In this posting of the blog we will have a complete look at the fuselage boom assembly. We will do this simultaneously as we are putting the fuselage boom kits together.
Saturday, August 29, 2015
Friday, August 28, 2015
"Make Sure the Pipe Fits"
In July 2015, EAA Sport Aviation Magazine started combining Experimenter magazine with Sport Aviation Magazine. Experimenter Magazine for many years had been an online publication. We are really happy to see it back into the main body of Sport Aviation.
As most of you know we are in now writing a monthly article in the Experimenter section. The column is titled "Technically Speaking".
The topic for the July issue was pipe fittings and their use in aviation.
Each month, after submitting our article to Sport Aviation magazine We reformat the article with additional information and pictures above and beyond what will fit into the space constraints within the Sport Aviation magazine article.
We will post this expanded article each month in the blog. We put quite a bit of work into these articles and they generally lend for really good reading.
Pipe Fittings in Aviation.
Pipe threads are used in virtually every aircraft built today, from ultralights to Boeing’s finest. In sport aviation we use the pipe thread fittings throughout the aircraft, including fuel systems, brakes, oil, hydraulic, coolant and even pitot static systems. The pipe fitting has been around for quite some time, however, after looking through the FAA’s extensive selection of maintenance publications, this seems to be an area that has only been touched on lightly. We continue to see confusion, problems, and even accidents as a result of misunderstanding the subject of pipe fittings.
Pipe Thread Types
The most common types of tapered pipe thread used in the United States are the NPT (National Pipe Tapered Thread), The ANPT (Aeronautical National Pipe Tapered Thread), And the NPTF (National Pipe Tapered Fine Thread)
The NPT (National Pipe Tapered Thread) are constructed using a “Seller’s” thread (truncated peaks and valleys) with threads having an included angle of 60° and a 1.7899° taper. (Figure 1)
The ANPT (Aeronautical National Pipe Tapered Thread) is essentially an NPT thread that undergoes additional quality assurance requirements.
The NPTF (National Pipe Tapered Fine Thread) is also referred to as Dryseal American National Standard Tapered Pipe Thread. (ANSI B1.20.3) This thread was designed to provide a leak free seal without the use of Teflon tape or sealing compound. It is essentially the same thread as the NPT with the root and crest of the threads modified to provide an interference fit during installation. Time has shown that this often works okay during the initial installation, but the use of fittings with the NPTF thread on subsequent removal and re-installation will almost certainly leak without the use of a thread sealant.
Pipe Thread Size
An experienced aircraft builder or mechanic can very easily identify the size of a pipe fitting visually from across the workbench. With the limited sizes which we use in small aircraft, and a little bit of practice, you will soon be able to identify them by sight as well. The most common sizes used in light aircraft are 1/8”, 1/4”, and 3/8”. Until you become familiar with the different sizes, you can use the size chart (Figure 2) to help with identification. Either place the physical fitting directly onto the diagram or take a measurement of the end of the pipe fitting with a pair of calipers.
For easy identification aircraft aluminum fittings are anodized blue and steel fittings are plated black. Commercial grade Brass fitting are, of course, brass colored. (Figure 3)
The problem of leakage arises as a result of the design of the threads. Particularly on an NPT thread where the root and the crest are truncated. (Figure 5) This design allows for a helical passage from the inside of the fitting through the root and the crest of each thread to allow fluid to pass around the perimeter of the thread until it can escape presenting itself as a leak. (Figure 6)
The purpose of thread sealant is to fill in this passage way between the crest of the male and female thread. It is not possible to stop a leak on a pipe thread by tightening the fitting. This is because tightening the fitting does not eliminate this passage way. If you find that you have a pipe fitting that is leaking, the only method by which you can eliminate the leak is to remove the fitting, reapply thread sealing compound, reinstall and tightened properly.
Tips for proper installation of fittings with the NPT (National Pipe Tapered Thread)
Tip 1. Before installation inspect both the fitting and the boss, the boss is the raised area on a component that is drilled and threaded for the fitting. (Figure 7) Inspect both the fitting and the boss for damage and cleanliness. Clean, if needed.
Tip 2. Apply the proper thread sealant to the threads of the fitting to be installed. The type of thread sealant that will be used will primarily depend on the type of fluid used in that system. Each manufacturer of a system component may also decide the proper thread sealant to be used considering factors other than the type of fluid such as temperature, environment, vibration, and whether the part is removed for service routinely. The amount of thread sealant needed is limited to the amount that will fill the void where the threads are truncated on the fitting. Ensure that no thread sealant extends to the end of the threads where it could be ingested into the fluid system. Many an engine has quit because of thread sealant or Teflon tape being ingested into a carburetor or fuel injection system plugging a fuel passage.
