Notices
RC Gliders, Sailplanes and Slope Soaring Discuss rc gliders,rc sailplanes and slope soaring in this forum. Thermaling techniques, airfoils, tips, etc

First Sailplane Questions

Old 08-04-2014, 04:02 PM
  #1  
crossman
Thread Starter
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default First Sailplane Questions

I have been flying glow, mostly a 40 trainer for a few years, but I have been considering an electric sailplane for awhile and these plans have caught my eye. http://www.modelaviation.com/thermix13
Since I am new to sailplanes, I do have a few questions about the plane. It seems like this would be somewhat over powered with the motor that is listed, am I missing something about sailplanes, or would something around 450watts be enough? is there anything about this plane that would not be good for a first sailplane? I do enjoy building, both kits and from plans, I have also looked at the Great Planes Spirit kit. Any advice is welcome, thanks.
Old 08-04-2014, 07:55 PM
  #2  
Flytoolow
My Feedback: (17)
 
Join Date: Feb 2003
Location: Coventry, CT
Posts: 403
Received 1 Like on 1 Post
Default

This would be fine for a first electric glider. It has so much power because you want to get up as high as you can and start soaring; also, to help balance out the model. As for its set-up, plug the rudder servo into the aileron spot as it will be easier to fly. Finally, balance it so it is level, with the absolute slightest amount of nose down. It will make it a very docile glider.

Good luck and I look forward to seeing your progress!

P.s. Make sure you have a little bit of washout on the wing tips.
Old 08-05-2014, 08:55 AM
  #3  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,425
Likes: 0
Received 22 Likes on 19 Posts
Default

It's a 64oz model which is a touch over 5 lbs. First off that seems a little heavy. And sure enough the wing loading is up at around 10 oz/sqft. That's a little high for a simple fly around model that you want to use for relaxed flying and thermal hunting. But once you learn a little more on an 8oz/sqft setup you might find that the added weight lets you move around the sky a lot easier with a better cruise speed.

It's pretty standard that with a 100watt/lb power loading that you can pretty much go just about straight up. So with the 700 watts setup providing 130 something watts per lb we're looking at a rocket like climb. But it's not over the top for contest work if that's your goal.

If you're only looking for flying for yourself and you don't mind if the model requires a minute of run time to reach 500 feet than you can get by with down around 70 to 75 watts per lb just fine. So a 400 to 450 watt setup will do nicely.

And the slightly lighter setup will aid in keeping the wing loading down a little.

It's a nice looking design that obviously pays some homage to the Bird of Time but uses more straight lines to make building a little easier.

But if I were building this design I'd modify it to lose the pod and boom like building method in favour of extending the pod fuselage back all the way to the tail. I'd do this for two reasons. First the sudden stop of the pod creates more drag than we want on a sailplane. But more importantly a stick build boom like this is bound to break frequently if the pilot catches a wing and causes a sudden side shift or full on ground loop on landing. The weight of the tail is simply going to whip the boom and snap it far too easily in anything other than a good smooth landing. A regular tapered box fuselage that extends to the tail will greatly aid in avoiding this aspect.
Old 08-05-2014, 12:02 PM
  #4  
rpschwenk
Junior Member
 
Join Date: Jan 2009
Location: cumming, GA
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default

Consider a radian from horizon hobby. A great way to start. The plane
flies great. Get the rudder elevator only, not the radian pro.
Old 08-05-2014, 12:48 PM
  #5  
Gadgeter
Junior Member
 
Join Date: Aug 2014
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Default

I started recently w the calypso 73" as my first 5ch sailplane. I have a DMX Radian that got me hooked!!!! but I wanted bigger and slower. I'm posting a piece looking for some setup help on DX6i but the plane seems like a winner when configured properly. I would recommend it so far.
Old 08-06-2014, 05:26 AM
  #6  
crossman
Thread Starter
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by BMatthews
It's a 64oz model which is a touch over 5 lbs. First off that seems a little heavy. And sure enough the wing loading is up at around 10 oz/sqft. That's a little high for a simple fly around model that you want to use for relaxed flying and thermal hunting. But once you learn a little more on an 8oz/sqft setup you might find that the added weight lets you move around the sky a lot easier with a better cruise speed.

It's pretty standard that with a 100watt/lb power loading that you can pretty much go just about straight up. So with the 700 watts setup providing 130 something watts per lb we're looking at a rocket like climb. But it's not over the top for contest work if that's your goal.

