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Airframe for the Ultimate Cub Float Plane

T

tdh

Registered User
Fairbanks, Alaska
I broke down at the Trade Show in Anchorage and put money down on a supercub kit from Airframes Inc. and Dakota. I have a wrecked 1955 PA18-135 Ag. model in the connex waiting for a rebuild. The plan is to build a high performance cub to be used only on floats.

The first question I need help answering is which airframe. Lee at Airframes Inc. can provide the 4inch wide body, the standard airframe or the standard agricultural airframe. The primary goal is to be off the water fast with a load. Plane will be used to get into and out of the small ponds that surround Fbks while hunting waterfowl and moose etc. Powerplant will be the Pen Yann Aero 180hp conversion.

Keeping it light goes hand in hand with the performance goal. Granted the widebody cub will be heavier but if I go with a std fuselage, I no doubt will hang a Firmin pod on it to have the room to haul the necessities. Assuming the widebody will negate the necessity for the pod, will I be lighter than the std/pod combo? Does anyone here with time in the widebody have any reports re: differences in flying qualities etc.

How about the Ag frame? Is there any truth to rumors that these airframes fly differently than the std frame and what are they?

Thanks in advance for any suggestions. BTW wing selection will be under a different post.
 
I haven't flown a wide body, but have a narrow body just like you describe. I have an I.A. friend that just built up a wide body for a customer like you describe. He said the wide body was a LOT more work to build then a narrow body and wouldn't want to do one again. He's built a lot of Cubs over the last 25 years.

I feel it depends on your body size as to which way you go. I am 5'10" 180 lbs, 34" waist. Sitting in the Wide body felt strange. Too big and loose for my small frame. The guy that built it up is 6'4" 280 lbs and he liked the way it felt. It also weighed 1,320 lbs, the one raffled at the Airmans show weighed 1,323 lbs so they can be heavier. My narrow body with Penn Yan O-360 is 1204 lbs coming off the same certified scales as the two above.

If you have good Piper wings, use them, nothing is lighter and this is a place where a lot of weight is gained.

Bottom line... a wide body is a great thing if you are a big guy. The only way I would go if I were over 6' and large framed. If you're not, why gain the extra weight and hassel of "custom" parts and labor when you don't need it. Best wishes! Crash
 
Crash, Thanks for the response. Like you, I have no interest in a 1300 lb cub on wheels - I hate to think what it would weigh with floats. However, if my memory serves me right, I remember someone on this site building a fairly light widebody. I still would like to know flight characteristics of the wide body. A number of people claim it flies faster than a std frame. Are there any other pros or cons? How about that agricultural frame?
 
As far as speed... the Wide body that my friend just finished runs 105 mph at 2450. It has extended slotted Dakota wings. My Dakota stock round tip wing and narrow body with the same engine and prop runs 105 at 2450 so no difference there. With stock wings I've heard the Wide body is 5 mph faster then a "like" narrow body.

Every thing you do to a Cub when modifying it from stock form is a trade off. Even my Penn Yan conversion has it's pluses and minuses. The minuses...odd nose bowl, odd bottom cowl, heavy dynafocal mount, odd air filter, odd air box, extra weight on the nose, no car gas. The pluses... faster by 15 to 20 mph, less fuel burn, climbs 500 fpm better, will lift any load off the ground, blows everything away in deep snow on skis, smooth as a sewing machine (dynafocal mount).

In the end, you pick your poison and run with it. The nice thing about a PA-18 is there's no other plane made that you can custom taylor to your wants and needs like it. Some mods I don't think are very good, but someone out there will swear by it. To each his own. Take care. Crash
 
tdh, I can't argue with any of Crash's points. He's spot on.

I'd like to add that you're kidding yourself if you think a 4" widebody will somehow negate the value of adding the cubic cargo room of a Firmin pod. Those pods weigh very little (23 pounds), and have ALOT of room for all the stuff you wannna bring along.

Another point. I've never though much about building light simply for good float performance, so this is new but: besides lightness, what will get you off the water sooner? Whatever that is, do it. (I'm stopping suggestions now so others can chime in )

DAVE
 
Dave, I totally agree with you re: the Firmin pod. Another major plus is being able to hose all the blood, guts and fish smell out at the end of the day. My wife says the cub I fly now would smell like a bag of garbage in the heat of the summer pre-Firmin. :eek:

Like Crash, I will probably build up a std fuselage, however, I've been known to change my mind based on responses from this forum. I wonder where all those wide body lovers are at? Does the wide body fly slower than a std body? Other than flying faster and being able to better fit the larger pilots/passengers, are there any other advantages ? At this point, the disadvantages to a wide body outweigh the advantages for the missions I have in mind.
 
