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Author Topic: A few P30 questions  (Read 2968 times)
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cglynn
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« on: September 23, 2013, 09:33:06 PM »

Greetings all.  I am about to try and put together my first P30 and have some questions.  What is everyone using for a wing and stab chord?  I know there are a bunch of designs out there, but what works consistently well?  Also, what have you all found to be a good hook to hook length for the motor? 

I appreciate the help and insight, and am looking forward to getting this build off the ground.

Thanks
CG 
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Rewinged
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« Reply #1 on: September 23, 2013, 11:32:24 PM »

CG,

The cool thing about P-30 is that there can be great variation in designs, with all of them having the potential to be competitive.  You can have huge chords and areas, like the "Window Plane," or small chords and areas, like the Bob White TwinFin.  Clint Brooks' Boomer is very successful, and I think it is another with a small chord.  Which leads to your next question...

The distance between prop hook and rear peg depends upon whether you wish to use 6 strands of 1/8, 6 strands of 3/32, or 4 strands of 1/8, and also whether you braid your motors.  You can choose between a fast climb or a leisurely one.  The fast one is better in wind and turbulent air, the slower climb better in calm and smooth air.  To use the smaller cross-section motors, the model needs to be built to near minimum weight; keep it at least under 44 grams, I think.

The distance between prop hook and rear peg can vary from 20 inches to maybe 28 inches, depending on the motor.  My TitanK has a 4 and 3/8 inch root chord, and has a distance between the prop hook and rear peg of 27.5 inches.  It has the rear peg about as far to the rear of the fuselage as possible.

A key, I believe, is to have the area match the motor and the prop.  At least, that was my big concern when I modified the Titan design.  I got lucky in that my hunches--which were based on my reading--paid off.

I suggest you get a copy of the Free Flight Quarterly P-30 issue.  That was the key reading for me.  Great info and a good value, IMO.

Of course, good trim is more important than anything else, and eventually air-picking becomes important.

--Bill
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cglynn
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« Reply #2 on: September 25, 2013, 08:25:12 AM »

Thanks RW.  I have a bunch of 3/32 Tan right now, so would probably start with 6 strands of that, though would like to build something that allows me to use 6 strands of 1/8" in the future. 

I have seen a little bit of research done on P30 props, and have seen the comparison to the Czech P30 prop and the Peck 9.5" prop.  Any ideas as to the difference in flight characteristics between the two?  Is there one type of plane/flight trim that suits one better than the other?

Finally, aside from looks, is it worth the time and trouble to roll a tapered fusealage?  If so, does one just use a tapered mandrel to accomplish the task?

Thanks
CG
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atesus
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« Reply #3 on: September 25, 2013, 11:45:49 AM »

I hope I'm not going to be be hijacking your thread with my P-30 motor related question.

How is the P-30 motor weighed? What's included in the 10g motor weight? AMA Rule book only specifies a maximum of 10g for a lubricated motor without going into any more details. Does the 10g include say the bobbin if one is used? How about crockett hooks or other rigid pieces used for hook-up, which may be attached to the motor semi-permanently if only for convenience? I believe if an O-ring is used for hook-up its weight must be counted in the total weight, is this correct?

Thanks and best regards,

--Ates     
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Tmat
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« Reply #4 on: September 25, 2013, 11:58:23 AM »

Just the rubber and lube only. Usually, you will have a small rubber band attached to hold the strands together. Typically the motor is weighed with that included, but it's not technically part of the weight of the rubber motor.

Tmat
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PeeTee
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« Reply #5 on: September 25, 2013, 12:02:02 PM »

Ates

I don't know the AMA rules, but would be surprised if they were out of step with those for other countries such as Britain & France. Over here the weight is just the motor and lubricant, nothing else - no O rings, rubber bands, bobbins, hooks etc.

Hope this helps.

Now for my sixpennorth on P30. Those that know better than me advise that the Peck prop is better with thinner motors such as 4-5 strands of 1/8" or 6 strands of 3/32". The Igra props go well with 6 strands of 1/8" As for  tapering rolled balsa fuselages, all the ones I've seen (rolled fuselages that is) are parallel & not tapered. The reason being that with a motor running most of the length of the fus, tapering towards the rear peg runs the risk of the motor knotting and jamming - unless of course you increase the overall diameter which rather defeats the object.

