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Electric Ducted Fan Jets Discuss electric ducted fan jets here including setup tips, power systems, flying techniques, etc.

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Old 12-30-2013, 04:38 AM   #1
fhhuber
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Default Dynam Me262 mods

You will see that my model has been around a while... Lost track of the number of flights and it bounced off a fire hydrant once. (straightened the wheels and went back to flying)

Stock as shipped, these have been clocked approaching 110mph. (with the bad CG) Moving the CG reduces tail downforce which also unloads the wing (and you don't have "dead lead" ballast) so they get a LITTLE faster. (maybe 112mph... haven't put a pitot tube in yet)

I got this plane to learn about the habits of the Me262 since I am building a 107 inch span one. The foamy paid for itself the first time I attempted hammering the throttle from a standstill, pointing out one of the worst habits the plane has... High power and no airspeed will flip the airplane.

#1: This plane needs the CG pushed BACK. Currently I use a spacer to keep me from pushing the battery all the way up to the front. I have it set at appx 1/3 inch back from the foam stiffeners/battery guide at the front of the fuselage. This is just about perfect when using 4S 4000mah.
CG as recommended in the manual is just WRONG and requires up to 8 oz lead to be added in the nose-gear wheel well.
OEM CG is to combat the plane's bad habit of the thrustline overpowering elevator at low airspeed with full throttle. Its better to just learn to manage the throttle, since the plane flies much better with the correct CG.


#2: Adding cooling airflow for the battery and ESCs.
Use a 1/2 inch dia brass tube, with sharpened end, to drill out the 4 gun ports as ram-air scoops.
(Mine are re-painted already)
Cut at an angle under the forward hatch magnets to allow airflow beside the battery. I also put in some foam tape to lift the battery so some air can go below it.
Then behind the wing I chopped a good sized air exit hole.
Further... I CAd the ESCs edge to edge with each other and chopped some windows in the heat shrink so the air flowing in the fuselage cools them better.
I can fly in 110F weather without having to worry about a thermal shutdown of the ESCs.

#3: Final mod is not complete and untested.
Set at the aft CG I have been flying with significant down elevator trim due to the keyed horizontal stab setting + downward 'lifting" tailplane airfoil effectively giving up elevator. This was needed to make up for the excessively forward CG as recommended in the instructions.
I broke the glue joints free, removing the horizontal stab and am in the process of converting the plane to have SCALE in-flight adjustable horizontal tailplane incidence.
(this will mess with my CG a little... I probably need to change my spacer)
I found that a Hitec 5245MG is a perfect fit for my desired servo location. This should be plenty of power for the purpose.
Carefully split open the glue seam on the upper back of the fuselage to route the servo wire and cut a relief hole in the fin well for the wire.
Re-glue the seam after running the wire.
Cut out the raised foam in the fin well (the bit that goes between the "tabs" on the fin is the same size as the servo) and relieve the fuselage side for the servo arm.
When the fin is screwed down the servo is secure
Install ply plates as pivot bearings for the horizontal stab's CF tube.
Final part is installing the front wire which the servo will act on to move the horizontal stab. This is pretty standard stuff for setting up a "flying stab" where the elevator is the whole horizontal stab.
The reasons for this mod are:
.... The horizontal was starting to come loose anyway
.... Experiment in how sensitive this will be on my larger model.


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Old 12-30-2013, 11:03 AM   #2
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Finished the linkage

The wire connecting the stabs at the front is secured with both screwed-on plastic straps and glued in place since it prevents the horizontal stabs from coming off the CF tube. There are clear screw straps on the top of the stab also since the foam won't hold a screw.


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Old 12-30-2013, 06:36 PM   #3
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Looking forward to seeing the rest of the mods I put mine away some time back as it was too fragile for my flying/landing conditions. If I get around to seriously reinforcing the nacelles with heat shrunk plastic cases, it might be a goer once again. Handlaunching required a bit of a headwind, but it is a fair bit lighter than stock, with no undercarriage, rudder servos and linkages. It flew rather well for what it is, but I am still undecided about the project as a whole. Great to see you are having a good run out of yours
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Old 12-30-2013, 06:49 PM   #4
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Ever since I got the 262 its been the plane I have flown the most.
I have to periodically straighten the LG struts but I fly off a decent paved runway.

The main gear did not come with set screws to hold the struts in place. They were just held in by friction. Not sure if that is typical or they left the screws out on mine.
I've also had the nosewheel steering linkage come loose. Just had to snug the nut back down and its fine.

Pretty slim complaint list really.
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Old 12-31-2013, 10:03 PM   #5
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In-flight adjustable stab incidence is all set and ready for test flight. I adjusted it to allow +/- 7 deg from the factory set incidence.

I expect that to have the elevator straight with the horiz stab that i will be flying at +3 to 4 deg vs original at high speed setting. (where I trim this airplane normally)

I may eventually mix the stab to the elevator in the computer TX. We'll see how this works out with it on a dial. Initial takeoff I plan to have it set + 3 with elevator straight in alignment with the stab. Last flight's (before this mod) trim had the elevator 7 deg down.

