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 on: Today at 12:45:56 PM 
Started by Jack Plane - Last post by Jack Plane
Picked up a lovely little Brown A-23 recently, never been used in a model.  I lightly oiled it and it ran beautifully for a couple of gas charges.  But when I tried a brief liquid charge, the valve in the filler-nozzle failed as soon as I withdrew the bottle and the pressure blew straight out!  All subsequent gas charges now also blow.

Having looked at an older thread on exactly the same issue, it appears that the valve in the Brown nozzle is some sort of tiny cone of unknown material, maybe some type of rubber?  Something light brown in colour can sometimes just be glimpsed below the pin which spans the threaded inside of the aluminium nozzle-part, but I haven't yet summoned the courage to try to drift the tiny soft aluminium pin out.

I assume that, once I've removed the pin, I'll find a shrivelled or fractured cone, which will need replacing with something to hand.  (In fact 'shrivelled' makes sense, as I presume the factory-fitted cone would have been big and firm enough to seat correctly and not rotate or jam.)

Then I'll need to replace it with something to hand.  I assume a steel ball-bearing isn't suitable (might distort the aluminium?), but what about the  black rubber ball-valves supplied in the spares packet of most Gasparin motors?

Or any other suggestions?

 on: Today at 12:40:05 PM 
Started by pedwards2932 - Last post by pedwards2932
They have lot of materials - PLA - Nylon - ABS - Nylon Polyamide With Chopped Carbon Fiber Strands and they vary in strength and properties.  I saw a demo that they used different filaments and there was a big difference in strengths.  I am using PLA for my experiments and it seems strong enough....my blade is .4 mm thick so I may need to thicken it a bit not sure at this point till I do some testing.  I like the lofting idea because I can easily make it thicker at the hub.  It doesn't matter as much with my 3 piece design.  The flexibility of the blade seems comparable to a commercial prop.

 on: Today at 12:22:15 PM 
Started by pedwards2932 - Last post by ironmike
So if I understand correctly in viewing your xample
the viewed twist is near the hub but the viewed twist
disappears from about 1/2 rad out toward the tip.
Notwithstanding the math involved.

 on: Today at 12:19:45 PM 
Started by abl - Last post by Jack Plane

... upper wing structure weighs 0.66 gram and the lower is 0.35 gram.

Excellent weight... long may the lightness continue!  Grin

 on: Today at 12:18:30 PM 
Started by pedwards2932 - Last post by Crabby
Good am Paul, The one thing that has mystified me about 3D printing is the material the printer is printing with. The typical complaint I have read from several guys is that the material seems brittle, which fair enough, is a bug that will be worked out by pioneers like yourself. How many different 3D printing solutions are available and what are the properties? Have you ever printed an item that doesn't snap or chip under stressful or traumatic conditions?

 on: Today at 12:09:20 PM 
Started by ironmike - Last post by ironmike
Thanks guys for the nice comments
This homely, knockkneed broad took on a unique charm
as I got more into her. But then again I have always loved
the Grumman prop jobs.

Before George sold Sams I would sell him laser cuts, prints and canopies.
He would turn them into full blown kits and offer them as Aerographics.
In that fashion shipping to the UK was spread out over a lot of product.
Now when I get an order for a single short kit from UK ship cost is around $20
just to get it there let alone the VAT your rulers add on.
So currently no supplier in the UK.

 on: Today at 12:03:31 PM 
Started by abl - Last post by Crabby
I think the wing incidence fix has worked and if an Andreason kit can be built much lighter than I've managed, it should fly really well.

Funny Andy you just about quoted word for word something my Olde Man said 30(?) years ago. A light Andreason was a goal he never achieved to his satisfaction. I have built several but they were kinda porky.

 on: Today at 11:59:02 AM 
Started by abl - Last post by Crabby
Good one Andy you managed to knock off almost 50% of your wing weight! I have a Mooney SRE that weighs 17.5 it came out really well for a porker! All is well, I happen to prefer porkers!

 on: Today at 11:33:36 AM 
Started by tonyshepherd - Last post by PaulBrad
Tony - I am joining this thread way late. I built the E36 Starduster from BMJR Model Products. It is a nice kit but builds a very heavy model. Mine is powered with the RedMax motor from Texas Timers turning a Graupner 7x4.5 folder. It is way over powered. The motor and prop pulls the heavy model up very fast, but being over powered it never did get full trimmed. It finally met its end due to a bad launch on my part. I have attached a few photos of my model for your reference.