Peter
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atesus
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« Reply #6 on: September 25, 2013, 12:27:04 PM »

Peter, Tmat, thank you for your answers.

I was thinking (and I believe I also read somewhere) that the O-ring may need to be included in the 10g as it stores energy, just like the rubber motor (albeit a poor one). Not that the 0.4g O-ring weight which I deduct from the proper rubber would be of any significance at my competitive level but, it's good to know neverthless Grin
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Tmat
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« Reply #7 on: September 25, 2013, 01:08:52 PM »

No, the O-ring shouldn't be deducted from the rubber weight. At least IMO.

Tmat
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rbrpwr
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« Reply #8 on: September 25, 2013, 02:22:16 PM »

The maximum weight of the motor is 10 grams, the min weight of the airplane is 40 grams.  If the O-ring, crocket hook, bobin is weighed with the airplane, then you get to use a full 10 grams of rubber and lubricant.  If the paraphenalia is weighed with the motor, then it counts against the totla weight of the motor. 

In other words, chose your poison.   If you can, make them part of the airframe and meet the minimum weight target and use the lightest combination possible.
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cglynn
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« Reply #9 on: September 25, 2013, 02:58:15 PM »

Thanks guys.  Rules clarification are always good.  Parallel tube is easy to make, and apparently pretty much the standard, so I will go with it.  I have settled on a wing length of just under 30" projected (like 5mm short to make measurement and account for errors in measuring) with a 4.5" chord.  Stabilizer to be about 20% of wing area with a similar aspect ratio. 

Those of you in the know, how does that sound for design specs?
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Tmat
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« Reply #10 on: September 25, 2013, 03:22:41 PM »

Sounds ok, but why make the wing so much shorter? I'd go for as close to 30" proj as I could, but that's me. ;-)

Tmat
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cglynn
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« Reply #11 on: September 26, 2013, 10:19:52 AM »

30" Exactly sounds good to me.  Also, I have been considering airfoil sections, and am leaning towards a max height of 8.5% at about 30% of the wing chord.  So on an 115 mm wing chord, max height of 10mm at 34.5mm from the leading edge.  I don't really have the time to run it through X foil or other analysis programs, so just going from experience, what do you all think of that wing section?  Is it going to be too highly loaded for P30 or provide insufficient lift?

Thanks all.  This is my first attempt at designing my own craft, and while I want to learn from it, I also want it to be somewhat successful.

CG
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« Reply #12 on: September 26, 2013, 09:26:36 PM »

CG, this is outside my area of expertise, but I think you will be fine.

In my opinion (based only on reading and watching a bunch of planes in different conditions, so not worth much) I don't think the airfoil is very critical for P30.  Probably the best is something like Tapio showed recently (Midic 309) in "the Show us your P-30's" thread, reply 693.  But a flat-bottomed airfoil somewhat thicker, to get the camber reasonable, is probably not too much worse at the speeds of a P30. But again, I don't have much knowledge in this area.

FWIW, here is a picture of what I used.  My root chord, as-built, came out about 9.6% thick at the root instead of 8.7%, but the tips were thinned a lot.

--Bill
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Re: A few P30 questions
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FLYACE1946
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« Reply #13 on: October 27, 2013, 10:38:36 PM »

Does the AMA rules place a penalty for a P-30 weighing more than the rules state? I have been told that but I am not sure I believe him.
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applehoney
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« Reply #14 on: October 27, 2013, 10:54:03 PM »

Minimum weight for a P30 airframe is 40 grams.   The only penalty for exceeding that weight is decreasing performance as the extra grammes add up.
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« Reply #15 on: October 29, 2013, 06:29:17 PM »

Thanks for the additional information. Now I can feel much better flying mine even tho it might weigh heavier than 40 grams. Need to get mine out for weight and flight purposes.

