Increasing Gross Weight

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Andy Garrett, Jan 7, 2020.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Jan 7, 2020 #1

    Andy Garrett

    Andy Garrett

    Andy Garrett

    Active Member

    Joined:
    Jan 3, 2016
    Messages:
    32
    Likes Received:
    12
    Location:
    Haysville, KS USA
    There has been plenty written herein about the Affordaplane and the engineering of the design. I am currently sourcing some engineering texts related to aeronautics, but perhaps someone here can offer a quick, yet academic answer.

    I want to make whatever changes are required to increase the gross for this design. This could mean any number of changes. I anticipate more wing area, perhaps stronger or more numerous fasteners at the wing roots, larger gussets, beefier landing gear, stronger struts, more thrust, etc.

    I'm trying to nail down the formula that rests at the heart of this 540 number. When I find it, I will then know how to manipulate it. Obviously, I won't be going the part 103 route.

    Any useful tips?
    Thanks in advance.
     
  2. Jan 7, 2020 #2

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,625
    Likes Received:
    2,515
    Location:
    Rocky Mountains
    There is no simple answer. :(
    You have to know what the limiting factor is before you can change it. The 540# you quote could be due to a structural limit or a performance limit. Even if you identify the first weak link in the chain you still have to find the second to make sure it is good enough for your desired weight limit.
     
    don january, Topaz, BJC and 3 others like this.
  3. Jan 7, 2020 #3

    BJC

    BJC

    BJC

    Well-Known Member HBA Supporter

    Joined:
    Oct 7, 2013
    Messages:
    10,196
    Likes Received:
    6,918
    Location:
    97FL, Florida, USA
    I would first ask the designer what would need to be done to accommodate the new, heavier, gross weight.

    Do you also anticipate a change in speeds? May as well ask him about that at the same time.

    As HW said, it isn’t simple, especially without the original design data.


    BJC
     
    Andy Garrett and don january like this.
  4. Jan 7, 2020 #4

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,150
    Likes Received:
    3,459
    Location:
    Saline Michigan
    It seems to this engineer and airplane designer that when you increase the gross weight, it must be treated as a new airplane. Certainly seek input from the original designer, but be prepared for "I designed it for x weight and y Vne. You will have to study the structure under your weights and speeds." Even if they do tell you that the stiffness of "this" or the strength of "that" limited things, that does not mean that you only will need to beef up those components. It could be that much of the structure will be below standard at new weights and speeds. Without treating it as a new airplane design, and doing full up analysis, you will not and can not know where your design is fine and where it will need help.

    Yeah, you are taking on design of a new airplane by doing this. Welcome to the Monkey House.

    Billski
     
  5. Jan 9, 2020 #5

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,905
    Likes Received:
    451
    Location:
    Sahuarita Arizona, Renton Washington, USA
    The AFP (Affordaplane) is an experimental airplane. As an owner/operator/builder/mechanic or whatever you can set the gross weight at what ever level you wish. You can take your airplane load it up to the desired weight and and see how it performs and what breaks or you can do the engineering and decide what you wish to change.

    Let us know which branch you decide on. I would pick the experimental route as former posts have indicated that it is difficult to impossible to get access to any real engineering data. Build or purchase an AFP to your liking and start doing load tests till you are satisfied with the results.
     
  6. Jan 9, 2020 #6

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member HBA Supporter

    Joined:
    Feb 13, 2010
    Messages:
    6,822
    Likes Received:
    2,478
    Location:
    World traveler
    If you’re doing this because you want to design a plane, then go for it! If you’re doing this because the Affordaplane isn’t quite big enough for your needs, there are other designs to consider.
     
    wsimpso1, Topaz and pictsidhe like this.
  7. Jan 11, 2020 #7

    Andy Garrett

    Andy Garrett

    Andy Garrett

    Active Member

    Joined:
    Jan 3, 2016
    Messages:
    32
    Likes Received:
    12
    Location:
    Haysville, KS USA
    I've studied the pros and cons of many designs and measured them against my needs and desires. For a variety of reasons, I have chosen the AP, not for its designed performance, but for its construction methodology.
    Like countless builders before me, I hope to add a degree of individualism to my ship by modifying it to suit my preferences. I realize that every departure from the published design has compounding repercussions throughout the build. I welcome this.
    To your point cluttonfred, I may very well be designing a 'different' plane, but I am starting with a 'template'--one which has an admirable service record, and what, to my layman's eyes, looks like a great deal of design flexibility. I believe a study of the existing fleet supports that assessment.

