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Thread: How to put a Piet on a diet?

  1. #1

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    How to put a Piet on a diet?

    Hi all-

    First time builder here contemplating starting a Pietenpol project this fall. I'm a little concerned about useful load. Me and full fuel doesn't leave much for pax, and I'm wondering about any relatively easy and affordable ways to shave weight and thereby boost useful load.

    I only need to pick up about 80 lbs. over standard useful load (450 lbs), which is normally specified with 65HP. I'm going with a 100HP Corvair. Will HP alone get me where I need to be?

    My specs so far are: 100 HP Corvair, long fuse, brakes, starter, basic instrumentation w/radio and preferably an intercom.

    THANKS!

    Rob

  2. #2
    steveinindy's Avatar
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    Me and full fuel doesn't leave much for pax, and I'm wondering about any relatively easy and affordable ways to shave weight and thereby boost useful load.
    It's a very light aircraft so the margin for useful load for most modern day adults is going to be pretty narrow.

    I only need to pick up about 80 lbs. over standard useful load (450 lbs), which is normally specified with 65HP. I'm going with a 100HP Corvair. Will HP alone get me where I need to be?
    You do realize that the size of the wing is the major determining factor in load correct, not the size of the engine? That is unless you're willing to tolerate an increase in stall speed, etc. That's not something I would honestly recommend because one of the benefits of small aircraft is a lower stall speed (which provides a slight increase in safety) but as you start adding in bigger engines, they come with (generally) a heavier motor mount, they consume more fuel (so either you tolerate a decrease in range or start carrying more fuel) and that puts you further away from where you want to be.

    Just my two cents but if you're that concerned, then instead of trying to make the design work for you, looking at something designed to have a more suitable useful load might be best.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  3. #3

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    the strength of the wing is based on the structure of the wing not the engine. the problem with a 1930's airplane is that it is designed with 1930's sized people in mind. ever seen pictures from the depression era? not many "fat americans" included.

  4. #4

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    Quote Originally Posted by steveinindy View Post

    You do realize that the size of the wing is the major determining factor in load correct, not the size of the engine?
    No, I don't Steve. That's why I'm here asking.

    What I'm looking for are realistic ways to help keep the weight down during my build. Someone has done it, and I'm curious to get their advice.

    I realize Americans are fat and that it's a small airplane. I'm not trying to change the design, I'm trying to find ways to save a little here and there and hopefully make a difference.

    Any helpful suggestions?

    Rob

  5. #5
    steveinindy's Avatar
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    I realize Americans are fat and that it's a small airplane. I'm not trying to change the design, I'm trying to find ways to save a little here and there and hopefully make a difference.
    By definition, technically you are trying to change the design. That said, your goal is probably not going to work without some serious structural modifications. The problem is that you're either going to have to put a bigger wing on it (which more or less changes the design entirely and will require you to re-engineer the structures) or deal with the aforementioned problems of simply slinging a bigger engine up front.

    Someone has done it, and I'm curious to get their advice.
    Shaving a hundred pounds off an airplane that weighs about 1000 lbs as it stands is asking for trouble. You might be able to save 10-20 lbs max before you're going to have to start cutting corners so far as major structure goes which is something no one in their right mind is going to recommend. I seriously just do not believe the Pietenpol is the correct aircraft for your needs. Just be very glad you realized this before you started building. A lot of people don't. Aircraft design involves a huge freaking tradeoff and a lot of people new to the hobby don't realize that.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  6. #6
    Eric Witherspoon's Avatar
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    In the wording of your original question, are you looking for something with 450 lbs payload, or something with 80 lbs over 450 lbs payload?

    Are you looking to run full fuel with the passenger, or are you willing to consider running it at reduced fuel load when "taking someone for a ride"? As you look into this more (at designs with 450-550 lbs payload), you will see that based on the fuel tank size, these most often can be run in the following combinations:
    Pilot + full fuel.
    Pilot + small child + full fuel.
    2 200-pounders + way less than full fuel.

    Just saying, think about the mission. In a low-and-slow flyer like that, the mission isn't going to be 2 people + full fuel + bags, etc. Local 1/2 hour to 1 hour sightseeing flight, will only need ~8 gallons and that will still include the required day VFR reserve.

