Multiplex FunJet Ultra RCBG

I've been sitting on my duff all winter building rockets and rc planes, basically ignoring my Strato Blaster and Gamma Star kits :sad: At the beginning of March I went to a large RC swap meet and in my trades I acquired a NIB Multiplex FunJet Ultra for dirt cheap so this build will start tonight. I hope to have it finished up within the next week or so.

The plan is to fly off of 24/40 E & F reloads as I fly in a small RC field and those reloads are cheap coming from HobbyLinc.

Pictured is all the parts needed minus a few connectors which I have in my work room. I have already lightly sanded down the foam to remove all the molding dimples. Let the fun begin :grin:

For this build thread I will only concentrate on the modified areas to make this a RCBG or where I deviated from the supplied instructions. Lets start with the aft CR-MMT area.


Cutoff the alignment tab from the inside, bottom of the plastic tail cone.




Made an initial CR to fit on the inside of the tail cone.




Since I used 1/8" Basswood Ply for the CR, I cut 1/8" of an inch off the back of the FunJet Ultra.




A quick test fit after a little sanding.




If done right everything should match up on the outside with the CR installed.

I wanted to vent the motor mount area. There is already a built in intake vent hole. I marked the CR for output vent holes.




I cut the the vent holes from the CR.




I scalloped the foam to accommodate the airflow to the CR vent holes.




A final test fit with the vent holes. Time to move on to the forward MMT CR.

Very cool! Looking forward to your build and flights.

Ari.

Cut the MMT at 6" and marked it 3/8" from the aft end.




Marked the fuselage and the back top 5 1/2" from the aft end.




Cut out the forward CR and the MMT end cap. I started with a piece of 1/8" plywood cut to 1 7/8" x 1 5/8", sanded to fit properly at the 5 1/2" mark. I then drilled a hole for the MMT. The center of the hole is 3/4" from the bottom and centered side to side. The end cap was cut about 3/8" larger then the hole.




I glued the end cap to the forward CR using medium CA. I wanted a glue that would penetrate the wood and dry fast. All this will be held together w/ epoxy in the next step.




Epoxied the MMT to both the forward and aft CR's using JB Weld. Note at this point I only epoxied the MMT to the CR's. I am only using the fuselage and the tail cone to help align the parts until the epoxy sets. All this will be pulled back apart once the epoxy sets.

This picture makes the MMT look to be at a strange angle but that is because the wing has an airfoil. The MMT is actually straight down the airplanes center line.




The MMT assembly is the hardest part of this build. I have gone over the mountain peak and the rest of the build should all be down hill from here :grin:

You'll have a blast with this. I have done the same thing to the older version of the funjet. Although I run with the 32/100 reload, I'll be interested in what results you get with the E motor. I am getting about 650ft on the F reloads and 850ft on the Gs.

Will you be launching vertically or using rails? Looking forward to seeing your results.

Catchya Planecrazy

You will indeed have fun with this jet. I'm also interested in your results using the smaller reloads. I like the F22J reloads in the AT 29/40-120 case. Would like to try the long burning F10 from Apogee, but the price is prohibitive. Might break down and order one anyway with the next order. Are you planning on-board ignition? It adds a different dimension to the sport and allows air drops if you have someone who can drop you. Its all fun....keep us posted. HAV

Planecrazy said:

I'll be interested in what results you get with the E motor. I am getting about 650ft on the F reloads and 850ft on the Gs.

Will you be launching vertically or using rails? Looking forward to seeing your results.

Catchya Planecrazy

Click to expand...

I plan to use the E18 reloads for initial test/trim flights and if I can get 350' - 400' that will work. I'll use F24 reloads for most flights and if I can get 550' - 600' I'll be good with that as I fly in a small RC fields and also those reloads are cheap so I can fly often on 24/40 F24.

My launch pad has a 1/4" x 6' rod along with two 1/4" x 4' guide rods in proper alignment. I will either use that configuration or I could add two more 1/4" guide rods to have a 4 rod "cradle" (not sure the proper rocket term.)

HAV said:

Are you planning on-board ignition? It adds a different dimension to the sport and allows air drops if you have someone who can drop you. Its all fun....keep us posted. HAV

Click to expand...