    So far, what I have learned is that wing structure is key to load carrying capacity. Advice from elsewhere has alerted me to the CGS Hawk line of aircraft. These have similarly built wings and they can carry up to 1000+ pounds in one model. The wing on the Hawk Plus interests me most, as that model carries 800lbs. I think the AP fuselage can bear at least 700lbs as designed, but I'm studying that, and I am fully prepared to be wrong. I also need to study possible changes in tail surfaces and landing gear. Weight will obviously increase, and so must horsepower/thrust. I'm studying that as well.

    I enjoy the intellectual challenge of large building projects and the rewards of seeing my progress. My boat build was the most rewarding thing I've done to date. I think building something somewhat 'original' while still being logical and sensible will suit me far more than just building another plane to plans.
     
  8. Jan 11, 2020 #8

    BJC

    BJC

    BJC

    Well-Known Member HBA Supporter

    Joined:
    Oct 7, 2013
    Messages:
    10,196
    Likes Received:
    6,918
    Location:
    97FL, Florida, USA
    Andy:

    In case you haven’t already found them, I refer you to the first three threads in the “Aircraft Design ... “ section.

    There are lots of references to academic texts, as well as straight forward information that would be useful to anyone seriously contemplating a design modification.

    Consider starting a thread here where you can share your design work.


    BJC
     
    Topaz, mcrae0104 and wsimpso1 like this.
  9. Jan 11, 2020 #9

    Andy Garrett

    Andy Garrett

    Andy Garrett

    Active Member

    Joined:
    Jan 3, 2016
    Messages:
    32
    Likes Received:
    12
    Location:
    Haysville, KS USA
    Thank you.
     
  10. Jan 11, 2020 #10

    Dana

    Dana

    Dana

    Super Moderator Staff Member

    Joined:
    Apr 4, 2007
    Messages:
    8,829
    Likes Received:
    3,173
    Location:
    CT, USA
    Andy,

    Spend some time looking at the many A-Plane threads here. Suffice it to say that many have questioned the design's structural integrity, they tend to come out significantly overweight, and there seem to be very few of them actually flying. Not what I'd choose as the basis for an even heavier design.
     
    pictsidhe likes this.
  11. Jan 11, 2020 #11

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    7,324
    Likes Received:
    2,106
    Location:
    North Carolina
    The 'simple' answer:

    1. Obtain the plans. You need to know all dimensions and materials.
    2. Calculate all loadings.
    3. Calculate component stresses and maybe some deflections.
    4. calculate strength margins.
    5. redesign with suitable margins and your new gross weight. It will get heavier. you may well find that some parts are already way stronger (heavier) than necessary.

    Yes, reverse engineering then redesigning does look like more work than designing from scratch...
     
  12. Jan 11, 2020 #12

    Andy Garrett

    Andy Garrett

    Andy Garrett

    Active Member

    Joined:
    Jan 3, 2016
    Messages:
    32
    Likes Received:
    12
    Location:
    Haysville, KS USA
    Thanks gents.
    I have read a great deal herein about the AP in various threads. I am aware of its detractors and the reasons they state for their position(s). These are areas I wish to address.

    I do own the plans and study them regularly and I've already learned a great deal in response to asking this question. What appeals to me most is the fuselage construction method. As I learn more about engineering stress analysis, I'll know just what I can do with this design. Thanks again.
     
