How to put a Piet on a diet?

[Skagit]

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

[steveinindy]

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.

[tonycondon]

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.

[Skagit]

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

[steveinindy]

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.

[Eric Witherspoon]

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)...

[steveinindy]

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.

[Zack Baughman]

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/pietenpol-list/index.html The folks there know everything there is to know about Pietenpols and can answer your questions with good authority.

Zack

[cluttonfred]

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. ;-)

[Skagit]

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

[Skagit]

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. ;-)

Heck yeah...I have 20 or 30 useful load killing pounds right here above my belt!

Rob

[Rick Rademacher]

Over twenty years ago, both my son, age 12 and I flew a Piet from Ohio to Broadhead with sleeping bags, tent, clothes and other necessities stuffed around us. I was hoping all of this stuff would cushion the impact of a crash. Thankfully, I made many good landings getting there and back.

One of my shortest biannual flight reviews was in this same Piet. As the instructor was a little bit heavy, I had to go around the trees at the end of the runway instead of going over the top as usual. He said “nice job and I have seen enough”. It was a hot day.

A good friend of mine closed off the front hole of his Corvair powered Piet. He is a big man and didn’t even want to be tempted.

Sold my Piet to a man who looked sizeable. I cautioned him about taking lessons in the Piet and to be careful of the load. So, he had his instructor check out the Piet first. Then, on the first flight with both in the aircraft, they couldn't seem to climb and crashed at the end of the runway.

So, if flown correctly, it is a great little airplane. But, weight does matter.


1802

[cluttonfred]

IIRC, going with the one-piece wing and not the optional three-piece one would also save some weight.


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. ;-)

[tonycondon]

I don't know much about Piet's except that I think I might like to build one some day. If there are any areas where Douglas Fir is called out as an option in order to save money, use Spruce to save weight. Also if you use Stewart Systems for covering and do so lightly you can save some significant weight. I saved 10-15 lbs on my glider by removing medium weight fabric with two coats of paint and replacing it with lightweight (uncertified) fabric and a thin coat of Stewarts System. Minimal instrumentation can also save a lot over a full panel. the lightest weight engine and prop combo also is natural, although make sure that that doesn't put your empty CG too far aft. Typically the lightest weight solution won't be the cheapest but life is all about compromises.

[David Darnell]

A silly question- whats your criteria for choosing a design? might help "broaden" our suggestions
As far as the Piets are concerned , might I suggest you go to the Piet gathering in Broadhead WI- if I recall its a week or two before Oshkosh

[Skagit]

A silly question- whats your criteria for choosing a design? might help "broaden" our suggestions

No problem at all...

2 seats
Wood construction
Corvair compatible
Would like to be able to haul 2 adults with full fuel if possible
Should look good...nothing too...ultralightey (sorry to the UL guys out there, just not my thing)
Reasonably affordable. I like that the Piet is appx. $10k.

That's about it...the Piet hits all of them except the useful load part. I have to say I've spent some time today looking at the Fisher Celebrity and I'm intrigued. I have an email in to them to see if I could hang a Corvair off the front. I do like the bipes...

Rob

[steveinindy]

I doubt Bill had a full fuel tank, but the Pietenpol is definitely a heavy lifter.

LMAO. *snort* OK Zack....I think you spend too much time around the really light end of aircraft and that's got your scale out of calibration.


Corvair compatible

Why the fixation on the Corvair engine?

[Hangar10]

No problem at all...

2 seats
Wood construction
Corvair compatible
Would like to be able to haul 2 adults with full fuel if possible
Should look good...nothing too...ultralightey (sorry to the UL guys out there, just not my thing)
Reasonably affordable. I like that the Piet is appx. $10k.

That's about it...the Piet hits all of them except the useful load part. I have to say I've spent some time today looking at the Fisher Celebrity and I'm intrigued. I have an email in to them to see if I could hang a Corvair off the front. I do like the bipes...

Rob

Love to see interest in the Pietenpol... I would agree with Zach that you visit the Pietenpol forum at http://forums.matronics.com/viewforum.php?f=7&sid=ff2062fa0ff5223a8905e91f66acf212

Rob, when you state "reasonably affordable" I think you are generally correct in relative terms... but unless you have a good supply of materials or are a good scrounger, I think you'd be hard pressed to build a completed airplane with engine conversion for $10k. I was hoping to complete mine for $12-$15... it looks like I'll be pressing $20k before I'm done, but I'm not upset about that at all. As my first project, there are some things that I had no idea about... plus, I was starting with an empty shop, so I've had to gather all my materials along the way. I'm not saying any of this to discourage you, and there are some things I could have done a little cheaper, but to each their own.

