build thread -- RCRG based on Autonomy-1

[mikec]

As promised here's the build thread for a 2.6"-diameter RCRG based on a downscale of the Autonomy-1 rocket glider designed by Boris Katan and Dave Lindbergh, discussed in this thread: https://www.rocketryforum.com/showthread.php?t=23130

This started out as a straight downscale but I have since tweaked it to use a lower-mass nose cone for better CG. The wing will be a single piece of Adams Readiboard glued to the bottom of the BT, but since I can't simulate this, the Openrocket file shows a mid-wing configuration like Autonomy-1.

My RC electronics is a Spektrum AR6100 receiver, a Dimension Engineering ParkBEC switching BEC, and two Turnigy 9g servos. Power is provided by a 2S 360 mAh lipo, and the total electronics weight is only about 3 oz.

My mass target is under a pound and the sim is at about 0.8 lbs without margin for glue, pushrods, etc. The design has a wing area of 261 in2 or 1.8 ft2, for a wing volume loading of 16/(1.8**1.5) = 6.6, which is pretty low. I'm wondering if I want a smaller wing.



View attachment rcrg26.ork

 

[AstronMike]

As promised here's the build thread for a 2.6"-diameter RCRG based on a downscale of the Autonomy-1 rocket glider designed by Boris Katan and Dave Lindbergh, discussed in this thread: https://www.rocketryforum.com/showthread.php?t=23130

This started out as a straight downscale but I have since tweaked it to use a lower-mass nose cone for better CG. The wing will be a single piece of Adams Readiboard glued to the bottom of the BT

My mass target is under a pound and the sim is at about 0.8 lbs without margin for glue, pushrods, etc. The design has a wing area of 261 in2 or 1.8 ft2, for a wing volume loading of 16/(1.8**1.5) = 6.6, which is pretty low. I'm wondering if I want a smaller wing.

Why would you consider going to a smaller wing for this? Sure, a smaller planform is 'tighter' and can take higher boost stresses, but not overly so. Also do not see your elevons modelled in your pic, guessing they are large enough.

Did you see the EconoGlider picture posted under Tampa TTRA launch report on hcmbanjo's (Chris') blogsite? That is about what you want to end up with, and since you're experienced with RC, would really love the outcome on low/mid F power.

Sure wish I had the chance for some 'seat time' with an experienced RC'er who flys RCRBG to get the scuttlebutt on all the electronics and gear setups.

 

[mikec]

Why would you consider going to a smaller wing for this? Also do not see your elevons modelled in your pic, guessing they are large enough.

I guess my concern is too much sensitivity to wind on boost; I really want to not have to hand-fly it on ascent, but maybe that's stupid.

I'm planning on the elevons being full-span and about 1.5 inches deep.

Did you see the EconoGlider picture posted under Tampa TTRA launch report on hcmbanjo's (Chris') blogsite?

I did see the photos; I couldn't quite tell if you had used a single sheet of readiboard or one for each wing joined under the BT. I sized mine so I could use a single sheet, figuring that would be more robust.

 

[burkefj]

Mike is this going to be RC only? So no backup chute? If so, you should be able to get well under a pound. If you considered some other construction materials and are using 24mm motors, even in this size wing, you should be able to get around 10-12 ounces, or less. Cardboard tubes and plastic cones are relatively heavy.

The spektrum 6100, a bec, 400mah battery, and two servos, as you say are around 3 oz, the loaded motor about an ounce and a half. At this size and a delta wing you shouldn't need much spar reinforcing or any fiberglassing. A simple 6mm depron box 35" long won't weigh much more than 2-3 ounces, and then the wing foam maybe another 2-3 at the most.



Frank

 

[mikec]

Mike is this going to be RC only? So no backup chute? If so, you should be able to get well under a pound.

This is RC only, no chute, and I'm sure you're right, with Depron or even Readiboard box construction one could build something much lighter. But I don't really feel the need to make it any lighter. My sims show that at this weight I should have an acceptable flight on an E15 and still be able to fly on an F22 without getting above 1000 feet, and the wing loading isn't crazy high. For this one it's more about ease of construction. After it flies (or crashes) I may feel differently.

The inspirational thing about the Autonomy-1 project for me was that it was basically a rocket with big fins, not a complex airplane with a rocket motor like the Phoenix and Delta Star. Airplanes seem hard to design, build, and fly, but even I can build a rocket

 

[AstronMike]

I did see the photos; I couldn't quite tell if you had used a single sheet of readiboard or one for each wing joined under the BT. I sized mine so I could use a single sheet, figuring that would be more robust.

