AVENGER - Evolution

The evolution of the AVENGER has taken roughly 2 years and 9 iterations.  I thought by documenting the evolution of the AVENGER I can for one, prove to Michele that we have in fact had 9 AVENGER designs and secondly thought it would be interesting for folks as I believe the AVENGER has very closely tracked the evolution in OPEN B.  Not to mention, for those new combat pilots and designers it may save some time when you decide to start designing a new killer combat machine

The first AVENGER, the 1.0, was designed and built prior to the Waverly, NE contest in June of 2001.  Prior to Waverly we had been flying the venerable Montana Mauler designed by my father Earl Seaholm.  The Montana Mauler was an outstanding flying B design and got it's inspiration from the revolutionary Raptor designed by Richard Oliver.   The Maulers suffered in the durability department and I set out to create a tougher design while still maintaining the high performance level of the Mauler

The pictures above show the Montana Mauler's design.  The down spot fuselage had a tendency to crack and come apart during a mid-air.  I also suffered from frequently breaking the glass filled plastic motor mounts.  Curing these 2 problems was high on the objective list for the new AVENGER

Before I put pencil to paper I took a Plastics Engineer friend of mine to lunch hoping to pick his brain.  I asked what material he would use to create an impact resistant fuselage.  He replied with polycarbonate, more commonly known as Lexan.  I liked the idea and felt it could be done with the profile fuselage idea I had been pondering.  Off to Home Depot I went in search of Lexan to build the first AVENGER.  Home Depot carried 1/8" thick Lexan, wanting a thicker fuselage I decided to use a core material to increase the over all thickness of the fuselage.  I decided bass wood would be the material due to it's high stiffness and minimal amount of grain.  I determined ply wood would likely delaminate if struck while the bass wood should remain intact, later this theory proved to be accurate.

The problem I had seen with other profile fuselage designs like the Raptor was the rigidity of the wing fixed to the fuselage.  During my engineering classes I had studied impact mechanics and learned rigidity in a structure is the enemy when trying to dissipate impact energy.  The longer the impact duration, or the time the impact occurs, the lower the impact forces on the airframe.   With this in mind I designed what I felt was a unique system of locking the wing to the fuselage while still allowing the wing to shift during an impact.  I hoped the rubber bands would absorb most of the energy while the notched and key fuselage and wing would keep the two aligned.

The AVENGER 1.0 wing design was very similar to the Montana Mauler except for the leading edge reinforcement. The wing used 1 pound density white foam with 1/4" x 1/4" spruce spars and a 1/8" piece of spring steel for the leading edge. The wing span started out at 55" but was trimmed back to 52" prior to it's first battle in order to increase roll response.  The 1.0 survived 3 of 6 rounds flown at Waverly and made it through 3 mid-airs including a nasty tangle with Mike Fredericks' JETT powered Bat Trick.

I was happy with the performance of the new AVENGER but realized the wing needed to be strengthened and the spring steel was far to heavy as leading edge reinforcement. While I was developing the first AVENGER a local combat pilot discovered a material called G10 at a salvage yard. He picked up 2 sheets measuring 3'x4' of G10 for $4 and built a combat fuselage similar to the AVENGER with this material. I had experienced Lexan cracking at the front of the AVENGER 1.0 fuselage resulting from the vibration of the engine and decided to give G10 a try

The AVENGER 2.0 was built using the new G10 material and after a few hard mid-airs survived very well. The main problem I was still experiencing was wing failure. The AVENGER 2.0 used hollow carbon fiber shafts for the leading edge but the spruce spars still were vulnerable.  The AVENGER 3.0 used the hollow carbon fiber tubes as spars to eliminate the spruce spars failures experienced in the 1.0 - 2.0 versions. I also went to the higher density 2 pound density blue foam for the 3.0 after competing against the kings of durability Rick Fraley and Mike Fredericks. The Bat Trick and T-Rex each used the higher density foam and put a hurt'n on a number of the early AVENGERS.

The AVENGER 4.0 had a number of rather significant design changes including lengthening the tail moment 1.5" and eliminating the cut out in the front of the fuselage. The fuselage cutout was a weak area and I soon discovered the fuel tank could be side mounted to the fuselage which used the cylinder of the engine for streamlining.

