what glider to build
I know this has been beaten to death but here we go.
I currently own a Roc Hobby V tail glider. It is a foam V tail of course which is 2.2 meters.
I have discovered I love to thermal. I also love to build.
I have been considering
A DJ aerotech Chrysalis
Oly II by skybench Maybe even the 3
A Bird of Time
and just because I have never built one of his kits before
the Stevens Aero Glider.
I want a glider that will blow my Roc Hobby foamy away!
I have been pretty successful at thermaling with it but I just think a balsa would fly better...
Will I really miss the ailerons and flaps?
If I decide I wanted full house which of the kits above would be easier to modify, and being in poor health, a motor is mandatory.
is way bigger really way better?
Oh ya... Why the hell isn't anyone making full house quality glider kits designed up front for a motor?
Any well built wood framed sailplane will outperform the foamies.
I'd start with Bird of time. Build is a little challenging in a couple of places but not hard if you pay attention to detail.
Use yellow wood glue (Alphatic resin... Titebone II, Elmer's Carpenter's Glue) for most of the build and use just the right amount for maximum strength with minimum weight.
You can convert just about any wood structure sailplane for motor-glider. Its possible to come out the same weight as a motor glider than as a pure sailplane because of the lead ballast typically needed for the sailplane. Then with modern digital mini or micro servos replacing the old heavy low power analogs the kits expect you can save even more weight (and often need ballast to make it fly right in windy conditions...)
You can't beat plain old yellow glue, or Titebond for building an airplane. As for electrifying these sailplanes, I did that to a number of models back in the mid 1980's, including a pair of Craftaire Viking 10 foot wingspan sail planes.
Both were first built as a pure sailplane, but after getting weary of winch launches, one was converted to electric power. That worked so well, the second one was converted the following year. Had a number of two hour plus flights on them. Heck, even in completely dead air, these models were capable of 30 minute flights. That was in the days of brush type geared motors, and boat anchor type Nicad Batteries. I used 22 "sub C" batteries and an Astroflight Geared 40 brush type motor. Now, with the LiPo batteries and high powered brushless motors, that would be a whole different ball game.
But, fair warning, when electrifying these larger models, be danged certain to put spoilers on the wings! These models can get caught up in thermals, where it is difficult to get them back down safely. Those spoilers make getting them back much easier.
One trick for dethermalizing is stand it on a wingtip and full up elevator... spin it down using rudder to keep the nose from going up.
Takes em out of 90%+ of thermals.
Or run in a straight line away from the thermal... wherever there s rising air, there is sinking air somewhere reasonably close.
Spoilers help... but won't get you out of some of the stronger thermals without good flying techniques.
OK what about the ailerons or flaps will I miss that?
Is it unanimous on not?
Ailerons and/or flaps can be fun to experiment with.
I've had 10 channels in a sailplane before. Not because you need that much, but because I like to play with strange mixing functions.
Those spoilers were nothing but a piece of trailing edge stock, inserted flush with the top of the wing. the hinge was plain old scotch tape. The servos pushed them up to a max of 90 degrees, on a linear control from the transmitter.
As to the size of the spoiler, it was about 1 1/4 inches by about 20 inches wide, that on a 10 foot wing. It was amazing just how effective that was on getting the model down.
You've gotten really good advice so far :)
I would add that with sailplanes size really does matter - a lot :) Id recommend the largest wing span you can afford.
The Crysalis is an outstanding 2 meter model but it will loose out to a larger wing span model most of the time.
I also highly recommend spoilers if you're not doing a full house model.
They will get you down most of the time just fine. For the real boomers you may still need to do what fhhuber recommended. I prefer to fly up wind if possible over spinning down but either will work. The spin maneuver is probably the most stressful option but sometimes its the only thing that will work.
Where spoilers really shine is in landings. Being able to land at your feet is really handy even if you dont ever fly in any contests. Sometimes its also really handy to be able to approach hi, then pop the spoilers and do a steep decent without picking up a lot of speed and then land in a small area - preferably near you so you dont have to walk a mile to retrieve the model :)
Of course, if you build a model with flaps and ailerons, then the flaps take over for spoilers as far as landing control and de-thermaling.
All the models you listed are RES - rudder, elevator, spoiler designs. If you want a ship with ailerons you need to look at different models. People have added flaps/ailerons to some of those models but I dont recommend it. They arent designed for that and will end up heavier - which is not the best option.
Also, I agree with fhhubers comments on weight.
Save weight everywhere you can and resist beefing anything up!
