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Author Topic: VP for pennyplane?  (Read 1590 times)
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Flyguy
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« Reply #75 on: June 12, 2022, 04:35:49 PM »

Thank you. Actually, I found your diagram earlier, and I saw that the carbon driver is .017 thick, pretty much the same as the .4mm (.016"). Interesting that it looks like you put a little reinforcer on the bottom, so maybe I should use .6mm. What I don't see is the width of the carbon driver, maybe I'm just missing it?
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Olbill
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« Reply #76 on: June 13, 2022, 09:49:04 AM »

You didn't miss it. I did.
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Flyguy
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« Reply #77 on: June 13, 2022, 10:48:06 AM »

OK, I'd guess it must be around 2mm wide, 3mm seems like too much and I thought 1mm was not enough for .020 wire. I think I'll order some .6mm x 2mm carbon strip, seems like that should do it.
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Flyguy
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« Reply #78 on: June 17, 2022, 04:04:18 PM »

Some updates - I bought some more carbon fiber strip, .4mm, .6mm, and .8mm thick. The .4mm strip, 2mm wide, seems pretty darn strong so I just used that, the 2mm width gave me plenty of room to drill the holes. I also noticed that all the PP dual bearings I have are all for .015 wire, so I'm going with that. Bending the driver with the .015 wire was not a problem, a shot of that with the driver bound and glued shown below. I have some .013 wire I'll probably use for the spring, curious to see how much this weighs so I should have it finished by the weekend.
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Olbill
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« Reply #79 on: June 18, 2022, 12:46:36 AM »

Here's the Sportline pedometer at Amazon.
https://www.amazon.com/Sportline-SP2795BK-340-Strider-Pedometer/dp/B0006VWRX6/ref=sr_1_3?crid=3OMWITIK6W5SM&keywords=sportline+pedometer&qid=1655526495&sprefix=sportline%2Caps%2C109&sr=8-3

Reed switch I used the last time I did a counter.
https://www.amazon.com/Cylewet-Normally-Magnetic-Induction-Electromagnetic/dp/B01NBPDU04/ref=sr_1_2?keywords=Cylewet+10Pcs+Reed+Switch+Normally+Open+%28N%2FO%29&qid=1655526925&s=industrial&sr=1-2

These switches are very easy to break. I glued mine to the side of the winder before I connected it to the pedometer.
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Flyguy
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« Reply #80 on: June 18, 2022, 09:26:52 AM »

Thanks Bill, that's very useful info, I have some old 20:1 winders that I'll probably modify with the pedometer. I don't have a 10:1 winder, so I bought the Johnson (Geauga) 10:1 winder from IFFS, it's really nice. I also ordered the counter that Don mentioned above, looking forward to getting it, I'll post some pictures when I get it.

Working on getting the prop done. I like to build a frame that has the pitch in it, makes it easy to cover. I usually build the frame right on top of the prop block, first pic shows it completed with the prop block behind it, second pic shows that you can then just plop the prop right down on the frame with covering without having to do anything else.
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Flyguy
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« Reply #81 on: June 18, 2022, 11:48:36 AM »

Dammit there's always something you don't think of! The problem is that with the wider (2mm) carbon driver there's less room for it to move in the screw holder, duh. I used some screw holders that I made earlier and the distance between the legs is 4mm. Quick solution was to file the driver thinner were it is between the screws, photo below, that seemed to work OK. However, I'm wondering if maybe I should make a new screw holder with more distance between the legs? What distances do people use for PP or F1M (Bill, do you know what it is in your diagram?). Any help appreciated. It's always something!
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Flyguy
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« Reply #82 on: June 18, 2022, 01:57:23 PM »

I had an aha moment when my friend Tom pointed me to Aki's diagram of his F1M hub, I see his driver bar is 20mm long whereas mine is about 12mm. So, with the longer driver, you'll get more throw and I can then probably use the current size screw holders that I have. So I'll make another one with a longer drive arm and see how it compares to the one where I filed the arm.
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Olbill
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« Reply #83 on: June 18, 2022, 01:59:44 PM »

The dimensions of the screw holder in my drawing are incorrect. Figuring out all the correct ones requires another trip to the basement which I don't have the energy for right now.

