? for Dholly

[birddog486 21]

Doug I saw a post you made saying the Avid aerobat had a gross weight of 1200lb. do you have something from the factory that talks about that? In the paperwork I have from Avid it states 911 lb gross which I assumed was wrong because the speedwing gross is 911 but, the Aerobat is rated at 850 max gross doing aerobatics up to 6 G's. I'm building what should have been the aerobat wing but I've added extensions and wasn't sure about a safe max weight on it.

Travis

[C5Engineer 1170]

There's a Heavy Hauler version of both wings that use bigger struts. My Heavy Hauler stol has the gross at 1085. The real gross weight on an experimental is whatever your brave enough to take off with.

[EDMO 1078]

There's a Heavy Hauler version of both wings that use bigger struts. My Heavy Hauler stol has the gross at 1085. The real gross weight on an experimental is whatever your brave enough to take off with.

And, to add more thought to that: I consider GW as "Landing Weight" - If I can take off 60 lbs over gross and fly in calm air for 2 hours, then I am back at GW for landing - But, that is my theory - not in the books.

Large aircraft, especially military, use this weight change all the time, and the authorized take-off weight is greater than authorized landing weight. Therefore they need to sometimes dump fuel before landing - YES, they also do it for safety in an emergency.

The Game wardens in Alaska flew their confiscated Cubs loaded so heavy that the fuselages were getting bowed in the middle - but they still flew ! Most small aircraft have a safety factor of at least 150% - Give that some thought. And, 6G's?

Has anyone, anywhere, seen an Avid or Kitfox, or clone, with broken wings from overloading? With no ground accident?

ED in MO

Edited 11 Sep 2012 by Ed In Missouri

[birddog486 21]

There's a Heavy Hauler version of both wings that use bigger struts. My Heavy Hauler stol has the gross at 1085. The real gross weight on an experimental is whatever your brave enough to take off with.

The wings I've built were the "Aerobat" with the .083 spars, 12" rib spacing and should have had a couple steel brace tubes but I have duel tanks that remove those and the plane uses 7/8" lift struts. The brochure I have shows the hauler at 1085 but still 911 for the aerobat unless doing high G manuvers.

I'm sure Avid updated the weights but the stuff I have is from mid 1990 when my father bought the kit.

Travis

[dholly 718]

Doug I saw a post you made saying the Avid aerobat had a gross weight of 1200lb. do you have something from the factory that talks about that? In the paperwork I have from Avid it states 911 lb gross which I assumed was wrong because the speedwing gross is 911 but, the Aerobat is rated at 850 max gross doing aerobatics up to 6 G's. I'm building what should have been the aerobat wing but I've added extensions and wasn't sure about a safe max weight on it.

Travis

Not in writing, sorry, but I will explain my reasoning.

First, I will assume you know the construction differences of Avid's four different wing designs. If you follow Avid convention, each Avid model (assuming no airframe modifications), would have the highest MTOW with Heavy Hauler wings, less for STOL wings, even less for Aerobatic Speedwings and the least with standard Speedwings. BUT, so many variations of wings using the same descriptors (ie., Heavy Hauler or speed) over the years (and even between same models) due to spar thickness and length, spar stiffener design, one or two wing tanks, rib and nose rib spacing, drag tube and trailing edge, lift strut wall and o.d., rod ends etc. it gets complicated in a hurry. Beyond all the various Avid model frames with their different construction and tubing strength etc., the wing construction and lift struts in use each come into play regarding MTOW and G loading.

