HOLVERSON DESIGNS SILVER HAWK BUILD THREAD

With all this time on my hands during this Covid-19 lockdown, I thought I’d put it to good use and focus some attention on a simple and fast build of an original kitted Holverson Designs Silver Hawk that I was fortunate enough to acquire. Working on a kit is a nice change of pace from hand-fabricating everything for a retro reboot clone. Everything in the kit is precut and all the parts and pieces are already provided so there’s no waiting to start. Interestingly there’s no laser char. (Skilled operator?).

UNBOXING
The parts are all accounted for and in excellent shape, considering the kit is in the vicinity of 16 – 21 years old judging by reviews and the 1999 copyright date on the display card. The glider uses a 13mm motor, though with its beefy 3/32” balsa it would make a good candidate for an 18mm A or B motor, especially if tissued.

For now I’ll stick with building it bone stock, as its specified 0.75oz weight should give it ample air time on the recommended 1/2A3-2T and A3-4T motors under calm (single digit) wind conditions. If it ends up being heavier, I’ll reconsider using an 18mm pod instead.


Note:
The last sheet of the patterns for the Silver Hawk available from oldrocketplans (https://www.oldrocketplans.com/hdi/hdi2002/hdi2002.htm) seem to be for an alternate version, and differ from the kit in that the wing and fuselage shapes are different. This last sheet is labeled v. 2 and shows a revision date of 9/10/2004 vs the kit’s display card, which indicates a 1999 copyright date. If you decide to build a clone, you can disregard this pattern sheet unless you’re interested in experimenting with the alternate design.

Congrats on scoring this. One of my favourite gliders.

Cape Byron said:

Congrats on scoring this. One of my favourite gliders.

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Thanks. Any tips on trimming? These small, light, unorthodox gliders tend to be real finicky and temperamental when it comes to balancing.

I found the Silver Hawk pretty easy to trim; Doug's trimming instructions are spot on.

My advice is build light, especially with finishing. Take it slowly with adding weight for trimming. Twenty test throws is better than one crash. I give mine a test toss before each flight.

Such a good design even the crappy foam Fun Rockets version flies pretty well!

Good to know, thanks for the feedback. Anxious to see how this thing flies (but I guess I'll have to wait on that for a while).

Sanded the recommended “best” airfoil into the wings. This seems more to streamline things than to provide lift. Since the instructions specifically state the airfoil “must be symmetrical”, I decided there must be a reason and didn’t deviate.

The kit thoughtfully included wing and rudder jigs to hold things at the right angle once glued, but I decided to build a sanding jig to ensure I got both the rudder and dihedral angles right vs just trying to eyeball it.


The rudders go on at a 10° outward angle, but since they appear to be vertical once the wing dihedrals are created, it seems logical that the wing dihedral is also 10°, so I’ll just use the same jig to sand both wings and rudder.

Should’ve sanded the outside corners of the rudder bottoms at a 10° as well. Because they’re square, they want to stand straight up instead of slanting outward like they should. Since the white glue was already beginning to set, I held it at the correct angle against the jig and tacked it in place with a couple of drops of thin CA.

Setting the dihedral on the wings using my sanding jig. As you can see, the rudders are now vertical as expected.

Looking good!

What is the wingspan? I can't quite make that out in the first pic.

Wings are done and so is the glider—almost. Since this is basically a flying wing (reminiscent of the Estes Nighthawk) they represent about 90% of the flying portion of the glider.


Wing and rudder leading edges get a dip in a line of thin CA to reinforce them against dings.

Crawf56 said:

Looking good!

What is the wingspan? I can't quite make that out in the first pic.

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Er...I'm not sure how to make a determination in this case. Because it has swept wings, it's either 12.5" (wing tip to wing tip at its furthest point) or 16.5", since each wing measuring from root to tip at mid-chord is 8.25".

Finished assembling and streamlining the fuselage, which is made up of a 1/8” core and two 3/32” doublers. Once sandwiched together, the slot for the pod hook and weight become evident. Neat; beats having to hollow them out and unlike a Manta-type hook, this technique actually saves weight.



I really appreciate the careful thought that obviously went into the design of the pylon and hook. The “Piece X”portion slots deeply into the fuselage, and that small hook at the front locks snugly into its own angled slot up front in the fuse like a jigsaw puzzle piece, preventing any misalignment or side-to-side movement of the motor pod and keeping it from coming loose during launch (a pretty common and chronic problem with some designs that I’ve flown).

I also like the clever design of the wings. The dihedral break between the inner and outer wing panels is angled outward so that they provide a modest amount of washout. The advantage is that the outer tip panels will stall before the main wing, increasing glide stability.


When looked at from the front, you can see the difference in angle of attack between the inner (root) wing panel and the outer tip panel (leading edge is lower than the trailing edge).

