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Author Topic: Hip Pocket E-Postal '08 - Operational Order Discussion  (Read 1863 times)
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Sundance12
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« on: March 09, 2008, 01:27:00 AM »

Operational Order

Hip Pocket Rocket Postal Competition.


This contest will begin March 31 st 2008 and run through to October 31 2008.

1. 20" strip of 1/8 rubber or equivalent (40" of 1/16)
2. Enclosed motor.
3. Built up covered wings limited to tissue or 1/4 mil mylar
4. Three rounds at 90 sec max.
5. One round must ROG or VTO (I say just trust people. Bad Karma for cheating)
6. Flyoff rounds are 90 seconds. Tape on a penny for each flyoff as you make them: 1st Flyoff: 1 penny, 2nd flyoff=2 pennies, 3rd flyoff=3 pennies. Keep going till you drop.
7. If you have no access to a US or Canadian Penny then a 2.5 gram weight can be substituted.
8. Multiple entries allowed but each is considered a separate entry.

Anyone who wants to participate in this Postal Contest is welcome to participate. There are no entry requirements. For the Hip Pocket Rocket Postal Competition, no data is required for registration but you can outline your design in this Builders Forum if you like. Pictures and development are encouraged.

All participants are encouraged to design an airplane from the beginning using the specifications listed above, there is no restriction to the number of airplanes you can use but each plane is considered a separate entry.

A tally and presentation will be made in the month of November 2008 of the results on this website. All times and data will be submitted in a form that comes up in a link found on this page.

The link for this will follow shortly.

Operating requirements

You fly three 90 sec rounds no matter what. If all three of your regular rounds are maxes, with one of them rising off the ground or using vertical take off, then you get to fly a flyoff round. In this class the time is not extended (which usually needs larger fields) you add a penny as ballast then fly. If it makes the 90 sec max you get to fly in the second flyoff where you add another penny. If you make another 90 sec. max with two pennies then the third flyoff requires three pennies. Each flyoff round makes the plane heavier so the difficulty goes up.

Enter your data into this form that we have listed here ..... and then you are ready to get in some official flights.

Prizes are to be determined.

Please play fair and have fun.

Sundance12
« Last Edit: April 05, 2008, 01:20:58 PM by Sundance12 » Logged

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« Reply #1 on: March 09, 2008, 09:17:27 AM »

Hi Bruce,

Back from Texas. Does the motor size equate to one loop of ten inches at the knot?

Thanks,

Outofbalance
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Sundance12
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« Reply #2 on: March 09, 2008, 09:27:34 AM »

Hi Rolf;

You can adjust the loop any way you want, but it must be equivalent to a loop of 1/8th rubber 20 inches long. Go back to this discussion to get the back story,
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=154.msg664#msg664

So if you want you could take the loop and double it up to a 4 strand, 10 inches long, or take 1/16th rubber and make it 3 loops, 13 inches long, whatever.... the quantity of rubber must be the same as a 20 inch length of 1/8th.

Now how this is really going to work out, I don't know but we will see how everyone handles it.

Glad you are back. there have been many changes...

Cheers

Bruce
« Last Edit: March 09, 2008, 04:17:14 PM by Sundance12 » Logged

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ramon alban
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« Reply #3 on: March 09, 2008, 07:14:51 PM »

Bruce, I gotta get me one of these pennies!

http://www.commercialappeal.com/news/2007/sep/25/hobbies-tiny-penny-posesmidtown-mystery/

Ramon
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Dan G.
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« Reply #4 on: March 09, 2008, 07:43:01 PM »

Just in attempt to keep things logical and consistent, I thought that one of the reasons for such an event was the simplicity of the power supply -- a loop of 1/8" flat. Now, if you start accepting "equivalents", maybe the power supply should be expressed in grams, like Wakefield ... no?

This would also eliminate the need to measure (any tension on that rubber? do we measure to the knot or to the outside of the knot). Compare that to throwing a bundle of rubber on a yes/no balance, or a gram scale.

Dan G.
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« Reply #5 on: March 09, 2008, 08:37:01 PM »

Boy, you try to keep something simple and!!! Dan, I agree that using a rubber weight would be simpler but these rules just kind of grew out of a myriad of proposals. Personally I would go with the dreaded 'spirit of the event' and measure out the strip, tie it and go. I plan on using 3 loops of 1/16 about 13" long. Or will it be 13.3333333"?

