jimmba

Hello to all ,

After a 40 plus year hiatus from building model airplanes ( control line) I find myself in my senior years attempting to build a rc plane from scratch. As usual , I have plunged in doing it by the " that feels right " method combined with what little experience I can recall.
The specs are as follows: length 96" , wingspan 132" , chord 19" , fuse width at widest 11" , fuse height at tallest
15", approx all up weight 34 lbs. this approximation obtained by piling all components on scale and adding a small percentage.
Design is high wing with constant chord with ailerons and flaps. Plan was drawn fullsize . I have a zenoah g62 I am hoping will be sufficient . At this point I am wondering if this bird has any hope of flying. I dont know if I can manage to post any pics but plan to try.

Any and all input will be much appreciated!

Thanks , Jim

jimmba

All Day Dan

My Feedback: (5)

Jim, the cabane area looks weak from here. You should have a substantial doubler of birch ply, 1/8 inch or thicker, from
an inch below the window line up. 3/8 inch spruce sticks along the windows frames are also needed. Put ¼ inch gussets in all the corners. I know it sounds heavy, but that’s a large model you are building. I'll attach some images of what I did on a 40cc Champ. Dan.

All Day Dan

My Feedback: (5)

Dan.

BMatthews

34 lbs may sound like a lot but with all that wing area I suspect it'll fly just fine. The worst you'll get is a "scale like" climb rate.

I have to agree with Dan about the cabin area. But you're clearly far from done there yet so I suspect it's too early to be concerned.

jimmba

Thanks Dan , Bmatthews!
I have been fretting over the strength ofbthe cabin area. The advice and pics are appreciated muchly! Ive attached some more pics of build . Please dont hesitate to point out whatever you think I need to know!!

jimmba

jimmba

Is there any way to have a clue about possible flying characteristics? Heavy ? Average? Float ?( I could wish !)
the airfoil is flatbottom. Confession time .... I just drew it ! There Ive said it ! It is not a known airfoil,
Flatbottom , 19" chord , 132" span , 2" thick at max.

jimmba

jimmba

A gee bee cowl found in the trash!

jimmba

I havent added the cabin doublers or gussets yet but this addition( fiberglass braces ) stopped all side to side deflection

jimmba

Dan , Ive added some cabin area reinforcement . Its 5mm doublers on inside , gussets in corners , and a lite white wood crossmember that is both. glued and screwed. Pics attached . What say you?

All Day Dan

My Feedback: (5)

Looks good from here. Nice job. Dan.

jimmba

Thanks Dan . Now Im stressing over weight ! If my calclations are close then she will have a 31 to 34 oz sqft wing loading . Remember , I was hoping to use my Zenoah G62. Ive read that larger scale models will fly fine with wing loadings that would be heavy in smaller scale ... Just not sure where Bertha is in all that.
Also , Im troubled by the weight of the foam core , balsa sheeted wings Ive built .... 4.25 lbs per side!

All Day Dan

My Feedback: (5)

JIM, this Tripacer has a wing loading of 47 ounces and is 50cc powered. No problem. Dan.

All Day Dan

My Feedback: (5)

oops, typo. It's 40 ounces. Dan.

jimmba

Wowser ! Really ! Take off roll? Landing speed?
What about the wing weight ? Is that in line ?
ive never built foam core sheeted wings before. Took a while to build the core cutter.
Im actually thinking of cutting "bays " in the wing to reduce weight. I read all the time .... Sorting it all out is another story!
Im surprised no one has said how weird the radial cowl looks with the prop shaft coming out of the top of the cowl!
😜

sensei

Cutting bays in your surfaces will reduce the weight nicely, been doing it for years. I reduced the weight over 2 1/2 pounds on this airplane with a 167" wingspan and a 26 oz. wing loading. Here are a couple of shots before and after covering.



Bob

BMatthews

There is very little weight to be saved by cutting away the foam. And in fact it gives the sheeting a spot to crumple inwards and produce a failure.