If you are planning to fly in E36 competition, I would suggest a design other than the Starduster. The Pearl design is easier to build light, and is a terrific performer. Also, listen carefully to Dan Berry. He has tons of experience and is a regular winner here in the States.

Paul Bradley

 on: Today at 11:30:25 AM 
Started by ironmike - Last post by Crabby
Mike, great job and you have a unique ability to apply your typical rakish appeal to your airplanes. They look like tough broads ready for a tumble instead of dainty dandies ready for a showcase. The markings look nicely under-stated instead of over-done eye make up!...oh well you get the picture! get out there and break some stringers!

 on: Today at 11:06:32 AM 
Started by pedwards2932 - Last post by PaulBrad
If you do get around to building your "dynamometer", remember that testing a prop in a static condition does not always give the best results. It will certainly let you see how your 3D printed prop compares to a commercial prop also in static conditions, but may not tell you if your 3D printed prop will perform better in flight. That is the reason I am using a swing arm so the prop is moving through the air. The factors I wanted to evaluate are motor run time and acceleration. Those are the factors that seemed to me to be the factors that would define the performance of a model in real world conditions. Developing a test that can give you meaningful data for making design decisions is always a challenge. So far I have been pleased that the results I have obtained with my swing arm test rig have been confirmed with the models.

One other caution. Testing can become addictive when searching for the best prop ever. Don't let your testing take you away from building Smiley.

Paul Bradley

 on: Today at 10:50:22 AM 
Started by pedwards2932 - Last post by pedwards2932
Really interesting.....I played with Curveloft in Sketchup and I was able to loft a test and it seems to work pretty good.  If anyone is interested then I can do a tutorial on how to loft using Sketchup as well as how to use a bucket to make a prop blade.

I like that you are testing your designs.  I want to design a "dynamometer" using a digital scale so I can see how the props compare with commercial props.  I know all this is all over kill but it keeps my mind busy.

 on: Today at 10:30:26 AM 
Started by abl - Last post by abl
Haven't managed to get a huge amount done over the last four days but the wings are now (just about) structurally complete.

The upper wing structure weighs 0.66 gram and the lower is 0.35 gram. There'll be a little extra for strut reinforcement and small fairings on the lower wing root, but just over a gram for both is perfectly acceptable; the original (now discarded) top wing was about 1.25 grams.

Planning to do the fin & stabiliser next. The fin will have a movable rudder because it's so useful, might also consider moveable elevators although they might not be strictly necessary. However, there's an extra static mark to be gained if the elevators are separate (1/2 point for each elevator)...

 on: Today at 10:28:17 AM 
Started by DerekMc - Last post by Jon S
Just heard back that this plan in not available in electronic form, only printed, for those who were hoping for a download.


 on: Today at 10:01:36 AM 
Started by pedwards2932 - Last post by PaulBrad
Mike- You can't really see a difference in a helical pitch prop and one with hypotwist. The hypotwist prop basically has the tips washed in. The pitch increases from a defined point on the prop radius in a linear fashion out to the tip. To pick up the prop and look at it everything looks just like any other prop. Where you see the difference is in flying performance.

To be sure I was seeing a real performance difference I printed a true helical pitch prop with a P/D of 1.5. I flew that prop and noted the overall performance of the model and the motor run time. I replaced the prop with one of the same diameter and blade profile that had the hypotwist pitch distribution. That prop had a P/D of 1.2 out to the 75% radius point. The P/D then increased linearly to 1.8 at the tip. The motor run time was the same as the helical pitch prop, but the model had a noticeably improved initial acceleration. The model climbed higher with the hypotwist prop and overall performed better. Those flights were made in no lift conditions.

