Author Topic: New Electric Twin project back on track (Read 114390 times)

wwwarbird · « **Reply #500 on:** June 15, 2014, 08:41:00 PM »

NOW we're talkin'!!!

I like how you went with a straight line over the top for rear portion of the "canopy", it looks more realistic than the Crossfire type.

Tom Niebuhr · « **Reply #501 on:** June 16, 2014, 05:23:44 AM »

Looks great!

Now the final work and graphics, clear coat and flight. The NATS are getting very close. I know that you have very good airplanes ready, but I hope that this will be your NATS plane.

Tom Niebuhr · « **Reply #502 on:** June 16, 2014, 09:10:20 AM »

Here is the new Huntmobile!

Bob Hunt · « **Reply #503 on:** June 16, 2014, 11:47:08 AM »

Quote from: wwwarbird on June 15, 2014, 08:41:00 PM

NOW we're talkin'!!!

I like how you went with a straight line over the top for rear portion of the "canopy", it looks more realistic than the Crossfire type.

Thanks, Wayne:

The Crossfire canopy treatment is meant to simulate many of the modern jets that have such shaped canopies. The twin is supposed to be more of a private plane look. Although it's always madness on my part, there is often method associated with it.

Later - Bob Hunt

wwwarbird · « **Reply #504 on:** June 16, 2014, 06:09:27 PM »

Quote from: Bob Hunt on June 16, 2014, 11:47:08 AM

The Crossfire canopy treatment is meant to simulate many of the modern jets that have such shaped canopies. The twin is supposed to be more of a private plane look. Although it's always madness on my part, there is often method associated with it.

Later - Bob Hunt

Yup, gotcha.

James Mills · « **Reply #505 on:** June 19, 2014, 09:37:00 PM »

Quote from: Bob Hunt on June 15, 2014, 08:15:31 PM

I spent Father's Day applying the red trim and a bit of the blue trim. Also got the canopy on. One more long day should do it!

Later - Bob Hunt

Bob,

Looks nice, look forward to seeing the finished product.

James

Air Ministry . · « **Reply #506 on:** June 20, 2014, 07:04:13 AM »

Wel l , That was quick .

Like good wine , I suppose .

wwwarbird · « **Reply #507 on:** June 29, 2014, 10:37:14 PM »

How's the paint coming along Bob?

Bob Hunt · « **Reply #508 on:** July 03, 2014, 07:51:17 AM »

Everything on the twin has come to a pause until after the Nats. I really wanted to get this thing done for the Nats, but everything in my life conspired to make that impossible for this year. I will finish it after the Nats and then get to work finishing up the new twin as well.

My thanks go out to everyone who has been following this long-running thread, and to those who have posted comments and questions. Trust me, these projects will reach fruition.

Later - Bob Hunt

john e. holliday · « **Reply #509 on:** July 03, 2014, 09:36:01 AM »

I'll be waiting. Have fun at the NATS.

Air Ministry . · « **Reply #510 on:** July 24, 2014, 02:14:34 AM »

RIGHT .

No Impediments NOW . !

Test Flight DUE . . . .

Tom Niebuhr · « **Reply #511 on:** July 24, 2014, 07:29:45 AM »

I little bird told me that the first twin will be in the air, possibly in less than a week, weather permitting.

Looking forward to the first flight report and pictures.

Bob Hunt · « **Reply #512 on:** August 11, 2014, 09:12:19 AM »

Okay, big news! Buddy Wieder, Tom Hampshire and I flew the testbed twin this morning!

Good stuff for sure and a few very minor glitches: First the good stuff. The motors ran perfectly throughout all 10 flights this morning. We flew a couple of one minute flights to be certain that everything was adjusted properly, and then flew some 4 minute flights. Trust me, you will not want to arm wrestle with Buddy and me after next year's season...

It was neat to be able to trim the amount of degree tangent to the circle that the airplane flew with the adjustable pot on the timer. We made the inboard motor run just about 100 rpm's faster than the outboard motor. We may be able to dial that back a bit since we have more than adequate line tension. Just wanted to be safe for the first few flights...

The wings are not yet perfectly level and I suspect that I may have a curl in the outboard flap. The flaps are raw 1-pound foam covered with .2 ounce/sq.yd. carbon, attached with thinned Titebond. They are a bit too flexible I think and I'm going to retrofit genuine balsa sheeted units.

The ship turns dead equal in both directions, grooved like a freight train, and is extremely easy to fly through maneuvers. It tracks beautifully through rounds, and it turns and locks on target for the legs of the squares, The bottoms are flat and predictable. It really flies like a great stunt trainer!