With electric launch, you do not need to add anything to these wood designs. In fact, you can lighten up the structure if you know what you're doing.
You also do NOT need tons of power for a sailplane. Extra power is just extra weight/ballast that you cannot remove.
Im flying my Mirage (112" 31oz) and my Bubble Dancer (127" 42oz) on about 80-85 watts/pound and thats enough for ALES contest flying. More than enough for sport flying. They will both climb out at more than 45 degrees and get to 652 ft/200 meters in 30 seconds.
If you do want to do contest flying, then 100-120 watts/pound would be safer for launching in windy conditions, but no more than that.
Most guys seem to want to power their thermal sailplanes like they were 3D models or Hot Liners. Thats just carrying unnecessary weight.
A light model will reward you in light conditions. You can always add ballast if you want/need to fly in wind. Its much harder to swap out a heavy motor/battery if you want to fly in light conditions ;)
By the way, I highly recommend the Mirage if you want a real nice floater that can also handle a little wind. Mine came out lighter than the pure glider version. Its an incredible floater and indicates the lightest lift very well.
You can easily get a much lower wing loading with a Mirage than with any of those models you listed. If its windy, you can add up to a pound of ballast if needed. Its my favorite sailplane after the Bubble Dancer.
Id call Isthmus before ordering though. He is a great guy to deal with but he has been having issues with his lazer cutter and the Mirage was back ordered for a while.
If you do decide to go with the Mirage I can give you lots of tips :)
By the way, the only reason I dont recommend the Bubble Dancer - even thought its a much better sailplane - over the Mirage is the build difficulty. Its a very technically challenging build. Just gathering all the information you need is a real scavenger hunt :) The Mirage build is a breeze by comparison.
My Viking sailplanes with 10 foot wingspans, some 1500 square inches of wing, and 120 ounces was powered by those Astroflight geared 40 motors, and a whole pile of Nicad cells.
Power came out to about 80 watts per pound, and that was enough for a climb out of 45 degrees, and keep on going until it was hard to see.
As for wing covering, they were covered with transparent yellow monocote. The sun lights up that transparent stuff like a stop sign, making it visible for really long distances.
Its amazing sometimes to think about what the advances in power systems and radio gear have done for us. My Bubble Dancer is over 10' in span and weighs 1/3 what yours did. The Mirage is a bit smaller but weighs 1/4 as much!
Much of that weight savings is in the power system. Im flying the Bubble dancer with a small 57 gram hacker motor, 3S 850 pack and a Castle P25. The Mirage has an even lighter motor.
Hi Everyone. I really appreciate the responses.
Everywhere I read I am seeing... (If you don't build your glider perfectly straight performance will suffer greatly.)
Because of this, even though I feel I am a pretty good builder, I have decided to go with the Bird of Time ARF. I will build a Mirage later I think. when I have a better Idea how these things go.
Thank you Larry for pointing out the Mirage. It looks like an Awesome kit.
I will Not be trying to add Ailerons or flaps.. Drag is my enemy, I don't ever plan on competing (aside from the other glider lover at the field) and I really wouldn't even consider aerobatics on a Thermal Duration Soarplane, so I really don't think I have a real need for ailerons,
I picked the BOT primarily because of cost, reputation, and the fact that I personally think it is the most beautiful shape for a glider. No matter how hard I tried to not consider looks, I just kept coming back to BOT because of its beauty.
I now have some questions...
1. I see on all the build threads that everyone is chopping the front, gluing in a Firewall and mounting the motor on the inside. This nearly always requires the addition of Ballast in the front to keep COG. Also they are adding a pretty big battery to help compensate.
My theory is to: mount the firewall and either mount a motor on the front, or even extend the motor further forward so no Ballast is needed. I know from my experience that I really don't need to climb out more than maybe 3 or 4 times, so I am thinking I can use a 1000 or 1400 KV battery which is Hi C rated. This worked fine on my Roc V-tail which weighs nearly as much as the BOT.
I believe that it might be possible to keep the weight down to near stock levels this way.
Is this a good idea? I would build a cover for the motor out of some plastic or balsa.
My understanding is that there is a compartment under the wing right at CG that can be used for ballast, so I thought I would make some little weights which would fill this area at various depth by lining with wax paper then bb's poured in mixed with Epoxy. Thus giving me ballast when I want it at various weights
I cut my teeth on a Hawk sky and still fly it all the time and also have flown my Roc V-tail a lot
I land both of these by flying close to the ground then just pushing them down when I want them to stop. (6 inches or so down) This has never damaged either one, and this is why I will fly my Hawk sky in any wind it can move forward into.