The overall dimension of the screw holder is .476" based on what I measured today and the space between the legs is .270".

The driver arm measures .115" in the middle and .097" where the holes are at the ends.

I took a bunch of pictures. If any of them are good I'll post in my next reply.
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Flyguy
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« Reply #84 on: June 18, 2022, 02:19:52 PM »

Wow, you're spacing between the legs is larger, .27" is about 6.9 mm, compared to 4mm, and your arm tapers from about 3mm to about 2.5mm, so it's a wider driver, that's why you have more spacing between the legs. That is very informative, thanks for the data, so much to think about! Yes, post the pictures if you can, that would be helpful.

I have another 4mm-wide screw holder sitting around, so I think I'll try a longer driver arm (20mm like Aki) and see what that does pitch-change wise with a (not filed) 2mm driver arm. Then I can compare that to the one where I filed the driver arm (and I don't have to make a new screw holder). I haven't even built the plane yet and I already have two VP hubs to try, though I'd rather have 1 hub that I knew was the right approach!
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Olbill
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« Reply #85 on: June 18, 2022, 02:25:33 PM »

VP photos. This hub has gotten a little beat up in the years it was in use including the blades getting destroyed at some point.

For my style of VP usage I needed a really wide range of pitch. My last F1M plans show a high pitch of 120 for Cat 1.
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Flyguy
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« Reply #86 on: June 18, 2022, 03:02:42 PM »

That's a nice-looking hub! You've convinced me to make a new set of screw holders (not a fun task) with more distance between the legs, probably 7-8mm, it certainly doesn't hurt, you can always put the screws in a bit. Have to get the rohacell sheet from the basement, arrgh. And I think I'll also use a longer driver arm, like 20mm, that combo should give me quite a bit of throw.

For my style of VP usage I needed a really wide range of pitch. My last F1M plans show a high pitch of 120 for Cat 1.

Holy cow, HP of 120?! I'm interested in Cat 1 flying because that's basically the flying situation in the armory. I know with my F1R that if I overdue the high pitch, then it will either 1)go down a bit until it burns off the torque, which I guess could be a flying strategy, or 2) if it's too much, it flounders around and dives. So I have to limit the high pitch.

F1M probably flies different, but I know on one of your plans it was 26 LP to 65 HP. At 120 the blades must be getting close to 90 degrees! I'm curious as to what happens at that super high pitch?
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Olbill
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« Reply #87 on: June 18, 2022, 04:17:16 PM »

Yes the blades are almost parallel to the motor stick. What makes them work is having 2 degrees of washout in the tips. So the tips are still producing thrust when the rest of the prop is stalled. The model will just maintain level flight at the beginning of the flight but the pitch is immediately changing as soon as the model is released and it continues to change until roughly maximum altitude is reached. At that point I want the prop to be at low pitch and working the best it can.

I think most people use the "two climb" approach where the model climbs, comes down a ways and then starts a second climb. I don't know which way is theoretically better.
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Flyguy
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« Reply #88 on: June 18, 2022, 07:32:16 PM »

Yes the blades are almost parallel to the motor stick. What makes them work is having 2 degrees of washout in the tips. So the tips are still producing thrust when the rest of the prop is stalled. The model will just maintain level flight at the beginning of the flight but the pitch is immediately changing as soon as the model is released and it continues to change until roughly maximum altitude is reached. At that point I want the prop to be at low pitch and working the best it can.

I think most people use the "two climb" approach where the model climbs, comes down a ways and then starts a second climb. I don't know which way is theoretically better.

I see, I think I'll give that a try. I know IFFS has a 28-26 pitch propform and I think that means that it goes down to 26 at the tips, which is washout. I can then compare it to the one I already made (on 28 p block). So back to the drawing board (and another order) - I'll get to work on the new prop and new VP hub.