The only problems encountered was with the timer - which is an experimental/beta test unit from Will Hubin. It ran the motors perfectly, but when the 5-second drop in RPM occurred, the motors kept on running for a full minute instead of for just five more seconds as usual. That's just a minor programming issue for Will, I'm sure. There was also a programming glitch in the retract timer; I could not set it to extend the gear past the 59 second mark. Again, just a minor thing and I'm confident that Will will quickly remedy that. For obvious reasons we did not experiment with the retracts this morning...

All in all it was a fantastic session. Buddy and I each flew several flights with the ship and we are very encouraged by the results.

The 9 x 6 APC props are turning just over 10,000 RPM, and the rotation is set to have the tips of the props turning towards the canopy. We will, of course, explore all the possible prop rotation options as we proceed. We'll also try larger props. We can go all the way to 11-inch props! Of course then my arm will just pull clean off and fall to the ground...

After a 4-minute flight I just put nominally 1400mAh back into the 4S 3300 mAh Hyperion packs. We should be able to fly complete 5 minute and 45 second flights, operating the gear up and down, and still be safely under the 80 percent rule!

It's been a long time coming, and I appreciate everyone's patience and interest in this project. With a bit more testing we are confident that our "real" twin ships will be successes.

Later - Bob

David_Stack · « **Reply #513 on:** August 11, 2014, 10:07:02 AM »

Congratulations on the successful maiden flight (and then some) Bob!

You mention flaps that are less than ideal from a torsional stiffness perspective... What about using a different form of carbon material instead of the carbon veil, something with some 'grain' to it? You could orient the fibers on a bias to help prevent the twisting. There are some awfully light carbon weaves being produced now, and in use in the R/C discus-launched glider community. Something along the lines of what is being discussed here: http://www.rcgroups.com/forums/showthread.php?t=2161133&highlight=vlad+tow

r/
Dave

Dan Bregar · « **Reply #514 on:** August 11, 2014, 10:58:21 AM »

Fantastic ! Way to go Bob. I'm staying tuned for the next chapter !

Dan

Tom Niebuhr · « **Reply #515 on:** August 11, 2014, 11:10:10 AM »

Bob,
Great progress to date.

I know that you had to make adjustments for the vertical c.g.

How much is that going to change with the gear up?

Matt Colan · « **Reply #516 on:** August 11, 2014, 02:09:03 PM »

Awesome Bob!!!

I think having the props turning in towards the fuselage will be best since it will eliminate having a critical engine. I'd imagine having a critical engine on an electric twin wouldn't be that huge of a deal because of the timer.

MarcusCordeiro · « **Reply #517 on:** August 11, 2014, 04:35:57 PM »

Plain and simple: NICE!!!!!

Marcus

Bob Hunt · « **Reply #518 on:** August 11, 2014, 05:43:42 PM »

Thanks to all who posted about the maiden flights. It's going well ahead of our projected schedule! I'm going to make new flaps from balsa covered foam and then carbon them as well.

I'm attaching a few photos of the building process of this test bed. I've posted some of these here before, but here they are in more or less chronological order. The raw foam wing with 1/8 x 1/2-inch basswood surface spars and carbon mat over the leading edge and the center section technique (That I'm calling the "Lost-Sheeting method...) has worked out extremely well. The wing is super stiff and it is light as well. The all-up weight, including battery and retracts is just over 65 ounces. The ship has a 670 square inch wing area, so it's not too bad. With all the disk span it flies like it's very light!

Enjoy the photos. It may take several postings to get them all up.

Later - Bob Hunt

Bob Hunt · « **Reply #519 on:** August 11, 2014, 06:00:46 PM »

More photos...

Bob Hunt · « **Reply #520 on:** August 11, 2014, 06:04:46 PM »

More photos yet...

Bob Hunt · « **Reply #521 on:** August 11, 2014, 06:06:21 PM »

Last ones!

Dan Bregar · « **Reply #522 on:** August 12, 2014, 05:22:42 PM »

Wow ! Fantastic work ! You are the best Bob ! I really like your stab jig too ! What adhesive did you use to put the carbon onto the foam ? Thinned white glue maybe ?

Dan

Randy Powell · « **Reply #523 on:** August 12, 2014, 05:36:00 PM »

Man, Bob, you do awesome work. That is just unbelievable. I like it a lot.

David_Stack · « **Reply #524 on:** August 13, 2014, 06:11:02 AM »

Dan;

Back in post #354, Bob discusses the construction of the wing, what her terms his "Lost-Sheeting method", and the adhesive used. You are correct in what you surmised regarding the adhesive used...

