RC Conversion of Estes Skydart II

[Crawf56]

I have found myself wondering about making my Estes Astron Skydart II into an RC glider......



Hmmm..... I would like to go rudder-only. In other words, one-channel.

The idea is to develop a RC boost glider that someone who has NOT flown RC could fly. Just trying to get the model to land in the general area you want.

 

[Flyfalcons]

You're gonna need more dihedral to make rudder-only work.

 

[burkefj]

You could try some sort of pull mechanism that still allows the pop up elevons but still allows you to pull one down against the elastic to dump lift on one side and give you some turning.

 

[georgegassaway]

See my post in the "Estes Astron Skydart II from Arkansas" thread:

https://www.rocketryforum.com/showt...kydart-II-from-Arkansas&p=1665269#post1665269

Actually, the SkyDart will be controllable in glide with rudder-only R/C. I tested a couple of models which proved it.

Because the delta wing, with the large amount of leading edge sweepback, there is a decent amount of "Dihedral effect" even though it is flat. IIRC 1 degree of dihedral effect for every 10 degrees of LE sweepback (an old Model Airplane Rule Of Thumb, which generally holds up).

The main issue with rudder-only R/C is that on boost, it won't roll the correct way. Right rudder on boost would cause left roll. This was an issue for my shuttle models that used Rudder for steering control (I only used mixed elevons once and after a spiral-crash, modified that orbiter for rudder to steer it) I solved that by making the rudder reversed for boost (right rudder stick caused left rudder movement, causing right roll on boost), then flip the boost/glide toggle switch to glide to make it move the normal direction.

But if you do a model that won't require boost correction in pitch, then roll reversal isn't a problem for boost. Of course if it is rudder only there's no option for correcting boost anyway.

 

[Crawf56]

George, thank you for commenting on this thread.

When I looked at your website, it seemed your Skydart(s) had a full rudder (going the full length of the vertical stabilizer).

How did your Skydart react to your rudder setup? [Edit: Hard turn? Soft turn? Do you know the rudder movement distance?]

What I have considered is making a small rudder, that is roughly half the length of the vertical stabilizer, perhaps located at the lower half of the vertical stabilizer.

George's Twin Gliders (see "Skydart Twins") website: https://georgesrockets.com/GRP/GLIDERS/Twingliders.htm

 

[georgegassaway]

See the drawing below which shows the hingeline location for the rudder (In the on-the-pad photo, the red stripe is red monokote as a hinge)

The above was a piggyback glider, so it had the luxury of storing the radio gear inside of the BT-50. As I mentioned in the other thread, with today's micro gear, it may be possible to store the radio gear in the side air scoops and keep the inside of the tube available for the internal pop-pod. But I really wanted to do a "Space Twins" type project with a core rocket and two piggyback R/C Skydarts, so it was easier to mount it all inside the BT-50. But I never did get around to making the 2nd glider.

The amount of rudder travel left-right, not sure (I did that one around 12 years ago). Probably no more than 3/8" each way (3/4" total), perhaps more like 1/4" each way. But I don't think I gave it full rudder very much. One thing about rudder-only models is that if you give hard rudder and hold it, while the model does turn hard, it also noses down and ultimately would spiral-dive until rudder was released, then it would begin to level off and the excess speed from the shallow dive would cause it to zoom up and stall some. So, rudder only flying while simple in a way, actually is a bit trickier for an R/C pilot who is used to having elevator control to hold a bit of up when turning, or giving some down elevator to kill off a stall.

So, the harder the turn, the more the nose will want to pitch down and the model will pick up speed. Better to give it gentler turns.

Rudder-only flying for a model like this, perhaps better to think of it as being able to "adjust glide trim" to gradually turn a little bit left or a little bit right, with very wide turns. So to do that, means not a lot of rudder throw to begin with, and limited control with the transmitter. For a project like this, if you have a computer radio or if it at least has dual rates, then set up the rudder for "low rate" that you'd use most of the time for smooth control, and only have "high rate" available on a toggle switch in case you needed more throw for some reason, or if on the first flight it turned out that low rate was just not enough so you needed more. Better to under-control than over-control.

