvet smooth. I'm using the RX-8 single rotor because I've been promised one as payment for work done in the past. Cobra Aviation in Melbourne, Australia have developed the engine, and it works well in their FW aircraft.

Finally, to celebrate the Razorback prototype moving up into the actual production phase (as opposed to the pre-prototype what-if phase) I've started redesigning the website to reflect the future direction of RTFM-aero as a serious aircraft manufacturer.

Thank you for all your help and encouragement so far.

Regards,
Duncan
 

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Duncan,

That tractor design looks nifty.

A lot of instability issues will be no problem with this nice looking tractor design.

It would be really nice to have this tractor/pusher option and training will be a lot easyer for the beginner.

Sounds like you have met some knowlegable people since we last saw you post.

Also sounds like you have been kicking a lot of good ideas around in your head too.

A two place design will be even easyer to make into a tractor by running the drive shaft through the center console.

Nice polished spinners on both ends is gonna be awsome looking.
 
Great to hear Duncan !
I hope my drawing of the adjustable pitch for my gyro was of some help in figureing out the rotor head you need <GRIN>
though I doubt I'll ever build the thing I hope the idea helped !
hehehehe
I admit I don't like the idea of the bent drive line in the single place tractor design.... I know universal joints can do that but it will be something that needs checked quite often... I just wish there was a way to go stright through the chest of the pilot...but that might hurt a bit ! hehehehe
as Mark mentioned in a 2 place the drive shaft could be less bent at such an acute angle... but in all honnesty I think you'll have truble with such a drive line in a single place unit. I have worked on many farm impliments that utilize acute angles in the drive lines powering things and they are a constant pane as they ware out very quickly... like every other season if that gives you some idea.
but if you know about it and check it often in the testing stages you should be able to come up with a decent time frame for the life time of the joints....
surely there are heavy duty joints that could be utilized that would last years... instead of months right ?
...
Here's wishing you all the luck in the world Duncan ! go for it Buddy ! do what ever it takes and make your dream come true !
...
Bob.......
 
Duncan
I dont want to wreck your day but
your sounding a bit like you are in 3 minds on a tractor or pusher or both
most surely this will involve some compromises, do you know what they are?
what work has been done on the tractor drive ?

the tandem seating will certainly ease your balance/config issues
 
Duncan
I dont want to wreck your day but
your sounding a bit like you are in 3 minds on a tractor or pusher or both

Hi,
You say this as if its a bad thing:lol:
But the way I see it, one doesn't have to make a decision set in concrete with this design. If you prefer a pusher, mount the engine one way. If you prefer a tractor, mount it the other. Sure, there will be some issues related to exhaust mounting and routing, drive train and some minor CG issues to contend with, but nothing major.

As the design now stands, the Razorback can equally easily be configured either way. Actually, neither configuration changes the CG much, since while the tractor config has the weight of a longer drive train up front, the reduction drive has to be on the forward side of the engine, and the engine has to be placed slightly further rearward to accommodate this.

The engine will be mounted on two rails which will allow 115mm lateral movement, so getting the CG right will be a matter of positioning the engine. The rotor head will be fixed in position (ie no adjustable cheek plates). The adjustments during the hang test is to the engine position, not the head position.

I really don't see any major problems with the hybrid design.

Bob:
You mention the issues relating to CVJs. And yes, this is the one less than optimal element in the tractor config. But CVJ technology is well established and mature, and I'm sure we can find something which will do the job for us.

Ga6riel:
Getting the CG right is probably the biggest challengs with the single seater. But mounting the radiator right up in the nose will help to keep the CG forward. I might have to investigate moving other heavy bits forward also. The tandem arrangement will be far easier in this regard, but in that configuration, the major issue is one of rigidity of the fuselage, since there will not be a main bulkhead behind the front seat to transfer the loads. But triangulation and lots of Graphlite reinforcing might do it. If not, I'll have to resort to a central pillar behind the front seat. Ugh! But it'll do the job.

Regards,
Duncan
PS I get the CAD drawings for 'tweaking" next week, and the foam is off to the CNC shop the week after that. I hope to have all the parts made and assembled by the end of Dec. Many photos as soon as I have something to show.
 
All Geniouses have more than one iron in the fire ! <grin>
Yah ...you could spred yourself too thin by doing all 3 designs at one time, but I got a feeling you can handle it.... as you'll be doing the one-at-a-time thing when building each one !
Its realy a slick idea Duncan, to be able to do both a tractor or a pusher and still have the COG the same... very nice !
I love the idea of moveing the engine rather than the cheekplates... as the cheekplates have alwayse been a serious Pain in the Ars ....why someone hasn't done what your doing is a mistery... but its about time someone did ! HAHAHHA !
because seriously... its realy much easier to move the engine back 2" than replace cheekplates... is it not ???
not to mention that if your a died in the wool prefectionest you gott'a replace all those bolts too !...when engine mounting on an adjustable rail system should be a piece of cake !
.....
But I still liked the wheels at the tips of the wings and the wings slanted down.... it does away with drag and is a elegant answer to the problem of wheels...
I just wish there was a way you could keep that inovation...
kind'a like the "Quickie" of Burt Ruttan fame.... now that's an aircraft ! <GRIN>
...
take care Duncan ... and glad things are looking up !
...
Bob.......
 
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