Hi all:

Just thought I'd give a progress report on my new twin electric design. I'm working on it quite a bit and hope to have it at the Nats.

It will be powered by either two E-Flite Park 480 motors or two E-Flite Power 10 motors. Provisions will be made to mount either set. The projected weight - with battery on board - is 59 ounces and... it has retracts!

Attached are a few photos of the model under construction.

Later - Bob Hunt

Hi Bob, That looks stunning so far. I love the wing. Can you let us have the weight of the wing as it is so far in the pic with the carbon veil? By the way.....where is the pic with the rudder fin??

Keith R

Very cool Bob!!!  Looking foward to  seeing the finished product, especially a twin with retracts!

Very cool, Bob.

I just realized that I am now 62 and really should start using that stuff!

I'll be 64 in a couple weeks.  Send me the rest of the good balsa.

Hi Mike,

The DO-335 is interesting, but the rear motor so far from the C of G would maybe cause a few problems like Len Neuman's "barbell-effect". The tail end would also have to be beefed up as well. You could of course, stick the motor further forward and use a long shaft to the rear prop, but I think that would be too much like hard work. I also prefer the looks of the C-337 layout. I would still like to know about how to work out the power needed and prop size on twins.

BTW.......I turn 60 in August, and then I'll start feeling like Bob and Howard..........I just don't have hoards of good balsa!

Keith R

Hi Keith:

 Every time Dean comes over I have to sweep up a bunch of mathmatical symbols that are left lying on the floor...

Bob

If you leave a couple of blank spreadsheets lying around, most of that stuff will stick to them - then just delete them ....   

You guys should have seen that shop just a week before.
signed,
      the troublemaker

A clean shop is a sign of a sick mind   

John W

Hi Matt:

I guess nothing is "totally original." This one is my interpretation and blending of many things I've liked about twins that I've seen over the years. You are far too young to remember the twin engine designs that were modified by the Army and Air Force in the 1960s. They, and a few dedicated twin designs, were dubbed "Coin Fighters" (Short for: Counter Insurgency Fighters). I was going to do this one in an aggressive pseudo military scheme and call it, "Coin Return." Alas when I bounced that name off of some friends - who were around in the 1960s - even they didn't get the connection and so that name was scrubbed.

By the way, your Oriental Plus is looking great! Just don't put on too much paint...

Bob

What goes around comes around.  Aviation Week had some recent articles about the COIN aircraft being brought back again to help in Afghanistan...

Here is an early drawing of the side view of the twin. I've made a few subtle changes since this was drawn. I'll save those as a surprise for the Nats. Just imagine this design with an agressive military-like paint scheme...

Later - Bob

That is an INSANE twin!!!!!!  Very slick, and cool looking

Edit:  What airfoil is that Bob?

Hi Keith:

The wing - ready to install - with flaps, tips, leadout guide, tip weight box, controls and carbon weighed 9.9 ounces. The fuselage with all the molded shells ready to install weighed 2.7 ounces. Yes, I'm using up a good portion of my best wood on this project. I just realized that I am now 62 and really should start using that stuff!  

I'm planning on using the new Hyperion batteries in this one. They are reputed to be able to be charged at a C5 rate. Not sure that I will go that far, but maybe i'll give C3 a try. Should be able to cut back just a bit on how many batteries I need to take to the field. The 4S2P 4000 mAh pack they have is priced around $100.00. That's far less than the Thunder Power 3850 V2 extremes that I'm using now. They are getting a great reputation with the RC Ducted Fan guys...

I'm not sure if I'm going to use the tail assembly pictured. It is light for its size at 2.5 ounces with horn and hinges, but it may be just a bit twisty. I'll have to carbon it and see how stiff it gets before I make a final decision.

Again, the projected all-up weight is 59 to 60 ounces with battery on board. That equates to a 53 to 54 ounce glow ship without 6 ounces of fuel on board...

This is a project that I've had in mind even before electric power became viable. I have been sketching twins for 50-plus years, but just never took the leap. I've spoken with Gordan Delaney - the recognized twin expert in the glow world - on several occasions and picked his brain on the technical aspects of designing one. It was, however, our moderator, Dean Pappas who finally convinced me that this is the time to try one. There are so many advantages to an electric twin. You can counter rotate the props and try them in both opposing directions. There were several full-size twins in which the props rotated outward on either side of the fuselage. The P-38 is a good example of this. I'll try them both ways and the beauty of this setup is that I can try that experiment right at the field. It is no big deal to reverse the rotation of the motors and just switch the props. Also, the spiral airflow problems ahould cancel out. I'll get 22 inches of "wetted" area of air blast due to the 11 inch props I intend to use. This disk area comes without the attendant problems of spiral airflow and prop ground clearance issues.

