The problem with the 200hp Ranger

[StephenLawson]

Greetings folks;

I would like to discuss the above topic with the aim at dealing with some serious concerns. First of all most modern full sized replica Fokker D.VII type aircraft employ the use of a 200hp Ranger. This is an aircooled inline engine that is usually installed inverted amd thus modified from its original intended profile.

The problem with the Ranger is lighter than the Merc or BMW originally used. Discussion with other builders note that the historically trim Fokker D.VII becomes tail heavy by about 80 to120lbs. Now while this is not a concern that can't be dealt with it does create two further problems. If left unchecked the tail heavy bird flies reasonably well until a stall puts one into a flat tail spin. Sort of like being sucked down a drain tail first senario. Then second to move the motor forward enough from its original profile lengthens the nose by about 8-11 inches. You could add additional weight but this means adding more than 150 lbs of dead weight.

Many replica builders don't know that there is now metal tubing available that has continous reduced crossections. So the tubing they use is constant in diameter this also adds to the dilemma.

In these types of replica aircraft the the water, radiator and its piping are not installed. Also the use of ammunition is often supplanted by a larger fuel tank or method for simulating the firing flashes from the machine guns. In some cases left empty. If anything these observations should serve to mark the replica builder with food for thought.

[worldcrusier]

I am somewhat familiar with Barny Petersons Ranger powered DVII. I tried to pick up the tail of the airplane in his workshop and darn near got a hernia. I think that looking very closely at weight and balance and also at the propellor used is a must. The aircraft was damaged years ago in a landing incident. Whether due to conditions, Tailwheel configuration,pilot inexperience or a tail heavy weight and balance, I do not know, but, I fly a tail dragger that is considerably heavier and yet has a lighter tail wheel loading.

[jumpinjan]

???What's wrong with using aluminum tubing for the tail surfaces?
I saw Petersons' D7 at the AF Museum and it seemed like the Ranger had to strain to get him up in the air. Again, too small an engine to swing the big prop? Am I wrong?
Jan

[worldcrusier]

I know that Barney built his own prop and that he has experimented some. I am aware,second hand, that one of the last props gave noticibly better performance. I can only imagine that if the weight and balance is off(tail heavy) and with a high center of gravity, that the D7 would be a bear to keep straight on landing.
Barney built a beautiful replica/reproduction, that, except for the engine is as accurate as he could make it. Which is why I assume, that he stayed with steel tubing in the tail.
If the W/B on the ranger powered replicas is off due to the engine being lighter, I wonder why the builders don't just add weight in the nose?? Sure its dead weight, but they would not be adding to the original weight of the aircraft.

[StephenLawson]

Dead weight means that it serves only one purpose and does not help the aircraft fly. All measures of a real Fokker D.VII were designed to assist the machine stay aloft. The forces on a tail plane won't allow for an aluminum construction. The metal is too soft. (consider ultra light aircraft and the size of their motors as a reference.) Steel tubing through out needs to be identical to the originals that decreased in diameter further back on the emmpanage.

Here's a small example from Jasta 64w bi-monthly reports concerning the problems with the Pfalz D.IIIa types and the 'Green Wood' used in their construction. Note someone's solution was adding dead weight.

'...The Pfalz D.IIIa types flown by the Jasta in the course of time have been found to have the fuselage warping to such an extent, that they pull to one side... After close investigation of the ‘tail heavy’ Pfalz D.IIIa 8138/17 we found two bags filled with iron filings (total added weight of 20.5 Kilos) under the engine supports. After removing this added weight, the aircraft was near to impossible to fly...'

If dead weight has to be employed something is very wrong. If that aircraft stalls at 80ft in the air your dead. One fellow I read about in the WWI Aero broke his back landing a stalled Fokker D.VII replica.

[worldcrusier]

I guess I shouldn't have used the phrase 'dead weight'. As I understand the situation, if a D7 is built to the original dimensions, with original materials and an original Mercedes engine, then the weight and balance is correct. When a builder uses a ranger engine the weight difference is 80 to 120 lbs. If the builder uses, say heavier tubing in the motor mount, or adds weight(securely) at the correctly calculated location in the nose to duplicate the original weight and balance, wouldn't the replica fly close to the original, having the same flight characteristics??

[Michael Scheetz]

What we need is a better alternative to the Ranger. We need a proper water-cooled inline. There were many types of our beloved AC that had them and we need something like it for building our replicas.

Observing,

Fee2b

I would agree, the biggest problem facing repro builders is, in most cases, the lack of a suitable engine. The Ranger seems to be the most viable choice, thus far in place of the original mercedes powered types. At this point however, I believe many are confusing a weight and balance issue with a power issue. Weight and balance is by far of the formost importance. One can deal with marginal power. One should not deal with questionable balance issues, EVER.

I see it as a matter of perspective. Spam Can drivers will regularly over load the baggage compartment or rear seats of their Cessna, Beechcraft, et al, at Tahoe or Reno, and then wonder why they're having stablity problems getting back over the Sierras. Most are thinking "usefull load" rather that how far aft of the CG they are placing the skis or have an unrealistic view of their own piloting ablity. I believe that properly balanced aircarft, even if it must have ballast added, is not carrying "dead weight" at all.

Aircraft are compromises on every level. If one wants a flying WWI replica, one is forced to make choices because one can't always realistically obtain many original type items. One choice I would make is PRESICE weight and balance, with ballast as nesesary, as it is a very usefull load.

I think it would be smart to build "lighter toward the tail", but any redesign in this area should be run past a competent engineer. Another cosideration is that the old Fokker designs were built using mild steel and not the high strength 4130 used today. Wall thicknesses will already be thinner, for greater strength and lightness overall. Again, run the numbers.

I know I have brought this up before, but has anyone ever looked into the the straight six which powered the MG C and the TR 6 as possible auto engine conversions? I remember it as a very heavy, yet powerful engine.

[jumpinjan]

visaliaaviation, The number one important requirement is how to swing the big prop? The big props need low RPM and the torque to get the thrust that the full size replicas need. It can be provided by using a huge displacement engine (like the old BMW & Mercs, 1,000 cu-in) or a higher reving, small displacement engine that works through a gear reduction box. I feel that even the Ranger (440 cu-in) is considered a small engine and since it has no re-drive box, it can only swing a medium size prop and that is just marginal power. I don't know what the answer is. The solution might be a commercially made & certified re-drive that can be adapted to various powerplants?
Jan

[StephenLawson]

First let me thank you all for your input. As many of you have seen our D.VII swings that small / medium prop. One answer that many replica builders have come to is scaling down the over all size to about 80%. The El Tigre motor being just about right for performance.