Blackridge & District Model Flying Club
Electric flight projects
F-15 Park jet, now kitted by BRC Hobbies
During a recent visit to the 2005 Woodvale International Rally we watched an F-15 model flying during the informal evening session and thought it looked great. Fast and very aerobatic the model was put through it's paces by the pilot who made it look easy and eventually just floated the model gently down after around 10 minutes of 'robust' flying.
The model is constructed almost entirely from 6mm Depron and was very light and superbly responsive. Although a 'park jet' the model is quite large with a wingspan of 28" and a length of over 40". A set of Depron parts (last one left) was purchased from the pilot after the flight and this included a CD with plans and construction manual. Additional sheets of Depron were also purchased and there are now three F-15 models under construction with the first having just completed it's test flight at the Club site.
Building the model
With a full set of parts cut out and the excellent construction manual printed off (all 27 pages with many pictures) construction was straightforward although some previous building experience is required. The model is constructed from 6mm Depron, a flat, lightweight, high density foam material. There are recommended glues for this material but this model was mainly constructed using PVA white glue with no problems. The wing spar is 6mm hardwood dowel, as is the all-moving 'stabilator' joiner (replaced by 3/16" dia. alum. tube in drilled out servo arm 'bearings' on this model).
As only one clear moulded canopy was purchased this model has a carved and sanded blue foam canopy and nose. Finishing the model is up to the builder, this one has an 'artistic licence' colour scheme made by combining several full-size schemes to make it a bit more colourful. This was sprayed on using Humbrol 'NEW' spray cans for plastic models and must be used with caution. Only the lightest of coats should be applied holding the spray can at a distance so the paint is part dried before it can cause damage to the Depron. Despite taking care there are several areas of this model which have been 'blistered' by the paint but with more care a satisfactory finish should be possible. There are 'foam safe' paints but colours are limited. More experimentation is planned for the other two models. This paint finish added 5oz to the flying weight!
With perfect weather (5th September 2005), warm sunshine with just the slightest of breezes there was no excuse for not making the test flight. A range check showed poor reception at much less than 100 metres which was fixed by re-routing the Rx aerial outside the fuselage. The control surface movements shown on the plan are huge (+/- 2" on stabilator, +/- 1.5" on ailerons!) and these were set to half on low rates which were used for the test flight. Also, 50% exponential was programmed in to make controls less sensitive around the first half of stick movements. For this flight a small ply launching grip was fixed to the fuselage bottom with Velcro as the fuselage is too wide to get a proper grip on. This will be removed when the pilot (Me!!) feels confident enough to try an underarm launch using the top turtledeck as was demonstrated at Woodvale. With the motor at half throttle and controls on low rates a firm launch from Johnny saw the model gently start to climb away at a steep angle but with no tendency to stall. Opening the 'throttle' to full, the AXI sent the model upwards at an impressive rate of knots - brilliant, exciting, very stable and controllable. After some circuits to trim out the horizontal pitch (the all flying stabilator is quite sensitive) the ailerons were set to full rates which improved handling quite a bit. The stabilator on low rates has plenty of movement for good control although for 3D manouvres high rate would no doubt improve flight characteristics. Landing was very easy, just wind the motor down and the model comes in nose high and can be slowed down to almost stop when it just flops down onto the grass. As a normally placid sports flyer, happy to stooge around with sedate models I was a bit worried about flying the F-15. With a small wing area, highly tapered wing, large control surface movements, almost non-existent moment arm, motor at the wrong end!! not my usual type of model and a definite candidate for the Club bin bag I thought!
Absolutely nothing to worry about!! Even at 4oz over the max recommended flying weight this model can be flown fast and aggressively or slowly and steadily with no bad habits. Outstanding flight characteristics and a joy to fly, even for an oldie like me! This is quite a large model for a 'park' jet and providing a full range receiver is used, can be flown over an area similar to that of a small IC sport model .
This model is now being supplied as a kit by BRC Hobbies at the very reasonable price of £29.99 plus £2.99 for a clear canopy (at the time of writing). Excellent value for money. Check here for full model spec at BRC Hobbies.
Test flight Model specification
Thanks once again to Johnny for taking the pictures and helping with the test flight. BG - September 2005