Actual Empty Weight of Pietenpol

Discussion area for builders of Pietenpol aircraft, both beginners and experienced folks. Share ideas, ask questions and help build the Pietenpol community.
Post Reply
PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Actual Empty Weight of Pietenpol

Post by PietenAsia » Wed Nov 13, 2019 8:23 am

Hello,
Here in Thailand a two seat ultralight can weigh 550 pounds empty. I saw the plans for the Pietenpol Air Camper in the 1932 Flying and Glider Manual.
It shows it to weigh 625 Lbs with water. If I subtract the engine of 244 and radiator of 21 it is 360 without engine. Add a Continental A-65 shown at 170 pounds and I get 530 so this works under the 550 pound limit.
Sadly upon reading about this plan on your forum I see that most Air Campers, even with an A65 weigh over 600 pounds and most weigh over 700 pounds up to almost 800 pounds. Why is this not the same as shown in the original Flying and Glider manual? Does the ship not weigh as Bernard said in the original plans?
I also read the following quote in one message posted:

? If using a Continental A65, thereare many Pietenpols that have been built with an empty weight of 650 lbs(295 kg) or less. Corvair powered Pietenpols seem to tend slightly heavier.Model A Ford Pietenpols tend to be lighter than 650 lbs, probably becausetheir builders know they don't have a lot of power to waste.

How can a Model A version weigh less than an A65 with an engine that is 95 pounds more? Is this really that much carelessness with extra weight.
If a model A powered ship can weigh under 650 why can’t I change the motor to A65 and save that 95 pounds and meet the 550 pound requirement? Is this possible? I intend no brakes, no battery or radio and only an airspeed indicator.

It is reasonable that with such a lighter engine I would need a longer engine mount for the proper balance so that may be a few pounds more of engine mount. I have also read that ships with the A65 can have problems of being tail heavy. I have also read that there are plans that show the proper conversion to using an A65. Does this conversion not adjust for the lighter engine with a longer engine mount or longer front fuselage and make this ship balance the same as the original Model A?

Also to save weight I consider this:
The ribs are show built of ¼ x ½ material. All the other planes I have looked at use ¼ x ¼ for this. Is there some element in the design that is compensated by these ribs needing to be twice the width? They seem to be about the same spacing as ribs of other designs. Also in regard to the longerons it shows 1’ x 1’ but it is the only plans I see calling for this. Other designs have a maximum of ¾” x ¾”, even if they have two seats. The manual says the ship is robust and built for hard use. Perhaps in 1932 there were no airports and it was intended to land in rough conditions.

Can an aircamper used on a good grass surface be built as most other planes of modern design with ¾” x ¾” longerons. Especially if the ship weighs only 550 pounds and maybe a pilot and passenger not much over 300 pounds total? Add some gas and good measure and say maximum landing weight ever of 1000 pounds.

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Wed Nov 13, 2019 10:46 am

PietenAsia: why bother with all of those revisions? Here's something that will meet your weight criteria without modifications: http://rogermann.org/ragwing/designs/rw1/

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Wed Nov 13, 2019 11:14 am

Yeah but it only has one seat and I want two. Also the weight class of a one seat ultralight here is much more restrictive leaving only mostly designs with two stroke engines as options. But that is a pretty plane. Thank you

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Wed Nov 13, 2019 11:54 am

OK, understood. If you want a 2-place but you're wondering about reducing the longerons and cross-bracing from 1"x1" to 3/4" x3/4", consider this. Here in the US, the design loading for "Normal" category certification (not Utility, not Aerobatic) is +3.8G and -1.52G. The usual design weight for an FAA-standard pilot is 170 lbs. Under maximum loading of +3.8G, a 170 lb pilot is therefore imposing 646 lbs of load onto the airframe, but two people are imposing almost 1300 lbs of load onto it. If you want to consider redesigning the primary structural members of the airframe to lighten it up, make it a single-place and you might have a better chance

-Oscar

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Wed Nov 13, 2019 5:54 pm

Thanks for the input Oscar. If the F and G manual is correct that it can be built at 625 with the model A engine so long as you don't "add things" (OK I'd add seatbelts to what the plans show) and my original logic of saving weight by changing to the A-65 is correct I really should not have to save any more weight by making structure changes.

