Psyche Glider Build Thread

[awseiger]

Hello All... Figured I'd post a build thread of the glider I'm building. This is my first attempt at a rocket glider, so if you have any comments\suggestions\criticisms please feel free. I've named it Psyche because this is the ancient greek word for "butterfly". At least I think. I usually name my rockets after the horses of greek heroes, but I feel as if something graceful like a glider doesn't deserve such a name.

At the moment I've already shaped the main delta wing and the rear vertical and horizontal tails. They're all glued on, and I'll check to see how well it flies tomorrow... Wind tunnel (Aka big fan and some string) tests show that it should fly quite nicely.



My idea is to have the central pod stick out a bit from the rear, and hold my elevator down. This would omit the need for fragile hooks, which is always nice. Of course, I have left the elevator off for the moment, because I'd love to get it flying nice without it. The less moving parts, the smaller the opportunity for mechanical failure.

The central pod will take 24mm motors, I'll build it to take an Estes E9-4. Of course, this means I could put one of those Aerotech 24mm F's in there, but then my precious glider may just fly off into the sunset.

 

[[POW]Eagle159]

The problem is.... that if you dont have a elevator, then nothing will make it want to come out of a dive...... This happened to me, BAD... Mine crashed hard.
Is there any dihedral to the wings? Some will make it fly better, How long is the wingspan and length? A bright color will also be good to see in the sky.
What is the diameter of body tube? Bt-60? Also, whats the nose cone, I've not seen the shape of one like that.
Also, a smaller engine is good so it doesnt go high and get lost.

Nice build, I like it.

 

[awseiger]

The problem is.... that if you dont have a elevator, then nothing will make it want to come out of a dive...... This happened to me, BAD... Mine crashed hard.

I shall use an elevator then. This makes sense... I can just see myself yelling "Pull Up! Pull Up!" as my brand new glider nosedives.

Is there any dihedral to the wings? Some will make it fly better, How long is the wingspan and length?

Yes, there is a dihedral to the wings. I used a cardboard form to make the seam, so it's as perfect as it could ever be.

A bright color will also be good to see in the sky.

I was going to paint the entire bottom OSHA yellow/orange. This has worked well for me in the past.

What is the diameter of body tube? Bt-60? Also, whats the nose cone, I've not seen the shape of one like that.

Body tube is a BT-55, and the nose was in the estes designer special kit I bought. I think it's supposed to be a boattail form, but hey, it works! I personally think it has a very airplane-like shape.

Also, a smaller engine is good so it doesnt go high and get lost.

I'll keep that in mind... I guess even a D would get this thing pretty high, and it's gonna drift significantly further. I'll go with an 18mm mount for now. I can always make a bigger mount for it if I decide to.

 

[awseiger]

Double post, but a build update!!!

First and foremost, I added my elevator to the back today. Hinges are 2 pieces of cardstock. Amazingly cardstock has a rather large amount of "spring", so I am able to adjust this control surface very easily. Eventually I will spring-load this with a nylon screw to adjust the pop-up height.



Second, A launch lug! I stole the tube from the Estes Sonic Igniters, I wanted a long tube to help strengthen the wing dihedral anyway.



Lastly, a gorgeous airfoil on the wings! I must have taken off at least 1/3 of the balsa doing this. The glider is much lighter now...



And of course, the most exciting thing is it flies! It's not going to win any glider duration competitions, but it glides nice and smooth, and has survived the abuse of me throwing it around my yard for a few hours getting the balancing all good. For a glider where the only measurements were "are the wings the same size?", I am quite happy.

 

[hornet driver]

I might be missing something --are you using a boom-tube on this ??

 

[iter]

In a rocket glider, there are typically two worries: CG shift as the motor burns out and changing elevator trim as you transition from boos to glide.

In my gliders, I solve the CG issue by moving the motor close to the CG (I use tailless deltas). I solve trim change issue by building R/C gliders where I can control pitch from the ground.

If you put a motor in the tail, it you start out tail-heavy and end up nose-heavy, which is the opposite of what you want for stability.

I wonder how you plan to address both these issues with Psyche.

Ari.

 

[kjohnson]

From the previous thread it sounded like the OP is going for a boom tube aka power pod like the Skydart.

kj

 

[iter]

Ah, this one: https://www.rocketryforum.com/showthread.php?37554-Some-Glider-Questions .

I build my gliders without boosters. I find it difficult to track two things coming down at the same time. Maybe it's my attention span... I have a hard time tracking the booster as it's coming down on a parachute while also flying the glider down. It's like if I'm trying to fly, and someone comes tugging at my sleeve, "look the other way, there's something you need to see over there!"

