Hobie Hawk Restoration

[Konrad]

Yes, less than half the weight but also 1/2 to 1/3 the wing area. By the late 70's just about any "modern" plane would out thermal my Windfree. I agree that the Hobie Hawk is best looked at as the slopish ship. Even giving the Hobie Hawk the advantage of slope lift off of Green Mountain it was a distant second to any of the other standard class and most 2 meter ships of the late 70's.

I think you are making my point, one needs to be a Bob Hoover or Chuck Yeager to get any kind of performance from the Hobie Hawk. Other than esthetics they really were a dud!

With this one I'll try to give the Hawk a fair shake in that I'll be setting her up with my preferences. It really isn't fair to compare ships that one hasn't spent time setting up. Borrowing ships is nice but one doesn't find the true nature of the ship until one spends time with her on the bench and in the air.

 

[Wayne]

I like them, and still think they are pretty. But your points are valid.

This day and age I much prefer to fly different airframes, that is for sure.

 

[Konrad]

We all know that all significant meaningful advancement in humanity are predicated on material advancements.

With all this talk about materials, I thought it best that I address an issue with how I moved the alignment rod. I used urethane glue to fill any voids behind the ABS wing root as a result of removal of the alignment tubes wing. This resulted in the urethane glue also filling the void in the ABS wing root. As the expanding urethane isn't very hard (stable) the tube might move over time. To regain the stability we had with the ABS wing root I removed the urethane for the depth of the ABS wing root cap. I back filled this void with an adhesive called Stabilit Express. I choose this glue as it will etch the ABS (most plastics) to aid in the bond.

BTW; I have flown at least 3 Hobie Hawk. And to a bird they all exhibited poor flight performance. That is they required a great deal of pilot workload. As these were borrowed ships and the owners were a bit too proud of them they didn't want to experiment with their set up. Well, didn't want me to hack away at their bird!

I believe the root cause of this poor performance was that they were all grossly nose heavy! I think guys felt that Hobie knew what he was doing setting the decalage where he did. And as a result did not want to risk their way over priced ARF going tail heavy (as defined by the stabilizer rigging compared with the stab fairing on the tail). Add to this fear, that the Hobie Hawk has a notorious reputation for tip stalling, getting a guy to move the CG aft was like pulling teeth!

I think there are two features that contribute to the strong tip stall phenomenon. The predominate one is that nose down stance of the fuselage when at low coefficients of lift. I love that the fuselage is aligned with the upward moving air mass. But to an RC pilot looking from afar this is, at first, difficult to comprehend. That is that a fuselage that is pointing down is flying level and maybe even climbing. As a result pilots pull up to level the fuselage stalling the wing. The second issue was that I don't think the wings had washout molded into the wings. The washout was held by the film covering. Over time, heck even during the maiden flight, there often wasn't enough washout. None of these issues can be properly addressed by nose weight!!

Guys, designers are usually human and as such are prone to errors. Stability is one of those issues that has a large personal component to it. It is also one that has a lot of dynamic forces involved. If your model doesn't perform as you intend please don't be afraid to rework it until it does.

 

[Konrad]

I like them, and still think they are pretty. But your points are valid.

This day and age I much prefer to fly different airframes, that is for sure.

Even back then, most would rather have flown a different airframe!

 

[Konrad]

Anybody know what glue was used to glue the threaded rods into the fiberglass push rod tubes? It is neat in that I can change the length of the push rod with a heat gun. When cooled down it stiffens back up. It is the white stuff in the fiberglass tube.

 

[Konrad]

Reading through this thread I have to ask if Mark (@gp49 ) has leap frogged ahead of me in the Hobie Hawk projets?

Hobie Hawk Restoration

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...

forum.alofthobbies.com

I've just had 2 minor set backs on this project. I will try to document them soon.

 

[Hank GB Z]

Looking back through the thread I see my post from 2019 is coming true.

Hank

I look forward to a flurry of building in the month of April.

Hank

 

[Konrad]

Looking back through the thread I see my post from 2019 is coming true.

Hank

Yep, we will start to call you the Oracle of Delphi. What’s 4 years amongst the gods?

 

[Konrad]

I found my Windfree box of 40+ years. Sort of a sad comment that the box has out lasted the model! What surprised me was the label was showing the Windfree's contest record going back to 1970! This gives one an idea of how poor and dated the aerodynamics of the Hobie Hawk were for RC, being set up as a 40's Free Flight, with her banana airfoil and 6+ decalage!

Ok, to be fair I recall Mark Smith winning the Chicago National's, a thermal contest, by flying the ridge lift off the tree line at the edge of the field!

