Onex Gross Weight

[vhhomer]

The specs for the Onex call for a fully aerobatic max gross weight of 950 lbs. Most aircraft, such as the Sonex have aerobatic gross and a standard category max gross weights. What would the standard category max gross be for the Onex? I ask this having just flown from Oregon to Oshkosh and back in my Jab 3300 powered Onex I can say that keeping under the 950 lb max gross is very difficult. My Onex has a 6 gallon auxiliary tank and with minimal baggage, well it's at a new max gross. We checked the fully loaded aircraft with me in the seat on the chapters W & B scales and found the CG to be in the forward part of the range, even with partial fuel in the main tank.

From a purely theoretical standpoint, increasing the max gross by 10% increases the stall speed by less than 5%. This puts the new stall speed at less than 50 mph, still under the LSA limit of 51 mph. An airframe rated for 6 gs at 950 lbs would be rated for ~ 5 gs at 1045 lbs. Of course takeoff distance would increase and climb rate would decrease at a higher max gross.

As a result of spending nearly 30 hours flying to and from Oshkosh I have a few conclusions:

1. a 2-axis autopilot is a must. I have only a single axis and spent the whole trip trimming for pitch. With no autopilot you couldn't even fold a map.
2. Auxiliary fuel tankage is a must, especially in remote areas. With 45 minute reserve you only get 2 hours per leg. Three would be better.
3. Even if the W & B allows it there's not much room for baggage.
4. A sunshade is mandatory.
5. More HP is better. I think the Jab 3300 is about right. The big UL or D-Motor might be better.

Vince Homer

[Gordon]

Onex Gross

Vince...........I was at Oshkosh all week and am sorry to say I missed seeing your airplane.....where was it parked? At the end of your post all your observations seem to be right on.

My Onex scaled out at 640 lbs with 5:00x5 tires and the long wing tips, etc, etc. Luckily I weigh 175 and with full fuel I am still only grossing 905 with out baggage. My Hummel 2400 is 85 hp but sure wish I had the 3300 Jab....it would put me a lot closer to my RV-7 performance that was used to.

Am a firm believer when it comes to horsepower....more is always better....sometimes it can get you out of a bad situation.

Gordon......Onex....Hummel 2400.....1st flight June 17, 2018

[vhhomer]

I probably saw your Onex if it was parked at the Sonex area. Mine was parked with the other Air Venture Cup racers on the flightline in front of the tower. I also spent a day and a half in the repair area down by the Vintage airplanes. My carb went south and the engine wouldn't idle below 1600. That made taxing and final approaches way to exciting so I bought and installed a new one before I left.

Currently, I have a Sonex and a Onex and after my xcountry to and from Oshkosh have decided to sell the Onex. It's a fun airplane if you don't want to go very far. The Sonex is much better for that.

Vince Homer

[vhhomer]

It has been suggested that I post about the Air Venture Cup Race, so here goes.

First, I must compliment the organizers and volunteers for making the whole process as easy and fun as possible. I suspect herding 50+ race aircraft and as many volunteers is no easy task.

I saw a bit about the race in a post on an aviation BB a few months ago and decided it would be a good "Bucket List" thing to do. Checking with the organizers I found out that there was some paperwork, of course, your wife has to give you permission and your insurance company has to supply a certificate insuring you during the race. Fortunately I have a good relationship with both and I was signed up.

The next was to figure out how to race an airplane with short legs and no transponder at a location 1200 miles away. I installed an old transponder that I had on hand, an Ebay encoder and antenna. It had to be mounted on the left side of the cockpit as there's no panel room or knee room to put it in front. It quit working as I passed through Missoula. So much for that effort. A wedge shape, 6 gallon fuel tank mock-up of cardboard was made and from that an aluminum tank fabricated. Once declared leak free it was mounted to the two cross beams behind the pilot and a fuel pump and appropriate plumbing installed. This allowed me to replenish the main tank in flight.

