Hobie Hawk Restoration

[Konrad]

I was out flying when an older gentlemen came up to me and said: I appeared to know what I was doing and would I like a Hobie Hawk. I said YES! Off he went, and ten minutes later he came back with a Hobie Hawk in its foam box. I’m glad I had landed as I’m sure I would have crashed from the excitement of seeing what looked like a complete Hobie Hawk. He said he knew it was worth $300 to $600 but that all he wanted was for it to go to a good home and get back into the air. I don’t know about a good home, but I’m going to try to get her back into the air.

She really is in good shape. The only real issues are that the ABS tail housing has broken off the fuselage. Mainly as a result of a poor 5 minute epoxy* repair. And that one of the wing tips is damaged about 2 bays in from the tip. Again this was improperly repaired with 5 minute epoxy.

She is in such good shape that I thought it best to do a decent restoration. The first thing is that the front fuselage is showing a lot of crazed paint. Most of this looks like bond failure as a result of impacts to the forward section. I think this is a Roto-molded Polyethylene piece, (AKA Dura-lene). These are horrible to refinish. I was hoping to be able to sand the gloss paint down to the primer and repaint. But looking at the failed paint in the canopy recess I’m now thinking all the paint needs to come off. Other than sanding does anybody have a good way to remove paint from Polyethylene. What have you guys used as primers for the post flame treated Polyethylene.

Now that broken off tail housing is looking like a blessing is disguise. One of the complaints I had when flying Hobie Hawks was that the decalage and CofG were way off (these go hand in hand). With the broken housing I can reattach it with the housing tilted aft. As I recall the original decalage is close to 6°. This is way too much for an RC aircraft! I’d like to get the force arangment closer to a modern sailplane. I’m liking the idea of kinking the aft end of the fuselage rather than trying to take out all the decalage by moving the wings. This is a problem with getting the wing to seat against the fuselage. Besides I want to keep the classic nose down look along with the elliptical dihedral as that is what makes the Hobie Hawk look like a Hobie Hawk. I know that with the undercamber wing she will never fly like a modern ship.

All the best,
Konrad

*5 minute epoxy has no place on a model! It might be used for field repairs. But with modern CA even that use as a field repair is very limited. The best thing that one can say about 5 minute epoxy is that it is often easy to fail with some heat. Making home repairs easier to do correctly after coming back from the field!

 

[gp49]

Hi Konrad,
Welcome to the Dark side. As you most likely know there is plenty of Hobie Hawk support on rcgroups - I would recommend that you stay away from the decalage discussion (that's the Dark Side for the old timers there) as most of the guys there are not interested in it . Paul Naton from Radio Carbon Art Videos ( http://www.radiocarbonart.com/blog/my-glider-1975-hobie-hawk-resto-mod-project/ ) restored and modified a Hawk recently. He changed the decalage by rotating the wing I believe - check out his restoration videos much easier to do and will keep your value in the Hobie. The material on the dorsal that is broken is very prone to breakage on landings. I just purchased a newly manufactured one from Tony at Synergy Composites in Washington he frequents the rcgroup HH forum as V1VrV2. It's $75! and well worth it - fiberglass/carbon molded design. He might still have some. Jack Trotter in Soquel is another good local source for advise. Canopies are available as well.

As far as your fuse it's the prep work for the nose section is what most people skip - it should be flame--treated. Klass Kote is what some use for the paint.

By the way I have two of them that I'm going to restore this winter, I hope....

Mark

 

[Wayne]

I really do hate this story everytime you tell it. Why of why couldn't the guy find me?

But I already have a couple of them, one does not need anything but radio and some covering patches. Don't ask what it cost me! It hung from a hobby shop for decades. Recently went to a sale and found a matching wing in rough shape, swear to goodness it is nearly the same color and scheme.. Not a factory job that i know of. (Blue/white)

I might have a spare clear ABS tail section, but I think that $75 option may be the better way to go! Those are a little delicate and this plane likes to swing around on landing with that nose down so low.

