Holverson Swinger RG – resurrection of a nostalgic classic

Discussion in 'Rocket Boosted Gliders' started by Rktman, Jan 18, 2019.

Help Support The Rocketry Forum by donating:

  1. Oct 24, 2019 #61

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Sounds like that would work great with the upscale I hope to build. No complicated fiddly bits to mess with, just a nice easy to construct solution. I like it!
     
  2. Oct 29, 2019 #62

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    I'm finally continuing with the Groundhog evolution. I re-read Jon Robbins Groundhog 16 article. It seems that he was most concerned with boost drag, and minimizing frontal area, while the real advantage of swing wings is that they have very low load during boost. Of course ideally you always want to boost high and establish a high enough sink rate that you keep thermals from stealing you model, while still winning. In practical terms you want to optimize over all three flight phases, boost, transition, and glide to maximize duration and then work with or around thermals. The Groundhog 16 was flown with a A5-2S, and has a very generous wing area. The large wing area is good because it is generally timed until the timers loose sight of it, and you prefer that timers lose sight of competitors models sooner. Sizing is one of the most important aspects of scaling the Groundhog to different motor classes. Through experience, I have found 1.5 " chord to be best for B motors, 1" for A (A3-2t) and 1/2A motors, 3/4" did not work well for 1/4A Motors, 2" for C motors, and 2.5" for D motors. I have not had occasion to fly E or higher R/G, but The swing wing should be best suited to higher boost speeds.

    The first evolution is to get rid of that heavy wire and piston, and use a simple burn string release. At the same time I moved the elastic out from the pivot to pull forward, much like on the Hot Turkey. If you do not constrain the wing tips, the wings will flutter on boost and often shred. I push a straight pin into the bottom of the fuselage, just ahead of the tail surfaces. Pull the pin out and cut it to a shorter length. Push it back in the pin hole and and use pliers to drive it in until just enough is remaining to catch the burn strings. I use a thin nylon cord of the type commonly used for parachute shroud lines. Cut a long piece of string and fix a a small Avery adhesive pad (the same material commonly used to secure shroud lines to parachutes) to one end of the string. Hook it around the pin and stick it tightly to the underside of the folded back wing at the trailing edge. run the string straight up the bottom of the fuselage, over a shallow notch cut in the front if the fuselage, loop it through the motor pod vent ports twice, forming an X in front of the motor, run it back over the notch and down the fuselage and around the pin in the pin from the opposite side the the other folded wing. Pull the string tight, there will be some elasticity in the nylon chord, and tape it to the other wing just like the first one, and trim off the excess. This has proven to be enough to keep the wings from fluttering on boost, and I have never had deployment failure, aside from catos and human error (forgetting to attach the elastic).

    The second evolution is using an undercambered airfoil. This will give about 15% more duration performance in glide with no boost penalty, due to the swung back wings. The undercambered wing will have more pitch down moment that will require more more trim down force from the stabilizer, or moving the CG aft. At this point it may be helpful to look at some AMA towline gliders. You can find designs with undercambereed lifting stabilizers, and far aft CGs. We could calculate the neutral point and establish aft CG stability limit, or find the condition that minimized trim drag. However, the R/G still has to contend with transition, so I recommend moving the CG just a little aft, but not as far as possible. You can pick an airfoil used by a successful towline glider flying a similar Reynolds Number, or you can pick one out of a catalog, or even design one. I'm not very particular about airfoils, I just use what seems about right.

    The third evolution is just materials. For the wings, I use thicker C grain contest balsa, but I sand most of that material away, but save your lightest wood for other projects. I cover the inner portion of the wing with tissue, and on large models I'll add an second layer of tissue on the inner most portion of the wing. The Spruce Fuselage on the B and smaller sized Groundhogs is fine, but is too heavy when scaled up. For a 2.5" chord model, I used hard balsa laminated with carbon fiber reinforcement. It will not have the impact strength of Spruce, but it will be stiffer and lighter. Covering the stab with tissue is also a good idea.

    The fourth evolution is simply a hodgepodge of improvements such as adding a pop up stab DT, more attention to streamlining the pivots, and making the wings/ pivots repairable by using replacing the pivot axles with nylon screws and bushings, and bit of plywood reinforcement.
     
  3. Oct 29, 2019 #63

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    I neglected the tow hook in the Fourth evolution. I added this to assist trimming.

