Cessna 152, Balsa 30% Scale Rescue from Hostetler Plans

[Joker 53150]

I haven't had great luck with "Great Stuff" expanding foam in modeling because it still remained partially flexible after it cured - which might not be ideal for your situation either. On the other hand, some flexing would still mean energy used to flex the foam is being bled off from impacting the rest of the structure, so it certainly wouldn't be useless. I know that I've run into some of this expanding foam that does get hard before - I just don't know which brand it might be, or if that's just a function of time curing it differently.

All the Stuff I've used gets fairly hard and is ridiculously sticky when wet. I don't know how much rigidity it would add, but I'm thinking of using it just to help hold everything together, kind of an insurance policy in case the CA doesn't get all the breaks. The other thought was Gorilla Glue, but that stuff scares me a bit more than Great Stuff.

 

[rockyboy]

Yeah, I think the expanding pressure of Gorilla Glue could bulge things out very easily, but the Great Stuff should be more managable for that. It seems to only do the big expansion for the first minute, unlike Gorilla's sneaky 30 minutes later it's foamed everywhere when you weren't looking.

 

[Joker 53150]

Yeah, I think the expanding pressure of Gorilla Glue could bulge things out very easily, but the Great Stuff should be more managable for that. It seems to only do the big expansion for the first minute, unlike Gorilla's sneaky 30 minutes later it's foamed everywhere when you weren't looking.

I've run into that same problem with GG - you *think* it's done expanding and walk away for 5 minutes, only to return and find it all over the part, your bench, the dog, and the roof of the house.

For the fun of it, I went out into my garage and looked at some Great Stuff that I used to seal a spot at the foundation that opened due to settling of the concrete pad over 60 years. It's a little dirty, but otherwise is in great shape. Poking it with a stick it was very stiff, but had some "give" (just like foam?). This was the name-brand Great Stuff original recipe, the same stuff I'm thinking of using on the Cessna. They do make a few other varieties, but I think this'll work.

 

[Tench745]

Personally, I don't think Great Stuff is a good idea; I would be worried about it deforming both inner and outer skins. We used it to make some fake pies for a musical one time and a couple hours after the tops had gone hard it bulged the bottoms of the pie tins out about an inch. Besides that, if you ever want to get in there in the future for repairs, running wires, or whatever you'll have to excavate all that foam first. If you're set on using it, there is a lesser-expanding version of Great Stuff made for use around doors and windows which I would recommend over the standard type for this application. Definitely make up a test piece before you try it in the Cessna.

Also, why carbon tube and not carbon tow or cloth for the skin reinforcements? I feel like a flat sheet would give you more surface area for less weight, and you really only need to make the skin strong enough to take the loads it was designed to.
Just my two cents.

 

[Joker 53150]

Personally, I don't think Great Stuff is a good idea; I would be worried about it deforming both inner and outer skins. We used it to make some fake pies for a musical one time and a couple hours after the tops had gone hard it bulged the bottoms of the pie tins out about an inch. Besides that, if you ever want to get in there in the future for repairs, running wires, or whatever you'll have to excavate all that foam first. If you're set on using it, there is a lesser-expanding version of Great Stuff made for use around doors and windows which I would recommend over the standard type for this application. Definitely make up a test piece before you try it in the Cessna.

Also, why carbon tube and not carbon tow or cloth for the skin reinforcements? I feel like a flat sheet would give you more surface area for less weight, and you really only need to make the skin strong enough to take the loads it was designed to.
Just my two cents.

I'm not too worried about the foam bulging the balsa in this case, it's 1/8" thick sheeting and fairly stout so it wouldn't take much to fill the cavity. "Blow holes" are also a must so the excess has room to escape. The lower expanding version is a good idea, I'll take a look at that as well.

For the carbon fiber, the tube (or rod) is mainly going to be to tie the upper and lower half of the fuselage together firmly aft of the door. Adding a simple rod/tube is as simple as cutting a pocket for it, gluing it in place so it's flush/slightly recessed, and filling over it for a smooth finish. If done correctly (another story completely) it won't be visible from outside after covering and will use less filler to smooth it all in. My understanding on the tow or cloth is that those are applied to the surface, and would therefore require more work blending it all in. I've never worked with tow or cloth, so I may be WAY off base...!

 

[Tench745]

I'm not too worried about the foam bulging the balsa in this case, it's 1/8" thick sheeting and fairly stout so it wouldn't take much to fill the cavity. "Blow holes" are also a must so the excess has room to escape. The lower expanding version is a good idea, I'll take a look at that as well.

For the carbon fiber, the tube (or rod) is mainly going to be to tie the upper and lower half of the fuselage together firmly aft of the door. Adding a simple rod/tube is as simple as cutting a pocket for it, gluing it in place so it's flush/slightly recessed, and filling over it for a smooth finish. If done correctly (another story completely) it won't be visible from outside after covering and will use less filler to smooth it all in. My understanding on the tow or cloth is that those are applied to the surface, and would therefore require more work blending it all in. I've never worked with tow or cloth, so I may be WAY off base...!