For this reason I am thinking I at least want to fly the BOT a few times without spoilers. I have modified most of my planes according to to these threads and a few times I have regretted it. I am concerned about adding drag.
Your comments about getting out of thermals concern me however ... I have never experienced anything that a downward pointing attitude combined with a turn wouldn't easily get me out of. That said, I have never flown anything of near this caliber, so....
I guess I am asking... How real is this threat?
Also will a full range Spektrum DSMx receiver have enough range for me to not be too concerned?
I have been planning on buying the new Freesky Taranis, and I know the range is much better on this. I just blew my budget on the BOT and various motors servos etc.
Putting the motor in front of the "firewall" will work just fine. Its a little more vulnerable to landing abuse, but thats a trade off to the balancing issue.
The risk of getting stuck in a big thermal is real, but it certainly doesnt happen every day :) Your landing technique will not work as well with the BOT as it does on the smaller span models. It will get into ground effect and can be very difficult to force down - due partly to the longer wing span and partly to its higher mass. It will be more difficult to slow down just because its heavier.
Id put the spoilers in now. Much better than regretting not doing it :)
Your receiver has as much range as anything on the market - you will be fine.
Thanks Larry... I WILL take your advice on the flaps.
How long do I need to make them, and where on the wing should I place them. Obviously, the nearer the fuselage the better for the wiring part. But will this cause tip stalling because of reducing the incidence on toward the fuselage? Also do I need full deflection?
So here is another question
this plane calls for one full size servo. they spec
This is the Futaba S3004 Light Weight, Ball Bearing Servo.
This basic servo is used in cars, boats, or where standard servos are used.
Note: This servo is not designed for use with glow-powered helicopters.
This is a replacement for the following servos.(S15)
This servo can produce high-current draw from your batteries.
If using NiMH or LiPo batteries, make sure they are capable
of delivering sufficient amps.
Notice that they are saying it draws high amps... Will my reciever be able to pass this current?
I am guessing that the power is just wired through but this is the 1st time this has come up for me.
The Futaba 2004 "stalls" (when load stops the servo from moving) at about 2.5 amps. Any RX can handle 4 of them stalled. The ESC's BEC is more of an issue than the RX regarding current capacity.
The wires typically used between ESC and RX are good for up to 7 amps continuous. Higher current for very long any you can melt the insulation.
You'll find that appropriate servos in a sailplane shouldn't be an issue even with a "full house" setup having 6 wing servos. as long as they are not digital. Digital servos have a higher idle current demand and using a lot of them can require a higher power capacity BEC than is typically in the ESCs. More than 4 digital servos generally requires a stand-along high power BEC/regulator.
I would operate the spoilers with mini or micro servos to save a little weight. HS-81 is a little less than half the weight of a full size servo such as the Futaba 3000 series.
I wouldn't worry too much about needing to add ballast with the e-power Bird of Time. Without the e-power it used a LARGE chunk of lead for ballast.
Extending the nose forward can affect the yaw stability and might require the rudder and fin to be enlarged.
Than your suggestion is... install spoilers.
leave the fuselage the same lengh
add lead to the front as needed.
Why no ballast. Cause this bird penetrates well... or cause I have no business flying it if I need ballast to penetrate.
Add whatever weight is needed to get to CG.
Bigger batteries if they fit... mixing epoxy and lead shot and filling as close to the nose as possible if the batteries won't get you to the desired CG.
Ballast on CG for wind penetration is fine up to a point. Best to use bigger batteries if you feel it needs more weight.
You do have to remember that more weight means more stress on the wing in high G maneuvers. If you add 2 oz and pull 8 g you added 1 lb of force to the wing. Some of the maneuvers you can reasonably pull with the Bird of Time can impose more than 40 G.
"Dynamic Soaring" can impose over 120G and would shred a Bird of Time... its not designed for this trick to gain speed.
Seriously 40g? what would cause that?... as far as Dynamic soaring. I would buy that. I would have thought though that to putll 40G you would have to more or less turn your main wings at 90 degrees to motion at full speed. Although there is a lot of wing there still that seems extreme to me. Not doubting you... Just amazed.
On a powered acrobatic electric model, doing a quick loop resulted in a peak G force of 9.5 G's. That was on a giant scale "Big Stick" 3000 watt model. Similar results showed up on a smaller 1200 watt Kantana model. I never hit over 14 G's on any of the acrobatic stuff attempted. Now, you can buy this sort of thing, for a bunch of $$$$.
