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Hobie Hawk Restoration
- Thread starter Konrad
- Start date
Konrad
Very Strong User
If I didn't know better I'd think Wayne was trying to sneek in some orange. The overlap of red and yellow make an orangish color.
Vanity thy names is Konrad (actually Hobie Hawk). As a result of trying to push the under skin patches under the skin the foam core has taken some hits. For purely cosmetic reasons I add some light weight spackel to smooth out the look as seen through the transparent covering.
Vanity thy names is Konrad (actually Hobie Hawk). As a result of trying to push the under skin patches under the skin the foam core has taken some hits. For purely cosmetic reasons I add some light weight spackel to smooth out the look as seen through the transparent covering.
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Konrad
Very Strong User
"I’ve got blisters on my fingers!”-John Lennon
I’m amazed that this product MonoKote has stayed on the market for so long. This stuff is horrible to work with! I now know why Vladimere Models uses Oracover Lite for all his open bay models.
I sorry to admit this but this has been the worst “Monokoting" job I’ve done in decades! Ok. its been decades since I last used MonoKote.
This model won’t win any best of show. A lot of that is because of the many issues with the model coming directly from the OEM. I’m positive that Hobie did grade the models. And that the lower grade of models were relegated to the opaque covering and such. While my Hobie Hawk is more than presentable she is not without a lot of flaws.
I still had issues with the epoxy flowing. This is because I needed to use high heat to activate the Monokote. Unlike the epoxy on the top of the skin the under skin splices where still good when the epoxy cooled.
Much to my surprise one DOES need to flatten the wings before applying the top covering!
Now for the elephant in the room, the repair of the fuselage...
I’m amazed that this product MonoKote has stayed on the market for so long. This stuff is horrible to work with! I now know why Vladimere Models uses Oracover Lite for all his open bay models.
I sorry to admit this but this has been the worst “Monokoting" job I’ve done in decades! Ok. its been decades since I last used MonoKote.
This model won’t win any best of show. A lot of that is because of the many issues with the model coming directly from the OEM. I’m positive that Hobie did grade the models. And that the lower grade of models were relegated to the opaque covering and such. While my Hobie Hawk is more than presentable she is not without a lot of flaws.
I still had issues with the epoxy flowing. This is because I needed to use high heat to activate the Monokote. Unlike the epoxy on the top of the skin the under skin splices where still good when the epoxy cooled.
Much to my surprise one DOES need to flatten the wings before applying the top covering!
Now for the elephant in the room, the repair of the fuselage...
Konrad,
"I am the hobbie hawk..." said no Rock n' Roll singer ever.
Did you end up recovering the whole wing instead of doing the patch? The repair looks great so far. So does the small glider. I'll be interested to see how you tackle the fuse.
Looking great and getting closer...
Hank
"I am the hobbie hawk..." said no Rock n' Roll singer ever.
Did you end up recovering the whole wing instead of doing the patch? The repair looks great so far. So does the small glider. I'll be interested to see how you tackle the fuse.
Looking great and getting closer...
Hank
Konrad
Very Strong User
The walrus is Paul.
"Whiter shade of pale" -My apologies to Procol Harum
It's a patch You might notice that there is one bay that is a bit pale. With the stresses induced in flattening the wing I thought it best to to cover the top in one piece. Then later cut the covering for a clearer sharper patch (color) stripe.
"Whiter shade of pale" -My apologies to Procol Harum
It's a patch You might notice that there is one bay that is a bit pale. With the stresses induced in flattening the wing I thought it best to to cover the top in one piece. Then later cut the covering for a clearer sharper patch (color) stripe.
Looks much better than your floor! 
Been moving heavy lathes around on that vinyl floor? Oh wait that looks much better than the flooring in the office or in my garage. Darn..
I think she looks really good! For sure a lot better then when you got her.
Dang, I do like these big ol' pain in the butt planes.
Been moving heavy lathes around on that vinyl floor? Oh wait that looks much better than the flooring in the office or in my garage. Darn..I think she looks really good! For sure a lot better then when you got her.
Dang, I do like these big ol' pain in the butt planes.Well being a “Big Lewbowski” fan I had to look it up and “I am the walrus” is John Lennon but he based the song “whiter shade of pale”.
