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Messages - Bob Krech

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Events / Re: URRF 4, June 23-25th
« on: April 17, 2017, 11:16:19 AM »
Registered and signed up for range duty.  Can fill in more if needed.  Looking forward to a good time.


Beginner's Corner / Re: Need to know basics
« on: December 20, 2016, 01:45:32 AM »
The DX3 MadCows come in a number of weights and .diameters  ranging from 2.6" fiberboard to 8" fiberglass  The most cost effective of an L1 cert than can also be launched on mid power motors is this 2.6" DX3 kit for $69.  Get a 3G 29 mm casing and (2) 1G grains spacers and you're good to go with F, G and low H impulse motors.
It's a really fine mid-power kit that will launch just fine on F and G motor as well as H motors for an L1 cert.  An L1 cert flight would apogee at ~ 2300.  Overall it will apogee at 600'-900' on an F motor, 1300'-2300'  on a G, 2200'-3400' on an H, and over 3400'on an I.  The  only issue you have is the wind drift on an H.  It will drift 1000' downwind on a full G in a 5 mph wind, 2000' in a 10 mph wind and 4000' in a 20 mph wind, so you really want a low wind day to launch it on an H.

You can go to and make the prediction I made above.

The LOC Fantom EXL is equivalent to an XL version of the 4" Fiberboard Super DX3  The principal difference is that the LOC has all the extra parts in the $150 price whereas the $90 Super DX3 doesn't include chutes, shock cords, payload compartment, etc. but the basic price of a 4" 4FNC with electronics bay will be $150 or more.  Either would be fine for an L1 and L2 cert, but would need to be flown with the payload on a high thrust G to fit into the Model Rocket FAA Class 1 status.

The choice is entirely yours.  If you're in not rush and what to launch mostly F and G motors with an occasional H, the 2.6" DX3 is an inexpensive way to go.  If you already have mid-power rocket, and really want to quickly get your L1 and L2 this year, a 4" rocket is the more economical way to get to L2 quickly.

Beginner's Corner / Re: Need to know basics
« on: December 18, 2016, 08:11:08 PM »
Hey Bob, I like to thank you for helping me out here. I need to know what insurance would be good for me to have if I am in MARS and URRG, which insurance would you take, Tripoli or NAR?? And why?

I would pick a kit HI-Tech rocket with ebay from LOC or Apogee as a good start with 29 mm motor into 38 mm rocket with special adapter. I would use this rocket as dual deployment later on but I would take the ebay out until I am ready for L2 certification. Right now, 29 mm motor up to G power until I am all go for H or I motor for L1 Certification.


Today there is little difference between NAR and TRA.  NAR is 50% larger than TRA and has a real model rocket program and gets you a free print magazine.  TRA puts a bit more emphasis on high power and has "Research" rocketry which means if your are TRA L2 certified you can make your own motors.  Both organizations have more than 3500 high power certified members and about half of the high power certified folks belong to both organizations.  NAR or TRA membership is equally good at URRG.  Both offer virtually the same insurance.

Getting your high power certifications is like getting a drivers license: you can't launch L1/L2 motors without it.  Most folks use a family car to take their driving test even if they plan to own a Ferrari, because without the license, you can't legally drive the Ferrari.   This is the approach I recommend for obtaining high power certifications.  You do not need to use electronic deployment for either L1 or L2 certification, however if the rocket is near minimum diameter, you probably need it to make recovery easier.

I personally like LOC rockets.  They are reasonably low cost, are very easy to assemble, and virtually all can be assembled using TiteBond wood glue.  The 2.6" HiTech is a fine rocket that flies fine on F and G motors as well as high power mtors, but you need to be aware that a 2.6" rocket will go rather high on L1 and L2 motors.  It will apogee at 1500'-1800' on a G, 2800'-3300' on an H, 3600'-5000' on an I and over a mile on a J.  This isn't necessarily a problem, but you need to be aware that smaller rockets using high power motors are harder to follow with 60ish eyes and can be easily lost on a farm with crops if you do not use tracking electronics and/or dual deployment electronics.

While many will disagree, I recommend doing your L1 flight, and your L2 cert with/without electronics, on a simple 4" 4FNC rocket.  The 4" LOC FANTOM 438 EXL will also fly on high thrust G motors without the payload section or electronics, but will also fly fine with H,I and J motors, especially with dual deployment with electronics.  The kit comes with all the necessary parts for dual deployment except for the altimeter.  It will apogee at 700-800' on a G, 1100'-1700' on an H, 1700'-3000' on an I and over 3000'on a J. 

