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Author Topic: Newcomer to P30-advice sought.  (Read 1732 times)
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Kevin M
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« on: January 21, 2021, 09:31:03 AM »

I’m new to P30 and currently building my second. The first was an own-design drawn up after looking at many plans and photos. I made no particular effort to keep it light, I just wanted to get one in the air and develop a feel for it. At the time of building that one my wood stocks were low and I just used what I had. The results were pleasing in that it trimmed out easily and flew very well (the rubber was arranged in six strands) but it was heavy at 69g AUW, and although the cruise and glide were good the climb was soft.

Pleased by its flying qualities aerodynamically, I decided to do a second version, but this time trying to keep the weight lower. The trouble is I am failing to get it down to the minimum (UK) mass, so I’m seeking help from those on here who really know what they are doing with P30.

The pictures show where I am at; the uncovered components as you see them are:
Fuselage (not inc. prop) 13.4g
Wing 12.1g
Tailplane (tissue covered, no dope yet) 3.8g

That lot comes to nearly 30g. The prop shown (Igra) crashes down the scales at 7.7g.
Now we are at 37.7g. A Peck prop would save 2.2g but then I might need nose-weight to balance. Add the shaft, tissue, dope and D/T system and it is clear that I am going to miss the minimum mass target by some margin. It will be considerably lighter than the Mark 1, but I’d like to do better.

So where am I going wrong? Does the basic design have flaws? Is it mainly about wood selection? Any ideas would be most welcome.

The pictures show the Mk 1, then a few views of the Mk 2 in the hope that someone can identify some opportunities to slim it down.

Thanks,

Kevin
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Newcomer to P30-advice sought.
Newcomer to P30-advice sought.
Newcomer to P30-advice sought.
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billdennis747
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« Reply #1 on: January 21, 2021, 10:16:42 AM »

Kevin, your quoted weights indicate that you already have the all-important milligram balance.
I would be surprised if many P30s are down to 40g. Mine is about 45g, so I might aim for that. If yours is 59g empty, it's a lot. I once entered an experimental contest where the model had to have 10g ballast, and performance was leaden.The model looks fine - no excess material. It took me a long time to realise that I was using wood that was unnecessarily heavy. Have you noticed that you might pick a piece eg for longerons that seems right, only to find that when it is built, it is far too strong? If using 3/32sg for longerons, then 0.9g does for me.
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Kevin M
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« Reply #2 on: January 21, 2021, 11:07:40 AM »

Thank you Bill.

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Have you noticed that you might pick a piece eg for longerons that seems right, only to find that when it is built, it is far too strong?

Frequently, trying to be better at that.

This looks as though it might come out at somewhere between 45 and 50g without rubber, so it's better, but I've read about people having to ballast these. I'll keep at it.
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Kevin M
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« Reply #3 on: January 21, 2021, 11:27:55 AM »

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If using 3/32sq for longerons, then 0.9g does for me.

That's clearly part of the answer, the four sticks i chose were in the 1.3g-1.4g region. I did try to use lighter wood for the uprights and spacers.
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dosco
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« Reply #4 on: January 21, 2021, 11:51:05 AM »

Nice looking plane!

Am interested to learn how you whittle the mass down with your subsequent versions.

-Dave
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DerekMc
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« Reply #5 on: January 21, 2021, 12:11:11 PM »

A 45 to 50gm plane can be competitive with the right motor and prop.  I'd go for 6 strand of 1/8" or equivalent.  The long run P30's really need to be close to minimum weight.
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Derek
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« Reply #6 on: January 21, 2021, 12:17:30 PM »

I would scrutinize the sheeting areas.  I personally haven't seed a built-up p-30 using sheeting in the wing center section and certainly not in the stabilizer.  Also the nose, while a particular vulnerable area, I think you could still reduce the sheeting there by half.  Go with the lightest prop and don't initially worry about the overall weight distribution of the fuselage until all of the components are complete.  Finally position the wing where it needs to be to get the best CG so that you don't have to add ballast.

