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Aug 16, 2017, 04:03 PM
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is this engine enough for 84" span plane


Hi,
This is my first post here on rcg. I have been following it for a long long time but never joined the site, I think I am the most stealth observer of this site
anyways coming to the topic i have built a high wing trainer with a wingspan of 84".
I have 61 size 2stroke asp engine laying around and i was thinking to use it for this plane. I want suggestions from you awesome and experienced guys out here as i am afraid of the drag created by such wing span and i want your openions whether this engine is enogh for this size of plane?
some basic info will be usefull I think so here it goes
wingspan 84"
lenght 58"
airfoil seems to be resembling clark-y
weight i assume will be around 8 to 9 lb including every thing.
construction is based on a drawing of cessna 182 but i just straightened the curves and made it boxy.
materials are aircraft grade ply for fuse, balsa for horizontal and vertical stabilizers and all control surfaces including ailerons and foam core wings with balsa and carbon tube spars with a very few balsa ribs in between to support foam. all fuel proofed.
this is my 2nd scratch built plane and i have made windows and also lightened the fuse by cutting out pieces in fuse parts. i used a laser machine to cut out each ply and balsa part and hotwired foam.
i purchased this engine from an experienced guy who was flying rc planes for 10 to 12 years and he told me that you can fly a plane weighing upto 6kgs with this size engine. engine had only 1 flight on it and looks new and has good compressions so what do you guys say should i put it in this plane? will it be able to fly it as i want it to fly as a gentle trainer. and its always windy over here in my part of the world. Looking up to you guys. Thanks in advance.
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Aug 16, 2017, 04:27 PM
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Nergall's Avatar
A SIG Kadet Senior has a 79" wing and flies OK with the cheap OS Max .46, so this should be similar. The Senior Telemaster, I believe, has a similarly large wing to yours, and is designed for a .60 engine. Both of these are very light airframes though.

However, for perspective, an aerobatic plane with an 84" wing would want around a 60cc engine (I think that is about 3.5 cubic inches).

So, it all depends on how you want to fly it. If you want something slow and glider like, the small engine is the way to go. However, it won't have much "get out of trouble" power, and may be very limited on what aerobatics it will do?
Aug 17, 2017, 03:37 PM
Scale Builder
Your .61 should have zero problems hauling around a 9 pound, 84 inch span high wing trainer type airframe. A strong .46 size two stroke would probably fly it just fine. Assuming of course, as noted by Nergall above, that you are not expecting it to be anything more than moderately aerobatic.
Aug 17, 2017, 05:37 PM
Registered User
The thing you have to watch out for with a big plane and engine choice is a little more than having enough power. You want an engine that balances the plane so you don't have to add a bunch of nose weight. A .60 should fly your plane with plenty of power but it also might take a lot of nose weight to balance. If you were to put a 90 or 120 four stroke in it you might not need nose weight plus you have more power to fly.

If you go whole hog and decide to put a real big motor in it then you have to watch out for prop size vs. landing gear clearance. The other factor is having so much power and a big prop you might not have enough rudder to compensate for all of that torque. Takeoffs can be difficult if it's a tail dragger.

It's all a manner of balancing it out.

carl
Aug 17, 2017, 06:21 PM
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thanks Nergall for clarifying it for me that a sig kadet senior can fly good on a 46 as i was thinking it is designed for .90 size engine. I just checked the specs again and it calsl for a 2 stroke 40 or 4stroke 65. though its flying weight is 6lb around 2 to 3 lb less then mine estimated weight, but still its giving me good hope for my setup
I am only expecting gentle flying from this plane as its my first nitro plane, am not looking for aerobatics yet but a little more power to use in events of trouble is a good thing which i guess i will be lacking severely.
Aug 17, 2017, 06:29 PM
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Quote:
Originally Posted by Chad Veich
Your .61 should have zero problems hauling around a 9 pound, 84 inch span high wing trainer type airframe. A strong .46 size two stroke would probably fly it just fine. Assuming of course, as noted by Nergall above, that you are not expecting it to be anything more than moderately aerobatic.
thanks chad for the reply but i am confused at one thing, as you said my 61 should have zero problems to haul this plane, i can undestand this, but then you mentioned a powerfull 46 will fly it fine, so isnt my 2stroke 61 much more powerfull then a 2 stroke 46? can you help me clear my confusion
Aug 17, 2017, 06:38 PM
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Thread OP
Quote:
Originally Posted by carlgrover
The thing you have to watch out for with a big plane and engine choice is a little more than having enough power. You want an engine that balances the plane so you don't have to add a bunch of nose weight. A .60 should fly your plane with plenty of power but it also might take a lot of nose weight to balance. If you were to put a 90 or 120 four stroke in it you might not need nose weight plus you have more power to fly.

If you go whole hog and decide to put a real big motor in it then you have to watch out for prop size vs. landing gear clearance. The other factor is having so much power and a big prop you might not have enough rudder to compensate for all of that torque. Takeoffs can be difficult if it's a tail dragger.

