Simon Chaddock Posted September 3 Share Posted September 3 Never one to shy away from trying something different the Vought 173. A small scale prototype of the proposed larger and much heavier XF5U. It was actually remarkably successful. first flown in 1942 by the time of its last flight in 1947 it had flown having flown no less than 176 times although the full size project for a Navy fighter was doomed by the advent of jets. It was powered by two Continental A80 flat 4 of just 80hp each. It was largely made of wood with fabric covering. As it flew so many times it seemed to me it should be possible to build & fly a foam electric version. Still thinking at this stage but one thing is for certain it likely would have "interesting" flight characteristics. 4 Quote Link to comment Share on other sites More sharing options...
Chris Freeman 3 Posted September 3 Share Posted September 3 Byron and I built the Chris Golds one many years ago. It flew well once we figured out how to get the motors to start at the same time. Very unusual in the air but was quite stable. 2 Quote Link to comment Share on other sites More sharing options...
J D 8 - Moderator Posted September 3 Share Posted September 3 The XF5Unever flew except for some short hops, project was canceled before vibration issues could be sorted. An interesting feature was those enormous props, their wing end position mostly eliminate wig tip induced drag which would be huge on such a low aspect wing. Not only were the props variable pitch but they also had cyclic control like a helicopter, the aim being to improve control/maneuverability. How this would work I do not know. Not seen a model of one. 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 4 Author Share Posted September 4 The V173 was simple compared to the XF5U and only 1/5 the weight. In its initial form the V173 actually used early F4U Corsair props but obviously at much lower RPM as each was driven by only 80hp rather than 2000! These were soon replaced lighter specially made props but of the same 13'4" diameter. The XF5U props were even bigger at 16' diameter! The intention is to size my V173 so 10x5 three blade are true scale diameter. It will thus need scale U/C and sit at the same ground angle! 3 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 6 Author Share Posted September 6 To keep a scale appearance I wanted to keep the motor bell within the diameter of the nacelle and be able to drive a scale prop. With a 10" prop the nacelle would be 28mm diameter. Using PLA about printing a test section of the nacelle and mounting a suitable Emax 2822 motor. This type of Emax uses a "drum" motor mount that is also 28mm dia . Nno prop yet but this is what the nacelle, motor and spinner looks like. The motor has a prop adapter fitted inside the spinner. The motor wires run down inside the nacelle. Exactly how the nacelle will be fixed to the V173 foam body is a problem for another day. Just for fun I ran it up "in hand" on a 2s. https://www.youtube.com/watch?v=vB0EphC7iK0 Next problem is to fit the 3 blade props when they arrive from China.! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 8 Author Share Posted September 8 This is what the nacelle pf my V173 might look like with a scale 10x5 three blade installed. Printed in LW-PLA. It does look odd to have such a small diameter nacelle compared to the size of the prop. This would be the RH nacelle as on the V173 as the props rotated "outwards over the top". Motor cooling could be an issue on a lomg flight but I expect I might be on the third airframe before such a flight occurs.😄 Quote Link to comment Share on other sites More sharing options...
Robin Colbourne Posted September 8 Share Posted September 8 (edited) I'm looking forward to following this thread. I've been fascinated by the Vought V-173 & XF-5U since reading an article 'Flying Pancakes' in Speed & Power magazine in the 1970s. Some video of the V-173 here. An R/C XF5U I'm sure the much smaller than scale props lose some of the benefits of the design though. Edited September 8 by Robin Colbourne Quote Link to comment Share on other sites More sharing options...