Requoted here:

"We used the same technique to build the wing for this testbed model as we did for the Joe Nall Cadet models. We call this construction the "Lost-Sheeting method." There is no balsa sheeting on the wing. The wing is a solid foam core made from 1-pound density foam. There is a slot cut in the center of the wing cores to allow the leadouts to get to the tip and have some adjustment. There are slots cut into the top and the bottom of the wing at the high point to accept 1/2 x 1/8- inch basswood spars. The spars run the full span of the wing. There are several shear webs imbedded in the core between the spar slots to prevent the spars from "racking." That is the technical term for what the spars want to do on either side of the wing during maneuvering. In an inside maneuver the top spar in in compression and the bottom spar is in tension. If there were no webs between them, they would try to "clap hands" under stress. The webs prevent the spars from trying to move and hence impart a tremendous amount of strength. Enough not to break under maneuvering loads by themselves? Not quite. After the spars are glued into the slots and are firmly glued to the vertical grain shear webs, we apply .2 (two tenths ounce per square yard) carbon mat using water thinned Titebond wood glue. The carbon is first applied from the back of the spar on the top, around the leading edge and ends at the back of the spar on the bottom. A thin carbon strip reinforces the trailing edge area, and an additional piece strengthens the entire center section area."

r/
Dave

Dan Bregar · « **Reply #525 on:** August 15, 2014, 08:50:23 AM »

Thank you very much David.

Dan

David_Ruff · « **Reply #526 on:** August 17, 2014, 05:52:51 AM »

Nice photos of construction. It helps me figure out how to convert my ARC Oriental to ECL.
Was wondering what the service ceiling was on engine out?

Dean Pappas · « **Reply #527 on:** August 19, 2014, 01:45:30 PM »

70 feet, of course!
later,
Dean P.

Bob Hunt · « **Reply #528 on:** August 26, 2014, 12:41:11 PM »

Okay, lots to report on about the second day out with the twin test bed... and it's all good!

First off, the timer problem that I thought I had was not a glitch in Will Hubin's programming. I just neglected to fully read the programming instructions. We adjusted the timer as per Will's instructions over the phone, and now the "Full Monty" is working.

On the first day we flew several five minute flights and then checked to see how much battery we were using. It turned out to be 2,450 mAh. Note, this was with the gear extended. Today we retracted the landing gear and flew a five minute flight and recharged the battery to find that we only used 1,800 mAh! Approximately 25 percent less! That should once and for all answer the question about landing gear drag... We then upped the flight time to the normal 5:45 setting and flew several patterns. I have not yet charged any of those batteries (too anxious to make this report...), but I will later today and report back.

We opened the handle about 1/2 inch per side (one inch total wider spacing of the lines) added just a touch of tail weight (about a quarter ounce), and added a bit more tip weight. The ship came alive with these changes and in now capable of an honest 45 degree pattern, although we still took it a bit easy... The ship turns just a bit better inside than outside, but it feels like the flap and that elevators are not yet in perfect alignment, so we'll experiment with that until the turn is equal. Inside loops are very clean and it tends to slide the tail just a bit on outside turns. The flap/elevator adjustment should remedy that.

This thing is not hurting for thrust. We flew the first few patterns today at about 5.6 to 5.8 second laps. Then we upped the RPM a bit and flew around a 5.4 second lap. Again, no power or thrust problems. The ship tracks through round loops beautifully and it transitions nicely. Again, it will get better with the aforementioned adjustment and even a bit more speed.

My son, Robby, took some quick time videos, but I have no clue as to how to upload them here. I'm sending them to Bob Storick and he'll post the link in another message on this thread (Thanks, Bob...).

Remember, this is just the second day out with the ship, and the very first full pattern flights that also had the gear going up and down (That part works flawlessly by the way...). Unfortunately, the videos are short and don't show too much of the pattern. I think you'll enjoy the "spool up" video, however...

Later - Bob Hunt

Derek Barry · « **Reply #529 on:** August 26, 2014, 02:52:02 PM »

Very cool!

Derek

Dennis Adamisin · « **Reply #530 on:** August 26, 2014, 03:39:38 PM »

U B twinning!

RC Storick · « **Reply #531 on:** August 26, 2014, 04:00:32 PM »

Hey Bob who's the old guy holding your airplane?

Bob Hunt · « **Reply #532 on:** August 26, 2014, 04:05:13 PM »

Hi Bob:

Not sure; but he looks a lot younger than the guy who built your Minado...

