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70cc Mamba build thread

Old 01-23-2019, 08:12 AM
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daveopam
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Default 70cc Mamba build thread

I thought it might be interesting to do a little build thread on this Mamba. A few things about me. I am a budget flyer so a plane like this is a rare treat. Along those same lines I have to use parts I have on hand. I am picky about things being right so I wont use any junk but this may make some of you question my choices. Also this is going to be a few month project. Time is hard to find.

For starters this thing is bigger than I thought. The 50cc extra I am replacing is a touch longer but the diameter of the fuse and cowl as apples and oranges different. After checking all the parts and sorting hardware I got started on one of the 4 wing panels. A words of cation. Each aile has 5 hinges. One of the hinges on each aile is turned 90 degrees so the surface will stay straighter during bagging (at least thats my assumption). So if you are like my and start deflecting the surface as soon as you pull it out of the bag you will ruin one hinge. It's an easy fix with a 1/4 Dubro I had on hand. The fit on this first wing half was excellent and required no extra work in the hinge area. I thought while I was making epoxy I would prep the control horns also and do it all at once. Another word of cation.The horns for the aile are slightly different than the horns for the elev. So count them. the ones you have 4 of are elev. The ones you have 8 of are aile. There are also several choices for the rudder as this can be set up for pull/pull or push/pull.
The install of the hinges and control horns was straight forward with no issues. I did have to clean the holes for the horns a little but that's to be expected. The holes were already opened which was nice. It looks like a soldering iron was used so a little covering residue is going to be in the way.
One of the pics I'm posting today is the cabane mount and it will be installed when I put the servo in.

Thanks guys, question, comments and hints are welcome.

david


Old 01-31-2019, 07:35 AM
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A little more progress. Both lower wing halves are done. Servo screw is missing because I don't have it centered as yet. One thing I like. The treaded rod has reverse threads on one end and a small wrench that fits in the center of it. This allows for fine tuning of the length without removing either end to rotate the ball link. The book gives the length of the rod on center as a good starting point. So it should be close. One mistake I did find. There is no way to get the 3+ inches of down throw on the ailerons. The supplied control horns hit the wing at 2-5/8" of throw. Now this is probable plenty for me as I am no QuiQue, but it may be an issue for some.
I really like the setup on attaching the cabanes to the wings. The blocks took a little trimming to get seated right but it was minimal. The fit is so good thin CA probable would have held them in place but epoxy takes an worry out of the mix. The rod that pushes through the cabanes and through the blocks is in the 4/40 range and is a very sturdy piece. Field setup is supposed to be a 3 minute job. I firmly believe it will be.

Thanks, David



Old 02-03-2019, 08:02 PM
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Old 02-04-2019, 07:31 AM
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Much progress as can be seen above. Upper wings hinged and ready for servos. (waiting on parts) Elevator servos in. I decided to go with two instead of one. QQ says use one 400oz servo with joiner wire to save weight. I fail to see much weight savings. The joiner wire weighs half of what the 2nd servo weighs. Add the epoxy I don't think there is much savings. I also prefer to use 2 servos on the the elev. I think it's a tighter more reliable set up. Just my opinion of course but it's my plane. The stab is in but not glued. I measured from the wing tube to get it straight but wanted to do the same using the wing tips. I got the wing bolted in but ran out of time. I am going to need to power up the Aile servos to get a good stable place to measure from.
These steps went pretty smooth. Small issue with the 2nd elev servo opening. The covering is cut for the location if you are going to use one servo. On the opposite side of the fuse there are 2 ply trays made for the 2nd elev servo and the rudder servo if you are going to use a push/pull on the rudder. Cutting the covering is no big deal but these servo openings are not the right size. There is no way two servos would fit here. I had to cut away 1/2 of the ply that divides these two opening to be able to fit one servo. The size is right fore/aft but not up/down. Not a big deal but I am picky. Only other thing on the top wing halves. Just like the lower wing throw is going to be limited to when the horns hit the wings. There is no way to get 3+ inches QQ calls for on high rate.

