Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin (Account/Technical Issues)  |  Contact Global Moderator
July 26, 2021, 01:09:18 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: 1 2 [3] 4   Go Down
Print
Author Topic: Newcomer to P30-advice sought.  (Read 1735 times)
0 Members and 1 Guest are viewing this topic.
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #50 on: January 27, 2021, 03:17:20 PM »

It seems the more I get into this , the more questions I have.

Sometime back in this thread Atesus suggested my fuselage could be slimmer; true. The reason it isn't is because the cross-sections at the nose and motor peg are designed to accommodate my blast tube, and then I designed a low-drag body around that. But do people usually wind their motors outside the model with built-up P30 fuselages? Sorry if this is a basic question, but I've never seen a P30 flown live, only video, and they don't show the winding!
Logged
atesus
Gold Member
*****

Kudos: 29
Offline Offline

United States United States

Posts: 811




Ignore
« Reply #51 on: January 27, 2021, 05:20:02 PM »

I seldomly see people winding P-30 motors outside. Maybe it's just not common where I am (in CA).

I use a piece of clear plastic aquarium tubing for a winding tube for a 6x 1/8" motor. The tube is quite slim at 9/16" ID. It has quite a thin wall so OD is not much larger. I got it long time ago at Volare Products. I don't see it on their web site any longer though. I also recently ordered the item below but have not cut it to size to use it yet. My main motivation to buy the new tube was that the older one is no longer straight.

https://www.amazon.com/gp/product/B000OMHJAS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Logged
calgoddard
Platinum Member
******

Kudos: 29
Offline Offline

United States United States

Posts: 1,045


AMA, NFFS & FAC Member



Ignore
« Reply #52 on: January 27, 2021, 06:49:09 PM »

Kevin -

Few fliers wind P-30 rubber motors outside the model.  I have done it but you have to make your own half tube. Then you need two stooges, one to wind the motor and one to hold the airplane. So I usually wind my P-30 models using a blast tube.

Winding outside the model is customary in flying high-tech F1B and F1G models. The people who fly those models wind very, very hard and do not want a motor to explode inside the model.  High-tech F1B and F1G models have super strong fuselages made of exotic materials like Kevlar, so I am not sure a blast tube would even be needed in winding them.  However, extracting a highly wound blown motor from a fuselage in the heat of world-class competition needs to be avoided. Also I have heard that world-class F1B fliers will wind two motors before an official flight for that flight. They have a wound spare ready to insert into the model in case the first one explodes near the end of a round.

The clear plastic tubing from Amazon is too thick and heavy.

Item 470 from Arcata Pet Supplies has just the right OD and ID:

https://www.arcatapet.com/sresult.cfm  

I prefer very thin walled Aluminum tubing for my blast tubes but have a very hard time finding it, even from our big suppliers like McMaster-Carr.

It is easier to machine the bayonet lock on the rear end of the blast tube in the Aluminum tubing than it is on plastic tubing. Use a Dremel and a file. Remove all sharp edges or else you will nick your rubber motors. A bayonet lock couples the end of the blast tube to the motor peg and prevents the blast tube from creeping forward.  One of my mentor's recently told me that you can avoid blast tube creep by wrapping a sufficient amount of tape around the blast tube to create a friction fit at the front end of the fuselage.

Atesus - we met in Perris, California a few years ago.  I have enjoyed your videos. Maybe we can see each other at a contest some day at Waegell Field in Sacramento after I get my vaccinations. You have some really nice models and know how to fly them well. I live in northern Nevada.

« Last Edit: January 27, 2021, 07:12:20 PM by calgoddard » Logged
atesus
Gold Member
*****

Kudos: 29
Offline Offline

United States United States

Posts: 811




Ignore
« Reply #53 on: January 27, 2021, 08:13:22 PM »

Atesus - we met in Perris, California a few years ago.  I have enjoyed your videos. Maybe we can see each other at a contest some day at Waegell Field in Sacramento after I get my vaccinations. You have some really nice models and know how to fly them well. I live in northern Nevada.
I didn't realize you live in Nevada. I'm looking forward to seeing you at Waegell. The first contest on the NCFFC calendar is approaching quickly. It's the SGMA Spring Bash on Sat, Feb 27th (Sun 28th is the backup day). I'm planning to go.
Best,
--Ates
Logged
calgoddard
Platinum Member
******

Kudos: 29
Offline Offline

United States United States

Posts: 1,045


AMA, NFFS & FAC Member



Ignore
« Reply #54 on: January 27, 2021, 08:17:33 PM »

Atesus -

I will miss the contest at Waegell Field at the end of February, 2021. I probably won't have full vaccinations by then.