 I would use 38 mm casings: 1G casings for G motors; 2G casings for H motor; 3G and 4G for I motors and 5G and 6G for J motors.  If you buy certification special kits: a 3G and 6G case and (2) 1G spacers, your can launched any 1G thru 6G reload by purchasing only 2 cases.


Beginner's Corner / Re: Need to know basics
« on: December 17, 2016, 07:00:26 PM »
Hi Ken

As I wrote above, URRG does not have regularly scheduled meetings because the average member lives several hours from Potter so you would be lucky to be able to get 3 folks together outside a launch.  The monthly launches are two day events, so meetings if necessary occur at the launch field or at Smugglers Corner, the local bar in Potter, on the Saturday evening of the launch weekend.

The BOD conducts our business via e-mail and telecom since few BOD members live within 100 miles of each other.

Beginner's Corner / Re: Need to know basics
« on: December 17, 2016, 04:30:46 PM »
Welcome to the URRG Forum.

URRG is a non-denominational club.  We don't mind if you belong to more than one club or if you belong to NAR or TRA.

It is quite common for folks to belong to more than one club as being a local club member supports the local hobby, the launch equipment and the acquisition of the launch site.  I belong CMASS and MMMSC in addition to URRG and belong to both TRA and NAR.

URRG, which has the best launch field east of the Mississippi, has members from all over NY state, New England, New Jersey, Pennsylvania, Ohio, and Canada.  Because of the diverse membership, meetings tend to occur at the monthly launches.  (That's one of the reasons for this forum.)

URRG has monthly launches usually from April thru December, weather dependent.  Most launches are 2-day events on a Saturday and Sunday since most members have at least a several hour drive to the field.  In June, URRG sponsors either URRF, a 3-day regional launch, or LDRS, the 5-day TRA national launch.  All launches are conducted under TRA Research Rules.  NAR high power members can launch commercial motors to their certification level.   Anyone can launch model rockets.

URRG has 2 L3 hydraulic launch tower, 2 L3 manual/electric launch towers and 4 megaweasel L3 pads, 24 L1/L2 weasel pads, and up to 24 model rocket pads.  All are used at URRF and LDRS, but for the smaller club launches, the number of pads set-up depends on the number of attendees.  URRG has a waiver to 16 kft MSL with windows to higher altitudes which varies with launch, weather and the FAA.

URRG has many High Power Certified members who are more than happy to help you out.   If you have more question, post them here.  I'll also put in a plug for the Rocketry Forum (TRF).  We are the largest web forum dedicated to hobby rocketry.  If yu can't get your questions answered here, you will get an answer on TRF.

Welcome aboard.

Bob Krech, URRG BOD, L2
TRF High Power, Propulsion and Research Forum Administrator

Outreach Opportunities / Re: Friday September 23rd. Universety of Buffalo
« on: September 09, 2016, 06:40:40 PM »
Check your e-mail for the Tripolitan.  It mentions that TRA has a downloadable trifold on the TRA website.   It might be just what the doctor ordered.


Outreach Opportunities / Re: Friday September 23rd. Universety of Buffalo
« on: September 08, 2016, 12:59:48 PM »
That's a reasonable rembursement considering the distance involved.  Does the club have any PR handouts to distribute?  If not we should make up a downloadable 8.5" x 11" trifold handout that our reps can print it and bring out with them.

A two-sided color printout cost about $0.10 to $0.15 per page when printed out at home.  If a club rep goes on a BOD approved PR mission it would be ok IMO if we allocated $5 for them to printout and bring a couple dozen trifolds.

I would also like to propose the club get 1000 generic business cards for members to handout.  The cards would list our website address and contact info.  This would cost $20 or less from a number of on-line printing companies.


Beginner's Corner / Re: L1 cert for a Madcow V2 4" kit....
« on: August 01, 2016, 12:43:29 AM »
Before you purchase anything, you need to understand several things about hobby rocketry motors.

1.)  Commercial hobby rocket motors are standardized to certain motor casing diameters and certain grain lengths.

2.)  For CTI, the casing diameters are: 24 mm, 29 mm, 38 mm, 54 mm, 75 mm, 98 mm and 150 mm.

3.)  For each casing diameter there is a nominal grain length: 1G in 24 mm is 1.25" long; 1G in 29 mm is 1.75" long; 1G in 38 mm is 2.30" long; 1G in 54 mm is 3.31" long; 1G in 75 mm is 5.33" long; 1G in 98 mm is 6.06" long; and 1G in 150 mm is 8.04" long.  The uniform grain length make it convenient and economical to assemble motors.

4.)  For each casing diameter there are nominally 7 casing lengths: 1 G, 2G, 3G, 4G, 5G, 6G and 6GXL.  We'll ignore the 6XL motors for now since the grain lengths used can be different than the nominal grain length for the casing diameter.