I am planning on on-board ignition but currently having an issue with this. Here is the setup:

Spectrum full range recvr.
2 x 12.5g high torque digital MG servos
3s Lipo
15amp brushed ESC.

The brushed ESC fires the ignitor immediately w/ full throttle so that function works but even with the throttle in the off position if I start rapidly moving the servos it gives my rcvr a brownout causing the servos to stop momentarily. That is not acceptable obviously. What I found is all brushed ESC's that I have researched only supply 5v to the rcvr and spectrum rcvr's really want 6v.

After some testing I have figured out if I use a standalone BEC (jumper configurable for 6v output) to run the rcvr and use the brushed ESC to only fire the ignitor my problems go away. This is the route I plan on taking.

If anybody has any other ideas or suggestions for on-board ignition please let me know ASAP as I want to maiden her 2 weekends from now.

ckreef said:

What I found is all brushed ESC's that I have researched only supply 5v to the rcvr and spectrum rcvr's really want 6v.

Click to expand...

I use Spektrum receivers all the time on 5V BEC power.

I run ignition off a separate RX that stays on the ground. It listens to the same TX, but has a big battery and is electrically separate from the flight RX.

Ari.

Set-up looks good. A separate BEC should work well. I have flown Futaba since 1970 and do not have hands-on experience with Spectrum equipment. I do know they are prone to brownouts and need higher voltages than Futaba Rxs. Did you loosen up the elevons? My elevons were fairly stiff and I had to work them quite a bit to get them to loosen up. Many cut them off and use regular hinges to lower the load on the servos...just a thought. I went with a 2 cell 500mah Lipo through an old GWS 10amp brushed ESC. Works like a champ for ignition. I'm using two of the ESCs for a Madcow DX3 DD rocket. I like having control of recovery I guess.... Keep us posted HAV

mikec said:

I use Spektrum receivers all the time on 5V BEC power.

Click to expand...

I really think it is a case of high end digital servos and not enough amps flowing out of the brushed ESC causing the brownout. A separate BEC solves that issue

iter said:

I run ignition off a separate RX that stays on the ground. It listens to the same TX, but has a big battery and is electrically separate from the flight RX.

Ari.

Click to expand...

I have given your setup lots of thought over the past months (we discussed this earlier.) I want to be able to do air starts on this glider but your setup would allow me to fire rockets without wires crossing over the rc pit area. I have decided to do both setups. Tonight I ordered a Castle Creations BEC to finish the air start setup for the FunJet. I also ordered a rcvr and an additional Brushed ESC to make a remote pad ignition setup. I have a small 2.4 ghz transmitter and some large 3s lipos to complete this setup. This allows me to go either way and to remote fire rockets without wires.

HAV said:

Did you loosen up the elevons? My elevons were fairly stiff and I had to work them quite a bit to get them to loosen up. Many cut them off and use regular hinges to lower the load on the servos...just a thought.

Click to expand...

I have not gotten to that stage in the build yet but will within the next few days. I don't want to cut them off and re-hinge. These small servos have good torque for their size and would rather have a stiff hinge line to reduce the chance of flutter on the boost phase. I will work the hinge line until I feel there is adequate play.

Thanks everyone for their input it helped make my decisions easier --- although I have spent more money because of the decisions. :eyepop:

The motors and a BEC is shipped and on it's way to my house. In the meantime I need to move on with the build.

I am using Foam-Tac Adhesive for the majority of the build except --- epoxy where needed in the MMT area --- If the parts might need to be removed some time in the future I used High Temp, Heavy Duty, Hot Glue (such as servo mounting, electronics etc.....)

Tonight I mounted the servos and installed the wings. The servos were a touch bit taller so I had to make the servo cutout areas a little bigger. The instruction would have you install the linkage at this point but in rc builds the linkages are almost always done last so I will wait till the end to do that step.

I did cut and loosen the hinge area. Seems good to me and will only install extra hinges if the hinge lines loosens up or gets week in the future.

HAV said:

Set-up looks good. A separate BEC should work well. I have flown Futaba since 1970 and do not have hands-on experience with Spectrum equipment. I do know they are prone to brownouts and need higher voltages than Futaba Rxs.

Click to expand...