If you're only looking for flying for yourself and you don't mind if the model requires a minute of run time to reach 500 feet than you can get by with down around 70 to 75 watts per lb just fine. So a 400 to 450 watt setup will do nicely.

And the slightly lighter setup will aid in keeping the wing loading down a little.

It's a nice looking design that obviously pays some homage to the Bird of Time but uses more straight lines to make building a little easier.

But if I were building this design I'd modify it to lose the pod and boom like building method in favour of extending the pod fuselage back all the way to the tail. I'd do this for two reasons. First the sudden stop of the pod creates more drag than we want on a sailplane. But more importantly a stick build boom like this is bound to break frequently if the pilot catches a wing and causes a sudden side shift or full on ground loop on landing. The weight of the tail is simply going to whip the boom and snap it far too easily in anything other than a good smooth landing. A regular tapered box fuselage that extends to the tail will greatly aid in avoiding this aspect.
Thanks for the input,

I am not thinking about contest flying at this point, just some lazy drifting on a sunny day, down the road, who knows. So I'm thinking a little less power would be ok, and would lighten things up as well. The note about strengthening the fuselage is something I will think about also.


As far as the suggested ARF's, I appreciate the suggestions, but I really do enjoy building, so I am looking at plans or a kit,
Old 08-14-2014, 05:40 PM
  #7  
ARUP
Senior Member
 
Join Date: Jan 2007
Posts: 2,343
Likes: 0
Received 1 Like on 1 Post
Default

X2 on the Radian. Buy an extra battery or two. Only $100 and those little things are fun! They are great early morning or later in the evening flyers (i.e. calmer weather) and thermal very well. I flew mine this morning before going to work and got in a 12 minute thermal flight!
Old 08-16-2014, 05:51 PM
  #8  
RV Winkle
Junior Member
 
RV Winkle's Avatar
 
Join Date: Aug 2013
Location: Bowling Green, Kentucky
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default

Goldberg gentle lady or some of kits from Ray at Skybench but I think he is on hold for orders right now would be my suggestion

love breathing that balsa dust!
Old 08-23-2014, 07:01 AM
  #9  
limeybob
My Feedback: (6)
 
limeybob's Avatar
 
Join Date: May 2003
Location: Rockwall, Tx, TX
Posts: 1,008
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by crossman
Thanks for the input,

I am not thinking about contest flying at this point, just some lazy drifting on a sunny day, down the road, who knows. So I'm thinking a little less power would be ok, and would lighten things up as well. The note about strengthening the fuselage is something I will think about also.


As far as the suggested ARF's, I appreciate the suggestions, but I really do enjoy building, so I am looking at plans or a kit,
laser cut kit here.
http://store.laser-design-services.c...roducts_id=318
Bob
Old 08-23-2014, 05:30 PM
  #10  
crossman
Thread Starter
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by limeybob
That looks quite interesting, but this morning I came across an estate sale with a basement full of RC Planes, I picked up a large box of balsa and ply pretty cheap, so it looks like I'll be cutting this one out myself, I also grabbed a complete unbuilt Goldberg Tiger 2 kit.
Old 08-24-2014, 05:17 AM
  #11  
aeajr
My Feedback: (2)
 
aeajr's Avatar
 
Join Date: Jan 2003
Location: Long Island, NY
Posts: 8,573
Likes: 0
Received 11 Likes on 11 Posts
Default

Originally Posted by crossman
I have been flying glow, mostly a 40 trainer for a few years, but I have been considering an electric sailplane for awhile and these plans have caught my eye. http://www.modelaviation.com/thermix13
Since I am new to sailplanes, I do have a few questions about the plane. It seems like this would be somewhat over powered with the motor that is listed, am I missing something about sailplanes, or would something around 450watts be enough? is there anything about this plane that would not be good for a first sailplane? I do enjoy building, both kits and from plans, I have also looked at the Great Planes Spirit kit. Any advice is welcome, thanks.
Welcome to the world of RC Soaring.

First about the weight The specs say it is 64 ounces which is exactly 4 pounds. His wing loading says 10 oz which would imply 67 ounces. Close enough to say that it is nowhere near the 5 pounds that someone posted.

AT that weight a 450 watt motor would be more than adequate. That would put you at 112 watts/pound. You should get a crisp climb of at least 45 degrees and maybe steeper. However I see he has the motor and battery all the way up front so they may be there to balance the glider. If you go to a lighter motor you may want to be sure to offset that with a battery that will balance the glider.

