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        Discussion The +'s and -'s of electric retracts on large jets

#1 Ron101 Mar 12, 2011 01:28 PM

The +'s and -'s of electric retracts on large jets
 
Iím new to electric retracts, just bought my first set for my new Habu. This craze has been building for some time and Iíve watched from the sidelines. While I do see the benefits for smaller planes like the Habu or maybe even up to 60 sized warbirds. I wonder if pushing electric retracts into larger planes doesnít open up a whole new set of problems.

Take for instance the 1/6 scale Jet Legend Hawk Iím building. It has large heavy gear, brakes and wheels. The plane has 7 gear doors, 5 of which need actuators the other 2 attach to the mains. The plane already has 8 servos for flight controls, now you would need to add 5 servos to work the gear doors, bringing us to a total of 13 servos.

So I see several issues at this point. One being, setup would seem like more of a mess than air cylinders. If you donít have 13 channels you now have to add expanders, how do you set up end points? Next I know from experience that gear doors in general need a little pressure to stay closed tight, this could lead to power drain on your system. What if a gear door or landing gear become jammed like they often can? Now you are putting huge strain on your system that could lead to brown out. How do you work the wheel brakes that are air actuated?

I would see the need for larger RX packs that can handle the strain or isolate the landing gear and gear doors to its own power system adding more complexity to the plane.

I have been using air retracts with great success for many years, when setup right they work great. The fuel to power them is as light as you can get, air! So why the need to add complexity, increase the chance of stalled servos or gear that could suck down your flight packs? Or the need to add bigger heavy RX packs?

I guess I donít get it? Iím a missing something? Is this a craze that will pass?

Sure seems like a hot item and everyone is jumping on board.... I agree for smaller stuff, but for larger planes I don't see the benefit.

So if you plan on moving on to larger stuff don't forget your air system skills you are going to need them :D

#2 Arngeir Blakseth Mar 12, 2011 01:48 PM

IMHO it only makes sense to use servos for gear doors if they are controlled by a sequencer, so only one wire plugs into the receiver and the rest is controlled by the sequencer. Stalled servos would be a bummer on gear doors, electric retracts usually have a overload protection curcuit so as to not blow any electronics or drain the battery down if they get hung up.

#3 Steve Haynes Mar 12, 2011 02:58 PM

Well, I would never use the RX pack for the gear, I would just use the signal wires from the sequencer than attach a seperate pack.

Really I am looking for simplicity and no leaks and not having to chug around with a pump.

Thanks for the link Erik!

#4 EDF Crazy Mar 12, 2011 04:57 PM

Ron, im with you on this one, but with my Hawk im going to keep it very simple and went with them because im not going to use cylinders or servos on my doors, The two main doors im going to leave off for now and just have the small ones attached on the struts, with the nose there are 4 doors on my hawk, im only going install two of them and make them close with a cable and have them spring loaded, these electric retracts are alot more powerful then the standard JL air retracts so it should work fine.

If i went with servo operated doors id use the jr expander, they can use a separate battery to power the servos that are plugged into them, so if one did hang up it would only drain that pack and not the main rx pack. you can set the end points on each servo with the expander.

#5 PhilLin Mar 12, 2011 05:20 PM

I've also been contemplating to give elec. retracts a try as a newbe. Looked into both the Eflite & RC Lander brands. Seems like the latter has more variety but Eflite has the larger units (60-120 size)? Sonic Electric (RC Lander) also suggest using ubec separate power. I understand while normal ops are at very low current, a stalled gear can gulp down 900ma:eek:

IIRC the Lander gear had a bout of poor gear teeth meshing problem. Hope they've corrected that problem. Like their controlled speed of motion.

Appreciate others sharing their experience.

Phil

#6 AIR SALLY Mar 12, 2011 05:52 PM

i have a set of elec retracts in a small 70mm Mig (exceed) i had some issues with the gear over loading due to a slightly bent nose gear wire ..cause a N/G up landing ...so the Elec. are not the end all system either. any way you do it you got to be smart and set it up correctly. air or elec. + one to what Steve said a seperate batt would be best ...that way you can still fly your plane ....you can usally fix a gear up landing damage.

#7 mpope1 Mar 12, 2011 08:24 PM

I have been using them in my T-45(90mm) and they really work great. The only problem that I am having is my nose retract slows down alot right before its done retracting. Can't seem to figure out why, no binding that I can see. The down side is it won't close the nose door, I had it working great, but now it stalls before the door shuts. Air wouldn't be an issue, would slam it shut!

#8 JimDrew Mar 12, 2011 09:31 PM

All of the electric retracts we have worked with have an over-current protection circuit that stops the motor in the event that the retract is jammed. This prevents a brown out from the current draw (which is less than 1A anyways when stalled before it shuts off). Considering that a single HS55 servo draws 750mA when stalled, this doesn't seem to be much of an issue using the receiver pack for powering these retracts. Now, having said that, we have not worked with the LARGE electric retracts, which surely draw more current. Isolating the retracts so they using their own power source is a simple matter of just using the GROUND and SIGNAL wires connected to the receiver, and the POWER and an additional GROUND going to a seperate battery.