david
Old 02-11-2019, 07:16 AM
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More progress. Stab is glued in. Elev halves are epoxied on with control horns in. Fin and tail wheel are on. Control horns epoxied in rudder. Everything went pretty smooth here. I did vary from the plans slightly. Since I am using two elev servos I thought it would be a good idea to fill in the holes made in each half with dowel rod. There is no hinge in that area but it is close to the control horn. I was afraid leaving a void there might weaken the structure.
David


Old 04-04-2019, 10:18 AM
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Progress is slow as shop time is at a premium right now. I did mange to get the rudder on, servo in and pull/pull ran. Landing gear is next. Then it's time to mount the DA-60.

David

Old 05-07-2019, 05:52 PM
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Looking good
Old 05-08-2019, 06:10 AM
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Like the cowl vents! What did you use for power?

David
Old 05-08-2019, 07:06 AM
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This is my second Mamba... first one lost due to a flame out at low altitude( fuel tank failure). First one by the book per flex instructions.....flew great.
so on the second one I went with the louvers so I wouldn’t have to cut the hole in the bottom of the fuselage.
whats the difference.....the plane is so much speed compared to the other one I love it!





Old 05-08-2019, 07:09 AM
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Everyone will say it’s not needed and it’s not but that’s the way I roll. Plane screams...DA70 awesome....unlimited vertical....love this plane so much I bought another one
Old 05-08-2019, 07:12 AM
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Next one ready to start
Old 05-08-2019, 07:13 AM
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Here is the crashed mamba
Old 05-08-2019, 07:19 AM
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OUCH on the yellow one. Thanks for the pics. Looks like a great set up. Mine is going to be DA-60 powered. All I need is time to work on it.

David
Old 05-08-2019, 07:19 AM
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It was about 25’ up in a hover and slowly came down gear first destroying the motor box and landing gear support. I’m going to repair it . Everything is fine except I need new cowl and of coarse repair the fuselage. I bought the new Yellow mamba cause I couldn’t pass up the deal from a near by modeler who needed to sell...got it for $550��
Old 05-08-2019, 08:11 AM
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I was wondering where that $550 Mamba went! I have been flying for about 46 years, and if I could only have 1 airplane, it would be a 70cc yellow Mamba. While I still have my original for now. I hope to build another one in the future, using a few of the things learned from the original. Your has louvers on the cowl, did you find them to be of any benefit, or was it purely for appearance. Thanks!
Old 05-08-2019, 02:45 PM
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Anytime you can get more air in and out the better off the engine will be
They help to vent hot air out with out running all that air through the inside of the fuselage and out a big hole in the bottom. The original stock set up works fine but my first mamba got real hot with the stock set up so I added the louvers. I believe it helps to keep the temps down. I have a temp sensor on temps run 260-300 degrees.
Old 06-05-2019, 05:59 PM
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Default Did u get the motorbox repaired?

I crashed my mamba. Just motor box damage. Trying to figure out how to make a new motor box. Was wondering if u completed yours
Old 06-06-2019, 06:01 AM
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I decided to wait on the repair for a while....hoping flex will offer a motor box kit. It is a well engineered kit but very difficult to repair.
Old 06-06-2019, 11:51 AM
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Mine is still gathering dust :-(((
Old 07-10-2019, 02:59 PM
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MUCH progress. Engine mounted. Center of upper wing installed. Tank in (twice). Ignition and power divider in. Only a couple snags in all this progress. One was the tank. I installed and plumbed my tank and then put the center of the upper wing in place. I little later in the day I decided to fit the canopy in place and realized it would not clear the tank I used. The tank I put in is about 3/4" longer than stock and there is a ply frame at the LE of the canopy that hit the back of the tank. Rather than modify the canopy I removed the tank and put the one in that came with the kit. Not a big deal but now the center section of the wing was in place and that made it tricky. Only other issue was something that has to be done with a lot of gassers. The hole in the center of the motor box would not clear the throttle arm, the choke arm or the fuel nipple. And this was with 25mm standoffs and not the 15mm called for. Can't blame Flex for this as the carb on the twin is not at the back of the engine. Also give Flex a pat on the back for making several places available to mount the throttle servo. I pushed the engine out 10mm because I am using a DA-60 not the 70CC twin called for. On the plus side the DA-60 is the same bolt patter as the DA-70 twin so the firewall was marked already.

