The following letter came from Cy Mao in Thailand. It caught my eye because many years of my childhood were spent in Thailand, where my father led the US work on infrastructure projects like Airbases and Hospitals. They were golden years for my family. We had the utmost respect for the nation that welcomed us.
I hope this is the right place to ask this. I apologize if your “comments” are not where you want this. If you prefer an email address to be used just tell me.
I want to build a Pietenpol in Thailand where a two seat ultralight can weigh 550 pounds empty. “Real airplanes” are very restricted in flight, sort of like flying IFR in the USA. Not so much fun. Ultralights can fly without being in constant radio contact with “our ATC”.
I saw in the 1932 Flying and Glider manual that a Piet weighs 625 pounds with water with a Model A of 244 pounds and radiator of 21. Take away 265 and add back an A65 of about 170 and it weighs 530 pounds which is legal by 20 pounds. This is my plan. Then I research this plane on the forum and see that this plane usually weighs over 700 pounds and I think it is due to a lot of changes by builders since 1932 likes batteries and brakes and such.
So I ask if you can help me build the lightest Pietenpol and if you think it can weigh 550 pounds or less. Then of course we will talk about CG – I watched your video about this too.
I prefer build wood fuselage. Is the metal version lighter? I can build steel if necessary.
What is lightest gear? I think old wooden gear looks lighter.
My place to build is not 30′ so I must build 3 piece wing. But if this adds too much weight I can look for a bigger place to build if this is important.
I plan only Airspeed indicator and oil pressure gauge.
No brakes, no battery, no radio. No upholstery, Only seatbelts.
You say always best to build long fuselage. Is this true even if empty weight is critical?
I like to have steerable tailwheel but can change to skid when finished if I need to lose a pound or two (but skid vs tailwheel may affect where I should have put the axle a bit to handle on the ground, and will move CG a bit also.)
I read about Oratex fabric that needs no heavy paint. I can use this. Some people say paint of airplane can weigh 30 pounds.
Do you think 550 pounds is possible?
If you think this is not possible by the plans then I wonder more:
Looking at other airplane plans I always see ribs built from 1/4 x 1/4. Piet uses 1/4 x 1/2. Is this important or only overbuilt? 1/4 x 1/4 can save almost half the weight of ribs (gussets still weigh the same of course) Rib spacing is close as any other plane and wing loading is very light. Do ribs need to be 1/2″ for some other reason? I don’t see much compression struts in Piet wing and wonder if they also serve this function and best to leave at 1/4″ x 1/2″
Also I notice fuselage longerons are 1″ x 1″ but many plans I look at make 3/4″ x 3/4″ much more common. Is this an example of rough landing areas in 1932 and not important anymore or is this not a good idea to make these smaller? Of course I don’t want a plane that will break apart.
Above, my father speaking with HRH, the King of Thailand, in 1974. Being born in Massachusetts and educated in Switzerland, The king understood both western and eastern worlds. To read the story, click here: Real moral power: HRH, the King of Thailand passes from this life
Your letter is an interesting challenge. Lets look at some numbers I’m sure of to see what can be planned:
Lightest 65 Continental powered plane I have weighed was 590. It was very lightly built, no brakes, hand prop, etc. I don’t think it is close enough to 550. The 170 pound weight for the engine is for the bare motor, its flying weight is closer to 190. The average 65 Continental Piet weighs over 700 pounds.
Lightest Ford powered plane I have weighed is 677. The average is 720 or so. These guys put more effort into saving weight than Continental builders. The numbers in the Flying and Glider manuals are optimistic guesses, not data. There is no way you could look at the 677 pound plane I weighed and see 50 spare pounds just sitting on it. Im reasonably sure the 625 pound number is a myth.
There is a lot of talk about steel tubing being lighter, but after the floorboards, tabs and mounting points are on it, the weight advantage of the steel tube plane largely evaporates. I would still build a long fuselage unless you are your passengers are less than 1.7 meters tall. The weight difference is small. Plan on building the fuselage out of 3/4 x 3/4, it is plenty strong and BHP built some of his later planes that way. Make sure you use Spruce, or some wood that is that light. Fir is significantly more dense.
The wooden gear and straight axle are much heavier than later J-3 style gear. The 590 pound plane used spun aluminum go cart wheels and very light tires, no brakes, and lightly built J-3 gear. I can show you how to make very light bungeeing gear that uses about 600 #8 rubber bands on each side. Don’t laugh, it flew on my Piet for 25 years before I got it.
Oratech fabric is a very real weight savings, perhaps 20-25 pounds on a Piet. It is not as expensive as people make it sound. 1/4 x 1/4 for cap strips is fine, that is actually the size in a Pitts Special. The Spars in some of BHP’s later planes were only 3/4″ wide. Consider this is the same as many Cubs. There is talk that the British built up spars are lighter, but routed 3/4″ spars would likely beat them. I can show you how to make a two piece wing with a very light joint in the middle. A one peice wing is clumsy to build and cover. There are steel fittings that could be replaced by aluminum in certain places. Aluminum lift struts are very light by comparison to other options.
With all this done, I still think you would have a very hard time getting into the 550 pound weight for sure. You could build the airframe and see if it could be Continental powered, but keep this as a back up: You could always use a Rotax 582 or a UL-260 on a long mount for the lowest possible engine weight. People will say that they can’t power a Piet, but that you are speaking of building is several hundred pounds lighter than a typical Piet. A 535 pound Piet with a 582 on the front would out climb almost any Pietenpol in the US.
Send me your address and I will mail you a copy of my weight and Balance manual as a gift. – this could be an interesting Project of International cooperation. ขอขอบคุณ.