1G in 38 mm is nominally ~120+/-  Ns, 1G in 54 mm is nominally ~ 400+/- Ns.

5.)  You can not only purchase the longest motor casing for a given casing diameter.  This is not allowed by the certification authorities for safety and performance reasons, so you have to buy several casing lengths in a given diameter if you want to use all the reloads in a given diameter.  To reduce the cost to the user, there are 1G spacers that allow you to use a longer casing than the reload would normally require.  For example, if you use a 3G reload you would normally use a 3G casing, however you can use a 4G casing with a 1G spacer, or a 5G casing with (2) 1G spacers.  You are only allowed to use a maximum of (2) 1G spacers in a larger casing so for example you can not use a 6G casing with (3) 1G spacers because using (3) 1G spacer is not allowed by the certification authorities.

6.)  The CTI has starter casing sets that consist of (1) 3G casing, (1) 6G casing, (2) 1G spacers, 1 delay adjustment tool, and in certain diameters forward and/or aft closures.  This allows you to use 1G thru 6G reloads with only (2) motor casing lengths.

7.)  38 mm starter casing sets cost $110 and 54 mm starter casting sets cost $220 from AMW Pro-X.

8.)  Smaller diameter casings are less expensive than larger diameter casings.

9.)  38 mm reloads are less expensive than 54 mm reloads because they have a lower total impulse and contain less propellant.   For example, a 1G 38 mm Blue Streak propellant cost $8 whereas a 1G 54 mm Blue Streak propellant cost $20.  The other components of the 38 mm reload costs ~$16 whereas the other components of the 54 mm reload cost ~$31.

The 2.6" FG Mad Cow V2 is a fine rocket but it is not one I would recommend as your first high power kit for several reasons.  It uses more expensive 54mm motors instead of less expensive 38 mm motors, and it is quite sensitive to CG location and will require nose weight for a stable flight so it's really not a good first high power rocket, and it is not set up for electronic deployment which will make recovery easier when you go high on a L2 motor.

A better choice for your first high power rocket in a Mad Cow 2.6" FG kit would be a dual deploy ready DX3, Screech, or Tomach with a 38 mm motor mount.  (They are basically the same rocket with slightly different fins.)  They can be flown with, or without, dual deploy, with, or without, electronics, and with, or without, the payload section.  They are much more versatile than the 54 mm V2, and much less expensive to launch, and more important to a newbie, you are less likely to loose it.

1.)  You can do your L1 without electronics in an apogee deploy motor ejection mode.  A simple up and down flight on a 3 grain Pro38 mm H motor.

2.)  You can purchase a PerfectFlite StratoLogger and build your e-bay and install the altimeter and simply monitor your next few flights on 3G or 4G H motors.

3.)  When you are comfortable with the electronics, set up the rocket for dual deployment and do that with a 4G or 5G I motor.

4.)  After you are comfortable with dual deployment , go for your L2 cert using the dual deploy with a 5G or 6G reload.

You can always buy the V2 first, but this is an easier approach to get to L2 using one rocket.



Photo & Video Gallery / Re: Photos from URRF3
« on: June 30, 2016, 09:06:27 PM »
Great shots Rick


Beer Garden / Re: Random observations from URRF3
« on: June 28, 2016, 04:29:33 PM »
•Having plenty of water and sunscreen is important
•The previous observation is more important then you think

     We had water for the staff and we should have made it clearer. I also had sunscreen in the Range Boss tent.

•A lot of fliers have little concept of proper rod/rail angle

     Rockets turn into the wind on ascent and go with the wind on descent. 
     Match up the difference and the rocket lands near the pad.......

•Man, that field is dusty!

     That so you can remember the good time you had each time you get into your car for the next few months.....

•When the pads are split between the left and right, there's a lot of back and forth to arm/disarm the pads.  The corollary to that is - pads apparently don't work well when disarmed  :o

     That would be the CATO pads.  The URRG pads are armed from the launch console.....

•A lot of fliers don't seem to have a good grasp of rod sizing.  I witnessed a number of folk putting 1/4" lugs on a 1/8" rod, etc.
•Related to lugs, I witnessed a number of fliers break their lugs - or a fin - off trying to load the rods. 
  One rocket fell of the pad when the wind exceeded the lug's grip on the body tube, leaving it wired and armed on the ground

     I've seen folks try to bend the launch rods to get their rockets on...... :-\

•Man, that field is dusty!


•Having LPR launch rods that drop down as easily as the rails do sure is handy

     That's something that needs work on the URRG setup.  It's hard for a 4' kid to put their rockets on the pad.

