Getting Started in GSR, A Rookie's Perspective

[joeraf]

bodywerks,
1. The black tube is part of an air induction system. Since the cowl closes up pretty tight, air needs some pathway to feed the engine. It's kind a a wag in designing an efficient system and I copied aero guru Robert Vess's system.

The 1" tube runs back to a NACA inlet.



I got the information for the duct on the internet. Just search for NACA inlet and you will get some basic scalable dimensions. I had to do a little bit of work in terminating the tube in the duct. But this was easily done carving balsa plug and making a fiberglass connecting piece

2. The alcohol engines tap crankcase pressure for positive feed. Since the fuel system is pressurized we simply branch a line from the engine inlet feed to outside the airplane. That line is pinched through an appropriately sized hole and controlled by a servo. When the line is unpinched the pressure dump instantly kills the engine.

It may be difficult to see, but the servo in the next picture is the engine kill servo



3 The fuel mixture is controlled individually thru each stack by the mixture control valves. These are available thru Bob Violett Models . You are correct in that as the throttle moves to full open the mixtures move toward a rich setting. This is done by a mix on the radio. We set the WOT mixture settings on the ground trying to balance cylinder temps with either an IR temp gun or mounted thermocouples. I use a data aquisition system and can fine tune the engine between heats.
This system was shown to me by engine guru Fred French as part of his engine modification package.

[Biff]

THANKS GUYS! Great info here. Bodyworks, caution my friend. If you head to Parker, you'll show up in Tucson with a real need for speed!!!

[bodywerks]

Biff, My need for speed is already satisfied with a 140MPH pylon racer that is smaller than a Shockflyer! Too bad you'll be busy all week or you could come out and see it. It's harder to fly than anything I have ever flown, and I've flown jets, too!
Thanks for the info. I have NACA scoops all around me (I'm an aircraft mechanic) so I know where to copy one from, lol!
I am not looking for sponsorship, but rather ecaxtly everything you just said about the advantages of a race team, particularly logistics. It would be nice to have someone with the time to haul the trailer around, and since I get a REALLY good discount on tickets, I can fly to the destination!

[TheTank]

This a great thread! You can really see the amount of thought and design that goes into these racers! Unbelievable!

[joeraf]

Notice the pushrods in the previous shot of the tail. I first mounted the rudder servo back near the stab. I mounted the elevator servos forward under the wing because of rumors that the plane tends to come out tail heavy. I had a difficult time finding suitable pushrod material. Arrowshaft material is usually cut to 32”. I needed 34”. I fished around on the net and eventually found an excellent source for all types of pushrods and carbon tubing.
The guys who build big kites use a ton of this stuff. http://www.kitebuilder.com/catalog/


Central Hobbies, the pattern suppy store, has some nice titanium rod ends in larger sizes . http://www.centralhobbies.com/control_linkage/pushrod3.htm


All of the servo mounts had to be fabricated and I had to figure out a control horn system for the elevators. The elevators had a 1/4” diameter torque rod built into each half. I tried fabricating my own horns and was never satisfied with the results. Again, google came to the rescue when I found Sierra Precision. http://www.sierragiant.com/products.html I knew that Sierra makes some beautiful giant scale retracts, but found these gems.





I modified the horns a little bit by drilling and tapping for a 2/56 socket bolt through the center of the clamping ring to provide for more bite on the torque rod.


I have been making servo mounts for years using aluminum angle. This is time consuming in getting a precision fit. I was pleasantly suprised when I saw that Sierra was producing these mounts.




I finished the construction with the landing gear and wheel pants. The gear supplied with the kit are carbon. I was concerned about the strength of the gear as several people told me that they tend to snap easily. I replaced the gear with a set of TNT 1/4” aluminum gear. I thought I could save weight by having a machinist friend cut a profile. He did a great job and polished the gear to a high gloss. I liked the look. Nice to have extra bling to psyche the competition.




