caliber302003

hi there just wondered if anyone had tryed putting retracts in a ripmax rapier?. i know there not supposed to be there, but i just wanted to try it as a little project as the weather in uk ( north east ) isnt to good latley.
im ok if it goes wrong as i have bloody 3 of these things lying about.[&:][sm=bananahead.gif]

i know i will have to bulk up around where the retracts would be going can anyone give me any ideas or tip that would come in handy.

thanks in advance [sm=thumbup.gif]

Mac-

Hi Caliber,

That's an interesting project!
I also fly have Rapiers so I can see your point of view. With no undercart you really need someone to launch it for you.

With ithe Rapier's ample delta wing mass a tricycle retractable u/c should not be a problem. A standard low cost mains mechanical u/c costs £19 in the UK and a trike set about £35!

The two rear legs would need to be behind the c of g position.
Weight for a mechanical trike retracts wouild be around 9-10ozs. Plus hardwood blocks epoxied beween the wing ribs which would need 1/16th ply doublers for reinfocement.

Perhaps you could fit only a main mechanical set and leave the nosewheel fixed?

The extra weight would add little to the overall wing loading and I would fit an Irvine .46 or similar which would add ample power.

Rapiers tend to be draggy in the turn and extra power during this maneuvre is needed.

If you need any further help let me know and I'll work some figures out for you.

Macx [8D]

caliber302003

hi Macx

thanks for the reply. do you think that i should just bulk the square where the retracts will screw onto or do you think i should bulk the whole lot i.e from l/e to t/e in one strip.

there is space for the nose wheel just behind petrol tank think i could squeeze it in there .

i will try and post some pics of progress if interested
also could you give me some sort of diagram if its not to much trouble please?

thanks alot

Mac-

Hi Caliber,

1) Only the immediate area where the hardwood supports will fit needs to be reinforced. The wing ribs either side need to be cut away to accommodate and support these blocks and reifoced with ply doubler ribs.

2) The nose wheel will need to go well forward so the rear of the fuel tank will probably be too far rearward. The tank access hatch could be removed and a 3/16th beech ply plate substituted to support the nosewheel.

3) I'll draw up a diagram for you. [8D]

Mac-

Caliber,

I estimate the revised weight of the Rapier with tricyle undercart/ mains retracts plus support blocks and retract servo at approx 76ozs ( 4lbs 12 ozs).
With a wing area of approx. 890 square inches this will give a wing loading of approx. 12 ozs per sq.ft.
A good .46 - .53 2/stroke will be required.

1 & 2) The support hardwood blocks for retracts will need to be about 1 1/2 to 2 inched in front of the wing skids. Wing ribs either side of retract will require reinforcing with 1/16th beech ply doubler ribs.

3) My diagram is self explainatory and is not to scale. The nosewheel should fit in the front 3 3/4 inch space between the front fuz. and tank hatch on a 3/16th beech ply plate. Wheels of about 2 1/2 inch diameter should be fine....but don't use foam types if flying off grass!


Rapiers require approx. 6 mm of up built in to elevons to aid takeoff ( reflex wing action).


Let me kow if you need any further help!