 

[Konrad]

I found another poorly done repair on my Hobie Hawk. I'm kicking myself As I should have really looked closely at the front end of the elevator push rod while it was out. I don't want to risk breaking the clevis or elevator bellcrank trying to remove the push rod.

Looking at the repait it was a poorly done tube splice! I removed the repair and used a threaded brass coupler.

I have to admit I was fit to be tied! While removing the wings I allowed the wing rod to drop through the wing covering!

 

[Hank GB Z]

Are you gonna re-cover the whole wing? As your friend I think it will be better for your mental health to just patch it.

Hank

 

[Konrad]

Nope. I don't have enough transparent red shelf paper passing as Monokote! And I have the patch on the other wing. I'm rapidly coming to the conclusion that the Hobie Hawk was all hype. I don't see the benefit of a full recover. After all it's not a collectors item!

 

[gp49]

Nope. I don't have enough transparent red shelf paper passing as Monokote! And I have the patch on the other wing. I'm rapidly coming to the conclusion that the Hobie Hawk was all hype. I don't see the benefit of a full recover. After all it's not a collectors item!

since it's not a collector item you should use the 'contrasting' color covering you purchased yesterday and save your valuable transparent red!!!!

 

[Konrad]

Hind sight is always 20/20!! I should have taken closer note of Paul Natons build. He was using Ultracoat (Oracover). But no I wanted to use as much original materials as possible. Only to find real MonoKote was gone decades ago! What I used was labeled Monokote but it wasn't near the same material that the Hobie Hawks were built with.

The Monokote I used has the strength of a soap bubble! I swear the rod dropped on the wing from about 6", no more than 8".

Now what Mark is making reference to was this roll of Fluorescent Yellow. We found some old new stock coverings as Saturday's swap meet.

 

[gp49]

Hind sight is always 20/20!! I should have taken closer note of Paul Natons build. He was using Ultracoat (Oracover). But no I wanted to use as much original materials as possible. Only to find real MonoKote was gone decades ago! What I used was labeled Monokote but it wasn't near the same material that the Hobie Hawks were built with.

The Monokote I used has the strength of a soap bubble! I swear the rod dropped on the wing from about 6", no more than 8".

Now what Mark is making reference to was this roll of Fluorescent Yellow. We found some old new stock coverings as Saturday's swap meet.

View attachment 14764

This picture does not show HOW BRIGHT that FLOURECENT color is . If you use it it would definitely show which way the hawk is going! I could not get myself to spend $5 bucks for it it was so bright. ( I did buy a 5m roll of white Solartex fabric though for $5!)

 

[Tahoed]

I like yellow...

 

[gp49]

I like yellow...
View attachment 14765

@Tahoed

That's a nice yellow! I think it stll needs the 'Hawk' Logo on the tails. Here is a small copy (I do not have bigger..)

 

[gp49]

@Konrad since you are getting close to Sunset and flying the Hawk, here are a couple of articles on the wing incidence and flying the Hawk from a couple of 'old timers' I'm sure you read thru these already before, but just in case you need a refresher here they are again.

 

[Tahoed]

Will this work?

 

[Konrad]

@Tahoed, Love the look of the fuselage to wing junction! looks well done. I've not seen box stock Hobie Hawks with that nice a junction. I assume you spent time fitting the wings to the fuselage.

On the subject of Yellow I too like it. I choose it on my 1989 Chile. Over the years the Fluorescent Yellow paint and dyes have faded at different rates. I knew this back then but didn't think this Hot Liner would have a long life with the wing loading carrying 16cell. Again this model (Chili) proved that weight is NOT the #1 enemy of flight!

@gp49, there is a lot written about the downward rigged fuselage. DR. MICHAEL S. SELIG wrote much on the subject and even published a glider called Opus (After the Penguin in Bloom County). This is why I left the wing to fuselage incidence as close as possible to stock. I did lower it a degree to get a better junction fit between the wing and fuselage.

I chose to kink the tail 4° ,as it was already broken, to try to remove as much decalage as possible. Hobie erred with that huge amount of decalage (6+), not in the downward pointing fuselage. We as RC pilots make the mistake of trying to use the fuselage as an indication for the angle of attack of the wings.

Having been in the room when the stability of the 787 was discussed, I disagree with papers explanation of the need for stability augmentation on the 787. As I said elsewhere the appendages on the 787 were redesigned at least 2 during flight testing! But yes the Hobie Hawk needs a lot more vertical tail volume. But I hate the look of the dorsal fin some add!

So my Hobie Hawk might be a very early Hawk as the incidence between the wings was found to be in gross error.