The AVENGER 4.0 white foam with hollow carbon fiber spars and a solid 1/4" fiberglass rod for the leading edge reinforcement. The lower density foam was used due to the weight of the solid glass rod in the leading edge. The 1/4" rod weighed approximately 3 ounces. The 4.0 was also a test bed for a number of different wing platforms trying to enhance turning performance and streamer grabbing area. Wing spans ranging from 48" to 56" were used trying to close the gap between the AVENGER wingspan the famous 72" Bat Trick flown by National Champion Mike "Dr. Evil" Fredericks. I experimented with extended coroplast wing tips as well but suffered stability problems, which I would later discover was from insufficient vertical area.

The AVENGER 5.0 was designed after once again taking a beating from the big dawgs of the sport at the Upper Midwest Nats outside Milwaukee Wisconsin. I destroyed 3 white foam wings and decided if you can't beat them join them. The 5.0 used the higher density 25 psi crush foam with hollow carbon fiber spars spanning 36" and the solid 1/4" leading edge. I also decided a 50" wingspan was competitive after successfully edging out Dr. Evil 3 times from June through July in 2001 with the shorter span. I chose to try Fredericks and Fraley's technique of using Rip-stop Nylon to cover the wings. The 5.0 was by far the best flying and most durable AVENGER yet. It proved to be a very durable design as the 4 wings survived through the final 6 contests of the season. I still have 2 flight worthy 5.0 wings in the shop after loosing number 2 late last year at a local C Class contest.

Following my first full season of OPEN B and 5 iterations of the AVENGER I came in second in the RCCA Open B NPS to Mike Fredericks.  Although I had unbelievably beat him head to heat 4 out of 5 times I still didn't have the big rounds in my NPS scores.   What I found was the 50" span could be flown consistently to 3-4 cut rounds but the big 5-6 cut rounds were nearly impossible, for my skills anyway.  So the fall of 2001 I set out to design a larger span AVENGER that could perform close to the 5.0 I had grown so accustom to.

The AVENGER 6.0 used the 5.0 fuse but I stretched the wing to 64".  Why 64", well if divide a 8' sheet of foam into thirds you get a 32" core, or a 64" inch wing span, pretty high tech I know.  Wes "Sheepy" Parmenter found a local supply of 60 psi crush foam to try on the new long winged AVENGER variant.  The first 2 6.0's used the same root as the 5.0 at roughly 10 inches in chord.  I experimented with 2 tips, the Selig 8035, and the Selig 8036 after many hours examining a wide range of airfoils with SNACK.  I also came up with a technique to use the foam core as the ailerons.  I simply cut out an aileron that measured 30% of the chords and then glassed the foam ailerons to add some rigidity.  The first test flight of the AVENGER 6.0 really impressed me.  Fredericks had been telling me for half a season that more wing area not only helped grab streamers but also made the planes turn harder.  He was absolutely correct as the AVENGER 6.0 turned far harder and in a shorter radius then the 5.0's from a year before.    

The debut of the AVENGER 6.0 was January 2002 at the Houston Winter Nationals.  OPEN B was flown on a blustery rain soaked day following a soggy bench racing filled morning.  Due to the wet conditions, we used the biodegradable flagging tape for all 4 rounds of the competition.  The first 3 rounds I scored very poorly as I found it difficult to line up on my targets with the larger span.  I was also without my trusted spotter Michele, so I suppose I was lucky to get any cuts at all.  It finally clicked in round 4 and I scored my first 5 cut round with the AVENGER and it appeared the long span was going to pay off. 

This big round revealed the first major problem to overcome with new 6.0.  The yaw with a couple streamers draped near the end of the long wing made it nearly impossible to stay in the mix.  To cure this issue I nearly doubled the vertical fin area and added a sub fin after discussing the problem with another Honeywell engineer, who has a wealth of aerodynamic knowledge.  To counter the added weight of the additional vertical fin I decided to try a full flying stab.  The full flying stab would cut the horizontal area nearly in half and more importantly reduce the tail weight to keep my CG close to the proven location.  The increased vertical worked better but I still snapped a plane into the ground with a streamer on the tip at a Wichita contest and decided to go even bigger.  The final vertical design was close to 75% larger then the AVENGER 5.0 and would hall 3-4 streamers on the same wing tip without missing a beat. 