I've wondered about the two climb approach as well. I have highly limited experience with VP right now (5 sessions with my F1L VP, 5 different sessions with my F1R VP) but I think my F1R has been flying the way you describe yours - it starts in HP, slowly comes down during the climb, then gets closer to low pitch shortly after it goes into the cruise phase, so I haven't seen two climbs, it's more like a really long cruise. It did 17:06 second time out, staying below 32', which is good for me (best fixed pitch time was 14:13). But I've been thinking of trying the 'a little later' approach so that you get the two climbs, probably would take a second thread of discussion to figure out what might be best, if either!

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Olbill
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« Reply #89 on: June 19, 2022, 09:37:24 AM »

That will be interesting.
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Flyguy
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« Reply #90 on: June 19, 2022, 07:30:22 PM »

I'll report when I get some flying results, but that won't be until the Fall.

I made two new larger screw drivers today, the one on the left is the usual rohacell with carbon fiber, soaked in a little CA, space between the legs is 7mm, weight is 70mg. Nice part about that approach is that I made a strip, so I can probably slice off at least 15 screw holders from that.

I thought I'd try something new so the one on the right is two pieces of laminated 1/20" bass strips that I wrapped around a 1/4" tube, I put a little balsa where it will mount, made the screw holes and hit it with some CA, weight is 46 mg, space between the legs is 6.5mm. The difference in weight shouldn't matter for PP, so I'll try them both, I think the bass one will work, took the screw holes well, but we'll see.
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« Reply #91 on: June 21, 2022, 08:09:14 AM »

Finished the re-designed PP VP hub, photos below. Driver arm is .4mm x 2 mm by 20 mm long, spacing between screw holder legs is 7mm, has tons of throw, should be more than enough, the screws will now come in handy! Came out to exactly 300mg, right on target, so I'm pretty happy with this hub. With the prop blades, total is 622mg, so I'm guessing it should be around 650 mg when covered, which seems good given that I was shooting for 600-800mg. I just use a drop of thinned ambroid on the wire and a small teflon washer to hold it on (red in the picture), I hope that's enough for such a large motor? I love how big these PP props are, looking forward to giving it a try!
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Olbill
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« Reply #92 on: June 21, 2022, 09:58:34 AM »

That looks great!
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Flyguy
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« Reply #93 on: June 21, 2022, 12:53:04 PM »

Thanks Bill, you were enormously helpful, as was Don, Aki, and others, saved me a lot of time, this forum is great! I'm making a second VP hub now so that I'll have two props to test in the Fall, the second with washout in the tips, very curious to try them out.

I finalized the design. I went back to the wide chord design, which is what attracted me to PP in the first place, and I agree with Don that that might have superior performance in a low-ceiling site, so my wing has an 8" chord. I already knew what the problem would be from earlier experience calculating a constant margin of stability (cmos) - when I tried different high aspect ratio wings for A6, the rear wing post location kept moving up as the wing got narrower and longer until finally the front post would actually be a little in front of the dual bearing. Similarly, when I experimented with really wide chord ministicks, I noticed that the wider the wing, the further back the rear post.

I started with dimensions from Jaeck's PP, which also has an 8" chord. As I expected, cmos specifies that the rear wing post is pretty far back, close to where the rear hook is (at 10"), that might be why they are tricky to trim, because the post is actually about an inch in front of that location. Best way to counter that problem and move the rear post forward a bit is to lengthen the tail boom, that's probably why F1Ms have really long tail booms. But given that you can't do that with PP, the only other way to move the rear post forward is to increase the stab size. So, I'm using a 5 x 18 stab, same size as a LPP wing! That brings the rear post up to about 9 inches, so it should be close to having a 10% margin of stability.
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« Reply #94 on: June 21, 2022, 01:01:50 PM »

One more PP VP.
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Flyguy
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« Reply #95 on: June 21, 2022, 02:27:07 PM »

Beautiful hub Tom. I see you did something that I've been thinking about - put the pivoting wire in the middle of the spar so that the rotation is true-er. I'll think about doing that on the next version, thanks for the photos!
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Tapio Linkosalo
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« Reply #96 on: June 22, 2022, 12:58:09 AM »