    If you really need more payload, then you will need to look at bigger airplanes. You will find to go from 450-550 lbs payload to 600+ lbs payload is a LOT more money.

    Beware of manufacturer payload claims. Try to find real numbers from customer-built examples if possible. What looks like a 550 lbs payload airplane in the brochure may really end up at 500 lbs or less in the "real world". Sure, there's lots of things you can do - I used to say lightening up the panel would be one, but that's one area where great progress has been made over the past several years. There's other areas - smaller wheels/tires/brakes, no autopilot, smaller fuel tank, no lights, no paint (metal airplane)...
    Murphy's 13th: Every solution breeds new problems...

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  7. #7
    steveinindy's Avatar
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    Beware of manufacturer payload claims
    And remember that for the most part the "four adults" claim is based upon a 170 or 180 adult male.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  8. #8
    EAA Staff / Moderator Zack Baughman's Avatar
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    I am by no means a small man, but Bill Rewey (all Piet builders/potential builders should learn his name) gave me a ride in his 65hp Piet at Brodhead back in 2004, and it hauled my fat butt (guessing I was about 250lbs then) around the area just fine. I doubt Bill had a full fuel tank, but the Pietenpol is definitely a heavy lifter. If you haven't already, I highly suggest subscribing to the Pietenpol List here: http://www.matronics.com/listbrowse/...ist/index.html The folks there know everything there is to know about Pietenpols and can answer your questions with good authority.

    Zack

  9. #9
    There's a longstanding line about Pietenpols, ""You can change Mr. Pietenpol's plans and build a good airplane. But if you don't change them, you'll build a better one." If I were you I would look to proven solutions and change the design itself as little as possible. An A-65 is going to get you 65 strong, low-RPM horses with a big wooden prop and fly the plane well. You can go with the smaller fuel capacity, light wheels and tires and the lightest covering you can manage. Then -- and don't take this the wrong way -- unless you are an athlete, then you can probably stand to lose a few pounds yourself, which might be easier and certainly safer than trying to shave too many off the Piet'! That's certainly true in my case. ;-)
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  10. #10

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    Quote Originally Posted by Eric Witherspoon View Post
    In the wording of your original question, are you looking for something with 450 lbs payload, or something with 80 lbs over 450 lbs payload?

    Are you looking to run full fuel with the passenger, or are you willing to consider running it at reduced fuel load when "taking someone for a ride"? As you look into this more (at designs with 450-550 lbs payload), you will see that based on the fuel tank size, these most often can be run in the following combinations:
    Pilot + full fuel.
    Pilot + small child + full fuel.
    2 200-pounders + way less than full fuel.

    Just saying, think about the mission. In a low-and-slow flyer like that, the mission isn't going to be 2 people + full fuel + bags, etc. Local 1/2 hour to 1 hour sightseeing flight, will only need ~8 gallons and that will still include the required day VFR reserve.

    If you really need more payload, then you will need to look at bigger airplanes. You will find to go from 450-550 lbs payload to 600+ lbs payload is a LOT more money.

    Beware of manufacturer payload claims. Try to find real numbers from customer-built examples if possible. What looks like a 550 lbs payload airplane in the brochure may really end up at 500 lbs or less in the "real world". Sure, there's lots of things you can do - I used to say lightening up the panel would be one, but that's one area where great progress has been made over the past several years. There's other areas - smaller wheels/tires/brakes, no autopilot, smaller fuel tank, no lights, no paint (metal airplane)...
    Hi Eric-

    The standard Piet useful load is appx. 450.

    I was hoping to achieve the two 200-pounders plus full fuel scenario. I can do that with another 60-80 lbs of useful load, depending on how long it's been since Thanksgiving. I'm not looking to do crazy structural modifications, just trying to trim weight here and there where I can during construction. That's my question...how do people trim weight?

    Your comment about mission is a good one. Honestly, 90% of my flying would be me plus a kid or DSW (dear sweet wife) and 1/2 to 3/4 fuel. In all of those scenarios I'm golden with standard useful load.

    I see that the Fisher Celebrity shows a 630 lb useful load. Even with the marketing fudge factor that may be something to look at. All wood, two seats, can accept a Corvair. Hmmm...

    Rob

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