TGoodwin

I have been working on putting together an FA/18 .20-.25 pusher and need some advice. The plane will have foam core wings and a composite fuse. It will not have ailerons on the wings but the flying horizontal stabs will be mixed to provide roll as well as pitch control. This is the same way that the little Wattage F22 electric is setup. I am trying to figure out what the high and low rate throws should be for this type of setup. I have never had or flown a plane configured in this manner before so I am unsure of what is enough throw. I am using all of the hardware from a crashed .15 size plane. I am still working on the plug but I should be ready to make the mold by this weekend. I am also debateing weather to make the wingspan scale or increase it slightly for added lift and lower wing loading. As it stands at the moment with the scale wings it will be 36" in length with a span of 26". I have and am planning on installing an OS .20 FP with a Macs pipe. I got the idea for this project after seeing a G&P sales F18 .60 pusher at the local field. Any and all suggestions are welcome. Here is a pic of the plug as of January 10th.

Thanks Ted

TGoodwin

Well I guess if nobody has any better suggestion then I will use the rec control throws for the Wattage F22 then. 3/4" roll and 3/4 pitch on high rates.

Thanks Ted

skyhawk-RCU

My Feedback: (8)

I agree with the 3/4" total throws; but you
could increase that with your high rate on
your TX for the initial testing and trimming. I am currently finishing
up an advanced design F-18 pusher [by another author]
using .32 technology to edge this very
clean copy well outside the speed envelope.
I will use a PA-2 gyro that levels both axis
during flight. The newer TX's can automatically
re-trim during the landing configuration
when the flaperons are deployed to slow
this rocket for landing. Length is 46" with
34" span using only 290 squares. Built from
plans. You may want to look
into "cheater doors" near the aft fuse [sides
and/or underneath]
to allow additional static flow into the
rear fuse to increase thrust during slower
flight to avoid high speed cavitation of
the pusher prop and supplement total volume
of airflow to the blades. Great forum
here at RCU.................skyhawk

TGoodwin

Looks good! Which plans are you building it from? The only plans I have seen were in Model Airplane News and it was an .25 size pusher. Is yours built up useing standard construction methods or is it composit? Good luck.

Ted

skyhawk-RCU

My Feedback: (8)

Regarding the above pusher, I acquired this
from a club member, I'm finishing up the tail
feather installation. I think it actually
originated from RCM or MAN plans.
It's completely built up and light as a
feather for its category. I'm also working
on a Space Shuttle pusher, almost ready to
fly, also acquired from a local flyer.
It has been flown and trimmed, this version
has the cheater doors I mentioned earlier.
IS this your first attempt at glass plugs?
I Always wanted to make a mould for
a Hurrikane 500 fuse. Do you have a site
that outlines the process? thanks..skyhawk
....Great site RCU!!

Mike James

I have a non-commercial web site at http://www.nextcraft.com that shows the whole process for making plugs and molds. Just click on the "Design and Building Tips" button.

Good luck! Warning... Molding is addictive!

TGoodwin

I am not really sure what you mean by cheater doors on a pusher configuration? I have seen them used on ducted fans before. Yes this is my first attempt at a glass fuse. This is sort of a learning project before I build the glass fuse for a larger ducted fan F86 model. I have a personal site with the progress of both the F18 and the F86 but have been having problems with my digital camera so it has not been updated. Here is a good non commercial site that outlines the process very well. http://www.nextcraft.com/rcindex.html I am almost ready to start laying in the glass. Just have to pickup some milled gllass to mix with the epoxy to glue the bulkheads in with when I do the layup. Here is an image of the bulkheads held in the mold with modeling clay.

skyhawk-RCU

My Feedback: (8)

Thanks for the above info and site on molds.
See picture below of my near scale Shuttle XP,
I acquired this one also from a local flyer,
it has been flown and trimmed previously
with a YS 45, very stable on approach.
The rear side doors visible in the pic help draft
additional outside air to supplement total
volume directed to the prop to help prevent
cavitation/tip stall due to poor
flow to the inside half of the blade airfoil.
These twin doors are operated by a micro-switch
activated on the low/mid side of the throttle
curve. I am considering installing stall
gates on the outer edge of the wing to help
contain the sideflow of air during slow flight.
This works well on most aerobatic craft like
my 60 Raven. Thanks for the info on molds,
will check out your site on the process.
Thanks again RCU.................skyhawk mich

TGoodwin

Well wish me luck. I layed up the glass in the mold and glued the bulkheads in place and then tightened it all down. Will know tomarrow how well my time was spent!

Ted

TGoodwin

Here it is fresh out of the mold!

Ted

TGoodwin

Mike James

Cool, Ted! Love the photos. Keep us updated as you get this ready to fly!

TGoodwin

Mikejames0- You are correct in your observation about the mold thickness. It is a little thin. Had a heck of a time getting it out without breaking the mold in half. Will make it thicker next time.

Now I think it needs an exaust cone cowl with air scoops to force air over the head and cool the engine. It gets pretty hot here and I am concerned that there is no prop wash over the head to cool it. Will wait and test fly it first though.

Thanks Ted

TGoodwin

Well I am in the process of building the wings. I had to increase the area a bit as the model is comming out over my original target weight and the wing loading would have been 35-40 oz sq ft with the scale wings. With the increased area it looks like it will be 30-32 oz sq ft with about a 1:1 thrust to weight ratio. Does anyone know what the upper limit for aricraft of this type for wing loading? I know that the smaller the plane the more effect it has on flight characteristics. I though 35-40 was way too high and 30-32 is borderline. I am not figuring the leading edge extensions as part of the wing area those numbers are strictly wing area.