Okay, personally, I still like a stock fuselage if I'm flying. It just fits better like Crash says. BUT, for widebody guys, the widebody Cub fits way better and allows easier access in and out for aforementioned widebody guys. Especially with doors on both sides like the Smith.

That said, when flying as GIB - CSO (guy in back - camera systems operator ha ha) and handling junk etc... I really like the widebody! My left knee always gets jammed between the pilot seat and the metal throttle channel on a stock Cub and for long distances it drives me nuts. :-? The widebody solves this issue plus I have room to carry cameras and can swing lenses left and right much easier. I also like the extra room in the baggage compartment to stuff stuff.

Another couple things that come to mind is One: the flap handle on a widebody is no longer in the way when you need full left aileron during landing. (a good thing) and Two, you can't see your track over rough ground as easily - for avoiding obstacles and debris (a bad thing). So advantages and disadvantages. Very cool though that you have a bunch of choices to fit your particular mission best.

Brad

(as more and more widebodies hit the fleet, parts should start to become more available for them)

(oh, one more item, I now officially despise die spring gear.)
 
Is the wide body approved for EDO 2000's? Any changes to the float struts? Seems like there would be. That a widebody would sit a little higher since the struts would be more vertical.

Just a inch or two off a front or back strut can make a big difference in how it comes out of the water. If you had to change the rigging much for a wide body I wouldn't use one as a airframe.
 
I was reading Brian's (PPI) constant speed prop conversion with the MT prob - that would make a bit of a difference on take-off on floats even against a borer climb prop. Nothing like getting full rpm right away.

weight of the MT constant speed was relatively equivalent.

And the static thrust, on their 0-320 test, was 20% higher at takeoff.
 
Whatever happened to the frame with the raised upper longerons and huge extended baggage? Airframes had one, than some other company I can't remember the name of. That would be the only frame that I would ever conceder trading my trusty old A model frame for.

If I wrapped mine around a tree, I'd definitely order the replacement frame with the removable rear seat bottom and full length flat floor of the A model.

I hope I never need one of those wide frames, I think I'd have one of those stomach bypass operations first. The visibility in the standard frame can't be beat. I fly the 18 with my knees braced against the cabin, really nice when it's extremely turbulent, kind of like a kayak with wings. I miss this in other airplanes.
 
I think I would also agree with Mark to a preference to the A model. I'm constantly using the removable seat as I have a full length floor board under it and haul lots of "stuff". I made my own metal headliner which goes completely against the top deck tubing, unlike Atlees which gives a lot more cargo volume.
The question was asked if the A flew differently then the standard. Given the fact that no two cubs fly totally the same, I haven't seen any notable difference. (have owned many different cubs over the last 32 years)
I was also surprised to hear that Airframes could provide an Ag model replacement fuselage. This has not been the case up until now and is not mentioned on their web site. The do make mention of an FAA opinion that it is OK to use the standard sense they are listed on the same type certificate. but I have also received FAA opinions that it isn't. The ones I have talked with thought that it should take an STC or field approval to avoid potential "questions". Try putting a 150 horse engine on a 135 hp cub without an STC and see how far you get. They are both listed on 1A2.
If this discussion is about rebuilding an old A model then I would suggest you check with the Feds before buying a standard type fuselage and get the approval before writing the check. (I know that many folks have done this and would love to know how they handled the paperwork etc.) If Airframes can give you a true A model fuselage then I would go that route.
 
Freestone, I too have read up on the MT prop and will consider it when the time comes. I actually put one on my 185, but the jury is still out on whether I'm a satisfied customer.

Mark and Cubpilot2, The fuselage was crushed by a collapsing hangar due to snow load. There is no question that the fuselage needs to be replaced. Lee does not offer the AG Frame, but he said I may be able to twist his arm for an extra charge.

Can anyone address Ag to Std fuselage paperwork issue raised by Cubpilot 2
 
float cub

Best set up I've flown is a light wieght, stock super cub 135 on EDO-2000's. Got off the water shorter than anything I've flown since. But it's all relevent to your mission.
 
fusalage

Oh ya, am I missing something here,my Airframes Inc. fusalage came with the removable rear seat crossbar and full length flat floor all the way to the back of the ext baggage and its not an A model ?
 
