Zenith 601HDS Performance, and why Vx and Vy are important.

Builders,

Larry Nelson sent in these rate of climb performance numbers for his Zenith 601HDS: 

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Outside air temperature at 175′ MSL …100F

Density Altitude…..3,000′

Unbroken climb from 175′ MSL to 4,000′ MSL…800′ per min. 

Airspeed for climb…..75 kts.

Engine sustained temps……….Oil-235F (max is 265F) CHT-330F (max is 420F)

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Aircraft:

709 pounds, empty (HDS’s are the lightest of the 601 family, and this is an exceptionally light one, notice it has no paint nor interior) Test was flown at 1,100 pounds.

Powered by 2,700cc, 100HP Corvair, Warp Drive 2 blade prop, 66″ diameter, set at 8 degrees at tips, turning 3,000 rpm in climb.

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……………

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Note: Larry is an engineer who works for the Department of Defense at Yuma Proving Grounds, testing vehicles and weapons systems. When he provides data, it is real. He does not put ego ahead of the truth. Our industry is unfortunately dominated by “Brochure Performance.” All tests I have ever done, dyno runs, weight and balance measurements, performance numbers, have all been done in public, where people can watch. Larry is flying his plane to the September Zenith Homecoming, where anyone can verify the numbers above.

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Above, Larry with his bird. This plane has my new nose bowl. Read this: STOL Bowl #4201-B, flying in video.  If his name sounds familiar, it is because he is also our selected oil analysis expert. Check out this story: Corvair Oil Analysis. This program will shortly be the subject of another video.  Larry is also remembered as the guy who paid for  the parts in his engine with ammunition: Acceptable methods of payment for Corvair parts. Quite a character.

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THE CRITICAL LESSON:

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Two months ago, we had a builder who had a 601-HDS like Larry’s, with the exception of it having tricycle gear and a 3,000cc Corvair tuned for 115HP.  He reported to me that his plane “barely climbed.” He told me he decided to remove the engine from the plane, and sell it for whatever he could get for it.

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After going over a lot of details, I finally asked him what airspeed he was using to climb, and he told me 95-100kts. I pointed out that this was way too high an airspeed to be climbing at on a plane with a top speed of perhaps 8-10 mph more. I pointed out that as a rule, all aircraft in level flight at their top speed have a rate of climb of exactly zero feet per minute. That light planes climb best at their L/D speed. (The only exception to this is aircraft with a very high power to weight ratio and fixed pitch props)

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The builder adamantly refused to climb the plane slower, claiming that it would overheat. I suggested that he revise his cooling, because I had just flown in Ken Pavlou 601XL / 3.3 Corvair, and we were a lot heavier, and had still had plenty of cooling for a 125HP Corvair engine at a normal climb speed. I pointed out that the phase one testing of the airplane required him to test the plane to determine Vx and Vy, and he had to enter these in the logs. If his plane ran a bit hot, it could be corrected, as proven by Larry’s data showing the performance at 100F.  Last we spoke, builder was not interested.

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These are not new concepts, I have written about them extensively, such as this story: Critical Understanding #3, Rate of Climb, the critical prop evaluation. If you had reasonably good flight instruction, or any kind of a rigorous biennial flight review, the instructor would cover these types of information. If you are new to flying, and you would like to understand more of these issues from the undisputed source, buy a copy of this book and read it: Greatest Book on Flying Ever Written,

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wewjr.

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Two very different Outcomes: Choose your own path.

Builders,

Here are two polar opposite stories, two builders of Corvair powered planes, who had radically different outcomes on their first flight this week. The difference in outcomes is solely attributable to decisions the builders made. If you disagree, and  think the difference is that some people are ‘lucky’, let me strongly urge you to get out of aviation, now while you are still ok.

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Success: Andy Mechling’s 3.0L Corvair powered Zenith 750 Cruiser. 

Andy called Dan and gave him a run down on the first two flights, both went very well, and he was showing real performance numbers like 110+ mph as a cruise setting with no wheel pats, larger tires and a climb prop setting. Engine was cool with a STOL Bowl , and everything is going very well. Satisfied builder at the beginning of many fine adventures.