Bob

Paul Taylor · « **Reply #533 on:** August 26, 2014, 04:17:53 PM »

Way Kewl Bob!
Spool up sounds great!

And old guys rule!

Randy Powell · « **Reply #534 on:** August 26, 2014, 04:41:40 PM »

bob,

Yea, something I noticed (with my neophyte knowledge) flying my electric last weekend. The thing pulls like a truck but is easy to fly corners and maneuvers. With an IC plane pulling that hard, it would take hydraulics to make a turn.

Dwayne · « **Reply #535 on:** August 26, 2014, 04:45:07 PM »

If 5 years ago you'd have told me I'd be watching this I would have laughed. What a time for C/L stunt we live in, outstanding!!!

Bob Hunt · « **Reply #536 on:** August 26, 2014, 06:08:45 PM »

Yeah, how about it, Dwayne!

Okay, I charged one of the batteries that we used for a complete pattern flight, with the gear retracted. You are just not going to believe this... I put back in 1,859 mAh! That's just amazing! It was hot and relatively calm. That's when the most juice is used in my experience. On a windy day the usage is even less.

Tomorrow we are going to try the 10 x 5 APC props that are matched left and right hand rotation. We are also raising the elevator a bit to equal out the flap travel. That should get rid of the slight unequal turn rate and the slight tail slide in outside maneuvers. Additionally we will be moving the battery aft to move the CG back a bit and get some more turn rate.

Obviously we are extremely pleased with the progress so far (only two sessions), and believe that there is much more performance to come as we try various trim changes and prop rotation and size options. I can tell you this much, it ain't boring at the field right now...

Later Bob Hunt

Dean Pappas · « **Reply #537 on:** August 26, 2014, 07:24:53 PM »

"So much time and so few experiments to do ... wait, reverse that."
With apologies to Willy Wonka,
Dean P.

Dan Bregar · « **Reply #538 on:** August 26, 2014, 08:50:49 PM »

Man, I just loves it !!! Fantastic. And to think it's only going to get better !

Dan

James Mills · « **Reply #539 on:** August 26, 2014, 10:01:44 PM »

Bob,

Ben said that was very cool.

James

Shawn Lenci · « **Reply #540 on:** August 26, 2014, 10:52:43 PM »

Very nice Bob...wish I could find a parking lot like that out here in CA to fly in.

Shawn

Bob Hunt · « **Reply #541 on:** August 27, 2014, 05:34:40 AM »

Hi Shawn:

Here's a lesson in problem solving... Move here!

Bob

Bill Little · « **Reply #542 on:** August 27, 2014, 06:35:28 AM »

Looks good in the air, Bob! I know the "real" bird will be better!

Bill

Bob Hunt · « **Reply #543 on:** August 27, 2014, 09:39:48 AM »

We just returned from our third session with the twin. Made some huge gains. Unfortunately we didn't take any video today. We will next time I promise.

The ship seemed to turn slightly better insides than outsides and it was sliding the tail through round outsides. We checked the flap/elevator neutral and found that the flaps were slightly down when the elevator was at neutral. I used the turnbuckle on the pushrod to raise the elevator a bit. Then, when I readjusted for neutral, the flaps were level as well. It made a huge difference and the plane is now turning dead equal in both directions and the tendency for the tail to slide through the outside rounds is completely gone.

I also moved the battery back 3/4-inch and that gave more turn. I also opened the handle a bit and added just a tiny bit of tail weight. Now the ship turns freely and is easy to fly at 45 degrees or even smaller if desired.

We noticed that in verticals and the up legs of the squares that the motors tended to "bog" a bit. We are switching from the 9 x 6 APC props to 10 x 5 props for tomorrow (or the next time we get out to fly...). That should correct that issue.

Each trim change we have made has yielded better performance. There are still a lot of things to try, but at this point I'm ready to declare this experiment a success and move forward with the new "real" stunt twins. Buddy's new twin is in the paint shop and should be ready for test flights in a month or so. My original, smaller twin is in paint and I'm going to try to have that ready to fly in about a month as well. My new, bigger twin will not be finished until next spring, and I intend to go all out on paint and surface detail to make that one very special.

I've already received requests for plans for the testbed twin. I'll try to get to those soon, but I have a ton to do right now at my job (making wings), and in getting Stunt News closer to being shipped on time. Needless to say the Lost-Sheeting method of building quick testbed or practice models is also a great success.

Robby is home for a few weeks and I'm spending as much time as possible with him at the field. Life is good.

Later - Bob Hunt

Tom Niebuhr · « **Reply #544 on:** August 27, 2014, 09:56:42 AM »

Bob,
Thanks for the very exciting reports.