Nick Cripps Posted September 8 Share Posted September 8 "Speed & power", that brings back some memories! 1 Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted September 8 Share Posted September 8 Great project Simon, following with interest. A pity the XF-5U became bogged down with engineering problems with no less than six gearboxes plus the two huge P & W radial engines buried within the wing. The decision to make the huge propellers have cyclic control like a helicopter added considerably to the delays. Might have made a great close air support aircraft on the basis of it’s projected wide speed range and performance. However, it lacked the simplicity and low wing loading of the V173, which flew so well. Lindbergh was enthusiastic about the V173 despite suffering an engine failure and having to land on a beach! 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 8 Author Share Posted September 8 The bit that puzzled me about the XF-5U was the lack of counter rotating props if this picture is to be believed. Although this may have been trial "mock up" as much appears incomplete. When the fully articulated blades were installed, note the much bigger prop hub, they were counter rotating. And outward rotating as Charles Zimmerman originally proposed. 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 10 Author Share Posted September 10 After a bit of testing it became clear that with the original concept motor cooling would likely become an issue so a slightly revised nacelle. The spinner is 26mm diameter comparted to the motor's 28mm so there is a 1mm annulus to force air into the motor. An air outlet is provided behind the motor With this arrangement the motor can be run at full power on a 2200mAh 2s for a minute without the motor or the drum mount getting too hot. I haven't measured the thrust but resisting the pull just holding the nacelle needs a really firm grip. I very much doubt full power will be needed for more than a few seconds and even then only when going "vertical" At least I have the stl files to create the other nacelle. Time to start designing the V173 body. Quote Link to comment Share on other sites More sharing options...
Robin Colbourne Posted September 10 Share Posted September 10 On 09/09/2024 at 00:25, Simon Chaddock said: The bit that puzzled me about the XF-5U was the lack of counter rotating props if this picture is to be believed. Although this may have been trial "mock up" as much appears incomplete. When the fully articulated blades were installed, note the much bigger prop hub, they were counter rotating. And outward rotating as Charles Zimmerman originally proposed. That prop on the right in the picture looks like it is on backwards. If you look at the blade root on the top right there is more projecting clockwise thabn anticlockwise, plus the lower right blade appears almost flat in the middle compared to the camber on the blades on the other side of the aircraft. Maybe it was a standard prop fitted just so there was something on that side for the photo? Quote Link to comment Share on other sites More sharing options...
J D 8 - Moderator Posted September 11 Share Posted September 11 I think you are correct in your thoughts about prop fitted for photo, seem to recall an Aeroplane Monthly article saying the same. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 13 Author Share Posted September 13 (edited) Starting to look at the V173 body I have run into a problem. With the 11x5 props at scale diameter the "pancake" is tiny with an area of just about 1 square foot. At this stage the best guestimate is it will weigh about 16oz giving a wing loading of 16oz/sqft. At such a figure a slow flyer it will not be! 😧 The problem is the 2822 motors are too powerful and heavy for such a small airframe and the props are no lightweights either. Each complete nacelle, motor and prop weighs 2.5 oz. Even 0n 2s the combined thrust will exceed its estimated weight. I want to keep scale diameter props so I am reluctant to simply make it bigger overall as with direct drive brushless motors the same problem is likely reappear. A smaller lighter motor but with the same kV and a lighter prop could be a possible solution. Even if I can get the all up down to say to 10oz it will still need that extreme ground angle to get a "slow" take off. We shall see. Edited September 13 by Simon Chaddock Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 16 Author Share Posted September 16 My chosen solution to the motor/prop weight problem is to use two 1300kV BR221 motors turning CW &CCW 11x3.8 SF props. They will be scale diameter but obviously only 2 blade. The motor and prop should weigh about 28g rather than 70g. With smaller OPTO 10A ESCs with a 2A UBEC and smaller battery 850mAh 2s I might stand a chance of getting the V173 close to 8oz (250g) all up. At that weight even with the much reduced power it will still have close to 1:1 thrust to weight. I just have to wait for the bits to be delivered. 😉 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 28 Author Share Posted September 28 After much trial and tribulation I have a video of BR2211 in a more or less scale nacelle for the V173. Nothing very exciting but it is a forward step. https://www.youtube.com/watch?v=LfEzKyLoh2g This BR2211 setup is just about half the weight of first nacelle, motor and 3 blade prop. It does look a bit odd to turn such a big prop direct drive from such a tiny motor. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 11 Author Share Posted October 11 This is all going rather slowly. After a bit more work on the scale drawings it became obvious that the nacelles had to be even smaller than the original 28mm diameter so were reduced to 26mm diam. This required the nacelles ,motor cooling ducts and spinner to be redesigned. All printed in LW-PLA so at 8g in total the "cost" of the filament was not significant even if the printing time was! To get an idea of how they might fit I built the leading edge of the V173 fuselage so the motors and prop could be test fitted. . There is an awful lot of prop! The leading edge is made of 3m, Depron with printed formers and acts as a box girder. The rear of the "pancake" fuselage will be more or less just a light weight structure to give the required aerodynamic shape and might end up tissue covered. A close up of the motor inlet and outlet cooling ducts. Each motor only draws 8A at full power so heating should not be too much of an issue. it should only need a 1000mAh 2s LiPo to run both motors. So far so good but then comes the disaster. The BR2211 I am using a=have a 1300kV which is amazing low for their tiny size. This means the windings are very fine to get the necessary turns in the available space. This in turn makes handling the lead out wires very delicate. Just a slight pull in the wrong direction and a winding wire breaks off from the lead out. Result is a scrap motor as it is virtually impossible to re solder. In the course of arranging the lead outs to pass inside the nacelles I have managed to do exactly the same on both motors. Neither work! 😡 New motors on order however as a precaution they will only be installed once and very carefully as almost the final operation when the rest of the plane is completed. 😉 3 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 17 Author Share Posted October 17 (edited) With the "duff" motors removed the rest of the "pancake" is built up. , A lightweight structure with LW-PLA ribs and 3mm Depron. It will be tissue covered. The rectangular box is where the battery (1000mAh 2s) is expected to go. A "stab" Rx will go in there as well. Next is to start work on the all moving elevons that stick out each side. The intent is to use a CF tube both as a spar and a torque rod extension so the servos can be buried in the fatter part of the wing. Edited October 17 by Simon Chaddock 8 Quote Link to comment Share on other sites More sharing options...
Futura57 Posted October 17 Share Posted October 17 Fine work Simon Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 20 Author Share Posted October 20 (edited) It now gets a bit more complicated. The "side" elevons made with 2mm Depron skins and their servos. There is an outer bearing adjacent to the elevon. The servo itself provides the inner bearing support. Although the V173 appeared to fly using just the side elevons I have my doubts despite the fact they are all moving surfaces that they will provide adequate pitch and roll control at this small size. My intent is to make the two part rear elevon (not yet built) work in conjunction with the side ones. Next will be the fins along with working out how a single central servo can move both rudders. Edited October 20 by Simon Chaddock 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 25 Author Share Posted October 25 (edited) The two part "tail" elevons added. They are LW-PLA printed items with temporary top tape hinges to check for positioning. Each of the side elevon rod connectors has an "arm" included so a link rod can be connected to the appropriate tail elevon. The whole set up will be connected as a "delta" controls. All the elevon linkage will be buried inside the wing. Still quite a long way to go! Edited October 25 by Simon Chaddock 2 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted Monday at 10:06 Author Share Posted Monday at 10:06 (edited) Still slowly creeping forward with the tail elevons connected to the side elevon servo. A short video of them all working together. https://www.youtube.com/watch?v=3I9Jk_bnkf4 So far it works but I suspect the surface movements will have to be significantly restricted. Still quite light as at this stage the airframe and control surfaces with two servos weigh just 59g. Next are the fins and rudders. Edited Monday at 10:11 by Simon Chaddock 4 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted Wednesday at 18:45 Author Share Posted Wednesday at 18:45 (edited) The fins & rudders are small, just 3mm Depron sheet with a this strip of carbon "tow" glued on each side to stiffen then up. The printed PLA hingers took far too long to get right! The fins in place. I just couldn't see a way to practically hide the linkage so it had to be simple but in the breeze with a central servo. Everything has to be arranged so anything "external" it can be temporarily removed to allow the "wing" to be tissue covered. The replacement motors will go on next, very carefully. I don't want any more brand new scrap motors with broken motor leads! Edited Wednesday at 18:46 by Simon Chaddock 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted yesterday at 13:14 Author Share Posted yesterday at 13:14 Can't put it off any longer the motors must be installed and assuming this process does not damage the motor lead to winding connection they can be tested. Each motor is wires up using 2mm bullets to a 10A ESC. Each ESC sits behind a duct open at the leading edge. This closely mimics the full size air cooling used for the 80hp flat 4s and includes scale top outlets to let the air out. Note how relatively huge the props are and the ridiculously tall undercarriage that will be required for prop ground clearance.😟 The final bit of "construction" will be the cockpit. This will be built on just before the tissue covering. 1 Quote Link to comment Share on other sites More sharing options...
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