Author Topic: Construction of the Pathfinder LE kit by RSM (Read 25538 times)

Randy Powell · « **Reply #100 on:** September 15, 2011, 12:18:36 PM »

You don't really need that. Opening in the front of the cowl, relatively smooth inside from cowl opening to end of pipe tunnel and an exit at the end of the pipe tunnel that is 3 times the area of the intake. I usually don't put any more openings in. The large exit area will vacuum air from the inlet all the way down the pipe tunnel and out as long as there aren't too many obstruction in the way. I have used a very small inlet that pours over the crankcase. It doesn't take much as long as there is sufficient exhaust to draw the air through.

Openings along the cowl or the pipe tunnel just serve to create hot spots.

John Miller · « **Reply #101 on:** September 15, 2011, 03:51:18 PM »

Peter, it's your build, and ultimately, your plane, but in my opinion, Randy is right. He's basing his remarks from the experiences of Ted Fancher discovering that he had to close up all those cowl outlets on his Trivial Pursuit, because they were allowing the heated pressurized air inside the cowl area to escape before it reached far enough back to cool the header, and the pipe. Ted experienced run problems before he figured it out, and closing the outlets cured them handily, as I recall.

Yes, you could install some small electric fans. Neat as that seems, wouldn't that be making the problem of cooling the power system more complex? There is a proven method that requires no additional energy, works great when the plane is under power, and shuts down when the power does. Both Randy, and now, myself are advocating you consider using it. Of course, it's ultimately your choice.

Speaking of cooling issues, at one time I felt that cooling outlets designed to get cool air to the crankcase would be beneficial. I set up the Legacy I was then building to extract air from the crankcase area. After many many flights, I've come to the realization that crankcase over heating is probably a non-issue.

As I've found out, the air entering the crankcase through the venturii is cooler than the upper part of the engine. This naturally cools the lower end, when the engine is running. The heat is created at the top of the cylinder, and at the exhaust, making these areas the most important to have adequate cooling.

I've also found that the spinner is usually cool right after the engine shuts down. It does heat up as it acts similarly to a heat sink, but the heat reaches a peak, to match the engine, then drops as the engine cools down.

In my experience with this design, the Pathfinder L.E., the cooling air should not be allowed to escape the cowl and tunnel, until after the rear manifold, and coupler when using a pipe.

I also took my version of the prototype down, and took some pictures of the cowl, and the mounting so you can see how the dowels are used at the Front of the cowl. This set up has proven out to be very secure on the prototypes.

Your build is moving along at a good pace, and looks good. I'm looking forward to future installments, and the finishing and trimming flights.

John Miller · « **Reply #102 on:** September 15, 2011, 04:23:04 PM »

Sorry, so many irons in the fire, I forgot to attach the pictures of the cowl mounting.

I use two 1/8" dia. dowels mounted towards the sides of the cowl. This puts them where there is plenty of meat to glue into. I also use a plywood half ring mounted to the front of the cowl. This also adds stregnth to the mounting system.

Notice I've only used one allen screw at the rear of the mount. This arrangement has held up well to flight and landing loads impossed where I fly. (Mostly thick grass, very draggy.)

Peter Nevai · « **Reply #103 on:** September 16, 2011, 07:22:06 AM »

Quote from: John Miller on September 15, 2011, 03:51:18 PM

Peter, it's your build, and ultimately, your plane, but in my opinion, Randy is right. He's basing his remarks from the experiences of Ted Fancher discovering that he had to close up all those cowl outlets on his Trivial Pursuit, because they were allowing the heated pressurized air inside the cowl area to escape before it reached far enough back to cool the header, and the pipe. Ted experienced run problems before he figured it out, and closing the outlets cured them handily, as I recall.

Yes, you could install some small electric fans. Neat as that seems, wouldn't that be making the problem of cooling the power system more complex? There is a prooven method that requires no additional energy, works great when the plane is under power, and shuts down when the power does. Both Randy, and now, myself are advocating you consider using it. Of course, it's ultimately your choice.

Speaking of cooling issues, at one time I felt that cooling outlets designed to get cool air to the crankcase would be beneficial. I set up the Legacy I was then building to extract air from the crankcase area. After many many flights, I've come to the realization that crankcase over heating is probably a non-issue.