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Wed Nov 13, 2019 10:15 pm

PietenAsia; not saying it can't be done, just suggesting that you not try to pare the weight down on structural elements without doing some structural analysis. My airplane was re-weighed in 2009 when I swapped the A65 on it for an A75. No fuel, no oil, no seatbelts or harness in the front cockpit, just air in the tires- 630 lbs. The airplane was weighed on calibrated race car scales by our EAA Chapter 35 tech counselor and his assistant, who as a team had performed aircraft weighing and W&B calcs on many different aircraft in our chapter. Before that, its original W&B had been performed by the builder using bathroom scales and the weight came out quite close to the new number, so I think it's pretty accurate. Of course, the A75 is virtually the same engine as the 65 except with some internal mods that allow it to reliably turn higher RPM to generate the additional 10 HP, so the weight and dimensions of the two engines are nearly identical. My old A65 had a mixed pair of magnetos (an older Bendix 'lunchbox' and a newer S4LN mag) and my A75 has a new matched set of Slicks, but that's it... maybe a bit lighter new mags than the old ones.

My airplane could lose some pounds, but it would be tough to find 80 lbs to get it down to 550. My airplane has an external venturi to drive the two vacuum instruments (turn & bank and vertical speed, both 3-1/8" size) and none of those are necessary so they could go away. The turn & bank is a pound and a half, the VSI is about a pound, so maybe there's 3 pounds with venturi, hose, and screws. I could go with small ultralight-style instruments (or digital readouts) for the other instruments and maybe find another couple of pounds. It's tough going to lose 80 lbs but it can be done. Just silver on the fabric (no color coats). Little or no seat padding. Lightening holes in seat backs and bulkheads. But 80 pounds-? Good luck.

-Oscar

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Thu Nov 14, 2019 8:43 am

Thank you for the detailed information. I am getting the idea that the 625 pounds with water equipped with a Model A of 244 and radiator of 21 more is not a reality, though it is as described in the 1932 F and G manual. This seems strange, that it would be misrepresented, but it is appearing to be the case - unless someone has actually done it but I don't see how given your descriptions of possible weight savings on yours.
Do you have brakes? I assume no radio/battery?
I really doubt that the materials used in 1932 mostly from hardware store are lighter than spruce and 4130 so I remain a little perplexed as to how the original numbers were published in 1932.

I can still build a Piet but I have to register it as an airplane, not an ultralight, which basically means all flights have to be conducted similar to how IFR flight rules behave in the USA, though not actually in the clouds of course. Not so much fun as just poking around as you please.

One other option is to build it on floats because floats do not count in the allowed 550 pounds. This would save the weight of landing gear but still it seems 80 pounds will be hard to find for removal.

User avatar
auburntsts
Posts: 8
Joined: Fri Nov 08, 2019 11:32 am

Re: Actual Empty Weight of Pietenpol

Post by auburntsts » Thu Nov 14, 2019 9:29 am

Just wondering if differences in construction/builder preferences could account for the weight discrepancy from the 1932 plan specs to today's average actual GWs? You know things like, steel tube landing gear vs wood, long fuse vs short, battery and electrical system, instruments, tail wheel vs skid, so on and so forth. On the surface that would seem improbable but I have seen minor mods in the RV world that by themselves are inconsequential but the cumulative effect of many mods ends up adding appreciable weight. Just food for thought....
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Sat Nov 16, 2019 9:42 am

Todd I do think there is something to your line of thought. I found some very helpful information in William Wynne's Weight and Balance studies and articles where details of many aircraft were printed. While it seems 550 pounds is going to be difficult (maybe or maybe not impossible) to achieve there were some with A65's that could have come close with minor changes like a metal to a wood prop and some Model A's that if a change to an A65 saved the 90 or so pounds that it does on paper.
I agree that MOST of the difference between "modern" Piets and the "orignal" is things like the 3 piece wing which adds brackets and more ribs skinned with plywood, tailwheel, brakes, cockpit "dress up", "prettier" paintjobs, instruments if everything (and more???) called out in FAR 91.205 is installed, and if an electrical system (seems not possible on a Model A or A65) or even battery and radio is added that could all add up to a substantial amount of weight. I suspect if you put all of those items in a box at once along with two gallons of paint and picked it up you'd be surprised at the weight.

