RE: Thorpe F-20 build
 

Terry,

Good luck on Friday.

RE: Thorpe F-20 build
 

BEST OF LUCK, ARE YOU FITTING A BELL MOUTH TO YOUR THRUST TUBE INLET? RON.

RE: Thorpe F-20 build
 

Ron- I have a bellmouth for the pipe but it no longer fits after cutting the pipe shorter to fit the plane. I may split it and try to make it fit. Do you think that I really need it? I thought they were sort of optional.

Terry

RE: Thorpe F-20 build
 

I HAVE NEVER SEEN A THRUST TUBE WITHOUT SOME FORM OF ASSISTED ENTRY. I USE A LOT OF WREN THRUST TUBES.THEY HAVE DONE A LOT OF WORK ON AUGMENTATION. THEY MERELY CREATE A SMALL FLARED LIP AT THE ENTRANCE. RON.

RE: Thorpe F-20 build
 

I was told that one of the reasons for the bell mouth was to support the front of the thrust tube
from collapsing as the engine thrust creates a vacuum which draws in the cooling air.

On my BVM pipe I did what Ron mentioned, jusr flared a small (3 mm?) lip at the entrance to the pipe.
So far, so good!

The flexible cables you used driving the control surfaces concern me. With your radio on can you push the
control surfaces back against the cables really firmly without them kinking? Also, are they 2-56 brass threaded
couplers soldered on the cables? I've never used these since one snapped where the threaded portion joins
the tubular section, happened on a friend's trainer on the elevator, you can guess the rest! [&o]

I only use the larger, steel 4-40 versions with maching clevises. - John.

RE: Thorpe F-20 build
 

Thank you Ron and Boomerang1 for your comments. I will try to make something work for a bellmouth. I can see the danger of collapse without something in place. I have concerns about the flex cables too. I have used this type of cable years ago on a few planes and they worked well. I have not had one break as you described but I can see how it could. Particularly if a flutter develops. That is my main concern. The rudder will kink back in one direction with significant force. More than I think it will see in flight. The others do not. You can easily drive the servos which are pretty stiff. I'll stop by the hobby store today and check out the 4-40 couplers and clevises.

RE: Thorpe F-20 build
 

Terry, when friday do you plan to fly the F20. I'd love to be there.

RE: Thorpe F-20 build
 

Good luck for Friday!;)
Love to see a video of it!



JT

RE: Thorpe F-20 build
 

Bob- I checked the weather for Friday and it doesn't look good. Have to wait and see. If Friday turns out to be good, I'll be up there by early afternoon. Otherwise, I may end up waiting and doing the maiden at Joyce Park on a calm day.

RE: Thorpe F-20 build
 

Just let me know!

RE: Thorpe F-20 build
 

Bob, let me know!!!....we can sell tickets and run a shuttle bus!!
Glenn

RE: Thorpe F-20 build
 

The plane was not ready and did not fly this past weekend. Someone asked earlier about how I was going to do the brakes. Attached are a few pictures of the brake valve and plumbing tied into the retracts. Retracts and brakes will run off the same air tank. I haven't figured out how to put a second air tank in the limited space as yet.

RE: Thorpe F-20 build
 

Here are a few more. You can see that I put the ECU battery in the space above the nose gear retract unit. The 5 cell NiMH receiver battery is in the space just below the retract unit. There is some extra room next to the ECU battery so I stuffed some foam in there. Will probably have to put some lead in there too to balance. Also took a pic of the mounting for the ECU, pump, and solenoid valves. A bit of a tight fit for sure.

RE: Thorpe F-20 build
 

Just got done balancing the plane. Glued in 3.5 oz of lead in the nose with 30 minute epoxy. Weight of the plane with the lead is 10 lbs 12 oz. So Glenn's guess was spot on.

Terry

RE: Thorpe F-20 build
 

The plane is ready to fly. Going to try to maiden in the morning at the HAWKS Field in Joyce Park, Hamilton, OH.

Terry

RE: Thorpe F-20 build
 

Thanks for the call and the heads up will be there.
Glenn

RE: Thorpe F-20 build
 

The plane did not fly today. It went down the runway very fast (35-40 mph) but wouldn't rotate and lift off the ground. I think the angle of attack needs to be increased. Ron- what agle of attack would you recommend?

I also had problems with the fuel system. The engine would not transition on startup after the first attempted flight. I would get a weak fuel error on the ECU. Took it home and replaced both clunks with heavy duty ones with larger holes in them. I had a felt clunk previously on the small 10 oz tank and a small brass clunk on the bigger 24 oz tank. But the kero will still not flow unrestricted. The engine will not transition on startup. I will now change the Tygon lines from 3/32 to 1/8th and see if that will works. Any tips would be appreciated.

Terry

RE: Thorpe F-20 build
 

Hi Terry, I would recommend at least 3 degrees posotive for your angle of attack. I also had the same problem with my Wren 44 gold. It turned out to be my battery. The Wren 44 needs to turn at a very high RPM (compared to larger turbines) to start, and if your battery is not putting out enough voltage it will not turn over fast enough to start. Mark

RE: Thorpe F-20 build
 

Hi Terry, Re ground a.o.l. get as much as you can. you have to fly this one off. Ron.

RE: Thorpe F-20 build
 

I lengthened the noseleg to give about 20mm nose up when sitting on the ground. This helps with the take off but my F20 needed quite a long take off run on tarmac runway. To overcome the elevator slop, I put mini servos in the rear of the fuz during the build and run solid pushrods directly to the elevators, which reduced the play which you will get with the long snakes.

Duthie.

RE: Thorpe F-20 build
 

My ducted fan version flys off a dolly no problem but does have a positive angle of attack.

I have attached best pic I could find

RE: Thorpe F-20 build
 

Thanks for all the responses guys. I'll work on the gear to get more angle of attack and program in more elevator throw. Still working on the fuel tanks. Checked the battery and it was almost at full charge. Soemthing is choking off the fuel supply.

Terry

RE: Thorpe F-20 build
 

Checked the filter under the fod screen and it was perfectly clean. Plumbed just the large 24 oz tank and tried to start again. Battery voltage was 7.55 at the time. The engine will start but not transition. As soon as the transition message comes up on the display, the flame goes out but the starter keeps turning the engine over and speeding up at that. After a number of seconds go by, at least 15 or 20, an error message states "weak fuel". Tested the pump motor by priming into a bottle. The prime is very slow but works. On the Wren 75, the longer you prime the faster the pump turns. But the Wren 44 did not do this. It just continued to pump slowly. I'm open to suggestions...

RE: Thorpe F-20 build
 

Call Ron!

RE: Thorpe F-20 build
 

Hi Terry. I had pump problems with my 44. It was delivered originally with a hausle pump and often on low throttle it used to flame out in the air. I was told that the pump was a little bit oversize and could not accurately deliver the very small quantity of fuel at very low turbine speeds. Wren then sold me a small flightworks pump which required the pump parameters changing in the ecu. This solved the problem but then I experienced your current problem. I am told that the pump shaft seal can be too tight on the shaft and is reluctant to turn with the low voltages needed to start it. I have a small battery pack and give it a quick burst before I start. Additionally your thermocouple, rpm sensor, or even the fuel solenoid could be at fault. All are easy to check. The data terminal should read ambient temperature prior to start up and rise during start up and obviously the temperature should show a rise. The solenoid valve can be temporarily by-passed. Ron.