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FAQ's
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All answers on this page are mine and what I believe to be accurate. This page is built by people asking me questions. I have copied my replies here to hopefully assist you in building your UH13P. Please email me if you have any questions.mikejacobson3@yahoo.com Your questions may help someone else. Scroll down to read FAQ's or click link to go directly to the question. Bow Layout Laying out the bow. (T.J.A.R. technique) That's Just About Right Learned from Dave Schneider Change the plans Is it worth your time? Gas Tank; Where did I get it? Lift Horsepower Theory and link to calculator One or two engines Pro's and Con's to both types. Plow In A bad thing? Props To build or not to build Prop Plan Layout How to use UH prop plans. Splitter Strength Should you build it stronger than the plans? Transitions/Attach strip material I have been asked by Bill Zang, to assist Universal Hovercraft in answering questions regarding the UH-13P. Some questions will be forwarded to me by UH. When I reply to your question, I copy or blind copy Universal Hovercraft. As you can imagine they get allot of emails. I should be able to answer your question within 48 hrs. (Unless I am hovering somewhere). If I cannot answer your question I will forward it to UH with a copy to you. Specific questions about other UH crafts send directly to UH.
Q. Is there any portion of the skid that takes more of a beating ... like the front or back. If so, maybe I could use something more durable in those areas? A. I just would not overbuild this one. You need to hover this year. If there was one spot it would be where the splitters/attach strips are. The landing skids in the area of the splitters get their support from the 1/8" ply splitters. I have taken several VERY hard hits to this area and had some minor damage. Nothing that stopped me from hovering. You could use a little extra glass in the area. Don't over do it. Attaching the skirt is done with Stainless steel pan head screws. On the inner attach strip you let the material lay straight down fold over the cut edge toward you and then screw into the wood through 2 layers of the material. After attaching the inside of the skirt, I set the craft on 8" building blocks. Actual height 7.5". set on nice level surface. Then screw in the front & rear corners, then keep halving the distance between the screws. On the outside attach strip, make sure you adjust the skirt as you go to avoid ripples in the skirt (see general Hovercraft construction manual from UH). You will fold the material inside toward the craft and screw through 2 layers. As you do it keep the skirt hanging even. screws should end up about 4" to 5"s apart (not critical). Props: To build or Not to build? Question: What did you do to prop 2 that was different then the plans? I want to build a propeller that will give me 50MPH. Answer: I built prop 2 according to the plans. I would get the plans from UH. Watch the video if you need to, and build according to UH plans. The mistake I made was using 3 - ¾ inch boards instead of making it 4 - ¾ inch boards thick. I did not read the plans properly I guess. Are you willing to take the time now to build one? If not... You can purchase one through UH. There props are excellent and they provide excellent thrust. I know they sell partially finished props of any size and will most likely have one in stock for the 13P. All you have to do is glass and balance them. Glass and balancing can dramatically effect the thrust output, so spend your time on that. After you get hovering you can spend time cutting you own prop for reserve use and you will have a model to go by. I spent allot of time and did not have a model to look at. If money is a problem, build your own. I figure I have about $15 to $20 in each prop I build. From what I have seen at rallies, I have not seen another prop produce more thrust per horspower that you can build, or buy, that compares to the UH wood 2 blade Prop. Ultralight props have a power curve that does not match our needs. A second comment about props... The design of the Universal crafts in general, allow maximum airflow to the thrust prop. That is why they perform so well. Just a small change in airflow can mean allot. My experience at hover rallies with many different crafts is that it has not been a problem. The wear on a prop from water and sand on the deck can be reduced by tapering the leading edge of the thrust duct at deck level slightly back and away from the inside of the duct. I made mine flow right from the deck and up into the thrust duct with nice airflow. Even with this I don't see prop wear as a problem. When I build my next one I will make this slight change. I could cut this taper in now but I don't think it is worth the 3 or 4 hours it would take to do it. If you like woodworking hovercraft.com also has prop plans for around $20 or $30 that will show you how to build your own prop. That is what I did. I would also recommend the video that shows how to use the plans. It is not the best quality but it does show some critical steps and will save you time on prop work and general hovercraft construction. I have not seen ANY props on ANY Hovercraft that "you can buy", that outperform the ones at Universal Hovercraft. "Horsepower to thrust ratio". And they are a simple Two blade wood! I have traveled over 400 miles this spring, May 2001 and mine does not need any repair, when it does it will take about a 30 minutes to rebuild the leading edge with a flox/epoxy mixture. The more you rebuild it, the stronger it becomes.
