# ULF-1 uses mostly pine (Kiefernholz)

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#### ULF

##### Well-Known Member
Hi, Just received the plans for the ultralight glider ULF-1, and as was to be expected, most of the spar and cap stripes are pine wood.
Now this is rather uncommon for the rest of the worlds homebuilts, they all use spruce or fir.
The planes call for a certain specific weight for the spars: no more than 0,55g/cm³ and a strain braking strength of over 100 N/ cm².
What would you recommend?, Buy spruce spars from aircraft spruce?
I read through AC 43- 13 a little bit, it says sandpaper is prohibited on spars. Is this true?
Thanks
Johannes

#### Himat

##### Well-Known Member
Hi, Just received the plans for the ultralight glider ULF-1, and as was to be expected, most of the spar and cap stripes are pine wood.
Now this is rather uncommon for the rest of the worlds homebuilts, they all use spruce or fir.
The planes call for a certain specific weight for the spars: no more than 0,55g/cm³ and a strain braking strength of over 100 N/ cm².
What would you recommend?, Buy spruce spars from aircraft spruce?
I read through AC 43- 13 a little bit, it says sandpaper is prohibited on spars. Is this true?
Thanks
Johannes
Spruce, fir and pine do all belong to the same family of threes. Exactly what the different threes are called do vary with the language. A quick check and I found that pine have a name similar to spruce in Norwegian. I have not built an airplane, but rebuilding my old house I have learnt that spruce is not just spruce. Depending on where the three have grown, the properties of the wood may vary considerable, maybe to an extent that examples of spruce, fir and pine can have the same specific weight and strength. Spruce grown in Canada or USA probably is not the same as spruce grown in Germany if you look at the local variants of the species. An example from that old house I have, for wood to repair the load carrying parts, I can not just buy wood from the ordinary builder supplies warehouse. That spruce is to light and weak, I have to go to local mills that have wood from threes that have grown slow and is denser and stronger.

I would guess that the designer of the ULF-1 designed around what was available locally. Your best bet is then to find wood with the specified strength and specific weight. If it is spruce, pine or fir probably is not that important. Remember to test that the glue you are using stick as it should to the wood. How well glue stick to the wood is another thing that differ between the species.

#### TFF

##### Well-Known Member
ANC-18 is a sticky on this forum section. It is about wood. If you are glueing, the surface should be scraped. How far you carry it depends. If laminating spars, planing or scraping would be best. Glueing corner blocks, I would not be concerned if sanded. If I sanded a corner of a wing rib because a piece is a little proud before gluing a gusset not worried. It is not finished furniture, a good looking structural joint looks different than one for a chair that is visual to people.

#### DangerZone

##### Well-Known Member
HBA Supporter
As much as I know German, Fichte is spruce and Kiefer is pine, while Kiefernholz might refer to the whole Pinus family (pine, spruce, etc). If the plans call for pine, I would build it with pine. Pine is quite stiffer and heavier than spruce so there might be a reason why the plans dictate pine.

The designed specifications of 0,55g/cm3 is a reference because both pine and spruce have to be aircraft grade and first class. This means at least 7 grains per cm to have the optimal stregth&stiffness. First class spruce is around 0,51g/cm3 and pine is 0,57g/cm if it has enough grains to staisfy the first class criteria. You could have pine with a mass of 0,55g/cm3, it would be lighter but might not have the minimal 7 grains. If having only 4 grains per cm and 0,55g/cm3, spruce with 7 grains could be of the same stiffness&strength but lighter than this piece of pine.

I have both 1st class alpine spruce and 1st class alpine pine with minimal 7 grains per cm, spruce is 0,51g/cm3 and pine is 0,57g/cm3 at normal humidity and moisture (very dry conditions). In the very common capstrip profile of 15mm x 20mm, this means 153g for the spruce profile and 171g for the pine profile per meter of length, with +-2g tolerance. If your design would need around 300cm3 of wood for structural parts, this would make a difference of 2kg tops. Calculate all the cubic centimeters of all woden material for yourself and see the difference. This is just in case you don't find 1st class pine which would be 0,55g/cm3 light and have 7 grains per cm.

Did you try to contact FN Profile of Austria to see what kind of pine they could offer you? They used to have good quality pine and might help you get the quality of wood you need.

FN wood-pro - Solid wood profiles - Profiles - FN Neuhofer Holz

#### ULF

##### Well-Known Member
Thank you very much ! This answered pretty much all my questions about the wood. Are you from around Austria ?

#### DangerZone

##### Well-Known Member
HBA Supporter
Thank you very much ! This answered pretty much all my questions about the wood. Are you from around Austria ?
I live in Zagreb, Croatia, which is a one hour drive from Graz and Austria.

Please be so kind to share information about good local/Austrian spruce sources here on the HBA forum, this helps other builders too. Alpine spruce is often out of sales due to shortages so every information counts.