Spektrum equipment is no more "prone" to brown out than any other brand of receiver. I've run both their and JR's 2.4GHz DSM2/X equipment for 5+ years now and never had one happen to me. The reason is that I use the equipment as recommended by the manufacturer. They brown-out at a higher voltage than 72MHz crystal Rxs, but that's because they are two very different technologies. I think the reason that most people have problems is that they stuff DSM2/X receivers into their 72MHz models and expect it to work every time even with the old abused 4-cell NiCD/NiMH Rx batteries and ill-maintained wiring harnesses.

Okay, I'm done ranting. I worked in a hobby shop for 4 years and had people complain that their new radio crashed their airplane. I sort of have an ingrained response to it. Moral of the story: read the instructions, learn the limitations of your equipment, and ground check.

All my parts came in the mail yesterday so I stayed up late to finish her up. Ready to maiden but rain today

Yesterday I did get to see Mac Hodges X1 rocket glider up close and took an idea off that for how to hookup the ignitor wires for on board ignition. I was going to mount small alligator clips but this is a much cleaner install. You strip 3/8" of insulation off the ignitor (I'm using First Fire Jr.) and then double the bare wire over making a tight loop. Do that for both leads. You then push each lead into one of these small sockets. I've ground tested this 3 times with my final wiring and it works great.

Will maiden and post pics and video as soon as the weather permits.

I flew the FunJet tonight for two successful flights on E18's. The on-board ignition and ignitor wire hookup worked as expected I set the launch angle for 80 degrees into the wind. Altitude was about 350'. I have two modes programmed in the Tx. A boost mode and a glide mode.

1st flight I basically did a hands off boost phase. I waited too long to nose her over so she stalled at apogee. I had to let her free fall for a moment or two until enough airspeed was obtained so the controls worked properly and I could pull her out of the dive. It was a slightly radical flight but I was able to land her without incident.

I tweaked my flight programming a bit and launched for flight two. This time I gave some slight inputs in the boost phase and nosed her over early enough so I maintained flight control the entire time. A much better/smoother glide phase and a graceful landing. She glided well and looked good both going up and gliding down.

I need to do a little more tweaking to the flight programming. I believe I can obtain a hands off landing once you have her lined up. Weather permitting I will fly her again Sunday. I will do 2 more trim flights on the E18's and then move onto the F24's.

For my 1st two RCBG flights ever they both were successful and I am very excited about this new phase in my rc/rocket hobbies. I do have launch videos which I will try and get posted by tomorrow night at the latest.

Congratulations on your achievement and thank you for sharing your experience!

Ari.

Well done! Looking forward to those videos. I don't know what the "Speed of Elapor" is but keep an eye on the wing and fin roots for stress cracks.


Richard

TheTellurian said:

Well done! Looking forward to those videos. I don't know what the "Speed of Elapor" is but keep an eye on the wing and fin roots for stress cracks.


Richard

Click to expand...

This is my 1st Elapor airplane but the foam seems basically indestructible. With the right electric setup the FunJet Ultra can go 200+ mph (a few different setups as seen on the forums), so I shouldn't have any worries using E or F reloads but I will keep an eye on things.

Here is a maiden launch picture and launch video. This was a hands off boost and she boosted/flew basically straight and true as built. Pictured is a 1/4" x 6' main launch rod. From here out I will use my 1/4" x 4' main launch rod as I feel the extra 2' was not needed.




[YOUTUBE]b3_ExykGK84[/YOUTUBE]

Charles, Looks like a good flight! Congratulations!

Excellent video! Go you!

Ari.

Well done indeed. Enjoy, and please keep sharing the videos.... HAV

Last evening I flew her 4 more times. 3 x E18 and 1 x F24. All great flights. On one of the E18 flights I did a roll on the way up and the F24 flight I did a roll on the glide down. I can see why one would want to fly her on a G motor. She is easily manageable on a F motor even in a small field. Only issue w/ F compared to G is the F24's from Hobbylinc are cheap and I like to fly often.

Even at a 80 degree launch angle she still seems to come over on herself in the boost phase especially with the F motor. I currently have dual rates/expo setup for boost and glide modes. On the boost phase the elevons are also set to neutral and in the glide phase a small amount of positive reflex is programmed. I think I am going to program a small amount of negative reflex (down elevator) for the boost phase so she boosts straight and true, that way I can concentrate on acrobatic maneuvers going up instead of correcting the flight path.