Thanks Ted

Mike James

Hi Ted,

It's not the type of model so much, as the size. At the size of your model, this is a hefty wing loading! It's tough to analyze someone else's design without seeing it in real life, and the following is certainly meant in a friendly way, not as criticism. At first glance, looking at your photos, I get the feeling you have too much "stuff" in the fuselage. You probably don't need as many bulkheads. Also, you may have added some weight by attaching all the carbon fiber, not from the CF itself, but from the epoxy.

I think the leading edge extensions will only help you at high angles of attack, although there may be someone else here who can shed more light on that.

If you want to (here, or by email) give me some more info on your project, I'll try and help you lighten it up. If you fly this size model with wing loading in the 30s, I'm sure you know it's not gonna be a glider! Also, the F-18 is one of those planforms that's know to bleed off energy quickly in a turn, so watch the low and slow turns.

Regardless, good work! Details above can be improved easily.

TGoodwin

Yeah small planes with high wing loading are interesting to fly for sure. I built a twin speed 400 electric ME262 from Mark Ritinger plans about a year ago. It has a small wing area. I glassed it and put in two MPI Cobalt 400s with a large 1250mah 10 cell pack. The loading on that plane is 33 oz. sq. ft.with a span of around 30". That plane feels like a brick but flies like a ROCKET on rails! Just don't bank too steep at slow speed!

My Word Models P51 weighs in at 7.5 lbs and a wing loading of 31 oz. with a .91 four stroke in the nose.

I like the solid feel of high wing loaded planes.

I guess if it is too much I can go in with my dremel flex shaft and trim some of the bulkheads down a bit. The wing area is 209" sq. and the finished weight looks like it will be about 2.75 lbs. dry the span is 31" and the length including engine will be 37.5". I used a thin 9% flat bottom airfoil also.

I did not have any milled or chopped glass so I cut stranded CF to 1/4" length and mixed it with the epoxy to secure the bulkheads in place. I cut the bulkheads 1/16 or so smaller than the interior then used the CF mix to fill that gap when I put the halves together. Probably did not need to do all that but it was easier as I did not have to have a precise fit with the bulkheads. I did a 2 oz 4 oz lay up and blotted out all the extra epoxy. I tried to put bulkeads in only where they were needed to secure internal equiptment.

If it is fast and tracks well then I will be happy. It does not matter to me how fast I have to bring it in for a landing.

Thanks Ted

Mike James

Cool Ted. Post some flight photos when you get it going. It ought to be fun!

TGoodwin

Looks like the test flight will be Saterday morning if weather permits. Will finish painting and detailing it later. If it flies!

Wish me LUCK!

Ted

Mike James

Yeah! Good luck Ted. Get the engine running GREAT, check all the controls at least twice, then take a few deep breaths.

First flights on an untried model are always exciting. Let us know how it goes. Good luck!

TGoodwin

Well I took it out this morning for the test flight. I had some serious problems controling it on the take off run after it got up on step. I did three high speed ground loops before I was finally able to get a decent track down the runway. On the fourth try I got a decent track and let it build speed before easing in back pressure on the stick. By the time I reached the end of the runway I was holding in full up elevator but it would not rotate! At the end of the runway when the ground fell out from under the plane I had already aborted but was still holding full pressure on the stick to try and unload the nose wheel for the down hill transition. As soon as the ground fell away it rotated just fine into a nose high stall and plumeted into the dirt. No damage at all! The plane impacted flat on the gear. Upon inspection it was determined that the cause was the main gear location being place to far aft of the CG. Will make the required mods and try again. Here is a link to some video of the crash.

http://www.lvcm.com/tgoodwin/FA18.rm

Mike James

Hi Ted,

I saw the video. Oops! Looks like some of my test flights.

When I was doing some research on F-18 models, several people emailed me and said that the F-18 is known for being difficult to rotate, but as you witnessed, the leading edge extensions will really crank it around fast, once you get the angle of attack up. (Same thing in a tight turn...Those extensions will help you turn, but will also cause a LOT of energy to bleed off.)

I suggest lengthening the nose gear strut a little, which should let you rotate without having to hold full up...always a risky proposition.

Let us know how it goes! Good luck... This is a neat little jet!

JohnVH

My Feedback: (38)

WOW, interested pop up there!! if you get it perfected I want one!

TGoodwin

After talking with soem people at the the field about the problem there were several suggestions to fix the rotation problem. One of them was like Mike suggested to raise the nose so it sets on the ground at a posative angle of attack and the other was to move the mains foreward about an inch or more. I have done both of these things and the model is much easier to pivit back onto the tail now. I think that the nose wheel was loading up after it got up to speed and that is why it kept spinning out once it got moving at a decent rate even with a straight track.

The common feeling of the spectators at the field was that the plane had plenty of speed and would have flown if it would have rotated off of the runway. I was hoping to try again this morning but the winds were 17 mph gusting to 25. Maybe next weekend I will actually get it the air. I am still a little concerned with the thrust to weight ratio being .6 to 1 with the final model comming out heavier than expected. Some of the jet flyers at the field did not seem to think this was a problem. Maybe I will put a hot .28 on it. Will test fly it first and see.

Thanks Ted

JohnVH

My Feedback: (38)

got any .40's?

TGoodwin

Actaully I do have a couple of spare .40's laying around. I would have to put 1/2 lbs of lead in the nose and make some stilt landing gear to clear the prop though. Wing loading would be in the mid to high 40's too! It only has a little OS .20fp with a tuned pipe now. I think with 25 or 28 it would really scream.

Ted