#### Jake Levi

##### Well-Known Member
I read this thread last week, and find it very interesting. I live in Northern Michigan, with a large lumber industry here, and white pine is a major product , along with white oak, and red cedar, and several other hardwoods including white ash. I have bought a lot of ash, and oak from a sawmill here, and had chance to look at a lot of their white pine, it seems to me to be a candidate for airplane building. Much of it satisfies the grains per cm test.
He sun kiln dries the wood he saws for sale. I am really tempted to get some and make a couple parallel test structures to the project parts. Thoughts? Comments?

#### DangerZone

##### Well-Known Member
HBA Supporter
I read this thread last week, and find it very interesting. I live in Northern Michigan, with a large lumber industry here, and white pine is a major product , along with white oak, and red cedar, and several other hardwoods including white ash. I have bought a lot of ash, and oak from a sawmill here, and had chance to look at a lot of their white pine, it seems to me to be a candidate for airplane building. Much of it satisfies the grains per cm test.
He sun kiln dries the wood he saws for sale. I am really tempted to get some and make a couple parallel test structures to the project parts. Thoughts? Comments?
Do they have spruce also with the same grains per cm count?

#### colinc

##### Active Member
Hi,

this caught my interest as i was doing some strength tests on Sitka Spruce yesterday.

Having done the Sitka, i made a test sample out of some joinery quality pine that had been used as a clamping spreader. I choose that because it just felt 'right' if you know what i mean.

Its bending strength was well above the minimum for Sitka, and density about 32lbs per cu. ft. (From memory). Cost was a fraction of the spruce.

What to conclude from that? Am not really sure. Perhaps it is not as durable as Sitka, or perhaps more brittle? I have no idea what the actual species was. As the impulse to test it came from reading that the Minimax kits were in white pine, it does lead me to think that there are alternatives available. The only thing i would say is that good clear lengths might be hard to find. Am off to a local timber merchant (not the DIY shed) in the next few days to see what they have.

regards,

Colin

#### plncraze

##### Well-Known Member
HBA Supporter
Wood quality covers a large range from Burn to beautiful. Pops, who is on this website, gets quality wood from a high-end woodworking shop. There was a Pietenpol mentioned on Piet website that was built from pieces of crates. A builder using Douglas for tested his pieces during building and found pieces that looked alike did not not always have the same strength. Read 43.13 available from www.faa .gov to find what is considered as acceptable wood for aircraft and you will find more wood than you would expect given that spruce is usually treated as the only choice. 43.13-1B is the full title of the book listed above and it is free to download. Read the section on wood before you go to the timber merchant. You will never believe how much "aircraft" they have.

#### Jake Levi

##### Well-Known Member
Wood quality covers a large range from Burn to beautiful. Pops, who is on this website, gets quality wood from a high-end woodworking shop. There was a Pietenpol mentioned on Piet website that was built from pieces of crates. A builder using Douglas for tested his pieces during building and found pieces that looked alike did not not always have the same strength. Read 43.13 available from www.faa .gov to find what is considered as acceptable wood for aircraft and you will find more wood than you would expect given that spruce is usually treated as the only choice. 43.13-1B is the full title of the book listed above and it is free to download. Read the section on wood before you go to the timber merchant. You will never believe how much "aircraft" they have.
This is what got me to thinking, I have seen some beautiful white pine at his saw mill, after the sun kiln drying it goes on storage racks under cover, unplaned but that's almost immediately available. Its all locally grown here in Northern Michigan. White Pine, White and Red Oak, some Red Cedar, and Ash. I am going to be taking a real close look at his Pine.

#### plncraze

##### Well-Known Member
HBA Supporter
Check out Abraham Leket's Fred project in the "Members Projects" section. His Fred is mostly made of pine but the soars are spruce. Public Lumber in Detroit has spruce.

#### ULF

##### Well-Known Member
Hi DangerZone,
I found a perfect wood suplier close to my place Vienna, he carries sitca, Douglas, white pine, and a lit more. NOW i ran into another problem: Building supervision. As far as Im now informed, one only needs to get the airworthines certified, no registration, b5t since they took this out of the Deacs hand costs for this could be 2300€ in Austria, and 80,000€ in Germany, which in either case nobody would spend. Now in germany every is waiting for a solution, it did cost only a couple of hundred €. Now I am looking for some building supervision, and to start on some smaller parts, until the situation improves agian, or I can find some EU authority like France, but in any case I need a proper built and dokumentation. Should all the wood be tested for bending and compression ? or do I just go by spec. weight and the count of anual rings?
Thanks Johannes

#### Jake Levi

##### Well-Known Member
Do they have spruce also with the same grains per cm count?
I haven't seen any commercial spruce here. There might be some isolated plantings, many states have them.

#### Jake Levi

##### Well-Known Member
Check out Abraham Leket's Fred project in the "Members Projects" section. His Fred is mostly made of pine but the soars are spruce. Public Lumber in Detroit has spruce.
Thanks, I will check them out.

