Dialing in the Thumper

This evening I worked on getting to know the machine and making it more pilot friendly.

First I set up the foot steering with all new webbing.

Then I remounted the tach at a better angle so that I’ll be better able to read it in flight.

Then I lowered the back pad so that I can look over my shoulder. It might be too noisy but it feels good and the additional visibility is great!

Last I mounted another mirror in the crook where the bullet bars come together so that I’ll be able to see the wing during the first seconds of inflation. I’m hoping this will be a temporary training device and I won’t need it.

No Fly Day…

65 degrees

light and variable turning strong from west

Got to the field by 3. Driving North on C 470 I saw moderately strong air coming from the East by North East. At the Hampden & Simms is was manageable but I soon noticed that it was swinging on a huge ack from south to East To North and back again.

I was a little skittish especially since I had guess that the prevailing wind would be from the East.

There were a couple of spectators watching when I set up to launch and reported that the wind shifted from the west just before I started the motor. The wing came up crooked and collapsed quickly. It’s probably a good thing I decided to about. It continued to build and when i unhooked and kited the wing… it was strong and twitchy. Both tips collapsed in a sort of complicated pattern. It looked like it was going to continue building and I wanted no part of a spring air that was being filtered by the Rockies.

Mechanical I’m not sure that using shock cord for the A Assists is the best answer. I suspect that I didn’t get the tension equal and it was part of the reason for the bad inflation. Next time hook em up but still get on the A’s with your hands!

263 264 First Colorado Thumper Vance Brand

Temp 45 to 50 f
Climb 200ft/minute
Decent 200/minute
3550 max RPM
Powerplay Sting 250

It was good to get this one past. I met Robert K and Marek M out at Vance Brand Airport.
We launched at 3pm in light winds from the North East. First attempt went bad when the A Assists were not putting enough pressure on the wing causing it to hang back. On the other launches I got on the assists manually and it came up just fine.
(change the endless clamps so the tails point into the cage instead of out where a line can get into them)
Another thing is to be sure the Starter/Tach bar is on the correct side when attaching the risers.

I accidentally killed the motor at 230 feet, when I noticed the starter bar was being pulled by the riser strap. I had time to try one restart but failed and came in dead stick. Smooth as a baby’s butt!

Second flight was great…no problems 200ft/min climb and about the same decent.

Monte’s Powerplay Sting was rock solid and the brake pressure was about what I was used to with the old rig.

Marek and I kited Brian’s wing…it is 2003… very light construction and absolutely not the right wing for this application….nuff said

I need to find a better way to hold the Throttle or get a different one. The ol fresh Breeze lever would probably be just fine.
The next time I’m going to try using light bungee cord for the A Assist to see if I can get some more pull on the A’s and not be pulled forward of the rest of the risers during flight.
One thing that has to be mentioned. At one point I hit this spot on the power band where the noise and vibration was reduced dramatically. It was eerie, for a second I thought the motor died. I think it was a combination of things including including belt slap, prop flutter, and who knows what else. It’s too bad that it was at 2250 RPM which won’t sustain level flight. But I’ll bet it would at sea level with a 62 inch prop!

Cage Netting


During the Salton Sea and at the Flying Circus there were plenty of opportunities to stand around the Thumper Bullet and critique the design.Whenever the topic of cage netting came up I was surprised when the first thing said was, “Your going to lose thrust!” or “Its a trike you don’t need it.” These comments came from respected pilots.So…How much thrust can it lose?Especially when your not as concerned about keeping hands out of the prop as that rare time when the wing does the unexpected and a line falls near the prop.The thumper cage is new and twice pilots hooked a line at the Salton Sea. PLUS…a four stroke doesn’t shut down as fast as a two stroke so there are going to be a couple of revolutions after you hit the kill switch.

You don’t need much…

I’m not talking about some of the “hammock netting” I saw stretched over the cages of brand new quads.I’ve posted pictures of a minimal net meant to protect from Line Strike. Zip ties make it easy to get the lines tight as a tennis racket and 300 pound deep sea braid is thin and easy to tie.