Brad, That might be it. To bad they screwed that one up by making it wide. I remember the one Airframes made was like a A model with the longerons raised and a baggage big enough to live in. Only saw it once and never heard about it again.

David, The A model rear seat bottom completely removes in addition to the back and tube, and the floor that stops in front of the rear seat in the standard 18 extends to the end of the standard baggage in the A. This is the way I would build up any 18 I personally owned, A model or not.
 
My 150-A (flat back) 1958 cub is about as stock as you can get. It has an extended baggage, brake boosters, 82X41 prop, 31" radial bushwheels, safety cables, a com/IC and a alternator. EW is 1091. It is faster off the ground than any other cub I have had and it handles quicker in the air. I think the flat back acts like a wing, just like a taylorcraft does and therefore flys better. BTW this plane is in great condition and has a low time engine. Best of all it is for sale for the low price of $73,550. You could fly it today!

http://sparky.supercub.org/photoclass/showproduct.php?product=118
 
Earlier I had raised a question here about using a standard fuselage as a replacement for the Ag model fuselage.
Today I did a bit more checking with a local (experienced) FAA inspector and asked what would be the best approach for handling this since there are no new certified Ag model fuselages available.

He agreed that it does raise important issues in that by making the swap you make a major change to the model type. The data plate says PA-18A but the airframe is now PA-18... Similar, but different model airplanes. The aircraft no longer matches what the data plate says it is.

He said that the simplest way to handle the situation is to first ensure that the aircraft meets the "standard" PA-18 model design and then apply with the FAA to "change" or amend the airworthiness certificate. This will indicate that the aircraft has been converted from the 18A to the standard 18. (essentially remove the "A" designation)
At that point he said that a "supplemental" data plate would be placed adjacent to the original data plate indicating the conversion.
He indicated that there really isn't anything to "field approve" as no modifications have taken place in the basic conversion. You are changing from one "certified" configuration to another "certified" configuration.
You just need to get the "paper work strait"

Has anyone went this route?
It sounds easy but is it really?
He also said that it would be "unwise" for anyone to sign off any cub that has been converted like this and not authorized/approved.
 
Saw an A that had the fuselage replaced with a Piper factory new fuselage. No other paper was there except a log book entry that the fuselage was replaced with a factory new one and it wasn't an A model frame.
 
TJ,

I agree there is a typing error as you point out.

From FAA.gov....

Sec. 45.11

General.

(a) Aircraft and aircraft engines. Aircraft covered under Sec. 21.182 of this chapter must be identified, and each person who manufactures an aircraft engine under a type or production certificate shall identify that engine, by means of a fireproof plate that has the information specified in Sec. 45.13 of this part marked on it by etching, stamping, engraving, or other approved method of fireproof marking. The identification plate for aircraft must be secured in such a manner that it will not likely be defaced or removed during normal service, or lost or destroyed in an accident. Except as provided in paragraphs (c), (d), and (e) of this section, the aircraft identification plate must be secured to the aircraft fuselage exterior so that it is legible to a person on the ground, and must be either adjacent to and aft of the rear-most entrance door or on the fuselage surface near the tail surfaces. For aircraft engines, the identification plate must be affixed to the engine at an accessible location in such a manner that it will not likely be defaced or removed during normal service, or lost or destroyed in an accident.

From FAR Part 1...

Fireproof--
(1) With respect to materials and parts used to confine fire in a designated fire zone, means the capacity to withstand at least as well as steel in dimensions appropriate for the purpose for which they are used, the heat produced when there is a severe fire of extended duration in that zone;
and
(2) With respect to other materials and parts, means the capacity to withstand the heat associated with fire at least as well as steel in dimensions appropriate for the purpose for which they are used.

I don't know if this has been changed in recent years, but it sure doesn't jibe up with the ALUMINUM data plates attached to the floor or baggage compartment lid with 4 X 1/4 screws as Piper did it!

I'm not piking a fight, I just happened to be reading this information for another application when I read ypur post on this thread...

John Scott
 
Typical... reference this AC. It starts out at #1 PURPOSE." This advisory circular (AC) describes one way, but not the only way, to comply" blah blah blah.
Can you say open ended interpretation?

jk
 
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