The planform is a 30" span by 30" chord delta as you saw. I use a single sheet for the spanwise portion, and this leaves needing a 10x10 triangle for the 'top section'. You can see where this is taped on. Yes, it is more robust for sure using a solid rear wing with a creased center than just joining two half-spans.

Also notice the top mounted elevator assembly the EconoGlider has rather than two outbound elevons. This is MUCH easier to actuate, from a free flight standpoint.

My version uses a regular BT80 36" long, and a cardstock rolled nose to save weight. The glider itself comes in at 8.7z, and with rear ejection weighted pod, 13.5z. That is about perfect for any E15 to F22ish motor. Since your RC gear weighs less than the pod does, there's no reason you cannot come in under 12z (you'd have to use standard BT80 and not the heavier stuff).

Why didn't I just use Depron, since I have so much of it? Well, the 6mm thick stuff doesn't weigh much less than Readiboard, plus it's not nearly as sturdy. Bear in mind, what Frank is doing is NOT the same as I do. He can use the 'barely gettin off the pad' E6 type motors since he's controlling it on the way up via RC. Myself, on the other hand, must use higher average impulse motors since they are free flight. IF you were to use the 24mm RC can motor like Frank, then Depron reenters the picture, but it does get pretty flimsy at increased sizes and spans.

I do like using the Quest D5 in Depron based gliders such as 2" Bomarcs and Marauder LV, plus some others.

 

[burkefj]

AstronMike is right, I'm building light, and can use a low thrust motor and steer on the way up. Since I don't need the high thrust, I don't have to reinforce as much. Carbon spars/strips go a long way to reinforce foam sheets. I have never used the redi-board so I'll defer to what Mike says on that.

The D-5's are neat motors, but they are about the same $$ as an E reload so I haven't used them much, they are lighter, but the burn is not as long, sort of a tradeoff.

If you have E-15's or F-22's and want to fly them, then yes, the extra weight will help limit the boost altitude, and damp down the boost velocity and make it easier to steer on the way up if there is any wind or trim issue.

I look forward to seeing it fly!

Frank

 

[AstronMike]

AstronMike is right, I'm building light, and can use a low thrust motor and steer on the way up. Since I don't need the high thrust, I don't have to reinforce as much. Carbon spars/strips go a long way to reinforce foam sheets. I have never used the redi-board so I'll defer to what Mike says on that.

Frank

I never have to reinforce Readiboard as long as I stay within E to F total impulse. Two plyed Readiboard works well on reloadable Gs, this is what the Astron SST (light version) is made of.

Whenever I use Depron in 20"+ span gliders using D+ impulse, then I usually reinforce it some. Usually go with the cheap shish-kabob skewers, these turn out to be cheaper than dowelling and seem stiffer. Sometimes have to splice two end to end to a wing's LE but that is no biggie. Minimal use of light weight chrome tape works best here.

Back in the 'old days', when I flew HPR gliders like mad 15-20 years ago, I'd go nuts reinforcing already strong stuff. Totally diametric to what I'm doing today.

 

[mikec]

I have the wing cut and mounted, the elevons cut and hinged on, the control horns mounted, and the vertical stabilizer glued on. I made the pushrods (old-school piano wire) and tried a quick dry fit of the servos. Looking good so far. Weight is 10.7 ounces without the battery.

 

[burkefj]

That looks good Mike.

Frank

 

[mikec]

Flew three times on AT E20 SU motors this morning. All in all I couldn't have asked for better performance. I programmed a slow roll into my transmitter and switched flight modes at apogee, so the ascent was hands-off. Glide trim wasn't too far off and while I could probably go to lower rates (I was using full rates and no expo for these initial test flights) it was perfectly controllable, though as I might have expected the L/D is not that great (I probably wasted a lot of glide doing turns.)

Next time on F22s? Or maybe F12s. Although the E20 seemed perfectly reasonable.

Video is at https://youtu.be/_qywtMh7D40

 

[burkefj]

Nice Mike, I think with gentler turns you could keep it up longer. Boost was nice with the slow roll.

Looked like maybe it ran out of elevator control near the landing, not enough airspeed/throw to flare much?

Frank

 

[mikec]

Looked like maybe it ran out of elevator control near the landing, not enough airspeed/throw to flare much?

Could be, or it could be my own marginal piloting skills. Most of my fixed-wing stick time is on a Parkzone Radian, which is so floaty that flaring isn't necessary.

I was paranoid about stability on boost, so I ended up adding about an ounce of nose weight (some in a larger battery) to insure that I had a solid 1 caliber of stability at launch. So it was pretty nose-heavy. I had 150% range of travel on the up elevator and full up was about 45 degrees of elevon deflection; trim was set at 70% elevator for glide and 20% aileron for boost.