While Dick says you could put a 4000 mah pack in it that would probably be around 14 ounces. That is a BRICK! Unless you need that heavy battery to balance the glider I would run an electric glider on much less, say 1300 to 2200 just to save weight, but that assumes you can balance it with a smaller pack.
Old 09-02-2014, 09:22 PM
  #12  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,425
Likes: 0
Received 22 Likes on 19 Posts
Default

You're right aeajr, 64oz is 4 not 5 lbs. I don't know where my math was when I posted that.

Common reports on models with 100 watts per lb suggests that the climb would be well over 45 degrees and closer to vertical. Some time back some brave soul here actually listened to me and put in a 75 watts per lb power system and reported that the model went uphill at about a 40 to 45 degree climb at a pretty fair clip and well above any sort of slow or near stall manner. So I tend to go along with the reports that 100 watts per lb is going to be more like a good clip at around 70 or maybe even more degrees.

I got a taste of this myself when I put together a flat foamie 3D model about 4 years back. With 120 watts per lb it not only prop hangs on about 2/3 throttle but it goes up vertically until I tell it to turn around on full throttle.

Last edited by BMatthews; 09-02-2014 at 09:25 PM.
Old 09-03-2014, 05:56 AM
  #13  
aeajr
My Feedback: (2)
 
aeajr's Avatar
 
Join Date: Jan 2003
Location: Long Island, NY
Posts: 8,573
Likes: 0
Received 11 Likes on 11 Posts
Default

A discussion on Watts/pound that I offer just for general reading, not directed to anyone in particular. Comments are welcome.

Note you can get high watts in two ways. You can go for a larger/wider prop or you can go for a deeper pitched prop. Both will drive up the watts/pound. However they favor different factors of flight performance.

A larger/wider prop tends to favor thrust which is what we look for on a thermal glider. Thermal gliders are optimized around lift at lower air speeds so we are not trying to make them fast, we are trying to get them to altitude quickly via a steeper climb capability. So we tend to go toward the wider prop that will produce the watts/pound we want. Think of this as working in a lower gear on your car in order to pull a heavy load.

Hot liners, pylon racers, etc. are built for speed. Here you spend your watts/pound on a narrower/deeper pitched prop that will produce a higher pitch speed. It might produce fewer ounces of thrust but will get the plane going faster in level flight. Think of this as high gear in your car to produce more speed but it might bog down the engine if you were trying to pull a heavy load.

The difference is that cars can go through a series of gears to get the power type desired at the speed desired. Aircraft with fixed props can't do that so we pick the compromise that works best for what we are trying to accomplish.

So, watts/pound defines a power pool that we tap into to achieve the type of performance we want. When I look at motor specs I am typically looking at what they will produce with the wider props. So lower Kv rated motors that spin big props but perhaps more slowly.

These are not hard and fast rules, they are generalizations. That is one of the reasons I turn to the calculators when I am trying to match up props with motors. Or I buy several different props, put them on the wattmeter to be sure they don't overload the motor, then run tests in the air to see what gives me the kind of performance I want.


What performance are YOU looking for?

The concept of over powered or under powered has to be measured against some performance criteria. Your criteria and mine may be different. 75 watts per pound is more than adequate for sport flying where time to altitude is more about convenience than any special target time or altitude.

I measure performance in how long it takes the glider to reach 200 meters. As an ALES contest pilot that is the spec I am most interested in when I am setting up a motor/battery/prop combination for a given glider. I have a device in the glider that cuts the motor at 200 meters so I time the climb at various angles to see what I get. My power target is typically 110 to 130 watts/pound. Higher works but this is my target range.

For example, my Radian, with stock prop, 9.75X7.75 reaches about 170 meters in 30 seconds at about 16 amps peak. Doesn't get me to the height I want in the time allotted. Change to a 10X8 prop and it gets to 200 meters in 28 seconds at about 19 amps. If I go to an 11X8 it gets to 200 meters in 22 seconds at 23 amps peak. I could try a 12X6 or a 13X? and see what they do if I wanted.

In doing the testing I take into account not only the time to height but the amps being drawn by the motor. Parkzone does not publish the max amps/watts for the Radian motor but I have looked at other "480" class out runners and they all seem to be able to take at least 25 amps on a burst so I figure 23 amps dropping off to about 21 is about as high as I want to push it and I don't need to get to 200 meters any faster than 22 seconds with a Radian.