I would NOT make the change at the tail.. Yuk. Normal is a new hole on the fuselage and it does seal up well. And don't get into the dorsal BS, this plane is great as it is, but if you are a stick flicker she will demand better from you on the rudder!

As a kid learning to fly one of the locals let me fly his Hobie on the slope to teach me to stop flicking my sticks. Dang I still remember that flight! I love a plane that can go slow and float, but also can go crazy on a slope, and trust me, the HH can go crazy on a slope when the pilot has a lot of time with the plane and knows her well.

Awesome planes! I have thought about putting together a modern kit version with a fiberglass fuse and maybe 1.8m span. Who knows.. maybe in the future..

 

[gp49]

Here are some of the dorsal references attached. BTW, I have a brand new unpainted fuse and the dorsal is not ABS, it's poly-carbonate. The image with the dorsal split into different components are the prototypes made by Tony. If you need, I also have the dorsal .stl files that I got from the rcgroups....

The R/S radio from the early 1970's is for the Hawks I'm fixing, but with slight change in frequency ?

 

[Wayne]

Wow, he is doing those very nicely. I like!

I think they were originally ABS, then poly-carbonate?? Or the other way around.. The spares I bought were the last plastic injected versions I am aware of, said to last longer and were clear. I think I paid $50 or more for each many years ago.

Love the radio too! Will be a sweet setup when done. What does your Hawk look like?

I should put mine together and hang it from the office here..

 

[Konrad]

Thanks guys.

To save me form floundering around on the RCGoof site can you please provide me with contact info? I have no way to contact folks on RCGoofs. I and the Tennessee "Hayseed" management at RCGoofs have parted company many years ago. No sense in adding to their Google ranking by giving RCG a lot of undeserved hits!

To be honest I've flown the Hobie Hawk on the slope and hated it! Well the one I flew. It actually flew worse than the Wanderers and Gentle Ladies! The Hobie Hawk felt a lot like a single channel (rudder only) ship. She was very sensitive to speed changes. That is she felt real nose heavy. If you gained speed you had to give a lot of forward stick to keep from making a loop. In the days of single channle (rudder only) ships we set them up like that. That is to loop we would do a spiral dive, straighten out the rudder and let the speed bring the nose up into a loop. To kill the climb we would make sharp rudder turns. Again this was all due to having far too much nose weight.

Bringing the CofG back would make this a lot smoother (easier to fly well). But we had to add a lot of down trim in the push rod rigging. So much so that we often ran out of down elevator movement as we bound up on the end of the control slot.

I have seen the wings rotated on the wing rod to get the decalage down to realistic numbers. But this came at the cost of loosing much of the Hobie Hawk esthetics, with the way the wing faired into the fuselage. The trailing edges of the wing "almost" meeting under the fuselage.

Taking out the decalage with a 4° or more kink in the tail should keep most of the esthetics that we think of as being the Hobie Hawk. That is the nose down flight profile, weird fuse to wing joint and the elliptical dihedral.

Thanks for the correction on the material for the stab mount (dorsal fin). Mine still looks a lot like ABS.

That is a very good point about the loads on the tail as tail slams down when the nose hits the ground. I was planning to make a thin walled carbon tube to replace the cone wedge in the drawing. Then I was going to add six or so layers of 0.7 oz glass across the joint on the outside. (As it is now the paint is so thick that I can flare these layer without causing a bump). I really think this joint needs a lot of fiber across it.

I may need to bring out my analog mixing Silver Seven. I don't think I have converted her to 2.4 ghz.

Wayne, guys won't throw models at your feet while you are flying if you don't go flying. I think there the issue you hang them in your lobby.

 

[Wayne]

I really don't have a good slope around here for the Hobbie. Save it for Sunset State Beach and similar.

The issue with landing is the nose touches down first, and if you have any energy, the plane will start to rotate and this is what snaps off the tails.

 

[Konrad]

Understood. Classic ground loop!

I'm sure Hobie didn't have this problem landing in the soft sands of the beach. I too learned of the Hobie Hawk wiggle. Smooth controls really made her look like a gracefull flier. But it wasn't her it was the pilot. I think with expo this issue will all but disapear.