I've not found anything definitive about the 1" routed spars vs 3/4" solid spars but I suspect the routed spars are lighter. Does anyone have definitive answer on that.
Also I see there has been some discussion about reducing the rib width from 1/2" to 3/8" (still wider than even the Pitts uses which much heavier wing loading) but has anyone ever actually done that. One thing I don't see in the Piet wing is the number of compression members that are seen in other designs. The Piet seems to have fewer so maybe the much heavier than typical ribs are handling this compression load.

Any thoughts or answers appreciated.

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Sun Nov 17, 2019 12:30 am

PietenAsia;

I concur that there are some things that can be changed or sacrificed to bring down the weight. Example: my Air Camper has 6.00x6 Cleveland wheels with hydraulic brakes and corresponding tires and one could easily build with 5" Azusa wheels and smaller tires and no brakes and save some weight right there. Good point.

As far as the wing ribs and spars on a Pitts vs. an Air Camper, be very careful when comparing the loading on a 1625 lb gross weight biplane with a 20 ft wingspan and interplane struts to that of a 1080 lb gross weight strut-braced high-wing monoplane with a 29 ft wingspan. There are a lot of variables involved.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Sun Nov 17, 2019 9:41 pm

Another thing to consider is that the Pitts employs the NACA M6 airfoil and has a 36" chord. The M6 is a 12% airfoil so that makes the depth of the wing ribs about equal to that of the Piet airfoil (12% of 36" = 4.32" for the Pitts) but the Piet airfoil is about an 8% (4-3/4" deep spars and a 60" chord = 7.9%) so it's much flatter and the rib caps must resist bending over a longer span. As I say, there are a lot of different factors to consider if you want to start reducing the cross-section or aspect ratio of structural members.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Mon Nov 18, 2019 7:56 am

Yes that's a good point that the rib is longer and thinner.
I think I'll just build it per the drawings and skip all the "add ons" except for seatbelts.
If I can find a long enough build area I'll build the one piece wing.
Hopefully I will come close to the stated weight and then save about 90 pounds with the A65 over the Model A.
I'm looking at the oratex fabric that does not need painted. That may get me to the desired 550 pounds.
If I succeed it would seem I'll have the lightest Pietenpol on modern record though.

User avatar
Richard Roller
Posts: 50
Joined: Mon May 22, 2017 11:14 am
Location: Olathe, Ks.

Re: Actual Empty Weight of Pietenpol

Post by Richard Roller » Tue Nov 19, 2019 5:35 pm

IMG_0239.JPG
I did the weight and balance for a local Piet in my area, Kansas City, Mo., by Virgil Chapman a long time builder. I believe it was his 4th project.
His Piet is built to the plans with a steel tube fuselage, Cleveland 6:00 x 6 wheels and brakes, Vi Kapler three piece wing, die spring shock struts on the landing gear, A-65 engine with a Lycoming starter ring and starter per Bill Rewey.

His is the lightest Piet I'm personally aware of. Empty weight as described, with oil, unusable fuel is 592 lbs. A very light Piet. I'm not sure a 550 lb. Piet is possible built remotely to the plans.

Anyone else have any weights they can share with this thread?

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Tue Nov 19, 2019 5:55 pm

That is encouraging!

I don't have any idea how the steel fuselage compares to the wooden one. Any input?
Also I don't know what landing gear is lighter, the "old wooden style" vs the style pictured. Input?

