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Knowledgeable STOL modification guru's

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Snax01

Registered User
First off I'm sorry this is not exactly cub related but this seems to be the best forum for exposure.

I am looking into purchasing a STOL project and had some concerns about one of the modifications to the airframe. Plane in question is a citabria(experimental airworthiness cert), current owner had a 200hp engine in it along with a 150hp shot of nitrous. I will be purchasing without the engine and will most likely go with a more conventional 160hp Lycoming and no nitrous.

Back to the question, on take off he was out of rudder authority because of how much power his motor was making. He stripped the fabric off the fuselage and extended the rear of the fuselage 2ft, this of course moved the rudder back 2ft and in therory would give him more rudder authority. I am concerned about the affects of this at cruise speeds on both the rudder and elevator controls. I feel like this was a sound modification to correct for take off but what will be given up at cruise speeds.

I'm open to hear any input you all may have and can answer any other questions if I did not provide enough input.

Thanks
 
A Citabria has a fixed stabilizer which provides a certain nose up force. If this has been moved two feet aft the nose up force will be the same at the same speeds, however since it's leverage arm is two feet longer it is likely to provide a stronger nose up moment. This means that you would need more nose down angle for the elevators to compensate. You might consider making the stabilizer angle adjustable. This could be done by installing a Cub trim system or just providing for the front cross tube to be moved on the ground. There are several ways to accomplish this.
 
I would be concerned about the ability to 3-point land the airplane with the fuselage extension. That additional 2 feet means the tail wheel will be lower than "stock" in a 3-point attitude. It can be challenging enough to get the mains down at the same time as the tail wheel, and I suspect you'd be landing tailwheel first more often than not – which would beat up your tail wheel assembly pretty quickly. Beyond that, I have no idea what this change might do -- that's why it's moved to the "Experimental" category: you're the test pilot! I suspect it will behave somewhat differently in aerobatic flight, as well...

And I'm not sure where you're located, but down here in the lower 48, I'd be concerned about the utility of the airplane, given that it's almost certainly not certified in the "Experimental Amateur Built" category that most people are familiar with... (By FAA rule, it cannot be registered that way, since it began life as a type-certified airplane.) It must be certified in one of the "other" Experimental categories (such as "Experimental - Exhibition") that are far more restrictive. (The "Exhibition" category requires notice to the FSDO of everywhere you're going to fly, in writing, etc. It can be a royal PITA, depending on how friendly your local FSDO is towards the category.) Be sure you completely understand the "operating limitations" that were issued for this particular airplane when it was approved by the FAA, and that those limitations won't prevent using the airplane as you intend to before you purchase. Those operating limitations are unique to each "experimental exhibition" airplane, and can be somewhat lax (AKA "Alaska Rules") or extremely limiting (50 nm radius of airport XXX, or as approved in writing by the FSDO), or anywhere in between. Make sure you read and understand the operating limitations issued to that particular airplane, and don't believe anything the seller tells you to the contrary.

PS - I would run, like the above two posters. There are tons of good airplanes for sale.
 
Airframe extension isn't new. Guys on this site will commend the Producer conversion to the Pacer, which extends the airframe and adds -14 wings. Great airplanes! My Rev is an extended airframe version of the SQ-2 and it works well. In the case of the Rev the purpose was to help balance bigger engines and CS props and to improve slow speed elevator authority. In the case of the Citabria airframe I'd use the Rev as a reference. Either use a heavier engine or extend your motor mount or risk having an aft CG airplane. Run standard Citabria W&B numbers with the tail extended out and you'll get an idea what to expect, and that's not considering the added 30-40# the extension will contribute in the back.
 
I have been reading up on the producer, one of the reasons I have even been considering this project. I do like the idea of adding adjustment to the horizontal stabilizer and cg will definitely be addressed. This project also has a modified engine mount to bring it to a zero thrustline setup, looks like it may already be extended to make up for some of the tailweight.

I Did look over the picture of the airworthiness certificate he sent me, it is classified as amatuer homebuilt and I do not see any operating limitations...are they listed on the back side?