Small world.
Hank
en.m.wikipedia.org
Small world.
Hank
I Am the Walrus - Wikipedia
Konrad
Very Strong User
While I love the esthetics of the Hobie Hawk I can't say as I’m enthusiastic about the aerodynamics. Despite the aerodynamic penalties for the banana airfoil the serpentine wing to fuselage joint and the overly downward pointing nose these add to the esthetics we all love. Now what has always bothered me was the gross decalage! I think the Hobie Hawk stock set up has 6 degrees built into the fuselage. I know of no one that actually flies a Hobie hawk with that much decalage. Wanting to keep the serpentine wing to fuselage joint and the downward point nose. I took the opportunity with the broken tail housing to change the decalage.
I was able to reattach the tail housing to remove about 4° of decalage. When looked at by modern standards for glider set up I’m still carrying far too much decalage of 2°. I'm hoping that when at a proper balance point, as determined by the dive test, that 1° to 1.5° trim off set won’t look as bad as the OEM rigging of the stab. I couldn’t remove more as the push rods start to bind in the narrow tail. As shown the tail assembly is just glued on with epoxy. I will add a fiberglass bandage that will consist of 4 to 7 layers of 0.75oz cloth.
I was able to reattach the tail housing to remove about 4° of decalage. When looked at by modern standards for glider set up I’m still carrying far too much decalage of 2°. I'm hoping that when at a proper balance point, as determined by the dive test, that 1° to 1.5° trim off set won’t look as bad as the OEM rigging of the stab. I couldn’t remove more as the push rods start to bind in the narrow tail. As shown the tail assembly is just glued on with epoxy. I will add a fiberglass bandage that will consist of 4 to 7 layers of 0.75oz cloth.
Konrad
Very Strong User
Here are some issue I’m having with the tail housing. First as the ABS housing has sheered at the the fiberglass tube there is no structural support from the coupling barb. This forced me to use a fiberglass bandage on the outside of the tail boom to tail housing. This bandage was made from 0.7 oz fiberglass that was cut into a narrow triangle. This allows the for automatic feathering of the layers as the bandage is wrapped around the joint. Start with the wide base of the triangle and wind the bandage keeping it centered over the joint. As shown I have about 8 wraps around the joint. I was surprised at how little this has disturbed the profile of the boom. After feather sanding this patch I’m thinking of doing the spiral wrap again. As you know I’m a strong believer in trying to get as much fibers across a joint as is practical. With all the feature changes in that area a slight bulge is barely noticeable.
With the outside bandage carrying the load this has allowed me to remove much of the now worthless tail housing barb. I removed all of it from the lower part of the boom to allow for the needed push rod clearance as a result of the 4° kink. I left the upper parts of the barb in place to aid with clocking the tail housing to the tail boom. Earlier I said I would try to make a centering sleeve out of carbon. This wasn’t practical and Is why I’m going with the outside bandage.
I see what I think is a manufacturing flaw in that the rudder push rod has sharp 90° bends. This allows far too much flex in the control rod. The push rod should have exited the fuselage further forward to allow less of a bend. I normally place the controlling servo on the opposite side from where the push rod exits the fuselage to try to gain a straighter shoot at the control horn. With the Hobie Hawk these crossed control rods were having far too much cross talk. Much to my surprise placing the rudder servo on the same side as the push rod exit makes for a much smoother control system.
I also found that the rudder hinge was dragging a lot. I thought is might be from too much paint on the tail housing. It wasn’t as the housing only has a primer and one finish coat of paint. I think the plastic rudder piece might have become distorted over time, or as a result of stress. So, I sanded some clearance into the back of the tail housing.
With the outside bandage carrying the load this has allowed me to remove much of the now worthless tail housing barb. I removed all of it from the lower part of the boom to allow for the needed push rod clearance as a result of the 4° kink. I left the upper parts of the barb in place to aid with clocking the tail housing to the tail boom. Earlier I said I would try to make a centering sleeve out of carbon. This wasn’t practical and Is why I’m going with the outside bandage.
