PA18-105 Special - HP?

[D.A.]

My -105 Special is one of the last S/N Tango's made, has two tanks and the large Super Cub tail feathers. I finally took the time and looked into the rear fuselage area with a flashlite tonight and I don't believe it has the 3/8th tubes in the fuselage though. If there were no consideration toward approvals, what is the largest horsepower that could be bolted on the front without any structural mods? Could you put a 360 on it? I couldn't find it in a search but I thought someone said the 3/8th tubes were not for HP but for GW?
Thanks in advance.

[Akbushrat]

2cd rebuild we went from a O-290 to a O-320 extra ribs were put in the wings and the upside down Y in the front baggage area. There was also one short fuselage tube in the tail welded in for the upgrade.


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[Steve Pierce]

The O-360 STC requires the airplane be in the PA18-150 configuration. Three tubes under the battery shelf and cabane fitting bolts upsized to go from 1500 lb to 1750 lb gross weight. The PA18-150 wings with more ribs raised the Vne.

[D.A.]

…Three tubes under the battery shelf and cabane fitting bolts upsized…

Thanks Steve. It’s probably been discussed many times but can you show a picture of the three tubes under the battery shelf? And do the cabane bolts end up being the same size as the gear bolts? I’m heading out to the hangar soon and I’ll check it out. Thanks in advance.

[Steve Pierce]

https://www.supercub.org/forum/showt...-150&styleid=3

Cabane vee bolts go from 1/4" to 5/16" and new cabane vee.

[bob turner]

Except for the toe brakes, these were delightful airplanes. Six gallons per hour in a Super Cub!

I would only change the brakes and seat pans - but if you must, consider the 160 hp. I have time in 150, 160, and 180 versions, and my opinion is hands-down the 160 is best.

Of course if your mission is 300 foot sandbars with obstacles, ignore me - I have zero sandbar experience.

[RaisedByWolves]

Sell it and buy a 150hp factory airplane.

You’ll be a 1500 gross no matter what. You will end up changing to balanced tail feathers, and you still won’t have flaps or double groove trim. You will be money ahead to sell yours and buy a 18-150 with flaps.


https://svennsaviation.com/product/s...llation-pa-18/


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[D.A.]

...I don't believe it has the 3/8th tubes in the fuselage....

Correction - After reading Steve’s post I went out to the hangar and looked again and the 3/8th tubes ARE there. I was looking too far aft. I’m used to guys welding in the 3/8 tubes in each bay all the way back and I didn’t see any toward the back of the fuselage. However, I was able to see a small area adjacent the battery area just behind the baggage compartment and it has the 3/8 tube. On the other hand, the cabane vee has the smaller bolts. The cabane vee is the only thing I’ve found so far that isn’t 150 configuration.

[D.A.]

Sell it and buy a 150hp factory airplane.

You’ll be a 1500 gross no matter what. You will end up changing to balanced tail feathers, and you still won’t have flaps or double groove trim. You will be money ahead to sell yours and buy a 18-150 with flaps.

Thanks Tom. Normally you’d be spot on and I know changing the lighter Cubs to 150HP configuration is kind of a hot button on this forum but this is a little bit different situation. I actually don’t care about 337’s, approvals, STC’s, flaps, GW increases, toe brakes (Well actually I don’t really like the toe brakes - LOL), ribs, certification, authenticity or resale value. I just want to know that I can put a higher HP engine on it and still have a safe structurally sound Cub.


Since the word got out about my buying this Cub, some of my buddies have come forward with engines that are or will soon be available, all the way from an O-290-GPU removed recently for higher horsepower to an O-360 currently flying on a Cherokee approaching TBO. I’d bolt any of them on and just go. I’m just trying to figure out what I can do with this airframe without having to do any structural mods. It already has 2 fuel tanks and the larger horizontal tail feathers but has the smaller cabane see bolts.


Thanks for chiming in Tom.

[skywagon8a]

This:

I actually don’t care about 337’s, approvals, STC’s, flaps, GW increases, toe brakes (Well actually I don’t really like the toe brakes - LOL), ribs, certification, authenticity or resale value. I just want to know that I can put a higher HP engine on it and still have a safe structurally sound Cub.

Is this to be used at the high altitudes where you operate your other Cub? If so, the 0-360 would be unlikely to produce more than 150 hp ever, due to the altitude. The extra displacement would give you the extra altitude boost to simulate a lower elevation operation. The only disadvantage would be a more forward CG due to the higher engine weight.

[RaisedByWolves]

Thanks Tom. Normally you’d be spot on and I know changing the lighter Cubs to 150HP configuration is kind of a hot button on this forum but this is a little bit different situation. I actually don’t care about 337’s, approvals, STC’s, flaps, GW increases, toe brakes (Well actually I don’t really like the toe brakes - LOL), ribs, certification, authenticity or resale value. I just want to know that I can put a higher HP engine on it and still have a safe structurally sound Cub.
Since the word got out about my buying this Cub, some of my buddies have come forward with engines that are or will soon be available, all the way from an O-290-GPU removed recently for higher horsepower to an O-360 currently flying on a Cherokee approaching TBO. I’d bolt any of them on and just go. I’m just trying to figure out what I can do with this airframe without having to do any structural mods. It already has 2 fuel tanks and the larger horizontal tail feathers but has the smaller cabane see bolts.