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Above: Get a good look at Andy’s expression the minute his engine fired up on the run stand at a 2016 finishing School we held at SPA. Read the full story here: Zenith 750 engine; Andy Mechling’s 3,000cc/120HP Corvair

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Not Success: Pietenpol completed by a man who elected not to talk with me about his project crashes on its first ‘flight’:

https://www.nbc4i.com/news/local-news/plane-crash-reported-in-heath/

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First, let me say I’m very thankful that the guy wasn’t seriously hurt or killed. The investigators today said he was doused in fuel, and it was something of a miracle he wasn’t killed. Much of the following info I share isn’t speculation, it is from the actual investigators. Additionally, the first flight was captured on video,a more reliable source than personal recollections.

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On June 20th, I wrote the following story on my blog, and yes this is the same aircraft: Need Help Contacting the Builder of this Aircraft ASAP. I wrote it because I was interested in speaking with the builder before he went flying and something went wrong. He contacted me the next day, and said I have to take his airplanes picture off my site, and off FB, as it was ‘Copywritten’ I wasn’t into debating it, my goal was to get him to reconsider some things I saw, even though he was not a builder of mine, and he never bought anything from me. The guy who sold him the project told him it was a WW conversion, it wasn’t, I didn’t care, just wanted to start a conversation with the guy to get him to reconsider some stuff. He wasn’t belligerent, but he wasn’t interested in talking. I’m a very serious respecter of personal choice, and it was his absolute right to make that decision. In the last few days some people on the net, with an axe to grind, have implied that no one tried to assist this man. That is complete BS, I did.

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The plane tried to take off from a 4,900′ paved runway. That is at least ten times longer than a Pietenpol would need to get airborne from. It never gaining tree top altitude, but the pilot apparently never pulled the power back.  The plane flew another 1/2 mile, was not going to clear a line of trees, and the pilot tried landing in a rough field. The planes wing was completely displaced on contact with the ground, the fuel tank ruptured, and the plane was destroyed.

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I have no idea if he read this 2016 story, but there is a reason why I selected it as story topic number one in the series.Critical Understanding #1, Take off distance.. If a pilot didn’t want to have this accident, all he had to do was pull the throttle back when he passed say 800′ and was still on the ground. Anyone who has seen Corvair powered Pietenpols taking off at Brodhead can see they only need 300-500′ for a modest regular takeoff. Still holding the throttle in thousands of feet down the runway isn’t a mechanical problem, it is a judgement error.  Any pilot, in any plane, who pushes the throttle forward without knowing his exact abort point on the runway, is making a judgement error, even if he never has an issue. The error is starting a takeoff with no plan. If you have been around homebuilding for a number of years, it is stunning how often this becomes a ‘first flight’ accident.

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If you have not seen the series, they are all listed right here: Critical Understanding Reference Page. My commitment to assisting builders starts with the things I write and teach. It extends all the way to trying to contact people who are not even customers of mine.

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The investigators mentioned that the plane likely had a home made prop on it, and that it never made full static rpm. I addressed both of these issues in this story: Critical Understanding #2, Absolute Minimum Static RPM.,  spelling out that no Corvair powered plane should ever be flown with less than 2700 static rpm.  Let me be very clear, it obviously wasn’t making anywhere near the level of thrust that even a very modest running Corvair turning a factory made prop would have. Included in the story is this sentence:

“No offense to any builder who wants to make his own Piet prop, but you have to look at what you are getting over a Warp Drive prop besides looks”

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I’m going to spell this out for new people: I could put a 66″ long 2 x 6 on the front of a Corvair and it would turn 2700 static rpm, but it would make Zero thrust, it would not even allow the plane to taxi at 2 mph. That is a ‘safe’ home made prop. I could put a 66″long Warp Drive prop on the same plane and it would 2700 rpm, and fly great, because it would make about 400 pounds of thrust. The trouble with many home made or small company props is they may make the required rpm, but that is no indication what so ever that they make enough thrust. They may make just enough to get the plane in trouble. I have written countless stories about this, like this one: Critical Understanding #3, Rate of Climb, the critical prop evaluation., and I genuinely hope the next guy flying a Corvair powered plane reads them, takes them to heart, and acts accordingly.

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ww.

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PS, if anyone is tempted to use the comments section here to say anything about the Piet pilot, Other than “I hope he fully recovers” , please don’t. The event has happened and nothing will change that now. The story here isn’t about one man’s mishap, its about making sure that your own personal first flight goes just like Andy Mechling’s. And that outcome solely depends on decisions you will make. 

 

Pietenpol Weight and Balance; Inputs for configuration calculation.