The other complicating factor is brought up by Ramon, very funny!, which penny is the standard? I was thinking the good old American penny when I proposed it and with my blinders on did not think about other countries and currencies. And then of course our pennies changed weight at some point. Don't know the solution to that one. I guess we could publish the weight of a US penny for other folks. Any other suggestions out there?

Derek

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Sundance12
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« Reply #6 on: March 09, 2008, 10:40:27 PM »

I have almost locked the rules in place, but there is still a bit of time left to tweak the program.

Hi Dan, I had considered the issue of a measured amount of rubber a while a go. I suggested the power be a 20 inch length of 1/8 inch diameter rubber loop which is 2 strands of 1/8th" ... Mine weighted 3.2 grams, but it's still a loop of 1/8 rubber. I am lucky to own a gram scale, many people are not so lucky. I also hoped this would not turn into a mini coupe or micro wakefield...

I like the penny proposition because in the flyoff it ups the ante and forces you to pack on the winds to get the same or better performance each time. This makes you take more and more risk each time while reducing the chance of a flyoff with the greater addition of power.

What is really open is peoples use of any kind of propeller as there are no restrictions to this design issue. I was looking forward to see how people would handle this design feature.

To understand the issues of the past one must read the last series of posts to see where we have been. This was a collaborative effort and it was meant to be.

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=154.msg664#msg664

Thanks everyone for their input, I guess I was hasty in closing the rules so soon.

Bruce
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« Reply #7 on: March 09, 2008, 10:53:59 PM »

Let's weigh some pennies. My Canadian one came in at 2.4 gms, but I'll try and collect 10 and weigh the bunch together, then take an average, since my scale doesn't go down past 0.1 gms it could be out by quite a bit.

I was planning on using 3/32 rubber cause that's what I got, lots of it, but if you stick to using 1/8, I think I've still got enough left to make 40". A 40" strip and 20 " loop, that is right isn't it?

Doug
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« Reply #8 on: March 09, 2008, 11:13:01 PM »

Okay! Okay! Sheeeeesh. I was trying to cope with complications already expressed by others ... I didn't bring up the subject of including the knot/or not in the measurement, or the multiple strands of thinner rubber. I was trying to figure out how to contend with prior queries. Sigh. I'm going to eat some worms.

Dan G.

That's a pretty funny posting, Derek ... does make you wonder if anything can ever be simple again.
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Sundance12
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« Reply #9 on: March 10, 2008, 12:11:24 AM »

Let's weigh some pennies. My Canadian one came in at 2.4 gms, but I'll try and collect 10 and weigh the bunch together, then take an average, since my scale doesn't go down past 0.1 gms it could be out by quite a bit.

I was planning on using 3/32 rubber cause that's what I got, lots of it, but if you stick to using 1/8, I think I've still got enough left to make 40". A 40" strip and 20 " loop, that is right isn't it?

Yes, that's it hermit, sorry to hear that you got some thinner rubber, I'm not sure how you compensate for the amount other than weight it. But weighting it was not the intent and this issue is going to cause me grief to some degree. For now use a 20 inch loop and go from there, you can try it with 1/8th later. At least the design will be ready for 1/8th when you are ready.

sundance12
« Last Edit: March 10, 2008, 12:19:08 AM by Sundance12 » Logged

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« Reply #10 on: March 12, 2008, 06:55:15 PM »

As to the issue of what penny to use, I think that it should be the Canadian one in honor of where Hip Pocket Builders forum is based. According to Wikipedia the Canadian penny has an illustrious history: http://en.wikipedia.org/wiki/Penny_%28Canadian_coin%29

One can see that the penny mass fluctuated quite a bit but the current version (2000) weighs 2.35 grams.

Since I do not have any Canadian pennies I think that I will make some out of lead and balsa and as long as the plane does not land in Canada I think I will be okay legally Grin A balsa/led disc of 19.5mm diameter, 1.45 mm thickness and 2.35 grams weight. No problem!

HipRocket 1 progress report: Fuselage sides are built. Wing ribs are cut. Moving right along. I will post some pictures as it comes together.
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« Reply #11 on: March 15, 2008, 05:13:20 AM »

Hi Derek:

This thread is a good a place as any for our posts for the time being.