I suppose if you have no R/C on the glider, it may be less of an issue.

Ari.

 

[awseiger]

Update! Physche has flown. Kind of...

[video=youtube;nP48AAE_Jjw]https://www.youtube.com/watch?v=nP48AAE_Jjw&feature=youtu.be[/video]

and

[video=youtube;Am3u5ufc6mg]https://www.youtube.com/watch?v=Am3u5ufc6mg&feature=youtu.be[/video]

Anyone have any pointers on how to fix this? Something tells me it's just unstable as a rocket along the plane of the main wing. However, I have as much mass as I can fit on the end of my tube...

 

[aerostadt]

This is the classic problem with boost gliders and rocket gliders versus pure rockets. Rockets need the center of gravity ahead of the center of pressure for stable flight. In other words fins are aft and the nose is heavy. You might be able to put weight at the front end of your ejection/motor tube, but it might take so much weight that the rocket cannot get enough altitude. Your wings are large and they are very far forward.

 

[awseiger]

If I were to convert this into a delta glider, would it work better? I figured this would be the case.

Also, the motor tube is already weighed down to the max.

 

[iter]

Alex, do you have the elevator up during boost?

Ari.

 

[JStarStar]

You also have a problem with the lateral center of gravity, as opposed to the vertical/lengthwise CG.

Lay the rocket down on the table and look at it lengthwise from the rear end.

When you launch, the thrust of the motor is pointing straight up through the body tube and out the nose cone.

In most rockets this is fine because they are built symmetrically and the direction of the motor thrust also goes right up through the lengthwise axis.

However, except for the relatively small rudder, all your balsa (wings, stabilizer) is attached to the bottom of the body tube. That represents a considerable shift of weight and now the motor's thrust is pushing hard on an axis maybe an inch above the lateral CG.

Plus if you want to get into the issue of the lateral CP that is off center as well with the drag of the wings and stab on the "bottom" of the rocket.

I think with the large wing area forward and the heavy motor in the tail, you probably have "conventional" CG-CP problems as well.

But I think your main problem is the thrust line and the lateral CG are not in line.

This MIGHT be somewhat solvable (as iter seems to indicate) if you turn the elevator sharply up before launch to compensate for the strong dive tendency of the rocket in its current configuration. I suppose canards forcing the nose up might help too.

Although both of these might cause problems in the post-boost glide phase, I guess my thinking would be, "well if it buries its nose into the dirt during the boost phase, the post-ejection glide phase doesn't really matter."

To find this out may require numerous test flights involving the rocket power-diving into the ground until it flies right. This could get costly quick.

 

[hornet driver]

After rereading, it looks like you are using a boomtube. Please send out a picture of that. From a practical point of view ,you used the hardest planform to turn into a rocket.As a rule--a pure or modified delta is the easiest to make work followed by a tailless swept wing and on down the line. If your going tp keep your current profile , I'd move the wing back quite a bit---best bet--if you can get the wing off---balance the body tube with tail on and no ballast or motor or boomtube- find the cg--center of lift of the wing needs to be a tick behind this point--usually 1/3-1/2 back on a wing .mount the wing here--you should need less elevator authority. figure out your cp- now mount the tube with engine and add ballast as needed to get the cg forward of the cp by a good margine. On a side note--sweeping your tail surfaces trailing edges back also helps to inch the cp back a tick --I would also increase the vertical tail size a bit---hope this helps---H

 

[awseiger]

Update!

I followed everyone's advice, and I have converted to a delta wing:



I also finalized how my elevator(s) pop up and stay at a predefined, but adjustable angle


And finally, the boom tube actually works to hold down the elevator!


I still have to do carboard Cutout to determine the Cp, but as far as I can tell, this one is stable, and will fly like a rocket until boom tube ejection, where it glides quite nicely :-D

Still to do is adding a streamer to the boom tube. I'm gonna fly this one naked for a while, It's easier to make adjustments without paint on it.

 

[Serenity]

Just an idea - if you need to or would like to save weight, consider using nylon screws instead of metal. If you need a source for nylon screws, Amazon.con has tons of nylon screws in all kinds of sizes - as small as 2-56, and on up to at least 1/4". Can't really tell from the picture, but I'm guessing the hardware you are using is something like 6-32, 8-32 or 10-24. Those sizes are definitely available.

Good luck with your test program.

 

[gdjsky01]

It's still great fun to read of your adventures. Keep trying!
- Jeff

 

[awseiger]

It's still great fun to read of your adventures. Keep trying!
- Jeff

Oh, I'm determined. A little too determined...