On my many sailplanes that were upgraded with electric motor power, I just extended the nose of the model forward to place the motor and battery pack at a location to allow balancing without the use of lead.
If you're scratch building your model, that's easier to accomplish, but on an ARF it's a bit more work. Be sure to buy your folding prop, and customize the fuse around the motor and prop so the propeller folds flush with the fuse.
As for the range of the Spektrum DSMX receivers, just about any 2.4 Ghz name brand radio will have several miles range. That is far beyond the ability to see the model.
As for those spoilers, I'd put them in. With electric power, you're able to get your Bird of Time model WAY up there consistently, where those thermals can become very powerful. And, spinning down a larger model such as this one can result in catastrophic failure.
Pattern RC aircraft have exceeded the limits of the Eagletree G meter for their telemetry system and they "peg" at 38G.
A snap-roll can be far higher G than a full pull loop.
Drum, are you going with flaps or spoilers? I'm adding spoilers. The wing outline is just too gorgeous to mess with. :)
The easiest way to do spoilers is use some 1.25" to 1.5" wide trailing edge balsa stock. Most hobby shops should carry it.
I would do one on each side of center panel towards the outer ends of the panel. I would start them 1 rib in from the end of the center section and make them 10" -12" +- long. They will be easiest to do if they are exactly 3 or 4 or 5 bays long starting at one rib and ending at another. They need to be just behind the spar or if the leading edge is sheeted past the spar, start them at the read edge of the sheeting.
Like fhhuber said - mini or micro servos should work well.
Added note. When cutting out the bays for the spoilers, be sure to beef up the left and right ribs on each side of the spoiler with a piece of perhaps 3/16 balsa sheeting, about 1/2 inch or so deep, parallel to the rib. The top of that beefed up 3/16 balsa sheet would be flush with the top of the ribs. Also, place a piece of balsa about the same size between the left and right ribs at the trailing edge of the spoiler, under the monocote. The leading edge of the spoiler would be at the wings spar. Then, hit the monocote with a monocote iron, securing the monocote to the balsa sheets.
If these areas are not beefed up, when hitting the wing covering with a heat gun or monocote iron, that rib is going to get pulled by the shrinking monocote. And, no amount of work will remove the resulting monocote wrinkle. Been there, done that.
Check out the oct 2006 RCSD article on adding spoilers to a BOT
Wow... I am so excited I could just.....
I ordered this cool motor from hobbyking
they have come out with a series of motor just for Gliders... It is an outrunner with a can around it to prevent friction in tight quarters. The wiring is just female connectors. Pretty cool
I ordered an 11X8 folding prop with 2 " hub
I am really startled by the pitch available on props. The 11X8 with a 950K V motor and 3 cell wants to go over 60... hmmmm
anyway I will definitely be only using 3 cell with this. I really wanted to find a nice 12 x 6 or so but couldn't find one.
Yakfishingfool I haven't decided yet.
Which Brings this up.
You guys have expressed that I really nearly Have to put spoilers or flaps on... I am not worried about landing... I know I can get this job done as I never even try to fly in close quarters..
That said the thought of getting caught in a thermal and not being able to get is terrifying....
Can someone PLEASE explain how this can happen?
I mean why can't I just turn out of it... or down elevator straight forward until I am out... Or use the throttle till I am out..
I don't understand how this can happen. I know from following the threads that you guys who told me this know what you are about... so I don't doubt that it can happen..... BUT
My analytical side has to know what the mechanism is that can cause this.
I really don't want to muck with this thing if I don't have to. I am buying it because I can get altitude on very little lift.. + as I said earlier... I just find it beautiful..
I don't want to add weight or muck with the shape of the wing....
So.... Someone please explain how it can happen and relate some experience.
Again I am not doubting you any more than I would doubt my Math teacher.... I just have a need to understand the mechanism, so I can assess the risk.
I purchased a Spektrum AR400 for this so if flaps are involved... I will be reversing one of them. Not a big deal I know of some nice hobbyking micros which I have done it on before. I usually use the Orange stuff. but I would hate to watch this plane just fly away from me and not be able to guide it back....Safety 1st. Or within reason... or I would have ordered one with an auxiliary reciever.
I am more excited about this than any plane before.... just cannot wait.
|All times are GMT +1. The time now is 07:32 AM.|
Powered by: vBulletin
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2005 WattfFlyer.com
RCU Eflight HQ