I hear UH crafts have a problem with plow in, is this a problem with the 13P? Answer Plowing in is not as bad as it sounds. (If the hull is designed properly) I use plowing in as a braking technique when hovering on water. I slow the front engine and sit forward. I have had a plow in at 52 mph, it is a rapid deceleration and did not plan it, however I remained in my seat and did not fly forward. If you stick to the plans and use one engine you will not have the extra 60lbs on the front of the craft to support. If you do plow, the hull is designed to skid on the water like a boat. I have also made the mistake of going sideways at about 40 mph and had leading side collapse and the craft just skidded sideways on the water until it re-inflated. It is scary the first time but it does not throw you around or out of the craft (if you are holding on). Construction...The craft has an elevator control. You pull back on the stick when you feel the front start to tuck, it lifts the nose slightly. Saw your web page on your UH-13P. I am thing of building this model. How come you went with a separate lift engine?
I built the UH-13P with 2 engines and have flown both the one and two engine crafts. The following is what I have found. As you have guessed there are pro's and con's to adding a lift engine to the UH-13P. Pro's of adding a second engine... „ Ability to maintain full hover at low speeds. „ Ability to hover craft without thrust. Con's of adding a second engine... „ More weight up front, upsets designed balance. „ One more engine for maintenance. „ Worse mileage (not much) „ More maintenance. (Belt system is exceptional) „« Much noisier. (Most noise comes from the front engine.) The UH-13P as designed (1 engine) will.. „ be Lighter weight. „ be better balanced. „ go further on a gallon of gas. „ run the same speed. (Believe it or not!) „ be much quieter. „ be less maintenance. You must decide what type of hovering you plan to do. Will you be low speed hovering in tight places? (Two engine better) Is noise a concern? The 13P with one engine is generally the quietest craft at rallies. When walking next to the craft while maneuvering for trailer loading/parking is easier with the two engine craft as you don't have the thrust that goes along with the lift. If the rear engine dies, maintaining the ability to hover makes the craft easier to get to a location for repair/back on the trailer. If you decide on the 2 engine craft, there are several changes in the plan that must take place. One thing I did not understand is that there is 3" of wood skirt attach strip from in the front area of the hull where it is flat. When shaping the front...you grind the tip to the bottom of the top piece and taper back about 18". The front motor adds approx. 60 lbs to the front of the craft. That is a drawback. As hard as it may be to believe...I don't think my craft goes faster/quicker than one with the belt. It is an exceptional design with very little maintenance or problems. I still choose a two motor setup. Pros... If one engine goes out I can still move it, for loading onto the trailer I don't need to run the thrust engine. To reposition the craft i just start the lift engine and move it myself. The one engine craft you have to throttle up which gives thrust when you may not want it. Two motor system is more difficult to drive. You can get by with an 8 hp motor in the front. I bought a 10hp because the weight is the same, and the price is nearly the same. You may be able to get by with a 6 hp for awhile but as they age they loose power and you do not want to loose power/lift at high speeds. I was told by Bill Zang from UH to move the dash back 6". I did not do this. This would have forced the weight in the cabin to be back 6"...this would be perfect with the motor in front. I have just disassembled my entire craft and rebuilding the front motor mounts out of 1" square aluminum tubing. I will be running the gas line, starter wire, tach wire, throttle cable inside the tubing. This is a very clean mounting system. I am building an entirely new dash system moved back about 3 or 4 inches from the previous dash and lowering the profile to reduce the amount of disturbed air to the thrust duct. Remember EVERY POUND makes a difference! Aerodynamics is HUGE! Part II Question: According to the calculations on this page... http://www.suncoastcomp.com/HW/lift_calculator.html a 13.5'x6.25' craft at 875 pounds total will need a 4 1/2 hp lift engine, if I ad on 50 pounds for the engine itself it would be a 6 1/2 hp. Anyway I will probably go with the plans for now, as long as I can