Maybe I can make the June contest.

Thanks for telling me about the SGMA Spring Bash.
Logged
cvasecuk
Gold Member
*****

Kudos: 11
Offline Offline

United Kingdom United Kingdom

Posts: 423



Ignore
« Reply #55 on: January 28, 2021, 05:39:14 AM »

In UK, I use 20mm conduit from B&Q. Very cheap.
Ron
Logged
PeeTee
Titanium Member
*******

Kudos: 52
Offline Offline

United Kingdom United Kingdom

Posts: 2,365



Ignore
« Reply #56 on: January 28, 2021, 07:30:38 AM »

I too use the 20mm conduit you can buy from hardware stores. The white stuff has lasted me for 20 odd years and is still going strong!

Peter
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 35
Offline Offline

Finland Finland

Posts: 1,336



Ignore
« Reply #57 on: January 28, 2021, 07:37:04 AM »

Re: winding outside the model. I have been considering moving to that, have laminated a half-tube from carbon and 3D-printed the rear bobbins to use. But have not had the time to try that out yet.

I would not need to do that to avoid model breaking if the motor blasts, as I use kevlar tube for motor tube and it can withstand the breakage. But taking the broken motor out of the tube is  unpleasant (and if it jumps to the read tube it may get tangled with the fuse line. But most of all, keeping the model in the stooge in windy days gets the model thrown around pretty bad, so I'd be happier to store the model in the tent while winding, and only insert the wound motor still in wind shelter after winding, and only after that expose the model to the elements.
   
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #58 on: January 28, 2021, 10:37:55 AM »

Quote
I too use the 20mm conduit you can buy from hardware stores

I've got 20 mm conduit too, which is effectively governing the fuselage cross-section. Calgoddard's stuff is a little slimmer, may let me reduce it a bit.

Quote
keeping the model in the stooge in windy days gets the model thrown around pretty bad, so I'd be happier to store the model in the tent while winding

An interesting thought Tapio, windy days are common even in the summer here nowadays.

Well this one is finished, ca. 48.5 g. I know I can do better on the next simply by better selection of wood, particularly longerons, but also wing LE and inner panel main spar. Many thanks to you all for setting me on the right path. I have no doubt I will have more questions when I start the Mk 3....
Attached files Thumbnail(s):
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
Logged
calgoddard
Platinum Member
******

Kudos: 29
Offline Offline

United States United States

Posts: 1,045


AMA, NFFS & FAC Member



Ignore
« Reply #59 on: January 28, 2021, 11:28:59 AM »

Kevin -

Your Mk 2 looks really nice. Your craftsmanship is excellent.

Don't worry about the weight of this P-30.  Fly it and have fun. It should do well in the windy conditions in the UK.

When you build Mk 3, trying slimming down the fuselage a bit as someone else mentioned.  Also, more careful wood selection should save a few grams.

Mount the viscous timer button closer to the nose, but not so close that you cannot freely grip the sheeted part of the fuselage when inserting the nose block. You always want as much weight forward as possible.  This allows you to move the wing forward.  Greater separation between the wing and the stab is almost always desirable.

As I mentioned before, determine if you really need the sub-fin.  While it looks great, it probably adds at least one or two grams, and those are added at the end of the tail boom, exactly where you don't want unnecessary weight. If you notice that Mk 3 exhibits a Dutch roll without a sub-fin, you can increase the size of the fin on the top or attach a sub-fin.  A Dutch roll is characterized by a sort of corkscrew motion of the tail or a wagging of the tail.  Too much fin can also induce spiral instability.  The McCombs book probably has formulas for figuring out the optimum fin area for your design.  

While I am on the subject, the McCombs book is considered the go-to treatise on building and trimming free flight model airplanes. While the focus of this book is scale free flight model aircraft many of the principles explained in the book apply to sport models, like P-30.  The full title is "Making Scale Model Airplanes Fly."  The author is William F. McCombs.  It only comes in an ancient typed format with hand drawn sketches.  The last I know you have to order a copy from an individual.  The cover of my copy lists the following person and address:  Susan Creamer, 1925 Clark Trail, Grand Prairie, Texas, USA 75052.