Preliminary glide tests show my glider to be... well... picky. If I throw it JUST the right way, it glides like a bird. Any other way, and I get a spiral nosedive. It is, however, Rocket stable loaded for launching, and glider-stable(ish) in glide mode, so this should go somewhat better than the last attempt. I'm beginning to think the wing should have been on the top of the body tube instead of the bottom.

I should be able to get another flight video Friday.

 

[hornet driver]

Oh, I'm determined. A little too determined...

Preliminary glide tests show my glider to be... well... picky. If I throw it JUST the right way, it glides like a bird. Any other way, and I get a spiral nosedive. It is, however, Rocket stable loaded for launching, and glider-stable(ish) in glide mode, so this should go somewhat better than the last attempt. I'm beginning to think the wing should have been on the top of the body tube instead of the bottom.

I should be able to get another flight video Friday.

The -twitchy- condition can be caused by a couple of things. Hang with me here this can get a little winded. 1--if it's a bit short coupled--in other words the profile is short vs. the wing span or area. A larger vertical stab--a tick taller and more swept can cure this at times , move the moment back a bit,the addition of ventral fins can have the same effect and help with the boost phase as well. 2-- any small differences-wing to wing will cause this ---ESP the smaller the scale--so the smaller you build the bigger the tiny differences make !!!! Remember all those screws and rubberbands are control sufaces in their own right---if they see the wind they affect it !! If you were to upscale your glider you might not notice any of these effects since in the bigger scheme of things they might be minimized---except for #1. Your challenge as I see it is one of fine tuning. If I was in your shoes I'd look at rudder authority first--easiest to fix and go from there--high wing or low you most likely will have the same problem--a high wing may even make the condition worse since you move the wing closer to the stab and begin to wash it out potentially. Also think about speed---if your elevons are reduced in size a bit or the angle reduced you gain the benefit of a tick more glide speed and more stability---you might just be too close to stall speed with your current elevon input---remember you want to fly the wing, not muscle it around !!

 

[philip]

Oh, I'm determined. A little too determined...

Preliminary glide tests show my glider to be... well... picky. If I throw it JUST the right way, it glides like a bird. Any other way, and I get a spiral nosedive.

It looks like it might benefit from having a longer fuselage with canards at the front. I'm sure that would make it more stable when gliding.

 

[iter]

It looks like it might benefit from having a longer fuselage with canards at the front. I'm sure that would make it more stable when gliding.

It bothers me that people give advice on changing planforms as a cure for instability (I'm not picking on you Philip; this thread is full of suggestions on what to do with horizontal stabilizers). Canards, deltas, conventional tails can all be equally stable or unstable. If you understand the aerodynamics, you can make any of these planforms work, and people have. If you don't, changing planforms cannot help stabilize your aircraft. The differences between these planforms are in secondary and tertiary factors that are irrelevant to where this project is. My own choice of delta planform for my RCRGs derives mostly from structural, rather that aerodynamic, considerations.

I'm hesitant to give Alex advice on his glider--he hasn't responded to my query about elevators, and I'm unclear on how much input he wants. But I want to encourage people who do give advice to clarify how many successful RCRGs they have designed and flown.

Ari.

 

[awseiger]

I'm hesitant to give Alex advice on his glider--he hasn't responded to my query about elevators

Oops! I do not have the elevators up during boost, they straight in the "Neutral" position.

 

[philip]

It bothers me that people give advice on changing planforms as a cure for instability (I'm not picking on you Philip; this thread is full of suggestions on what to do with horizontal stabilizers).Ari.

Just offering a suggestion on what I found when I was building similar gliders a while back. They were not RC but did achieve some good glide performance with canard configurations in conjunction with a relatively long fuselage. Thought that might be helpful, not aiming to bother anyone.

 

[aerostadt]

Boost gliders and rocket gliders are inherently difficult, because they combine two flight trajectories together (boost & glide). Thus, they can be frustrating, but also rewarding. The variations in designs are fascinating. I am always learning something by watching others on the forums. It seems like the R/C people know this field very well. I like looking at the builds, but the bottom line is a good flight. The proof is in the flight.

 

[iter]

Boost gliders and rocket gliders are inherently difficult, because they combine two flight trajectories together (boost & glide). Thus, they can be frustrating, but also rewarding. The variations in designs are fascinating. I am always learning something by watching others on the forums. It seems like the R/C people know this field very well. I like looking at the builds, but the bottom line is a good flight. The proof is in the flight.