As I understand it, the early C model standard Speedwing and Aerobat both have a MTOW of 911 lbs. However, the early 911 lb. gross model C model Aerobat is limited to 850 lbs. max MTOW -while performing aerobatic maneuvers. I believe the limitation is applicable to all early C models using 3/4" .035" wall lift struts. Some later C models, including Aerobats, used 7/8" lift struts. The later STOL and HH wing C models with 7/8" struts went up to 1050 and 1100 lb. MTOW respectively. Although I never saw a brochure printed by Avid Aircraft showing +/- G ratings for a late C model with standard or Aerobat Speedwings, an increase in MTOW for both of them as well due to the heavier lift struts only makes sense. I do know that a local builder of a late C model Aerobat in my area said "Jim Tomash told me, for my airplane, I could think of 950 as my"aerobatic" gross, 1050 as my "utility" gross, and 1150 as my "normal category" gross. That was sort of useful. My FAA paperwork uses 1150. So far, I fly using 1050 and feel comfortable and safe doing that."

As a point of reference, the STOL wing on a 911 lb. MTOW model C w/ 3/4" lift struts (I believe this has the same wing loading spec as 911 lb. MTOW early C model Aerobat with 3/4" struts) was static tested to +5.7/-2.25 G's at max gross (vs. brochure +3.8/-1.5 G's at max gross). I have a print brochure for the Mk-IV models showing 1150 lbs. MTOW (+4.4/-2.2 G's) for STOL wing and 1050 lbs. MTOW (+6.0/-3.0 G's) for standard Speed wing, wing loading at MTOW was the same for both at 9.36 lbs. I would, therefore, personally presume that the Mk-IV with Aerobatic Speedwings would at least be the equal of the Mk-IV with standard Speedwings... and almost assuredly more. You probably know the HH wings with .083" wall spars and 7/8" lift struts were stress tested on a Mk-IV to 1150lbs --without spar stiffener inserts-- and the wing found to comply. I have also read that Dean successfully tested these wings to a 1500 lb. load at 6.0 G's before adding the stiffeners and never bothered to test after adding the stiffeners.

Dunno if that last bit is true but, remember, Avid did subsequently (and 'officially') increase the MTOW of the Mk-IV from 1150 lbs. to 1200 lbs. to compete with Kitfox 4-1200. There were zero structural changes whatsoever made to the aircraft when this happened. In light of all everything above, plus the 'unofficial' comments I've heard and read by Bob Stone and Steve Winder over the years, I do believe a Mk-IV fuse fitted with Aerobat Speedwings is good for 1200 lb. gross easy. Of course, like earlier limitations, it would stand to reason that one would want to limit MTOW to something less while performing aerobatic maneuvers. Maybe 1000-1050 lbs. max MTOW? I'm certainly no expert so you're on you own there.

In any event, how I came up with 1320 lbs. MTOW for my Avid+ with what are essentially 144" x 1-1/4" twist Aerobat Speedwings can be found HERE. Not interested in going upside down on floats so I never tried to figure my particular +/- G's.

[EDMO 1078]

Seems to me that all of this is sort-of "unknown territory" until someone breaks a wing in flight. HOPE THAT NEVER HAPPENS!

When I was a young pilot, a friend was flying a home-built (no kits back then) and a weld broke and wing folded and it killed him.

This made me afraid of homebuilts and I would not even consider flying one until 30 years later when the aluminum tube wing spars and apparently safer crossover tube construction and wing attach fittings were made available by Dean Wilson on the Avid.

Yes, I know that others had tube wing spars, but I didnt see any published reports or tests on them until the Avid.

ED in MO

Edited 14 Sep 2012 by Ed In Missouri

[dholly 718]

Seems to me that all of this is sort-of "unknown territory" until someone breaks a wing in flight. HOPE THAT NEVER HAPPENS!

Me neither Ed, but I would reiterate that no one is blindly pulling numbers out of a hat here. MTOW's for most Avid models are well known and there is well documented stress test info available for several of the various Avid frame and wing combinations. In fact, unlike many in the day, it strikes me that that Dean's Light Aero and it's successor Avid Aircraft were conservative enough to leave a fairly large 'safety factor' when it came published specs. I've heard almost as much as 50% or so. If this is true, and much of the published info seems to support it, a pretty reasonable case can be made that there is some margin of 'wiggle room' when it comes to Avid MTOW.