 

[Crawf56]

OK, let's cut up a perfectly good glider. Here we are:

 

[Crawf56]

The CG for the glider (without motor & pod) is 5 inches from the back of the fuselage/tube. I marked it with a silver Sharpie:



My plan is to locate the servo, battery, and receiver along the outer side of the fuselage. Must do this so that they do not interfear with the pop-pod. I plan to hold the servo in-place with epoxy or hot glue (or both).

 

[Crawf56]

More "progress". I have the receiver in place. The idea is to "hide" a portion of the receiver in the wing cross-section.

 

[Crawf56]

More looks at the receiver. This is a Futaba R2006GS; it is a standard size receiver, although it is light.

 

[Crawf56]

Looking from the wing edge.

 

[Crawf56]

Front view:



Trying to keep the front area "balanced". I plan to add balsa in front of the servo & receiver to help with aerodynamics.

 

[Crawf56]

Cut out for the rudder:

View attachment 311591

 

[Crawf56]

Rudder held to the fin with Blenderm tape. Here is the assembly:

View attachment 311592 View attachment 311593 View attachment 311594

 

[Crawf56]

OK, rudder cut out again:

 

[Crawf56]

Rudder assembly, again:

 

[Crawf56]

Without RC gear, the Skydart weighs 56 grams.

With the receiver, servo, and a 1s 3.7v 350mAh Lipo battery, the Skydart comes out to 85 grams.

But I still need to add some balsa to shield the servo & receiver.

 

[Crawf56]

You could try some sort of pull mechanism that still allows the pop up elevons but still allows you to pull one down against the elastic to dump lift on one side and give you some turning.

I haven't explored this option, but it is a pretty good idea.

I also considered two servos, and flying with a setup similar to your Dynasoar delta wing rocket gliders.

The receiver and servos that I chose are simply items that I have on hand. I was inspired by the "rudder only" control of the Skydart at George's website.

FUTURE PROJECT: Flyzone INUM Micro https://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXEVZW&P=0

What I have also been wondering about is a "kit bash" of a Tower Hobbies INUM Micro. For $40, you get a radio, a battery, and a powered micro RC airplane. The model is two-channel control: motor [elevator] and rudder. The INUM Micro is an indoor flyer.

The thought is that you take the rudder off the INUM Micro, and put it on a Skydart. Use the RC gear, and you have an RC boost glider trainer for about $60 total cost.

 

[Crawf56]

Here is a "flight test mode" glider:



At first I thought, "Yeah, I'll just stick the battery underneath." Later I thought, "Are you nuts?"

 

[Crawf56]

Here is a closer look:



I packed the battery connection between the fuselage and the balsa in front of the receiver.

 

[Crawf56]

GLIDE TESTS:

Well, I got that feeling again: This may be a Bad Idea.

The Skydart DID 'sort of' glide. But it was hard to tell if it was successful. Since I have more weight, I also have a steeper glide slope; and hand-launching doesn't get you a good enough height.

The small rudder seemed ineffective.

So, here is what I'm going to do:

1) Move the battery to the top of the glider.

2) Increase the size of the rudder.

By adding the balsa, my overall weight went up to 88 grams. I find myself wondering if the weight should be 70 grams, or less. :eyeroll:

 

[TheTellurian]

The thought is that you take the rudder off the INUM Micro, and put it on a Skydart. Use the RC gear, and you have an RC boost glider trainer for about $60 total cost.

The rudder on this is driven by an actuator, you can see the orange thing on the middle of the tail, and has no power at all for anything bigger or faster than the INUM. Save your cash unless you want an indoor flier. I had a Silverlit original version which was fun for a couple of weeks but there's much better stuff out now.


Richard

 

[Crawf56]

The rudder on this is driven by an actuator, you can see the orange thing on the middle of the tail, and has no power at all for anything bigger or faster than the INUM. Save your cash unless you want an indoor flier. I had a Silverlit original version which was fun for a couple of weeks but there's much better stuff out now.


Richard

When you say "no power at all", are you saying that you do not think the rudder mechanism will survive boost? My thinking was to attach the INUM fin and rudder to the fin of the Skydart.

 

[mr_matt]

When you say "no power at all", are you saying that you do not think the rudder mechanism will survive boost? My thinking was to attach the INUM fin and rudder to the fin of the Skydart.

You might want to try one of these:

https://www.micronwings.com/Products/ReceiverRx62H-DSM2CompatibleLinear5ChBrick/index.shtml

You can also tear one out of an old Ember or some sort of horizon hobbies plane.