Builders,

If you are one of the Pietenpol builders who picked up a copy of our new Pietenpol Weight and Balance manual ,, and you would like to send in your data so we can assist you in getting your wing and landing gear into optimized locations, here is the information I will need:

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(A) The type of engine and the proposed propeller.

Ie: ” Ford with wood prop” or Continental 65, hand prop , Wood Prop” Or Corvair with a Warp Drive” Or “O-200 with electric start and a metal prop”

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(B) Length Of fuselage.

Long or Short (IMHO, no one should build a short fuselage plane if they are just starting. It has no advantages. )

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(C) The Pilots’s weight.

Your weight, dressed in a jacket, with headset, ready to fly. It also helps to know the pilots height, as the CG of a  5’6″ 200lb guy is a bit forward of a 6’4″ 200lb guy

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(D) The range of pilots weights

If you have friends who will test fly or likely be trusted to fly your plane, this important, and the most Piets can be set up to cover a 120–150 pound range of pilots.  So let me know if you are one of the lightest or one of the heaviest people who will fly the plane. Consider if you will have a kid or grandkid who might fly it when they are in the 120-130lb range.

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(E) Fuel Tank Location(s) and capacities.

Let me know where the fuel tank is, and what capacity it is. If the tank is in the fuselage, please reference its location in inches from the firewall. If you have a 12 gallon fuselage tank, and it is 16″ long, send me a note saying something like “12 gallons, with the center of the tank 9″ aft of the front face of the firewall.”

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(F) Unusual features: 

A full plywood fuselage; A glove box with a capacity of more than 8 pounds; Unusually heavy or different tailwheel and spring arrangements; Super light covering like Oratec; Pilots seat back location tilted more than 1.5″ from where the plans show. Please note these differences.

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Where do you  send (A) though (F)? 

I would greatly prefer if builders send the information right to the comments section here. If you send the information to the comments, in a few days I will come back with a specific recommendation.

If you are a bit concerned about sending your actual weight out on the internet because Cameron Diaz haunts your profile page on Match.com where you shaved 20 pounds off the actual number, and now you don’t want to get busted and have it ruin her image of you as a scrupulously honest character, no worries, I understand completely. Just send the info with your initials, and when she calls me with her suspicions, I’ll totally deny it’s you.  Thank me later, it just the kind of guy I am.

Seriously, don’t send in ‘optimistic’ numbers, the subject is a little too serious for vanity to show up in your numbers. Over the years we have had at least 6 successful pilots of Corvair Powered planes who had personal flying weights in the 300+ club, I can get your Piet weight and balance in range if I know the number. If you are 265#, sorry, it will not even make honorable mention in pantheon of pilots who could have been NFL defensive linemen.

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If you would like to watch a one hour forum I gave on Weight and Balance of Pietenpol’s, including an extensive question and answer session, click on the youtube link above, it will take you directly to my channel. If you have not yet done so, please take a moment to subscribe.

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WW.

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Mark Baenen’s Corvair Powered 750-STOL, at Oshkosh ’19, on Video

Builders,

Below is a walk around Video shot at Oshkosh, its Mark’s CH-750 STOL, powered by a 2700cc Corvair.  We spent a few evenings hanging out at the tent with Mark, he is really great company, a hilarious story teller. A great character to have in the world of Corvair building.

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At the Zenith Dinner, Mark went to the podium and shared a great story of his arrival at Oshkosh; He stopped at a 500′ paragliding field near his dad’s house, picked him up, and together they flew into AirVenture. This captured the attention of  every aviator in the room. On the car ride back to Wittman field, I told Mark that of all my 30 years in aviation, no day was on the same plateau as the day I took my father flying, and for that reason, Mark’s story would be my favorite of Oshkosh ’19.

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wewjr

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If you enjoy this style of video, or have a suggestion, use the comments section here to share the thought. If you have not yet done so, please take a moment to subscribe to our youtube channel.

Shad and Gary Bell’s 525 hr. Corvair Pietenpol, new video

Builders,

Below is the latest video, we shot this on the flight line at Oshkosh. We saw both elements of the father son team at Brodhead, and Shad flew the plane up too Oshkosh. We all had a good time catching up there.

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If you like this type of video and the information, please take a moment to subscribe to my youtube channel.

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Thanks, WW.

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Saturday Night,Oshkosh 2019.

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Show nearly over; midnight at air center, USAF vet Ron the Drummer and a C-5A.

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Oshkosh Friday, 2019

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Photo contest; name as many of these Corvair people as you know in the comments ❤️🙂