I am only running for 30 seconds and that drops off to about 21 amps after a few seconds so I think I am OK. The motor will have 5 to 10 minutes to cool before I restart or land.

There is also structure to consider. The Radian is a foam glider. I am spinning an 11" prop now. The wider I go the greater the torque on the nose of the glider. If I put any bigger prop on this the torque of the prop might eventually twist the foam nose and warp or break it. I did see one person replace the Radian Pro motor with a very powerful motor and a 14" prop. Twisted the nose right off the glider.

My e-Supra is 68 ounces (3.4 meter wing) and the motor is putting out about 480 watts for 112 watts/pound. The motor/gearbox combo is spinning a 17X11 prop. The glider makes 200 meters in about 24 seconds and that is fine for my primary ALES contest glider. The Radian is my back-up.

So, just a discussion of considerations when you plan your motor/battery/prop combos.

Naturally, your smileage may vary.

Last edited by aeajr; 09-03-2014 at 06:21 AM.
Old 09-06-2014, 05:28 PM
  #14  
crossman
Thread Starter
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default

I appreciate all of the advice and suggestions. I have plans in hand and wood on order. I hope to start building soon and will return here for more advice, I'm sure. Prop size is probably my next big question.
Old 09-07-2014, 01:53 AM
  #15  
perttime
 
perttime's Avatar
 
Join Date: Dec 2005
Location: Tampere, FINLAND
Posts: 1,726
Received 7 Likes on 7 Posts
Default

The linked article said: "The motor I used—a BP Hobbies’ A2826-4 with a 14 x 8 folding propeller and a 4-cell LiPo battery pack—is more than is needed for relaxed flying. A smaller power setup could be used, but I enjoy the straight-up climb capability at times."
People have different wants and needs for electric sailplanes, including how fast they want to go up and how fast they want to glide.
One thing to consider is that the glider apparently balances with the suggested gear. If you use much smaller motor and battery, you MIGHT need to add some weight that is doing nothing.
Picking an electric setup has its pitfalls, so it is advisable to study the matter in some depth - or use combinations that somebody else has already proven to work well.
Old 01-18-2015, 04:57 PM
  #16  
Gadgeter
Junior Member
 
Join Date: Aug 2014
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Default

I can Recommend Phoenix Evolution or 2000 Made by Lanyu Now Volantex
I just crashed my Phoenix Evolution and I am extremely pleased with the way it held up. It came apart where expected and can be fixed The fuselage suffered no damage.
I would Highly recommend it for a beginner. It is also convertible from 1.6m to 2.6 m wing span.
Well built plane...EPO is incredibly strong. I don't know why all planes aren't made of this particular density EPO
Attached Thumbnails Click image for larger version

Name:	IMG_0042.JPG
Views:	251
Size:	1.59 MB
ID:	2065261   Click image for larger version

Name:	IMG_0038.JPG
Views:	256
Size:	1.34 MB
ID:	2065262  

Last edited by Gadgeter; 01-18-2015 at 05:44 PM.
Old 01-18-2015, 09:42 PM
  #17  
D400webb
Member
 
Join Date: Dec 2014
Location: South Central British Columbia
Posts: 35
Likes: 0
Received 0 Likes on 0 Posts
Default

I realize that you said you have yor plans and wood, but I still thought I'd add another two cents in terms of comments.

I'm in agreement with another commenter who suggested that the Thermix is a relatively heavy glider to start off with. If the comments suggesting that the large motor and battery pack are necessary to balance the plane are correct, then I suggest it is poorly designed for a starter thermal ship, since it will make for a pretty fast-flying glider. The motor seems like overkill. To give you something for comparison, the original Olympic II (an older, but highly successful starter thermal design) plans offered a glow-powered option (this was pre-e-glider days). The recommended glow engine, iirc, was a little .049 - this was considered perfectly adequate to launch this comparable airframe. The Oly II was a standard (100") glider with a flat foil (modified Clark Y), and has very gentle characteristics, one of which is a slow air speed, yet good lift. This is important in a starter glider since it gives the pilot a much improved ability to spot and react to thermals, which is of course the whole point of gliders.

Since you have powered flight experience, the added mass that would have a detrimental impact effect for true beginners crashing occasionally won't be much of a issue for you, but I still don't think this Thermix design is your best option to start off in thermal soaring.

Just my opinion.

Last edited by D400webb; 01-19-2015 at 08:54 AM.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.