@Steve... Why the fixation on the Corvair? Simple... smooth running 100HP that looks and sounds great. Many say that flying behind a Corvair feels like having an electric motor out front. More? The conversion process can be accomplished by anyone. Maintenance is easy and affordable (I picked up a cylinder for $10). Lighter than an O-200 and MUCH smoother. With 1.7million manufactured, they are widely available.

Shazam! Becky Shipman's engine as completed at the recent Corvair College #22 in Georgetown, Texas.
1803

Want to hear what one sounds like? Click this link to see John Franklin's engine run for the first time, also at Corvair College #22. http://www.10.eaachapter.org/apps/videos/videos/show/16152988-corvair-college-22-

[steveinindy]

Why the fixation on the Corvair? Simple... smooth running 100HP that looks and sounds great. Many say that flying behind a Corvair feels like having an electric motor out front. More? The conversion process can be accomplished by anyone. Maintenance is easy and affordable (I picked up a cylinder for $10). Lighter than an O-200 and MUCH smoother. With 1.7million manufactured, they are widely available.

Cool. I've have zero experience with them one before so I figured I would ask. I don't have much use for a 100 hp engine but it's still good to know.

[David Darnell]

Well, I'm not the expert on wood aircraft around here, but will throw out one name- Roger Mann. Understand all of his designs are wood.

[EdM24680]

I've built a FlyBaby and worked on a Piet. Within specification limits for wood density, try to get the lightest materials in spruce and plywood. There is a lot of it in the Piet and care in selection is needed. Covering can be heavy too. Use Dacron and the lightest finish you can find. Don't use thicker gage metals as they are heavy too. I was a heli aerodynamicist for 6 years and landing speed and stall speed are a function of wing loading - pounds per square foot. Excess hp gives you only greater rate of climb and usually costs weight - engine + extra fuel. Lift devices are only good when extra thrust is available to pull the extra drag. The safest weight reduction is around one's waist!

[tailwind5]

Have you considered the steel tube fuselage? I hear it's lighter.

[braywood]

Hi Rob - I'm no expert, as I am starting to build a Piet; and I have the same problem, I am not a small guy either!! I agree with one of the other replies, that the better Piet is the one built to the plans - just read the build articles by Mr. Pietenpol to understand why.
If you look through the records for existing Piets, and note their empty weights, you will see there is a wide variation. If you want light, you have to eliminate all the optional stuff: no starter or electrics (wiring, battery, alternator, switches, electrical gauges, etc.), use Sitka, not Douglas Fir, minimum paint, no radio, maybe even one-piece wing! You will probably want to include brakes and tailwheel, but those are optional too, if you are up to that challenge! All these things are compromises for either convenience, comfort or cost. Safety is non-negotiable, so stick with the proven plans as Bernard intended.
It is just a process of using aircraft materials, but only what is needed to do the job. We tend to add stuff during the build to make it our own, and those often add weight. Stick to the plans and you will have as light as possible, with a robust, safe, aircraft.
Me, I plan to lose some weight to improve my situation - I just have not figured out exactly how I will do that!!

Good Luck,

Mark:)

[cluttonfred]

You might also consider the Oratex fabric covering system. It uses a heat-activated adhesive (something like tiny little beads of hot glue suspended in water) pre impregnated in the fabric and painted on the structure and attached with an iron. The fabric is pre-tinted and the whole system appears to be very easy to use, though it's not cheap. It could easily knock 10 lbs off the finished weight of the aircraft vs. even a light traditional Dacron covering job. See http://www.g-tlac.com/oratex.html and http://www.oracover.de/index.php/katalog/nlayer/5129-1-oratex_ul_600.html. The colors are limited and not as vivid as other systems, but should work well for an old-fashioned look for a Piet': antique (cream) and Fokker red or Corsair blue, for example.

[highflyer]

The best and easiest way to trim weight from a Pietenpol without hurting strength and durability is simply to use Orrin Hoopman's steel tube fuselage option. It is quite a bit lighter than the standard wooden fuselage. Also leave off the starter and electrical system and battery. That alone would give nearly the 80 pounds you are looking for.

[MrLithium]

Use a Lithium starter battery to save 10 to 15 lbs

[johnnysdrop]

Rob
Advice from the UK, use the "Jim Wills wing", it's a built up ply and spruce spar 3 piece design actually approved by the LAA here (hard to do) and weighs a lot less than the routed solid spar!
Look for more info here: http://www.pietenpolclub.co.uk/
H (http://www.pietenpolclub.co.uk/)ave fun,
English Johnny

[cluttonfred]

Did anyone find a source for the Wills wing modification at this site or elsewhere? I didn't see it there.