I popped the block out so I can push the battery forward... I need to compensate for the weight added to the tail.
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Old 01-16-2014, 07:29 PM   #6
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Finally got around to flying it with the adjustable stab. I didn't give it enough travel and it still has a slight down elevator trim with the LE of the stab as far up as it goes. But the adjustable stab does work. I can trim for level flight and loop on just the adjustable stab.
A little more carving to open the slot and an adjustment of the ATV will take care of that.

Overall its a successful mod.

The weight in the tail requires 4S 5000 mah to be as far forward as possible. 4S 4000 now have the CG too far aft.
Looks like I need to carve the fuselage foam a bit to let the 4000's slide forward more since my 5000's are getting old and are not giving the performance they used to.

I seem to get 3 1/2 to 4 years of use from a SkyLiPo (Nitroplanes.com) pack regardless of how many charges.
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Old 02-20-2014, 12:20 PM   #7
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Doing a pre-flight for this weekend, I noted the servos starting to fall out of the wings, so I went over the whole airplane.

I found a trailing link (not scale) aluminum strut nose-wheel retract at Nitroplanes and near-scale all-aluminum retracts for the mains at Hobby King. It looks nicer with these installed and they operate slower than the originals which is appropriate for the full scale aircraft's slow retract cycle speed.

I also altered the movement range of the in-flight adjustable stab since I had it at the + incidence (forces nose down) limit all the time and was still using some down trim at high power.

I've still been using slight up trim for landing approach. In power-off dive tests the plane holds a 45 deg dive from close to stall all the way down when trimmed for landing, so I know I'm very close to correct stab angle and CG.

I plan to mix the stab to the throttle and disable the TX's knob when I get the relationship figured out. More throttle forces the nose up so it needs pitch trim mixed to throttle.
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Old 04-01-2014, 04:16 PM   #8
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Crunchy noises Planted the 262 hard.

I found a weak spot that failed. The rear vertical stab mounting screw's plastic insert in the foam leave too small of a foam perimeter around the plastic. It takes this a while to fail, but you can expect it to fail eventually, just like the hinges.
It did take this one over 300 flights (well over 1 year) to fail... about 50 flights after the tailplane mod.

Probably not a fatal failure without my moveable horizontal modification. I'd expect it to show inconsistent elevator trim in time to find it.
In my case, the foam breaking free let the added servo move and that made the horizontal stab move, disabling the elevator.

Replacement ME-262 ordered... I'm just going to mount the stab at the angle where the old one flew best. +5 deg incidence vs the factory setting.
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Old 04-01-2014, 06:13 PM   #9
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Cool Fred,

Still on my bucket list. Eventually will be able to recycle a pair of 70mm edf's. and go with a kit version. How does she hold up on grass?

Wounded Warrior Fun Fly - Aug 16th ,2014 - Grapevine TX - Info link: https://support.woundedwarriorprojec...ising/RCPilots
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Old 04-01-2014, 08:02 PM   #10
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Depends on the grass...

The original gear has sort of soft metal strut, not spring steel/music wire. If the grass is rough it will bend the gear. They straighten easily, but you might break the plastic decorations off ("scalish" struts and gear doors)

If all else fails you can do a gear up landing and accept the scuffing of the nacelles. they are rugged but you'll scrape em down slowly.

Do not attempt hand launch... applying enough power at the essentially zero airspeed will have the thrust force the nose up leading to a stall and crash. Won't hurt much but you won't get in the air. Thes need a fairly smooth surface 9good gras can work... rough grass won't) for a decent take-off run.
I can get the plane up in 50 ft with no wind... but I normally apply power SLOWLY and take the full length of our club's 300 ft paved strip. Applying power too rapidly can easily result in uncontrolled pitch-up., stall and crash. I've looped it from a standstill just by hammering the throttle.
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Old 04-01-2014, 11:41 PM   #11
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Originally Posted by fhhuber View Post
Depends on the grass...

The original gear has sort of soft metal strut, not spring steel/music wire. If the grass is rough it will bend the gear. They straighten easily, but you might break the plastic decorations off ("scalish" struts and gear doors)

If all else fails you can do a gear up landing and accept the scuffing of the nacelles. they are rugged but you'll scrape em down slowly.

Do not attempt hand launch... applying enough power at the essentially zero airspeed will have the thrust force the nose up leading to a stall and crash. Won't hurt much but you won't get in the air. Thes need a fairly smooth surface 9good gras can work... rough grass won't) for a decent take-off run.
I can get the plane up in 50 ft with no wind... but I normally apply power SLOWLY and take the full length of our club's 300 ft paved strip. Applying power too rapidly can easily result in uncontrolled pitch-up., stall and crash. I've looped it from a standstill just by hammering the throttle.
Sorry to hear you put this one in. My S&B 262 is still flying after at least 30+ crashes, but it is a little unfair to compare EPP with a taped finish to the eggshell foam on the Dynam. I found the nacelles took a real battering on anything but the gentlest long grass landing, even when WBPU'd and glassed. Can't agree with the handlaunch thing entirely though; My GWS version hand launches very easily, the S&B needed a headwind, likewise the HET ( which was crap, if I have not mentioned it before), and the Dynam just needed a stiff breeze at 1/2 throttle. Of course it is a lot lighter than standard, with no U/C, retract and tail servo's etc. The pitch up is over stated in my opinion, and related more to abrupt changes in thrust, than the low thrust line. If you really hammer it at low speed ie: just after hand launching, it will try to 3D on you, but a steady gentle increase in power really dampens this. Treat it like the real thing; quick to think and slow to react. The original pilots on these things learnt very quickly that ramming the throttle to the firewall on take off was certain disaster.