#### DangerZone

##### Well-Known Member
HBA Supporter
Hi DangerZone,
I found a perfect wood suplier close to my place Vienna, he carries sitca, Douglas, white pine, and a lit more. NOW i ran into another problem: Building supervision. As far as Im now informed, one only needs to get the airworthines certified, no registration, b5t since they took this out of the Deacs hand costs for this could be 2300€ in Austria, and 80,000€ in Germany, which in either case nobody would spend. Now in germany every is waiting for a solution, it did cost only a couple of hundred €. Now I am looking for some building supervision, and to start on some smaller parts, until the situation improves agian, or I can find some EU authority like France, but in any case I need a proper built and dokumentation. Should all the wood be tested for bending and compression ? or do I just go by spec. weight and the count of anual rings?
Thanks Johannes
Hi Johannes,

There are many obstacles you will face when starting to build an aircraft, and the administration&bureaucracy will be the most challenging one. The national authorities are following some EASA guidelines and many of them are becoming restrictive to homebuilt aircraft at a local level. This is a clear case of maladministration but with so many complaints in the EU there is simply no time to deal with all of them separately. The German, Belgian, Austrian, Croatian and some other administration authorities will rise the prices so high that any homebuilder gets destimulated in building aircraft. Even if you would have money to pay for it all, they would overcomplicate procedures so you would be fed up after some time. They do this on purpose so you would go elsewhere, meaning they would have less work&responsibility in issuing you a Certificate of Airworthiness. Thus Begians register their homebuilts in France, Germans and Austrians in Hugary or Italy, and so on. Most of the administrators in the civil aviation authorities are simple bureaucrats, not aircraft specialists, even though many of them have some formal connections to aviation. Most of them would not know the difference between grades or kinds of wood used in an aircraft, the same goes for glass, carbon or aramid fibers in an aircraft. The problem is that you will need to comply to rules of such bureaucrats, and fulfill all they ask for. Thus chosing the right country/authority and class of aircraft should be taken with great care.

It seems you live in Vienna, which is quite close to Hungary, Slovakia, Czech Republic and Italy, making it easier to chose the right aviation authority that would be best for your homebuilt. You will also have to chose the cathegory in which your aircraft will be registered, most probably an experimental rather than a glider if the criteria to be fullfilled is simpler. Besides a supervisor, you might need a controller who will confirm that both you and the supervisor have done a good and solid construction according to all engineering specs. The administration process from the mentioned countries is simplest in Italy, in some cases/classes you litterally need only a couple of photos of the finished aircraft and a demonstration you can fly. Since you fly at your own risk, this makes sense and this is currently one of the best places to register an experimental in the EU. Hungary is also easier than some other countries when such a registration is needed, the fees are also lower than elsewhere and you might find support from local builders who could help you with the administration process. The problem is the language, most Italians and Hungarians speak only their native language so you would have to find an interpreter or someone who speaks a common language. The Czechs sometimes speak German, so this might help. The Czech civil aviation aithority is also a rare one with competent and rational people working in the civil aviation authority, so this might also reduce the efforts with the administration hassle. There is also an option to see the minimal requirements for what is legally considered an aircraft and check whether the ULF-1 could pass as a paraglider/hang glider to reduce the administration. If done that way, you might not even need to get a CofA or a licence. This would save you not only money but precious time (and peace of mind) you would lose with dealing with bureaucrats.

The wood you will aquire to build the aircraft should be tested by by non-destructive tests and destructive testing. After gathering the wood you will be building the aircraft with, take the 'weakest' samples and submit them to testing. Make two different sets of testing parts, see if they conform to the specified criteria. Document it all with measurements, pictures, videos and written reports. Break at least two testing parts, one coplex part and a simple part to demonstrate the limits of the materials. Usually a complex joint bond and a simple finite element analysis part would be enough to get the idea if the wood conforms to the requirements. This will also allow you to get confidence in seeing how strong wood can really be. If you ever get a chance to see some other material testing methods, do it. You might be surprised how some materials perform better than anticipated while others succumb to some simple physical stresses. After starting to build parts, make a double part of a critical element. Chose the 'less perfect' one and test it to 200% of max loads. Most wooden aircraft parts should be able to withstand it if engineered well. Test the wingspar too, this is the most critical part of your aircraft. See the designer's specifications and aks the designer about the wingspar destructive testing results (every designer has done it to test the aircraft's ultimate limits). If the designer is dead or unavailable, do your own calculation before starting the build. Physics is a great tool, in the end every wingspar has to conform to it. Verify the claims with physics if this is a unique aircraft never built before, consult experts who could help in verification. Try to get in touch with someone who has already built such an aircraft, ask for advice and thoughts. Trying to fly the aircraft before building it is the best way to go, but contacting a previous builder who flies it regularly is the second best option.

Good luck.

D.