    There are several issues with the Groundhog. The wing aspect ratio of 24 is extremely high for duration glider. The fuselage length is very long, making the short period mode highly damped, and the phugoid mode lightly damped.. The wings actually flex quite a bit during the phugoid oscilations. If you shortened things up it would have better dynamics, and move closer to the XP-2. Induced drag can be minimized with an elliptic lift distribution, but at an aspect ratio of 24 it is already very low. One could change to an elliptical planform, or twist the wings (washout) which will also eliminate tip stall. I generally try to select wood with a suitable twist or try to build in twist when I cover the wings with tissue. I'd also like to try a tapered wing, say 1.75 at the root and 1.25 at the tip, with the wing thickness tapered as well. Although, this would increase the pivot size and drag, and we might not be able to call it a Groundhog. So, there is still scope for further evolution even in a classic well used design.
     
  4. Oct 30, 2019 #64

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Much thanks. Lots of great info here applicable to glider design; invaluable when scratch-building original designs and making improvements to older proven ones.
    Since I now have the opportunity to build all those gliders that I always wanted to as a kid but never got the chance to, I'm on a quest to do as many as I possibly can get to. Doesn't matter if they were superior fliers or just average, since I'm doing it just for sport and the fun of it, not for competition.
    It's also been a good learning experience that has allowed me to dabble in some original designs along the way, which is why I find your input valuable.
     
  5. Oct 31, 2019 #65

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    Thanks. There are probably dozens of things about the Groundhog that I have not said, or even totally forgotten. One on them is that the dihedral shown in the Groundhog 16 plans is much greater than needed. It is sad that I have acquired so much skill and experience, and there no one to pay it forward to, at least not locally. I have yet to build a 1/8A, or an E or larger Groundhog, there would be no point.

    I've been waiting for John Bean to release his mark 4 altimeter. What I really want is a similarly sized follow on product, a DT release, or maybe an altimeter with DT function built in. This would make sport flying B/Gs and R/Gs practical.
     
  6. Oct 31, 2019 #66

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    [QUOTE="Alan15578, post: 1932230, member: It is sad that I have acquired so much skill and experience, and there no one to pay it forward to, at least not locally. I have yet to build a 1/8A, or an E or larger Groundhog, there would be no point.[/QUOTE]

    I'd say you're certainly paying it forward here on the Forum by sharing your knowledge and expertise gained from years of experience. It's invaluable to BARs and those just getting into the sport. I'm a glider fanatic but don't have the benefit of an aeronautics, engineering, or even balsa glider flying/design/construction experience, so any knowledge I gain here or from other online or printed sources is always much valued.

    For myself, the point of building a 1/8A or 24mm Groundhog or other swing wing would just be for the challenge and fun of it, to see if I could get it to work successfully and what I could learn in the process of designing, building, and flying it. (My one attempt at a swing wing, as a clueless newbie 3 years ago, was an eye opener...it unintentionally spun like a top on the way up and refused to fully deploy its wings. I sure learned a lot from that less than stellar attempt). Now that I'm a little bit wiser, I intend to give it another try this winter.
     
  7. Oct 31, 2019 #67

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    Rktman likes this.
  8. Oct 31, 2019 #68

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    You, sir, are a fount of knowledge! Great info, and just what this forum category could use, especially since there seems to be more beginners here (than on YORF) and we can really benefit from a deep knowledge library like this. Really helps to build it right the first time, and not to have to make the same mistakes that someone else has already made and found the solutions to. Hopefully others will also leave tips and advice gleaned from hands-on experience or their background.
     
  9. Oct 31, 2019 #69

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    You are very welcome . . . I hope that everyone benefits from it !

    Dave F.
     
  10. Nov 2, 2019 #70

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Couldn't make this month's launch, looks like my next opportunity is the 16th of this month if the winds drop below double digit.
     
  11. Nov 9, 2019 #71

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Looks like I'm going to have to postpone the Swinger's maiden yet again. With sustained double digit wind speeds and 43mph gusts forecasted, it'll have to wait for next month's Tripoli East launch date. :(
     
  12. Nov 10, 2019 #72

    BABAR

    BABAR

    BABAR

    Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter

    Joined:
    Aug 27, 2011
    Messages:
    4,806
    Likes Received:
    655
    Good choice!
     