Thanks for chiming in Tom.

If you do have the fuselage 3/8 tubing under the stock battery location, you could use the borer (i think) 1750 gross, drill out the cabane v fitting and replace the V. Going through this with a 18-125 right now. Borer, or atlee, i cant remember, on the drawing shows to ream the fitting. If i remember right the borer doesn't call out for double groove trim, the early super cubs had single. The Cubcrafters 320 STC basically says convert to 18-150, double groove trim flaps gw tubes etc

[PA-22/20-160]

Only the very 1st few 18-1 through 18-548 1950 supercubs had the single grove trim, all of the 51 cubs and newer that I’ve had over the years all had double system.

[D.A.]

If you do have the fuselage 3/8 tubing under the stock battery location...

Here's a shot of what I THINK I have from what access I have currently.

[PA-22/20-160]

https://www.wagaero.com/stc-conversi...faa-stc-d.html
If you have the tubes use this STC or the Borer one slap an O-320 on it and go forth and commit some Avation

[PA-22/20-160]

You need the 3/8 tubes that are the next ones behind that one

[RaisedByWolves]

Had a friend with a 105 special who wanted to put a 320 on, but had single groove trim. His was an early one ended in Kilo.

Sounds like DA's 105 is the military, with no flaps, which wouldn't be covered by wag aero? The borer calls out 105's in the stc.


https://www.supercub.org/forum/showt...-150&styleid=8



The svenn requires no modification aft of the firewall.

[PA-22/20-160]

[RaisedByWolves]

https://www.supercub.org/forum/attac...2&d=1395603474

[PA-22/20-160]

One other thing when switching to a larger engine on the early cubs is the torque tube, you have to change it with cubcrafters but not the other STC’s but you’ll wish you did if you leave it, they fly like dump trucks with the old tall tower straight sticks and big engines. Other thing too is you’ll need to have the later heavy wall engine mount to comply with the AD too.

[D.A.]

You need the 3/8 tubes that are the next ones behind that one

I printed out your drawing before I went to the hangar and sure enough, I do NOT have the tube in yellow.

One other thing when switching to a larger engine on the early cubs is the torque tube…

Glad you reminded me. I remember Mongo from years ago rewelding his pivot point and said it was like going to power steering.

…Other thing too is you’ll need to have the later heavy wall engine mount…

Good info, thanks!

[D.A.]

Sounds like DA's 105 is the military, with no flaps...

As close as I can figure, my Cub is a mixture, it has the double groove trim pulley (I checked tonight) it has 2 tanks and the larger counterbalanced tail feathers but does not have the 3/8 tube below the battery (Bummer) and also has the smaller cabane bolts. I wish I could see if it has flap provisions. I'm not necessarily going to install flaps, I'd just like to know what I have.

[PA-22/20-160]

The tangos never came with flap fittings because the master cylinder for the toe brakes would interfere with the handle and the front seat sits lower. You can install flaps on Tangos and piper has a drawing for it, The handle ends up being by your knee.

[PA-22/20-160]

Here’s the best picture I’ve got of the flap handle on a tango

[Cubus Maximus]

Same airplane, different pics:

[D.A.]

Same airplane, different pics:

Thanks Brad. I still think of that O-235 power SC your friend had for sale years ago. That would have been a nice ship!
Looks like I might not be able to reach that flap handle possibly. Low and forward, that might be a challenge for an old guy - LOL. I may have to track down Tango Cub with that flap arrangement on this side of the country and see if I can reach it.

[D.A.]

Here’s a variation to the original question. Instead of the O-360, can I just bolt on an O-290 in place of the O-235 without doing any structural mods? I know the best way to clear a Super Cub Christmas party is to stand up and say you love O-290’s, but one is available to me that I can just bolt on and go and I’d really like the extra HP. When/if I reach overhaul I’ll find another engine so I’m not worried about the O-290 overhaul, just want to know if I can install it without welding on my fuselage. Also, can I use the O-235 engine mount or should I use a heavier one?
Thanks

[TurboBeaver]

The 0290 has great performance in a lite Cub, great weight/HP. Sips fuel. But most do blow oil
out, just part of that engines design.

The "modification" is done in accordance with Piper Drawings for the PA-18-135 (or) -150. Get the drawings, modify the aircraft and make a 337 form out the plane was modified in accordance with "Piper Drawing No. XXX for PA-18-XXX"

No other data is required and no further approval is required because the aircraft has been modified in accordance to FACTORY approved data. Very simple.
Note: Data plate remains the same "105".
Good Luck
E

[1934A]

Here’s a variation to the original question. Instead of the O-360, can I just bolt on an O-290 in place of the O-235 without doing any structural mods? I know the best way to clear a Super Cub Christmas party is to stand up and say you love O-290’s, but one is available to me that I can just bolt on and go and I’d really like the extra HP. When/if I reach overhaul I’ll find another engine so I’m not worried about the O-290 overhaul, just want to know if I can install it without welding on my fuselage. Also, can I use the O-235 engine mount or should I use a heavier one?
Thanks

If you have access to a good O-290, bolt in on and fly! Nothing in the world wrong with one, except the parts for them require a little scrounging around to find