That finishes the build highlights

Next prepping, testing, racing

[CRG]

Totally excellent thread Joe! Lots of good info here that helps people understand what goes into a racer. It's only natural after a while to take certain stuff for granted and skip over items that someone new to GSR might not know.

Craig.

[joeraf]

Thanks Craig,
This was mostly Robert's idea and he assigned me the job. I think he wanted me to quit bugging him about "the project" and thought this would keep me occupied

[joeraf]

I joined the USRA in early 2005. I thought that I would receive useful information on the organization, racing information, contact numbers, etc. I was disappointed when the only confirmation that I had any contact with the organization was a canceled check. This year was much better as my renewal was promptly confirmed and a member number assigned.


Prepare to be frustrated at times. A simple question such as “what race number should I paint on my plane?” turned into a time consuming research project.

The short answer to race numbering kind of materialized on the USRA discussion forum earlier this year. This is what I deciphered.... Paint any number you want on your airplane, but don't duplicate the numbers of veteran racers because it tends to make them peevish. How do you know what numbers are being used? Easy, just sift through the last five years worth of pictures on the USRA site. I did this diligently and sure enough even then duplicated a long time racer's number.


There is good information on the USRA website but it is not all inclusive. Wade through all of the sections and if something is unclear ask questions on the USRA forum or here. KennyMac who has posted here is extremely knowledgeable. Best of all he is a consistent winner who is willing to share this knowledge. Luckily, teammates Robert Vess and Larry Lewis had gone through the same experience as they prepared for their first race that year. Don't obsess over the small administrative things as most of these would be taken care of at the race.


I was ready to test fly my airplane in early June. Vess secured a super secret test site, really just a farmers small private airfield, and the fun began. The F1 generally is easy to fly as long as a good CG is established. Control surface throws are very small. I started with 1/4” up and down elevator and aileron throw with all the rudder I could get, about 1 1/4” left and right. A smooth flying plane is a fast plane and with the exception of the turn, abrupt stick movements just slow you down.
I didn't get the cg far enough forward on the first test flight. I was told that the airplane would be “a bag of cats” with an aft CG and this turned out to be the case. The plane was difficult to trim and difficult to fly a smooth racetrack pattern. A subsequent check showed that I miscalculated MAC and was flying at 26% verses the 22% recommended to me by Fred Sattler. Why did I have to do this calculation? Remember that the plane came with no instructions or specs. You just have to go with the best information you can get. Moving the CG forward resulted in a stable, smooth flying plane. The downside was the requirement for a lot of lead in the nose.


I decided to run in the GT class for my first race. The engine is easy to operate and makes that variable manageable. I talked about break in earlier. Reset the magneto gap to the width of the thickness of two business cards. Needle settings hardly move.... 1 1/4 to 1 1/8 turns on the high end 1 1/4 on the low. This is almost universal on the GT-80


Every landing in F1 is a dead stick landing. The high pitched props and low drag airframes make powered landings almost impossible. Robert coached me through the first landing. Idle power, burn off excess energy, set up a good down wind, kill the engine, don't turn in too early. Still, the plane shot by waist high gliding a long way and finally stopping near the end of the 2500 ft strip. I learned to control the landings a little better by paying attention to the nose attitude adjusting the nose up slightly when too fast to bleed excess speed and nose down slightly to extend the glide. Add a little crosswind and things get interesting. Don't touch the rudder on the race course but be prepared to use all you have for the landing.


After the third test flight I was satisfied that I wasn't going to embarrass myself in front of the GSR crowd. On to Rantoul for my first GS race.

[CRG]

I had the same issues with the race number, and was part of the discussion on the USRA forum. I thought I had found a number I liked and that nobody else was using, only to take the airplane to Rantoul and see another GT entry with the same number. Seems protocol in that case is the first guy to register gets to keep it, the second has to add an 'X' or 'a' or whatever to differentiate.