As I've found out, the air entering the crankcase through the venturii is cooler than the upper part of the engine. This naturally cools the lower end, when the engine is running. The heat is created at the top of the cylinder, and at the exhaust, making these areas the most important to have adequate cooling.

I've also found that the spinner is usually cool right after the engine shuts down. It does heat up as it acts similarly to a heat sink, but the heat reaches a peak, to match the engine, then drops as the engine cools down.

In my experience with this design, the Pathfinder L.E., the cooling air should not be allowed to escape the cowl and tunnel, until after the rear manifold, and coupler when using a pipe.

I also took my version of the prototype down, and took some pictures of the cowl, and the mounting so you can see how the dowels are used at the Front of the cowl. This set up has proven out to be very secure on the prototypes.

Your build is moving along at a good pace, and looks good. I'm looking forward to future installments, and the finishing and trimming flights.

I am toying with the fan Idea. Something I may play with in the future, not for this project. I sent Ted a PM asking him to add his experience to this thread, we'll see if he responds. I could easily fabricate some sliding shutters inside the cowl to adjust the amount of air that would flow through the openings, that are of less weight than the material removed to create the openings themselves. I find the scoops to add to the overall appearance of the model. I can see the possibility of diverting air away from the engine and header before it has a chance to flow past the components. In that case it becomes more a matter of the placement of the openings as opposed to the total area of the openings themselves. I located the openings on the side of the cowl strategically to be slightly aft and adjacent to where the exhaust header would fall. This in theory should pull more air past the header just before venting it outside.

I can easily test the temperature of the internal components by using small manufacturing / test lab temperature indicator tabs. These are little strips with dots on then. You attach the strip to the object you wish to get the temperature of and perform the test. The you remove the test strip and depending which dots have turned black gives you the a rough idea of the max temp achieved.

http://www.grainger.com/Grainger/WAHL-Temperature-Indicator-6FYY2?Pid=search

As far as the pipe tunnel goes I was going to treat it as a separate area, with it's own inlet and outlets. I feel that the entire drive train and exhaust path be kept at reasonable temps, as the materials and adhesives we use soften or get brittle when heated past a certain point. It makes me wonder if that is the potential cause of some models using sandwiched carbon veil and balsa as opposed to the traditional ply balsa combo for engine crutches is the overheating of that area. Balsa reflects less heat than Plywood (Balsa is much more porus and has many more internal air spaces, and air heats faster) and perhaps the epoxy used is softening. Could be a contributing factor on Matt Colans structural failures in his TP.

Peter Nevai · « **Reply #104 on:** September 16, 2011, 08:13:50 AM »

Quote from: John Miller on September 15, 2011, 04:23:04 PM

Sorry, so many irons in the fire, I forgot to attach the pictures of the cowl mounting.

I use two 1/8" dia. dowels mounted towards the sides of the cowl. This puts them where there is plenty of meat to glue into. I also use a plywood half ring mounted to the front of the cowl. This also adds st regnth to the mounting system.

Notice I've only used one allen screw at the rear of the mount. This arrangement has held up well to flight and landing loads imposed where I fly. (Mostly thick grass, very draggy.)

Hi John,

The dowels work if you have the necessary clearance to tilt fit the cowl to the fuse. I did not build in that clearance. The only way I can get the cowl on is by dropping it into place. The cowl has to be exactly flush with the nose ring and the rear fuse cut out for it to fit in place. To make it tilt in back and to have the play to fit the dowels into the nose ring holes, I would have to cut the cowl so there is sufficient gap at the rear so it would be able to swing into place after the dowel pins as inserted into the holes up front. Also I would have to open up the hole for the venturi as it is quite long and has to be able to fit into the cowl before the pins could engaged the holes in the nose ring. I hate gaps in cowl, fuse fits. I also want to keep the engine compartment sealed as best I can to help with the sirflow dynamics in that area. Gaps allow air leakage which mucks with airflow paths, and decrease the effectiveness of air outlet ports.

Thats a pretty tall engine. The VF comes no where near the bottom of the cowl. It falls short by at least .25 inch, so I am not cutting a big round hole for cylinder head clearance. I will have a hidden jack to power the glow plug.