On a flight to Missoula for the AOPA fly-in in my Sonex my radio failed and I found out that a hand held with a little whip antenna is useless in the air. So, for the race i installed a 22" wire antenna and a mount on the right side of the cockpit for my handheld. A small tool box was fabricated that fits just in front of the wing spar and a minimal mountain survival kit assembled in a backpack. I left the smoke system in, but ended up not using it. Three sets of eighteen inch tall race numbers were obtained and slapped on and I was ready to go. Or, at least ready to fly 1200 miles to Mitchell, SD.
The three day flight from Independence, OR to Missoula, MT and Sheridan, WY finally to Mitchell, SD was long and involved lots of climbing topping out at 11,000 feet a couple times to get through the mountains.
Arriving at the race start I found out I would be in the same class as Midget Mustangs and Variezes, which meant I wasn’t competitive. Oh well, it’s the experience. On race day we were launched as rapidly as possible with some of the slower aircraft, a PT-23 and a Cub, going first. As it turned out there were headwinds all day at all altitudes so most of us flew at 2500 feet. The course was about 430 miles long with a midpoint fly-over at Owatonna, MN. With the head winds I didn’t have enough fuel, even with the auxillary tank, to make the whole race in one hop, so I stopped there for fuel. During the race I saw very few other planes and monitored activities on our own frequency. Of the 45 participants only one did not finish for mechanical reasons. The race finish was a fly-over at Merrill, WS then on to land at Wausau, WI.
As expected I placed 4th, out of four, in my class with an average ground speed of 131 mph. Considering I was low and the headwinds that’s not too bad. I did the calculations for climbing to at least 6000 feet where I would see faster true air speeds, buy the time to climb cancelled out the advantages.
It was now Sunday afternoon and I flew over to Oshkosh to land and take my place in the Race Aircraft viewing area on the flightline. How naïve! Rain the previous two days had hopelessly backup Witman Field. After two hours of circling the controller told us to go away and come back tomorrow. I did and got in race parking on Monday after nearly two more hours of circling.
The trip back was long and hot and somewhat tense as I was flying on a new Rotec TBI that I installed at Oshkosh. The replaced TBI would not idle the engine making final approaches and taxying difficult and over exciting.
Takeaways; Without finding a new class to race in the Onex, even with a Jab 3300, will not be competitive in the Air Venture Cup Race. Even if you’re willing to run your engine at redline the Midget Mustangs and Variezes will still run away and hide on you. One could pick up some speed with additional streamlining and maybe a wing tip config change. The Onex will not fly stable like a 172. If it did no one would want one. As a result you really need a 2 axis autopilot for long flights. I have a heading hold and had to fly pitch for the entire 30 hours of the trip. With a Jab 3300 in the nose one can put in at least a six gallon auxillary tank. We fully loaded the aircraft, including me in it, and weighed it. The CG was less than 1 inch aft of the forward limit. Without the auxillary fuel it was even less. The problem is the gross weight as I addressed in the post that started all this. You also really need a canopy sunshade. Even with one my arms were cooked by the time I got back to Oregon.
Anyone has question or comments?

[WaiexN143NM]

hi vince,
well thats quite a story. what was the first tbi that was on the plane?and what happened to that one that you had to remove it?
i did see your plane in the repair area. by vintage. from a distance. is it a tri gear or taildragger?

WaiexN143NM
Michael

[vhhomer]

My Onex is a trigear. The tbi I flew in with was an old model Rotec. The problem was apparantly with the fuel regulator and the engine wouldn't idle below 1600-1800 rpm. Rotec was at Oshkosh and they suggested a fix that I could have done at home, but not there. So, I purchased another Rotec TBI because any other carb would have more difficult to install in the grass. Fortunately, it worked as advertised although I must say it had my full attention on takeoff from Oshkosh.

Vince Homer

[builderflyer]

Thank you for the report, Vince. Perhaps next year there could be three or more Sonex product pilots willing to give the race a try. That way even if we are thrown in with the Midget Mustangs and Variezes, we could claim "braggin" rights amongst ourselves. That could be a lot of fun and serve to bring some level of truth to who has the fastest airplane, again amongst us. Now is the time to begin to prepare for next year's race!

Art,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[WaiexN143NM]

hi vince,
good to hear the new rotec tbi worked well and got you home. the older mark 1’s after they came out , had a fix to run a balance tube from the tbi to the regulator . the factory started incorporating that into the production models. also at osh at rotec booth , paul had the upgrade diaphram kits for the mark 1’s and earlier mark 2’s . that is a must to swap out. a few people have had engine outs becase of the older diaphram design.
i hope your onex finds a good home. im sure its fun to fly with the jab 3300.

WaiexN143NN
michael

[Sonex1517]

Thank you for the report, Vince. Perhaps next year there could be three or more Sonex product pilots willing to give the race a try. That way even if we are thrown in with the Midget Mustangs and Variezes, we could claim "braggin" rights amongst ourselves. That could be a lot of fun and serve to bring some level of truth to who has the fastest airplane, again amongst us. Now is the time to begin to prepare for next year's race!

Art,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

I would be one to sign up. Been wanting to try it for years.

[vhhomer]

I just got my invitation to the Air Adventure Cup race for 2019. It will be from Mt. Vernon, IL to Wausau, WI, some 400+ miles. Anyone interested should contact joe.coraggio@avcrace.com for entry info. I won't be attending this year as we have something else planned for Oshkosh.

Vince Homer