It's all a manner of balancing it out.

carl
thanks for the suggestions carl. it has a trike style landing gear. and clearance for prop is enogh to have 12 size prop on it with a little more hieght from ground to prevent prop from hitting anything. its my first nitro so definitely i want just gentle flying from it. i chose balsafor tail surfaces so as to keep the weight as down there as possible but yeah it may need nose weight, i will post here once i reach the stage of balancing it.
Aug 17, 2017, 07:03 PM
Registered User
If I may make a suggestion. As a (final) test once assembled, rather than plan on taking off on your first test runs, maybe accelerate moderately hard and see how far it needs to go to break ground? As soon as it breaks ground pull the power back completely prior to allowing it to gain much altitude, and land it. Doing this 2-3 times should be all you would ever need to convince yourself if you have the power to fly safely. If the point it lifts off the ground is half or less of the room you have, you should be fine. More than half, and things could get dicey on you.
Aug 17, 2017, 11:09 PM
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Nergall's Avatar
Quote:
Originally Posted by noobdude
thanks Nergall for clarifying it for me that a sig kadet senior can fly good on a 46 as i was thinking it is designed for .90 size engine. I just checked the specs again and it calsl for a 2 stroke 40 or 4stroke 65. though its flying weight is 6lb around 2 to 3 lb less then mine estimated weight, but still its giving me good hope for my setup
I am only expecting gentle flying from this plane as its my first nitro plane, am not looking for aerobatics yet but a little more power to use in events of trouble is a good thing which i guess i will be lacking severely.
I recently replaced my original Kadet Senior with a new one with flat wings, ailerons, and a .72 four stroke engine. It's as aerobatic as one could expect from a trainer. I also checked the specs on the Telemaster Senior - it has a bigger wing, it is heavier than yours, and still flies on a .60 size engine. Rumor is that it flies very well, in fact.

Couple of points though in regard to the other comments here.

1. As to nose weight, I'm in total agreement that I'd rather add more engine than lead. However, since it is a custom design, you could also just extend the nose so it doesn't need as much weight to balance in the first place.

2. My old Kadet Senior was definitely not short take off. My aerobatic airplanes can mostly take off in the width of the runway, but that old Kadet with the .46LA often took well over half the runway to get started.
Aug 18, 2017, 12:27 AM
Scale Builder
Quote:
Originally Posted by noobdude
thanks chad for the reply but i am confused at one thing, as you said my 61 should have zero problems to haul this plane, i can undestand this, but then you mentioned a powerfull 46 will fly it fine, so isnt my 2stroke 61 much more powerfull then a 2 stroke 46? can you help me clear my confusion
Absolutely correct noobdude, your .61 two stroke is more powerful than a .46 two stroke. The point I was trying to make was that I think a 46 would be enough power to fly the airplane and since your 61 is even more powerful it should easily fly the airplane with power to spare.
Aug 18, 2017, 07:36 PM
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Thread OP
Quote:
Originally Posted by ahicks
If I may make a suggestion. As a (final) test once assembled, rather than plan on taking off on your first test runs, maybe accelerate moderately hard and see how far it needs to go to break ground? As soon as it breaks ground pull the power back completely prior to allowing it to gain much altitude, and land it. Doing this 2-3 times should be all you would ever need to convince yourself if you have the power to fly safely. If the point it lifts off the ground is half or less of the room you have, you should be fine. More than half, and things could get dicey on you.
thats a clever suggestion achicks i will definetly look into it. thanks
Aug 18, 2017, 07:42 PM
Registered User
Thread OP
Quote:
Originally Posted by Nergall
I recently replaced my original Kadet Senior with a new one with flat wings, ailerons, and a .72 four stroke engine. It's as aerobatic as one could expect from a trainer. I also checked the specs on the Telemaster Senior - it has a bigger wing, it is heavier than yours, and still flies on a .60 size engine. Rumor is that it flies very well, in fact.

Couple of points though in regard to the other comments here.

1. As to nose weight, I'm in total agreement that I'd rather add more engine than lead. However, since it is a custom design, you could also just extend the nose so it doesn't need as much weight to balance in the first place.

2. My old Kadet Senior was definitely not short take off. My aerobatic airplanes can mostly take off in the width of the runway, but that old Kadet with the .46LA often took well over half the runway to get started.
yes Nergall i have left quit much of side walls in the front of the fuse. the idea was to provide side cover to my engine for aesthetics, but yes it can provide a place to mount firewall further ahead. i even have market a new point for fire wall in case it was hard to balance, we both are on same thinking line
Aug 18, 2017, 07:49 PM
Registered User
Thread OP
Quote:
Originally Posted by Chad Veich
Absolutely correct noobdude, your .61 two stroke is more powerful than a .46 two stroke. The point I was trying to make was that I think a 46 would be enough power to fly the airplane and since your 61 is even more powerful it should easily fly the airplane with power to spare.
oopsa my bad chad veich. actyally i misunderstood what you were saying initially. I thought you were saying that my .61 must be 100% powerfull to fly this plane but now i got it. you mean it will not have any problem dragging this plane. I was actually doughtful for my engine size and i was self assuming that it may be underpowered for this application so my thought process was also going that way. thanks for making it clear for me. have a nice day
Aug 19, 2017, 05:26 AM
Suspended Account
Quote:
Originally Posted by ahicks
If I may make a suggestion. As a (final) test once assembled, rather than plan on taking off on your first test runs, maybe accelerate moderately hard and see how far it needs to go to break ground? As soon as it breaks ground pull the power back completely prior to allowing it to gain much altitude, and land it. Doing this 2-3 times should be all you would ever need to convince yourself if you have the power to fly safely. If the point it lifts off the ground is half or less of the room you have, you should be fine. More than half, and things could get dicey on you.
So exactly how much is "half or less of the room you have"?
Aug 19, 2017, 06:55 AM
Registered User
Let's just cal it maintaining a safety factor.

Bottom line, if it's not off the ground in half the length of the area you are using (foot ball field, baseball diamond, dad's front yard, whatever), I would question the wisdom of continuing to accelerate beyond that point out of concern for getting it stopped undamaged, or it's ability to climb at a rate allowing it to clear any obstructions at the far end.


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