3 fins at 90 degrees

[geof]

In principle, I can't see anything wrong with 3 fins placed at 0, 90, and 180, with no 4th fin at 270. I'm looking at a sort of airplane design with the middle fin at 90 being much smaller than the wing fins at 0 and 180.

I also know there are a lot of fighter-style rocket kits that work just fine. So my question is more nuanced: what "gotchas" are there? Will Rocksim faithfully and accurately represent the flight? Are flights somewhat squirrely unless the wings are canted down a bit? Other hints?

Geof

 

[wwattles]

Typically, the "fighter-style" rocket kits don't have their "wings" mounted directly at the 3 o'clock and 9 o'clock positions, even though they stick out at what looks like 90 degrees from the BT.

In this recent thread there's a really good pic of what I mean about 5 or 6 posts down, and the pic is called "wingsfromrear.jpg".

By shifting the attachment point slightly, it alters where the fin forces act upon the BT, allowing for an asymmetric fin shape (top and bottom).

WW

 

[geof]

So from the photo you referenced, it seems that you are suggesting that the wings get mounted *nearer* to the upright fin, rather than *farther* from it? And, in terms of degrees or % of tube radius, how *much* nearer? (Let's say the straight 3 o'clock / 9 o'clock would be at 100% of the radius and wings touching the upright fin would be 0% of the radius.)

I understand what you are saying about the angle of attachment.

 

[wwattles]

In the case of the Estes Screaming Eagle, it's got those huge honkin' jet engine nacelles that contribute to drag on one side, so they offset the location at which the force works on the BT by moving the connection point towards the "top" of the plane. Without the nacelles, you get something more like Star Wars Lambda, where the wings cant downwards.

I'm not an aerospace engineer, so for any other questions, some of the folks with more experience in that area are gonna have to speak up... (that's a hint to all y'all out there lurkin'!)

WW

 

[Stymye]

I've noticed everything has to be well aligned, no matter where the are on the radius. you can even put a wing on a fin, like my F-104. I also agree on the importance of distributing the drag force if you have cockpits, nacelles, ect. sticking out.

 

[Delta-IV]

Originally posted by wwattles
......I'm not an aerospace engineer, so for any other questions, some of the folks with more experience in that area are gonna have to speak up... (that's a hint to all y'all out there lurkin'!)

WW

My son and I have been able to adapt F-16 type lower strakes in some scratch designs that have flown quite well.

Attached is a photo of my son's latest, It has an aircraft style tail, 2 large clipped delta wings (slightly above the center of BT) and two smaller strakes. Flown twice so far.

 

[Micromeister]

PMC Modeler's have been flying models with wing fin alignments that are much more oblique than your talking, I toally agree with both WW and Stymye alignment of the wing/fins and canting them really helps keep the model flying in right direction

If you look at the F-16 and F15 Eagle I think you'll see the "balance" you looking for, keeping the thrust line alignment is Oh SO important as well. I squeezed the motor tubes just a tad out of alignment on this 1/32 F15 when installing the upper body. while everything on the outside of the model Wing, tails and elevators were perfectly aligned that minor thurst misaligment caused the model to Arc after. Had to disassemble and realign to get a straight and stable boost.

 

[adrian]

I built this model of the Feuerlilie F25 based on the plans on www.luft46.com. It flies well enough, although it does tend to roll a bit, but certainly doesn't arc or go unstable.

This model pretty much fits the description in the original post - large delta wings in the 3 o'clock and 9 o'clock positions, smaller tail fin in the 12 o'clock position, nothing in the 6 o'clock position.

 

[Micromeister]

Originally posted by adrian
I built this model of the Feuerlilie F25 based on the plans on www.luft46.com. It flies well enough, although it does tend to roll a bit, but certainly doesn't arc or go unstable.

This model pretty much fits the description in the original post - large delta wings in the 3 o'clock and 9 o'clock positions, smaller tail fin in the 12 o'clock position, nothing in the 6 o'clock position.

Your wing tiplets take the place of canting the wings.

 

[Micromeister]

The F-16 might fit your airframe alignment a bit closer. This 144th F16-XL's delta wing and smaller elevatorless tail might be what your looking for? Since i'm flying this one wheels out, they may add drag fin force to the flght but it flys very nice for a LPB type model. It's Heavy for a micro model

 

[teflonrocketry1]

Originally posted by geof
Will Rocksim faithfully and accurately represent the flight?

Geof,

Can you post the sim so we can look at the design?

Bruce S. Levison, NAR #69055

 

[geof]

I'll try to email it to you. I don't want to post it because the model is for a contest. After the contest is over, I'll post it.

Geof

 

[maricopasem]

I did a build and launch with my Scouts last week. One of the straightest flyers in the group was a rocket with fins like you described. I say do it.

 

[geof]

Bruce, check your email. Thanks!