I decided to go with a rear-eject system to prevent pod and glider from becoming entangled in its own recovery gear (https://www.rocketryforum.com/threads/ending-the-“red-baron”-curse.158166/).
Interestingly the pop pod uses an 18mm tube instead of a minimum diameter 13mm tube. Because it came with the smaller motor mount tube and CRs, it was a no-brainer to adapt it as the “piston” section of the rear-eject system. The MMT end of the shock cord is anchored with steel fishing leader (probably too much but I have a ton of the stuff and I didn’t want to leave behind a too-short section that I couldn’t use for something else later). The rest is #250 kevlar with a shock-absorbing “bungee” setup up front. It’s epoxied in place inside the nose cone, which will be glued into the pop pod.


The self-adhesive decal is a nice touch. It not only looks good, the heat ablative metal foil serves as protection against wing charring. Very classy.


Since I’m a sport flier I decided to add some strength and humidity-protection with 2 coats of dope. The weight penalty was negligible at +0.67g (0.02oz) and it’s way sturdier now.
Since I’m pretty much limited in my color palette, my default is orange permanent marker, which is about the only thing that shows up well against both green grass and yellow/tan crop stubble. Motor pod will have to wait for paint until the weather is more cooperative.



The glider, with 1.57g of preliminary trimming weight, weighs in at 13.18 grams (0.47 ounce). That’s less than the 0.75 oz weight listed in the kit specs, which probably includes the weight of the pop pod. Because the glider itself is so light, I’d prefer to fly it under single digit wind conditions.

The right wing is noticeably heavier so it has a tendency to swerve in that direction. I’ll have to adjust that with some clay, then get outside at one point to toss it into the wind to retrim it. Of course, a textbook hand toss glide doesn’t guarantee it’ll fly the same way once it’s launched, but I won’t be able to maiden it till…well under the circumstances I’m not sure how long it’ll be before I can do that. Anxiously looking forward to it though.

Nicely done!

kuririn said:

Nicely done!

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Thanks kuririn. Hope you & family and fellow club members are doing okay over there. Guess launches at Sandy's are off the calendar for now? All club launches suspended here.

Nicely done!

Rktman said:

Thanks kuririn. Hope you & family and fellow club members are doing okay over there. Guess launches at Sandy's are off the calendar for now? All club launches suspended here.

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Yep, parks are closed. First couple of days they were just advising and educating the public. Now they are issuing citations. Up to a $5000 fine.
Funny thing is you can walk across a park to get access to a beach and surf. You cannot stay in one spot and sunbathe.
Go figure.
Stay well, Rktman.

Cape Byron said:

Nicely done!

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Thanks, appreciate that!

I built a Silver Hawk from the plans online and found it to be a thoughtful attempt to improve on the Estes Nighthawk. My glider needed little ballast, and boosted well on an A10-3T or even an A8-3 (very similar thrust profiles!) With the Nighthawk I've found that the glider tends to tumble near the end of boost on these motors, and really benefits from a B4-2. My Silverhawk was airbrushed, which in hindsight seemed to weigh the glider down far too much. Magic marker is a much better way of adding color for visibility without weighing the glider down!

brewster_rockit said:

I built a Silver Hawk from the plans online and found it to be a thoughtful attempt to improve on the Estes Nighthawk. My glider needed little ballast, and boosted well on an A10-3T or even an A8-3 (very similar thrust profiles!) With the Nighthawk I've found that the glider tends to tumble near the end of boost on these motors, and really benefits from a B4-2. My Silverhawk was airbrushed, which in hindsight seemed to weigh the glider down far too much. Magic marker is a much better way of adding color for visibility without weighing the glider down!

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Thanks for the info. I have the laser cut parts for a Nighthawk waiting in the build stack. Considering that for my next project. you say "tumble", do you mean end over end or spiraling? I'm wondering if it has something to do with the "canard" wings on the motor pod.
Any pics of your Silver Hawk you can post?

It ain't pretty, but it's my boost glider! I changed the pylon shape, but the motor (and CG) location are largely unchanged.

I checked my flight logs for my Silver Hawk and Nighthawk, and I've seen end-over-end tumble at the end of boost on both when flying with A8-3 or A10-3T motors. Wish A3-2T was still being produced!

I originally flew my Nighthawk without canards, but it has a strong tendency to roll onto its back and fly horizontally before ejection when flying with B4-2. Adding canards didn't really help with the tumble on A10-3T; haven't flown with B4-2 yet after adding canards.

brewster_rockit said:

It ain't pretty, but it's my boost glider! I changed the pylon shape, but the motor (and CG) location are largely unchanged.

I checked my flight logs for my Silver Hawk and Nighthawk, and I've seen end-over-end tumble at the end of boost on both when flying with A8-3 or A10-3T motors. Wish A3-2T was still being produced!

I originally flew my Nighthawk without canards, but it has a strong tendency to roll onto its back and fly horizontally before ejection when flying with B4-2. Adding canards didn't really help with the tumble on A10-3T; haven't flown with B4-2 yet after adding canards.

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Odd behavior, but maybe it's something peculiar to flying wing designs. The fact that both your Silver Hawk and Nighthawk did the same thing seems to be too much of a coincidence. Maybe because of the shorter moment-arm with a minimal fuselage and no tail? Just conjecture but it could also have something to do with the motor's thrust curve. On short duration motors (under a second) my gliders tend to start going horizontal near apogee as the thrust curve tends to flatten and go down as it "runs out of steam". Maybe when the thrust stops suddenly it causes the glider to tumble because it's still going faster than glide speed?