Here is what I have so far as well, I am designing it in ModelCAD and presenting the plans for later. I should be close to completing the plan soon. So based on some theories and no practical experience, I am putting forth my proposal.

Length 31 inches
Diameter widest 1.5 inches
Span of 25.5 inches
Wing Area 90 in
Chord 3.5 in
Tail Moment of 21 in
Stab Span of 12 in
Stab Chord of 2.5 in
Tail Volume Ratio 1.5
Prop Diameter 7.125 in
Pitch 10.71 in
Target Weight less rubber 13gms
Wing mounted 1.5 inches above thrust line.

Sundance12
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Re: Hip Pocket E-Postal '08 - Operational Order Discussion
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« Reply #12 on: March 15, 2008, 07:59:30 AM »

Good grief, Bruce, that's pretty big for a loop of 1/8! Derek, yours is probably the most sane of the three undergoing design at present. I'm working on a 24" fuse with 3x20 wing and 50% stab. Target weight remains at 5 grams, but I'll be happy if it comes in less than 8. Time for some carbon fiber...
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« Reply #13 on: March 15, 2008, 10:29:56 AM »

Ok I hear what you are saying there Maxout, but I am a going to test a few things that I feel are important to this design and event. I am testing the ratio of climb to glide and I want a balance between both. I will be explaining myself a bit more.

Dan G. You may know where I am going with this design.

Sundance12
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« Reply #14 on: March 15, 2008, 12:34:50 PM »

Of course, you know what is going to happen? We are going to build esoteric designs,(well my own is not that esoteric, but its main design goal is to VTO!) and the winner will be someone flying a slightly modified embryo! It would serve us right Tongue Of course it looks like the airplane designs are going to be all over the place which makes the class very interesting indeed. I am looking forward to see what you guys build. Some cool ideas out there. Maxout, what size prop are you planning on using? Ae you going to carve it or mold it?

A simple way to build an airplane that would fly would be to pick up a lazercut One Night 16" from Tim Goldstein at A2Z Corp. (http://www.peck-polymers.com/store/images/products/pp013_400.jpg) Sand the ribs to half thickness, scrape down the prop and you would have a plane that could fly well.

Should we post pictures in some of the other appropriate forums to publicize the fun?
 Now to draw out the prop forming block. Where did I leave the protractor?

Derek
« Last Edit: March 15, 2008, 12:41:23 PM by DerekMc » Logged

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« Reply #15 on: March 15, 2008, 12:54:53 PM »

Hi Derek:

You are right, designs that are all over the map, and when the time comes, someone will fire up an old embryo and use it and get good times all with a loop of 1/8th... Lol, I am interested to see what others will do, like you said.

A One Night 16" would work and really rip on a 20" loop of 1/8th and there will be nothing wrong with that, go for it.

If you want to post elsewhere on the net to expand the players, be my guest. Might me interesting to have a few others get on the program.

I have yet to figure on how to make my prop. SBF sounds neat. Maxout, got any prop diagrams?

Cheers

Bruce
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« Reply #16 on: March 15, 2008, 05:10:22 PM »

Sorry Sundance ... I can't see your place yet (unless you're intending to extend your motor run with a high-pitched prop and gentle climb). I'm as curious as anyone.

Is it the current trend -- to use such large tail volumes? Your stab seems large to me, Sundance, but Maxout's at 50%? Maybe my thinking has become obsolete, but I'll take it up with anyone ....

Dan G.
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« Reply #17 on: March 15, 2008, 08:28:08 PM »

I guess I'm going to go back to the drawing board and make a few adjustments. After some reconsideration I need to remeasure.

Sundance12
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« Reply #18 on: March 15, 2008, 09:24:59 PM »

Curiouser and curiouser ...

Dan G.
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« Reply #19 on: March 15, 2008, 09:28:28 PM »

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Is it the current trend -- to use such large tail volumes? Your stab seems large to me, Sundance, but Maxout's at 50%? Maybe my thinking has become obsolete, but I'll take it up with anyone ....

I like this question, cause I need it answered too if I'm going to have a chance at getting something airborne. heehee For scale ships I've been using stab at 20% to 25% of wing area, and fin at 15% to 20%. What sort of guidelines should I be using for a performance beast like we're aiming at? Any different?