I see what I think is a manufacturing flaw in that the rudder push rod has sharp 90° bends. This allows far too much flex in the control rod. The push rod should have exited the fuselage further forward to allow less of a bend. I normally place the controlling servo on the opposite side from where the push rod exits the fuselage to try to gain a straighter shoot at the control horn. With the Hobie Hawk these crossed control rods were having far too much cross talk. Much to my surprise placing the rudder servo on the same side as the push rod exit makes for a much smoother control system.
I also found that the rudder hinge was dragging a lot. I thought is might be from too much paint on the tail housing. It wasn’t as the housing only has a primer and one finish coat of paint. I think the plastic rudder piece might have become distorted over time, or as a result of stress. So, I sanded some clearance into the back of the tail housing.
Konrad
Very Strong User
I may have found another degree of so that I can loose to bring the decalage closer to a more realistic value. If I lower the wing incidence I get a much better fuselage to wing joint. Getting rid of the gap towards the rear of the wing will cut down on drag (a lot)! And at the same time lower the decalage another degree or so. Win win in my book!
Now the fuselage alignment bore is fully encapsulated for its full run in the fuselage. This makes moving the pin down in the fuselage rather troublesome. But the wing side alignment bore looks to be held by the ABS wing root rib. I’m thinking that I could use a 5/32 hole saw and remove the alignment tube in the wing. Then move the hole upwards about 2mm for the best fit against the fuselage.
Does anyone know if there is more structure behind this root rib other than blue foam?
All the best,
Konrad
Now the fuselage alignment bore is fully encapsulated for its full run in the fuselage. This makes moving the pin down in the fuselage rather troublesome. But the wing side alignment bore looks to be held by the ABS wing root rib. I’m thinking that I could use a 5/32 hole saw and remove the alignment tube in the wing. Then move the hole upwards about 2mm for the best fit against the fuselage.
Does anyone know if there is more structure behind this root rib other than blue foam?
All the best,
Konrad
Konrad
Very Strong User
What am I dealing with here? The cracks in the paint go all the way into the Dura-lene fuselage. I tried to heat strip with no luck. I had to sand off the paint. This resulted is the skin showing the rotor molding grain. This plastic doesn’t seem to flame polish at all, unlike like the plastic I’m use to with the Bob Martin fuselages.
The bad news is that my fuselage distorted a bit when I tried to flame polish it. I should still be able to block sand this out if i can figure out a prep and painting process.
The bad news is that my fuselage distorted a bit when I tried to flame polish it. I should still be able to block sand this out if i can figure out a prep and painting process.
Konrad
Very Strong User
Ok, I learned a bit more. What I thought were lines from the rotor molding are in fact just belt sander marks from the removal of the molding flash at the mold part line. This explains some of the low spots in the fuselage on the starboard side. You might see some low spots on the port side (brown tint). This is where I distorted the fuselage trying to flame polish out the belt sander marks. As pissed as I am at myself for causing this damage. In the long run it might be a good thing, as it will force me to fix the OEM damage on the starboard side.
I still don’t know if the fuselage caused the paint to crack. Or if the paint cracked causing the parent material to distort under the cracks.
I still don’t know if the fuselage caused the paint to crack. Or if the paint cracked causing the parent material to distort under the cracks.
Konrad,
Looking good, I’m certainly learning lots of stuff. Stuff like if I ever come across a hobbie hawk I will just try to sell it on at a profit.
Seriously though, it has been a enjoyable experience watching you turn a model that is outdated and worn out into the model you want.
But I think I’ll get my hobbie hawk fix from flying yours...some day
Hank
Looking good, I’m certainly learning lots of stuff. Stuff like if I ever come across a hobbie hawk I will just try to sell it on at a profit.
Seriously though, it has been a enjoyable experience watching you turn a model that is outdated and worn out into the model you want.
But I think I’ll get my hobbie hawk fix from flying yours...some day
Hank
gp49
Very Strong User
Hi Konrad,
Watching your posts on the Hobie and collecting your the knowledge for my future rebuilds.
Recently I came across a post on rcgroups written by Bob Martin (Duralene Coyote and later Hobie manufacturer) on flame treating.
https://www.rcgroups.com/forums/showpost.php?p=44135173&postcount=3927
One of the interesting bits I learned from it that the plastic should be painted with in 15 minutes of the flame treating.... A lot of the guys rebuilding the Hawks use the Klass Kote epoxy paints.