    Rktman likes this.
  13. Dec 1, 2019 #73

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Finally got the chance to launch the Swinger yesterday. It would've been a glorious flight...if it had not gotten hung up on the launch rod.
    With the wings still folded, the top wing got charred pretty severely. Guess metallized mylar tape wasn't a good protective solution. The heat from the ejection charge also caused the piston to swell and jam in place. Well, at least the wings deployed perfectly--though that seemed more anti-climatic comic relief than dramatic.
    I need to take a closer look but everything looks fairly easy to repair. Unjam the piston and use a strip of aluminum tape to protect top wing and she should be ready to fly at the next launch in 2 weeks.
    IMG_3862.JPG
    1st flight damage.JPG
     
  14. Dec 22, 2019 #74

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Followup:
    Was surprised when I maidened my Swinger yesterday; it stalled like crazy, doing several deep U-shaped dive-and-recover loops before doing a nose plant 15' above the ground. Trying to diagnose the problem. My CG (with wings extended and an expended motor casing in place) is EXACTLY where the plans indicate it should be but it's obviously tail-heavy, something I rarely experience with an RG. The glider deployed smoothly after a straight boost, and it glided beautifully during hand-trimming tosses both before and after, so this is a real head scratcher.
     
    Last edited: Dec 22, 2019
  15. Dec 22, 2019 #75

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    Eric,

    Hmm . . . Maybe a Wing Incidence or Stab Incidence ( Decalage ) issue ?

    It might behave "normally" during hand-tossing, where velocities are low and the initial "glide angle" is controlled by you. However, when deployed at Apogee, it may be undergoing the "sequence" . . .
    Dive . . . Acceleration . . . Pull-Out . . . Climbing Glide . . . Stall . . . ( Cycle repeats ).

    Thoughts ?

    Dave F.
     
    Last edited: Dec 22, 2019
  16. Dec 22, 2019 #76

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Sounds very plausible. Easiest fix would be a bit of clay on the nose. Could also affix small trim tabs to the tail. Both options somewhat of a PITA since how much clay or trim tab angle is pretty much a shot in the dark and the only way to determine how much is to launch and assess. Oh well, gotta do what I gotta do. Good learning experience and gives me an excuse to get out and do some test launches this winter.
     
  17. Dec 22, 2019 #77

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    Eric.

    I sent you Doug Holverson's email address, via private email.

    Dave F.
     
    dhbarr and Rktman like this.
  18. Dec 22, 2019 #78

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    Thank you kind sir!
     
  19. Feb 15, 2020 #79

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    I'd say you're certainly paying it forward here on the Forum by sharing your knowledge and expertise gained from years of experience. It's invaluable to BARs and those just getting into the sport. I'm a glider fanatic but don't have the benefit of an aeronautics, engineering, or even balsa glider flying/design/construction experience, so any knowledge I gain here or from other online or printed sources is always much valued.

    For myself, the point of building a 1/8A or 24mm Groundhog or other swing wing would just be for the challenge and fun of it, to see if I could get it to work successfully and what I could learn in the process of designing, building, and flying it. (My one attempt at a swing wing, as a clueless newbie 3 years ago, was an eye opener...it unintentionally spun like a top on the way up and refused to fully deploy its wings. I sure learned a lot from that less than stellar attempt). Now that I'm a little bit wiser, I intend to give it another try this winter.[/QUOTE]

    A MM Groundhog might be interesting, but a Bumblebee like design with a trim tab would likely be better. E and F Groundhogs are too easy with the Estes E12 and F15 motors, and just use up more money and materials.
     
  20. Feb 15, 2020 #80

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    With airflow from a normal launch, the aluminized mylar tape should be adequate. Actual Metal foil will hold up better to the type of failur that you experienced.
     
  21. Feb 15, 2020 #81

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    Alan,

    I think you will enjoy the glider material in this thread :

    https://www.rocketryforum.com/threads/glider-design-trimming-library.155758


    Dave F.
     
  22. Feb 15, 2020 #82

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    I am guessing that you did not get anything helpful from Doug Holverson, or at least nothing to share. I'll take a WAG at this, but understand that the Swinger is an atypical design that I have not flown.

    The design CG is one of the most important specifications. You should always balance to the prescribed CG, then adjust or trim surfaces. I think the Swinger has a rather aft CG location and the stabilizer actually produces lift in gliding flight. Your build might be be considerably better that the nominal Swinger. It is possible that the stab stalls before the wing, producing the pronounced pitch up that you observed. You always want the wing to stall first, or in the case of a canard configuration, you want the canard to stall first.
     
