|Sep 05, 2011, 03:04 PM|
E-Mirage with VLP and a few other changes
That was a dirty trick throwing out an odd ball abbreviation like that. Hope I can keep your attention long enough to help me come up with some good ideas
VLP is Very Low Power-loading.
Im wanting to build a Mirage with a power system that has a final weight no higher than the original design - maybe even a tad lower. Id love to end up in the low 30 oz range.
The main reason for this is I love soaring and trying to find light lift - BUT - I have 2 bad knees, a bad back and bad right shoulder. That makes hi-starts, winches and discus launching pretty difficult for me.
Getting old sucks!
Most power systems in sailplanes are capable of getting the model up in about the same time as using a hi-start or winch and they are designed to allow multiple climbs.
That means adding a significant amount of weight in motor and packs.
I dont want to add any extra weight if i can avoid it. My goal is to preserve the original thermaling capabilities and flying charactistics of the model as much as possible.
That means some trade-offs.
Im willing to give up steep, rapid climbs and multiple climbs. I dont mind if it takes 2 minutes of gentle circling to get to hi-start altitude and I dont mind recharging between flights although two climb outs with a slight reserve will be my target.
Im going to start out with a +- 70 watt setup (30-35 watts/pound) which should weigh under 3 ounces total. 2S 740 lipo, 27 gm Custom CDRom motor, Phoenix 10 esc.
The thing is - I have no experience in trying to fly a big model like a Mirage on such a low power loading. I think it will work ok, but I'll have to try it and see.
I am hoping someone has already tried it and can give some advice
First flights will be with a simple rubber band prop saver and non-folding prop until I get a feel for what I will need for the final set-up. Then I'll change over to an appropriate folder setup.
Which brings me to my next question - does anyone know of any really light weight folding prop setups? Size will likely be in the 10"-12" range.
Ive only used the Aeronaut Cam setups and was hoping for something less beefy - I dont need all that strength
Some other ideas Im going to try for weight savings else where.
1) Borrowing from DLG's - a pull-spring linkage setup for elevator, rudder.
2)Single spoiler servo mounted in the center of the wing with pull-springs again.
The next several ides I got from Riserflyer - Thanks again!
3)Thin carbon fiber tape on the TE after scalloping to help with strength. Im worried about the covering distorting the TE after scalloping plus hanger rash etc.
4)make up some 'balsa-ply' bulkheads instead of the ply supplied in the kit.
5)Ballast tubes that can be inserted from the front canopy.
6) removable tail surfaces. I may just do a removable elevator if i can think of a light enough way to do it.
Other than the things above, the wings will be stock with no extra strengthening added.
Oh - I may do carbon tube type wing joiners on the outer tips. Have to think about that some more - dont want them toooo strong.
I dont need all the strength for hi-start or winch launches or for contest landings, so I will skimp where I can.
Any advice, tips etc would be welcome
|Sep 05, 2011, 04:05 PM|
I'am in the same boat with the bad legs etc so i have two E powered planes in the works a 60" & 144" both using a Mirage wing, my concern is that you might be too under powered to get to 500 ft without a thermal because the airspeed is so slow that you use up the batterys before you get there.
I too am concerned about the extra weight of the power system but with these very light floaters sometimes you need a bit of ballast to get them going, my Paragon was stock and it was 45 oz and flew pretty good in all weather with no extra weight ever.
So on my 60" i will have some extra power and just learn to fly it that way and my big one will be the same way as i like the idea of having the reserve power to get out of trouble if need be and save my plane's.
Just my thoughts on E birds after doing a lot of thinking about the same thing you are.
|Sep 05, 2011, 04:39 PM|
Im a little worried about being under powered too. On the other hand, Ive seen many setups that were in the 100 watt/pound range that still climbed like home sick angels!
I started restoring an old 2 meter glider for my grandson to learn on. He would much rather start off with a turbine F-16, but this is what he will get Its almost ready to go. I need to get him over to help with sanding, covering and other details so he feels like its "his".
I will play with it first to see just how low a power loading I can get away with.
Im also going to put the pull-spring controls on it and add a spoiler, so I'll get some practice before the Mirage starts
|Sep 05, 2011, 10:31 PM|
Flys great at 40.5 oz
I wouldn't get too concerned about weight. My Mirage weighs 40.5 oz with this power set up:
Speed control: Turnigy Plush 40, 33grams, $23. But since I only draw 21.1 amps max,(249 watts), a Turnigy Plush 30, 25grams, $12 would work fine.
(from Hobby City)
Motor: KDA22-20L with 10-6 Graupner CAM folder. Motor weighs 85gram, $14.
But you might get by with the less powerful KDA22-20M.
Note: I reversed the shaft on this motor for in-front-of-firewall mount and built a balsa shrould around the motor out of a balsa block.
battery: I am using Zippy 2200mha, 3s, 20c, 180gram, $9.