Note regarding the use of Teflon Tape: Although there are some instances where the manufacturer recommends the use of Teflon tape on a pipe fitting, this is an area to tread carefully. The potential of Teflon tape being ingested into a fluid system is a high enough risk that most manufactures recommend the use of a pipe sealant instead. In addition, the use of Teflon tape substantially reduces the amount of friction during installation. This can lead to over torque of the fitting and cracking of the boss in which it is installed. And because of the low friction of the Teflon tape, this also leads to loosening of the fitting in high vibration environments.
Tip 3. Install the fitting ensuring that it remains concentric to the hole in the boss during the installation process. Pipe threads are notoriously easy to cross thread. The fitting should rotate 2 - 3 turns smoothly by hand until finger tight. If it rotates less than 2 turns or more than 3 1/2 turns, this is an indication that there is a possible problem.
Tip 4. Once installed finger tight, continue to tighten using a wrench. For the smaller size fittings 3/4” and smaller tighten between 2 - 3 turns beyond finger tight. Because of the nature of the tapered pipe thread, the tightening procedure is somewhat discretionary. Although torque guidelines can be found in some publications, the proper installation requires that you develop a “feel” for the proper torque. A good rule of thumb is to turn until the fitting is tight enough to prevent movement or loosening and then slightly more, if needed, for proper fitting alignment. Not tightening enough could result in the fitting becoming loose and leaking. In contrast over torquing could result in cracking the boss. (Figure 8) Cracking is particularly common when over torquing where there is a thin cross-section at the boss and the material is manufactured from aluminum or magnesium. The quality of the threads both internal and external very greatly and will have some effect on the amount of tightening necessary. After final installation, you should have between 3 1/2 and 6 threads fully engaged.
Tip 5. Ensure that there are no side loads or bending loads applied to pipe fittings. There are literally hundreds of examples of system failures and airplane crashes as a result of improperly side-loading a pipe fitting.
The photo to the right is a classic example of improper use of threaded pipe fittings. In this case, a Rotax 912S powered Tecnam light sport aircraft was modified to accommodate the installation of a Hobbs meter pressure switch (Figure 9). The original oil pressure sender was removed from the oil pressure port on the side of the engine. A commercial grade brass tee fitting was installed with a 1/8 inch brass pipe nipple into the oil pressure port. The oil pressure sender and the Hobbs meter pressure switch were installed into the tee fitting. The added weight and the extended arm of these two components resulted in overloading and subsequent failure of the brass pipe nipple. This caused a loss of oil pressure and an off field landing, resulting in substantial damage to the aircraft (Figure 10).
Now that we understand a little bit more about the use of pipe fittings in aircraft, we should be able to approach the pipe fitting from a little different perspective. We have provided some generic information and rules which should help you to make better choices regarding the use of pipe fittings. However, the tips and information here should never take precedence over the manufacturer’s recommendations for your particular aircraft.
For additional information about the use of pipe fittings in aviation applications we recommend the following references:
Mechanics Tool Box (John Schwarner)
FAA-H-8083-30 Aviation Maintenance Technician Handbook General
Each one of the bulkheads that are manufactured for the fuselage boom assembly are referenced in a 7 page PDF document.
This document can be utilized by the builder of the aircraft as well as the technicians within the shop that are manufacturing the parts.
Page 1 of the PDF shows and overall view of the flat layout and reference dimensions that can be used for many different purposes during the building as well as during the manufacturing of the components from the technician standpoint in the shop.
Wednesday, August 26, 2015
Vertical Stabilizer Assembly
55-10 Is the Code for the Vertical Stabilizer Assembly.
We have been updating the builder database with new drawings. These are the most current drawings available to the builders. However, it is important that you recognize that only the drawings that are contained within the builder database are updated. Any changes to the drawings occur only on the drawings that show up within the builders database. To have access to all of the builder database you need to become a EMG-6 member and receive a serial number.
To find out more about becoming an EMG-6 builder and member and get started on building your own aircraft. Click here
Thursday, August 20, 2015
EMG-6 "Shop Notes" and Index for the month of August 2015
In our upgrade the progress blog for the EMG-6 we will be formatting our process slightly different than we have done in the past. Previously we have just rambled on and taken pictures on a daily basis of everything that's happening in the shop. This works out great for following along and just seeing how things work, but in the future we will try and have each post have a little bit more continuity with the previous posts. We will make a page called shop notes an index for each month but we will make changes to each topic page as we progress. This will show a single subject matter from start to finish and help tie all the things that happened over the previous months together with a single subject. Any subject matter worth pictures and explanation we will create into its own post.