More to come soon I hope.



Old 07-18-2019, 06:32 AM
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In the final stages!! Test fit the wings and set the throws and end points on all the servos. Got the Red Wing power box set up. I debated about using this unit. Many said it was not worth the extra complexity. In the end I went with it cause I lost a 50cc Extra to a bad switch. This unit is going to have 2 3200mah LiFe batteries that are going to run the RX and the ignition. It even has a built in kill for the ignition. I think it was the right choice for me. Cowl is mounted. Prop/spinner on. I'm a little concerned about the cooling. Rather than butcher the big cowl any further I am using the tunnel for the pipe as a vent. I took some Monocote and closed in a section of the inner fuse and cut out the area in the bottom of the fuse that is designed for the pipe exit. This should get the hot air out. If not I can always vent the cowl later.
The to-do list is down to just a few things. Mount the switch for the power box along with the led that indicates low voltage. Do a full assemble and check the CG. Get the two batteries mounted and run the DA. It's really close and I am getting excited to fly it.
David



Old 07-23-2019, 12:09 PM
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So close I can taste it. My next post should be a flight report. I have the batteries mounted in the stock location but have not set the CG. So this may change. I do have room to move the engine forward 1/4" or so if it ends up with an AFT CG. And it might. The DA-60 is lighter than the DA-70 the plane was designer around and I used 2 elev servos instead of one. The Power Box also sits behind the CG and it comes in at 4oz. I do have 10mm longer standoffs than called for so that might be the saving grace. I'm going to try and balance it a little differently than I have done in the past. It is measured from the leading edge of the lower wing at the tip. So I am going to tape a 3" piece of LE stock to each wing panel at the tip set at the 3-3/16" CG. Then set the plane between two folding tables letting it teeter on the LE blocks. This should let it sit while I slide the batteries around. Even if I am way off fore or aft it should still sit on the tables.
Everything on the final setup has gone smooth. I did realize the inter plane struts have a left and a right and a top and a bottom. If you try and use them the wrong way the 4/40 pins that hold them in place will not slide into the hole on the wing section. I do need to take a round file and clean up two little trouble spots. The top left wing can be slid onto the wing tube and metal pins but is vary hard to get off. Also the top right wing hold down screw is difficult to start. 2 minutes with a round file should fix both issues. The wing bags came this week. They are a good fit, and have a place for both wing tubes and the struts. A bargain at $65.
Only things I have not done is install the LE shark teeth and apply the decals. I'm not 100% sure I am going to do either. I will probably maiden like it is and then do the teeth and some of the decals. I am curious to see the difference with and without the teeth in high alpha.
Other thing that struck me is the amount of throw this thing has. This is not my 1st 3D style plane but my first 3D style in this size. The ELEV for example hit the ground at full down deflection. I can see now why QQ said 400oz servos everywhere.

David
Old 09-10-2019, 12:31 AM
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Default Dle 120

Can this plane fly with 100 cc engine?
for extreme 3d flying?
Old 09-10-2019, 03:16 AM
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Absolutely not! It’s a rocket with a 70cc
Old 09-10-2019, 04:03 AM
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Originally Posted by rcalbuquerque View Post
Absolutely not! It’s a rocket with a 70cc
Rocket
​​​​​​..!
thanks..

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