All in all this is a project that is keeping my interest peaked!

Later - Bob Hunt    

P.S. Attached are a few more photos. I needed to get the wire harness for the motors and the retracts out to the nacelles. I rolled a balasa tube araound a dowel and than used that dowel wrapped with sandpaper to make a perfect radius in the nose of each of the cuffed area's ribs to accept the tube. It is now actually an additional spar! The "cuffed" area was employed to put the wire harness tunnel well ahead of the bellcrank and leadout so there would be no interference issues. Besides, it looks cool! - Bob

So, are  you running that retract battery out to the tip or is it part of the motors power supply?  By the way...I have been waiting a few years on you to come back to this project! I must assume it was an on going research saga during the lapse?

I see that you have a flat stab platform for a tapered stab. Are you making this removeable?
I am using an airfoiled stab/ el assy. also. Got the wings skinned you sent and will be getting some pics together of this build and down load to a disk...based on the request you sent

Hey one more thing, I see you are not using geodetic construction in the fuse...or atleast not yet.....?

Lookin' sweet Bob!

Your model looks terrific Bob! As usual your building techniques are very clean and well done. I'll be watching this project with great interest.

Rob

Dorin,
I am going to ask, even beg, you to start a thread in either the Engineering or Design fora on the CNC cutter, especially the software.
Thanks,
Dean

P.S. I will also start a new thread on extending the subject of motor/prop and battery selection to include twins, sometime soon. This next week is going to be way too crazy.

Here is an early drawing of the side view of the twin. I've made a few subtle changes since this was drawn. I'll save those as a surprise for the Nats. Just imagine this design with an agressive military-like paint scheme...

Later - Bob

 Apparently I'm not familiar Bob, what Military scheme uses white with copper and orange???

 What are the dimensional specs Bob?

 The twin Bob. What's the wingspan?

So Bob, VSC's over, let's get back to work on this twin!  

 ...Oh yeah, CONGRATS too!

I'll bet he ain't writun cuz he's buildin!     Plus i'll bet he got a dose of twin-envy @ VSC... 

AMEN, Unca Deano!


BTW. APC has now brought out the 9x4.5 as a PUSHER, they will be going on my PF twin.  Hope we can get APC to do pushers of the 10x5 and the 11x5.5 too.

Hope to lobby them next weekend at Toledo...

 What's the latest Bob???

Excellent project Bob. I understand you flew Gordy's wet twin. Impressive isn't it? That plane has 640 sq inches, roughly nearly the same as your project. I believe that over the years, twins have been over built, over powered, and too large. Watching Paul W. fly his B-17 was an eye opener, and proved that multi engined models can be powered by engines smaller than most would consider.

I beleive that one of the advantages of twins, has to do with the smaller dia. prop, but because there are two of them, you still have a lot of prop diameter to do the job. The smaller dia. prop seems to have less moment to impart prop forces so the turns seem to be much better, but the area allows it to have the traction to pull the plane through.

Using a pair of .15's instead of a single .40 or .46 on what is basically the same plane, the Pathfinder, seems to show that propped correctly, great performance can be achieved with engines, and I'll presume, moters as well, 60 to 75% the size, (when added together) for the same design, running a single engine.

Dennis A. has built and is currently flying one of Gordy's twin Pathfinders on e-power. At first he was running larger engines, and bigger props, but recently has gone to something much closer to what Gordy is running. Smaller motors, turning 9" props. I believe he has reported that the plane flies extreemly well on the smaller motors and props. If my memory is correcct, it flies better on the latest set up.

Best of luck and success on your twin Bob. It really looks great, and i love the lines of your sketch. Impressive Master Bob.  

bin wondin , if the TRIM alters gear up / gear down , but if its straight up & late down , youd have to reprograme it to see if it was worse Gear Down .
Which would be counter productive in effect .

Good to see it DID go in the Nats .

indeed , the ' prop disc area ' Vs prop inirtia PLUS the Thrust over the Flaps gets it all going good .