Also I don't know what instruments/radio he is equipped with but probably more than no radio and an airspeed indicator and oil pressure gauge as I would install so I'd guess that is several pounds available if he is compliant with FAR 91.205
An ELT is not required here as I understand is on 2 seat airplanes in the US (not sure if the pictured Piet has that or not)

Probably a lighter wheel/tire could be found but I'd probably start with the 6.00 x 6 and try to pass the test.
Starter/ring gear/ and apparently a battery can be removed. Though he is likely already equipped with a fairly lightweight battery and starter.
Brakes system can be removed.
Tailwheel (likely installed on pictured Piet) can change to tailspring, though I'd prefer a steerable wheel but that is something that COULD be sacrificed at the end if a couple more pounds needed to go to pass the inspection.
Oratex fabric reportedly weighs similar to ceconite and such and saves all the weight of the spray on products which some say could way 30 lbs per aircraft.
One piece wing (if I had to) would save some, probably less than two pounds though. Input?

All that could make the needed 42 pounds from 550 to 592.

Thanks for the input. I am again encouraged about the original numbers printed in the 1932 F&G Manual. This could be possible.

Of course there are "ultralights" that would meet the 550 pound limit, but I'd much prefer to have a Piet

User avatar
auburntsts
Posts: 8
Joined: Fri Nov 08, 2019 11:32 am

Re: Actual Empty Weight of Pietenpol

Post by auburntsts » Tue Nov 19, 2019 6:24 pm

Might be worthwhile to reach out to Pietenpol and Corvair engine guru William Wynn. He has developed a Piet W&B manual and will provide help to builders. Take a look at this page:
https://flycorvair.net/2019/08/14/piete ... lculation/

He discusses the manual here:
https://flycorvair.net/2019/07/10/piete ... ual-video/

If anyone can figure out how to build a very light Piet, it will be him.
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Tue Nov 19, 2019 10:29 pm

Thank you for the links.

I will see what he can add to my search for info.

User avatar
Richard Roller
Posts: 50
Joined: Mon May 22, 2017 11:14 am
Location: Olathe, Ks.

Re: Actual Empty Weight of Pietenpol

Post by Richard Roller » Wed Nov 20, 2019 5:26 pm

Another consideration. The weights you are referencing for the A-65 and the model A might not be accurate. I can say from weighing the Ford A in Ken Perkins Piet that the engine weight, for HIS engjne, was 256lbs., but that included oil, 2 gallons of water, and a wooden prop. The engine also has an aluminum head.

The weight you quote for the A-65 is probably low. Continental typically quotes the weights on these old engines dry, no oil, and with no accessories. No carb, no mags, no nothing. I would think you'd find the actual flying weight to very close to 190 - 195 lbs.

Admittedly it's been a long time since I worked with these engines on a daily basis, maybe one of the builders using this engine can quote an actual installed flying weight.

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Fri Nov 22, 2019 6:02 pm

Thank you all for input. I have made contact with William Wynne as you suggested. He is very helpful.
I think consensus is that it will be difficult to achieve 550 pounds because the origianal Flying and Glider plans had weight that was maybe a bit optimistic and that A65 is closer to 190 pounds when ready to fly as some of you have also suggested.
Also big reason for difference in expected weight and real world weight is a lot of things since 1932 like radio, battery, brakes and such.

550 Pounds may be possible. I will try. Mr. Wynne has some ideas such as aluminum struts and some other things that can help and that oratech fabric can indeed save real weight. Some have come within maybe 40 pounds of my desired weight. Maybe 40 more pounds can be removed, but not so easy as it first looks.

I will let you know.

Thank you for input.

ArthurD
Posts: 19
Joined: Tue Jun 26, 2018 2:00 pm

Re: Actual Empty Weight of Pietenpol

Post by ArthurD » Sun Nov 24, 2019 6:44 pm

Most of your weight savings will come from engine/prop choice and using oratex. A couple weight saving ideas not discussed yet:

It's pretty common not to use nails on any of the gussets since they are just there to hold things in place while the glue sets up.
I routed out material from the wing leading edge. I suspect you could route out some material from the aileron spars too. You could also eliminate the front cockpit controls. Wing tanks are a little heavier than cockpit tanks for the same volume since they are shallow whereas the cockpit tanks are closer to a cube also they require shorter fuel lines.If you could find some way to make a rotational molded plastic tank that would probably be the lightest. I saw someone who eliminated some of the turnbuckles by tensioning the wire rope before crimping the sleeves.