I have some landing video footage that I will try and post tomorrow night. Also two club members got some full flight footage that I can from them on Sunday.

The vertical fins have a lot of drag on that side of the fuze and will pull it to that side. Doing the negative reflex on boost is the way to handle it short of adding drag to the other side or modifying the thrust angle.

Looking forward to those vids.


Richard

TheTellurian said:

The vertical fins have a lot of drag on that side of the fuze and will pull it to that side. Doing the negative reflex on boost is the way to handle it short of adding drag to the other side or modifying the thrust angle.

Looking forward to those vids.


Richard

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I never thought about the drag caused by fins on one side for the boost phase. Also the thrust angle could be a little off. The aft centering ring is just a circle with the MMT hole in the center. The forward centering ring is a non symmetrical rectangle with the MMT hole in "just the right place". Did I get it in "just the right place" ??? I tried hard to align it correctly but I could be off by a smige.

Posted below is a short video from last nights launches. It is 4 launch's and 3 landings. The way she boosts compared to the wind direction (smoke angle), you can tell she weather cocks into the wind gracefully. Hard to really see how she comes back on herself as that happens more as the boost phase ends. These videos were captured with a GoPro 2 setup for launch video so if you want to see the landings you need to go to full screen mode.

One day soon I will have a proper full flight video :wink:

[YOUTUBE]AZ5W8XKkJFc[/YOUTUBE]

ckreef said:

Did I get it in "just the right place" ???

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Likely close enough. Though a smidge in the right direction would tend to compensate for the pitch up on boost. How much, would be trial and error without some aeronautical whiz to calcukate it out.

Waiting for Sunday.:wink:


Richard

TheTellurian said:

Waiting for Sunday.:wink:

Click to expand...

Unfortunately I have to work on Sunday so I will not be able to pickup the video and I will not be able to maiden my newest rc airplane. This is only the 3rd Sunday we have had to work in 11 years at this company and I am bummed


I did fly her 3 more times this evening. Added some negative reflex and went up on a F24. I really didn't like it so won't do that again.

I removed the negative relex and went up on another F24. I decided to try a roll just after she leaves the pad during full motor burn phase. Now that was a very crazy boost that ended with a less then graceful landing. Won't do that again. Need to wait for the motor burn out before doing a roll on the way up.

I was going to go home after 2 flights but since I wasn't happy with those 2 flights I loaded my last E18 motor. This time I did a loop towards the end of the boost phase. The loop looked way kewl with the smoke trail and I went home with a smile.

TheTellurian said:

Likely close enough. Though a smidge in the right direction would tend to compensate for the pitch up on boost. How much, would be trial and error without some aeronautical whiz to calcukate it out.

Waiting for Sunday.:wink:


Richard

Click to expand...

Unfortunately, the amount of downthrust/reflex required changes based on the motor characteristics, speed, and glider configuration. Getting it "close enough" is about as good as you can do, even with an aerospace engineering degree. The rest is testing, tweaking, and pilot skills. Bob Parks of Aerotech Phoenix fame makes his high performance gliders with an adjustable height motor mount and moves it up and down until he gets the thrust line just so, then glues it firmly in place. He does it for all of his gliders, even of a design he's built before.

TheAviator said:

Bob Parks of Aerotech Phoenix fame makes his high performance gliders with an adjustable height motor mount and moves it up and down until he gets the thrust line just so, then glues it firmly in place.

Click to expand...

Thats a great idea! Certainly better than even an educated WAG. I have several RCRGs that have not been flown yet and may just get a refit in the motor mount department. Have you any data on the design of this adjustable mount?


Richard

TheTellurian said:

Thats a great idea! Certainly better than even an educated WAG. I have several RCRGs that have not been flown yet and may just get a refit in the motor mount department. Have you any data on the design of this adjustable mount?


Richard

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I've not seen precisely how he does it, as he covers the mount with a plastic shroud after fixing it in place. I believe that he uses a pair of carbon rods mounted vertically to the bottom of the motor tube that nest in a pair of tubes in the tail boom. A few wraps of tape on either side of the boom is enough to hold it on boost. When it is where you want it, wick thin CA between the tubes and then back up with some 5min epoxy. Clip off the excess that sticks out of the bottom of the boom. Add a plastic fairing for awesome aerodynamics.