Fat Avid

[Marshawk]

I have a chance at buying an unfinished Fat Avid with the 100 h.p. Subaru,it is 10" wider in the cabin and 18" longer in total lenght. It is an Avid heavy hauler C model with a gross weight of 1050. I origianally was keeping an eye open for a kitfox 4 but this avid seems to have quite a bit going for it,its around 85% finished,new covering ,lots of storage space and lots of extra parts since the guy is getting out of flying. I guess my question is the avid fly similar to a kitfox 2 which I currently partners in, I know there quite similar an know the subaru will be quite a bit heavier than our 582 rotax.Anyone have experience in a Avid with Subaru engine? Any input greatly appreciated.

Thanks Willis

[DesertFox4]

Willis, I think after flying a Kitfox with a Rotax you will be in for a let down if you flew that combination. The Subaru would turn me away immediately on any 1050 lbs gross weight aircraft not just an Avid. You might end up with a single place airplane when you put full fuel and a pilot on board. Since the early Kitfox's and Avids share some similarities in design the best way to remove the fun factor from either is put too much weight on them.


Plenty of viable projects out there to invest your time and money in that when completed you will enjoy flying and owning. Find a model 4-1200 and a Rotax 912, build it light and enjoy every flight.

[Mnflyer]

Hi Willis I have to agree 100% with Steve not a good engine at all on a 1050 airplane wither it be an Avid or Kitfox or any other make.

[Marshawk]

Thanks for all the input, the owner told me he flew his Avid C with the subaru in it and what he told me was it took about another 50'-100' to get off the ground but out climbed the original 532 rotax he had in it.Of course it could be a sales pitch. Thanks again All

[wannafly]

I had a Fox IV with a subaru...switched to 912s. IMHO the subaru is way to heavey:( and you are getting a sales pitch. I did not know what I was missing till I made the switch. Not sure but I dont think there is a light subaru especially at 1050 gross weight. Send me a private message and we can talk more off line or come to Lethbridge and we can go for a ride.

[avidflyer]

I'm suprised that he said the gross weight would be only 1050. I thought when they made them a Fat Avid, the gross was about 1200 lb. Now if you could come up with the cash to put a 912 on there, you would really have a nice performing plane. As far as the 1050 gross weight, isn't that what the Kitfox 3 is and the Kitfox 2 is 950 lb. That's what my memory says anyways. Take care, Jim Chuk

[dholly]

Hi Willis-

I'm building one of the few complete Avid Plus kits sold by Airdale, so I feel I better add a few comments. First, in no way, shape or form do I believe a Fat Avid with Sube FWF will fly or perform like a 582-powered KF-2. Make no mistake, you are simply comparing apples to oranges there.

Compared to either my KF-3 or Avid Mk-IV, I consider the Avid Plus a big upgrade. Many, many improvements, and not the least of which is the added cabin size. It would be quite similar to moving from a KF-2 to a KF-5 or 6 in that regard, but with more legroom. As another point of reference, the Avid Mk-IV frame weighs in at ~70lbs. and the Avid Plus frame ~80lbs., so very little incremental weight increase for a longer, stronger, wider fuse with adjustable seats, larger balanced rudder, improved controls, open baggage area, etc.

Assuming the same engine and empty weight, I believe performance measures for both planes are very similar overall. As a result of all of the above, I felt the Avid Plus was more desirable than a KF-4 1050 or 1200. Several of my KF-4 owner buddies have echoed that sentiment as well after seeing mine. Clearly each of us know a KF-4 is a terrific plane, but an Avid Plus can be built every bit as light or lighter and I sure as heck know my backside and passenger will enjoy each flight just as much or more with the added cabin comforts.

With regard to the most appropriate engine choice, that is a much tougher call. You probably know there were many Sube-powered Avid Flyers built and flown despite the weight penalty and nose-heavy CG. The Avid Plus fuse was designed, in part, to accommodate a Sube FWF properly, so no problem there. Most of these fuses were sold to existing Avid owners as the Fat Avid upgrade, as appears to be the case with the one you mention. Airdale provided the new fuse with doors, instrument panel and dash, and owners swapped their existing Avid rudder, elevator, H.S. and braces, tailspring/wheel, main gear, rudder pedals & brakes, control system etc.

Important: They also swapped existing Avid wings with lift and jury struts which --and this is most important given the number of different wing/rib/strut combinations possible-- effectively limits the M.T.O.W. of their Fat Avid to their original Avid Flyer. This obviously is a critical safety matter, and you really have to be certain of the wing specs.