Regardless, Travis is not talking about ignoring kit manufacturer specs. If he is simply doing the same as Avid itself did, ie. replacing the exact same parts, why won't he safely achieve the same increase in gross as Avid did? Start with a 911 lb. gross C model Aerobat and add 7/8" lift struts, he ends up with a 1050 lb. gross C model Aerobat just like Avid did. Add Speedwing extensions and I think it's safe to say MTOW just went up again. Ie. if all fuselage and wing components in Travis' C model extended Aerobat speedwing are the same as in the later C model HH with a 1150lbs. MTOW, why wouldn't that be the case? Yes I realize rib profiles are different, however, the wing cord and area is exactly the same.

Being "experimental", the kit builder is classed as the designer and can stipulate the gross weight he wants REGARDLESS of what the kit manufacturer recommends. Obviously that can be "unknown territory" and dangerous if unjustified. I do not believe that to be the case when a kit builder incorporates known oem structural improvements that resulted in an increase of recommended MTOW by the kit manufacturer. Add the improvements, do your initial certification to reflect them and go fly confidently at the higher gross knowing you had the benefit of the kit manufacturer's R&D and testing rather than pulling a number out of yer azz. That is a long way from being reckless or stupid, IMHO.

Of course, since the +/- G loading is based specifically on MTOW and Avid clearly stated that max MTOW vs. max aerobatic MTOW are entirely different, one must not only understand ALL the differences in EACH airframe and wing and how each of the seemingly endless combinations impacted the factory gross recommendations, they must respect a lower gross limitation while performing aerobatic maneuvers. Again, we are fortunate that Avid provided some good guidelines, eh?

Just... ...take with a grain of salt and do your own thing!

[birddog486 21]

Doug, Thanks for taking the time to put in your two cents, It's all as clear as mud

Travis

[EDMO 1078]

Doug,

I agree with you 100% - No one should go "into the unknown" without some kind of logic, and the kit manufacturers have surely protected themselves and reputations by being cautious and having a large safety factor, and lots of stress tests.

To add to what you said about Avid, we also have the Avid clones and mods info to look at, aka Kitfox, Magnum and Airdale, so it is easy to make comparisons on GW, structures, wings, etc.

Then, there are the Aerobatics, which most of us dont even consider because we do not do them.

A bigger factor in most cases would be hard landings or turbulance with a max load - then, we get into that old bugaboo that some like to agrue about where light wing loading is more dangerous than heavy....I dont even want to get into that discussion again.

Best thing I can say for myself is: Build it strong - Fly it well - enjoy the view.

ED in MO

Edited 18 Sep 2012 by Ed In Missouri

[EDMO 1078]

Travis,

FYI: My Magnum manual has an additional insert that describes all of the maneuvers for the Aerobat. I havent read it - Guess it is available from Avid, or was?

I just try to fly from A to B, and try to keep it between the telephone poles!

ED in MO

[dholly 718]

Travis,

FYI: My Magnum manual has an additional insert that describes all of the maneuvers for the Aerobat.

ED in MO

This for a Aerobat version of the Magnum? Or Avid Flyer? I have a copy of the factory supplied 'Avid Aerobat Manual' for Avid Flyer. Not dated but I believe this was distributed with the C model Aerobat. It gives entry speeds and basic techniques for how to perform Loops, Barrel Rolls, Snap Rolls, Wing Overs and Spins.

[EDMO 1078]

This for a Aerobat version of the Magnum? Or Avid Flyer? I have a copy of the factory supplied 'Avid Aerobat Manual' for Avid Flyer. Not dated but I believe this was distributed with the C model Aerobat. It gives entry speeds and basic techniques for how to perform Loops, Barrel Rolls, Snap Rolls, Wing Overs and Spins.

All it says is Aerobat - no model listed - no weights. Only 4 pages. No clue if there was an Aerobat Magnum - but something may be in the builders manual - I havent looked for it.

ED

Edited 19 Sep 2012 by Ed In Missouri