Bending Die Design
As most of you know that have been following this blog's progress. We have been in a transition period trying to retool as a result of Quicksilver Aeronautics no longer being able to any of our parts. One of the areas that we were outsourcing was the bending of the large diameter tubes that are used for the fuselage keel tube as well as the wing tips on the EMG-6. Several months ago we purchased a production tube bending machine which didn't come with any tooling. Much to our shock, we found that the tooling costs are outrageous for the dies and mandrels. To purchase a die set for the 9 inch radius needed for the keel and the wingtip. The cost was going to be $2000. In identifying the requirements for bending these 1 inch diameter 6061 T6 aluminum tubes. We realized that on a large radius like this. We could easily manufacturer our own bending die. We designed the die to fit our machine and have begun the process of building the individual segments that we will assemble to make the overall 9 inch radius die. We only need 180° of bend capability. So this is what we ended up with for the design.
Tuesday, August 11, 2015
Monday, August 10, 2015
This is the un-boxing video that we shot back in May 2015. Un-boxing videos are fairly popular because of their revealing nature of what to expect when purchasing a new product. If you are going to spend several thousand dollars on a new engine it's kinda nice to see more information about the product before it shows up on your doorstep. So we look at how the engine is packaged and shipped along with what we should expect to see inside of the box with all of the extra components and accessories. It is also a candid look of our first impressions of the motor.
Sunday, August 9, 2015
The Many Ways to Configure the EMG-6 Aircraft
BasicThis is the basic configuration for the primary structure for the aircraft.
The aircraft could be built and flown as an experimental amateur built aircraft in this configuration.
In this configuration the builder of the aircraft could assemble a significant portion of the airframe themselves saving a great deal of cost. Our goal is to be of the build this aircraft for under 10 K.
As a single place experimental aircraft the aircraft could be flown with either a glider rating for a private pilot's rating or as a sport pilot rating. As an experimental aircraft no glider rating is needed for single pilot operations.
Saturday, August 8, 2015
10 Blog Navigating Tips.This blog is currently being populated with information from the old electricmotorglider.com progress blog and once we have completed the propagation of the old information we should have nearly 1000 postings.
As you might imagine finding the information that you're interested in could be a bit challenging.
Hundreds of great articles and resources are at your disposal with just a few clicks.
Friday, August 7, 2015
EAA video hints for home-builder's section is a great resource for learning about building and maintaining aircraft. We have been participating in the video development for this section of EAA's website since 2008. We have done over 100 videos and webinars. We have provided a link here so that you can take a look at some of the videos that we have done to date.
Click here for link to EAA Hints for Home-builders
If you book mark this link it will automatically update with any of our new videos that are published.
Click here for link to EAA Hints for Home-builders
If you book mark this link it will automatically update with any of our new videos that are published.
Thursday, August 6, 2015
Rainbow Aviation Services is currently working with Polini motors to become a major US importer and service center for the complete line of Polini motors. After we complete our initial investigation and testing of the Polini 250 dual spark engine we will make a determination as to the future potential for the Polini 250 being used in the EMG-6. All of our initial testing gives us great optimism that this is the perfect Reciprocating engine Power plant package for the EMG-6. After we have made our initial investigation and decide that this is the motor that we want to invest more time and money this direction we will begin to stock both engines and parts as well as setting up the shop for doing major overhauls and repairs of the Polini series of motors. Combination of Rainbow Aviation and the light sport repairman courses maintenance program should make for the premier service center for the Polini motors. Rainbow Aviation Services will also be visiting the factory in Italy early next year for additional training.
Saturday, August 1, 2015
The Polini Motor is one of the Power Plant option that we have adapted for the EMG-6 for those that are wanting longer cross county capability or just in the interim until the electrical power plant systems are more refined.
- The piston, gravity cast at high silicon content light alloy, reduces thermal expansion and the coupling slack. The design of the piston top is specific to optimize the compression ratio.
- It is provided with a balancing countershaft; this feature cancels the vibrations and guarantees comfort never felt during a flight and a longer life for the engine itself. The counter-rotating rollers decrease greatly the upsetting torque-steer for an extra comfort in flight.
-The centrifugal clutch is in oil bath with helicoid mechanical reduction.
- The electric starting is standard but to offer the maximum safety the engine is also equipped with manual starter with easy system thanks to the flash starter device that speeds up and simplifies the movements.
- It is equipped with the comfortable closed-circuit system for the recovery of fuel during transportation and the 12 V output for any use.
Small and compact THOR 250 DUAL SPARK engine has an extraordinary power to weight ratio.