While I might agree that the heavy Sube FWF and additional 10lbs. of fuse weight eat pretty deep into a 1050lb. gross, it may or may not factor into your decision. Every choice a builder makes includes compromise and I know folks who went the Sube route without reservation for their Fat Avid upgrade. You can read comments from one flying with that engine although I believe he may have had a Mk-IV w/ 1200lb. HH wings. I also know another Avid Plus tri-gear owner (built from a full kit, not a Fat Avid upgrade) with 100hp 912 and 1200 lb. HH wings who says his plane climbs like a homesick angel and is simply fantastic for the mountain and backcountry strip flying he prefers. I did my own research and think a 912ul on this frame will make a most excellent and comfortable all-around TD performer for me, even knowing I'll eventually float it.

Again, different strokes for different folks. If you like the Fat Avid fuse and the price is right, but the Sube FWF or gross weight of this particular Fat Avid is a concern, don't dismiss it without some serious consideration. As you saw, it will make a very nice LSA and you can gain some more usable load with a few relatively easy options. As Jim said, sell the Sube and finish it with another engine choice. Or, fit some 1200lb. gross Mk-IV HH wings and struts. The 'official' gross of the Avid Plus kit with that exact same wing is 1250lb., due to improvements such as stronger fuselage, larger dia. rear carry thru tube and 2" longer spar stiffeners. I had the benefit of starting from scratch and built custom wings with a few other mods looking for 1320lb. M.T.O.W., details on that at the previous link as well.

In any event, my apologies for such a windy post but I felt a need to caution on the gross vs. wing thing. Hope it helped some. If you have other specific questions, the Fat Avid group are a good bunch of guys and I'm sure we can find you answers.

Regards,
Doug

[avidflyer]

See if you can get a measurement of the wall thickness of the spars. The standard wing had .063 and the Heavy Hauler spar wall thickness is .083. Also, the spacing of the ribs on the standard wing were 17" and on the Heavy Hauler, they are 11". Take care, Jim Chuk

[Marshawk]

Thanks Doug ,that is the best information I got so far,I appreciate it alot. I figured because it was originally a Avid C that my gross would the 1050 ,I like the idea of keeping an eye open for the larger wingsand maybe the 912 rotax It seems like a pretty good deal $9500.00 for fat avid about 85% finished 200 hrs on rebuild subaro engine ,extra subaru short block rebuilt,plus old fuselage ,503 and 532 rotax plus everyhthing to finish it.
I was very impressed from the pictures of the room it has in the cabin :).I will probably go look at it in a couple weeks ,as long as our tax man stops draining me I'll probably pick it up. Its great to know someone else with similar project.

Thanks again Willis

[Marshawk]

Thanks Jim ,I'll check that info out when I go look at it, I believe he says it is a heavy hauler registered as a Model C, thats were I came up with the 1050 ibs gross

Thanks Willis

[dholly]

Willis,

1.) Please do take Jim's advice. There were so many combinations of Avid fuselages and wing components bought, built, or cobbled together over the years it can be very difficult to determine exactly what M.T.O.W. you have unless you physically measure spar thickness, tubing diameter, or even cut a tube to verify wall thickness.

Again, for anyone interested in the Fat Avids, it bears repeating for safety sake... when Airdale LLC sold an Avid Plus frame as a Fat Avid upgrade, they clearly stated that the gross weight of the upgraded model was as per the existing Avid wing construction. So, while the Avid Plus frame etc. was designed for a gross weight of 1250lbs., if you fit a STOL wing from an Avid A model gross weight of the Fat Avid would be 850lbs., fit a HH wing from Avid B/C model and gross weight of the Fat Avid would be 1050lbs., fit a STOL wing from Avid MkIV or Bandit and gross weight of the Fat Avid would be 911lbs-1000lbs. Fit a Avid MkIV HH wing and gross weight of the Fat Avid would be 1150-1200lbs.

In case anyone is confused by all this... the Avid Flyer wing differences that affect M.T.O.W. extended primarily to spar thickness, spar length, lift strut o.d. diameter, airfoil, rib spacing and drag tubes. In general, the STOL and Heavy Hauler wings used long spars with under cambered ribs, while Aerobat and Speed wings used short spars with flat bottom ribs. All wings called for (2) nose ribs between wing ribs, though an additional nose rib per bay was often added on the Speed and STOL wings due to their wider rib spacing.

The name ‘Heavy Hauler’ was attached to several Avid models but actually came about with the later Avid B and C models. Those kits only had the .083” spars and larger 7/8” lift struts. Ribs were spaced every 18" o.c. which meant only one short rib between the long ribs acting as flaperon hinges. The M.T.O.W. of these B or C model HH’s was 1050lbs. Very late Avid C models could be ordered with HH wings which had .083” spars and two short ribs between the long ribs. Ribs were spaced every 12" o.c. but M.T.O.W stayed the same. The Avid Mk-IV HH also had .083” spars, ribs 12" o.c. with two short ribs between the long ribs plus other changes, and was originally 1150lbs. and then, to compete with the KF 4-1200, "re-marketed" as 1200lbs.

