17 Aug 98 - Additional photograph & comments inserted.
This is a semi-scale F117A stealth fighter, built from the plan in the August 1996 issue of Radio Control Models & Electronics. I modified the design to take spring air retracts to improve flight performance and look in the air.
|Number of launches||13||
Note: Not all flights included
|Total Time||1 hour 33 mins|
|Wingspan||40.5 in.||1.03 m|
|Wing Area||900 sq. in.||58 dmē|
|Flying Weight||6 lb. 5 oz||2.9 kg|
|Wing Loading||16.2 oz / sq. ft||50 g/dmē|
|Motor||MDS 48 Pro with standard muffler|
|Propeller||APC Clubman 11 x 7|
|Batteries||1300mAh NiMH for RX|
|Receiver||Futaba FP-R105M - modified to 7ch - 35MHz|
|Servos||4 x Hitec HS-101MG for Elevons and 'V' tail, 2 x Ripmax Diamond 200 for Throttle and Retracts, 1 x Fleet FPS-20 for Nose wheel steering. A 'Y' lead splits the rudder signal from the RX between nose wheel and an electronic V tail mixer.|
|Static Performance||Maximum of 12000 rpm and a stable idle at 2500 rpm.|
|Flight performance||30° climb and about 540° / second roll rate. Looks extremely good in the air especially wheels up.|
It was originally powered by my MDS40 but this produced insufficient power. It was extremely marginal on take off but once flying it was OK. The MDS Pro 48 now fitted has about twice the power of the MDS 40. I have now flown it with the MDS Pro 48 and the take off run and flight performance are much better. I have remade both of the elevator linkages using a long solid push rod, reinforced with carbon fibre rods to stop flexing.
It may seem obvious but the nosewheel steering only works when it is on the ground. Once the model has rotated the nose wheel steering is lost. This is exacerbated by another unforeseen problem - the side area of the front fuselage causes the model to weathercock away from the wind. This only seems to happen on the ground with the model showing good yaw stability in flight. Before conversion to full V tail this meant that you couldn't start to rotate until flying speed was achieved and caused a few problems until I got used to it.
After landing the other day I noticed that the elevator servo horn had snapped. The elevator authority during the flight did seem a little poor and it is just as well the ailerons have elevator mixed in when selected (fortunately it was selected). I had noticed that due to the control rod angles the horn flexed a little in operation - it was obviously to much flexing.
To get over this problem and give steering once rotated I have fitted 2 Hitec HS-101MG servos on place of the single servo previously used. The rudder output from the RX is split using a Y lead and fed to the nose wheel steering servo and to an electronic V tail mixer (design by Ken Hewitt). The elevator output is also fed into the V tail mixer and the 2 servos are plugged into the output connectors.
I wrote the model off in a crash on 2 Aug 98. One the elevator linkages came adrift at about 50 feet up and caused a roll to occur every time elevator was applied. I lost orientation and the model hit the ground almost vertically. As the construction was almost entirely pink foam it disintegrated on impact. All the radio gear, motor and the retracts appear to be OK and will be fully checked out before further use.
I have added an additional photograph that I just got back from the developers. It shows the internal layout, wiring & plumbing of the model (wheels up).
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