find a second hand motor, I don't want to put out $1500.00 plus only to wish I had gone with two and then the thrust one would be a horizontal. Yes a 6.5 would probably do it. I was able to find a brand-new 20HP Vangard Briggs engine on Ebay for $600. I know you can find them on special at www.tulsaenginewharehouse.com for about $800. A 25 hp one engine craft would be very nice. Even the 20hp with one engine would be fine. I figured that one engine craft would lose about 5 or 6 hp just turning the front fan. I have not found that to be true, I don't know why. I used a vertical shaft 20 hp engine and turn only the rear thrust. It sounds inefficient due to running it over the idler pulley's. I believe I gain more thrust from having the engine further away from the prop than I would gain by not going over the pulley's and using a horizontal shaft engine. If I used a horizontal shaft to run just the thrust, I would move the 8" pulley near the prop, to in front of the pillow block supports which would move the motor ahead and away from the air flow to the prop. This would cause some other changes in design that may not be worth the effort on your first craft. I do remember the guys at UH saying you could get by with a 6 hp. I just see them all with 10 hp on their crafts. It may be because that's the motor they get the best price on, I don't know. I do know that you do not want a problem with lift. I got the tank from Northern Handyman. It is a 6 gallon tank from a "long run" generator. It has two valves already plumbed, and 4 screw attach points underneath. I used 1"aluminum strap as you can see in the pictures. There is no problem with the weight that high. Don't forget to purchase the tank before you finalize the width of your cabin area. I made mine 6" wider than the plans to make it more roomy inside and to accommodate the gas tank. I don't believe I lost any airflow to the prop by doing this. I would not change the plans very much the first time you build one. Once you get the first one done and drive 30 or 40 hours and go to Hover rallies you will have a good idea if your concepts will work. I have not seen any clutch fans personally. Stick to the plans and you will be happy! Check out all the plans and details at www.hovercraft.com All designs were created by an aeronautical engineer who has tried just about every concept I could think of over the past 30 plus years. Changing designs are VERY time consuming, every change you make effects something else that may not become apparent until it becomes a problem. I would not recommend it until you have more time in the sport. Finishing the project... I have found that most people who start a project and don't finish it are the people who make a change from the plan and it creates other problems that they had not thought about, then they get frustrated & quit the project. When you stick to the plans you have a path to follow and you will be hovering much sooner. Not only can you get the plans at hovercraft.com but you can get all the parts you need to do the project. Some may be difficult to find depending on where you live. The prices are as good as I could find locally. Once I decided to build the 13p, I first decided that I did not want to be out looking for all the parts to piece this thing together. I just called the guys at universal and said send me all the hardware/epoxy/cloth/marine ply/skirt material etc. for the 13P. They knew exactly what was needed. When it arrived I did not spend as much time running around to hardware stores etc. This saved allot of time. You can also buy the 13P in the Kit form which comes with partially assembled hull, lift duct, thrust duct, motor etc. When I finished my craft I had just as much money in it as if I would have just bought a kit. Question: I am starting to construct my craft now...Looking at your hull construction site I am curious about the method you used with the screws to draw the shape of the hull. It looks like you used about 10 screws on each side. I am marking it the same way. Did you use a straight edge to draw a line from each screw to screw or did you use some other method? Answer: I put a screw dead center in the front of the foam. Then I put one on each side where the taper begins. Then I split the difference in half and in half and in half etc. until the shape was there. I drew a line where the string was and used a sawsall or jigsaw to cut just outside the lines. Maybe ½ inch. Then I used a carpenter's rasp to file it down to the lines...I just used the lines as a general guide and not exact. I rounded where the lines were straight. The