Mark
Watching your posts on the Hobie and collecting your the knowledge for my future rebuilds.
Recently I came across a post on rcgroups written by Bob Martin (Duralene Coyote and later Hobie manufacturer) on flame treating.
https://www.rcgroups.com/forums/showpost.php?p=44135173&postcount=3927
One of the interesting bits I learned from it that the plastic should be painted with in 15 minutes of the flame treating.... A lot of the guys rebuilding the Hawks use the Klass Kote epoxy paints.
Mark
Konrad
Very Strong User
Hank,
This isn't unique to the Hobie Hawk but is typical of just about all cult classics. When looked at in detail it is clear why they aren't mainstream. But yes, a wise man would sell it as fast as he could. In my case I've flown a few Hobie Hawks and didn't like them. But that can be said of many other models I've flown that I didn't set up. So to give the Hobie Hawk the benefit of the doubt I need to set one up and see what I can get out of her. Maybe there is a gem in there, not likely.
Mark,
I did that flame polish, but unlike what I recall in the past the surface did not turn glossy. I was waiting for the "surface change" when I over heated the fuselage and caused that distortion. I don't know if this was a function of the age of the material or a process thing on my part.
That surface ion charge is a real issue. We fought this a lot in the metal plating and metal flame spray shops.
I will be using PPG catalyzed urethane primer and paint.
This isn't unique to the Hobie Hawk but is typical of just about all cult classics. When looked at in detail it is clear why they aren't mainstream. But yes, a wise man would sell it as fast as he could. In my case I've flown a few Hobie Hawks and didn't like them. But that can be said of many other models I've flown that I didn't set up. So to give the Hobie Hawk the benefit of the doubt I need to set one up and see what I can get out of her. Maybe there is a gem in there, not likely.
Mark,
I did that flame polish, but unlike what I recall in the past the surface did not turn glossy. I was waiting for the "surface change" when I over heated the fuselage and caused that distortion. I don't know if this was a function of the age of the material or a process thing on my part.
That surface ion charge is a real issue. We fought this a lot in the metal plating and metal flame spray shops.
I will be using PPG catalyzed urethane primer and paint.
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Konrad
Very Strong User
One of the things I like to do along with holding management accountable is destroying the mystique surrounding whatever.
In the case of the Hobie Hawk I showed that the wings are often mis-manufactured. And now that the fuselage has a lot of issues with the manufacturing process as a result of the choice of materials used.
While I really wanted a Hobie Hawk when I was in high school, I’m so glad I didn’t spend my hard earned money on one the the late 70’s!
In the case of the Hobie Hawk I showed that the wings are often mis-manufactured. And now that the fuselage has a lot of issues with the manufacturing process as a result of the choice of materials used.
While I really wanted a Hobie Hawk when I was in high school, I’m so glad I didn’t spend my hard earned money on one the the late 70’s!
Konrad
Very Strong User
I hope the glass is strong enough. it has to be stronger than the original ABS insert.
My concern with that fix is that it rakes the hinge line even further aft (adding a bit of up with every rudder input??). But as that is what I do to make a turn it might not be a bad thing. Like you said first flights will show if what I come up with is any good.
My concern with that fix is that it rakes the hinge line even further aft (adding a bit of up with every rudder input??). But as that is what I do to make a turn it might not be a bad thing. Like you said first flights will show if what I come up with is any good.
T
Toomanyplanes
Guest
Hi guys. I have parts for the original Hobie Hawk that are nearing completion as well as a group of 20 Superhawk G1's that are mid assembly if anyone is interested. I have stabilizers and rudders coming soon (as in this week) and carbon fiber dorsals as well. I am on a "Covid vacation" and this is my pet project at the moment. I see there a few posts here mentioning my work and you can be assured that I am a serious Hawk nut and all parts/planes made are to the highest standard. They are all made with materials that were used in 1975 (the exception is the poly nose pod. Nickel molds are WAY to expensive! YIPE!). I also have rod and pin sets that are available in alloy aircraft aluminum and Titanium. Thanks for the bandwidth, I love this plane and will keep making parts as long as its worthwhile. Turbulence and barfbags! Tony Johnson, Synergy Composites.