Here is a little more detail from a post I made on the Avid Group a few years back:


Speedwing: .065" thick 2-1/2" o.d. spars; 108-1/2" spar length; 3/4" dia. lift struts; Avid flat bottom airfoil; (7) ribs ~ 18" o.c.; (3) 1/2" dia. W-2 alum drag tubes; (3) W-3S Short 5/16" dia. alum root rib brace tubes; (1) W-4 Short 1/2" dia. alum root rib brace tube; (1) W-3L Long 5/16" dia. alum tip rib brace tube*; NOTE: Wing tank replaces (1) W-2, (3) W-3S and (1) W-4 alum rib brace tubes at the root end of wing; Key rib dimensions (long rib flaperon hinge) are 35-1/2", 71" and 106-1/2" o.c. from tip rib

Mk-IV HH: .083" thick 2-1/2" o.d. spars; 144" spar length; 7/8" dia. lift struts; Avid undercamber airfoil; (13) ribs ~ 12" o.c.; (1) 1/2" dia. W-2A steel drag tube; (3) 1/2" dia. W-2 alum drag tubes; (3) W-3S Short 5/16" dia. alum root rib brace tubes; (1) W-4 Short 1/2" dia. alum root rib brace tube; (1) W-3L Long 5/16" dia. alum tip rib brace tube*; NOTE: Wing tank replaces (1) W-2A, (3) W-3S and (1) W-4 alum rib brace tubes at the root end of wing; Key rib dimensions (long rib flaperon hinge) are 35-1/2", 71", 106-1/2" and 142" o.c. from tip rib

STOL: .065" thick 2-1/2" o.d. spars; 144" spar length; 3/4" dia. lift struts; Avid undercamber airfoil; (9) ribs ~ 18" o.c.; (4) 1/2" dia. W-2 alum drag tubes; (3) W-3S Short 5/16" dia. alum root rib brace tubes; (1) W-4 Short 1/2" dia. alum root rib brace tube; (1) W-3L Long 5/16" dia. alum tip rib brace tube*; NOTE: Wing tank replaces (1) W-2, (3) W-3S and (1) W-4 alum rib brace tubes at the root end of wing; Key rib dimensions (long rib flaperon hinge) are 35-1/2", 71", 106-1/2" and 142" o.c. from tip rib

Mk-IV Aerobat: .083" thick 2-1/2" o.d. spars; 108-1/2" spar length; 7/8" dia. lift struts; Avid flat bottom airfoil; (10) ribs ~ 12" o.c.; (1) 1/2" dia. W-2A steel drag tube; (2) 1/2" dia. W-2 alum drag tubes; (3) W-3S Short 5/16" dia. alum root rib brace tubes; (1) W-4 Short 1/2" dia. alum root rib brace tube; (1) W-3L Long 5/16" dia. alum tip rib brace tube*; NOTE: Wing tank replaces (1) W-2A, (3) W-3S and (1) W-4 alum rib brace tubes at the root end of wing; Key rib dimensions (long rib flaperon hinge) are 35-1/2", 71", and 106-1/2" o.c. from tip rib. *Applies to wings with wire trailing edge only, not required with metal trailing edge.2.) Finally, I can't help but add my .02 cents on the deal. For all you mention, that sounds like a very good price IMHO. And -bonus- it's 85% done?! IIRC, the Fat Avid upgrade package was priced somewhere around $5-6k, and the complete Avid Plus kit around $15-16k without FWF and instruments (I bot my complete kit second hand).

Personally, I would buy it and sell off all engines and the Avid frame with wings, together or separately. Heck, that's a fair chunk of change and somewhere there is a need for those parts. Then I would buy new HH wings and struts from Airdale to bump the M.T.O.W. to 1250lbs. (or, a bit more with simple spar stiffener mods) and start a new engine penny jar. Keep an eye out for a used 912ul while you build the wings, or buy some Lotto tickets if you want a new one. Or, sell everything and put a used 912 on the nose now to pick up some useful load and fly with the 1050lb. wings while you can locate or build new 1200lb. wings.

Lotsa options! With a little effort you could have a 90% new, wide cabin LSA with higher gross than a KF 4-1200, all in relatively short order for a net investment of ~$20k. Perhaps well under if you luck into a really good used engine bargain. OK, going to take off my cheerleading skirt now. If you still have my tel# and want to talk just give a shout. :)

Good luck!