It is a little hard to see the gear up and down for landing. I am sure that the small and larger twins will be a work of art.

We will all be anxious for more reports and for the flights of the new twins from you and Buddy.

This also gets me excited about getting back to work on my new electric stunter with retracts.

john e. holliday · « **Reply #545 on:** August 28, 2014, 09:11:16 AM »

Bobby, I am so excited to hear of the success you are having with the twin. I guess the electrics is the big secret. Tell Robby hi from the old man.

David_Ruff · « **Reply #546 on:** September 01, 2014, 03:12:53 AM »

Quote from: Dan Bregar on August 15, 2014, 08:50:23 AM

Thank you very much David.

Dan

Nice...sort of how Phil Cartier makes wings...

Bob Hunt · « **Reply #547 on:** September 10, 2014, 05:08:18 AM »

Time for an update!

Buddy Wieder and I have been flying the test bed twin for a while now and we have several full patterns on the bird. We had hoped to be able to get away with a 3,300 mAh battery to run both motors and power the retracts. And, as I wrote in my last update post here, we did go from the 9 x6 props to the 10 x 5 props. The bigger props worked much better, but there was still a "bog" at the tops of the maneuvers. Turns out we needed a 4,000 mAh pack and higher Kv motors.The first motors we used were too low in Kv, and the motors "bogged" on the tops of maneuvers. We consulted with Dean Pappas and he suggested going to the 4,000 mAh pack, and 1100 Kv Power 10 motors, and even predicted the exact amount of mAh we would use for a 5 minute, 30 second flight.

We put in the 1100 Kv Power 10 motors and the 4,000 mAh Hyperion pack and flew the ship. The bog was totally gone! The new motors and battery combination worked to perfection. And, Dean's prediction on power usage was absolutely spot on to the exact number he said we'd use. We are now putting 3,000 mAh back into a 4,000 mAh battery. That's exactly on the 75 percent rule! Dean is just flat amazing...

Okay, at this point the problem became the CG. With the 3,300 mAh battery it was a bit far forward. With the 4,000 mAh battery it was way too far forward. We added 1 1/2 ounces of tail weight to get the model to turn properly, but that produced an inertial effect and made the tail swing past the turn point noticeably. Rats.

We decided to rearrange the wiring to allow us to move the battery back 2 1/2 inches. That allowed us to take out the tail weight entirely and achieve a very nice corner without the tail slide. Main problem solved!

At this point we are down to fine tuning the flight trim of the ship. It appears that the outboard flap is a bit too effective and it is lifting the outboard tip in both inside and outside maneuvers slightly. We have installed an area tab on the inboard flap and we are heading out to the field for some test flights. Interestingly, we have pretty much forgotten about the motor runs and the retracts. All that is working perfectly and now we are just down to trimming this behemoth for proper flight trim just as we would any other stunt model.

I'll try to get a post in later today to update everyone on the flight trim. The main objectives for this test bed have been met, and I'm ready to declare that "Electric Twin Stunt" is here to stay and it will become a major factor in this event in short order. I've received many requests for the plans for the test bed model, and if I get some free time (yeah, right...), I'll draw them up in pencil and make them available along with a list of powertrain components.

Later - Bob Hunt

Bob Hunt · « **Reply #548 on:** September 10, 2014, 10:07:17 AM »

We are just back from the most productive field session yet. We got in 11 flights today. In fact, we are now just practicing maneuvers with the test bed twin in preparation for the Palisades Park meet this weekend. Buddy and I have decided to both fly the twin at that meet just for fun.

All of today's trim changes worked. The area tab on the inboard flap solved the flaring up of the tip in both inside and outside maneuvers. In fact, we were able to take out about a half ounce of tip weight! The ship is now flying extremely clean through all maneuvers and is about as easy to steer and place as any model I've ever flown; maybe better!

When we started out today it was chilly and we were turning 5.2 second laps. As the heat increased, the ship eventually slowed down to a 5.3 and change lap time. It still pulled like the Queen Mary out there...

I'm in love with twins! (Don't tell my wife!

)

Later - Bob

Randy Powell · « **Reply #549 on:** September 10, 2014, 10:35:06 AM »

>>It still pulled like the Queen Mary out there<<

That's something I noticed with mine. The pulls like a truck. With IC planes, when the pull like that, they are usually quite hard to turn from level flight. Takes a ton of stick pressure to get them to want to turn. With this new electrical beast, it was pulling quite hard but turned very easily and precisely. I found that odd.