On your airfoil. I hate to say this but it's not a really great shape. The blunt nose with very forward point of maximum thickness and the flat upper rear is possibly going to give you an earlier stall when flying slowly.

There have been many, many good and well known designs that did not use name brand airfoils. But the better ones look strongly similar to name brand tested airfoils for a reason.

I'm also a bit confused at your choice for using sheeted foam when you did such a nice job of building up the fuselage and tail surfaces in sticks with some sheeting. I'd have expected to see a wing done in the classic ribs and spar style.

sensei

There is very little weight to be saved by cutting away the foam. And in fact it gives the sheeting a spot to crumple inwards and produce a failure.

That is your own opinion and in fact, no fact at all. IMO if you really think there is very little weight to be saved by removing excess foam core and sheeting and furthermore believe doing so will only produce a failure then you should stick to aerodynamics because airframe design and weight reduction are not your things.

Bob

jimmba

Very nice ! Thanks for sharing the pics . You put a ton of work in that one ! As I think about it I realize that any weight I can remove without compromising strength in needed areas is a good thing ! It will fly better lighter! So my efforts will continue in that direction .
I realize that I could have approched this whole " build it from scratch , plans and all " in a more orderly and conventional way . However , there were /are reasons why I went about it in this way . I have a brother that used to build and fly years ago and he had an accident causing brain damage albeit slight . This project was started in part to get him off his chair and enthused about doing something .
B Matthews , that is the reason for building a foam cored wing .... He used to build that way and he was encouraged by the idea to build a new foam cutter etc. I appreciate your input regarding my airfoil , Ive been worried about it all along.
In short , I was in a hurry to get this build going while he showed interest . However , regarding the cutting of open bays , my wing is already sheeted . I would be removing both foam and sheeting , as shown in the pics provided by Bob/ Sensei Dan , i really appreciate your encouragement and the pics of that good looking Tripacer. I hope " Bertha" can finish out under 40 ozsqft! Im gonna do my best to make it so .
BTW , the ply used in fuse construction is 5mm underlayment , about 15 $ a 4'x8' sheet

jimmba

Bob , what method did you use in cutting your bays ? Thanks , Jim

sensei

I made a set of two matched hot wire templates from the cheapest wall paneling Lowes offers, attached them to the top and bottom of the core with dry wall screws, then using a hot soldering iron punched holes in the center of each bay. Finally I used a deep hot wire, running the wire though each hole, powering on cutting each bay out, powering off, repeating until finished. It takes a little time but is very easy and effective to do. While we are on the subject of weight reduction, you are correct in keeping things as light as possible, lighter flies better, most don't know just how light you can build to carry the flight loads.

These airframes pictured below were built up from medium density 3/8" X 3/8" balsa wood with 1/64" thick plywood gussets, the motor box from 3/32' thick basswood plywood, 3/4" medium density balsa tri stock, and 1/4" thick birch plywood firewall, fuselage and motor boxes glued entirely together with thin and medium CA. No epoxy anyplace on my wood structures as all my builds are done this way. Now keep in mind that these airplanes are 12' in length and wingspans of almost 14', powered with only 200cc engines. That is a very small power plant for airplanes this size, and again these have around a 26 oz. wing loading because of lightweight construction methods and removing all excess core. These videos shows the slow flight capability, the aerobatic capability and the abuse an extremely light airframe will take. Most don't fly stuff this large or abusive so may as well build light, airplanes are made to fly, not crash anyway.



Bob

jimmba

Thanks ! I appreciate the info and videos . Something I havent mentioned is my plan to make as many of the components needed myself . Also to use non traditional wood sources to reduce expense.
Looking at a variety of sources for information regarding my home drawn airfoil I have been somewhat encouraged . My aspect ratio , wingtip shape and lift coefficient seem good . I am hoping the large flap area will help it slow down for landings.

jimmba

BTW , nice flying !��❗