Here are a couple of pictures of my new hub for F1M. It follows the same construction that I use for F1D, but with larger dimensions. The hub is made of carbon parts laminated in 3D-printed molds, in addition to some parts of pultruded carbon rods, hypodermic tubing, piano wire and nylon bolts. The idea of molding the parts is to make the hub as square as possible, so that pitch change would be equal on both blades. I use the long pultruded rods in the hub to bring the pivot points as far apart as possible - my idea is that it reduces surface pressure and thus reduces binding, making the hub as smooth as possible. Unfortunately it also adds weight, the hub weights 390mg as is. Still light enough to build the model to minimum weight. You may also note that the spring has quite a few turns. I'm trying to adjust my models for Super Sport rubber (tired of old Tan II breaking all the time). The Sport rubber has flatter torque curve and thus my old VP's don't work with it, but I need much softer springs for the hub. Note also the solid fork for adjustments screws. I have found that a sandwich of carbon and foam sometimes delaminates and breaks, this solid construction is firmer. 

First picture is the finished hub (no blades built yet), and the second one is screen capture from the 3D model of the hub. Inverting the parts of the latter makes the 3D prints for molding the components.
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Flyguy
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« Reply #97 on: June 22, 2022, 04:08:42 PM »

Nice looking hub Tapio!

Unfortunately it also adds weight, the hub weights 390mg as is. Still light enough to build the model to minimum weight.

This is exactly what makes Pennyplane (and F1m) attractive - weight isn't an issue so you can do a full VP hub and use high and low pitch screws. I started my VP venture with an F1L VP, the first one had a screw holder, first photo, which is nice because it gives you precise adjustment, but it weighed 140mg which is just too heavy for F1L. I have an old J&H F1R VP hub which gets rid of the screw holder and just uses balsa for the spring, so I used that approach for the second F1L hub, second photo, which got it down to 104 mg, a little more reasonable (but still kind of heavy for F1L).

After that, I turned to the F1R, which was the real goal since VP is legal for F1R. I used the same approach with smaller tubing and wire, photos 3 and 4. That came out to 70 mg, not too bad. I also refurbished my old J&H hub - I probably put something heavy on it so the driver arm had to be replaced, I also added a little extra glue to the tubing joint, and that came out at 54 mg, very good! However, that uses .008 wire and I used .009 for the hook because I've had .008 unbend. I might be able to get my hub down a little from 70 mg when I make a new one next Fall.

So now the PP hub seems huge and I enjoyed making both the hub and the blades, some big lumber so it's fun, I admit the F1R can be a little more stressful, though I really like flying it - one flinch and it's over! Also, you have to keep everything small for the F1R to keep the weight down, so you can't do much with the hub, but for PP this isn't an issue. Looking forward to flying with the PP hub.  Smiley
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Olbill
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« Reply #98 on: June 23, 2022, 12:36:38 AM »

Just out of curiosity why were you using a VP on an F1L? Was this just for fun?
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« Reply #99 on: June 23, 2022, 10:43:09 AM »

It was for learning. Everything with the F1R is very small and delicate, so I wanted my first VP hub to be on something a little bigger and easier to work with, like the F1L's I've been flying for a while. It's also pretty relaxing to fly the F1L (the sturdiness thing), so it seemed like a good place to start to learn something about trimming with a VP. But I certainly wouldn't recommend VP for F1L - it's illegal and I also think the wing loading is too high to justify the extra weight, however for fun purposes it did seem to add a few minutes to the flight times. Once I had some experience with the F1L VP, it was easier to shrink everything down for the F1R and I also had some idea of what I was doing at that point!

I've only gotten out a few times with the F1R VP, but I've already raised my best time by over 3 minutes and I don't even have it fully adjusted yet, so this is encouraging. Now I've become a fan of the VP because with low ceilings you really need something to keep you out of the girders and extend the cruise (or two climbs). So then I started checking to see what other indoor planes you can legally fly with VP, and that led to this penny plane thread!
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