Rob
Advice from the UK, use the "Jim Wills wing", it's a built up ply and spruce spar 3 piece design actually approved by the LAA here (hard to do) and weighs a lot less than the routed solid spar!
Look for more info here: http://www.pietenpolclub.co.uk/
H (http://www.pietenpolclub.co.uk/)ave fun,
English Johnny

[David Darnell]

At the UK site- found this- hope it helps.
http://www.lightaircraftassociation.co.uk/engineering/TADs/047%20PIETENPOL%20AIRCAMPER.pdf

[cluttonfred]

Thanks, but the LAA type sheet seems to point back to the same web site noted above. I wrote James Buco to ask him directly.

This whole thread has got me thinking how I might build a Piet' within the 450 kg (472.5 kg with ballistic chute) gross weight limits for a two-seat microlight in Europe. That would be great fun and seems quite doable, especially with the steel-tube fuselage and Wills wing.

[Hangar10]

450kg is nearly 1000 pounds... not only is it likely that you can build lighter than this, but it probably won't fly if you don't. Most Air Campers are somewhere around the 700 pound (320kg) range.

[cluttonfred]

Thanks, Mark, but I think we may be talking apples and oranges. Bernie Pietepol listed the original Air Camper empty weight at 610 lbs, though most are definitely a little heavier than that. That 450 kg limit for European microlights is gross weight ready to take off with two passengers, fuel, etc. Air Camper gross weight is listed at 995-1000 lbs so definitely doable as a microlight. The problem, of course, is that while fuel, oil (and water if you've got a radiator) weigh the same as they did in 1929, many people do not. Still, with a little care, it shouldn't be too hard to keep the weight down (perhaps ponying up the money for a Rotax 912) and it would be great fun to bring an antique-looking Piet' to fly-ins to play with the tube-and-dacron, composite and metal modern microlights.


450kg is nearly 1000 pounds... not only is it likely that you can build lighter than this, but it probably won't fly if you don't. Most Air Campers are somewhere around the 700 pound (320kg) range.

[Hangar10]

Ahh, I see. I was indeed thinking empty weight.

[braywood]

Hi Rob - I bought the original plans from Don Pietenpol in 1994 - never really got serious, and now I find myself in the UK - having to build following the UK rules - these include the Wills plans. There are lots of changes from the original plans, some of them good.......I think the wing spar design is a material/cost savings as you need long pieces of 1" x 1" (or 1 1/8") spar caps with 1/8" ply webs in place of the solid spar. It is probably lighter (I have not done the comparison) but certainly makes it easier to find the material.

I do not know if you can still purchase the Wills plans from Jim - they are wrapped up in lots of legal jargon that prevent you from making more than one aircraft, copying, etc. but I think his contact info is on the LAA website. You can let me know if you can't find it, I can dig it out.

If you can get to Brodhead, you will certainly get a ride and see for yourself the load issues. Talk to Piet pilots and you will have the facts. You (or maybe it was another poster) mentioned contacting James Buco - I think you meant Alan James, builder and pilot of G-BUCO - a UK Piet flying here now for 20 years! Alan is a great guy and will answer any questions you have, I am certain.

Another friend of mine suggested that if a person can physically fit in the front pit of a Piet - then the Piet will fly with them! I think it is as much about flexibility to get into the Piet as weight.......I know, I am old and fat!!!!
Good luck with your search
Mark

[johnnysdrop]

Matthew
The Pietenpol is unlikely to meet the wing loading requirements regarding stall speed to meet the 450kg class. The max weight all up allowed in the UK is 1200lbs as a normal light aircraft, most weigh over 700lbs empty!
Johnnysdrop

[cluttonfred]

Thank, johhnysdrop, but I am pretty sure that in France the wing loading is a guideline and you can show demonstrated flight performance in lieu of the low wing loading. Published stall speed of a Piet' that I have seen is 30 knots (34.5 mph, 55.5 kph) so well within the microlight requirement of 65 kph minimum speed. But, as you suggest, the key is going to be keeping the weight down in order to keep a reasonable useful load.

[Lars Gleitsmann]

You might also consider the Oratex fabric covering system. It uses a heat-activated adhesive (something like tiny little beads of hot glue suspended in water) pre impregnated in the fabric and painted on the structure and attached with an iron. The fabric is pre-tinted and the whole system appears to be very easy to use, though it's not cheap. It could easily knock 10 lbs off the finished weight of the aircraft vs. even a light traditional Dacron covering job. See http://www.g-tlac.com/oratex.html and http://www.oracover.de/index.php/katalog/nlayer/5129-1-oratex_ul_600.html. The colors are limited and not as vivid as other systems, but should work well for an old-fashioned look for a Piet': antique (cream) and Fokker red or Corsair blue, for example.

In all of North-America the exclusive source of Oratex is actually www.BetterAircraftFabric.com
We are also glad to send out lots of detail photos of Oratex-covered Pietenpols and get Oratex-Pietenpol Builders in contact with each other.
See here some Oratex-Pietenpols:
Best Regards, Lars 907 229 6792

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