But I could easily use the Zippy 1800mha, 3s,20c, 152gram, $11.
Or, you could buy a high discharge 1200mha 3s battery
Spinner: 30mm dia./3mm shaft # FS30-3.0, $3.50.
Note: be sure and use thread locker on the two nuts holding blades.
Blades: 10-6 Graupner CAM folder. Buy from Esprit or Hobby Lobby.
Like I said, this draws 21.1amps max and climbs out very nicely.
So, I think you would not be unhappy with a weight between 35-40 oz.
Like yourself, I am addicted to light weight RES sailplanes. But this 3 meter Mirage does all I want at 40.5 oz.
By the way, I use two HS-55 servos for spoilers, mini servos.
The only mod is to the center wing. I applied one strip of carbon to bottom of spar(probably not required). I also wrapped the spar in select areas with kevlar thread.
|Sep 05, 2011, 11:28 PM|
Thanks for the feedback Craig. You're probably right about the weight.
Still, Id really like to see if I can get a no-penalty power system to work.
Your power system comes in at about 10 oz. That means your airframe came in close to 30 ounces. That sounds like a very good weight for the Mirage.
Did you do anything to lighten the structure? Light weight linkages or?
Ive been playing with MotoCalc and its predictions look promising. I tried it with the Sig Riser 100 as the model, lowered the weights to what Im expecting and it looks like I can get a 300+ foot/minute rate of climb with around 75-80 watts. That would be good enough for me I think.
I may need to increase the pack size some to get two full climbs with some reserve though.
|Sep 06, 2011, 07:03 AM|
Don't know what makes the biggest weight savings. But try to look on your problem this way.
I think most weight of the power system is in batteries (cca 180 gram using craigrrr's setup). When using speed control with BEC, this makes light to no issue.
Then comes motor - cca 85 gram. You can have it a bit lighter, but this will not save too much weight I think.
ESC - not too much effect going with some lighter one.
You can save some weight on servos (one standard servo = 45 grams, one micro servo = 20 grams).
Another point of view is weight distribution. Heavy nose (motor) will make you to add ballast to have CG right.
Sorry - lot of ideas but no advice
|Sep 06, 2011, 11:39 AM|
Joined Jan 2005
My glider version of the Mirage came out to 36 oz with 4 oz of lead in the nose. So I would think you should be able to stay under 36 oz with motor and battery. Also, if there is any wind I use several ounces of ballast and during TNT last year I had about 10 oz of ballast for 10-15 mph winds.
|Sep 06, 2011, 04:43 PM|
United States, CA, Davis
Joined Oct 2006
My pure glider Mirage (short kit) came in at 35 oz and I ballast to 39 or 41 oz when the wind gets up to ~10mph. It flies very well in this weight range. I use JR 368s for rudder and elevator (over kill, could use lighter servo), a 5 cell NiMH, about 1.5 oz of nose weight and two hs45s in the wing for spoilers. I also beefed up the center panel with selected hard balsa LE, spruce spar caps, with carbon on top and bottom, as well as shear webbing all the way through the center panel spars and half way out the tip panels, tapering in thickness as one moves out the wing, All stringers on center panel are spruce and the spar caps on the tips are spruce rather than hard balsa. I did the scalloping and used transparent light iron-on on the tips and worked hard to keep the tips light. The center panel is strong as a result and I used heavy transparent monocoat on the center panel to help ward off flutter on hard launches.
All of this tells me, with care, you can build an electric Mirage well below 40 oz, perhaps close to 35. It will fly well and you will enjoy it. Don't be afraid to strengthen the wing! I can push mine pretty hard on a winch and that is much more stressful than your motor climb.
I retained the ply tip joiners, but used 5 ply instead of 3 ply supplied and added a little carbon ribbon along the bottom/sides. You should let them break under duress. Much easier to replace the joiners than rebuilding a shattered wing.
|Sep 06, 2011, 11:27 PM|
Thanks for the encouragement guys.
I guess all that remains is to see just how low i can go with the power system and still be practical.
One thing that occurs to me - if I can get the packs located on the cg, then I could use batteries as ballast. Use small packs on no wind days and larger ones when its blowing. I will likely need longer run times in wind so I think I try to make that work.
|Sep 11, 2011, 02:49 AM|
I was given an old 2x6 that was in really rough shape. I decided it would be perfect for my grandson as a trainer - and to experiment with to see how low a power loading is practical.
I just got my Mirage kit but its going to take a week or two to build ( ), so the 2x6 will let me get a feel for what will work on the larger model.