Also not worried about the 3point landing issues brought up, it's on a monster set of gear, 29" ABW's and tailwheel gear upgrade
 
Airframe extension and engine offset aside, the Citabria once had an enlarged deeper chord rudder available. It was maybe sold by Wag-Aero and if I recall correctly was for aerobatics. Not sure of the source just still have a mental picture of the part.

Hope the experimental works ok.

Gary
 
Run, don't walk, away. It's almost certainly experimental-exhibition which is hugely restrictive, and the Citabria was never any STOL queen to begin with. Given enough H.P. I suppose they'll rocket off the ground pretty good, but they land hot compared to a Cub.
 
The longer gear will fix the angle of attack with the longer tail... also larger tires. (29" are small:lol:)

The extra weight in the tail, and distance from Datum is something to think about. All these planes seem to get tail heavy really quick. Moving back to the 160 hp will exacerbate the heavy tail, making it fly terrible I bet. Extending the mount will do some, but now you lose the visibility.

A nice 160 hp Citabria is what? $50k?

Seems to me for you to buy the engine and plane, then make it work you will have lots more into it all said and done.

If you are convinced you want to play with it- go for it! Just consider that a bigger motor will make up for the tail weight, and 200 hp up front will not over power the controls... but 350? yea, NOS is cool in the competitions and show world, but EXPENSIVE in the real world.
 
PerryB said:
Run, don't walk, away. It's almost certainly experimental-exhibition which is hugely restrictive, and the Citabria was never any STOL queen to begin with. Given enough H.P. I suppose they'll rocket off the ground pretty good, but they land hot compared to a Cub.
Click to expand...

Andy Crane schooled the boys at New Holestien on just the opposite of what you say

Glenn
 
With enough crap hung on the wing they are ok but not a Cub. Close if stripped and rebuilt light are a fun plane. But the wing chord is less and they gain weight quickly. Had a couple - once.

Add: On floats and skis I flew over 14,000# of building materials 90 miles west of Fairbanks in one. So they can haul a good load and have lots of room inside. Put a 20" gas range in mine behind the seat. Don't start the useful load comments. It's no longer my concern.

Gary
 
Last edited:
PerryB said:
I suppose they'll rocket off the ground pretty good, but they land hot compared to a Cub.
I've flown a Citabria and it's not any great STOL plane.
Click to expand...
Both statements are true however with a few modifications they will closely match a stock -18. I had a 7GCB with slightly extended wings and Ferguson droop tips, 9:00-6 tires and an 80" prop. It would go anywhere that a stock Cub would go. Quite impressive actually.
 
PerryB said:
The exp-exhib. part or the STOL part? I've flown a Citabria and it's not any great STOL plane.
Click to expand...

Anyone have any video of Andy from last years flyin when he was going in and out of his Moms 300 to 400' backyard with obstacles?

Glenn
 
Maybe he needs leg exercises. I don't buy "ran out of rudder." Wooooff. The Pacer was shortened to start with but not the Citabria. 200HP Denali Scouts don't run out of rudder. Send it the bone yard and run like hell.
 
Snax01 said:
Andy sounds like a fun guy! I want to hear more about his citabria!
Click to expand...

I have had the same opinion as everyone else about a Citabria not quite doing the job. But watching Andy start to wear this airplane has been an eye opener. It's still not a Cub but he's got it doing Cub things.

Glenn
 
It may be a good performer. The only advantage of the tail moving back will be to utilize a high lift wing, but I still say you’d be better off with a bigger engine. If you move forward with it, will you be in the pilot seat for the first flight?
 
Here is an interesting video for Citabria/ Champ dislikers.
Old 7 GC with no flaps with 20 gals of gas in it. 60 degree air 6/8 mph wind. How does this compare to what your used to??? No nitrous involved just an old 0290.
https://youtu.be/lkdAmDGcD8U
 
My '78 7GCBC had Crosswind's STOL kit (cuff/fences/flaps to fuselage), Madras tips on extended wings, end plates on the outboard flaps, 80" CS prop, and the first set of Scout gear for AOA. And based on ski tracks in deep snow it would fly within a fuselage length of a lighter Cub with the Crosswind's kit on a stock wing and Borer.

But doing that gets them fat so then there's that to contend with.

Gary
 
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