Now if someone would machine a apinner back plate with impellor fins as used in some vacuum cleaners without adding significant weight. We could use some of the engine power is most of our completely over powered beasts to force cool outside air through the engine compartment and pipe tunnel. But I suppose all this is moot as we'll all be flying electric within the next 5 years anyway. Sniffle...........

Did you know that a well engineered Tower or notebook PC run cooler with the case all closed up and panels attached? It's true the electronics will run hotter in a completely open environment as opposed to being sealed up in a properly designed enclosure.

John Miller · « **Reply #105 on:** September 16, 2011, 08:21:50 AM »

Good point Peter. My intent for posting the cowl mounting pics was to show how it was done on the plane I built. As you've noted not all are the same, even with the same design. Factors like you've noted, esp. shortening the nose for balance considerations may dictate different solutions. I'm sure that what you come up with will be well thought out, and efficeint.

Randy Powell · « **Reply #106 on:** September 16, 2011, 12:17:28 PM »

Might take a look at Claudio Chacon's Trivial Pursuit (painted like the Voodoo race plane). He set up intake and outlet holes in the cowl then used separate intake and outlets for the pipe tunnel. He tells me it worked OK, but he had to be careful of getting a hot spot between the two.

http://flystunt.com/AIRPLANE/VOODOO.htm

Peter Nevai · « **Reply #107 on:** September 26, 2011, 11:18:07 AM »

Now that's sweet. The cooling hole are right in line with what I have in mind. Gotta love paint finishes, they make finishing the openings so much easier than treating them with film. Anyway just an update. I've been working on myriad of detail items of the kit, mainly sanding flaps, shaping and sanding the wingtips, you know getting all the bits an pieces ready for assembly. Nothing really to post photos of as everyone generally knows how to sand, prepare parts.

I just realized that I did not order any hinges for this plane. I will have to get on that right away, as I assemble everything before covering. While sanding the wingtips to shape I noticed that the trailing was not straight. I used a straight edge and checked and only at the trailing edge it wandered from true. Weird, not so much as a warp but a minor wiggle. Well I soaked the trailing edge down at the area of the wiggle, laid a aluminium ruler along the trailing edge and have it weighted down flat against the building surface. That took the wiggle out of the TE and It's now straight. This should be a heads up to all to check the height of the TE at each rib location as it seems that the ribs may not lie at equal heights in spite of the built in Jigging system. The wiggle in my TE spanned the center 4 ribs only, and those are the ones that are assembled first as the basis of the rest of the wing.

Out board of the first 4 the TE was straight and true the rest of the way out on both halves. I now remember why I despise built up wings. It is a real pain sanding a 57 inch wing without accidentally snapping a rib here and there either with the sanding block or by grabbing it too hard in the wrong place to steady it. Wings this size are unwieldy and sheeted foam is just so much more durable, not to mention sanding block friendly. It is turning out rather light though, the wing complete is lighter than (without film covering) than 12 ozs (comparing it against the weight of the VF46). I don't have a scale handy to weigh it, the fuse is quite a bit lighter than the wing. If my guesstimates are correct then I figure that the airframe will come in between 26 and 32 ozs uncovered and be 44 to 50 oz. fully finished. This is using only the wood supplied with the kit. Although this would be the full up weight, I never consider the weight of the engine as a limiting factor except for balance as no matter what engine you put in a plane that item has to be there and you can not really change the weight of the package.

It is a given the VF comes in at 12 ozs in CL trim. And out of any component the engine is usually by far the heaviest single component. I always prefer to gauge how heavy the airframe turns out with it's ancillary components.

Peter Nevai · « **Reply #108 on:** October 03, 2011, 11:35:24 AM »

All righty then, I figured I would post an update, just so people don't think I've abandoned this thread. I am at the point of endless sanding, the part of the build process I despise. Hours of getting the everything to the final shapes shown on the plans. Then more sanding to get the surfaces as close to the final condition ready for cover. Here is where covering with film starts to diverge the building process from those who choose to paint and or use silkspan, or other covering materials. As after assembly the next step is the final finish, with no more intermediary steps. The balsa has to be filled and as smooth as it can possible be (Or as filled and smooth as I have patience to make it). As I cover the model after it is completely assembled it is easier to get the lions share of sanding done before any assembly.

