Curtiss Jenny Restoration
Welcome! We hope you enjoy following the restoration process of a 1918 Curtiss JN4D Jenny. Once completed, the aeroplane will be flown and displayed at the Candler Field Museum in Williamson GA (30 miles south of Atlanta). You can contact me below by clicking on "VIEW MY PROFILE"
- Name: Brian Karli
- Location: Peachtree City, Georgia, United States
Wednesday, September 23, 2015
Monday, August 10, 2015
Jenny update - carburetor
The engine was was smooth...and happy...but without brakes and a tail skid, we could not stop the airplane on the ground. The idle was just too high.
But, the arm of the carburetor was back as far as it would go. Something was not right. It was time to dig into the Hisso manual.
The manual showed a neat diagram following the path of the fuel at idle (red color).
The Stromburg NAD-4 carburetor is a unique creature. At idle, fuel is drawn up an internal tube to a small idle port in each venturi (there are two). There are two bleed screws there. Unlike modern carburetors which adjust the amount of fuel, the NAD-4 adjusts the amount of air.
The book identifies these screws as "idle adjustment needles". Even better!
With the engine running, we tried rotating the bleed screws. The idle speed stayed at 800 rpm, but smoke poured out the stacks as the mixture enriched excessively. Turn the screws the other way. Too lean. Engine ran rough. So much for that idea.
Air comes in around the bleed screws. Perhaps it's not getting enough air. As you can see, there needs to be a gap in the threaded bleed assembly. Small holes allow air to enter and the screw meters it even more.
We adjusted the assemblies until the holes were fully exposed. No change.
There was much head scratching and frustration. How could we fly this thing if we can't get the idle low enough for the plane to stop on the ground. I know what you are thinking. No...I'm not installing brakes. No way.
I jumped on the internet and tried searching every conceivable combination of "Stromberg NAD-4 carburetor idle problems" but there was little information available.
Again, I checked the physical stop on the throttle arm. Indeed, the butterfly valve was closing. Whatever we were hitting, it was a physical stop.
Another good thing about old airplanes is the plethora of help out there if you just ask. I sent emails to Frank Shelling, who has way more experience with these engines than I do, Glen Peck, Paul Dougherty, Kevin Connor, John Saunders and David Cretchley in New Zealand, Andrew King......I fell fortunate to have many friends.
I was looking for a smoking gun, but the advice they gave me was clear - pull the carburetor and look around.
We pulled the carburetor. The butterfly valves moved smoothly and hit the stop.
We pulled the fuel screen and checked the spring that operates the float arm. It was fine.
Then we noticed something unusual. The bleed assembly was flush in the right side of the carburetor venturi.
But the assembly on the left side was protruding.
Here was the problem! The butterfly valve was hitting the protruding bleed assembly and it wouldn't close all the way. There was a gap between the valve and the venturi wall.
So the throttle was never fully closed...even when it was "closed".
Very gently, we pushed the bleed assembly back flush with the venturi and reassembled the carburetor. I am happy to say the engine idles perfectly at 400 RPM now!
I'm posting this because someday, someone will search "Stromberg NAD-4 carburetor idle problems" and rather than finding nothing, this will show up to help them.
Time to go flying.
Monday, July 06, 2015
Back in the air !!!
Sunday night Ron, Brian and I met at the museum. We tracked down two little leaks and pulled the Jenny outside. It was a perfect evening for flying. We spent a bunch of time messing with the idle setting, and Brian almost reached his hand propping limit, but around 830PM, Ron took the Jenny for a 15 minute flight. Enjoy the video.
Usually there is a crown at the museum and I get tons of video of the Jenny in the air. But for some reason, we were nearly alone. Tommy and Amanda Denton came to see the flight as did Christy Eberly. I apologize for the amateur cinematography. I was too busy watching the flight.
Good excuse to fly it again....
Saturday, June 27, 2015
Engine has arrived
Friday afternoon was more of the same - hooked up the throttle, mixture, temperature and pressure lines.
By 6PM, it was time to take Jenny out into the sunlight.
Success !! It started right away. Ran smoothly.
Sunday, June 21, 2015
Thursday, June 18, 2015
Tuesday, June 16, 2015
Here are the bearings inserted into their races.
Meanwhile, the crankshaft gets the connecting rods installed.
The two halves are given a sealant.
And the crankshaft is lowered into place.
Tomorrow, the cylinder banks will be installed.
Sunday, May 03, 2015
Where do I start? OK, how about the valves. As mentioned before, all the valve guides were worn beyond tolerances. We decided the best course of action was to make threaded sleeves. Here you can see two sleeves and one sleeve already threaded into a guide.
The sleeved guides were inserted into the cylinder banks.
On to the camshafts.
The left camshaft gear was missing a spacer. Not anymore.
Also one of the end caps was missing. A new one was made.
Pistons - since the rings in the engine were worn out, new rings were ordered.
Each piston was cleaned, inspected and measured. Seven of the pistons were fine. But the eighth one......
It was trashed. As you can see, part of the piston was eroded away. Blow by from the bad rings? I don't know. There was no way we could use this piston again. So, a call to Ross Pistons in California was placed and eight more pistons are being made.
They no longer make the long, heavy original style pistons as you see on the left. The new ones are shorter and have one less ring. I worried about the difference until I talked to my friend John Saunders. John has two Hisso's of his own, knows a ton about them and assured me the pistons would work fine. Jack Kearbey has been running a set in his SE5A powered Hisso for a long time without any problems.
More bad piston news. Several of the piston pin caps were deformed.
New ones had to be made.
April 10-12 I completed a bucket list item by entering the Jenny in the Weak Signals model show in Toledo, OH where it was awarded Best in Class. Please note that your blog is credited with a detail source in the display presentation. The history of the original airplane is quite interesting – well traveled to say the least.
It would take too many words to describe all the tooling built to make parts, most the same as yours – just smaller. The bead roller for the fuselage cowlings, tooling to fabricate 100 shackles, hand forming the brass radiator, etc. The stick assemblies are ball bearing mounted, as are the rudder tiller bearings and elevator bellcranks – all operated by servos hidden beneath the rear seat. Even the aileron cable pulleys are fitted w ball bearings. One thing for sure, 1/6 scale provides many challenges as parts are small – lots of 00-90 capscrews.