Souper P-30 BTW. Shocked Shocked Shocked Shocked Shocked Shocked
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applehoney
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« Reply #16 on: October 29, 2013, 07:21:36 PM »

Simple but  a good model

Good flying!
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Dave Andreski
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« Reply #17 on: October 29, 2013, 08:01:41 PM »

Simple is good!
Dave
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lincoln
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« Reply #18 on: October 29, 2013, 10:35:55 PM »

I think the Reynolds number for that 4.5 inch chord works out to around 25k to 30k. Maybe a bit less if your airfoil gets a lot of lift. If it was me I'd either use a thin section, concave on the bottom, like you see on Wakefields or something, or else maybe a 7 percent flat bottom if I was feeling lazy. This is not based on P-30 experience but on some theory and flying some other ff planes. I suspect the freewheeling drag the large prop is more than that of the wing, so it may not matter all that much.

This is going to sound weird, but I think, given the span limit and the freewheeling prop, a biplane might be called for! It works on pennyplanes. Of course, that's not exactly simple!

I read a paper long ago concluding that P-30 aspect ratios are not particularly critical. If you look at some of the designs that have won at the US national level (not just the Nats), that hypothesis seems to be supported:
(there may be some repeats in here)
http://www.modelaviation.com/images/article/plans/p30centaur.jpg
http://www.modelaircraft.org/plans/images/1984/453.jpg
http://4.bp.blogspot.com/-VQtj4rwd5qo/UjYjpHCYe3I/AAAAAAAADH0/FgordfDRSCQ/s1600/Cyrano-II-P-30.jpg
http://outerzone.co.uk/images/thumbs/models/4212.jpg
http://www.modelaircraft.org/plans/images/1988/603.jpg
http://media.airagestore.com/media/catalog/product/cache/14/image/500x500/602f0fa2c1f0d1ba5e241f914e856ff9/f/s/fsp03803.jpg
http://www.brooklynskyscrapers.org/pix/Bob-Hatschek.jpg
Can't find pics on line, but Marie P-30 had 4 inch chord and "Marie Super Skinny-E" had 4.765 (that's what the designer said!) Both were Nats winners.
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lincoln
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« Reply #19 on: October 29, 2013, 10:43:17 PM »

P.S. I think I may ignore all the technicalities and make my first P-30 an enlarged Sleek Streek. Easy and fun.
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danberry
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« Reply #20 on: October 30, 2013, 10:27:09 AM »

Thermals solve all of the aero deficiencies.
To make three minutes you will need some help from a thermal.
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Starduster
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« Reply #21 on: October 30, 2013, 02:27:17 PM »

For what it's worth:

Quite a few years ago, I designed a P-30. It had a fully elliptical, high aspect ratio wing. The aspect ratio was about 17, so with a 30 inch span, the chord was 1.75 at the root. This gave it a wing area of about 41.5 sq inches. The wing had a simple 'V' dihedral.

And, to top it off, the airfoil was a simple flat bottom Clark Y, though a bit thinner than a true Clark Y.

The tail was also elliptical.  The fuselage was rolled balsa tube.

This airplane completely out of the norm for the day. In those days, it seemed like everybody was trying to get as much wing area was they could (Window Pane came out about then) But you know what? It flew great. I never competed much with it, but I'd do pretty well when I did. I should look through my plans to see if I still have the drawing and up-load it if I do.
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« Reply #22 on: October 30, 2013, 08:44:24 PM »

Sounds interesting, Iceman. I hope you find it.
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« Reply #23 on: October 30, 2013, 10:03:38 PM »

Look forward to flying with/against Dan Berry someday--likely another friend I haven't met.
"Thermals solve all of the aero deficiencies."

For sure.  Hence my current byline, "Good air don't care."

On the other hand, "To make three minutes you will need some help from a thermal."  Don't think I agree with that.  I'm pretty sure I can do 3 minutes plus in dead air, although it's nigh impossible to know one is in dead air.  Stan B told me he could do 3:40 with his AirShark.  On the other hand, I've found it really easy for a 3-minute airplane to do less than 2 minutes in bad air.  Bad air don't care, either.

--Bill
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danberry
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« Reply #24 on: October 30, 2013, 11:03:04 PM »

We can probably count the three-minute planes on one hand. It really doesn't matter. Three minutes is the fifth flight at a meet. The nuetral air is gone by then.
R.P. Hanford flew by the credo---You don't have to have good air but you cannot survive bad air. Half of the maxes I ever saw him fly were simply launched into sunshine after a cloud went through.
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