Contrary to many who work with film I cover the entire airframe with the material and cover after it is completely assembled. There are reasons for this and I'll touch on a few right now so you can understand the reasoning behind it. There are tricks with film coverings that go a long way to ensure the durability and appearance of a film covered model. I do not like mixing media. While good results can be accomplished the places where the media overlap can and usually does present problems that can take a while to crop up. So I use film exclusively and If I were to paint I would use that exclusively as well. Paint and film just weather and wear at different rates. It does not take long for your wings to start looking different than the fuse if you should to decide to do one in paint and the other in film, also you run into problem areas where the two meet.

Anywho, to get the best all film results you should start on the bottom and work from back to front, meaning that any rearward pieces should underlie those forward of them. The reasoning behind this should be clear so and seams are not facing the airflow. This way they will not loosen and peel backwards (unless you have a peculiar habit of flying backwards) Starting on the bottom and working up also allows you to easier hide or place seams where they are least noticeable.

Of course the thing most of you are thinking about is "What about the Wing to Fuselage joint? Got any smart answers for that part?" Yes, those you cover very first before covering anything else. I have used this white pre mixed stuff sort of like microballoons really light weight and comes premixed in a jar. I use this for the fillet material at the wing joints. You can use just about any material in this location. Run a nice radius fillet between the wing and the fuse and at the stab areas as well. Let what ever material you use completely dry or harden, namely outgass as much as practical.

The nicer and more gradual the radius is at these locations the nicer your film will lay. Cut a strip of covering only a 1/4 inch wider (either side) than the fillet. Just enough to cover over all of the fillet material. Starting from the wing TE attach the covering to the filleted area and gently stretch the film as you iron down the film onto the curve of the fillet. The trick is to heat, stretch, tack, in that order. Focus mainly on the center line of the fillet running from rear to front. You will notice if you are heating and stretching before applying pressure to iron down the film the edges of the film will naturally conform to the curve of the fillet. Keep working forward past and half way around the leading edge. You will have to stretch a bit more to get a good fit around the LE radius. Once it is down you can go back with the iron and a dampened rag and work out any small wrinkles or air bubbles. Heat with the Iron and then attach and cool using the damp rag. A pin and a tiny pinhole for more persistant air bubbles. The trick is to move steadily forward working the length of the strip an inch at a time before moving forward. A bit more finesse is required at the leading edge. The nice thing about working with this narrow strip of film , is that if you totally blow it, you can just heat it up and peel it off and start again. It may take a coupl tries before you get the hang of it to yeild a nice smooth film surface on this part of the airplane. Make the strip quite a bit longer than you need, it make it easier to handle and you just trim off the excess anyway.

Covering the Wing / Fuse and Stab / fuse interfaces in this fashion makes the rest of the process go much smoother. You do not have to try to man handle larger wing or fuse panels to fill this gap. Your seams location is more flexible for both the wing panels and the fuse panels.

So now perhaps you can appreciate one reason to assemble then cover and why you need to get all the wood as smooth as possible before assembly.

NOTE: Take a damp rag or lint free cloth to the area you are about to cover. The surface should be as dust free as possible. Balsa dust should be cleaned off of the surfaces. Otherwise your film will attach mainly to dust and not the airframe. leading to sagging, lift ups and other covering problems down the line.

Randy Powell · « **Reply #109 on:** October 03, 2011, 12:13:06 PM »

Yea, sanding and sanding. Then, more sanding. You have to develop a certain Zen toward it.

Peter Nevai · « **Reply #110 on:** October 03, 2011, 01:02:17 PM »

Zen my Butt. Although you do need a great degree of inner calm not to smash the damn thing into kindling when you get the Trailing edge all smooth and integrated into the wing tips only to find that somhow you've managed to sand nice craters into the rib cap strips. Or the real life journey into the laws of dminishing returns whilst trying to get the wing tips symetrical to each other and on each axis. I suppose one of those things that have a zillion moveable rods that trace the contours of an object would help in this regard they are useless when you find that you don't have enough material to sand to shape on one end or the other in the first place.

I think I have set the record in having the number of repaired ribs in a plane that had not even flown yet.