 

[Wayne]

She rewards a smooth stick..

I was very impressed when a thermal guy pulled out a beauty and launched one on a high start then cored out a thermal to a spec. I really didn't think the planes were light enough to do that. They are not feathers..

 

[Konrad]

She rewards a smooth stick..
...

Don't all sailpanes do this?

 

[Konrad]

I really do hate this story everytime you tell it. Why of why couldn't the guy find me?
...

Hey, didn't you tell a story of you getting a ready to fly F3F ship for penies on the dollar!

I'm not feeling so bad that you didn't get this HH. ?

 

[gp49]

Here is my #2 Hawk for some reference. The black dorsal is the new replacement from Tony. Looks really good just needs a little finishing before paint. It's much stronger especially when comparing it to my polycarb one on the new fuse.

Mark

 

[Konrad]

This is how she looked when she came into my heart.

 

[Konrad]

She rewards a smooth stick..

I was very impressed when a thermal guy pulled out a beauty and launched one on a high start then cored out a thermal to a spec. I really didn't think the planes were light enough to do that. They are not feathers..

This and the Graupner Cirrus taught us that weight really was a secondary consideration when setting up gliders. That is in the real world minimum sink will loose out to maximum glide ratio in glider design, in all but dead calm air. It really was/is all about drag reduction. Now the under-camber airfoil held on in the Hobie Hawk, but by 1975 even Dave Thornburg’s Bird of Time had a thin (8%), for its time, flat bottom airfoil. And this was achieved without carbon!

To be honest flight performance wasn’t the strong point of the Hobie Hawk. She was one of the best, if not the best flying ARF. I think in the ARF market there was only the sad Hobby Shack’s Spirit of 76 to compete with her. But her real appeal was in her unusual esthetics. That elliptical dihedral, the wing to fuselage joint and yes her bulbous nose, still to this day make her a beauty.

All the best,
Konrad

 

[Konrad]

I just watch Naton’s videos on his HH. (I hate how long it takes to get information across in most videos). Even using his hot iron I’ve never had good luck removing iron film (MoneyKote) that has been properly applied without leaving the color behind.

Anybody know of a good paint (black) that will not eat the blue styrene foam core and hold up to the heat needed for applying the iron on film. I read that Hobie thought that a black structure would have look good seen through the transparent covering.

All the best,
Konrad

 

[Hank GB Z]

Hey Konrad, Don't bad mouth the Spirit of 76! We had a great 45 min flight on that one before the battery died...

I always liked the Hobbie Hawk. There's a hobbie resturant in SNA airport and they have a Hawk hanging from the ceiling. Seems someone is always looking at it seeing if they can buy everytime i'm flying out.

I'm also wondering if the decalage issue changes now that the equipment we have is lighter don't need such high AoA to maintain lift...


Back in 2001 i worked in a hobby shop and a guy came in with 3 hawks in boxes, all had been flown and had some damage. My friend handed him 100 dollars for the lot and the guy was over the moon. My friend fixed and sold them for 250 a piece...


Hank

 

[Konrad]

As I recall that Spirit was far from stock, like a 4 servo wing!

The loss of radio weight would mean that the wing can work at a lower angle of attack (lower Cl = lower drag). The decalage is more of a CG trim issue. Again a drag reduction concern with trim drag.

Yep, the HH does hold her value. But I don't think of my hobby purchases as part of my investment portfolio.

 

[Hank GB Z]

Konrad,

The 76 mods was a 2 piece 2 servo wing with an added wood spar. Like 2 degrees of dihedral. We did set up the mixing for spoilerons on the throttle stick.

We need a 4 servo wing HH!

Hank

 

[Konrad]

Not from me.

 

[Konrad]

I hate loosing a model to radio/ battery failures!!!

Just saw your Spirit of 76 photos. This is like comparing a longshore man against a ballerina. I’m sure the added ailerons will give the Spirit a lot more flexibility. But really, if you came to the slope which one would you like to be seen in your arms.

Image is everything-Canon