carpenters rasp is one of the best tools I found to work with Styrofoam. Also I used an 8" long 2X4 and stuck some #40 grit self stick sandpaper to it. It works excellent to do the final shape after the rasp. Transitions/attach strip material? Q. What is the best type of wood to use to make the skirt attach strips and landing skids out of? A. I used pine from a 2x4 and ripped it on my table saw. It will break if it has bad knots so pick the good stuff. I ripped extra pieces of everything and stacked it so I had a supply while I was building. Q. I was more concerned about the nose or tail areas. Are they high wear areas? A. The nose takes allot of hits on steep transitions. This is reduced when you learn how to fly. You can use your elevator control properly at just the right time and or just before you hit the transition you can turn 90 degrees to the transition and go up or down sideways. The rear outside tack strip takes hits when you don't turn early enough. You then take a chunk out of the rear corner and hopefully miss the rudders. Try not to set down on solid ground until you stop motion. It comes with practice. Question: I have received the UH plans and am having a difficult time trying to figure out how to apply the plans. A I am glad you purchased the UH prop plans, after you figure them out it will be easy. The link you talked about "detailed prop link" is not working because I have been unable to scan the pictures at a high quality enough to read the notes. I will continue to work on this. I hope these instructions will help you. Please let me know if you do not understand them. I would print them out and place them next to the UH plans while you layout the prop. The description below is for a standard rotation lawn mower engines used in the UH plans. Prop Plans: I took the plans and taped them to a well-lit window and then taped several sheets of printer paper together, enough to cover the plan. I then traced the prop onto the printer paper. I cut out the shape, labeled it and put the fold on the fold line. I am assuming that you have already glued the boards together, found the center, scribed to the prop tips and cut them to length. There are 3 major measurements you must make to lay out the prop. Orienting the Prop. Lay the prop down so the leading face or front of prop is up (top flat area). Lay the prop so the center is in front of your left arm. You will be working on the right side. You can label the top of the prop (front or top flat area). The side facing you (leading edge) and the side away from you (trailing edge). These labels are for the right side of center. You then rotate the prop clockwise and label the other blade if you like. #1 Trailing edge: Take the template you made and lay it on the blade front of your right arm. There will be about a 3/4" piece of that template that lies on the top of the wood (fold line). The rest of it will be folded over the back side ie. the side that is away from you (trailing edge) The template will be out to the tip of the prop as shown on the template you just copied. (tip) Trace the shape that the template makes from the tip down to where you hit the table you are working on. Spin the prop clockwise and do the other blade. #2 Top Flat Area: The leading edge will be closest to you on the right side and opposite of the side you drew the trailing edge, the top flat area is facing up. Still working on the right half of the prop... working on top of prop and the closest edge to you on the top of the prop, lay out the measurements shown in the prop plans for the top flat area, root etc. Scribe a line between the tip and root measurements. #3 Leading edge: The leading edge will be facing toward you on the right side of center. Again the trailing edge you scribed earlier should be away from you on the right side of center. Mark the leading edge as directed in the prop plans from tip to root. Scribe a line between the two. Shaping: Grind from the top flat area line, to the trailing edge until you have a perfectly straight line between the two. I run a straight edge to ensure uniformity between the two lines and two blades of the prop. Grind from the leading edge line to the trailing edge until you have a perfectly straight line between the two. Again run a straight edge between the two scribe lines to ensure accuracy. Round over the square leading edge from tip to root to create an airfoil shape. See the UH general construction manual and the instructions that came with your plans for the exact shape. Hint: I ground down to just above the lines then hand sanded down to the lines. |