This reminds me of my experience learning to design autogyros a few years back (eventually, for I while, I sell an autogyro kit of my own design). Lots of people in forums (including R/C luminaries such as Hal DeBolt) think it's just an airplane with a rotating thing on top. They find autogyros frustrating in the now-it-works-now-it-doesn't way. Turns out, if you understand helicopter aerodynamics, building autogyros is easy. If you start from a helicopter mindset and move the thrust source around, you can build all sorts of working, stable-flying autogyros.

It appears to me that a lot of rocket people view gliders as rockets with extra-large fins. I remember reading a kit review for a perfectly stable and very-well designed RCRG kit (I've built and flown that kit to great pleasure) where the reviewer decides to move the CG forward of what the instructions say "for an extra margin of stability" and then complains that the glider nose-dives after apogee. If you start from a rocket mindset, it makes sense. From an airplane perspective this sounds incredible.

I find nothing magic about two different flight regimes on an RCRG. It has a wing, a horizontal stabilizer and a thrustline, just like any other airplane. The flight profile is similar to duration motor gliders (where you have a set amount of fuel of battery runtime and then glide down; longest flight is the winner). Every airplane with an engine has to deal with vertical thrust offset issues. A term you may want to google is "downthrust" or "upthrust." In addition, every airplane has to deal with the fact that lift is proportional to speed, and most airplanes fly faster under thrust than gliding. In some ways, RCRGs are simpler than designs that use a propeller: with a propeller, you have additionally to deal with torque (you turn the propeller clockwise, it turns the airplane counter-clockwise), gyroscopic precession of the propeller, sipstream and p-factor, which all want to turn you in some direction you don't expect when you apply power. There are many parkflier designs out there that fail to take these into account and have violent pitch changes in response to throttle changes. In an R/C airplane, you can cope with these pitch changes by adjusting your elevator setting every time you adjust the throttle.

OK, with this rant out of the way, and for those of you still reading, I can make some observations about Alex's specific design.

Ari.

 

[iter]

Oops! I do not have the elevators up during boost, they straight in the "Neutral" position.

This is somewhat irrelevant now that you've changed the design, but if you find that on boost the model wants to pitch down, you may want to adjust the elevator up for boost. You may find, with the motor under your CG, that no elevator adjustment is necessary at all between boost and glide: the thrust offset cancels out the nose-up pitch from your elevator. Many Edmonds gliders have no moving elevators at all, relying on thrust offset angles and distances to cancel elevator pitching moments during boost. With sort-of-random combination of thrust angles and offsets you have, you may need some elevator adjustment at apogee, but probably a lot less than your intuition.

With your new design, I encourage you to first make sure it can glide stably--and recover from unusual attitudes. The booster tube may come out when the glider it pointing straight up, or straight down, or somewhere in between, and it needs to be able to recover from that. I encourage you to post your observations here, and if you like, I can make recommendations on the strength of these observations.

I like that you're making the elevon angle adjustable. Your screw design is unusual, but seems to work.

I encourage you to verify your CG location. The operative term is Mean Aerodynamic Cord (MAC), and you want the CG at about 20% MAC for a new model (you may be able to move it back for slower, longer glide once you trim the model for stable flight). On a straight, rectangular wing, all cords are the same, and you can simply measure 20% from the leading edge of the wing root. On any other planform, the MAC is different from the root cord. There are online calculators that can help you find the MAC, e.g. https://fwcg.3dzone.dk/

I'm looking forward to your observations, and to a successful launch.

Ari.

 

[aerostadt]

With apologies to Alex for diverging from the Psyche thread, but I would like to ask Ari what did I do wrong on the Edmond's Darcy II. I forgot to put the forward nose cone housing on the Darcy glider when I launched it, but I would think that this would not make much difference to the glider's flight. When the motor pod ejected, the glider went into a steep dive. I could make the glider turn left or right a little bit, but the dive persisted. The forward receiver mount was broken on landing, but I can probably fix that. What am I doing wrong?

I really don't like the way the control horns engage the servo output arms. I am wondering if I should convert this model into a boost glider.

 

[iter]

Thank you for your trust in my analysis @aerostadt. I'm unaware of a Darcy glider. I've built and flown an Arcie II (https://edmondsaerospace.com/RC.html). Arcie II is a boost glider where the booster tube separates at apogee and comes down on a parachute while you fly the single-channel, aileron-only glider down. I eventually convert mine to a one-piece RCRG configuration. My configuration ejects the empty motor casing at apogee to shift CG back for glide.

I recommend you start your own thread on this. The first question that comes to mind is about your CG. The missing nose cone can have interesting effects, too (the open tube acts as a tube fin, and it's ahead of the CG, and it wants to amplify whatever deviation you have from straight-and-level) but I'd look at the CG first. I encourage you to post pictures of your glider.

Ari.