  13. Jan 12, 2020 #13

    Lendo

    Lendo

    Lendo

    Well-Known Member

    Joined:
    Feb 7, 2013
    Messages:
    383
    Likes Received:
    71
    Location:
    Brisbane
    Andy, Don't forget the wing loads.
    George
     
    Andy Garrett likes this.
  14. Jan 17, 2020 #14

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    Have you checked out the Texas Parasol? I don't actually know if it's a good airplane, but I've read that it has a 600 lb. gross and is made with rivets and aluminum. I don't know if I believe it, but the specs say it can handle an absurd amount of power.

    Also, I'd guess you could learn to weld and build a Legal Eagle XL faster than you could design and build something new. If designing is the part that you like, maybe that's ok. However, it would be prudent to do more, and more careful, flight testing on a new design.
     
  15. Jan 17, 2020 #15

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    P.S. If you're ditching part 103, you don't need to increase the wing area unless you need to land just as short or fly just as slowly. The somewhat heavier loading might mean you could handle a little more wind. OTOH, an extended wing would require less power than the original wing at the same gross weight.
     
  16. Jan 17, 2020 #16

    radfordc

    radfordc

    radfordc

    Well-Known Member

    Joined:
    Feb 5, 2008
    Messages:
    1,266
    Likes Received:
    516
    I have some personal experience with increasing the gross weight capability of a design. My Eindecker was orginally designed as an ultralight with a published gross weight of 450 lbs. The wing was 23 feet in span and 92 sq. ft. area giving 4.9 lbs/sq. ft loading. The wing has a two spar design (leading and trailing edge aluminum tubes) and was braced with two wires below and above the wing. My plane weighed 350 lbs empty rather than 250 as designed. This put me at 600 lbs gross weight (6.5 lb/sq. ft). The stall speed was about 35+ mph in level flight and top speed was only 55 mph giving a very narrow margin for flight. I flew the plane like this for a while until I got into a stall/spin situation at low altitude (pulling around in a banked turn) and barely recovered in time. I stopped flying the plane until the problem was corrected.

    Discussions with the designer resulted in us building a much bigger wing...28 feet span and 130 sq. ft. of area giving about 4.6 lb/sq. ft. of loading. Now the plane flys as it should with no adverse stalling tendency....you can put the plane in a 45 degree bank and pull as tight as you want without the plane snapping over into a spin. The new wing has the same size aluminum tube spars but is braced with 4 wires above and below the wing.

    Small wings...
    image2.JPG

    Big wings....
    IMG_1860.JPG
     
  17. Jan 17, 2020 #17

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    12,038
    Likes Received:
    3,468
    Location:
    Memphis, TN
    Increasing gross is usually those aircraft that are already known robust. Redesign like above is a rare fix. I know this is about ULs but the best examples are certified. In that world let’s say you have a plane that is certified standard and utility. What they do is eliminate the Utility. You want to fly more weight? Ok but you can’t ever fly with higher G ratings. Usually you are just using up capacity already built in.
    A design fix is usually harder than picking something that will work as is. Lots of options out there. Getting hung up on an idea better be worth it.
     
    cluttonfred likes this.
  18. Jan 17, 2020 #18

    blane.c

    blane.c

    blane.c

    Well-Known Member HBA Supporter

    Joined:
    Jun 27, 2015
    Messages:
    3,781
    Likes Received:
    676
    Location:
    capital district NY
    Not suggesting you move to Alaska (though not a bad idea) but possibly understanding how this is rationalized may help.

    § 91.323 Increased maximum certificated weights for certain airplanes operated in Alaska.
    (a) Notwithstanding any other provision of the Federal Aviation Regulations, the Administrator will approve, as provided in this section, an increase in the maximum certificated weight of an airplane type certificated under Aeronautics Bulletin No. 7-A of the U.S. Department of Commerce dated January 1, 1931, as amended, or under the normal category of part 4a of the former Civil Air Regulations (14 CFR part 4a, 1964 ed.) if that airplane is operated in the State of Alaska by -

    (1) A certificate holder conducting operations under part 121 or part 135 of this chapter; or

    (2) The U.S. Department of Interior in conducting its game and fish law enforcement activities or its management, fire detection, and fire suppression activities concerning public lands.

