Boof's Build thread

[Boof69]

I originally posted this thread in the project list page. So now I started this build thread in case anyone may be interested in following along with the design process.


I've decided to model this GR-7 Formula one racer. A designer by the name of Robbie Grove created this in the late 80's. There were only two made #55 "Bummers Bullet",and #96 "Blue Streak". Although not a winner the blue streak was a top qualifier in 1989 clocked at 242 mph. The only design info I can find on this one is that it has a high aspect ratio wing for turning stability. Also there's a pic of # 87 Madness (formerly #96)without it's cowling, and a four cylinder engine is clearly visible. Maybe someone could tell it's make just by looking. Also anyone who might be able to make a guess as to the airfoil would be a big help. Anyways its a racer just like the "little tony" found in G3 expansion pack 3. There are some differences though especially at the tail section. This is a very small full size aircraft and I'm not sure what size I should make the RF model. So i'm open to suggestions on that.

 

[Boof69]

First day's progress

This is the end of the first days work on the GR-7. This the progress this far!

 

[Boof69]

with wings

I went ahead with modeling the wings. Would've posted last night but Comcast went down in my area last night.

 

[Boof69]

Six hours in

Around six hours into the project and the model itself is done. Pivots are set, naming done, and parenting. Time to export and set up some physics. I think I may scale this one up a bit. maybe a 50%. sounds big I know but the full scale is a very small single seat racer. 26 foot wing span. Unless someone can convince me otherwise.

 

[Boof69]

Setback!

Well I thought i'd go a little further an proboolean the holes in the cowl for the exhaust. when I did it seemed to have deleted the fuse. I was zoomed in and hadn't noticed what had happened. then my video card crashed and scared me into a save. Needless to say I have to redo the fuse.

 

[Boof69]

Fuselage redo

Well because of my own stupidity I had to redo the fuse, but after a couple more hours it's once again a complete model. One good thing came of it. I reduced the poly count by 474. Oh and the original had an extra set of polys to the rear of the canopy added making it too long. Oh well stuff happens.

 

[bmz_loop]

Looks good Boof! Fast Progress too! Can't wait to fly this beauty.

 

[Boof69]

Thanks I can't wait either. I'm setting up physics today and starting mapping to prep foe the color scheme

 

[dhk79]

As for your airfoils, most of these modern high-speed racers use full symmetric airfoils that are fairly thin. Without actually making measurements, I'd say start with 9-11% airfoils with 0% camber on the mains and NACA 0008 on the stabs and you'll be on the right track

 

[Boof69]

Thanks I'll start there. I'll let you know how it goes

 

[Boof69]

Well I believe I have this GR-7 model setup the way I like it in RF. I went with a NACA 0010-34 from root to tip. I added 1 degree of incidence to the main wing. I see some incidence in the photos. The engine I chose was the "pylon 1.60 2-stroke". Not sure if it's an engine thats default in RF or if it's imported with one of the many downloaded planes I have. It's turning a 18x12 Mejzlik carbon fiber narrow prop. Servo speed is .23 and all the servos are digital.It seems well balanced and the stall severity is set to 80% on all flight surfaces. I'm sure it's not the final configuration but for now it's a start. Here it is in temporary green for the test phase in RF. Next I think I will model a cockpit because it is currently only 4212 poly tri's> I think all said and done it will be bellow 10k.

 

[dhk79]

Question - Do you have an engineering reason for overriding the stall?

For example, does the aircraft have some wing modifications that RF cannot simulate. If not leave those kinds of things alone. The only physics override you should consider is the frontal drag on fuselage/moving pod items that are not "rectangular" in their frontal aspect.

 

[Boof69]

You recommended it!

Actually I was following a recommendation I read in a physics setup tutorial, you wrote I believe, stating that RF default setting of 0% for stall severity was non realistic and that even stable aircraft should have settings over 50%. and settings of closer to 100% or more for aerobatic planes. Has your stance changed on this and I missed that thread or did I misinterpret?

dhk79 posted on 7/05/2007
"A good catch from opjose is that the default Stall Severity for all airfoils is zero. This value make the stalls in G3 unrealistically gentle and makes certain aerobatic maneuvers nearly impossible. In playing around with the effect of this setting, we have determined that all airfoils should have at least 50% (even the most docile). Mid-lift airfoils that are commonly used in most sport models in the 70-80% range and low-lift airfoils found on 3D craft closer to 100%"

 

[willsonman]

He's right there Doug. Honestly... I would set it up with closer to 90-95% myself. I reserve 50% for big bombers and 95-100% for jets. This would be my recommendation for the wings... The fuse is a different story. huh, then I guess you are both right.

 

[flip3d]

Default Value:

Boof! Put it wherever you wish.

In my experience the "Stall Severity %" is as relevant as "Snap Roll Boost %". "Snap Roll Boost %" doesn't do squat! At least in the most recent version of RF. Maybe it's a remnant of previous versions.

By the way... Love the video of GB! Speaks volumes.

 

[Boof69]

Boof! Put it wherever you wish.

In my experience the "Stall Severity %" is as relevant as "Snap Roll Boost %". "Snap Roll Boost %" doesn't do squat! At least in the most recent version of RF. Maybe it's a remnant of previous versions.

By the way... Love the video of GB! Speaks volumes.

I don't know about snap roll boost,but stall severity does work. It's small but at low speeds while applying rudder this setting will give more realistic tip stall. try it with a tail wind too. It just adds a little. I feel RF has a bit of a floaty feeling. therefore the planes usually are easy to fly. This does help a little. In my opinion anyway.

 

[flip3d]

I don't know about snap roll boost,but stall severity does work. It's small but at low speeds while applying rudder this setting will give more realistic tip stall. try it with a tail wind too. It just adds a little. I feel RF has a bit of a floaty feeling. therefore the planes usually are easy to fly. This does help a little. In my opinion anyway.

Try altering wing lift, post stall moment factor, fuse aerodynamic percent. These parameters in conjunction with component weight (overall airframe weight) will show the greatest benefit.

 

[Boof69]

I'll do just that thanks for the helpful tips. If you have any more please don't hesitate to send them my way.

 

[flip3d]

I'll do just that thanks for the helpful tips. If you have any more please don't hesitate to send them my way.

Concentration of mass within the airframe may be usefull as well. Essentially adding a "Mass Component" (Ballast) in specific location(s).

Oh yes... Before I forget. Don't be afraid to turn up the "Feel Good Component %".

 

[dhk79]

That old recommendation was based on G3 defaults being a bit unrealistic. I guess that with G4-G5, there really isn't any default any more, since it always bases the initial physics off of a plane that you choose. So you're probably right in that you have to do something with it by considering what type of plane it is. That being said, with the airfoils you are using (i.e. 0% camber = 0 aerodynamic lift) and on a racer the value should be very close to 100%.

I do stand by the adage that if you don't understand why you are making an adjustment, you probably shouldn't.