Redundant Zip Ties

( one under tension)

Tweaking the Thumper

A assist with rope ratchet

— On Wed, 2/18/09, jo3jo2003 wrote:

Terry Chad,
I’ve been dialing in the “Colorado Bullet Thumper 4stroke”.Epoxy Gel and a new longer split fuel hose anchored the motor end of the throttle cable. It was moving around and preventing a true idle.The engine is max at 3800RPMidle at 1800RPMI can probably Pitch the IVOs more…BUT?Chad…how far can you pitch the IVO blades and how do you know when to stop?Can you “over warp” them and damage the system?Maybe I should learn how to measure the pitch just for the “pure research” as you put it Terry.I was glad to read about “belt Flop” on the slack side of the drive system. I’ve noticed some flop and wanted to ask how to determine correct belt tension. If I understood you right what I’m seeing is about normal.Last…Terry ….what do you think? The local Briggs & Stratton guys say I can install the high altitude carb kit in 15 minutes or less. I’m going to be launching from 8200+ MSL a few times this summer and the rest of the time will be at 5300 MSL. I’m thinking that it might be a good if I used Hi Alt jets here in Denver and the mountains and switched to the stock jets for the coastal stuff. These guys are willing to show me how to install and adjust them for the price of the labor Don’t worry….Before I start changing anything I’ll see how it does at the home field. But I wanted to run it by you.It’s just too damn cold and the best I can do is tweak the machine.

Hi Joe, I was thinking of you today.

I think 3800rpm is fine.

Belt ‘flop’ on the slack side is normal, but I find it’s best not to watch it;); BTW, I have never lost a belt or even had the belt jump a groove. Belt tension is not something you need to worry too much about..tension it about like you would your underhood car belt. If the belt ‘flops too much to suit you, tighten it a little more, you won’t hurt anything (however it’s probably just fine right where it’s set now)

I don’t know about hi elevation carb kit, but I am curious about it..I wonder what the kit includes? Smaller jets? Different air filter?
One thing that might help is to remove all the filters from the intake shell. Please let me know what you learn about the kit.

It’s cold here too; I delivered a new unit to Indianapolis on Sunday and I demo’d it for the buyer; a 5 minute flight was plenty for me.


Flying Circus Wrap Up

The drive home was good. I had a massive cold front following off my left shoulder all the way from Albuquerque. At one point the shadow from the leading edge was playing tag with the truck and we were doing 80 mph! Fortunately it stalled at Raton and I never had to deal with icy roads.
The Arizona Flying Circus was great….frustrating but great. Lots of vendors including ParaToys who would never have been welcome or inclined to attend under Bob’s ownership. Nirvana and Paradrenaline were there and their “factory Pilots” put on a great demonstration of flying in ratty air and high winds.
I spent most of my time dealing with equipment issues. The first morning was the most heart breaking because I walked off the field when the battery died. It was two days later that I realized that all I had to do was use the pull start. Doh !
The new cage arrived on Friday afternoon and I spent the afternoon working with Bob Pelloquin to get it assembled and mounted on the frame. As fate would have it there was a crowd of luminaries standing around when it was time to fire it up. Sure Nuff there was a prop strike and one of the tips was damaged. That evening after dinner with Jim King and a couple of other pilots I sat in the hotel room and replaced the blade with one that Johnny Fetz had repaired while at the Salton Sea.
The IVO Prop is an amazing design that enables you to adjust the pitch of all three blades simultaneously by turning a bolt in the hub. Counterclockwise to increase pitch and clockwise to reduce pitch. I had to take it apart and assemble it twice before I got it right but that seems par for the course for me at this fly-in.
The next morning I attempted a launch but the wind picked up and I didn’t react fast enough when the wing pulled me backwards. The buggy rolled to the left and I was forced to kill the engine and abort. Jeff Goin was filming so he was able to brief me on what the wing did. I’m going to have to increase the tension on the steering bungees so that it rolls straight. While I was out there a pilot asked me to start the machine so that he could hear it. Right away it was obvious that the prop was badly out of balance.
The rest of the day I spent working on the machine. Bob and I did some creative bending to increase the clearance and Kent helped me out with shortening the blades by 2 inches. I was wary of making the cut but Kent dug in and they are looking good and well balanced now.
Saturday afternoon was the Bowling Ball Cannon and later the Banquet. It’s all Good.