About Me

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I live in the Florida Keys. I've been in the military and worked inside the Beltway. I've had 22 technical books and two novels published. I fly, boat, dive, shoot, and swim pretty damn well.

Wednesday, August 22, 2007

Dave's Batplane Flies Again!

A Really Nifty

It looks a lot like Batman's personal Batplane. You might have seen a sister ship in the EAA magazine and in other publications. N18DW, a JD-2 Dyke Delta, was built and recently rebuilt by Dave Williams who is a member of EAA Chapter 1241 in the Florida Keys.

N18DW first flew in April of 1972 and in the 70s, wearing yellow and black colors, it was on the covers of several books and magazines. The aircraft had been in storage since the 1980's, but Dave decided a little more than a year ago to get her back into the air. This time it is fitted with a 210 HP Lycoming IO-390-X that is 30 more HP than the original configuration. He added a three bladed MT Constant Speed Propeller. The target cruise for this retractable is 195 mph and a range of 900 miles or more.

Dave had help from Tom Bauer in Sabastian for some well needed assistance for the flight. Tom built his Delta a few years ago and his has over 2000 flight hours in it. Tom’s Delta was shown at Sun and Fun two years ago.

Dave took the airplane up to Immokalee in a trailer for the initial test flight. The open airspace and two long runways have a lot of appeal for this kind of activity. Here is Dave's description.

“I think that the initial flight of an experimental aircraft can best be compared to being locked into a confined space with all your ex-wives and girlfriends, all at the same time…………It will either be one of the best days of your life or the last day of your life!

Wooh Hoo!! Last Saturday was definitely one of the very best days I have ever known. Thanks to Tom Bauer's help, N18DW flew for the first time in 28 years. The remaining taxi tests were completed between rain showers at ambient temperatures of 98 to 108 degrees F. The temperature in the cock pit likely topped 120 degrees F. from run up to runway exit when I was able to open the canopy as I exited the runway. This really slowed me down. In fact, we shut down the taxi tests early on Friday because the OAT indicated 108 degrees F in the run up area and I thought I could easily make a bad mistake under those conditions.

The first flight went like this: The aircraft took off and climbed out just like old times. The conditions were turbulent from the heat generated thermal activity and the turbulence lasted until 3500 feet. I climbed out to 5000 feet, above the first layer of broken clouds to feel the aircraft out.

The primary purpose of the exercise was to determine the stability and get the approach and rotation speed of the aircraft. I tested the turn and roll rate at various air speeds and then determined that I would use 120 indicated for the downwind leg, 110 indicated for the base leg and 105 indicated for the final approach speed. I could have come down final at 100 but there was a lot of turbulence over some trees on the approach end of runway 9. I always add a few mph in turbulence. Please note that I don’t yet know what the airspeed indicator error is and the speeds were determined without prior experience biases. The speeds were determined by how the aircraft felt and a generous margin above stall speed for the first final approach.

After making the decisions on the pattern speeds, I dropped down in 1000 foot intervals to 1000 ft and felt the aircraft out in the above context at each 1000 ft interval. When I got down to pattern altitude I shot three or four twenty-foot high approaches to determine the power settings required to fly in the pattern and have good control of the rate of decent.

During taxi testing, I lifted off and flared to land so I already knew how the aircraft would behave after touchdown. The only missing component of the first landing that I had not yet experienced was the actual screech of the wheels at touchdown so it was time to make the first full stop landing. The first landing went well but I dropped the aircraft in the runway a bit hard. No cigar, but a good landing anyway.

Consider what happens with a constant speed prop when the engine can not make up the set point rpms. The governor causes the pitch to go flat in order to allow the engine to speed up and make the set point rpms. Also when the pitch goes flat there is a lot more drag and the aircraft will slow down quickly. If the aircraft slows quickly the rate of decent will increase and cause the aircraft to land hard and bounce. That is exactly what happened. The solution I discussed with Tom Bauer was very simple……SQUEEZE THE POWER OFF GENTLY AND YOU WILL GET A NICE L O N G S C R E E C H AT TOUCHDOWN..

When I rebuilt the airframe in the early 1980s I added an airspeed brake under the main spar which I removed in January of 2006 because I felt it would be unsafe because it would cause an unwanted downward pitch during deployment. I felt bad about removing it but the drag was below the center of lift and center of gravity and it would not have worked as desired. Had I been able to use the drag brake, I thought I could reduce the landing distance by 20 percent.

Lady luck was on my side however, because it is possible to use the constant speed prop as a drag brake simply by pulling the power completely off after flair and I can actually feel the deceleration. This will make for a significant reduction in the landing distance. It is too soon to tell but I may have achieved the effect of the drag brake by accident with the constant speed prop. I am excited to explore this aspect of the performance.

I won’t bore the group with the remaining flights, but they consisted of gear retractions, low approaches, crosswind landings and touch and goes. Turbulence was always there on approach, but then I learned to fly on the desert in El Paso, TX so it was more of a nuisance than a deterrent. The most critical part of a flight is after the flair and just before touchdown and the turbulence is 500 feet behind the approach end of the runway. I departed Immokalee on Monday for the 175 mile tow back to Key Largo. Towing the aircraft 350 miles to and from Immokalee was uneventful.

Special thanks to Tom Bauer for spending the week in Immolakee with me and N18DW. I really needed someone to bounce thoughts and ideas off and I could not have picked a better person then Tom Bauer. THANK YOU AGAIN TOM !

If anyone is going to test fly a Delta be sure that you bring along another Delta pilot, not just any airplane pilot. Although I have 500 hours of delta flight experience, I found Tom’s presence both helpful and reassuring. Twenty eight years is a long time to remember everything about handling the JD-2. "

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