I've also built two scratch versions as well, with no ill effects. Angling the nacelles down slightly is preferred, and your mod of +5 degrees on the horizontal stab is a really good idea. Good luck with the replacement version.
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Old 04-02-2014, 03:22 AM   #12
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Original full scale... hammering the throttle tended to blow the engine apart.

Can't complain about a plane being smashed if it hits near vertical at appx 110 to 120 mph...
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Old 04-02-2014, 08:13 PM   #13
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Originally Posted by fhhuber View Post
Original full scale... hammering the throttle tended to blow the engine apart.

Can't complain about a plane being smashed if it hits near vertical at appx 110 to 120 mph...
Guess 110 mph vertical would do it....you must have been reasonably high to put her into a dive that fast with no hope of levelling out. My experience showed that 35 mph would probably have done the job if it had been a vertical nose in. Broke the S&B 262's fuse in half one time doing an out side loop at distance and got disorientated up from down. Hit very hard nose first.....1/2 hour with the hot glue and some tape and she was flying again My Dynam had its tail broken from a direct strike by a masked plover, ( psychotic birds at nesting time), but gorilla glue fixes the foam fairly well. When I finish weather proofing mine in time for winter, I'm going to attempt bungee launching using a plywood plate just ahead of the wing saddle. Where the nosewheel is supposed to go is being used as a battery hatch, so there is room to work with.

No one is suggesting anything in common with the Jumo 004, but in practice, the principal is the same; a strange kind of scale quirk for totally different reasons....
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Old 04-04-2014, 05:05 PM   #14
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Note ... I probably could have gotten out the epoxy, gorilla glue and tape and put the old one back together. I just didn't want to work that hard.
Squished the nose , snapped off a wing just outboard of the tubes and ejected an engine nacelle. Getting the wing back together straight would have been the hard part.
It broke 3 blades off one fan (took a small branch up the intake), but the plane came with 2 spare fan rotors.
Now I have 2 spare fans and ESCs along with hardware and servos for another project... Almost $200 worth of parts if bought separately (the foam airframe turns out to not really cost much when you think of it this way) AND a good looking STRAIGHT airframe.

The new "RX ready" plane arrived.

Preventing what put the old one in... I am glueing the vertical stab to the fuselage in addition to attaching with the screws.
Lots of glue surface area.

Sanding off the paint before making any glue joint. And using a toothpick to punch holes in the foam so the Gorrilla "dries white" quick setting polyurethane glue can grip better. (nacelles to wings, horiz to vertical and vertical to fuselage)

EPO tends to have glue and paint peel off when it flexes, so roughing the surface and using any "trick" available to make the glue hold better is a good idea.

Then I plan to apply clear packing tape and skids to prevent scuffing the model as much if I drag a nacelle or wingtip. The runway I use most often is like landing on a big 120 grit sanding block.

***************

Note RE "recycling 70 mm EDFs" mentioned above.
The Dynam packages are essentially RX ready or "RTF" (gotta glue the same places on both) The only differences between the packages are : TX, RX, Battery and cheap charger are in the "RTF" package. Both versions come with pre-installed servos and fans.

There is another EPO Me-262 (same wingspan) out there that comes in ARF, no servos, fans or retracts... at almost the same cost as the Dynam's RX ready version. There won't be much difference between the two if you dropped in the Dynam fans ($45 X2 for fans with ESCs and some servos) There are some nicer retracts available, as mentioned, appx $60 to get them. So to have essentially the same plane you'd be spending $150 to $200 more.


People have driven the stock Dynam Me-262's fans and ESCs on 6S with no issues.
I don't see any need to push the thing with more than 4S. Performance is good already. I do have appropriate packs to do 6S 4000 mah if I wanted to.
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Old 04-04-2014, 10:58 PM   #15
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Sounds good; as much as it is a bit of a downer when you plant your plane, the upside is that the replacement one can get all the mods it needs from the start. Looking forward to seeing how the next one turns out
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Old 04-05-2014, 01:44 AM   #16
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The holes for letting cooling air in through the gun ports will be neater. because I'll use a better sharpened tube to drill them.

No moveable horiz stab, just glued on at the angle determined to be best instead of going by the alignment tab (toothpicks to pin it on place as the glue dried and they are buried so they never come out)

And the paint isn't beat up... yet.
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