I understand the goal with the carbon now. I keep forgetting how big this thing is that you could hide tubing in the structure. I haven't worked with tow or cloth either, but they seem to work like any other fiberglass to me.

 

[Joker 53150]

Damage review has given way to repairs beginning. I let it sit for a few days so I could think on it before starting the work - no sense in rushing things.

- The BLACK arrow below shows the horizontal crack line found on both sides.
- The GRAY arrow is a very slight vertical crack just behind the door frame.
- The LIGHT BLUE arrows are where the crack is found from inside the plane.
- The PURPLE arrow is a small crack only on this side.
- The YELLOW outlines the "boxed" section on both sides that I'm probably filling with Great Stuff expanding foam.

To start the repairs and stabilize the structure I thinned some 30 minute epoxy with denatured alcohol. With a plastic syringe I applied it all along the horizontal cracks (both sides) as that is right where the crack is. This alone will probably be enough to hold it together so I can remove the block under the tail. That block is just there to force the gaps closed and get the tail back into it's proper orientation.

After the epoxy cures I'll cut the grooves to install the carbon fiber rods, that will extend from up by the wing, down through the side panel and into the lower fuselage, bridging the cracks and tying it all together. Last will be the expanding foam followed by fixing the covering.

 

[Joker 53150]

Well, the first step is done, and thinned epoxy was injected all around the inside where the crack was. It had time to cure for a few days and the tail feels very solid again, although I know it's not as strong as it really needs to be now. I'm glad I didn't just jump in and start cutting to install the carbon fiber rods though. The original though was to cut grooves into the sides and lay the carbon fiber rods in with epoxy, followed by filler, sanding, and re-covering. After thinking about it for a while I decided on a new fix that was far less invasive. Two small holes are drilled into the top of the plane and the carbon fiber rods are then inserted down through the ceiling and along the INSIDE of the big B pillar (the area between the side window and rear window). The rods are long enough to extend down about 2" below the horizontal crack, and unfortunately I have to do a little minor cutting from the outside to get them down that far (notice the two small cuts along the crack).

Once all 4 rods are in place I'll trim them to length and do a final placement of each, along with more epoxy. That should tie the structure together nicely before I move on to the next step, which will possibly involve some carbon fiber flat bar along the rear window center brace.

And yes, the covering looks absolutely horrible with this extra bright LED on it. It's sagging and torn from that crash and I HATE to see it like this, but shrinking the covering now won't help.

 

[Joker 53150]

Well, tomorrow I should know two things. #1, if the engine runs properly (which I'm sure it does), and #2, if the tail repairs can handle the stress and vibration of the test run. I think the thinned epoxy that was applied first really worked well in stabilizing the wood, and the carbon fiber should be good insurance.

The repairs will be ugly until I get the holes patched/filled/re-covered. I'm still thinking about making a couple more holes to get some Gorilla Glue or Great Stuff foam in there as well. GG is a heck of a lot stronger, but harder to get good coverage and it won't fill the cavity as well. Maybe I'll start with GG and finish with GS.

 

[Joker 53150]

Well, crap. The Cessna may be cursed as it just doesn't want to stay in the air. It's not obvious at first in the pic below, but the nosegear is collapsed and the front of the plane is being held up by the partially broken prop. The muffler pipes are also bent/broken.

But for some good news, the previously made repairs after the first maiden attempt held perfectly, and there was no additional damage from today's attempt at flight.

So weather was good (a bit hot, but no real wind) so I took the plane up to my dad's field to fly. Since it hasn't been flown since the first maiden, I fired it up without wings installed and taxied it around the field for a while. Once I confirmed the repairs were solid I installed the wings and sent it up.

Good thing there is a long runway at this field, as the plane is VERY heavy. The plane's designer calls for a 2.5 to 4 cubic inch engine. My 58cc is 3.5 cubic inches which should be enough. Well, it is, but just barely. It flies scale, like a Cessna 150/152 should, but some additional power would certainly be nice for getting airborne.

After getting some altitude I throttled back a little to do a couple circuits of the field. It was flying very nicely - very stable and controlled in the turns. That's when I found the throttle wouldn't advance again, and I was stuck at about 70% throttle. I wasn't sure what the problem was at that point, but the best plan was to bring it down and check it out. Circling around a bit more I lowered the throttle some more, and again it would only drop, and not advance. I added a notch of flaps to give me a little more lift at the reduced power and lined up for a good approach to the runway. When I knew the plane was clear of the brush at the end of the runway I cut the throttle to land.

Remember when I said the plane is heavy? Well, without power it dropped much more quickly than expected, and even with full up elevator it came down HARD, and the nosewheel hit first. Turns out the strut for the nosewheel doesn't like that kind of abuse and it broke loose and bent heavily, letting the engine dig into the ground. It appears the engine is toast, as the muffler took a lot of the impact and I think in-turn it damaged the cylinder. My assumption is that the throttle servo (which is new) failed.