    Rktman likes this.
  23. Feb 15, 2020 #83

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    That's what I couldn't understand, I had the CG spot on according to the plans but it was still stalling. I added a bit of clay to the nosecone, but made the mistake of bypassing the sticking piston by using a burn string. The string severed alright, but for some reason the wings didn't deploy and it came in ballistic. Oddly I never found the front half of the motor pod. Good thing Holverson designed it pretty stout, everything else survived intact.

    Not sure what to look for with the stab to diagnose if it's the culprit. I built everything exactly as specified and had everything but the wings laser cut to ensure accuracy.
     
  24. Feb 15, 2020 #84

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    I'd say you're certainly paying it forward here on the Forum by sharing your knowledge and expertise gained from years of experience. It's invaluable to BARs and those just getting into the sport. I'm a glider fanatic but don't have the benefit of an aeronautics, engineering, or even balsa glider flying/design/construction experience, so any knowledge I gain here or from other online or printed sources is always much valued.

    For myself, the point of building a 1/8A or 24mm Groundhog or other swing wing would just be for the challenge and fun of it, to see if I could get it to work successfully and what I could learn in the process of designing, building, and flying it. (My one attempt at a swing wing, as a clueless newbie 3 years ago, was an eye opener...it unintentionally spun like a top on the way up and refused to fully deploy its wings. I sure learned a lot from that less than stellar attempt). Now that I'm a little bit wiser, I intend to give it another try this winter.[/QUOTE]
     
  25. Feb 15, 2020 #85

    Alan15578

    Alan15578

    Alan15578

    Well-Known Member

    Joined:
    Feb 11, 2018
    Messages:
    208
    Likes Received:
    35
    [/QUOTE]
    You don't need the befit of an engineering degree. I did far more interesting B/G and R/G experiments and developments before I ever went to college, and one can learn from or share with just natural interest and talents.
     
    Rktman likes this.
  26. Feb 17, 2020 #86

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    You don't need the befit of an engineering degree. I did far more interesting B/G and R/G experiments and developments before I ever went to college, and one can learn from or share with just natural interest and talents.[/QUOTE]
    Agreed!
     
  27. Feb 17, 2020 #87

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    Eric,

    You just need "a little help from your friends" . . . The Beatles were right !

    Dave F.

     
    Rktman likes this.
  28. Feb 17, 2020 #88

    Rktman

    Rktman

    Rktman

    Eric Noguchi

    Joined:
    Mar 5, 2017
    Messages:
    847
    Likes Received:
    38
    The best kind!
     
  29. Feb 21, 2020 at 4:08 PM #89

    BABAR

    BABAR

    BABAR

    Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter

    Joined:
    Aug 27, 2011
    Messages:
    4,806
    Likes Received:
    655
    Any chance that the position of the components is different after an apogee deployment than it is when you are doing test flights on the ground? In other words, the action of the aerial deployment may be positioning the wings or other components slightly different than when you are ground testing. One thing you could try and is that if it is flying well on ground test and you launch it and it doesn't fly well would be to take the immediately recovered rocket and try to do ground test tosses with it. Does it still glide well or does it porpoise like the flight? My suspicion is that there is something "slightly "different between the position of the components when deployed on an actual flight than when you are ground testing. Another possibility is that aerial deployment initial forward velocity is near zero (essentially like just releasing it in dead air at altitude rather than the forward momentum imparted with a ground level "toss") that's always a challenge for configuration transition type gliders (as opposed to @iter 's gliders that use remote control to transition their vertical velocity to horizontal velocity). Swing wing, pop pod, elevator release mechanisms have to assume the glider starts with zero velocity in dead air.
     
  30. Feb 21, 2020 at 4:50 PM #90

    Ez2cDave

    Ez2cDave

    Ez2cDave

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,971
    Likes Received:
    663
    BABAR,

    That is an interesting theory and bears further investigation . . .

    Eric,

    My hypothesis ( slightly different ), based on BABAR's theory, is that the wings may not be fully deploying at ejection. Since the glider has forward momentum and aerodynamic drag is always a factor, the wings may not be "snapping open" at deployment, unlike what they do on the ground.

    Try this . . . When doing your glide tests, first allow the wing to "snap open" and test it. Second, restrain the wings during opening and only allow the elastic to gradually pull them into position ( DO NOT "push them forward", at all ) and the repeat the glide tests, to see the difference.

    If this is the situation, it should be correctable by increasing tension on the deployment elastic or replacing it with a stronger elastic.

    Thoughts ?

    Dave F.
     
    Last edited: Feb 21, 2020 at 7:27 PM

Share This Page

Group Builder