    (b) The maximum certificated weight approved under this section may not exceed -

    (1) 12,500 pounds;

    (2) 115 percent of the maximum weight listed in the FAA aircraft specifications;

    (3) The weight at which the airplane meets the positive maneuvering load factor n, where n=2.1+(24,000/(W+10,000)) and W=design maximum takeoff weight, except that n need not be more than 3.8; or

    (4) The weight at which the airplane meets the climb performance requirements under which it was type certificated.

    (c) In determining the maximum certificated weight, the Administrator considers the structural soundness of the airplane and the terrain to be traversed.

    (d) The maximum certificated weight determined under this section is added to the airplane's operation limitations and is identified as the maximum weight authorized for operations within the State of Alaska.


    Also there are waivers that can be obtained, I have flown both DC-4 and DC-6 aircraft that had 115% weight increases because my bosses obtained waivers. These aircraft are 80,000lb-ish and 100,000lb-ish. Just in case waivers is not the proper word, we had paperwork signed by the FAA that allowed us to operate at 115% weight whatever such paperwork is called.

    Anyway Alaska is magic, aircraft can fly heavier there.
     
  19. Jan 17, 2020 #19

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member HBA Supporter

    Joined:
    Feb 13, 2010
    Messages:
    6,822
    Likes Received:
    2,478
    Location:
    World traveler
    That's a very cool plane, radfordc, though somehow I have this urge to see it through the windscreen and crossed wires of a Nieport 11 Bébé just before firing my Lewis gun. ;-p
     
  20. Jan 17, 2020 #20

    Andy Garrett

    Andy Garrett

    Andy Garrett

    Active Member

    Joined:
    Jan 3, 2016
    Messages:
    32
    Likes Received:
    12
    Location:
    Haysville, KS USA
    Great comments guys! This is really helping my thought process.

    Ir27, I considered higher wing loads and faster approaches, but this seems like trouble squared to me. If I keep the wing load consistent with the original design, logic suggests a far better chance of success since such loading is already proven. radfordc's comments seem to confirm that suspicion. I also prefer to keep my stall speeds in the 30mph range. The slower my relative speed to the ground when I make contact with it, the happier I am.
    As for welding a Legal Eagle..., It's just too ugly. I'd build another Airbike first and maybe modify it to get my knees inside.

    radfordc, VERY useful info there! Thank you. I enjoyed the owning and flying the Airbike you built. A similarly flying ship with a bit more climb power is what I'm after. That's why I', interested in the AP design most. If you recall, we once discussed the Challenger design, which you indicated was like a leaf on the breeze. I don't want that feeling anymore than I want to go too fast on landing--it's a balancing act. However, I lived in hot, humid, and WINDY Kansas at that time. The flying weather here in the Treasure Valley of Idaho is a world apart from Kansas, especially in these light craft.

    TFF, your point about using up the existing potential is well received. This is what I see when I look at the fuselage of the AP--unused potential. There are subtle ways to make what already appears strong even stronger at minimum weight gain. If the numbers prove me correct, then there seems to be little limit to what can be done. A bigger, stronger wing to keep the load at 5 lbs per, a strengthened gear set-up for the added weight, more power to have better climb than I did with the 447 in Kansas, and perhaps a strengthened tail, though it seems pretty solid as it. Of course, it won't be that simple, but the broad strokes seem encouraging. Many fuselages have been shared among planes of different performance characteristics (Panther and Cougar, Bonanza and Baron, all kinds of twin and single Pipers), so logic suggests that if the AP fuse is indeed robust, then it should be adaptable to a slightly higher performance (read: 30-40% higher gross). A-planes are already flying which prove that to be true (180 lb engines, etc.), unless they are just at the ragged edge of airworthiness and one stiff bit of turbulence away from breaking up in mid-air.

    To my simple mind, increasing weight means you increase the load bearing ability of those components which must bear that weight and the forces associated with them in all phases of flight within the intended envelope. ...and I'm a mellow pilot--never a hot-dogger.

    Great feedback gentlemen! I appreciate you taking the time.
     

Share This Page

Group Builder
arrow_white