Marlin
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gman
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« Reply #7 on: January 21, 2021, 12:24:03 PM »

Hi Kevin, I agree with everything Strat-o has just said. There's too much balsa about. How's your Mylar covering? Several grams to be saved over tissue.
Gavin
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Red Buzzard
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« Reply #8 on: January 21, 2021, 12:29:04 PM »

Hi Kevin,

Strat-o just took some of the words out of my mouth. I agree with his "sheet" suggestions and would also look at your tail end in general. Do you really need that slab in the sub-rudder? What about your rudder's anchors to the fuselage and stab platform? But what strikes me is you have done a beautiful job on your nose block, but some of that grace and beauty may not get you to the finish line. You can limit your nose block to a couple of pieces of balsa with a ply backer and Peck nose button if you get right down to it. As Derek suggests, though, you also need something there to complete all five flights on a windy day when you are going to get swept across the field or tumbled upon landing. There's too heavy, just right, and too fragile. The balance is beautiful and 45g. is survivable.

Bill
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Kevin M
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« Reply #9 on: January 21, 2021, 12:31:03 PM »

Thanks very much for the replies, don't know how I'd get on without the resource of this forum.

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I'd go for 6 strand of 1/8" or equivalent.

That's what I will do.

Quote
I would scrutinize the sheeting areas.  I personally haven't seed a built-up p-30 using sheeting in the wing center section and certainly not in the stabilizer.  Also the nose, while a particular vulnerable area, I think you could still reduce the sheeting there by half.  Go with the lightest prop and don't initially worry about the overall weight distribution of the fuselage until all of the components are complete.  Finally position the wing where it needs to be to get the best CG so that you don't have to add ballast.

I'll follow all that advice, thanks. The sheeting is all low density, about 1/20" over the wing c/s and 1/32" over the tail, but I agree, most of it doesn't need to be there at all.

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Am interested to learn how you whittle the mass down with your subsequent versions.

Well I'll keep posting my efforts. I like building, and I'm quite prepared to keep on building more variants until I get somewhere near.
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Kevin M
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« Reply #10 on: January 21, 2021, 12:33:25 PM »

Gosh, good advice coming thick and fast, and all suggestions I will follow. Thank you all.
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Kevin M
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« Reply #11 on: January 21, 2021, 12:36:47 PM »

Gavin - I have hardly used Mylar before, and then under tissue, but I'm very prepared to try new things. Perhaps on the Mk 3.
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DerekMc
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« Reply #12 on: January 21, 2021, 12:37:16 PM »

What kind of DT are you using?  It looks like stab only?  If so, be prepared to lose it in a thermal.  P30's love to fly and are hard to get out of thermals. A combination of wing and stab DT or pop off wing are the most effective.  Something to think about as you build lighter.  Smiley
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Kevin M
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« Reply #13 on: January 21, 2021, 12:48:02 PM »

Derek, as drawn this has pop-up stab, but I have been seriously considering pop-off wing, and may well do that on the next one. I found the CB design notes on the pop-off wing for the Boomer on the internet and should be able to adapt it for this.
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DerekMc
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« Reply #14 on: January 21, 2021, 12:52:29 PM »

Good. The pop off wing is what I use.  The first time you see it in action is wild. It looks like the plane falls apart.  Don't forget a swivel in the line! 
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Kevin M
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« Reply #15 on: January 21, 2021, 12:58:24 PM »

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The first time you see it in action is wild.

Never seen it in action. Do you have any links to video clips of it working?
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DerekMc
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« Reply #16 on: January 21, 2021, 01:10:06 PM »

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The first time you see it in action is wild.

Never seen it in action. Do you have any links to video clips of it working?

No. The plane is usually far away when it happens!
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« Reply #17 on: January 21, 2021, 01:13:22 PM »

Kevin –

Nine replies were posted while I was writing my reply so some of what follows may be redundant.

Your two P-30s look very nice. I see good designs and excellent craftsmanship.

It is difficult to build a P-30 that is reasonably strong and under the 40-gram weight limit in the U.S. rules.  I have done this and the models carry a tiny amount of ballast to bring them slightly over that limit to make them legal.
Unless you are going to use the long motor run approach (4 x 1/8 or 6 x 3/32) a 45-gram P-30 will be very competitive.  A 40-gram P-30 with a long motor run will not perform well unless the conditions are very calm. In the UK, I would think you would need a heavier, studier P-30 with a rapid climb, which takes a 6 x 1/8 rubber motor.