So, what to do with it.... It could be repaired without too much headache, and a new engine installed (I have two more Turnigy 58cc gassers in my stash). However, it's way too heavy as-is, and to do it right the plane would need to go on a major diet which would include stripping the fuselage (again) and doing major surgery. At the end of all that work it still wouldn't be exactly how I wanted it to be. I love the color scheme of the plane and think I'll just end up buying the plans and building the replacement from scratch. I could drop in another Turnigy 58, or a Zenoah G-62. Building a replacement would also let me skip all the work I was facing on the wings and struts (only the fuselage and electronics were re-built on the plane). I'll let it rest for a while before making a decision.

 

[BMW2GO]

Well, crap. The Cessna may be cursed as it just doesn't want to stay in the air. It's not obvious at first in the pic below, but the nosegear is collapsed and the front of the plane is being held up by the partially broken prop. The muffler pipes are also bent/broken.

But for some good news, the previously made repairs after the first maiden attempt held perfectly, and there was no additional damage from today's attempt at flight.

So weather was good (a bit hot, but no real wind) so I took the plane up to my dad's field to fly. Since it hasn't been flown since the first maiden, I fired it up without wings installed and taxied it around the field for a while. Once I confirmed the repairs were solid I installed the wings and sent it up.

Good thing there is a long runway at this field, as the plane is VERY heavy. The plane's designer calls for a 2.5 to 4 cubic inch engine. My 58cc is 3.5 cubic inches which should be enough. Well, it is, but just barely. It flies scale, like a Cessna 150/152 should, but some additional power would certainly be nice for getting airborne.

After getting some altitude I throttled back a little to do a couple circuits of the field. It was flying very nicely - very stable and controlled in the turns. That's when I found the throttle wouldn't advance again, and I was stuck at about 70% throttle. I wasn't sure what the problem was at that point, but the best plan was to bring it down and check it out. Circling around a bit more I lowered the throttle some more, and again it would only drop, and not advance. I added a notch of flaps to give me a little more lift at the reduced power and lined up for a good approach to the runway. When I knew the plane was clear of the brush at the end of the runway I cut the throttle to land.

Remember when I said the plane is heavy? Well, without power it dropped much more quickly than expected, and even with full up elevator it came down HARD, and the nosewheel hit first. Turns out the strut for the nosewheel doesn't like that kind of abuse and it broke loose and bent heavily, letting the engine dig into the ground. It appears the engine is toast, as the muffler took a lot of the impact and I think in-turn it damaged the cylinder. My assumption is that the throttle servo (which is new) failed.

So, what to do with it.... It could be repaired without too much headache, and a new engine installed (I have two more Turnigy 58cc gassers in my stash). However, it's way too heavy as-is, and to do it right the plane would need to go on a major diet which would include stripping the fuselage (again) and doing major surgery. At the end of all that work it still wouldn't be exactly how I wanted it to be. I love the color scheme of the plane and think I'll just end up buying the plans and building the replacement from scratch. I could drop in another Turnigy 58, or a Zenoah G-62. Building a replacement would also let me skip all the work I was facing on the wings and struts (only the fuselage and electronics were re-built on the plane). I'll let it rest for a while before making a decision.


View attachment 173595

Sorry to hear about the dead stick landing - bummer! May I ask how much does your plane weight wet?

 

[Joker 53150]

Sorry to hear about the dead stick landing - bummer! May I ask how much does your plane weight wet?

I’m not sure, it’s never been weighed. The construction is too heavy in many areas, and it all adds up quickly. My guess is at least 30 pounds.

 

[BMW2GO]

I’m not sure, it’s never been weighed. The construction is too heavy in many areas, and it all adds up quickly. My guess is at least 30 pounds.

At 30 lbs, your wing loading is 31.31. That is about 3x more than the full scale. Hostetler's plans call for the flying weight to be 24-26 lbs which would still make the wing loading heavier than full scale.

 

[OliverW]

At 30 lbs, your wing loading is 31.31. That is about 3x more than the full scale. Hostetler's plans call for the flying weight to be 24-26 lbs which would still make the wing loading heavier than full scale.

Hostetler has his weights at least 10 pounds lighter than what it ends up to be for the most part. My dads hostetler 336 weighed 49 pounds

 

[BMW2GO]

Hostetler has his weights at least 10 pounds lighter than what it ends up to be for the most part. My dads hostetler 336 weighed 49 pounds

Most manufactures tend to under-report the true weight of their planes. I met someone last week at a fly-in that had the most amazing scaled out Hostetler C150. The yokes and rudder pedals moved with the elevator and rudder controls. The elevator trim tab actually worked via the trim wheel. Only negative - the plane weighs around 44 pounds. Here are a few photos I shot of his plane.

 

[speedbirdted]

I’m not sure, it’s never been weighed. The construction is too heavy in many areas, and it all adds up quickly. My guess is at least 30 pounds.

A guy in my club built a Hostetler C150 some years ago and even with not a lot of scale detail and being really attentive to weight, it still came out at 28 pounds. A Quadra 50 flew it slow but it flew pretty scale. I'm pretty sure the stated flying weight on the plans is pretty much unattainable.