The foam ailerons of the AVENGER 6.0 proved to be time consuming to build and I was determined to reduce build time while still maintaining the excellent aileron roll authority.  I had also decided the Selig 8036 tip airfoil was a slightly better performer and figured it would make a suitable root airfoil as well.  The first Selig 8036 airfoil wing was actually built by my father after I e-mailed him the new templates.  He used 1.5" aileron stock for ailerons with rip stop nylon and an updated slab fuselage on his new Mauler design.  We test flew the new wing design while I was home visiting and it was immediately clear the Selig 8036 had amazing potential.  His Mauler was turning unbelievably hard and had very good roll authority for quick changes of direction.  I knew I was on to something with the Selig 8036.

The AVENGER 7.0 was the first design that used the full Selig 8036 airfoil and updates from later versions of the 6.0.  At the Houston Winter Nats, Mike Fredricks and I had discussed his CNC foam cutter and I asked him to cut wing cores cut from 40 psi crush foam.  His prices were very reasonable and his cores were all nearly perfect. 

The first contest for the 7.0 was Paris Texas in 2002 where it performed very well and helped me secure a victory for a second straight year.  The 7.0 also helped me score my first ever 6 cut rounds at the Dixie Nationals in May to help me win over a very tough group of competitors.  I sold AVENGER cores and instructions for the 7.0 at Paris and Dixie.  The feedback I received was people were having difficulty with the full flying stab.  The full flying stab decreased the margin for error with aileron reflex, CG location, and elevator throw.

Neal Rohrke from www.waverc.com approached me following the Dixie contest with a proposition to kit the AVENGER.  With the feedback gathered from the 7.0 sales I once again redesigned the AVENGER with the objective of making airframe set up more user friendly. 

The AVENGER 8.0 used a conventional style horizontal stab and to offset the additional weight the nose was lengthened slightly.  The first 8.0 was flown at a local contest to verify the changes worked.  That first round I collected all 7 of the opponents' streamers and it flew like it was on rails.  I felt bad and put the 8.0 away and flew the remaining rounds with 5.0's left over from the year before. 

 

While producing the 8.0 in kit form I continued development for future releases.  I began receiving reports about the wing lock system loosening the bottom spar after a hard mid-air.  The system that had worked so well on the shorter wings was now failing due to the additional leverage from the longer span.  About this time Stan Erwin had released his Bandit design.  Stan's velcro wing hold down was ingenious and I did as all good combat pilots do, borrow the great ideas.  I began building my AVENGERS with the velcro wing hold down and eliminated the spar-loosening problem. 

The AVENGER 9.0 has been redeveloped with the lessons learned from the previous 8 versions.  The weak areas have been strengthened and the flight performance has been increased slightly.  I experimented early in the season with a new airfoil and larger wing.  The new wing design needs some more development before it's ready for prime time so I decided to fly out this season with the slightly modified but battle proven wing design of the 7.0 and 8.0.  I entertained the idea of using a HDPE fuselage but decided against it after noticing HDPE's tendency to warp and bend on hot summer days.  I did however incorporate the HDPE for the 9.0's landing skid and removable motor mount.  The 9.0 performed well in both Paris Texas and in Ashland City, TN.  

 AVENGER Tid Bits: 

Canard:  I experimented with a canard on the AVENGER 5.0.  The canard didn't have much authority due to it's short moment from CG to AC of the canard.  It looked pretty neat though. 

Coroplast Wing Tips:  The flat wing tips brought the wingspan to 58".  Stability issues arose with the relatively small vertical fin 

Spars, spars, spars:  There have been about a dozen spar combinations associated with the AVENGER design including spring steel, carbon fiber, glass, spruce, pine, and others 

Foam:  There have been 4 different density foams used with the AVENGER, white foam, 25 psi blue, 40 psi blue, and 60 psi crush strength foam.. 

AVENGER Images

I hope you've enjoyed this look into the evolution of the AVENGER.  I believe it outlines fairly well the vast number of changes we've seen in the sport of the past 2+ seasons.  If you have any questions or would like a digital copy of a set of plans, don't hesitate to drop me a line.  Be sure to look for the new AVENGER 9.0 on a six near you...


A.J. Seaholm
Publshed: 10.28.2002

This article was first published on the RCCA website www.rccombat.com