Randy Powell · « **Reply #111 on:** October 03, 2011, 01:42:40 PM »

Well, I have two thought. First is, take the sanding slowly. There's less chance of mistakes. I've certainly pitched many parts away due to sanding mistakes.

The other thought is to remember what Windy always said: no finish is ever completed, only abandoned. Learning the rule of "good enough" is a tough go sometimes.

Peter Nevai · « **Reply #112 on:** October 14, 2011, 02:35:01 PM »

Construction Update.

While fitting the custom controls by Tom Morris, I found that there was no way the adjustable elevator horn and ball link assembly would fit in the space between the fuselage sides. I had to cut out the Fuse former that came with the kit and make a new one to increase the spacing between the sides at the horn location. With Tom Morris controls this needs to be significant! It kind of messes with the fuse profile back under the stab but as it is under the stab It is not too obvious. Because of this I had to cut an additional former to fit above the location of the one on the plans as well. If you are bending your own or using a slimmer profile adjustable control horn set up back in this area you may not have clearance issues.

In addition I felt that the fuse bottom under the wing where the pipe tunnel will go has not enough structure. The Fuse bottom in the final will have large areas cut out to fit the pipe. I felt that this area needed more than just the 1/8th in fuse side to 1/4 inch fuse bottom plank interface. After pipe installation quite a bit of strength imparted by the fuse bottom would be compromised basically leaving just the fuse above the wing as the main support structure. Also if I left only the fuse sides tied to the bottom plank at this location, when I cut this section away to install the wing then the balsa sides attached to the bottom sheet would spring out of shape because there is no other support for the fuse sides at this location directly under the wing. What I did was add the 1/4 X 1/4 balsa sticks to the fuse sides as seen in the photo, I used this additional surface area to glue the bottom plank to. This addition will stiffen up the area below the wing and provide additional support when the opening for the pipe has to be cut. It also helps hold the fuse sides in alignment when the bottom section is cut apart to install the wing.

Shown is my method for securing the cowl. I will use some screws and blind nuts to secure the cowl to the 4 plywood posts. I will bush the holes with some delrin tube to prevent the cowl sides from crushing when the cowl is tightened.

NOTE: Check the clearance for you elevator control system BEFORE cementing the horizontal fuse former under the stab!

Jerry Reider · « **Reply #113 on:** December 25, 2011, 09:27:48 PM »

Quote from: Peter Nevai on August 01, 2011, 01:44:13 PM

Starting on the wing. The great thing is are the guides and the built in tabs that allow the wing to be built without a jig. I followed the instructions in the FM article on how to set this up. The really really bad thing is that the bellcrank mounts are not cut properly in the kit. They are too narrow! I discovered this only after gluing the lower bellcrank mount on to the center ribs with epoxy. Because the mounts are cut improperly there will be insufficient contact area between the mounts and the upper and lower spar that caps the mounts!

I am upset that this error was make in the kit fabrication at such a critical part of the model. I am uncertain how I can now fix this deficiency, I can not afford for the bellcrank mounts nor the center section of the wing to structurally fail. As the parts have already been glued to the rear shear web spar and then glued to the 4 ribs, I would have to trash the entire assembly and cut new bellcrank supports as shown on the plan in the photo below. The supplied plywood supports are no where close to the parts shown on the plans.

This is a major fault please note this when constructing your kit!

I can probably fill in the space left by the too narrow supports but I fear that it will never have the structural integrity that a proper width pieces would offer. The killer thing is that the way the bellcrank mounting is designed there is not much in the way I can satisfactorily reinforce this area.

NOTE: In the photos you can see just how narrow the supplied laser cut bellcrank supports are compared with the drawing.

I know you're way past this point by now, but for future problems like this (parts epoxied together wrong) it is a whole lot easier than you would ever imagine to cut the epoxy joints apart with a hot #11 blade or whatever knife you need to use. I heat the knife up with a combination of my Monokote iron and my heat gun. I also heat the area that I am going to cut apart.

louie klein · « **Reply #114 on:** December 26, 2011, 08:13:33 AM »

Hi Peter. It's been A while but how are you doing? The plane is looking awsome! The fits are fantastic. I am just puttering around with flying stuff when I can. We are down in VA. for the holidays, be back in NY next week. I guess the spring will be the next step for flying. The cold bothers this old man unless it is a dead calm day, but I do keep my battery charged just in case. If I can help in some way let me know.---LOUIE

Dick Pacini · « **Reply #115 on:** January 31, 2012, 02:55:20 PM »

Peter, how about an update?