The receiver (including both actuators) and a one cell battery together weigh maybe 8 grams. That is probably less than 1/2 of what just one of those servos you have weigh. I have used this on 2 different rocket gliders and they work fine, very robust.

 

[Crawf56]

Some of the Spectrum compatible receiver/servo combinations look good, but I am constrained to Futaba or Tactic equipment.

I did find a Tactic (see Tower Hobbies) micro receiver and servo that might reduce my flight weight.

The receiver, servo, and 350mAh battery that I am using come to 26 grams. With a micro receiver, micro servo, and a 70mAh lipo, I can reduce the weight to 8 grams.

 

[georgegassaway]

Definitely make the rudder bigger.

The receiver, servo, and 350mAh battery that I am using come to 26 grams. With a micro receiver, micro servo, and a 70mAh lipo, I can reduce the weight to 8 grams.

Man you added a lot of weight. I'm really surprised by the 350 mAh battery. I hope that's single cell. I don't even fly duration R/C RBG's with more than about 110 mAh, unless they need noseweight or if I expected to try to set a duration record (though most of the duration models are using 2S 7.4V packs). 50 mAh to 70 is more like it for this (Actually there are some 30 mAh LiPo's too)

I'm using Spektrum gear, so I do not have a good idea on a suitable receiver (I'd look at what Hobby King lists, not necessarily buy from them but as a good place for researching options. And I have used some micro "Orange brand" HK receivers that worked well enough for limited-range models like this). While my first-ever R/C gear (1975) was rudder only with a magnetic actuator (Ace Pulse Commander with "Baby" actuator), I like using servos (I do count the exposed worm gear types as "servos" too).

OK, there is this 2 gram servo. I think it is the same one kind I used a few years ago. Crazy small. Like 1/4" thick and about 18mm wide and 20 mm tall. Worked pretty well, but a year or two later two of five 2-channel models that used them had a dead servo (20% dead servo rate). At least they were dead at start-up, never died in flight. Now, that was years ago so perhaps they solved that issue (I must admit I have had a couple of "Ember Brick" receivers also have one of its servos go dead over time). In any case since this is rudder-only, not elevator, I think it'd be OK to use for this.

https://hobbyking.com/en_us/hk-282a-single-screw-ultra-micro-servo-2g-0-2kg-0-08sec.html

As for the glide slope being poorer, actually the angle of the glide slope should be about the same. The heavier the model, the faster the glide.

 

[TheTellurian]

When you say "no power at all", are you saying that you do not think the rudder mechanism will survive boost? My thinking was to attach the INUM fin and rudder to the fin of the Skydart.

That actuator is a magnetic coil with a magnet floating inside. No gears or anything to hold position as in a regular servo. That means it will have no force available to hold the rudder in position since its movement is based on the amount of current in one direction in the coil and that direction is where the force of the servo will be applied. At rest there is no current so it applies minuscule force to counter act any motion caused by the control surface fluttering. The foam is also weak so yes I think it will likely shred on boost and probably not have enough strength to do any work in a model of that size. mr_matt or George's suggestions are far superior or you could get individual linear servos that are only a gram and a half.



Richard

 

[Crawf56]

That actuator is a magnetic coil with a magnet floating inside. No gears or anything to hold position as in a regular servo. That means it will have no force available to hold the rudder in position since its movement is based on the amount of current in one direction in the coil and that direction is where the force of the servo will be applied. At rest there is no current so it applies minuscule force to counter act any motion caused by the control surface fluttering. The foam is also weak so yes I think it will likely shred on boost and probably not have enough strength to do any work in a model of that size. mr_matt or George's suggestions are far superior or you could get individual linear servos that are only a gram and a half.



Richard

Thank you. A very good explanation.

 

[Crawf56]

OK, decided to follow the excellent advice I have received on this thread; I removed the 'heavy' RC components.



In the next couple of weeks, I will get micro components.

 

[Crawf56]

And....the micro components have arrived. Old receiver, 350 mAh lipo battery, and Futaba 3114 servo on the left. New Tactic micro receiver, 70 mAh lipo, and micro servo (says its 2 grams, it weighed 3 grams).



Components on the left: 27 grams.

Components on the right: 7 grams!