#9 tomme21 Mar 12, 2011 09:33 PM

i own and fly the flyfly F-4, the Sapac Grippen, the hobby lobby Eurofighter and SU-34, the Flyfly mirage 2000, all are 90mm jets and of a big size.
i use nothing, and i mean nothing but electric retracts on all of these planes.
i tried the air thing, too many leaks you cant stop or find, and carrying around a handheld compressor or hand pump, well :censored:
i dont use a special battery pack for them, just plug them into the gear channel on my old fm radio and go out and enjoy my day.
yea, a problem here and there but NOTHING like air or mechanical retracts i used before.
i say embrace this new technology, its getting better all the time, stay away from the cheap electric retracts and you will be rewarded.
we need a company here in the good ole USA to start making these.
im just tired of all the chinese junk coming over on the boats.
buy yourself an airframe only and put in the good stuff and JUST GO FLY, thats what its all about, not wondering who you loaned your air pump to and now dont have it.
im loving this new stuff and i embrace it all the way.
i just wish i was younger so i could get to see whats coming down the road in the next 10 or 20 years.:)

#10 Ron101 Mar 12, 2011 09:37 PM

Humm... interesting
I thought for sure I was going to get jumped by everyone loving there eletric retracts :D. But it sounds like you guys are pretty realistic about them.

They can work good, but also have there down sides, is what I'm hearing here.

I'm old school I guess, I like air systems and enjoy setting them up...
But see how convenient electrics can be... For my Habu I just want to run out after work and bring just packs and the plane, so electrics should be perfect for it.

#11 stumax Mar 12, 2011 09:49 PM

Ron, the trick with servo operated gear doors is to make the holes in the linkage oversize and use small rare earth magnets to keep the doors shut. The oversize holes is so the magnets can shut the doors without fighting the servo, and it means you don't have to get the servo end points spot on as the magnets do the rest. It also means when the doors are closed there's no load on the servo, which is very important as you don't want the servo drawing current all the time. I used HS85MG servos for the big main doors on my Fei Bao F5E, just because I had them, but I'd recommend these:

http://www.hobbyking.com/hobbyking/s...idProduct=5709

or these:

http://www.hobbyking.com/hobbyking/s...idProduct=5503

I use them both in another model and they're great servos. I made my own sequencer, though, it plugs into the Rx and tells the doors to open, then the gear to come down, then closes the doors, and vice versa, and it regulates the speed of the doors to about 1 second opening or closing speed, which is important to reduce the load on the servo in flight (slam them open at full servo speed and the aerodynamic loads will be huge). Bear in mind that I can program my sequencer to limit the servo travel of each servo, so it makes life a bit easier. I can't believe that the electric gear manufacturers haven't some up with something like this themselves, it would make their gear much more usable in scale models. I've thought about making mine into a product but there's a lot of work to get in into a production item.

Stu.

#12 lightningmcnul Mar 12, 2011 10:08 PM

I use air in a lot of models, both warbirds and edf's i have a sequenced system on my tamjet and can say without doubt that as long as you take the extra 20 minutes to set them up they are great, my kits don't leak and work every time.

on the other hand i can deffinatly see the attraction with the electrics and will buy some in the future, the main plus i can see is that you don't have to have the pull-pull system associated with most air nose gears, this imo is the worst thing to have to deal with on a plane!!

I have seen electrics fail in my friend's planes a few times, he has chewed the worm gear in the nose wheel twice due to slightly heavy landings which i know air would have survived.

As has been said before i would deffinatly use electrics but there not perfect.


who here has tested the cheap HK/chinese electrics and what did you find out?

#13 jfetter Mar 12, 2011 10:38 PM

Quote:

Originally Posted by Ron101 (Post 17665087)
Humm... interesting
I thought for sure I was going to get jumped by everyone loving there eletric retracts :D. But it sounds like you guys are pretty realistic about them.

I'm with you, I like the solid, firm movement of air systems. I like the fact that if I have brakes and have air already, air retracts are the logical choice. I like the fact the gear can be beefy yet still snap up with authority, nothing prettier than a jet just clearing the ground and the gear goes up evenly and quickly (no slap though, you have to use restrictore to avoid that!). Electric is slow, sounds like a toy and most of the time looks spindly, no thanks, air for me!

Jack

#14 Erik v. Schaik Mar 13, 2011 01:11 AM

Quote:

Originally Posted by jfetter (Post 17665478)
I'm with you, I like the solid, firm movement of air systems. I like the fact that if I have brakes and have air already, air retracts are the logical choice. I like the fact the gear can be beefy yet still snap up with authority, nothing prettier than a jet just clearing the ground and the gear goes up evenly and quickly (no slap though, you have to use restrictore to avoid that!). Electric is slow, sounds like a toy and most of the time looks spindly, no thanks, air for me!

Jack

I thought restrictors may cause locking down issues on spring-air systems?

Regarding the worm gear, what will happen if a fail will occur halfway the retract movement? Will the worm be stripped on an unfortunate "belly" landing or will the retract be ripped out of the plane. Air retracts have this pro over electric when not locked...

#15 monkamarm2000 Mar 13, 2011 01:28 AM

Air is proven and reliable but can't really be all injection molded, nor made for a nickel in china, therefore I'm sure electrics from hobbyking will be in all our futures! Lol

Barry


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