WhittleN · « **Reply #116 on:** February 08, 2012, 07:52:25 AM »

Peter
Who is this George Delaney? Is he also known as Gordan Delaney the famous stunt flyer from Utah USA?

Norm Whittle
Infamous stunt flyer from Utah USA

Dick Pacini · « **Reply #117 on:** February 16, 2013, 11:02:00 PM »

Peter Nevai has abandoned this build thread and has not been active here since last August. It is a shame that his Pathfinder was never finished, or he chose not to share the completion with us. Does anyone know what happened?

john e. holliday · « **Reply #118 on:** February 19, 2013, 12:38:18 PM »

I don't think he could take the comments that were made. Also when trying to help someone, it pays if they would read and comprhend what is said/written. I am bad about that myself.

Peter Nevai · « **Reply #119 on:** February 11, 2015, 10:58:37 PM »

Still a work in progress, Work has been a whirlwind and I get home and all I can think of is zoning out. Not having a real work space here is contributing to my procrastination.

Dick Pacini · « **Reply #120 on:** February 12, 2015, 05:42:17 AM »

That looks good! Hope you will post more progress soon.

Gordan Delaney · « **Reply #121 on:** February 24, 2015, 06:04:53 PM »

Quote from: John Miller on August 24, 2011, 01:34:32 PM

The tip weight specified being permenently installed is to limit the amount of weight needing to be stuffed into the tip weight box. On both of the prototypes, we wound up with about 3/4 oz of tip weight. Any percentage permenently installed will allow less having to be installed in the box.

The amount , 1/4, or 1/2 oz is specified to let the builder decide how much weight he wants to have for adjustments, and is, of course, a choice left to the builder.

Before you shorten the nose, may I suggest you send Gordan an e-mail. He's currently running a PA .61 I believe. He is running the shorter nose, but he may also have found it necessary to add nose weight. I'm running the stock nose legnth, but my Stalker .51RE is lighter in weight. and I needed no additional trim weight.

Peter, Some times John get facts and numbers mixed up. The nose moment on my Pathfinder is 10inches. The engine is a PA .51. And I have no nose weight in it. But, I do glue in a half an oz. of tip weight. Hope this helps.

Gordan.

E-mail is gordandelaney@yahoo.com

Peter Nevai · « **Reply #122 on:** November 29, 2017, 10:57:52 PM »

Well, ya'll probably thought I dropped off the face of the earth, I have not and nor is the saga of the pathfinder build run it's course. Although little additional progress has been made since the last post, I did get all of the surfaces hinged, fitted and ready for glue. But in the interim because of work and then moving back home to south Florida, the Death of a family member and then moving to a new place in south Florida.....psst a really nice place. I have not had the time to dedicate to modeling. Still have unpacking to do and the garage to put in order. Also sometimes you just get tired of working on the same thing getting bummed out that it seems to take forever to finish. That is the stage I am with the pathfinder, besides the hangar rash it developed from the fist move from NY to Florida and then from one address to another which needs repair. Then I still have to order a tuned pipe and all sorts of other small items to finish it, for me at the moment seems a bridge too far. Anyway what I did do and most likely finish before the Pathfinder is I purchased a Control Line Specialties Forerunner kit. The foam wing version, profile. Got a new LA46 to stick in it. Just need to order a Venturi and needle valve assembly, tank. It should go together rather fast and is a perfect knockabout model to get into the air with. Durable, can be easily be flown off of grass (The pathfinder would have issues taking off of good old Florida Bermuda grass more than an inch high. I flew the heck out of the last one I had. Flew it until from fatigue the wings folded up in mid air. I'll post the construction details in a new thread just for posterity as the model is no longer in production so I do not know how much it will help others unless they also have one to build. Stay Tuned... Now I have to get the garage squared away among a encyclopedia's (Yes, it was a collection of actual Books that had all the stuff worth knowing before the internet) worth of other chores.