I could definitely use dual rates on aileron because the thing is more responsive in roll than pitch.

Next time I'll fly a keychain camera so I get a record of the control inputs. I had one yesterday but forgot the memory card

What kind of CG/CP do you use on your gliders, Frank?

 

[AstronMike]

Nice flight there, Mike, for starters to get your feet wet!

As far as boost CG goes, better a little nose heavy than not, unless you are Frank, and don't needn't worry about such trivial things

Once you have this dialed in it will be even more impressive. Can't wait to see the vids when that occurs!

 

[burkefj]

Mike, on non criciform fuselage styles, with a rounded or vertical profile fuse only, I use a normal 10-15% stability margin for airplanes, for cruciform style fuselages or things with a lot of flat forward area, I've found the normal CP calculation not that good, and my CG normally has to be much further forward than a normal wing calculation would indicate. I've also tried using rocketry and RC plane calculators using extra fins simulating the forward fuse, but that isn't really that close either. I rely on my glide testing to bracket the rearward and forward CG range and have had pretty good success with that.

For boost I normally can get away with 1/4" of rearward CG on boost and still be controlable for a model that size, and then just run a lot of control throw for the CG shift.

For your plane with a rounded fuse and a simple delta wing, the CP calculations should be accurate. It sounds like you had plenty of throw, most probably just a tad nose heavy.

Frank

Could be, or it could be my own marginal piloting skills. Most of my fixed-wing stick time is on a Parkzone Radian, which is so floaty that flaring isn't necessary.


What kind of CG/CP do you use on your gliders, Frank?

 

[Adrian A]

Not that I don't have enough half-baked rocketry projects, but it occurred to me this morning that I have several RC flying wing gliders (Windrider Bee) for slope soaring, and several 38mm rockets. Maybe I should strap them together? Before I fly it as a rocket, though, I should see how much pitch control I get with elevon-only controls and a fixed tail.

I already had fun last spring duct-taping an SU E motor to the back of a Bee when the ceiling was too low for regular launches. On the second try, it even worked.

An I49 or I59 would be great for this.

 

[mikec]

An I49 or I59 would be great for this.

There's a guy in my club who regularly flies a big wing on a hybrid -- I think he's using a RATTworks I80. So it's definitely doable.

 

[mikec]

You can see some photos of the wing I mentioned in the last message at https://picasaweb.google.com/107158031171199223319/PlasterBlaster2011#slideshow/5675422560708112674 starting eight slides in.

Note that some of the covering appears to be coming off the starboard upper surface.

You should probably start a new thread if you pursue this, I've never flown a wing so I can't contribute much.

 

[philip]

Could be, or it could be my own marginal piloting skills. Most of my fixed-wing stick time is on a Parkzone Radian, which is so floaty that flaring isn't necessary.

I was paranoid about stability on boost, so I ended up adding about an ounce of nose weight (some in a larger battery) to insure that I had a solid 1 caliber of stability at launch. So it was pretty nose-heavy. I had 150% range of travel on the up elevator and full up was about 45 degrees of elevon deflection; trim was set at 70% elevator for glide and 20% aileron for boost.

I wonder whether adding a detachable upper section which ejects at apogee would make the glider more stable during boost? How to eject at that point would be another question.

 

[AstronMike]

I wonder whether adding a detachable upper section which ejects at apogee would make the glider more stable during boost? How to eject at that point would be another question.

I've done exactly this on both Saucer Gliders as well as the infamous Astron Triple Eagle, both of which you'll find reviews and reports of on rocketreviews.com.

It's like ejecting a nose cone with payload section on its own chute, with no shock cord to attach it to the 'body', which is the glider in this case. Sure, you're then gliding with the open tube, but at such low speeds, the extra drag isn't really bad.

Just ask Brainc of this Forum how his Astron Triple Eagle glides that way :eyepop:

 

[BobH48]

It's like ejecting a nose cone with payload section on its own chute, with no shock cord to attach it to the 'body', which is the glider in this case. Sure, you're then gliding with the open tube, but at such low speeds, the extra drag isn't really bad.

That would mean that you mount all of the radio gear outside of the body tube.

mikec, Is that how you did it? I didn't see any hatches in the picture.

I would like to try something like this but haven't done much of any R/C flying in the last dozen years or so. Can you get away with using something like Hitec HS-55 servos or would you need something stronger?

I was hoping that I could use my old World Engines Expert transmitter from the late 1990's and just get a lightweight receiver and servos. It has dual rates for aileron and elevator along with endpoint adjustments but alas, no elevon mixing.