William McCombs was an early mentor of Don DeLoach who is one of the preeminent free flight masters in the US.  Mr. McCombs was a Princeton educated Senior engineer for Vought Aircraft.  
Logged
Red Buzzard
Silver Member
****

Kudos: 4
Offline Offline

United States United States

Posts: 149



Ignore
« Reply #60 on: January 28, 2021, 12:17:28 PM »

Wow, Kevin,

Down from 69 g.!! You win the prize. Fly it. Now is when you start watching and picking air as your model will survive at that weight. Nice design and as others have said great workmanship. May still be a couple of grams in the nose block, but then your wing moves back. Combine that with a re-imagined sub rudder.

Great stuff.

Bill
Logged
PeeTee
Titanium Member
*******

Kudos: 52
Offline Offline

United Kingdom United Kingdom

Posts: 2,365



Ignore
« Reply #61 on: January 28, 2021, 12:50:47 PM »

Have a look at the Teachers Pet by John O'Donnell, it has the fin above and below the centre section. Having said that, I prefer the fin above but JOD won lots of comps with that design.

Peter
Logged
billdennis747
Palladium Member
********

Kudos: 68
Offline Offline

United Kingdom United Kingdom

Posts: 4,605



Ignore
« Reply #62 on: January 28, 2021, 01:21:06 PM »

Have a look at the Teachers Pet by John O'Donnell, it has the fin above and below the centre section. Having said that, I prefer the fin above but JOD won lots of comps with that design.
I suspect John was the major factor. I've got a TP but the underfin hasn't won for me yet!
All I would add to the debate is that I watched John spending ages fixing a broken underfin
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #63 on: January 28, 2021, 01:42:31 PM »

Quote
All I would add to the debate is that I watched John spending ages fixing a broken underfin

A good enough reason to remove it then. I put it there because my DLGs have that arrangement, as do nearly all others, and I like the way it looks, but I'll probably dispense with it on the next.
Logged
atesus
Gold Member
*****

Kudos: 29
Offline Offline

United States United States

Posts: 811




Ignore
« Reply #64 on: January 28, 2021, 02:15:25 PM »

Quote
All I would add to the debate is that I watched John spending ages fixing a broken underfin

A good enough reason to remove it then. I put it there because my DLGs have that arrangement, as do nearly all others, and I like the way it looks, but I'll probably dispense with it on the next.

I fully agree with the comments on the subfin. I too love the looks of it, but the only way I found to make sure that it didn't break at each landing of my XL-56 involved adding more weight at the tail. I'm stuck with it because it is in the original design.

Your design has very pleasant lines. Great weight reduction too, congrats!
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #65 on: January 30, 2021, 09:42:54 AM »

Thank you for the nice comments and thoughts for development.

The leaner, meaner Mk. III is underway. The fuselage design has been slimmed a bit, all unnecessary sheeting has gone. The ventral fin has been dispensed with, the remaining dorsal fin has had the area increased a bit to compensate, but there is a net reduction in area. Hope the new fin is big enough, it "feels" as though it is. One of the main culprits on the Mk II was the density of the longeron wood I used, I've managed to find just enough approx. 1g sticks for this one. I don't have any lighter 3/32 sq. left, so most of the uprights and cross-pieces have been changed to 1/16 x 3/32", stripped from some reasonably light 1/16" sheet.

Pics show the design changes and how it looks so far. All of the changes are in response to suggestions made on here. If anyone has any more suggestions, please chip in before I get too far...
Attached files Thumbnail(s):
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
« Last Edit: January 30, 2021, 10:24:55 AM by Kevin M » Logged
Yak 52
Titanium Member
*******

Kudos: 77
Offline Offline

United Kingdom United Kingdom

Posts: 2,792


Jon Whitmore



Ignore
« Reply #66 on: January 30, 2021, 10:53:05 AM »

That's a really attractive P30  Cool

I put it there because my DLGs have that arrangement...

One reason why DLG's have this is because they have to cope with massive yawing forces in a discus launch. Mounting the fin centrally (ie a sub fin) gives aerodynamic balance and helps avoid turning this yaw force into torsional twist of the boom.