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Fri Nov 29, 2019 11:33 pm

I also plan to tighten cables before crimping to eliminate many turnbuckles. Save money too!

And yes can make only controls for back then later if have weight left or after certification on scales can build front controls.

Thank you for input

Earl Brown
Posts: 1
Joined: Mon Nov 04, 2019 12:24 pm

Re: Actual Empty Weight of Pietenpol

Post by Earl Brown » Sat Nov 30, 2019 11:19 am

ArtherD- where did you route out material on the leading edge?

ArthurD
Posts: 19
Joined: Tue Jun 26, 2018 2:00 pm

Re: Actual Empty Weight of Pietenpol

Post by ArthurD » Mon Dec 02, 2019 10:58 am

This is a riblett airfoil so the leading edge is larger than the normal pietenpol airfoil.
Attachments
IMG_7127.JPG

User avatar
Richard Roller
Posts: 50
Joined: Mon May 22, 2017 11:14 am
Location: Olathe, Ks.

Re: Actual Empty Weight of Pietenpol

Post by Richard Roller » Mon Dec 02, 2019 2:28 pm

Ken Perkins did the same thing to the leading edge of his wing. His has the Pietenpol airfoil.

User avatar
auburntsts
Posts: 8
Joined: Fri Nov 08, 2019 11:32 am

Re: Actual Empty Weight of Pietenpol

Post by auburntsts » Mon Dec 02, 2019 4:20 pm

I saw a video series where a builder fabricated rounded rib nose pieces that he attached to each rib and then wrapped the leading edge with plywood vs. creating the leading edge with a board. Seemed easy and light without sacrificing strength. Thoughts?
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Mon Dec 02, 2019 7:42 pm

What is this Riblett airfoil you mentioned as opposed to Pietenpol airfoil please?

User avatar
taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Actual Empty Weight of Pietenpol

Post by taildrags » Mon Dec 02, 2019 10:23 pm

PietenAsia; the Riblett airfoil is the GA30-612, which as I understand Mr. Riblett's nomenclature means that it's a General Aviation airfoil with its maximum thickness at 30% of chord, and at that point it's 12% deep. So, for a 60" chord such as on the Air Camper, the maximum thickness would be about 18" aft of the tip of the nose and at that point it would be about 7.2" deep. This gives several advantages, one of which is that it may be possible to use thinner (but taller) wing spars and it should be possible to fit a higher volume fuel tank in the deeper wing section between the spars. You can find more information and a graphic comparison of the two airfoils here:

https://aviation.stackexchange.com/ques ... npol-airfo

In my opinion, you'll spend more time adapting the Riblett to an Air Camper wing and supporting geometry than just building it with the stock wing, and the performance won't be much different. However, there are builders and pilots using the Riblett airfoil on their Piets who can provide their own first-hand experience with it, and that's certainly better than my guess or my opinion.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

PietenAsia
Posts: 12
Joined: Mon Nov 11, 2019 8:33 pm

Re: Actual Empty Weight of Pietenpol

Post by PietenAsia » Tue Dec 03, 2019 3:47 am

I see. That is interesting. I had not heard of aircamper with other airfoil. Curious, but I think like you said simpler to build ordinary wing.

Thank you for answer.

User avatar
auburntsts
Posts: 8
Joined: Fri Nov 08, 2019 11:32 am

Re: Actual Empty Weight of Pietenpol

Post by auburntsts » Tue Dec 03, 2019 6:45 am

Here's the link to the video I was referring to above regarding the leading edge. This builder chose to go with the Riblett airfoil. https://youtu.be/x_gGrvXM2cQ?list=PLRJi ... bhJID0GqFn
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

Post Reply