It was in rough shape, so I stripped it down and made the following changes and up-grades.
removed the push rods and lead nose weight
re-built the rudder with about 20% larger area
removed excess gobs of epoxy, glue etc
gave the fuse a lite paint job instead of covering
added 2 spoilers in the wing with a single servo mounted in the center of the wing and pull-spring linkages.
added pull-spring linkages for rudder and elevator.
The new power system is a small Custom CDrom motor, Castle ICE lite 50 esc (for logging) and TP ProLite 2S 1320 pack.
The pack and speed controller are larger than I think I will need, but Im using them to start off so I have more flight time and logging.
All up weight is now 27 ounces.
Stock weight is normally 30 ounces and this one was about 33 to start, so Im ahead of the game already even with the added spoilers and larger tail and power system.
Once Im done logging I will switch to a Castle Phoenix 10 and save another ounce or so. If this works as I think it will, I will also be able to fly with even smaller packs for even lower all up weight - I hope.
For starters Im going to try props that will give me 30 watts and 45 watts peak. Thats with 9x5 and 10x5 props and is only pulling around 5- 7 amps peak.
Thats 17 watts per pound and 26 watts per pound. Well below what is normally considered the minimum power to fly.
I will be happy if I can climb to 300-400 feet in one to two minutes and do it at least two times with a little reserve for go arounds or returning up-wind.
We will see how it goes tomorrow on the maiden
|Sep 11, 2011, 02:28 PM|
Thats a pretty slick trick the DLG guys use. I dont have any pics taken yet but if you do a search in the DLG section, there are lots of posts.
Basically, you use a single string ( I use spektra fishing line) running from the servo to the horn on the control surface. You have a spring in the control surface at the hinge line that pulls the surface one way while the servo pulls it the other way.
With elevator for example - you have the spring installed so that it constantly pulls the elevator in the UP direction. The horn and string are installed so that the servo pulls the surface DOWN. When the servo relaxes, the surface goes back up. If the string breaks, the elevator goes to full up. Thats better than no control at all though
It works surprisingly well. I was very doubtful when I first read about it. I was worried about the servo being under constant load and would the spring be strong enough to actually move the surface. if it was strong enough - would the servo be strong enough to over come the spring etc.
Then I tried it and was very pleased with the results. It works great! A side benefit is that you get excellent centering even with normal servos!
True, the servos are under constant load but its not that bad. Just adjust your battery consumption allowances to compensate.
I just got back from the maiden and all surfaces - spoilers, elevator and rudder - worked perfectly with the pull-spring setup.
I even did some fast steep dives testing CG and the spring on elevator had no trouble pulling the model out of the dives.
If you were very nose heavy it might be different, but with good cg locations the forces on our sail planes are not that large.
I need to crunch some numbers from the logger and altimeter, but Im very pleased with the results so far just based on eyeballing the climb rates.
I'll post some numerical results shortly.
|Sep 11, 2011, 02:30 PM|
By the way - the pull-spring setup would make hooking up and removing the linkages on the tail of your Mirage much easier than what you're doing now. I'll take some closeup shots of how I did it. It turned out much better than I was expecting
|Sep 11, 2011, 03:25 PM|
MrE - I have a Mirage that was built just after the kit first came on the market. I'm not sure when that was but the model is probably about 30 years old. The model is standard except for added spoilers - which I have decided are not necessary.
About a year ago I put a light weight 200 watt power plant in the model, and had to put the battery in the nose to get it to balance with no additional weight. In fact the battery, servos and receiver are as far forward as possible. The model has a steady but modest climb and is very enjoyable for nice day thermal flying. As it sits the model weighs 42 ounces and thermals beautifully at that weight.
I suspect that you will not be able to put the battery on the CG of your model unless you add extra nose weight to balance.
|Sep 11, 2011, 04:42 PM|
Herks - what are you using for linkages in the tail?
If you're using any type of push rods, then the pull-spring setup will save a bunch of tail weight. Every gram out of the tail is equal to about 5 grams in the nose.
My pull-spring setup is probably well under 1 gram total weight including the springs. So if your push rods weigh say an ounce total, thats equal to about 5 ounces of nose weight. If they weight 2 ounces, then that might equal as much as 10 ounces in the nose.
That should be enough for me to balance the way I want to - I hope
Worst case, I may have to extend the nose a tad to move the motor forward, but I hope not.
Im hoping that the weight savings in the tail will allow me to balance the way I want to.
Im still crunching numbers on the first flights, but it looks like somewhere around roughly 20 watts per pound is giving me over 300 ft per minute climb rate.
Thats better than I had hoped for!
It looks like with an 800 mahr packs I can fly full throttle for about 4 minutes with enough reserve to soar power off for about 1 hour.
That means a total climb on that pack of 1200+ feet. So 2 climbs to 600 feet or 3 climbs to 400 feet etc.
Im going to do some more testing this afternoon - I forgot to plug in the altimeter for the first few flights on the smaller props, so Im missing some data.
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