	Quote: Originally Posted by joeraf
	Prepare to be frustrated at times. A simple question such as “what race number should I paint on my plane?” turned into a time consuming research project. The short answer to race numbering kind of materialized on the USRA discussion forum earlier this year. This is what I deciphered.... Paint any number you want on your airplane, but don't duplicate the numbers of veteran racers because it tends to make them peevish. How do you know what numbers are being used? Easy, just sift through the last five years worth of pictures on the USRA site. I did this diligently and sure enough even then duplicated a long time racer's number.

[KennyMac]

I'm glad you hung in there with us Joe... We still don't have a readily available one-stop source for all of the info you need to go racing. But as you found out, it's not because we aren't willing to share the info, it's because we are too busy building and racing to put it together!....OK, poor excuse....

The racing number thing sure seems like a simple issue, but it's not...as you found out. We used to publish the heat races and series points with the pilot's name and tail number attached. It was easy to then look at past results online and find out what numbers were being used. I don't know why we stopped doing that, but we did. An idea was floated around about registering numbers, but that has drawbacks as well. I think it is likely that the USRA will publish tail numbers in use so that new racers can pick one easier, but that won't be a guarantee that someone else won't pick it too. An imperfect system, but it ruffles the fewest feathers and rewards those who pre-register early and help out our race promoters.

KennyMac

[RobertV]

Why don't we help the USRA implement an "Assigned Race Number" table on their website that users can log onto and see what's in use. Our local club (RDRC) uses this method to allow members to see what frequencies are in use and it's easy and effective.

See it at : http://www.scootworks.com/rdrc/freq.html

[joeraf]

Kenny, I'm wondering about the need for required numbering in it's present configuration. Can the pylon workers really see them from that far away? I would not mind using vinyl in the aft fuselage area. Makes it easy to change. But the big numbers on the bottom of the wing in my opinion need to be painted on.
Joe

[joeraf]

The event schedule is usually Thursday...set up, tech inspections, practice, Friday-Sunday...racing.
Without tech inspection the plane doesn't race. There are specific guidelines spelled out on the USRA site.


All new planes must be inspected and approved by a designated inspector, then issued a logbook. I opened up all access panels and left the wing off the plane before tracking down Scott Hanbury to do the inspection. Be prepared to answer questions about construction, battery maintenance and servo specs. The airplane gets measured to ensure minimum dimensions are met. Scott took a couple of pictures required for the log book and signed the plane off. Records are kept in the logbook pertaining to major repairs and battery maintenance. If the ownership of the plane changes the logbook remains with the plane.





It's then off to radio check. With logbook and tech sheet in hand, the radio is range checked with the engine running. Once the range check is passed, the logbook is handed over to race officials until the event is over.

Range check lineup. Vess photo



With tech inspections completed it's time for practice. This is an informal session to fine tune the plane and get used to the race course. Planes usually fly one at a time to minimize potential conflicts. It was exciting when the polecat fired right up and I made a nice straight takeoff toward pylon 1. Flameout, a quick 180, downwind landing, good to have the long runway, drag the plane back. That's when my teammate, one of the finest aerodynamicists in the country jumps in to analyze the situation. “Didja gas her up?” My blank stare confirms the validity that Roberts' teammate (me) is an idiot. Racing is all in the details.

[KennyMac]

Robert...I think a table for the race numbers would be a great idea. I would just leave out the word "assigned". But that's a debate for another time and place.

Joe....you are right that the pylon judges can't see the numbers, but the timing and scoring folks and flight line personnel can. Do they need a number on the bottom of the wing? Probably not. I think it's good to question these things. I think we could solve most of the number problems with a published list/table of numbers used in each class.

Keep up the cool thread! Let me know if I'm interrupting you too much.

KMac

[RobertV]

	Quote:
	Robert...I think a table for the race numbers would be a great idea. I would just leave out the word "assigned". But that's a debate for another time and place.

Kenny, I guess I meant it to be more of a "already in use" list that will inform everyone what numbers are supposedly out there, however active or inactive, so that people know what they should be able to use without potential conflict.