Mac-

caliber302003 just sent you a private message at 12/30/2003 12:23:55
PM:

~~~~~~~~~~~~~~
repier
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hi macx
thanks for your reply are you saying theat i should move the tank back?

----------- End of Private Message (PM) -------------


Caliber,


No.....leave the tank where it is, the closer to the engine the better!

You could epoxy a 1/16th or 1/8th ply plate inside and a 1/8th ply plate outside the fuz. front at the position indicated then mount the nosewheel to this. There should be just sufficient room for this without interfering with the fuel tank!

I also suggest that you fit a 10 x 8 prop if using a .46![8D]

caliber302003

right

i have managed to start a little by stripping the undersize of its pro film and have taken a pic so you can have a look yourself and may get a better idea.

so i will move the fuel tank back and where the skids are thats where they will mount?

caliber302003

ahhh ok i think i know what you mean so the tank will stay [&:]

Mac-

Your nosewheel is too far rearward. Refer to the c of g shown. The nosewheel needs to be in front of the c of g. approx at the front of the fuel tank. You could block off the bottom fuel tank access hatch with beech ply and make a new access at the top of the fuz. and make the cockpit removeable to accomodate this.

The rear wheels should be far enough back to allow the model to rotate at takeoff and a healthy 'nose up' attitude when landing. This model at slow speed needs a predominant nose up attitude due to its delta wing configuration. If you make the rear wheels too far back it will impede this action!

caliber302003

i bought the wood you said today and hopefully i will start building tomorrow im a bit doubtfull about the nose wheel as i think it might not work there aint mush space but lets see

caliber302003

macx

dont mean to sound like a pain but could you draw me up a scetch how to reinforce the ribs? for the retracts



regards

Mac-

Caliber,

Fig.1) This shows where the ply reinforcement goes...either side of the main rib (pink). Or you could cut out the balsa wing area (black) and substitute for 1/8th ply to the same profile and epoxy into place.

Fig.2) This is a plan view of the reinforcement ply positioning.

Fig.3) The black block areas need to be cut out for the hardwood undercarriage supports. The pink area shows the retract positioning.

I'm not sure if you have decided to go for a fixed or retractable nosewheel?


Note: The Rapier would probably be too tail heavy if the wheels where fitted further back. You will maybe need to move the flight pack from the rear to the front with retracts fitted, hence a heavier/more powerful engine will be needed ( eg .46/.53 Irvine although these are the same weight!).


Should look interesting with retracts fitted![8D]

caliber302003

cheers for that helped alot
do you think i should leave the skids on incase of retract failure?

Mac-

It can't do any harm...and there's not much of a weight penalty!


Let me know if you have any problems with the nosewheel![8D]

caliber302003

OK THANKS BE SURE TO HEAR FROM ME SOON LOL

OH HAPPY NEW YEAR TO YOU TOO

caliber302003

i have the left hand side all done and ready to put in where do you think i should put the servo ?

Mac-

1) If the retract servo cannot be fitted in the centre fuz. section (B) you can offset it at position (A) as close to the fuz. side as possible. At Position (A) the weight of the retract servo on the port wing can be offset by the muffer on the opposite side.
Remember to latteraly balance the wings later by holding in the forefinger and thumb at the fuz. centre!

2) You could make some wheel wells with 1/16th sheet lined with 1/64th ply....strong and light!

Note: GWS do a low-profile retract servo with 7 kgs. of torque that weighs only 34g at £18!

Flypaper 2

Probably to late now, but the main gear should be barely behind the CG. I have a Hustler delta. When I first flew it, it would roar down the runway at about mach two and wouldn't rotate. When I bent the gear forward till, if you pushed the tail down it would almost stay down. fine after that. Deltas are so short coupled, they don't have much leverage to raise the nose. Hope I'm not to late to help.

caliber302003

hi flypaper 2

no your not too late all suggestions are VERY welcome as i will need as much help with this as posible as its my first project


thanks

Mac-

The Rapier will perform like the Concorde. Its delta configuration creates a lot of drag at the trailing edge requiring a reflex section to compensate at low speeds (this is why you must have aprox. 6mm of up built in to the elevons). This 'reflex' section is effectively moving the c of g temporarily further back at take-off/landing. The Concorde perfomed this operation by phsically pumpiing fuel further back at take-off and reversing this procedure once airborne and accelerating!

When your Rapier is finally airborne you will need to physically cancel out the up trim as its speed picks up to counteract climbing then reverse this procedure as the speed bleeds off!

Flypaper2 is no doubt correct but be careful not to move the u/c too far forward under its 'secondary c of g' position.

Mac-

Caliber,

This may help!


Flypaper2,

Does your delta have any 'up' elevons built in at its neutral setting?

Mac-

The lower yellow strips represent the c of g position for normal flying of the Rapier. But initial takeoff creates additional drag at the wing trailing edge requiring additional up elevtor to compensate. This effectively pushes the c of g further rearward to approx. the white strips as indicated.
Fitting the retract wheels too close to this rearward c of g point may cause the model to tail-tip at takeoff. So, imo, the rear wheels should be at least 40mm behind the white strips.