Anybody building their own?

[Guest StRaNgEdAyS]

Just thought I'd ask...;)

 

 

I've spent quite a lot of time (close to two years) working on the modifications to the original plans to get to here.

 

 

I originally wanted to use a Rover V8 for the 200 odd HP I allowed for in the redesign but I'm currently redrawing for a Subaru engine to do the same, cheaper with less weight.

 

 

And just today I came up with a panel design I actually like. :D

 

 

And I was wondering is there anyone else out there doing this?

 

 

[Guest Glenn]

Looks good Pete

 

I'll have to see if I can get some photos of the Brumby that has just been built here. The Brumby has a Jabiru engine.

 

 

[djpacro]

Why the 4-blade prop. I'd guess that there's enough diameter available to use 3 blades. Have you looked at vibration characteristics?

 

What was the original design?

 

What CAD tool are you using?

 

Looks good.

 

 

[Guest StRaNgEdAyS]

The 4 blade prop is there mainly because it's the only one I happened to have on file at the time..

 

I was originally looking at using an MT VP prop, but the lower cost of the IVO is beginning to override the creepies I get when I think of the way they vary the pitch. I guess it will come down to what I end up getting out of the Subie engine I end up using. If all goes to plan and I end up with a nice turbo EJ25 I'll quite possibly end up with well over 200HP and in that case I'll need to look harder at my choices. For those that are new to prop theory (I still have a bit to learn in this regard too) is the basic driving factor for number of blades vs diameter is having enough blade area to absorb the HP being produced. Too little blade will lead to an overspeed situation. So for a smaller diameter (69" is really as far as I want to go with this one) you will need more blade area per HP.

 

The CAD package I use is Rhinoceros 3D.

 

The design was originally a KR2S, but it is now larger, heavier and faster, with retractable undercarriage.

 

 

[djpacro]

Another thought for you:

 

Putting landing gear impact loads into the wing main spar adds a risk of additional damage. Is it still a wooden spar? If so, ground loads can cause cracking which may not be detected and lead to in-flight failure. Have you considered attaching the main landing gear to secondary structure rather than direct to the main spar?

 

How does it compare with the Whisky http://www.homebuilt.org/kits/littner/whisky.html or Falco? http://www.seqair.com/

 

 

[Guest StRaNgEdAyS]

The spars are somewhat stronger than the original plans specified as well, it is larger and the caps are made of 4 lamentations rather than a single piece as per plans.

 

The loads are borne on both sides of the main spar and the twisting moment (impact loads) transmits via braces to the aft spar.

 

I chose to put the gear on the ends of the stub wings for three reasons. First, the Plans put them there, and the standard fixed gear loads are borne entirely by the main spar. Second, I needed the room in the stub wings (which became gloves) to accommodate the retracted gear as there would not be the room in the fuselage, and Third, the reason I have them folding inwards rather than outwards is I wanted the extra track width for ground stability as it is still rather closely coupled and being a taildragger, if it got too narrow it would tend to groundloop easier.

 

 

Just in case you are wondering, I'm revising the aft Wing Attach Fittings, that's why they do not appear in this render. I'm also investigating other methods or operating the retract mechanism, currently show is a worm gear overcentre setup as per the original Taylor Monoplane design. I'm looking at replacing it with a bellcrank style of system, but whether the loads will be too great to operate with a simple lightweight drill motor and manual crank override will need to be determined.

 

 

[djpacro]

Sorry, but I still don't like attaching main landing gear to a wooden spar. A heavy landing can overload the spar, regardless of how well it was designed. Attaching the gear to secondary structure has two advantages:

 

- less risk of catastrophic wing failure due undetected spar damage

 

- easier repair after a heavy landing

 

The two braces from the landing gear to the rear spar - I assume that there is additional bracing i.e. at the kinks?

 

I suggest that you do some research on failures of CAP 10's.

 

On a different subject - I'm interested in the structural analysis?

 

 

[Guest StRaNgEdAyS]

Interesting information.

 

I'll be checking it out you can be sure of that.

 

On another note, I've started to do some rework in the engine department. I was far from happy with my original Rover V8 conversion, it was just too long and too heavy. The headaches it was giving me keeping the CG in check were enormous so I have opted for a lighter way of obtaining the 200+ HP I desire. The Subaru EJ25 Turbo conversion I am looking at now will come in close to 100lbs lighter bringing my expected gross weight down below 1300lbs and even with the long PSRU kit (Sub4) also shortens the FWF package by a shade over 11". A few up sides to this change of heart, it makes my CG worries pretty much go away with a shorter moment and less weight, any worries about the attach points holding the weight are significantly reduced as they have been drawn up with the heavier Rover in mind, the Subie has a better SFC (approx 6gph at cruise (as reported by the RV drivers using them) over the 8gph (estimated) Rover), the Subaru has had a lot more development in regard to experimental aviation than the Rover, and parts are easier to come by.

 

 

I've still got the engine block to complete, the engine mount and the redrive to go, but you get the idea.;)

 

Oh also, I've been a little lazy in some of the fuselage drawing, there are many cross braces and doublers to be added, something I intend to correct over the next week or two time permitting. I'll be wanting to have it completed soon so I can send the file away to an aeronautical engineer friend for a final analysis check before I start to cut wood (if all goes well) in then next month or 2.

 

 

[djpacro]

I'll be wanting to have it completed soon so I can send the file away to an aeronautical engineer friend for a final analysis check before I start to cut wood

Your friend is an old guy I assume - its been a while since they taught wooden structures at uni?

I know little about the use of auto powerplants in aircraft so no comment from me.

 

 

[Guest StRaNgEdAyS]

You could say that. ;)

 

He's been a big help to me in my quest to learn more about aircraft design. They still do quite a lot in the way of wooden aircraft work in the US, so he won't have to remember back too far.:)

 

I've got to clean up the surface lofts on the fuselage too while I'm at it, they're not as neat as I'd like them. They should come in better once I have the extra bracing in too. (more curves for reference in the network)

 

 

 

[djpacro]

They still do quite a lot in the way of wooden aircraft work in the US

Yep, in the '90's I worked at a company in the USA which was still building wooden aircraft.Aaaah "lofts" - I haven't heard that word for ages.

 

 

[Guest Glenn]

Here's the brand new Brumby going out for a flight. Sorry I couldn't get a side on shot because I was busy photographing the DC-3's coming in at the same time this was going out.