Agree about the 3 - 4 second delays, my smaller 13mm gliders do much better with shorter delays.

Rktman said:

Odd behavior, but maybe it's something peculiar to flying wing designs. The fact that both your Silver Hawk and Nighthawk did the same thing seems to be too much of a coincidence. Maybe because of the shorter moment-arm with a minimal fuselage and no tail? Just conjecture but it could also have something to do with the motor's thrust curve. On short duration motors (under a second) my gliders tend to start going horizontal near apogee as the thrust curve tends to flatten and go down as it "runs out of steam". Maybe when the thrust stops suddenly it causes the glider to tumble because it's still going faster than glide speed?

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Eric,

Good morning, Eric, & greetings from "the Bunker" - LOL !

I am curious if a "velocity-induced stall" might be involved with this glider behavior ?

If so, at pod separation, the glider might sharply "pitch up", rapidly decrease its airspeed due to aerodynamic drag, and go into an unrecoverable stall, due to the short moment of inertia and weak "correcting force", inherent in a flying wing design.

The diagram below is unrelated . . . I just thought it was cool !


Dave F.

Ez2cDave said:

Eric,

Good morning, Eric, & greetings from "the Bunker" - LOL !

I am curious if a "velocity-induced stall" might be involved with this glider behavior ?

If so, at pod separation, the glider might sharply "pitch up", rapidly decrease its airspeed due to aerodynamic drag, and go into an unrecoverable stall, due to the short moment of inertia and weak "correcting force", inherent in a flying wing design.

The diagram below is unrelated . . . I just thought it was cool !


Dave F.

View attachment 411907

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Great to hear from you Dave! Hope you and your fam are well and safe and weathering this covid craziness with an adequate supply of essentials.

Interesting hypothesis, could well be what's happening. The fact that flying wing designs can function without a stabilizer and just a minimal fuselage (if at all) still amazes me. I take it that traditional designs are much more stable, efficient, and predictable. Otherwise we'd be surrounded by commercial and military flying wing craft.

I'm not familiar enough with the aerodynamic principles behind these flying boomerang shaped things to diagnose why they might "tumble", other than to guess that it might be motor-related, or because they lack the stabilizing effect of a fuse and stab, or be caused by what you suggested. I'm hoping I won't have have that strange stability problem, because I wouldn't know how to correct it. At any rate, I don't think either the Silver Hawk or Nighthawk would have been kitted and made available for sale if they didn't work correctly.

Anxious to fly it--or ANYTHING, really, but it looks like the flying season has been torpedoed for this year. Keeping the cabin fever at bay by prototyping some gliders and whittling down my build stack. Hope you're finding things to keep you busy too.

Rktman said:

I'm not familiar enough with the aerodynamic principles behind these flying boomerang shaped things to diagnose why they might "tumble", other than to guess that it might be motor-related, or because they lack the stabilizing effect of a fuse and stab, or be caused by what you suggested. I'm hoping I won't have have that strange stability problem, because I wouldn't know how to correct it. At any rate, I don't think either the Silver Hawk or Nighthawk would have been kitted and made available for sale if they didn't work correctly.

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Eric,

I suspect the culprit might be an Angle of Incidence issue, combined with a CG location factor on the glider itself, making the glider over-react in the Pitch axis. The short moment makes recovery from the stall nearly impossible

That, of course, is purely theoretical on my part.

Dave F.

Or I may not have this particular problem at all (though I have to say that smaller gliders, and unusually-shaped ones like this, tend to be harder to hand trim and rarely fly the way they're trimmed once launched). Some have surprised me by gliding far better than when I hand trimmed them, while others do all sorts of unpredictable things. Probably why I'm so attracted to gliders--figuring out and correcting whatever's wrong (course sometimes I never do; got 3 on the shelf I've never figured out, and 4 where I finally did, but they had to sit there for a couple of years before I stumbled on the right fix).

Delta winged gliders seem to have far fewer problems doing well "right out of the box". I've built/flown several Delties, an upscaled Raven, and Pterodactyl/Mini Dactyl's and even a Jet Freak and they were all real sweethearts. Doing some self-designed delta scratch builds is definitely on my to do list during lockdown. Should keep me busy and out of trouble for several months.

Rktman said:

Delta winged gliders seem to have far fewer problems doing well "right out of the box". I've built/flown several Delties, an upscaled Raven, and Pterodactyl/Mini Dactyl's and even a Jet Freak and they were all real sweethearts. Doing some self-designed delta scratch builds is definitely on my to do list during lockdown. Should keep me busy and out of trouble for several months.

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Here's one for you, Eric ! PDF's below . . .

Dave F.

Ez2cDave said:

Here's one for you, Eric ! PDF's below . . .

Dave F.

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THANKS!

Eric,

Several year ago, SIG put out a very interesting publication about Balsa Wood. I don't know if it is still out there. or not.

My version is from 1995 . . . PDF's below !

Dave F.