If the 3/32 x 3/32 sticks you cite that weigh 1.3 – 1.4 grams were 36-inches in length, John Barker’s chart indicates that they are 16# and over. That is way too heavy. I would use 0.83 – 1.00-gram sticks for the longerons, at the very most. That translates to 10 – 12# wood.

The uprights and cross-pieces can be lighter 3/32 sticks, e. g. 6 – 8#.

The wing tips on your P-30s could be slimmed down.  You don’t need double ribs at the dihedral breaks.

You may be able to eliminate the sub-fin. Look for a Dutch roll. If that appears, substitute a sheet fin made of light 1/16 sheet balsa with the grain oriented diagonally.  Make the fin the standard size, e. g. by copying the fin of the Majestyk P-30 for example.

The sheeting at the nose can be 1/16 instead of 3/32.

The nose block of your P-30 designs is a bit thick. Use a 9 ½-inch Gizmo Geezer prop assembly, not to save weight, but to enable precise and easy thrust line adjustments and have reliable free-wheeling.
Just as strat-o says, adjust the longitudinal position of the wing to get the CG at the optimum location. Don’t use ballast to set the CG where you want it.
Don’t forget to use a DT or else you won’t have the model very long.

If you want to build a 40-gram P-30 you should use a weight budget and be careful with wood selection.

It is easier to build a strong P-30 to the minimum weight if you use some carbon-fiber spars and/or rib caps and a rolled motor tube. Mylar covering also helps, as it is lighter than tissue. All this is not necessary to win most P-30 contests. Your P-30 at 45 grams can easily win with proper trim and winding.

Attached are pictures of two P-30 models that I built which are each under 40 grams. The one on the left with the green prop has the motor peg under the stab since it uses a 6 x 3/32 rubber motor.  The one on the right has the motor peg ahead of the stab so that it can use a 10 x 1/16 rubber motor. Each has a carbon fiber main spar in the wing. Both of these lightweight P-30 models have a pop-up wing and pop-up stab DT.  A DT which only pops up the stab is too risky when the model is at or near the 40-gram minimum.

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Re: Newcomer to P30-advice sought.
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PeeTee
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« Reply #18 on: January 21, 2021, 01:13:47 PM »

Kevin

Bear in mind that the pop-off wing is being advised by our US chums and they do not fly in such a windy little island as us. I haven't flown P30 for nearly 5 years (haven't flown anything sadly) but Gavin & Don have and they are better able to advise you. As regards props, I recommend trying the Orange props, they have a slightly higher pitch and I converted all my P30s to that type.

Peter
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DerekMc
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« Reply #19 on: January 21, 2021, 01:21:55 PM »

Kevin

Bear in mind that the pop-off wing is being advised by our US chums and they do not fly in such a windy little island as us.

Peter

Interesting comment. I've flown at the contest wind limit many times with my pop off wing P30 and regular type DT's.  I've chased tumbling airplanes and picked up the parts.  The pop off wing p30 doesn't tumble as much.    It is harder to get out of a tree due to the lanyard so if it leaves the field you could be in trouble.  Balance that with the speed of descent after dt.
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Kevin M
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« Reply #20 on: January 21, 2021, 01:35:41 PM »

Calgoddard, thanks very much for your thought-provoking and comprehensive reply. All of what you say sounds very sensible and I will try to follow your advice.

PeeTee, Orange props? New to me, where do I get them? Interesting thoughts about UK vs. US conditions, and Dereks comments. I'm keen to try it though.

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Kevin M
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« Reply #21 on: January 21, 2021, 01:38:51 PM »

PS Calgoddard, beautiful models in your pics. Are those the Gizmogeezer props? The blades look quite Peck-like.
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Indoorflyer
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« Reply #22 on: January 21, 2021, 01:55:00 PM »

what kind of glue are you using?
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DerekMc
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« Reply #23 on: January 21, 2021, 01:56:29 PM »

Volare Products is a US based source for the orange Chinese props.  I just ordered a few for a bit of testing.

https://volareproducts.com/blog/?product=12-chinese-prop
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Kevin M
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« Reply #24 on: January 21, 2021, 02:02:26 PM »

Indoorflyer, I'm using aliphatic, trying to be frugal with it by applying with a cocktail stick and wiping away any excess.

Derek, thanks, I'll check their website.
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