Doug
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« Reply #20 on: March 15, 2008, 09:33:26 PM »

Dan, I had to go back and re-design... However, what is the recommended Stab size? I have understood that anything from 36% up to 50% could be usefull. What is your opinion on Tail Volume ratios and Stab areas with respect to wing areas.. We need help...

Grin

Bruce
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« Reply #21 on: March 15, 2008, 10:49:42 PM »

Hi Sundance,

My experience is mostly with gliders, and although it applies to Wake and Coupe, maybe it's different having a largish, free-wheeling prop in front.

With those categories with a restricted, total wing area, the intention is to not waste lifting area on stabilization, but we wish to have adequate, even optimum stability. With normal tail moments, 15% area does it for a glider, likely no more than a couple more percent on the rubber ships (but I don't really remember). You might wonder at what point a model is said to be over-stabilized -- to have too much tail volume.

I don't know about the power phase and maybe it is not an issue.

In the glide, the effect is subtle and it affects the stall recovery and even the propensity to stall. The plane needs to be able to free fall at a certain point in a stall and to pitch for'd at a certain rate. A large stab will hold the plane at its climb angle until it runs quite out of speed, and then it will hold that tail up there so that when the nose finally does drop, it does so hard and further than is desirable, leaving the plane in a steep dive position -- that is a violent stall. A weaker stab will allow the tail to begin falling earlier in a stall, and when the nose does drop, the tail will not hang-up so badly. A well proportioned tail will be able to mush earlier, when the plane still has forward speed, and sometimes avert the stall altogether. If the stall does actually occur, the plane won't pitch so violently. I see some of this as a controlled fall, prior to regaining flying speed.

During this maneuver, at the top, if the balance is fortunate, the plane also has an opportunity to swivel, just when the speed is its lowest and all the forces are barely there, and the turn is very beneficial. Often, the initial upset is due to the plane's meeting rising air and that is the best time to turn. This speaks to its thermal hunting and centering capabilities. I'm a believer in stab-tilt and it may be playing a role here, and to make sure the turn is initiated a little before a full-blown, massive stall, I'll stall the inside tip a little early with wash-in.

With a large tail, the ship flies a very predictable pattern as if on rails, with little deviation except for excessively violent, altitude-killing stalls. My impression is that this was normal design and flying characteristics before WWII. After the war, fins really came down in size, to the point of barely allowing a little dutch roll. This seemed to allow the plane to straighten out its flight in mushy times (down draught), just for a few seconds until everything settled out and it regained its normal flight circle. This is nearly thermal hunting or at least, downer-avoidance. Big tails keep everything on rails with little liveliness, bounce, or reaction -- inured to what's going on around it,

Oddly enough, and I don't truly know why (or even think I do), some fin area is interchangeable with the stab. One adequately sized surface can help make up for a lacking in the other. I guess the corollary is that if both are too small, you've no hope, and if both are too large, you've no hope; but in between, there is some forgiveness in the individual sizes if compensated for.

However Sundance, this might apply to clean ships which are more able to exploit these subtle effects and characteristics, which may not be so available to rubber ships which may operate under different criteria ... I'm just afraid to assume too much (Donald Rumsfeld again). My own experience was inadequate with rubber to verify these types of things. I seem to recall that if I just got a good fold, into a smooth transition, I was pretty happy. I've a lot more experience with gliders.

Dan G.
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Sundance12
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« Reply #22 on: March 16, 2008, 08:31:29 AM »

Thanks Dan for the explanation, I now understand what it is I need to be managing with the size of the tail. The size of the tail that I will use is related to how my airplane will come out of transition into the glide. With the power I have available from the propeller I expect that there is much stall being moderated at the top of the climb to level flight by propeller slipstream and thrust. With gliders this power phase ends very abruptly and I can see how gliders would stall at the top of a hand launch where in this same point with a power plane such as I want to build, the power phase makes the airspeed drop off much more moderately into the cruise phase. However, if the airplane had a moderate climb there is little airspeed loss to contend with at the top of a climb and the model moves into a cruise phase without experiencing much stall at all.

Based on what is being discussed I am going to make my stab 37% of my wing area and then work up from there.

I thank you for your discussion and I remember what you are saying as I watched you fly your hand launched gliders and I remember some of the glide characteristics that we have discussed in the past.

Cheers

Bruce
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