I also made myself a swing arm test rig for testing the props. This allows the props to "fly" to better approximate real world conditions. I saw the same early prop acceleration results on the test rig as were observed with the test model. With the test rig I measured motor run time and the time required for each revolution. You could easily see the lap times for the hypotwist prop were quicker in the early laps compared to the helical twist  prop. It was the test rig that lead me to the hypotwist pitch to diameter ratios of 1.2 to 1.8. I did not want to spend forever printing and testing props so I did not evaluate where to locate the point on the prop radius where the P/D value should start changing. I just went with the value presented in Bruce Holbrook's article.

Paul Bradley

 on: Today at 09:48:00 AM 
Started by Pete Fardell - Last post by Work In Progress
Presumably a safety feature. Wire cutter?

Exactly that, for telephone or overhead power lines.

 on: Today at 08:19:43 AM 
Started by ironmike - Last post by billdennis747
It looks great, Mike and I like the scheme.
I see the short kit is now on your site. Do you have a UK supplier?

 on: Today at 05:22:41 AM 
Started by ironmike - Last post by cast_off_vortex
Far from a plain Jane there - I think the printed tissue really came out great.  Cool

I am a fan of Grumman aircraft, and USN aircraft bearing postwar/Korean War era US Navy color schemes, and frankly you nailed it. I don't think it could have come out better without adding weight (paint). Really good job on the canopy and framing too. Best of luck with the trimming and flying.

 on: Today at 12:42:58 AM 
Started by marcelop - Last post by OZPAF
Nice work Marcelo.


 on: Today at 12:21:53 AM 
Started by ironmike - Last post by OZPAF
Thanks Mike.


 on: Today at 12:08:45 AM 
Started by pedwards2932 - Last post by ironmike
Hi Paul

I'm intrigued

can you show us in close ups and views what hypo twisted looks like

Mike Midkiff

 on: November 22, 2017, 11:43:36 PM 
Started by pedwards2932 - Last post by pedwards2932
I have a Anet A8 I got it from Banggood cost about $170.00 (so they really are getting affordable) spent a lot of time printing improvements when I got it.  I am still learning about the printing part of it.  I added a pic of the hub design.  I am still trying to get the fit right....printers aren't always perfectly accurate so you have to either sand or compensate.  Not sure how well this hub design will work.  I need to build an alignment/pitch jig, which is my next project

 on: November 22, 2017, 10:48:24 PM 
Started by tonyshepherd - Last post by danberry
Curious about your comments on the 1/2A Viking model.  Currently building one to be powered by a new Holland Hornet. I'm not a serious competitor, more of a serious sport flyer.  Never could afford this model when it came out but now I'm older and richer.  It was NFFS Model of the Year back in 2011 so I figured it wouldn't be a bad project.  Comments please!

The 1/2A Viking turned more 15 yr old boys away from Free Flight than pretty girls did.
It wasn't MOY in 2011, it was the One-Design plane sponsored by Bill Vanderbeek.
If you're gonna fly it -- be ready to repair it.
It will fly right or left under power. Whatever it does on the first launch is what you want to continue with.
The Holland Hornet crankshaft is just a time bomb.
Good luck.

 on: November 22, 2017, 10:40:10 PM 
Started by tonyshepherd - Last post by flydean1
Watch the Holland Hornet.  Weakish crankshaft.

 on: November 22, 2017, 09:33:30 PM 
Started by pedwards2932 - Last post by frash

Your first illustration shows a prop that resembles the 5.5-in, 6-in, and 7-in build your own prop kits that are available from RetroRC in the US. We used a 5.5-in prop for Science Olympiad in the local middle school last spring and a 6-in prop for my Bostonian. Both were from a 5.5-in RetroRC kit and worked well. I still have two other kits and each kit makes 5 props so I will not need to order soon. I could not tell exactly where the hub-to-blade joint occurs in your design. For RetroRC system, the blade is molded from 0.010-in to 0.015-in white polystyrene sheet. Molding uses heat from hot tea or coffee or water. Microwave also works. For the RetroRC system, the blade is glued into a laser-cut slot in a plywood stub which is inserted into an Al hub tube. (Please note that I did not attempt to spell Al properly! <Grin>) 


You recommendation of ABS and of orienting the prop face down for printing were not obvious to me and may prove useful if I ever get into 3D printed props.

Fred Rash

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