•An off-road bicycle for range duty isn't a bad idea

     It's good exercise.  You need it to work of the calories from the evenings beer.....

•Even with a new-fangled Chute Release, the wind can still carry a rocket pretty far

     Especially if they come out at apogee.  But you don't have to worry about a long walk if they don't deploy.....

•Volunteers can be hard to come by, even when baited

     Gosh, gee wiz.  We only paid $5 per hour. 
     Not quite minimum, but then most folks didn't do the math and see that we added $10 to the launch fee, and they got it back when they did (1) 2 hour volunteer

•Some folks don't see the need for smaller rail button systems.  Others think they're great.

      If you don't use them you don't care.  If you do then you need them. 
      I'll guess that less than 1% of fliers use them at present.  The real advantage of the small rails is that an inexperienced person can't bend them.....


Tracking / Re: How are radio frequencies managed at larger events?
« on: June 01, 2016, 11:54:39 AM »
I knew we had the white board last year, but I did not know it worked that well.  At a less rural field, you could simply have the flier list his cell phone number, but the cell coverage is not good in Potter so you have to chase down the flier or make a PA announcement.


Tracking / Re: URRG Member Tracker Frequency List
« on: May 28, 2016, 10:23:49 PM »
Our local ham club offers the ham test on the 4th Saturday of each month.  I've been planning to take it for the last 50 years so I finally bit the bullet and took it today.  The Technician test is Element 2, the general test is Element 3 and the Extra test is element 4.  Elements 2 and 3 are each 35 questions and you can get no more than 9 wrong,  Element 4 has 50 questions and you can get no more than 13 wrong.  I took the first 2 tests and passed both so they handed me the third test, but it was hot and I had a barbeque go to and I wasn't certain if I could pass it without studying and I didn't want to keep the 10 examiners hanging around for another 40 minutes so I passed the test back.   I'm happy with a general license for now.


Tracking / Re: How are radio frequencies managed at larger events?
« on: May 28, 2016, 10:03:40 PM »
For years, the AMA has required that every flying field have a frequency board with frequency pins.  All transmitters are impounded and/or turned off unless the flier has physical possession of the a frequency pin, and has left his AMA card in the pin's slot on the frequency board.  In the RC world, apparently it is bad form to keep the frequency pin longer than 20 minutes.

URRG could have a similar frequency board system.  The multi-pocketed board would have all the available band frequencies labeled on the board's card slots and each slot would have a card with the same frequency.  When a launcher want to use the frequency for his tracker, he would remove the frequency card and leave his TRA/NAR card in its place.   That way you know who controls the frequency or if the frequency is available.


High Power / Re: Altitude, GPS vs Altimeter
« on: May 20, 2016, 12:04:07 AM »
Some of the GPS/inertial program in you phone will display the number of satellites used for the fix, their positions overhead and the standard deviations of the lat/lon position and the altitude.  You will observe the larger uncertainty in the altitude versus the lat/lon position unless there is at least one satellite overhead.


High Power / Re: Altitude, GPS vs Altimeter
« on: May 19, 2016, 09:30:23 PM »
In theory a good barometric altimeter is more accurate below 30 kft than GPS which is why TRA has their altitude records set up that way.

GPS is very good a lat-lon (x-y) locating because there is a high probability that several satellites are located within 20 degrees of the horizon spread around 360 degrees.  To get accurate altitude (z) value there should be at least 1 satellite overhead, but this is not always the case so the z value can have an error that is 10x higher than the x-y values.

A good barometer has a digital barometer chips with 16 to 24 bit internal ADCs, however older altimeter use analog barometer chips with a separate 8 to 12 bit ADC.   The digital chip have 4"-6" resolution while analog altimeters have typically 1' to 10' resolution.  Noise typically reduces the resolution unless many readings are averaged together.  This is always done in the digital barometer and is not done with analog barometers so the accuracy of the digital units is far better than the analog units.

The errors due to non-standard temperature conditions are not compensated for in any barometric altimeters unless post flight processing is perform so while the relative values are very accurate and that's why you can use altimeter for highest altitude contests, the absolute accuracy is less accurate whenever the temperature differs from 59F, but currently no one does the post flight corrections.

If you measured the launch site temperature and used the standard temperature offset to correct the for the density difference versus temperature, you should be able to get better agreement.

As you are using the RRC2, RRC3 and MARSA, you should be able to use the manuals to figure how much resolution the altimeter have and by looking at the noise in the altimeter, figure out what accuracy you can expect.  If you can find out what the ground temperature was for the time of launch, you can correct the reported altitude for the temperature difference.


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