Do you think that dual rates is that important? I have a transmitter with elevon mixing but no dual rates or expo.

Or do I bite the bullet and get a 2.4 Ghz radio with all those features?

 

[mikec]

That would mean that you mount all of the radio gear outside of the body tube.

mikec, Is that how you did it? I didn't see any hatches in the picture.

My receiver, BEC, and battery are mounted on a small plywood shelf attached to the base of the nose cone. Servo extenders run through the BT and out to the wing-mounted servos.

I would like to try something like this but haven't done much of any R/C flying in the last dozen years or so. Can you get away with using something like Hitec HS-55 servos or would you need something stronger?

I'm using cheap HobbyKing 9gram servos no better than the HS-55. Since I'm not really using the servos on boost there's not much load.

I was hoping that I could use my old World Engines Expert transmitter from the late 1990's and just get a lightweight receiver and servos. It has dual rates for aileron and elevator along with endpoint adjustments but alas, no elevon mixing.

Do you think that dual rates is that important? I have a transmitter with elevon mixing but no dual rates or expo.

I didn't have dual rates or expo set in my test flights to date and it was twitchy in roll but by no means uncontrollably so.

Or do I bite the bullet and get a 2.4 Ghz radio with all those features?

Usable 2.4GHz transmitters/receivers can be gotten from Hobby King for around $30, less than a modern 72 MHz receiver. I'm not certain of the feature sets, but the 6ch ones have mixing. Documentation is not great, but there are days when I wonder if my $200 DX7 is much better

 

[BobH48]

mikec,

Thanks for your quick reply. I think I will try this.

The receiver I have for the transmitter with elevon mixing is a little big by today's standards but not overly heavy. I'm sure it will fit in a Series 175 tube and I would just need to buy the BT and nose cone.

I think I saw in one of Frank's (burkefj) posts that he just attaches the servos to the wings with CA. The servos are certainly cheap enough to permanently attach.

One thing I have thought about and I'm just throwing this out for opinions.

What about small canards? They would be left straight at boost and then the trailing edge angled down when transitioning to glide to give a little lift to the front. That way I could keep the CG a little further forward for boost and hopefully not have to have too much up elevon for glide.

 

[mikec]

What about small canards? They would be left straight at boost and then the trailing edge angled down when transitioning to glide to give a little lift to the front.

I thought about this and actually bought an Edmonds Ecee Thunder to experiment with. Ultimately I didn't know exactly how to do the design; the Ecee allows the canard to float on boost, and fixing it may result in instability. But someone who knows more about canard design will have to comment.

Check this out:
https://www.upaerospace.com/Lockheed-Martin-Tech-Demo-Launch-II.html

 

[mikec]

I got three flights in this morning, all on Aerotech F35 motors (more thrust than I wanted but the closest thing I had in my range box.) The first two flights were excellent, with durations of 38 and 54 seconds. On the last, I experienced a lot of elevon flutter during boost and in the subsequent attempt to recover the elevons got stuck in full down position. I managed to glide inverted for a little while and then nosed in. No damage though I will have to check the servos carefully; it's as though the servo arms turned on the shafts.

I knew this motor would probably exceed the airspeed that my overly-flexible pushrods and cheap, weak servos could handle, but those first two flights were nice anyway!

Onboard video:

[YOUTUBE]GOjz7qRj77A[/YOUTUBE]

 

[hornet driver]

Nice flights--very cool sounds-back in one piece--priceless

 

[[POW]Eagle159]

NICE, I must ask what video cam did you use for the onboard!? That was amazingly clear! Good work:wink:

 

[burkefj]

Could have slipped the gears internally, that was a lot of flutter, you can see it happeneing a bit on the earlier flights. You can always glue the pushrod into a carbon tube and then z bend the ends to make them stiff if they are overly long.

Glad it wasn't hurt. Flutter is one of the reasons for my profiles I try to keep the thrust moderate for the weight. Sometimes you don't really have a lot of options though.

Frank

 

[mikec]

NICE, I must ask what video cam did you use for the onboard!? That was amazingly clear! Good work:wink:

These are just "808" #3 keychain cameras. https://chucklohr.com/808/

Unfortunately the newer #3s drop a lot of frames when the scene is changing rapidly, but at $15 apiece I can tape them onto airframes without worrying much. I got mine from a seller on RCGroups, but https://www.bayouratrocketry.com/ also has them (I think his are a different type than the #3.)

 

[philip]

Mike,
do you have any idea how much the camera weighs? And do you have to buy a seperate memory card?