I'm fairly sure you'd get a slight drag reduction with a slightly larger single fin on your latest iteration since there will be some interference drag around each of the root/fuselage areas. A DLG won't have this since the boom is so skinny at this point.
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #67 on: January 30, 2021, 11:10:10 AM »

Thanks Yak52, true, there also used to be a theory that ventral fins helped mitigate roll moments due to slipstream effects on the power burst on rubber models once. They are also quite common on tow-line gliders, but I'm not sure what the theory is there. They look cool though!
Logged
Yak 52
Titanium Member
*******

Kudos: 77
Offline Offline

United Kingdom United Kingdom

Posts: 2,792


Jon Whitmore



Ignore
« Reply #68 on: January 30, 2021, 11:22:02 AM »

Yes, that's the theory. I suspect any spiral slipstream effect is a very minor with everything else that's going on though. I'm afraid I'm no expert on rubber duration (listen to Peetee instead  Wink)

I understand that in towline gliders having the fin area low helps stability on the line. I think Hepcat wrote about this at some point...
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #69 on: January 30, 2021, 11:38:22 AM »

Quote
I suspect any spiral slipstream effect is a very minor with everything else that's going on though

I think you are probably right. I think sometimes there are features of a successful model that get copied widely, whether or not that feature was a reason for the success of the original.
Logged
calgoddard
Platinum Member
******

Kudos: 29
Offline Offline

United States United States

Posts: 1,045


AMA, NFFS & FAC Member



Ignore
« Reply #70 on: January 30, 2021, 03:29:14 PM »

Kevin –

McCombs put forth the formula listed below in his book that he says will give a fairly reasonable estimate for the tail size for a free flight model.  He says the ideal size for the vertical tail means less drag and weight, easier trimming, less sensitivity to inadvertent warps and no spiral instability troubles.  However, McCombs also says you can really only determine the “ideal size” by flying.  

Av = N x Aw x b/Lv

Where:

Av is the vertical tail size in square inches

N is a numerical factor from a chart that lists different types of free flight models (it is .033 for
              an outdoor rubber duration model)

Aw is the wing area in square inches

b is the wingspan in inches

Lv is the distance in inches from the CG aft to the “center of the tail” (apparently the center of
             the vertical tail)

I have read that a sub-fin can be beneficial during the power phase in countering roll. I prefer to rely on thrust line adjustments to handle this trimming issue.
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #71 on: January 31, 2021, 03:08:22 AM »

Calgoddard

Thanks, using that formula the "ideal" fin area comes out at 10.1 sq. in. for my model. I took Lv to be from C.G. to fin A.C.

My fin as drawn comes out at 11.1 sq. in. including the fuselage bit below it, whether McCombs followed the convention of including that bit I don't know. If he didn't mine comes out at 8.5 sq. in. So mine is in the ballpark.

As he says this gives a starting point, but the formula, in its coefficient, makes fixed assumptions about several factors e.g. keel area distribution and fin CL-alpha characteristics. My Mk 1 has good directional and spiral stability, and as has been mentioned a larger single fin brings some efficiency gain, so it seemed O.K. to accept something slightly less than the total fin area of the ventral-dorsal arrangement.

It doesn't take long to make a new fin if this isn't right, but it is good to have a starting point.
Logged
Kevin M
Gold Member
*****

Kudos: 15
Offline Offline

United Kingdom United Kingdom

Posts: 323

Topic starter


Ignore
« Reply #72 on: February 06, 2021, 01:27:22 PM »

My progress continues....

The pictures show the Mk. III with the woodwork complete. It appears that this one is 4 to 5g less than the Mk. II was at the same stage. so I have hopes of a sub-45g model at the moment. We'll see, the covering and finishing process always adds more than I think it will. Fingers crossed.
Attached files Thumbnail(s):
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
Re: Newcomer to P30-advice sought.
Logged
DerekMc
Platinum Member
******

Kudos: 55
Offline Offline

United States United States

Posts: 1,535

WWW

Ignore
« Reply #73 on: February 06, 2021, 04:37:02 PM »

Nice!
Logged

They fly better when you smile!
Derek
Red Buzzard
Silver Member
****

Kudos: 4
Offline Offline

United States United States

Posts: 149



Ignore
« Reply #74 on: February 07, 2021, 01:19:14 PM »

Kevin,

Now that looks pretty airy!

Bill
Logged
Pages: 1 2 [3] 4   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!